United States
Environmental Protection
Agency
Water Division (WH-553)
Washington, DC 20460
EPA-841-R-93-002
May 1993
vvEPA Fish and Fisheries
Management in
Lakes and Reservoirs
TECHNICAL SUPPLEMENT TO
Lafre and Reservoir Restoration
al
-------
-------
Fish and Fisheries
Management in
Lakes and Reservoirs
TECHNICAL SUPPLEMENT TO
The Lake and! Reservoir Restoration
Guidance Manual
Prepared by the
Terrene Institute
in cooperation with the
U.S. Environmental Protection Agency
Office of Water
Office of Wetlands, Oceans, and Watersheds
Assessment and Watershed Protection Division
Washington, DC
1993
-------
The information in this document has been funded wholly or in part by
the U. S. Environmental Protection Agency under assistance agreement
CX-818191-01 to the Terrene Institute. It has been subject to the Agency's
peer and administrative review and has been approved for publication
as an EPA document. Mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
Cover photograph:
Courtesy of Dave Wagner, Devils Lake Water Improvement District,
Lincoln City, Oregon.
This document should be cited as:
Baker, J.P., H. Olem, C.S. Creager, M.D. Marcus, and B.R. Parkhurst. 1993. Fish
and Fisheries Management in Lakes and Reservoirs. EPA 841-R-93-002. Terrene
Institute and U.S. Environmental Protection Agency, Washington, DC.
ii
-------
ACKNOWLEDGMENTS
This manual represents a summary of existing knowledge on fish and fisheries
managed in lakes and reservoirs. It was written by Joan P. Baker, Harvey
Olem, Clayton S. Creager, and Benjamin R. Parkhurst. Significant contributions to
the manual were made by Robert W. Wiley, Steve McComas, and Gareth Good-
child. Editors were Gretchen Flock and Roberta F. Shulman.
The manual draws on the many good books, papers, and reports on fish biology,
fisheries, and ecology cited in the references. In particular, substantial background
material was extracted from the two previous manuals in this series: The Lake and
Reservoir Restoration Guidance Manual and Monitoring Lake and Reservoir Restoration,
The quality and scope of this document benefited greatly from discussions of
a preliminary draft at a 1992 peer review workshop in Denver, CO, attended by
Les Ager (Georgia Department of Natural Resources), Mike Alexander (U.S.
Army Corps of Engineers), Tom Davenport (U.S. Environmental Protection
Agency), Joe Eilers (E & S Environmental Chemistry, Inc.), Bill Funk (Washington
State University), Frank Lapensee (U.S. Environmental Protection Agency), Dave
Marshall (Wisconsin Department of Natural Resources), Pat Marinez (Colorado
Division of Wildlife), Spence Peterson (U.S. Environmental Protection Agency),
Susan Ratcliffe (U.S. Environmental Protection Agency), Dick Wedepohl (Wis-
consin Department of Natural Resources), Ray White (Trout Unlimited), and Bob
Wiley (Wyoming Game and Fish Department). Written comments were also
received from Sandy Engel (Wisconsin Department of Natural Resources), Rick
Hoopes (Pennsylvania Fish Commission), Mike Jones (Ontario Ministry of
Natural Resources), Tom Powell (Colorado Division of Wildlife), and Richard
Ryder (Ontario Ministry of Natural Resources).
Completion of this manual would not have been possible without the advice
and assistance of these many scientists and resource managers. In addition, many
State and provincial resource agencies provided helpful written materials includ-
ing the Alabama Department of Conservation and Natural Resources, Arkansas
Game and Fish Commission, Delaware Division of Fish and Wildlife, Georgia
Department of Natural Resources, Idaho Fish and Game, Illinois Department of
Conservation, Iowa Department of Natural Resources, Kansas Department of
Wildlife and Parks, Louisiana Department of Wildlife and Fisheries, Maine
Department of Inland Fisheries and Wildlife, Minnesota Department of Natural
Resources, New York Department of Environmental Conservation, Oklahoma
Department of Wildlife Conservation, Ontario Ministry of Natural Resources,
Pennsylvania Fish Commission, and Wyoming Game and Fish Department. Use-
ful reference materials were also provided by the Sport Fishing Institute, Flathead
River Basin Commission, and Devils Lake Water Quality Improvement District.
Hi
-------
-------
PREFACE
k I 'his document is part of a series of technical guidance manuals on lake res-
JL toration and management prepared for state and local use under a coopera-
tive agreement with the U.S. Environmental Protection Agency's Clean Lakes
Program. The Lake and Reservoir Restoration Guidance Manual (EPA 440/4-90-006)
provides an overview of the principles and techniques of lake restoration.
Monitoring Lake and Reservoir Restoration (EPA 440/4-90-007) presents more
detailed guidance on designing and implementing a lake monitoring program,
necessary for characterizing lake problems and evaluating the success and effec-
tiveness of restoration projects. This manual focuses on one component of lake
ecosystems: fish. Historically, fisheries management and lake water quality
management have been treated as separated disciplines and handled by separate
agencies or departments in both state and federal governments. An important
objective of this manual is to encourage the development of an integrated lake
management program that addresses fish, other biota, the physical and chemical
characteristics of the lake habitat, and the associated watershed as an interdepen-
dent unit.
Additional technical guidance manuals for state and local use are planned on
other topics of interest. The staff of the Terrene Institute would welcome your
suggestions and comments. Please address your comments and requests for the
manuals to:
Terrene Institute
1717 K Street, NW
Suite 801
Washington, DC 20006
-------
-------
CONTENTS
Chapter 1: Introduction
Purpose of the Manual 1
Scope of the Manual 2
Lakes and Reservoirs 2
Whole-basin Approach 2
Management = Protection + Restoration 2
Fish and Fisheries Management 3
Additional References 3
Intended Audience 3
Manual Organization 4
Units of Measurement 4
Chapter 2: Lake and Reservoir Ecosystems
Chapter Objective 7
Lake Morphometry 7
Lake Hydrology . . . ; 9
Water Balance and Hydraulic Residence Time 9
The Lake and its Watershed 11
Sediment Loads and the Bottom Substrate 11
Light in Lakes 12
Lake Circulation and Thermal Regimes 13
Organic Matter Production and Consumption and Nutrient Cycling 15
Photosynthesis and Primary Productivity 15
Respiration and Decomposition 16
Limiting Nutrients 17
Trophic State and Eutrophication 17
Aquatic Biota 18
Microbes 18
Phytoplankton 19
Periphyton 20
Macrophytes 20
Zooplankton 20
Macroinvertebrates 21
Fish 22
Other Animals 24
The Trophic Pyramid 24
Top-Down Versus Bottom-Up Lake Management 25
Special Issues in Reservoirs 26
Chapter 3: Fish Ecology
Chapter Objective 29
Definitions 29
Fish Growth Rates 29
The Energy Balance 30
VII
-------
Factors that Influence Growth Rates 30
Seasonal Growth Patterns 32
Weight-Length Relations 33
Fish Longevity 34
Fish Reproduction 35
Fish Fecundity 35
Reproductive Strategies 35
Spawning Habitats 36
Spawning Periods 36
Age at Sexual Maturity 38
Factors Affecting Reproductive Success .38
Hybridization , 39
FishMortality 40
Compensatory Mortality 40
Fishing Mortality 41
Acute and Chronic Lethal Limits 42,
Winterkill and Summerkill - 42,
Fish Population Dynamics 42
Population Age Structure 43
Length-Frequency Distributions 45
Fish Production 48
Fisheries Yield ' 50
Natural Factors that Influence Fish Production and Fisheries Yield .... 50
Population Genetics 51
Fish Habitat 53
Fish Communities 54
Fish Community Types 54
Factors That Influence Fish Community Composition 55
Role of Community Analyses in Fisheries Management 56
Special Issues in Reservoirs 57
Chapter 4: Key Concepts in Fish and Fisheries
Management
Chapter Objective 59
Important Underlying Principles 59
Importance of Recreational Fisheries . 61
Historical Perspectives . 61
Components of a Management Program 63
Regional Perspectives 65
Chapter 5: Setting Goals, Specific Objectives, and
Priorities
Chapter Objectives -67
Who Should Be Involved? '. . .' 67
Gathering Information on User Characteristics and Public Values 68
Building Consensus and Public Support 69
Alternative Goals in Fish and Fisheries Management 72
Ecological Integrity and the Public Trust . . 72
Fisheries Management 73
Using Fish Management for Water Quality Management 74
viii
-------
Chapter 6: Problem Identification and Diagnosis
Chapter Objectives 77
Problem Statement 77
Problem Identification 80
Putting Problems in the Proper Perspective 80
Indicators of Fish Community Status and Fisheries Problems 81
Problem Diagnosis ; 87
Common Causes of Fisheries Management Problems 90
Water Quality Problems that Can Be Alleviated by Fish Management 93
Chapter 7: Who can Help?
Chapter Objectives 95
State and Provincial Agencies 95
Federal Agencies 96
Private Organizations 97
Professional Societies 99
Environmental Consultants 99
Chapter 8: Management Techniques for Improving
and Maintaining Fisheries in Lakes and
Reservoirs
Chapter Objective . , 101
Selecting the Appropriate Management Technique 101
Habitat Management 103
Habitat Protection 105
Control of Toxic Contaminants . 106
Reducing Nutrient Loads and Nutrient Availability . . . i 107
Lake Fertilization 109
Lake Aeration and Other Approaches for Increasing
Levels of Dissolved Oxygen in Critical Fish Habitats 110
Lake Liming and Other Methods for Decreasing
Water Acidity 114
Spawning Habitat Management 115
Addition of Physical Structures for Fish Cover 117
Aquatic Plant Management 119
Water Level Management 122
Reservoir Construction 124
Manipulating the Fish Community 125
Game Fish Stocking 125
Controlling Undesirable Fish Species and
Stunted Fish Populations 132
Prey Enhancement 139
Managing Fishing Pressure and Harvest and the Fishing Experience 141
Regulations and Their Effects 143
Fishing Derbies and Tournaments 146
User Conveniences 146
Conclusions 147
ix
-------
Chapter 9: Methods for Using Fish to Improve Water
Quality
Chapter Objective 149
Background .149
Grass Carp for Aquatic Plant Control .'.... 150
Control of Bottom-Feeding Fish to Reduce
Internal Nutrient Loads and Water Turbidity 154
Top-Down Management of the Pelagic Food Web to Reduce Algal
Biomass and Improve Water Transparency .155
Inedible Phytoplankton -157
Zooplankton Composition and Abundance 161
Optimal Biomass of Fish Planktivores . 162
Optimal Biomass and Types of Piscivorous Fish 163
Instability ........ 164
Importance of Behavioral Responses .166
Influence of Trophic Status , .166
Interactions with Fisheries Management . : .167
Chapter 10: Designing a Field Sampling Program
Chapter Objective 169
Sampling Objectives 169
The Sampling and Monitoring Plan 171
What to Measure ....'. 172
How To Sample 173
When and Where to Sample 176
Number of Replicates and Sampling Frequency 177
Quality Assurance/Quality Control .178
Data Management . . . 179
Effective Presentation of Results 180
Chapter 11: Role of Modeling in Fish and Fisheries
Management
Chapter Objectives 183
Definitions 183
Why Model? 184
Importance of Conceptual Models 185
Questions that Modeling Can Help Address 185
Types of Models Used in Fish and
Fisheries Management 186
Habitat Evaluation Models 187
Regression Models of Fisheries Yield and Other Fisheries Attributes . . .189
Mortality Models . . . 192
GrowthModels 193
Population Dynamics Models 195
Ecosystem Models ., 198
Chapter 12s Case Study Examples
Chapter Objective .203
Lake Chicot, Arkansas 204
Background '. 204
-------
Restoration Activities . . . . 204
Cold Springs Lake, Iowa 206
Bear Lake, Wisconsin 209
Lake Opeongo, Ontario 211
Flaming Gorge Reservoir, Utah and Wyoming 214
The 1960s .'.... . . 215
The 1970s 215
The 1980s 216
The 1990s 216
Flathead Lake, Montana 217
Background , 217
The Fisheries 218
Water Quality 219
Hydroelectric Developments 230
Water Quantity 221
Fisheries Management 221
Lake Washington, Washington 222
Appendix A: Background Information on Selected
Fish Species
Appendix Objective 229
Threatened and Endangered Species 229
Largemouth Bass, Smallmouth Bass, and Spotted Bass 230
Habitats 230
Reproduction 230
Food Habits 230
Management Concerns ......;...: 231
References 232
Sunfish and Crappie 232
Habitat ; 232
Reproduction 232
Food Habits 232
Management Concerns 232
References 233
Striped Bass and White Bass . 233
Habitat 233
Reproduction 233
Food Habits 234
Management Concerns 234
References 234
Bullheads and Catfish 235
Habitats 235
Reproduction 235
Feeding Habits 235
Management Concerns 235
References 235
Walleye and Yellow Perch 236
Habitat 236
Reproduction 236
Feeding Habits 4 236
Management Concerns 236
References 237
xi
-------
Pike, Pickerel/ and Muskellunge -237
Habitats • • • • .-238
Reproduction 238
FoodHabits • • • -238
Management Concerns 238
References 239
Trout and Salmon 239
Habitat • • 240
Reproduction 240
FoodHabits • • -241
Management Concerns 241
References 242
Threadfin Shad, Gizzard Shad, and Ale wife 242
Habitats -242
Reproduction • -243
Food Habits 243
Management Concerns , ...>..... .243
References 243
Appendix Bi Methods for Assessing Fisheries Status
Appendix Objectives -245
Techniques for Surveying Anglers 245
Creel Surveys 245
Angler Diaries 247
Questionnaires to Obtain Angler Use or Opinion Data .249
Techniques for Surveying Fish Populations and the Fish Community 251
Passive Capture Methods , 251
Entanglement methods 251
Entrapment methods 252
Active Capture Techniques 256
Fish Toxicants 259
Observational Techniques 259
Marking Fish for Identification 260
Fish Measurements 263
Assessing Fish Size, Age, Growth, and Condition 264
Processing fish in the field 264
Laboratory procedures for aging fish using anatomical structures . . .265
Back calculation of length at age 266
Length-frequency analysis 267
Condition factors and relative weight 268
Sex, Maturation Rate, and Fecundity 268
Estimating Fish Population Size 269
Fish Genetics 271
Assessing the Food Base 272
Quantitative Description of Diet 272
Diet Indices • 272
Phytoplankton , 273
Zooplankton 274
Benthic and Littoral Macroinvertebrates 274
Assessing Water Quality 276
Toxic Chemicals 276
Dissolved Oxygen 277
xii
-------
Temperature 277
pH 277
Salinity 277
Suspended Solids 278
Assessing the Physical Habitat 278
Morphometric Measurements 278
Flushing Rate and Water Levels 279
Cover 279
Substrate 279
Vegetation 279
Appendix C: Addresses and Telephone Numbers
State Agencies 281
Provincial Agencies 288
Professional Societies 289
Private Organizations . 290
Glossary 291
References 297
xiii
-------
-------
CHAPTER 1
Introduction
Purpose of the Manual
Historically, fish populations in lakes have been managed by fisheries managers
interested primarily in increasing the number and size of fish caught by anglers.
Fish stocking to introduce new fish species or supplement reproduction was the
major management tool used to increase fishery yields, with relatively little con-
sideration given to the potentially adverse effects of these stocking programs on
other fish species and biota or alternative lake uses. In a similar manner, water
quality managers focused on improving water clarity, decreasing noxious algal
blooms, and other aspects of lake water quality. They paid relatively little atten-
tion to the potential effects of lake restoration efforts on fishing quality. Training
programs for fisheries and water quality management were distinct, emphasiz-
ing different management objectives, types of expertise, and techniques. Further-
more, in most States fisheries and water quality have been and continue to be
managed by separate agencies or departments.
Fish, however, are an integral component of lake and reservoir ecosystems.
In addition to being a desired resource for lake users, they play important roles in
energy flows, nutrient cycling, and maintaining community balance. The physi-
cal, chemical, and biological characteristics of a lake or reservoir are major deter-
minants of the types, number, and size of fish available for harvest. At the same
time, fisheries management affects not only fish and the quality of fishing but
also the ecosystem as a whole. The introduction of a new fish species, for ex-
ample, can have a cascading effect on the abundance of other organisms and, in-
directly, nutrient levels and water clarity. Fisheries management, therefore,
cannot be considered in isolation but must be viewed as one part of an overall
lake management program. Fishing is only one of many often conflicting lake
uses. An important goal of lake management is to achieve the appropriate
balance among these uses.
This manual is written to provide
• water quality managers with a better understanding of the concepts
and techniques of fisheries management as well as the role of fish in
the lake ecosystem and the potential use of fish management as one
method for improving and maintaining water quality;
• fisheries managers with a better appreciation for the broader, ecologi-
cal consequences of fisheries management activities; and
• both water quality and fisheries managers with a basis for incorporat-
ing fisheries management into an integrated lake management pro-
gram.
Biota are all plant and
animal species occurring
in a specified area.
An ecosystem consists of
interrelated organisms
and their
physical-chemical
environment including
the lake and surrounding
land and streams that
drain into the lake.
[Fisheries management
affects not only fish and
the quality of fishing but
also the ecosystem as a
whole.
-------
Fish and Fisheries Management In Lakes and Reservoirs
A lake's quality and
productivity depend
largely on conditions in
the surrounding lands
that drain into it, either
directly or through feeder
streams or rivers.
Integrating fisheries management into a lake management program can serve
three important purposes:
» Maintain the health of the fish community, an important component of
the overall health of the lake.
• Enhance public support for lake management and restoration activities
by addressing the concerns of the fishing public.
• Publicly — and explicitly — recognize the interdependency between
fish, water quality, and the lake ecosystem as a whole.
An integrated program will ensure that management decisions consider the
full range of options and effects as well as potential trade-offs among alternative
objectives and all lake uses.
Scope of the Manual
Lakes and Reservoir's
This manual focuses on the management of fish and fisheries in lakes and reser-
voirs. The term "lake" is used generically to include both natural lakes and those
made by humans, which are called "reservoirs." Because reservoirs are con-
structed for different purposes, such as flood control, water supply, and recreation,
their design and characteristics vary greatly. On average, however, reservoirs tend
to have larger drainage areas, shorter water retention times, and more convoluted
shorelines than natural lakes. Distinctions between natural lakes and reservoirs
are discussed only when the management implications are important. Special con-
siderations required to manage small farm ponds (generally less than five acres
and privately owned) are not included in this manual.
Whole-basin Approach
A lake's quality and productivity depend largely on conditions in the surrounding
lands that drain into it, either directly or through feeder streams or rivers. Most of
the silt, nutrient, and organic matter inputs to a lake often derive from human dis-
turbances in these surrounding lands or upstream waters rather than from direct
discharges to the lake or in-lake sources. Furthermore, many fish species rely on
areas in connecting streams for reproduction or as nurseries for young fish. Migra-
tions of fish are common between a lake and its inflowing streams and also among
interconnected lakes in the same drainage basin.
For these reasons, effective lake management requires a whole-basin ap-
proach. This encompasses not only the lake itself but also land uses and activities
in the surrounding watershed as well as the coordinated management of all lakes
and streams in the basin. A whole-basin approach to water quality management
has recently been adopted by some States (for example, see Creager and Baker,
1991). This manual emphasizes the importance of a whole-basin approach to both
water quality and fisheries management.
Management = Protection + Restoration
Lake protection is the most cost-effective and long-term approach to lake manage-
ment; that is, management actions that prevent the degradation of lake quality or
attainable lake uses. Once degraded, however, a lake restoration project may be
needed to improve lake quality and bring it back to (or closer to) its natural state
and natural attainable uses (see Natl. Res. Counc. 1991). The term "lake manage-
ment" in this document refers to a comprehensive program that incorporates both
protection and restoration activities, as appropriate, to effectively improve and
maintain the quality of the lake ecosystem.
-------
Chapter 1. Introduction
Fish and Fisheries Management
A fishery is the act or occupation of fishing — the harvesting of fish from water-
bodies for either commercial or recreational purposes. Recreational fisheries,
which are the primary focus of this document, are managed to maximize and
sustain the overall quality of the "fishing experience." Although the definition of
a quality experience varies among anglers, it incorporates more than simply the
quantity and type of fish caught. Likewise, fisheries management involves much
more than just managing fish. Managing a fishery requires not only managing
the fish populations being harvested but also the habitat and food supplies re-
quired to sustain those fish populations, the anglers participating in the fishery,
and the broader environment in which the fishing experience occurs.
This manual discusses both fish and fisheries management. The objective of
fisheries management is to achieve and sustain the optimal level of fishing
quality that is consistent with the overall lake management objectives and
desired balance among lake uses. By contrast, fish can be managed for multiple
purposes: to improve the quality of fishing, to control unwanted growths of
aquatic plants, to improve water clarity, or other objectives intended to improve
and maintain lake quality and a variety of lake uses.
Additional References
This manual is an up-to-date technical summary of the state-of-the-science of fish
and fisheries management in lakes and reservoirs. It provides a scientific and
technical foundation for the development of workable and practical lake
management plans that can be approved by a governing body, funding agency
(such as EPA's Clean Lakes Program), or private organization or individual.
Material from other supplements in this series (Olem and Flock, 1990; Wedepohl
et al. 1990) is summarized as needed to comprehensively cover all relevant
topics.
This supplement is not intended to serve as a stand-alone reference on fish
and fisheries management, however, or as a how-to manual with step-by-step in-
structions for implementing management techniques. Additional sources of in-
formation are listed in the reference section for readers interested in obtaining
more detailed guidance on specific topics.
Intended Audience
The primary users of this manual are likely to be
• lake managers (water quality managers, fisheries managers, and lake
associations);
• local lake restoration project managers and their sponsors;
• state personnel involved in lake restoration and management
activities;
• Federal employees involved in lake management; and
• consultants and contractors participating in lake management and
restoration projects.
It is important to note that, in most waters, fish are a public resource, the
management of which is the responsibility of State and tribal fisheries agencies.
Thus, State and tribal fisheries management personnel must be contacted before
any of the activities or management techniques discussed in this book are imple-
mented and should be actively involved in project planning. Many of the
A fishery is the act or
occupation of fishing—
the harvesting of fish from
waterbodies for either
commercial or recreational
purposes.
[I]n most waters, fish are
a public resource, the
management of which is
the responsibility of State
and tribal fisheries
agencies.
-------
Hsh and Fisheries Management in Lakes and Reservoirs
management techniques presented require permits; some can be conducted only
by State agencies. Additional information on the role of State biologists and as-
sociated State regulations and requirements is noted in appropriate sections
throughout this manual.
EPA's Clean Lakes Program addresses problems in lakes and reservoirs in the
United States. The information in this manual, however, is widely applicable to
lake and fisheries management in general. Case studies, references, and contacts
are included to assist with design and implementation of projects in Canada.
Manual Organization
The manual is divided into five parts: background (Chapters 2 and 3); project
planning and design (Chapters 4 through 7); techniques and management tools
(Chapters 8 through 11); case studies (Chapter 12); and Appendices A through C.
• Chapters 2 and 3, which provide background information on terms
and basic scientific principles and concepts, are designed for readers
with relatively little technical training in ecology, limnology (the scien-
tific study of freshwaters) or fish biology. Other readers may wish to
turn directly to Chapter 4.
• Chapters 4 through 7 introduce concepts of fish and fisheries
management and outline a framework for developing comprehensive
management plans that integrate fisheries and water quality manage-
ment and address the underlying causes of lake problems. People and
organizations who can help with fisheries management are also iden-
tified.
• Chapters 8 through 11 describe methods and management tools
used in fish and fisheries management.
• Chapter 12 presents case study examples to illustrate how problems in
lake and fisheries management have been approached and resolved.
• The glossary supplements the text with terms pertaining to fisheries
and lakes.
• The reference section lists citations by chapter as well as additional
reports and papers that might prove useful.
• Three appendices are included: Appendix A: Background Informa-
tion on Selected Fish Species; Appendix B: Sampling Methods; and Ap-
pendix C: Sources of Information and Assistance.
Units of Measurement
As with the other technical supplements in this series, most of the units presented
in this manual are in British/U.S. form. Most scientific publications, however, use
metric units. Table 1-1 provides a listing of metric to English conversions for units
of measurement commonly used in lake and fisheries management.
-------
Chapter f. Introduction
Table 1-1 — Metric to English conversions.
METRIC UNIT
Length
Millimeter
Centimeter
Meter
Kilometer
Weight
Microgram
Milligram
Gram
Kilogram
Volume
Milliliter
Liter
Cubic meter
SYMBOL
mm
cm
m
km
ng
mg
g
kg
mL
L
m3
= 0.001 m
= 0.01 m
= 1.0m
= 1 ,000 m
= 0.000001 g
= 0.001 g
= 1.0g
= 1,000g
= 0.001 L
= 1.0L
= 1.000L
ENGLISH UNIT
inch
inch
yard
mile
(no reasonable equivalent)
grain
ounce (avoir)
pound
ounce
quart
cubic yard
CONVERSION
FACTOR*
0.03937
0.3937
1.094
0.6214
0.015432
0.03527
2.205
29.57
1.057
1.308
* To convert metric to English units, multiply by the conversion factor; to convert English to metric, divide
by the factor.
Other Useful Conversions:
1 gallon = 3.785 liters
1 milligram/Liter = 1 part per million
1 hectare = 2.47 acres
1 acre-foot = 32,590 gallons
1 cubic meter = 264 gallons
-------
-------
CHAPTER 2
Lake and Reservoir
Ecosystems
Chapter Objective
The focus of this manual is on managing fish resources. However, informed
decisions regarding fish and fisheries management require a basic understanding
of the major physical, chemical, and biological processes that influence lake and
reservoir ecosystems. The environment within which fish live plays a major role
in determining the types of species able to survive and reproduce, fish produc-
tion and growth rates, and the management problems likely to be encountered.
This chapter provides a brief overview of the ecological processes of greatest im-
portance to fish and also of the role of fish in the lake ecosystem. Several basic
texts on limnology and freshwater ecology are listed in the reference section for
the reader interested in more detailed discussions of ecological concepts relevant
to lake and reservoir management. The Lake and Reservoir Restoration Guidance
Manual (Olem and Flock, 1990) provides further background information on
many of these topics; many sections in this chapter summarize discussions in
that publication.
Lake Morphometry
Lakes come in many different shapes and sizes, and morphological charac-
teristics, such as a lake's area, maximum depth, mean depth, and total water
volume, have a significant effect on nearly all of the major physical, chemical,
and biological processes in lakes. For this reason, development of a bathymetric
map (Fig. 2-1), showing the shape of the shoreline, water depth contours, and
locations of any inflowing streams (tributaries) and lake outflow(s), is an impor-
tant first step for most lake management programs.
The shallow, nearshore region of a lake, where adequate light can penetrate
to the lake bottom to allow for the growth of rooted aquatic plants (presuming
other conditions are suitable), is the littoral zone. Because it often receives high
nutrient inputs that run off the surrounding land and may support rooted plant
growth, the littoral zone can contribute significantly to total lake production. All
else being equal, shallow lakes with large littoral areas (relative to the total lake
area) tend to be more productive than deeper lakes or those with steep-sided
basins and little or no littoral zone. Many fish species live, feed, or reproduce in
littoral zones; therefore, the extent and nature of a lake's littoral zone directly af-
fect fish community composition and productivity.
Morphometry relates to a
lake's physical structure
(e.g., depth, shoreline
length).
[MJorphological
characteristics... have a
significant effect on nearly
all of the major physical,
chemical, and biological
processes in lakes.
All else being equal,
shallow lakes with large
littoral areas tend to be
more productive than
deeper lakes or those with
steep-sided basins and
little or no littoral zone.
-------
Fish and Fisheries Management in Lakes and Reservoirs
WARDS POND
TENTHS OF KILOMETER
2m ISOBATHS
N
Figure 2-1.—Example of a bathymetric map for Wards Pond, Maine, showing the shape of
the shoreline, locations of tributaries and lake outflow, and depth contours (lines connect-
ing points in the lake of equal depth) at 2-m intervals (about 6 feet) (source: Davis et al.
1978).
The pelagic zone is the open-water area not directly influenced by the shore or
the bottom. The profundal area is the deeper part of a lake that lies below the light-
controlled limit of plant growth. Lakes that have a large fraction of the total water
volume in the profundal zone generally have relatively low productivity per unit
volume.
Another aspect of lake morphometry often correlated with productivity is
referred to as "shoreline development." In limnology, shoreline development (SD)
is the ratio of the length of the shoreline to the circumference of a circle with the
same area as the lake:
length of shoreline
' 2 V~(area of lake) • it
SD.
It describes the degree of shoreline convolutions, that is, the extent to which
the shoreline shape departs from a circle. A lake shaped like a perfect circle would
have a shoreline development factor of one; lakes with highly convoluted
shorelines have much greater values. Generally, lakes with a high shoreline
development value have disproportionately large littoral areas and high littoral-
to-lake area ratios and tend to be more productive.
8
-------
Chapter 2. Lake and Reservoir Ecosystems
Lake Hydrology
Hydrology is the science dealing with the distribution and circulation of water
on the surface of the land, in the soil and underlying rocks, and in the atmos-
phere. Lakes and reservoirs represent one component of the hydrologic cycle
(Fig. 2-2), the process by which water is circulated from the atmosphere to the
earth (as precipitation) and then back to the atmosphere (through evaporation
and transpiration) in a continuous cycle. The subsections that follow summarize
two important hydrologic concepts: (1) water balance and residence time within
lakes and reservoirs and (2) the role and importance of a lake's watershed.
SEEPAGE
INFILTRATION
GROUNDWATER FLOW
WATER TABLE
BEDROCK
Figure 2-2.—The hydrologic cycle (source: Olem and Flock, 1990).
Water Balance and Hydraulic Residence Time
Important physical characteristics that influence the lake and reservoir ecosystem
include its quantity (volume) of water, the rate these waters are replaced and
replenished, and the sources of water entering the lake.
A lake's volume is determined by the shape of its basin and by the relative
balance of water inputs and outputs. Water inputs include direct precipitation,
groundwater, surface stream inflow, surface runoff during storms or snowmelt
events, and any point source discharges of wastewaters (e.g., from sewage treat-
ment facilities). Water outputs include discharges through the lake outflow(s),
evaporation, losses to groundwater, and water withdrawals for domestic,
agricultural, and industrial uses. If inputs exceed outputs, lake volume will in-
crease and the lake level will rise. Conversely, when lake outputs exceed inputs
(for example, during a summer drought period), the lake level will fall.
Lakes that experience large fluctuations in lake volume as a result of either
natural or human-related causes have unique management problems. Large
drops in lake level can hinder user access to the lake, and the exposed shoreline
may be aesthetically unpleasing. The shoreline may be subject to greater erosion
from wave action and runoff, increasing the silt load in the lake or reservoir.
Plants and animals that live in shallow nearshore areas may be adversely affected
by exposure and desiccation. For fish species that spawn in nearshore areas,
decreased water levels that coincide with periods of egg laying and incubation
can affect reproductive success. Large changes in lake level are common
Surface water is standing
or flowing water on the
land surface, such as
streams, rivers, lakes, and
oceans.
Groundwater is water that
infiltrates the soil and
underlying rock layers,
eventually flowing into
lakes and other surface
waters.
Surface runoff is excess
precipitation or snowmelt
that does not infiltrate the
soil but flows over the
land surface.
Lakes that experience
large fluctuations in lake
volume as a result of
either natural or
human-related causes
have unique management
problems.
9
-------
Fish and Fisheries Management in Lakes and Reservoirs
All else being equal, lakes
with longer residence
times are generally more
productive than lakes with
shorter residence times.
problems in some reservoirs and in arid regions where evaporation rates are high
and water inputs are low. At the same time, however, controlled changes in water
level, at the right time and of the appropriate magnitude, can be a useful fisheries
management tool (see Chapter 8).
A second important lake characteristic is its hydraulic residence time, defined
as the average time required to completely replace a lake's water volume. In
simple systems where the inflow and outflow rates are equal and water in the lake
is completely mixed, the water residence time (Tw) equals the amount of time that
would be required for the water inflow or outflow (Q) to replace the volume of
water in the lake (V):
TW = V/Q
Lakes with large inflows and outflows relative to the lake volume have short
residence times. Water in the system is replaced rapidly, generally within days or
months (e.g., Fig. 2-3). Large lakes with relatively small inputs and outflows, on
the other hand, have long residence times, on the order of several years or
decades.
Inflow =
10 acre-ft/day
Outflow =
10 acre-ft/day
Water residence time = 500 acre-ft -s-10 acre-ft/day = 50 days
Figure 2-3.—Hydraulic residence time is the average time required to completely renew a
lake's water volume. The simple formula given in the example above assumes that inflow
is equal to outflow (source: Olem and Flock, 1990).
A lake's hydraulic residence time influences management decisions in two
major ways:
1. Lakes with longer residence times will generally exhibit longer lag
times; that is, a longer period of time will pass before restoration ef-
forts (such as reductions in external nutrient loads) will result in dis-
cernible changes or improvements in lake quality. Such lakes have
relatively poor ability to "cleanse" themselves by flushing.
2. In-lake processes (such as internal nutrient cycling) are more impor-
tant in lakes with longer residence times, while lakes with short
residence times are influenced more by the quantity and types of exter-
nal inputs. All else being equal, lakes with longer residence times are
generally more productive than lakes with shorter residence times. In
waters with very short residence times, the development of plankton
communities (small plants and animals that live suspended in the
water column) may be hindered by the rapid flushing rate.
10
-------
Chapter 2. Lake and Reservo/r ecosystems
The Lake and its Watershed
The land area that surrounds a lake and drains into it (either directly or through
feeder streams or rivers) is called the lake's watershed. Water and the dissolved
and particulate materials it carries enter the lake from its watershed. If a lake is
dominated by surface inflows, the characteristics of its watershed and activities
occurring there play important roles in determining water quality and prqduc-
tivity. Important natural features include watershed topography, vegetation, and
soil fertility and erodibility.
Land uses in the watershed also directly affect both lakewater quality and
quantity. For example, large areas of impervious surfaces (paved areas or packed
dirt) decrease the infiltration of water into the soil and groundwater system,
thereby increasing the quantity_of-stormwater discharged directly into the receiv-
ing lake or stream as surface runoff. Watershed disturbances that remove natural
vegetation, such as farming or construction, can greatly increase the amount of
silt and nutrients exported from the land to the lake. Managing land uses and ac-
tivities within the watershed is, therefore, an important component of a com-
prehensive lake management and restoration program.
Sediment Loads and the Bottom Substrate
Waters entering a lake generally carry suspended particles, including organic
matter, clays, and silt washed from the watershed and carried downstream to the
lake in rivers and streams. These particles settle once they reach the relatively
quiescent lake environment; as a result, lakes are extremely efficient sediment
traps. Although filling with sediments is a part of a lake's natural aging process,
poor land management practices can speed this process significantly. Watersheds
that have soils with a high clay content, more erodible soils, and more exposed
soil and disturbance contribute greater quantities of suspended sediments. In ad-
dition, sediments can carry substantial quantities of adsorbed nutrients and
chemical contaminants. Thus, lakes receiving high sediment loads frequently
also receive excessive inputs of nutrients and toxic contaminants.
Much of the sediment load entering a lake, together with the particulate mat-
ter produced internally (primarily dead organic particles from plants and
animals living within the lake), eventually settles to the bottom. The rate of
sedimentation and the types of materials deposited determine the physical char-
acteristics of the \bottom substrate (see Table 2^), which, in turn, influence
oxygen levels in and near the bottom sediments andlihe types and productivity
of organisms that live there. Many fish species deposit their eggs in these bottom
sediments; different fish species prefer or require different substrate types. For
example, lake trout require well-oxygenated, gravel-rubble substrate with little
silt or clay. High sedimentation rates, resulting from large inputs of suspended
sediments to the lake, may smother and kill eggs deposited on the bottom.
Table 2-1.—Substrate types and general characteristics.
Bedrock: All exposed rock
Boulder: All rock over 10 inches (25 cm) in diameter (approximately)
Rubble: Rock material between 3 and 10 inches (8-25 cm) in diameter
Gravel: Rock material between 1/8 inch and 3 inches (0.2-8 cm) in diameter
Sand: Material of crystalline rock origin less than 1/9 inch (0.3 cm) in diameter but still large
enough to be palpable as grit
Silt: Inorganic material of various origins but finer than sand
Clay: A material of organic origin (aluminum silicates) with a greasy feel between the fingers
and no apparent structure
Muck: A soft material largely of organic origin with silt and clay intermingled
Marl: A light gray, calcerous material derived principally from agal activity and mollusk shells
Detritus: An organic material in which large pieces (sticks, leaves, remnants of decayed aquatic
- plants, etc.) are common
Managing land uses and
activities within the
watershed is, therefore, an
important component of a
comprehensive lake
management and
restoration program.
Although filling with
sediments is apart of a
lake's natural aging
process, poor land
management practices can
speed this process
significantly.
11
-------
Fish and Fisheries Management in Lakes and Reservoirs
In lakes with a high
concentration of
suspended particulates,
most of the incoming light
is absorbed or
backscattered in the first
few feet of water.
In photosynthesis, light
energy is converted into
chemical energy and
stored as organic
compounds to support
biological growth and
production.
[LJight energy with
shorter wave lengths
penetrates deeper into the
water column.
During periods of heavy
snow and ice cover, very
little light penetrates into
the lake to support plant
growth.
Light in Lakes
Light is essential for primary production. It is also the primary source of heat for
lakes. Thus, the amount of light available and the depth to which it penetrates are
major driving forces that directly and indirectly affect lake productivity and a
wide range of other lake properties and processes.
A portion of the light reaching a lake is reflected off its surface; the greater the
angle of the sun, the higher the percentage of light reflected. Near noon on a clear,
calm summer day, about 5 percent of the incident light is reflected, while over 50
percent is reflected by late afternoon (Wetzel, 1983).
The light that enters a lake is
• absorbed by the water and converted into heat;
• absorbed by plants and converted, through photosynthesis, into organic
matter;
• absorbed by inorganic particles in the water and converted into heat;
• scattered back out of the lake by particulates in the water; or
• reflected or absorbed and converted to heat by sediments on the lake
bottom, if it penetrates through the water column.
In lakes with a high concentration of suspended particulates, most of the in-
coming light is absorbed or backscattered in the first few feet of water. Deeper
waters receive little heat input and have inadequate levels of light for pkint
growth. Low light may, in such waters, be a major factor limiting plant growth and
lake productivity.
Water strongly absorbs light in the infrared and' red range of the light
spectrum (range with longer wave lengths); and 40 to 90 percent of the light ener^
gy at these wave lengths is absorbed by pure water within the first three feet
(Hutchinson, 1957). By contrast, the same depth of water absorbs less than three
percent of the green, blue, and ultraviolet light. Thus, light energy with shorter
wave lengths penetrates deeper into the water column. One result of this differen-
tial absorption of light is that deeper waters and lakes with relatively low levels of
suspended solids generally appear bluish green.
Dissolved organics increase the absorption of ultraviolet, blue, and green light.
While all waters absorb infrared and red light, waters with high concentrations of
dissolved organics absorb all wave lengths of light and, as a result, all or most of
the incoming light may be absorbed in the upper few feet of the water column.
Heat input is concentrated in the top layer of water and plant growth inhibited in
deeper waters.
Light availability may vary seasonally (see Fig. 2-4). Algal blooms in the sum-
mer may prevent light from penetrating into deeper waters. Immediately follow-
ing rainstorms or snowmelt, water clarity and light penetration may be reduced
by large influxes of suspended sediments in surface runoff, especially in water-
sheds where soils and the natural vegetation cover have been disturbed.
Snow and ice cover during winter may also reduce light levels. The percentage
of light reflected by and transmitted through clear, colorless ice is not greatly dif-
ferent than that for water. Light absorption increases greatly, however, if the ice is
cloudy (with air bubbles) or stained with organic matter. Snow cover also marked-
ly increases both light reflection (about 75 percent) and light absorption (90 per-
cent by four inches of new snow). During periods of heavy snow and ice cover,
very little light penetrates into the lake to support primary production.
12
-------
Chapter 2. Lake and Reservoir Ecosystems
Lake Trari4|iarency
JUN JUL AUG SEP OCT NOV DEC JAN FEB MAR APR MAY JUN
Figure2-4.-Varlations in the Secchl disk transparency of Wlntergreen Lake in south-
western Michigan in 1970-71 (source: Wetzel, 1975). Water clarity and the depth of
light penetration can be measured In several ways. One of the simplest and most
common is with the Secchi disk. Secchl depth transparency is the greatest depth at
which a disk 20 cm in diameter Is visible when lowered into the lake around midday.
Seasonal changes in Secchl depth transparency or over time provide a good indica-
tion of trends In water clarity and the approximate depth to which light levels are
adequate for plant growth.
Lake Circulation and Thermal Regimes
The movement and mixing of waters within a lake or reservoir also are key fac-
tors that influence lake productivity as well as the suitability of lake habitat for
various fish species. Wind is the primary energy source that drives water move- -
merit and mixing. Differences in water density, caused by differences in tempera-
ture and/or the concentration of dissolved solids, may limit the depth and extent
of wind-driven water circulation.
The density (weight per unit mass) of water is temperature-dependent. As
waters become colder (down to 39°F or 4°C), they also become heavier. Because
sunlight is the major heat source, waters near the surface that receive direct heat
inputs warm faster than deeper waters. During the summer, this process often
creates a stable thermal stratification pattern (Fig. 2-5): a warmer, lighter layer of
water, the epilimnion, floats on a colder, heavier water layer, the hypolimnion.
The intermediate area of rapid temperature change is the metalimniori.
The differences in water density between the epilimnion and hypolimnion
provide an effective barrier to lake mixing. The greater the temperature differen-
ces, the more energy is needed to circulate the water. During summer thermal
stratification, waters in the epilimnion circulate but little water exchange occurs
between the epilimnion and hypolimnion. When the lakewater cools, as in the
fall, this temperature-controlled zonation breaks down and water mixes
throughout the lake (fall overturn). Likewise, in many lakes thermal differences
also are small in the spring and the water column mixes completely (spring over-
turn).
Water reaches its maximum density at 39°F (4°C). At lower temperatures,
density decreases slightly until the freezing point (32°F, 0°C) is reached. When
water freezes, ice forms and the density decreases sharply (Fig. 2-5). Because of
this decrease in density at temperatures near and at the freezing point, ice forms
at the top of lakes rather than at the bottom. During the winter, this ice cover in-
sulates the lake from the wind. Thus, even though the density gradients are rela-
tively minor, little water column mixing occurs.
The differences in water
density between the
epilimnion and
hypolimnion provide an
effective barrier to lake
mixing. The greater the
temperature differences,
the more energy is needed
to circulate the water.
13
i
-------
Fish and Fisheries Management in Lakes and Reservoirs
Mixing occurs throughout
the water column twice a
year, in the spring and. fall.
[A] lake's thermal regime
and temperature
variations are important
factors that influence the
types of species and fish
communities able to
survive and reproduce in
that environment.
Water density is also
affected by the
conceiitration of total
dissolved solids (TDS)...
(a)
TEMPERATURE AND THE DENSITY OF WATER
0 5 10 15 20 25 30 °C
(b)
-5
1 .00000
0.99900
0.99800
0.99700
0.99600
0.99500
0.92
0.91
TEMPERATURE °C
0 5 10 15 20 25 30
0 0.99600
LIQUID TO ICE
THERMOCLINE
The density of water is
greatest at 4°C. Water
becomes less dense as it
warms or as it cools.
20-25 °C = 60-75 °F
15-20°C = 45-65 °F
4-15 °C = 39.2-45 °F
:•:!:•:!: EPJ LIMN j_0 N '20^25°C :•:•:•;
8 M£TALI MM O N J 5^0 °C}|
Figure 2-5.—The temperature-density relationship of water (a) enables deep lakes to
stratify during summer (b) (source: Olem and Flock, 1990).
Most lakes in temperate regions undergo a fairly predictable seasonal pattern,
alternating between stratification and complete mixing. During the summer and
winter (in ice-covered waters), lakes are generally thermally stratified, with mini-
mal mixing of surface and deeper waters. Mixing occurs throughout the water
column twice a year, in the spring and fall. Shallow lakes, however, especially
those lakes in areas with strong winds, may circulate continually or periodically
even during summer. By contrast, very deep lakes, especially small, deep lakes in
steep-sided watersheds that limit wind speeds, may mix only once a year, infre-
quently, or not at all. (Mixing and stratification patterns in reservoirs are discussed
further in the subsection, Special Issues in Reservoirs.)
Lake stratification has direct and indirect effects on fish communities. The
colder, deeper waters of the hypolimnion, if well-oxygenated, can serve as a
refugium for fish species that prefer (or require) cold water temperatures. Different
fish species prefer to live at different temperatures (see Table 2-2); thus, a lake's
thermal regime and temperature variations are important factors that influence
the types of species and fish communities able to survive and reproduce in that en-
vironment. However, because of the limited water exchange between the epilim-
nion and hypolimnion during summer, nutrients tend to accumulate in the
hypolimnion. Also, the lake's deeper waters can become depleted of oxygen. Low
levels of dissolved oxygen may restrict fish distributions and limit the types and
numbers of fish in the hypolimnion.
Table 2-2.—Fish species are often classified as coldwater, coolwater, or warmwater
fish, depending on their preferred water temperatures. Example species in each class
and the approximate midpoints of the preferred temperature range (Magnuson et al.
1979) are noted below. .
COLDWATER FISH
(50-60'F)
COOLWATER FISH
(68-77'F)
WARMWATER FISH
(77-86'F)
Brook trout
Lake trout
Rainbow trout'
Kokanee salmon
Walleye
Yellow perch
Northern pike
Muskellunge
Largemouth bass
Bluegill
Channel catfish
Carp
Water density is also affected by the concentration of total dissolved solids
(TDS): waters with higher TDS are heavier than waters with lower TDS (Table 2-3).
If deeper waters have substantially higher TDS than surface waters, a stable pat-
tern of lake stratification may result. Often, in such cases, the stratification is per-
manent; the lake rarely if ever mixes completely.
Lakes that are permanently stratified as a result of differences in TDS are
referred to as "meromictic lakes." Merpmictic lakes are relatively rare, however.
Most fresh waters have TDS levels between 0.01 and 0.5 g/L (Wetzel, 1983), con-
14
-------
Chapter 2. Lake and Reservoir Ecosystems
centrations that have comparatively little effect on water density. Generally, dif-
ferences in water density and patterns of lake stratification are determined
primarily by differences in water temperature; IDS concentrations play a secon-
dary role.
Table 2-3.—Changes in the density of water (at 39°F, 4°C) with total dissolved solids
(TDS) (source: Ruttner, 1963).
TDS fa/L) [
0
1
2
3
10
35 (mean seawater)
DENSITY
.00000
.00085
.00169
.00251
.00818
.02822
Organic Matter Production and Consumption
and Nutrient Cycling
Photosynthesis and Primary Productivity
Chlorophyll-bearing plants in aquatic ecosystems (e.g., planktonic algae, benthic
^algae, epiphytic algae, and rooted aquatic plants in the littoral zone) use the ener-
gy from sunlight to convert carbon dioxide, water, and nutrients into organic
matter, oxygen, and water (Fig. 2-6). This process, called photosynthesis, con-
verts light energy into chemical energy (stored as organic compounds), which
can then be used to support biological growth and production. The rate of
photosynthetic uptake of carbon to form sugars and other organic compounds is
called primary productivity. The amount of plant material produced and remain-
ing in the system is called primary production and is also referred to as the stand-
ing crop or biomass (total weight) of plants in a farmer's field. The molecular
oxygen produced during photosynthesis is the primary source of dissolved
oxygen in the water and oxygen in the atmosphere.
CO2 + H2O + NUTRIENTS
+ SUNLIGHT
PHOTOSYNTHESIS
RESPIRATION &
DECOMPOSITION
(CH20) + H20 + O2
Figure 2-6.—The equilibrium relationship between photosynthesis and respiration-
decomposition processes (source: Olem and Flock, 1990).
Because of the requirement for light, primary production by aquatic plants is
restricted to that portion of the lake that receives adequate light for photosyn-
thesis, referred to as the photic zone. The thickness of the photic zone depends
upon the transparency of the water and generally corresponds to the depth to
which at least 1 percent of the surface light penetrates.
Chlorophyll is a green
pigment in algae and
other green plants
essential for the
conversion of sunlight,
carbon dioxide, and water
to sugar — photosynthesis.
The molecular oxygen
produced during
photosynthesis is the
primary source of
dissolved oxygen in the
water and oxygen in the
atmosphere.
15
-------
Fish and Fisheries Management In Lakes and Reservoirs
The chemical energy
stored in organic
molecules is released
through the processes of
respiration and
decomposition.
Decomposition occurs
throughout the water
column but is often
concentrated in deeper
waters and in the bottom
sediments.
Primary production of planktonic algae is controlled mainly by, water
temperature, light and nutrient availability, hydraulic residence time, and the rate
at which they are consumed. When light is adequate, nutrient availability fre-
quently is the major limiting factor. Production of rooted aquatic plants is control-
led more by temperature, light, and bottom substrate type because most rooted
plants obtain nutrients from the bottom sediments.
While in-lake photosynthesis is the dominant source of organic matter for the
lake's food web, most lakes also receive significant inputs of energy in the form of
dissolved and particulate organic matter from their watersheds. Watershed char-
acteristics, lake type, and hydraulic residence time determine the importance of
these external inputs relative to in-lake photosynthesis.
Respiration and Decomposition
The chemical energy stored in organic molecules is released through the processes
of respiration and decomposition (Fig. 2-6). Plants and animals break down or-
ganic molecules to produce the energy needed for their survival and growth in a
process called "respiration." Organic matter decomposition is a collective term for
the net conversion of organic material back to inorganic compounds through the
respiratory activities of all organisms, including bacteria, fungi, and otHer
microbes. Both processes consume oxygen and release energy, carbon dioxide,
water, and nutrients.
Decomposition occurs throughout the water column but is often concentrated
in deeper waters and in the bottom sediments. Dead organic matter (detritus) ac-
cumulates on the lake bottom, and in productive lakes, the amount can be sub-
stantial. Under these conditions, the quantity of oxygen consumed in deeper
waters by decomposition can exceed that available or produced through
photosynthesis (Fig. 2-7). Oxygen depletion can be particularly severe in thermally
stratified, productive lakes during summer. Then the deeper waters of the
hypolimnion are isolated from the epilimnion where photosynthesis and water
circulation recharge the oxygen supply. In severe cases, dissolved oxygen may be
PHOTOSYNTHESIS EXCEEDS INSPIRATION
EPHUIHION
Flint nutrlont upinh*. pholoiynth»l» of
orginlc monoi «nd dluolvtd oxygon.
• THERMOCLINE
Consumption of tflMolvori oxygon In
rMplroflon'dteompoiltlon procoaaot. nulrlont
rog«nor«tlon by orginle mittor decomposition.
Accumulation of nutrionti and orginlc
Mdlminu, >*|MM of dl»olvod nuirlonti from
••dlmonii to w»t«r.
Figure 2-7.—Influence of photosynthesis and respiration-decomposition processes and
organic matter sedimentation on the distribution of nutrients, organic matter, and dis-
solved oxygen in a lake during summer thermal stratification (source: Olem and Flock,
1990).
16
-------
Chapter 2. Lake and Reservoir Ecosystems
depleted completely in waters near the lake bottom or in the entire hypolimnion.
Similar conditions may occur in productive lakes during winters with prolonged
ice and snow cover that limit both water mixing and light penetration.
Oxygen concentrations not only affect the suitability of the habitat for
aquatic animals but also control many important chemical and physical reac-
tions. For example, under anoxic conditions (no dissolved oxygen), some metals,
nutrient compounds, and gases (e.g., hydrogen sulfide [HaS] and methane [CHi])
become increasingly soluble and are released from the bottom sediments into the
hypolimnion. At fall overturn, the nutrients and other compounds may reenter
the photic zone and stimulate algal productivity. Nutrients that reenter the water
column from sediments constitute an internal nutrient load to the lake.
Limiting Nutrients
Of the various elements required for cell growth, nitrogen and phosphorus often
limit lake productivity. Nitrogen occurs in several forms, as nitrate (NOs-), am-
monium (NH4+), and molecular nitrogen gas (Nz). Some algal species, par-
ticularly blue-green algae, can satisfy their nitrogen requirements by using N2
from the atmosphere. As a result, phosphorus is most often the limiting nutrient
in lakes (Hecky and Kilham, 1988).
Many human activities produce waste products with high concentrations of
phosphorus, such as agricultural drainage waters, some detergents, and
municipal sewage. If allowed to enter lakes, these wastewaters can artificially
stimulate algal production and result in nuisance algal blooms, noxious tastes
and odors, and oxygen depletion in the water column. Therefore, lake manage-
ment and restoration projects often focus on controlling phosphorus loads.
Some systems are nitrogen-limited, however, and some lakes need to be
managed for both phosphorus and nitrogen. For example, many of the high-
elevation lakes in the western United States are nitrogen-limited (Morris and
Lewis, 1988; Eilers, 1991). For these systems, the nitrogen dissolved in precipita-
tion (as NOs- and NH4+) is the dominant nitrogen source (Likens and Bormann,
1972). As a result, increases in nitrogen deposition from atmospheric emissions of
nitrous oxides from power plants, industrial sources, and motorized vehicles can
increase both the availability of nutrients and productivity of these lakes.
Trophic State and Eutrophication
Lakes are frequently characterized according to their trophic state:
• Oligotrophic lakes are nutrient poor and relatively unproductive. In-
sufficient organic matter is produced in the epilimnion to reduce
hypolimnetic oxygen concentrations; thus, the hypolimnion remains
relatively oxygenated throughout the year.
• Mesotrophic lakes have intermediate nutrient availability and
biological productivity.
• Eutrophic lakes are nutrient rich and highly productive. Decomposi-
tion of the abundant organic matter may often exhaust the dissolved
oxygen in unlighted zones, leading to anoxia in the hypolimnion.
• Hypereutrophic lakes, which are extremely productive and rich,
often experience pea-soup conditions because of high concentrations
of algae and/or excessive densities of rooted aquatic plants.
Multiple trophic states can exist within large lakes and reservoirs; for ex-
ample, the upper reaches of a reservoir may be oligotrophic while lower reaches
or regions receiving tributary inflows with high nutrient loads may be eutrophic.
Oxygen concentrations
not only affect the
suitability of the habitat
for aquatic animals but
also control many
important chemical and
physical reactions.
Nutrients that reenter the
water column from
sediments constitute an
internal nutrient load to
the lake.
If allowed to enter lakes,
these wastewaters can
artificially stimulate algal
production and result in
nuisance algal blooms,
noxious tastes and odors,
and oxygen depletion in
the water column.
Trophic state is the degree
of a lake's eutrophication.
17
-------
Fish and Fisheries Management in Lakes and Reservoirs
A kike's trophic state has a
major influence on the
potential fish production
and types offish
communities best suited to
the water.
Habitat is a place where
plants or animals live and
grow.
Lake eutrophication is a natural process that results from the gradual ac-
cumulation of nutrients, increased productivity, and a slow filling-in of the lake
basin, generally over hundreds of years, with accumulated sediments and organic
matter from the watershed. Human activities can greatly accelerate this process,
however, by dramatically increasing nutrient, soil, or organic matter loads to the
lake in a process called "cultural eutrophication." Some lakes and reservoirs are
naturally eutrophic because they are located in naturally fertile watersheds. Other
lakes are naturally oligotrophic and, if undisturbed, will remain so for thousands
of years. A lake's trophic state has a major influence on the potential fish produc-
tion and types of fish communities best suited to the water. Therefore, natural dif-
ferences in trophic state must be recognized and accounted for when designing; a
fisheries and lake management program.
Aquatic Biota
Most of the major groups (taxa) of biota are represented in the biological com-
munities that occur in lakes and reservoirs, from one-celled bacteria and algae to
the birds and mammals that rely on aquatic ecosystems for food or habitat. For
convenience, many of these taxa are grouped according to their primary habitat
and/or lifeform. For example:
• Microbes refers collectively to some bacteria, fungi, and other micro-
scopic organisms involved in organic matter decomposition.
• Plankton are microscopic organisms that live suspended in the water
column. The plankton community includes both plants (phytoplankton)
and animals (zooplankton) and several different major taxa (phyla, clas-
ses, families, and species of organisms).
• Periphyton are organisms associated with submerged substrates, such
as bottom sediments, aquatic vegetation, docks, and other surfaces. The
periphyton community includes periphytic algae as well as the micro-
scopic animals and microbes that feed on that algae.
• Macrophytes refers to the larger, macroscopic aquatic plants and
algae, most of which grow rooted in the bottom sediments. Some, how-
ever, are free-floating forms.
• Macroinvertebrates are the larger, multi-celled animals without
backbones, including many species of mollusks, insects, other crus-
taceans, and worms (oligochaetes), which generally live on or in the bot-
tom sediments (benthic invertebrates) or attached to macrophytes in the
littoral zone.
Fish feed on all of these organisms, although different species prefer different
types of prey. Brief descriptions follow of each of these major components of the
biological community in lakes and reservoirs.
Microbes
Freshwater microbial communities are composed of a diverse array of bacteria,
fungi, yeasts, mold, protozoans, and other microorganisms that are found free-
living in the water column, associated with suspended organic matter, mixed in
with bottom sediments, and on submerged surfaces, such as plants, rocks, and
decaying organic matter. These communities play a major role in the breakdown
of organic substances and nutrient recycling as well as the nutrition of animals
that feed on detritus and other organic materials. The activity of microbes (termed
"conditioning") makes detritus more digestible; and the microbes themselves are
an energy source for detritus-feeding organisms, which include many benthic in-
vertebrates and some fish species (e.g., carp and some members of the sucker
family).
18
-------
Chapter 2. Lake and Reservoir Ecosystems
Phytoplankton
Phytoplankton are microscopic algae that live suspended in the water column.
Most phytoplankton are slightly heavier than water and will gradually sink or
settle out of the water column if not maintained by water turbulence or wind-
driven water circulation. A few species have buoyant, gelatinous coatings and
float to the surface, forming algal scums. These phytoplankton occur primarily in
nutrient-rich, highly productive waters where light is the major factor that limits
algal growth.
The taxonomically diverse phytoplankton community is composed of a
number of different kingdoms and phyla, such as the green algae (Chlorophyta),
blue-green "algae" (Cyanobacteria), and diatoms (Chrysophyta). Different
species tend to thrive under particular types of conditions. Blue-green "algae"
often dominate in productive eutrophic or hypereutrophic lakes because they can
fix nitrogen gas from the atmosphere.
Seasonal changes in environmental conditions within a given lake generally
result in seasonal changes in the types and abundance of algae (Fig. 2-8). Algal
production and biomass usually are low in the winter because of low water
temperatures and low light availability. In the spring and early summer,
phytoplankton biomass tends to be high as a result of increasing water tempera-
tures and light availability, relatively high nutrient availability, and low losses to
zooplankton grazing (consumption by microscopic animals). As grazing pressure
increases and nutrients in the epilimnion are depleted by continued algal growth,
the algal biomass generally declines from early to midsummer, only to rise again
in the late summer and fall when water column mixing increases the supply of
nutrients. Diatoms often dominate the phytoplankton in the spring and fall,
green algae in midsummer, and blue-greens in late summer.
Phytoplankton serve as a food source for zooplankton and other animals, in-
cluding'some fish species (e.g., many minnows) that feed directly on planktonic
algae. Phytoplankton standing crops are generally a good indicator of a lake's
trophic state and nutrient loadings that, in turn, influence potential fish produc-
tion.
N D J
Figure 2-8.—A typical seasonal succession of lake phytoplankton communities. Diatoms
(solid circles) dominate the phytoplankton in the spring and fall, green algae (open
squares) in midsummer, and blue-green algae (open triangles) in late summer (source:
Olem and Flock, 1990).
19
-------
Fish and Fisheries Management in Lakes and Reservoirs
Rooted mocrophytes are
classified into three groups
based on their life-form:
emergent, floating-leaved,
and submersed.
Trophic level is a step in
the trophic pyramid, the
hierarchical classification
based on the types of
organisms other
organisms eat and that eat
them.
Periphyton
Periphytic algae typically contribute a rather insignificant amount to the energy
budget of lakes; for example, generally less than 6 percent of the total in-lake
primary production in oligotrophic lakes (Schindler et al. 1973; Jordan and Likens,
1975; Sondergaard and Sand-Jensen, 1978; Kairesalo, 1980). Their relative contribu-
tion to primary production is greater in shallower lakes. Most species are single-
celled or exist in small, microscopic colonies. Some periphytic algae, however,
grow in long filaments, visible to the naked eye. Excessive growths of periphyton
can occur in highly productive waters as well as acidic lakes, can alter the bottom
habitat, and are unattractive. Few fish in temperate lakes feed primarily on
periphyton. However, large growths of filamentous algae can provide a sheltered
habitat for small, young fish.
Macrophytes
Macrophytes serve as breeding, feeding, and nursery grounds for many fish
species and are an important food source for waterfowl, some mammals (e.g.,
muskrat, moose), invertebrates, and detritus-based organisms. Macrophytes also
serve as sites for egg deposition by insects, zooplankton, and some fish; as sub-
strate for periphytic algae and various attached invertebrates; and as
microhabitats for small fish and invertebrates avoiding predation. Finally, macro-
phytes help to stabilize bottom sediments by binding them and reducing wave ac-
tion.
Rooted macrophytes are classified into three groups based on their life-form:
emergent, floating-leaved, and submersed. Emergent macrophytes, which grow
on water-saturated or submerged soils and extend mature leaves into the air, in-
clude cattails (Typha spp.), pickerel weed (Pontederia cor data), and arrowheads
(Sagittaria spp.). Floating-leaved macrophytes also are rooted in the sediment, taut
their leaves float on the surface of the water when mature, for example, the water-
lillies (Nuphar spp.). Submersed rooted macrophytes grow entirely below the
water's surface and include numerous mosses and macroalgae (Cham) as well as
vascular plants such as watermilfoil (Myriophyllum spp.), bladderwort (Utricularia
spp.), and pipewort (Eriocaulon spp.). Free-floating macrophytes, such as duck-
weed (Lemna spp.), occur in sheltered areas of some lakes.
Many macrophytes grow through the spring and summer and then die back
when water temperatures cool in the fall. In shallow lakes with large, extensive
beds of macrophytes, decomposition of this dead organic matter can deplete
oxygen levels and may, in extreme cases, result in fishkills. Low levels of dissolved
oxygen may also occur periodically in dense beds of macrophytes during summer,
following extended periods of cloud cover and low light input, or during the
night, when the oxygen consumed by plant respiration exceeds that produced by
photosynthesis. , '
Zooplankton
Zooplankton are a diverse group of aquatic invertebrates, generally smaller than 2
mm (less than one-tenth of an inch). The three most numerically dominant
taxonomic groups are the rotifers, copepods, and cladocerans (water fleas) (Fig.
2-9). The zooplankton community includes both herbivores (animals that feed on
plants, primarily the phytoplankton) and predators, which feed on other animals.
Zooplankton grazing can have a significant influence on phytoplankton species
composition and productivity through selective grazing (e.g., feeding on larger or
smaller phytoplankton, depending on the size of the zooplankton) and by recy-
cling nutrients. Zooplankton, in turn, are eaten by fish, waterfowl, and other larger
animals and thus play an important role in the transfer of energy from,
phytoplankton to higher trophic levels.
20
-------
Chapter 2. Lake and Reservoir Ecosystems
B
Figure 2-9.—Examples of zooplankton: (a) rotifer, (b) copepod, and (c) cladoceran
(adapted from Wetzel, 1975).
Because fish feed on zooplankton, which feed on phytoplankton, changes in
fish species composition and abundance may cause marked changes in both
zooplankton and phytoplankton communities. Fish tend to feed selectively on
large zooplankton. Therefore, the introduction of plankton-feeding fish
(planktivores) into a lake can result in the rapid decline of large-bodied
zooplankton species, an increase in smaller-bodied forms, and in some cases, an
overall decline in zooplankton abundance and biomass. This, in turn, may lead to
a shift in phytoplankton species composition (favoring larger forms on which the
smaller-bodied zooplankton feed less efficiently) and a net increase in
phytoplankton abundance.
To avoid fish predation, some species of zooplankton, particularly large, preda-
cious zooplankton, exhibit a diel vertical migration in lakes. During the day, these or-
ganisms remain near the lake bottom; at night, however, they move up into the
metalimnion and epilimnion to feed on phytoplankton in the photic zone.
Macroinvertebrates
Most macroinvertebrates live on or in the bottom sediments or attached to mac-
rophytes in the littoral zone. Some species (called "nekton," as a group) live on or
immediately under the lake surface, in association with the water's surface film.
Benthic macroinvertebrates feed mostly on the detrital matter that settles to the
lake bottom. They play an important role in the mechanical breakdown of dead
organic matter and the associated release and recycling of nutrients bound in
these organic materials. Other macroinvertebrates are herbivores and feed on
periphyton. Predators feed on other invertebrates or even small fish. Many fish,
waterfowl, and other bird species rely on macroinvertebrates as their primary
food resource.
Common macroinvertebrates in lakes include many species of aquatic
worms (oligochaetes), leeches, insects (e.g., mayflies, dragonflies, damselflies),
other crustaceans (e.g., crayfish, amphipods), and mollusks (e.g., snails, clams).
Some species of insects live their entire life cycle in aquatic environments. Many,
however, occur in fresh waters only as immature forms. Upon metamorphosiz-
ing into adults, they emerge from the water, mate, and then lay eggs in aquatic
habitats. Often, these terrestrial adult stages are short-lived. For example, imma-
ture forms of mayflies develop for one to two years in aquatic environments but
live only one to three days as terrestrial adults. Adult emergence frequently oc-
curs over a fairly short period for a given insect species and in a given lake.
During this hatch, fish feed heavily on the emerging adults.
21
-------
Fish and Fisheries Management in Lakes and Reservoirs
[TJhe occurrence of red
bloodworms (Tubificidae)
in bottom sediments is
indicative of low levels of
dissolved oxygen because
these organisms can
survive at much lower
oxygen levels than most
other animals.
Different species of benthic invertebrates have varying tolerances of environ-
mental stress, such as low levels of dissolved oxygen or high concentrations of
toxic substances. Therefore, benthic community composition is often used as an
indicator of environmental condition. For example, the occurrence of red blood-
worms (Tubificidae) in bottom sediments is indicative of low levels of dissolved
oxygen because these organisms can survive at much lower oxygen levels than
most other animals. Substrate type also has major impact on benthic community
composition.
Fish
All of the previously mentioned organisms are eaten by fish; however, different
fish species have different preferred food types and mechanisms of food capture
(Table 2-4). An animal taken by a predator as food is referred to as its prey.
Table 2-4.—Preferred types of prey consumed by adults of selected fish species.*
DOMINANT PREY
EXAMPLE FISH SPECIES
Phytoplankton
Zooplankton
Benthic invertebrates
Macroinvertebrates associated
with macrophytes
Fish
Gizzard shad, brassy minnow
Alewife, American shad, cutthroat trout, rainbow trout, kokanee
salmon, golden shiner (plus juvenile fish of many species)
Lake whitefish, bluntnose minnow, lake sturgeon, white sucker,
shorthead redhorse, brown bullhead, channel catfish, slimy sculpin
Bluegill, white crappie, yellow perch (plus juvenile fish of many
species)
Longnose gar, grass pickerel, muskellunge, largemouth bass,
striped bass, walleye, lake trout
* Most fish, however, are opportunistic feeders and can eat a diversity of prey, depending on the types that
are most readily available. In addition, dominant prey types often change as fish grow and become larger.
Fish that are planktivores — for example, alewifes, cisco (lake herring), smelt,
and kokanee salmon — feed primarily on zooplankton and, to a lesser degree, on
phytoplankton and other organic particles suspended in the water column. Many
planktivores filter fairly large quantities of water through their gill rakers (Fig. 2-
10), which act as sieves to collect the larger particles. The mesh size of these gill
HEMIBRANCH
GILL COVER
A GILL FILAMENT
LOWER GILL ARCH
Figure 2-10.—Fish gills and gill rakers. The gill rakers act as a sieve to collect plankton fil-
tered from the water (adapted from Scott and Grossman, 1973).
22
-------
Chapter 2. Lake and Reservoir Ecosystems
raker sieves varies among species and by fish size; thus, some species are able to
capture smaller plankton than are others. All planktivores also rely to some de-
gree on visual contact and pursuit to capture zooplankton prey. Planktivores that
actively select their prey tend to feed on larger, more visible zooplankton species
and also can feed more effectively in waters with higher transparency.
Other fish species — for example, suckers, carp, bullheads, and sculpin —
feed primarily on organisms on the lake bottom, including benthic macroinver-
tebrates and periphytic algae as well as detritus. For some, but not all of these
species, their benthic feeding habits are evident from their mouth morphology
(Fig. 2-11). Some of these fish species (such as carp) feed fairly passively, sucking
up large volumes of bottom sediments and then expelling all but the edible par-
ticles. Most fish, however, rely on sight or other senses to identify individual prey
items, which are then removed from the bottom. Bullheads, for example, seek out
food by using the tastebuds on their barbels (Fig. 2-12).
Figure 2-11.—Side and bottom views of the mouth of a white sucker, which feeds primari-
ly on benthos (source: Scott and Grossman, 1973).
Figure 2-12.—Brown bullhead, illustrating the barbels near the fish's mouth used to help
locate prey (adapted from Scott and Grossman, 1973).
Finally, some fish (called piscivores) feed primarily on other fish, often
referred to as forage fish. Most large sport fish species are piscivores, including
lake trout, largemouth bass, walleye, northern pike, and muskellunge. Piscivores
can, if necessary, feed on other food resources, although such a shift in dominant
prey generally results in substantially slower growth rates. Changes in diet also
occur as the fish ages and grows; when young, most fish species feed primarily
on plankton and/or macroinvertebrates.
Although fish have preferred prey, most species are fairly omnivorous and
adaptable; they feed most heavily on the types of prey and groups of organisms
that are readily available. The quantity and quality of available prey and the ef-
fort required for fish to obtain sufficient food are major factors determining fish
survival, growth rates, and reproductive success (see Chapter 3). At the same
time, fish predation affects the composition and abundance of plankton and ben-
thic communities as a result of their selective feeding on preferred food items and
prey species.
The quantity and quality
of available prey and the
effort required for fish to
obtain sufficient food are
major factors determining
fish survival, growth
rates, and reproductive
success.
23
-------
Fish and Fisheries Management in Lakes and Reservoirs
Other Animals
A diversity of other animals — amphibians, reptiles, birds, and mammals — play
important roles in lake and reservoir ecosystems. Some, such as kingfishers,
eagles, and loons, are important fish predators. Others compete with fish for food;
for example, duckling growth can be inversely affected by fish that feed on the
same benthic macroinvertebrates as the waterfowl (Hunter et al. 1986). A few
animals, such as amphibian larvae and tadpoles, are eaten by fish. Beaver activity
in small lakes can alter the lake's physical habitat as well as that of inflowing
tributaries and affect the suitability of the lake for fish survival or reproduction.
Lastly, lake restoration and fisheries management actions may have both direct
and indirect effects on amphibian, reptile, bird, and mammal populations that rely
on lakes and reservoirs for food, habitat, or as sites for breeding and nesting.
The Trophic Pyramid
The transfer and general progression of energy from primary producers to her-
bivores, planktivores, and then to large predators constitutes the lake's trophic
pyramid (Fig. 2-13). The actual complex of feeding interactions that exists among
all of the lake's organisms is called the food web.
PISCIVOROUS
RSH
-------
Chapter 2. Lake and Reservoir Ecosystems
By constantly producing wastes and eventually dying, all of these organisms
provide nourishment for detritivores (detritus-feeding organisms) and to bac-
teria and fungi, which derive their energy by decomposing organic matter.
Detritivores and microbes are, themselves, often eaten by higher level organisms,
which recycle a portion of the stored energy. In addition, organic matter
transported into the lake from the watershed can decompose and supplement in-
lake production. Decomposition releases the nutrients tied up in organic matter,
making them available for further plant production (nutrient recycling).
Top-Down Versus Bottom-Up Lake
Management
Historically, the central paradigm of limnology has been that the productivity
and dynamics of lake ecosystems are regulated almost exclusively by the inputs
of nutrients and energy at the bottom of the trophic pyramid (Magnuson, 1991).
Efforts to improve water quality focused on reducing internal and external
nutrient and organic loads. Increasingly in recent years, however, scientists have
recognized that these bottom-up approaches to lake management may not be suf-
ficient nor necessarily the only means for achieving desired management objec-
tives and levels of lake quality.
Shapiro et al. (1975), Carpenter et al. (1985), and others have proposed using
top-down management as a complementary approach to bottom-up lake
management. The underlying principle of top-down management (also called
biomanipulation) is that human-controlled manipulations of the food web,
especially of top predators such as fish, can control the abundance and produc-
tivity of lower trophic levels, such as algae, which in turn can affect water
clarity, nutrient recycling, and other physical and chemical lake characteristics.
Given a typical trophic structure, such as that illustrated in Figure 2-14, the basic
hypothesis of top-down management is that an increase in the biomass of large
piscivorous fish should cause a decrease in the biomass of the small
planktivorous fish on which they feed. This increases the biomass of her-
bivorous zooplankton on which the planktivorous fish feed and finally
decreases the biomass of phytoplankton on which the herbivorous zooplankton
feed (Fig. 2-15). Carpenter et al. (1985) refer to this sequence of interactions as
the trophic cascade. Bottom-up factors (nutrient loading and organic energy
transfer) establish the potential lake productivity, while top-down factors
(predation and food web processes) determine the realization of that potential
(Carpenter et al. 1985; Carpenter and Kitchell, 1988). Both are important;
neither, by itself, is sufficient.
Lake ecosystems are highly complex. Rarely, if ever, are food web interac-
tions as simple as those described in the previous paragraph. Examples of factors
or processes that contribute to this complexity include, in addition to predation,
competition among species for limited resources, behavioral responses, physical
mixing patterns, the spatial heterogeneity of lakes, temporal variations in en-
vironmental conditions (such as climate), and the lag times in response that com-
monly occur (e.g., between a change in the abundance of piscivorous fish and the
subsequent change in abundance of its prey) (Carpenter, 1988; Wetzel, 1983).
Recognition and understanding of these factors can lead to more accurate predic-
tions of lake responses to management actions and, ultimately, to more effective
lake management.
Further details on top-down management are provided in Chapter 9. The
biomanipulation techniques and example applications presented there illustrate
the usefulness of these approaches as well as the complexity of and variations in
lake responses.
The underlying principle
of top-down management
(also called
biomanipulation) is that
human-controlled
manipulations of the food
web, especially of top
predators such as fish, can
control the abundance and
productivity of lower
trophic levels....
25
-------
Fish and Fisheries Management in Lakes and Reservoirs
PISCIVORE
INVERTEBRATE
PLANKTIVORE
VERTEBRATE
PLANKTIVORE
SMALL
CRUSTACEAN
ZOOPLANKTON
LARGE
CRUSTACEAN
ZOOPLANKTON
NANNOPLANKTON
EDIBLE NET
PHYTOPLANKTON
INEDIBLE
PHYTOPLANKTON
Figure 2-14.—Conceptual model of trophic structure in a typical lake (source: Carpenter et
al. 1985).
| PLANKTIVORE HERBIVORE
I
I
PHYTOPLANKTON
CO h-
to u
CD a.
PISCIVORE BIOMASS
Figure 2-15.—Hypothetical relationship between piscivore biomass and the blomass (solid
line) and production (dashed line) of vertebrate zooplanktivores, large herbivores, and
phytoplankton, assuming a trophic structure similar to that In Figure 2-14 (source: Car-
penter et al. 1985).
Special Issues in Reservoirs
Although all of the preceding physical, chemical, and biological processes also
apply to reservoirs, they have several unique features that deserve note. The major
distinctions relate to reservoir hydrology and water circulation patterns.
Typically, reservoirs have one or two major tributaries, very large watersheds
compared to the lake surface area, relatively short hydraulic residence times, and a
high shoreline development factor. The inputs of dissolved and particulate organic
and inorganic materials from the watershed are also likely to be very high. In some
26
-------
Chapter 2. Lake and Reservoir Ecosystems
ways, reservoirs occupy an intermediate position between rivers and natural
lakes in terms of their hydraulic residence time, degree of riverine influence, and
other environmental factors that control water quality and biotic productivity.
More so than in most natural lakes, the volume of the inflowing water from
major tributary(ies) can be an important factor in determining water circulation
patterns and flows in the reservoir (Fig. 2-16). Often, the inflowing river water
and the reservoir water differ in temperature or total dissolved solids and, there-
fore, in density. If the river inflow is warmer than the reservoir, the less dense
river water will spread over the reservoir surface as an overflow. If the river is of
intermediate density because of intermediate temperatures or moderately high
levels of TDS, the inflow will plunge from the surface and proceed
"downstream" as an interflow at the depth at which the river and reservoir water
densities are equal. If the river inflow is denser (cooler or having substantially
higher TDS) than the entire reservoir water mass, the inflowing river water will
plunge and flow along the reservoir bottom as an underflow. This downstream
flow of water usually controls the transport and distribution of dissolved and
suspended particles.
Under stratified conditions, cooler, more dense water may pass through an
entire reservoir along the bottom or at an intermediate depth without contribut-
ing significant amounts of nutrients or oxygen to the upper waters in the epilim-
nion. This short-circuiting underflow allows the often nutrient-laden water from
the watershed to flow through the reservoir without contributing significantly to
algal productivity in the epilimnion.
Figure 2-16.—Types of density flows in reservoirs (source: Olem and Flock, 1990).
27
-------
Fish and Fisheries Management in Lakes and Reservoirs
Reservoirs, especially
those with subsurface
outlets, are more efficient
at trapping sediments
than at retaining
nutrients. Therefore,
sedimentation and the
filling of the reservoir
basin with riverborne silts
and clays is the dominant
aging process.
In most reservoirs, the deepest point is just above the dam, near the lake out-
flow. This unique basin morphometry can also affect water circulation and
stratification patterns.
A distinctive feature of some reservoirs is their subsurface outlet. While in
natural lakes the lake outflow draws primarily from the lake epilimnion (during
stratification), reservoir subsurface outflows generally draw from the hypolim-
nion. As a result, the waters exported are colder and often have higher nutrient
concentrations and lower plankton biomass. Subsurface outflows also tend to
promote subsurface density flows and, thus, the short-circuiting of inflowing
tributary waters. Discharge of colder waters downstream may allow for the crea-
tion of a coldwater trout fisheries in the reservoir's "tailwaters."
Reservoirs, especially those constructed for flood control or water supply, fre-
quently undergo fairly large changes in water level. As discussed earlier in this
chapter, water level fluctuations can cause a myriad of problems; however, if con-
ducted at the right time and of the appropriate magnitude, they can be an effective
part of a lake's management program. Reservoirs can have extensive littoral zones
but relatively little macrophyte growth because of both water-level fluctuations
and high turbidity (and associated light limitations).
Finally, reservoirs on average tend to become eutrophic more rapidly than do
natural lakes because, as a rule, most of them receive higher sediment and nutrient
loads. Newly filled impoundments may go through a relatively short period of
trophic instability. Initially, reservoir productivity may be quite high because
nutrients are received both from external sources (i.e., the watershed) and internal
sources (leaching of nutrients from the flooded soils of the reservoir basin and
from decomposition of the submerged terrestrial vegetation and litter). As these
internal sources are depleted, reservoir productivity declines from this initial
"trophic upsurge" and stabilizes. Reservoirs, especially those with subsurface out-
lets, are more efficient at trapping sediments than at retaining nutrients. Therefore,
sedimentation and the filling of the reservoir basin with riverborne silts and clays
is the dominant aging process.
For additional information on the characteristics and ecology of reservoirs, see
Thornton et al. (1990).
28
-------
CHAPTER 3
Fish Ecology
Chapter Objective
Chapter 2 of this book provided an overview of the basic concepts of lake and
reservoir ecology — the major physical, chemical, and biological processes that
influence the quality of the environment for fish and the role of fish in the lake
ecosystem. Chapter 3 also provides a general review of basic ecological concepts
but focuses more specifically on the biology and ecology of fish. This chapter
steps through the processes and factors that influence fish growth, reproductive
success, mortality, and population dynamics; fish genetics; habitat considera-
tions; fish communities; and finally, a discussion of special issues in reservoirs.
An understanding of the basic principles of fish ecology is required to effectively
assess problems and identify appropriate solutions to managing fish and
fisheries in lakes and reservoirs. Additional information on fish biology and ecol-
ogy and the scientific basis for fisheries management can be found in the texts
and references listed in the reference section.
Definitions
A fish population is a group of fish of the same species that occurs within a given
lake or reservoir. In very large systems, a single population may consist of multi-
ple fish stocks; that is, subsets of the population that are reproductively isolated
from other fish stocks. The fish community within a lake or reservoir is the collec-
tion of all fish populations; i.e., all fish species. The terms "population" and
"community" are used similarly for biota other than fish to refer to single-species
and multiple-species assemblages, respectively, within a given ecosystem. Final-
ly, fish habitat is the place or type of area where a fish normally lives and grows
— the physical and chemical features of the environment on which fish depend,
directly or indirectly, to carry out their life processes.
Fish Growth Rates
Most people like to catch big fish. Faster growth rates mean that fish reach larger
sizes (length and weight) at a younger age, which may translate into more big
fish in the angler's catch. Understanding and manipulating the factors that con-
trol fish growth rates, therefore, are important aspects of fisheries management.
Humans and most other warm-blooded animals attain a maximum size after
a definitive period of time, generally soon after sexual maturity. After that time,
little further growth occurs except for the addition of fatty tissue if feeding condi-
tions are good. By contrast, fish growth is relatively indeterminate. Fish can
An understanding of the
basic principles offish
ecology is required to
effectively assess problems
and identify appropriate
solutions to managing fish
and fisheries in lakes and
reservoirs.
A fish population is a
group offish of the same
species that occurs within
a given lake or reservoir.
Understanding and
manipulating the factors
that control fish growth
rates are important
aspects of fisheries
management.
29
-------
Fish and Fisheries Management In Lakes and Reservoirs
The rate at which fish
grow is a direct function
of the amount of energy
consumed as food and the
efficiency with which it is
used.
continue to grow, in length and weight, throughout life (Fig. 3-1). On the other
hand, if conditions are poor (e.g., limited food intake), fish grow very slowly, if at
all. Populations may "stunt," with fish reaching sexual maturity and very old ages
at a relatively small size. For example, bluegills as small as 0.5 ounces have been
known to successfully reproduce and may reach only 3 to 4 inches in length by 5 to
6 years of age in slow-growing populations. Although fish near starvation may
stay the same size for an indefinite period of time or, in extreme cases, actually lose
weight, they still retain the capacity to grow rapidly, with no long-term ill effects,
should an abundance of food suddenly become available.
Figure 3-1.—Growth (increase in average length and weight with age) and specific growth
rate (G, the instantaneous rate of growth per unit weight, expressed as percent per year)
for a population of bluegill sunfish in Spear Lake, Indiana (source: Ricker, 1975; Wootton,
1990).
The Energy Balance
The rate at which fish grow is a direct function of the amount of energy consumed
as food and the efficiency with which it is used. Specifically, the energy available
for growth equals the caloric content of the food consumed, adjusted for the frac-
tion of the food ingested that is actually digested, minus the energy required to
maintain the fish's basic metabolism (i.e., the basic biological functions of respira-
tion, blood circulation, excretion, etc.) and minus the energy expended gathering
the food and also on reproductive functions.
Growth = f [(food intake) (fraction digested) - metabolism - food collection - reproduction]
Factors that Influence Growth Rates
Each of the components in the general growth equation is influenced by a number
of environmental variables that influence, in turn, fish growth rates. The single
most important factor is food availability. However, food availability is more than
30
-------
Chapters. Fisrifcofogy
simply a measure of the total quantity or biomass of suitable prey organisms that
occurs within the lake or reservoir. Instead, the amount of food consumed will be
determined equally by both the quantity of prey available and the total number
of fish and other predators competing for the same food supply. Competition for
food may be both intraspecific (among members of the same fish species) and in-
terspecific (among different species with the same feeding habits). Problems with
slow growth rates result as often from overcrowded fish populations as from in-
adequacies in the food supply.
Food quality and the types of prey available also affect the energy available
for fish growth. Fish species are adapted to efficiently capture and digest
preferred types of prey. In general, larger prey items provide more net energy for
growth per unit of energy expended in prey capture. Thus, fish feeding on other
fish tend to grow faster than do those of the same species feeding on zooplankton
or other smaller prey (see Box 3-A). Prey at low densities as well as prey that are
hard-to-find or difficult to capture also result in lower growth efficiencies be-
cause of the greater amount of energy required for food collection per unit of
food consumed.
Another important factor influencing fish growth rates is water temperature.
Temperature directly affects the rate and efficiency of food digestion and the
energy required to maintain a fish's basic metabolism and indirectly affects prey
availability, capture efficiency, and fish reproduction.
Fish are cold-blooded animals; that is, their body temperature varies as a
function of the temperature of their environment. At colder temperatures, their
metabolism slows. Thus, the amount of energy required to maintain basic meta-
bolic functions decreases. At the same time, however, their digestive rate also
slows and they tend to become lethargic, feeding less actively. As a result, fish
growth rates (especially for warmwater fish species) are generally slower in
colder environments — for example, fish living in lakes at high elevations or
northern latitudes.
Different fish species have adapted to different temperature regimes and, as a
result, have different optimum temperatures for growth. At temperatures higher
or lower than optimum, growth efficiency will decline. The classification of fish
species as coldwater, coolwater, and warmwater reflects these general differences
in preferred temperatures. Extreme temperatures above or below the optimum
range may also be lethal and will be discussed in the subsection on fish mortality
later in this chapter.
Other factors also influence fish growth rates. For example, different fish
species inherently have different growth rates or growth potentials. Some species
will never grow as fast or large as others, even under equivalent conditions.
Likewise, in some species, one sex may grow faster than the other; males may
consistently grow faster than females or vice versa. Age also influences growth
rate. In general, very young fish and old fish tend to grow somewhat slower in
absolute terms (i.e., the incremental increase in fish length or weight per year)
than do fish of intermediate age. As a result, the annual growth curve for a
species, especially for fish weight, may be sigmoidal (S-shaped, see Fig. 3-1).
Finally, stressful water quality conditions can also decrease fish growth.
Small decreases in dissolved oxygen or increases in the concentration of toxic
substances in the water may be too small to be lethal but can sublethally stress
fish, affecting growth efficiency as well as feeding activity and other behaviors.
These sublethal effects may be masked, however, if poor water quality conditions
also decrease fish survival. In such instances, food availability for the fish that
remain may increase because of decreased competition (fewer fish competing for
the same or even lower food supplies). As a result, even though growth efficiency
declines, the absolute growth rates of the surviving fish may increase.
[T]he amount of food
consumed will be
determined equally by
both the quantity of prey
available and the total
number offish and other
predators competing for
the same food supply.
Problems with slow
growth rates result as
often from overcrowded
fish populations as from
inadequacies in the food
supply.
Different fish species have
adapted to different
temperature regimes and,
as a result, have different
optimum temperatures for
growth.
[SJtressful water quality
conditions can also
decrease fish growth.
31
-------
Fish and Fisheries Management In Lakes and Reservoirs
Fish tend to grow at faster
rates during certain times
of the year.
Box 3-A.—(influence of Food Type and Availability
1 on Fish Growth Rates
Differences in fish growth rates
occur not only among lakes and
years but also among individual fish
within a given lake and year. Shel-
ton et al. (1979) examined growth
rates of largemouth bass in West
Point Reservoir on the Alabama-
Georgia border. Substantial varia-
tions were observed in the growth
of individual yearling bass during
the first year of impoundment 1975-
76 (Fig. 3-2). In general, largemouth
bass longer than 4 to 5 cm (total
length) feed increasingly on fish.
However, some individual fish begin
to feed on forage fish earlier than
do others. This tendency, though
not initially size-related, results in a
growth advantage for those fish
able to prey on forage fish at an
earlier age.
In West Point Reservoir, these
natural variations in prey utilization
were amplified by the relative
shortage of smaller forage fish that
could be consumed by smaller
bass. As a general rule, a lar-
gemouth bass can swallow shad up
to one-half its total length and sun-
fish up to one-third its length. In
West Point Reservoir, shad < 10 cm
and sunfish < 7 cm were scarce
during the 1975-76 study period.
Therefore, preferred prey for bass
shorter than 10 to 15 cm was practi-
cally nonexistent but abundant for
bass longer than about 15 to 20 cm.
The result was a bimodal size dis-
tribution for the 1975 bass year in
the reservoir (Fig.3-3). Growth rates
for bass < 10 to 15 crn were slow,
while those bass able to take ad-
vantage of the available forage fish
grew rapidly during their first year of
life, attaining lengths of 30 to 40 cm.
Figure 3-2.—Largemouth bass of the 1975 year
class in April 1976 (source: Shelton et al. 1979),
July-Aug. 197!)
N > 4828
75
Sept.-Oct. 1975
N> 810
40
30
20
10
4O
30
10
40
30
20
10
40
30
20
10
5 10 15 20 25 30 35 4O 44 50 55 60
Total length (2.5 cm group)
Figure 3-3.—Length-frequency of the 1975 year
class of largemouth bass from West Point
Reservoir (source: Shelton et al. 1979).
May-June 1976
N- 452
75
July-Aug. 1976
N »76I
Seasonal Growth Patterns
Fish tend to grow at faster rates during certain times of the year. These differences
are particularly pronounced at northern latitudes, where cold temperatures result
in little to no fish growth during the winter. Periods of rapid growth coincide with
increased food supplies and optimum temperatures, while periods of slow growth
are associated with cold temperatures and scarce food. These seasonal patterns in
growth rate generally provide the basis for determining a fish's age (See App. B,
Fig. B-12). Furthermore, the length of the growing season as an index of a lake's
thermal regime plays an important role in determining fish growth rates.
32
-------
Chapters. Fish Ecology
Weight-Length Relations
Fish that are longer also tend to be heavier; a strong correlation exists between
the length (L) and weight (W) of a fish:
W = aLb
where the constants a and b are determined for a fish population or other group
of fish by linear regression analysis, using the logarithmic transformation of each
fish's length and weight [log (W) = log(a) + blog(L)].
Often, the increase in weight is proportional to approximately the cube (or
third-power) of a fish's length. That is,
W = aL3
The constant, a in this case, is referred to as the condition coefficient or condition
factor, abbreviated as C for English units of measurements or K for metric units.
The condition factor for any given fish can be calculated, therefore, as follows:
C = W/L3
For ease of reporting, C in the above equation is generally multiplied by 10,000
when length is measured in inches and weight in pounds; K is multiplied by
100,000 when length and weight are in millimeters and grams, respectively.
The condition factor is widely used as an index of the well-being of a fish or
fish population. Fish that are plumper and heavier relative to their length have
higher condition factors and are generally considered "healthier."
However, condition factors are influenced by a number of extraneous vari-
ables that must be considered to properly interpret the condition factor as an
index of fish well-being. Different fish species have different "typical" condition
factors simply because of their different body shapes. Robust (wide-bodied) fish,
such as bass and sunfish, tend to have higher condition factors than narrow-
bodied species, such as northern pike and trout. For many trout species (for ex-
ample, brook, rainbow, brown, and cutthroat trout), a C value near 3.6 (or K = 1)
indicates trout in "normal" or "good" condition. On the other hand, C values of
4.6 to 5.5 and 7.1 to 8.0 have been suggested to be indicative of "average" or "nor-
mal" condition for largemouth bass and bluegills, respectively. A fish's condition
factor is also influenced by sex, season of the year, stage of sexual maturity,
stomach fullness, and fish length. For example, immediately before spawning,
mature fish, especially females, have higher condition factors because of the
weight of eggs or milt (sperm) ready to be spawned.
Comparison of the condition factor (or the length-weight regression equa-
tion) for a fish population in a lake or reservoir to "expected" or "typical" values
for healthy fish populations in the region (e.g., statewide average values for the
species, accounting for the confounding factors noted above) provides a simple
and easy-to-use tool for fish population assessment. Fish in poor condition (rela-
tively low condition factors) may be indicative of overpopulation, starvation, or
disease. High condition factors may result from a high temporary food supply
(such as during insect hatches) or indicate that fish densities are low relative to
the total food supply available, perhaps because of overfishing or poor reproduc-
tive success.
Two other weight-length indices are also commonly used as indices of fish
well-being. The relative condition factor (Kn) (LeCren, 1951) explicitly recognizes
the fact that b in the first weight-length equation does not always equal 3. The
relative condition factor is calculated for each individual fish as follows:
Kn = W/(aL")
where W and L are the weight and length, respectively, of an individual fish and
a and b are the constants from the weight-length relationship calculated for the
population of fish or for some other standard group of fish of that species. An ex-
ample is a statewide average weight-length relationship or a weight-length
The condition factor is
widely used as an index of
the well-being of a fish or
fish population.
A fish's condition factor is
also influenced by sex,
season of the year, stage of
sexual maturity, stomach
fullness, and fish length.
Fish in poor condition
(relatively low condition
factors) may be indicative
of overpopulation or
disease.
33
-------
Fish and Fisheries Management in Lakes and Reservoirs
relationship for fish considered to be in "good" condition. Kn equals 1 if the
weight of the individual fish is the same as that for a fish of the same length in the
standard group. Values less than 1 indicate weights less than expected or desired.
The relative weight index (Wr) (Wege and Anderson, 1978) is a further refine-
ment of the concept Kn. Wr is given by the equation:
Wr=(W/Ws)x100
where W is the weight of an individual fish and Ws is a length-specific standard
weight.
The standard weight functions are of the form:
Ws = a' Lb>
a' and b' are constants for an ideal population of the species, selected so thai a
well-fed, healthy fish would have a Wr value of 100. Wr values well below 100 in-
dicate an inadequate food supply or other related problems. Standard weight
functions for calculating Ws are presented in Table 3-1 for selected fish species.
All three of these indices of well-being, based on the relationship between fish
length and weight, have their limitations. Cone (1989,1990) provides a discussion
of the assumptions and common pitfalls encountered in applying and interpreting
each index.
Table 3-1.—Standard weight functions used in the calculation of relative weights for
selected fish species: intercept (a') and slope (b') constants for equations using
English units (inches and pounds) and the recommended minimum length for ap-
plication (source: Murphy et al 1991).
SPECIES
Rainbow trout
Brook trout
Chinook salmon
Northern pike
Striped bass
White bass
Largemouth bass
Smallmouth bass
Bluegill
Black crappie
White crappie
Walleye
Sauger
Yellow perch
INTERCEPT (a1)
-3.499
-3.467
-3.243
-3.727
-3.358
-3.394
-3.490
-3.347
-3.371
-3.576
-3.618
-3.642
-3.669
-3.506
SLOPE (b')
3.098
3.043
2.901
3.059
3.007
3.081
3.191
3.055
3.316
3.345
3.332
3.180
3.157
3.230
MINIMUM LENGTH
7.9
5.1
7.9
3.9
5.9
4.5
5.9
7.1
3.1
3.9
3.9
5.9
2.8
3.9
Fish Longevity
The maximum age to which fish live varies among species. Because fish growth is
indeterminate, fish species that live longer also tend to be those that grow to larger
sizes. For example, many of the large sport species, such as largemouth bass, wall-
eye, and northern pike, in northern latitudes may live to be 10 to 25 years old. Lake
trout frequently live 25 to 50 years, and lake sturgeon 50 to 80 years. By contrast,
many small species, including most minnow species, generally live only one to
three years. Typical life spans for selected fish species are presented in Table 3-2.
Variations in longevity occur even within a given fish species. Fast-growing
fish populations tend to have shorter life spans than do slow-growing populations '
of the same species. The exact reasons for this inverse correlation between growth
rate and longevity are not known. Many hatchery strains of fish also tend to have
34
-------
Chapters. Fish Ecology
shorter life spans than do wild strains of the same species, perhaps because his-
torically faster-growing fish were selected in the hatchery as brood stock for sub-
sequent generations. Hatchery strains of brook trout, for example, often have
maximum ages of two to four years, while wild strains in the same waters may
live five to eight years.
Table 3-2.—Approximate life spans of selected fish species (source: McComas, in
press; Scott and Grossman, 1973).
SPECIES
Lake trout
Largemouth bass
Walleye
Northern pike
Muskellunge
Bluegill
Brook and rainbow trout
White and black crappie
White bass
REGIONS
north
north
central and south
north
south
north
north
LIFE SPAN IN YEARS
25 to 50
14tO 16
9 to 12
15 to 16
10 to 12
16 to 17
16 to 17
5 to 8
5 to 8
4 to 7
2 to 5
Fish Reproduction
The ability of a fish population to reproduce itself is clearly critical for population
success. For a population to maintain itself at steady-state (with no long-term
change in fish abundance), one pair of adults (male and female) must produce
sufficient numbers of young to replace themselves with a new pair of mature
adults. Otherwise, the population will decline and/or natural reproduction must
be supplemented through artificial means, such as fish stocking.
Most fish species are oviparous with external egg fertilization. That is,
mating partners come into close proximity within the waterbody and then spawn
simultaneously. They release their sperm and eggs (spawn), directly into the
water, where chance collisions result in egg fertilization. The embryos develop
essentially on their own, food being supplied by the yolk within each egg. Even-
tually, the embryos hatch into larvae. For a period, these larvae continue to rely
on yolk for food and are called "yolk-sac fry." As the yolk sac is depleted, the lar-
vae begin to feed. At the same time, they also begin to swim actively in the water
column. Thus, at this stage, the young fish are referred to as "feeding fry" or
"swim-up fry."
Ffsfi Fecundity
The number of eggs produced by a single female fish is termed "fecundity" and
is generally determined by counting the number of eggs contained within the
fish's ovaries just before spawning. Larger fish typically produce more eggs;
thus, fecundity is often expressed as a function of fish size: the number of eggs
per unit length or weight of the female fish. An estimate of fish fecundity times
the estimated number of spawning females provides an index of the reproductive
potential of the population.
Reproductive Strategies
In general, fish spawn large numbers of eggs per female. Largemouth bass, for
example, each year typically produce between 2,000 and 7,000 eggs per pound of
female; some very large females may spawn up to 100,000 eggs. A single, large
The ability of a fish
population to reproduce
itself is clearly critical for
population success.
Most fish species are
oviparous with external
egg fertilization.
35
-------
Fish and Fisheries Management in Lakes and Reservoirs
The reproductive strategy
offish, in general, is to
produce large numbers of
eggs but provide their
young with relatively
little or no protection.
The availability of suitable
spawning areas and
substrate, therefore, is an
important lake
characteristic to consider
when selecting fish species
to be targeted for fisheries
management.
female northern pike may spawn 500,000 to 600,000 eggs. Salmonids generally
have somewhat lower fecundity; the number of eggs per female brook trout, for
example, ranges from about 100 for a small female (6 inches in length) up to 5,000
eggs for a 20-inch brook trout.
Although large numbers of eggs may be spawned, relatively few of these
embryos survive through their first year of life or even to the swim-up stage. The
reproductive strategy of fish, in general, is to produce large numbers of eggs but
provide their young with relatively little or no protection. As a result, mortality
rates are high during these early life stages. For many fish species, typically fewer
than 1 percent (or even less than 0.01 percent) of the eggs spawned survives to one
year of age. Survival rates for salmonids tend to be somewhat higher but are still
generally 10 percent or less. Most mammals and many warm-blooded vertebrates,
by contrast, have very different reproductive strategies. Compared with fish,
mammals produce few young, expend considerable energy nurturing and protect-
ing the young, and survive at relatively high rates.
Reproductive strategies do vary, however, among fish species. Some species
randomly deposit their eggs in the spawning area, with absolutely no follow-up
parental care. In general, these species tend to have the highest fecundity and
lowest early life stage survival rates. Examples include northern pike, common
carp, yellow perch, alewifes, and striped bass. At the other extreme, sticklebacks
build quite complicated nests within which their eggs are deposited, and the male
actively guards the young until they swim away from the nest. Likewise, males of
most centrarchid species (including largemouth and smallmouth bass and surifish
species) also build nests for spawning and actively guard their schools of young
for several days or weeks after swim-up. Salmonids also spawn in nests (referred
to as redds), although the female rather than the male develops the site and, in
most species, provide no parental care after the eggs are spawned. Salmonid eggs,
however, are relatively large, with large quantities of yolk. As a result, salmonid
larvae are larger, more motile, and less susceptible to predation, compared to the
larvae of many other fish species. As a general rule, fish species that provide some
parental care and/or have larger eggs have lower fecundity and relatively higher
early life stage survival rates.
Appendix A provides further information on the reproductive habits and
strategies of specific fish species.
Spawning Habitats
Many fish species require certain types of physical habitat or habitat charac-
teristics for reasonable survival of their eggs and yolk-sac fry (Table 3-3; App. A).
Many trout species, for example, spawn only in clean gravel substrates in tributary
streams, rather than in the lake proper. Northern pike spawn in shallow, weedy
areas along the lake edge or in flooded areas in tributary streams. If such habitats
are not available or rare, reproductive success may be poor or nonexistent. The
availability of suitable spawning areas and substrate, therefore, is an important
lake characteristic to consider when selecting fish species to be targeted for
fisheries management. If natural reproduction is insufficient, the population will
have to be supplemented or maintained through stocking, requiring substantial
added expense and effort. In some instances, it may be possible to artificially con-
struct additional spawning substrate in the lake or reservoir, which may also im-
prove reproductive success (see Chapter 8).
Spawning Periods
Different fish species also spawn at different times of the year (Table 3-3). Further-
more, some species have very short spawning seasons, lasting only a few days;
others may spawn for one to two weeks; still others spawn intermittently over a
period as long as three to four months. Temperature and photoperiod are the two
36
-------
Chapters. Fisfi Ecology
Table 3-3.—Spawning habitats, times, and water temperatures for selected fish
species (source: McComas, in press; Scott and Grossman, 1973).
SPECIES
Bluegill
Largemouth bass
Grapples
Channel catfish
Yellow perch
Northern pike
Muskellunge
Brown trout
Brook trout
Lake trout
Rainbow trout
Cutthroat trout
Walleye
TIME
late May to early August
early May to late June
late May to late July
late spring/summer
mid-March to mid-May
early spring
April to June
October to February
September to December
early October to late
November
mid-April to late June
three to five weeks after
ice breakup
spring, after ice breaks up
TEMP. OF)
65 to 70
62 to 70
(north)
60 to 70
(north)
75 to 80
45 to 50
35 to 50
48 to 60
50 to 65
48 to 55
37 to 50
50 to 60
about 50
451050
PREFERRED SPAWNING HABITAT
sand and gravel areas with some
vegetation near shorelines of ponds
and lakes
sand and gravel areas with some
vegetation near shorelines of ponds
and lakes
sand and gravel areas with some
vegetation in water usually less
than 1 0 feet deep
undercut banks, log jams, or rock
piles, either in the littoral zone or in
slow-moving tributaries
weedy or brushy areas in shallow to
deeper water of ponds and lakes
shallow, weedy areas of lakes; also
migrate up tributaries to flooded
areas
shallow bays of lakes in muddy,
stumpy bottom
tributary streams or rocky, shallow
areas of lakes
small gravel brooks or gravel
shorelines of lakes
gravel or rocky bottoms of lakes or
reefs at varying depths
beds of fine gravel in inlet or outlet
streams
areas in small inlet and outlet
streams with clean, gravel substrate
shoal areas of lakes or tributary
streams
most important cues that trigger spawning. As a result at more northern latitudes
and in colder waters, fish that spawn in the spring tend to spawn later in the year
and fall-spawning fish do so earlier in the year, compared to spawning times at
more southern latitudes and in warmer waters.
Many coolwater species (see Table 2-2), such as northern pike, walleye, and
yellow perch, typically spawn soon after the ice goes out in early spring at
temperatures of 45 to 50°F (7 to 12°C). Warmwater species, including most
centrarchids (bass and sunfish) and ictalurids (bullheads and catfish), generally
initiate spawning in late spring or early summer when water temperatures reach
55 to 75°F (13 to 24°C), depending on the species. Some, such as the bluegill, will
continue to spawn intermittently throughout most of the summer. Some
coldwater species, such as rainbow and cutthroat trout, spawn in the spring just
before or soon after ice-out in the lake (at 50 to 60°F, 10 to 15°C). Most coldwater
fish, however, including brook trout, lake trout, and kokanee salmon, are fall
spawners, depositing their eggs as water temperatures decline (generally at
about 40 to 55°F, 4 to 13°C). The eggs hatch in late winter, and the young fry
swim-up and begin feeding as the ice recedes from the lake. Additional informa-
tion on spawning times for individual fish species is provided in Appendix A.
The rate of embryo development and time from spawning to hatching and
larval swim-up are also dependent on temperature. Thus, in warm years or in
warm lakes (e.g., at more southern latitudes), not only does spawning occur ear-
lier (for spring and summer spawners), but early life stages tend to grow and
develop more rapidly. Because these early life stages are particularly susceptible
The rate of embryo
development and time
from spawning to
hatching and larval
swim-up are also
dependent on temperature.
37
-------
Fish and Fisheries Management in Lakes and Reservoirs
[TJhe age of sexual
maturity varies with
latitude, elevation, lake
productivity, and other
factors that affect fish
growth rates.
to environmental stresses and predation, the rate and timing of embryo /larval
development relative to the timing and occurrence of stressful conditions (e.g.,
cold spells or episodic incursions of toxic substances), water level fluctuations,
heavy predator concentrations, or food limitations may be critical for reproductive
success.
Age at Sexual Maturity
The age at which fish reach sexual maturity also may influence fisheries manage-
ment decisions; for example, in setting size limits for fish populations with a
shortage of reproducing fish. Again, different species reach maturity at different
ages, ranging from ages 1 to 2 years for short-lived species, such as many min-
nows, up to 15 to 25 years for a long-lived species like the lake sturgeon. Fast-
growing populations tend to mature at an earlier age than do slow-growing
populations of the same species. Thus, the age of sexual maturity varies with
latitude, elevation, lake productivity, and other factors that affect fish growth rates
(see Fig. 3-4). Not all fish within a given population reach maturity at the same age
or size; furthermore, once a fish is mature, it may not spawn every year. The age
and size at which fish reach sexual maturity can be easily determined by collecting
a sample of fish during or immediately preceding the spawning season and iden-
tifying, measuring, and aging those fish that are sexually mature, as described in
Appendix B.
10
9
8
7
UJ6
CO
<5
4
3
Z
II 13 15 17
19 21 23 25 27 29 31 33 35 37
GROWING DEGREE-DAYS (xlCT2)
39 41 43 45
Figure 3-4.—Relationship between the age at which female walleyes become sexually ma-
ture and the length of the growing season, expressed as centigrade degree-days above
5'C (41*F). The lower line and solid circles indicate the age at which mature females first
appear In the population. The middle line and solid triangles indicate the first age at which
50 percent or more of the females In the population are mature. Finally, the upper line and
open circles represent the first age at which all surviving females are sexually mature.
Data presented are for 22 lakes ranging from Texas to the Northwest Territories in Canada
(source: Ont. Ministry Nat. Res. 1983).
Factors Affecting Reproductive Success
The ultimate measure of reproductive success is the number of new fish or recruits
introduced into the population each year. Recruitment is the addition of new
members to the population or fish stock of interest; recruitment success is delter-
38
-------
Chapters. Fish Ecology
mined by not only the numbers of eggs produced and hatched but also the num-
ber of young that survive until a given age or size, generally when they can first
be collected and evaluated using available fish sampling techniques. Recruitment
success can vary substantially from year to year as well as among different lakes.
Strong year classes (relatively large numbers of new recruits in a single year) and
weak year classes are common, and a wide diversity of factors may limit fish
reproduction and young-of-the-year survival in any one year or lake.
Differences in recruitment success among lakes result from variations in both
the intensity of spawning activity (i.e., fecundity, the number of fish spawning,
and total number of eggs spawned) and the survival of eggs and young fish. For
species with fairly specific spawning requirements such as many salmonids, the
quantity and quality of suitable spawning habitat may be an important limiting
factor. For example, brook trout require areas of ground water up welling and/or
well-oxygenated gravel substrate in small tributary streams or along the lake
shoreline for spawning and adequate survival of eggs and yolk-sac fry. Little to
no brook trout reproduction will occur in lakes without such areas. In lakes with
suitable spawning habitat, limiting environmental conditions (e.g., high acidity,
low oxygen levels), high rates of predation, or overcrowding and competition for
food among young may result in low early life stage survival rates and poor
recruitment success.
Because of the large number of eggs spawned per female, year-to-year varia-
tions in recruitment success (year-class strength) are determined more often by
differences in egg and larval survival than by the level of spawning activity.
Strong year classes in previous years may result in poor young survival and a
weak year class because of cannibalism or increased competition for food. A sud-
den cold snap or rapid decline in lake level soon after spawning may cause high
levels of egg or larval mortality and, subsequently, a weak year class. Several
studies have shown that the severity of wind and wave action, which may
mechanically damage eggs and yolk-sac fry, is a major determinant of year-class
strength in some largemouth bass populations. Thus, fluctuations in a number of
environmental and biological factors can result in natural year-to-year variations
in year-class strength.
Problems with fisheries production may be traced, in many cases, to
problems associated with fish reproduction and young fish survival. Thus, ef-
forts to determine recruitment success and the major factors limiting recruitment
success are important components of the process of problem identification and
diagnosis in overall fisheries management (described in Chapter 6).
Hybridization
Hybrids are the offspring of parents of different species; for example, a cross be-
tween bluegill and green sunfish. Naturally produced hybrids are common
among members of the sunfish family. A variety of other crosses have been artifi-
cially induced in hatcheries, such as the splake (a cross between lake trout and
brook trout), tiger musky (a cross between northern pike and muskellunge), and
the white bass-striped bass hybrid cross. Generally, hybrids are infertile or have
reduced viability, and reproduction is minimal. Hybrids continued presence in a
waterbody depends, therefore, on continued natural crosses between the parent
species or on stocking. Frequently, hybrids grow faster and have greater vigor
than the parent species, making them desirable targets for fisheries management
in some situations and types of waterbodies. The introduction of hybrid species
may, however, adversely affect native fish populations through competition or by
interfering with natural reproduction. While hybrids do not successfully
reproduce, they do spawn and may spawn with native populations of either
species, reducing the reproductive success of the native populations.
[Fluctuations in a
number of environmental
and biological factors can
result in natural
year-to-year variations in
year-class strength.
Frequently, hybrids grow
faster and have greater
vigor than the parent
species, making them
desirable targets for
fisheries management ...
39
-------
Fish and Fisheries Management in Lakes and Reservoirs
If fish mortality rates
increase as fish density
increases, then, to some
degree, a population may
be able to self-adjust itself.
Fish Mortality
Fish die as a result of diverse causes, both natural and human-induced. Examples
of important sources of fish mortality include predation, starvation (although fish
weakened by starvation usually die of other causes, such as predation, before they
actually starve to death), disease, fishing, and lethal water quality conditions (such
as low oxygen levels, high temperatures, or high concentrations of toxic substan-
ces).
Fish mortality rates (i.e., the proportion of fish dying over a given period of
time) and major sources of mortality vary with fish age and among lakes. Mor-
tality rates are highest during early life stages, as eggs and fry. In some popula-
tions, high levels offish mortality also occur immediately after spawning. Immune
systems are weakened by the stress of spawning, making the fish more susceptible
to infections and diseases. Predation and competition for food are especially im-
portant for young, small fish, while fishing mortality becomes increasingly impor-
tant for large, old fish. Fishing mortality also tends to be higher in waters that are
more heavily fished. Mortality rates resulting from predation, starvation, or dis-
ease, on the other hand, are likely to be highest in waters with high fish densities
and overcrowded conditions. Marginal water quality because of pollution or
natural causes (e.g., when a coldwater species lives at the southern edge of its
range and temperature tolerance) can also be a significant factor limiting fish sur-
vival in some lakes and reservoirs.
Compensatory Mortality
Some types of mortality are density-independent; that is, the proportion of fish
dying is not affected by the number or density of fish in the population. For ex-
ample, mortality caused by a toxic pollutant is likely to be density-independent. If
one of every 10 fish is sensitive to the toxicant, then 10 percent of the fish will die
whether the fish population is 10 or 1,000 fish.
By contrast, other types of mortality are density-dependent. In some instances,
as with competition for food, the more fish in the population, the higher the per-
centage of fish that are likely to die. In a few cases, as for some types of predation,
the reverse may also occur; higher densities of fish may mean that a lower propor-
tion of the population is lost to predation. Deaths resulting from food shortages,
diseases, and cannibalism are almost always density-dependent, with the propor-
tion of fish dying increasing with fish density. Predation, on the other hand, may
be density-independent or density-dependent and either positively or negatively
correlated with fish density.
If fish mortality rates increase as fish density increases, then to some degree, a
population may be able to self-adjust itself. Theoretically, with perfectly balanced
density-dependent mortality, population abundance would remain constant over
time. While natural populations are far from perfectly balanced and typically ex-
perience large fluctuations in abundance as a result of short-term changes in both
mortality and reproductive success, they do tend to regulate themselves in the
direction of some long-term average density.
Density-dependent mortality also may counterbalance, to some degree, chan-
ges in density-independent mortality rates. For example, if more fish are removed
from the population by fishing (higher fishing mortality), the fewer fish that
remain may have more to eat per fish, decreasing the number of deaths resulting
from starvation or inadequate food with little or no change in the total mortality
rate. Such shifts in density-dependent mortality that serve to moderate the effects
of density-independent mortality are referred to as compensatory mortality.
The degree to which populations are able to compensate, by. decreasing their
natural mortality rates, for increases in mortality caused by fishing or toxic pol-
4O
-------
Chapters. Fish Ecology
lutants is one of the major uncertainties in fisheries management and an active
area of research. Clearly by itself, compensatory mortality is not adequate in all
circumstances, since many examples can be found of long-term fish population
declines caused by overfishing and/or pollution. Uncertainties regarding the oc-
currence and magnitude of compensation, however, limit our ability to quantita-
tively predict fish population responses to environmental stresses.
Compensatory mechanisms in fish populations are not restricted to changes
in density-dependent mortality rates. Growth and fecundity also vary as a func-
tion of fish density. At lower densities (given a constant food supply), fish grow
faster, mature earlier, and usually produce more eggs, all of which act to increase
the biomass and abundance of fish in the lake. At high fish densities, growth and
fecundity are reduced, limiting or decreasing population size. This balancing of
forces — processes of increase and growth versus forces that work to limit or
decrease population size — is a fundamental concept of fish population
dynamics, discussed in greater detail later in this chapter.
Fishing Mortality
Fishing activities increase fish mortality, either by the direct removal of "keepers"
or as an incidental result of the added stress on fish associated with capture and
handling (see Box 3-B). Fishing mortality rates are a function, therefore, of the
total fishing effort and the types of fishing methods allowed. If fishing mortality
rates are high, it may be necessary to reduce fishing effort (e.g., by limiting lake
access) or alter fishing regulations; for example, by initiating a catch-and-release
fishery or establishing minimum and/or maximum size limits (see Chapter 8).
The effects of fishing mortality on fish populations can be distinctly different
than those from other mortality sources. Mortality rates that result from fishing
generally increase with fish size and age; anglers preferentially remove large, old
fish. By contrast, other types of mortality act primarily on early life history
stages; mortality rates decrease with age or remain relatively constant at ages
above 1 to 2 years. Many natural mortality factors are also density-dependent
and thus, to some degree, are self-regulating. As a result of these differences, fish-
ing mortality cannot be viewed as a substitute or replacement for natural mor-
Box 3-B.—Response of Largemouth Bass to
Angling Stress (source: Gustaveson et at. 1991)
The stress associated with hooking, playing, and handling, by itself, can result in in-
creased fish mortality, even if all fish caught are released (e.g., in a catch-and-release
fishery or for fish smaller or larger than the allowable size limit). Hooking mortalities up
to 98 percent have been reported for largemouth bass caught and released during
tournaments and can also be high in nontournament public fishing (Champeau and
Densen, 1989). Improvements in tournament procedures have reduced mortality from
capture and handling, but rates of 20 to 60 percent can still occur (Chapman and Fish,
1985). Lee (1989) reported mortality rates as low as 2 percent in recent bass tourna-
ments regulated by the California Department of Fish and Game.
Gustaveson et at. (1991) evaluated physiological stress responses in bass caught
at different temperatures and with varying amounts of hooking and playing time. The
level of stress increased with both increasing temperature and increased playing time.
Stress responses were low for fish hooked and played for 1 to 5 minutes in the coldest
water (11 to 13°C, 52 to 55°F); moderate for fish hooked and played at 16 to 20°C (61
to 680F), and severe for fish played for five minutes at 28 to 30°C (82 to 86°F). Thus,
mortality caused by angling stress is likely to be higher for fish caught at higher
temperatures. Lee (1989) also observed relatively high mortality in early summer,
which was attributed to a decrease in fish tolerance immediately following spawning;
and in winter, as a result of decompression when bass were caught in deep water.
41
-------
Fish and Fisheries Management in Lakes and Reservoirs
Young fish tend to be
much more sensitive to all
environmental stresses
than older fish.
While fish have an
extremely large
reproductive potential, a
number of physical and
biological checks act to
keep this potential and the
population in balance.
tality. Relatively low natural mortality rates but high levels of fishing mortality
may lead to a number of management problems, including stunted populations
dominated by large numbers of small, young fish.
Acute and Chronic Lethal Limits
To establish water quality regulations or evaluate the effects of pollution on fish
populations, it is necessary to know what levels of toxicants and other water
quality variables are likely to cause significant fish mortality. These concentrations
or values are commonly referred to as lethal limits. An acute lethal limit is the con-
centration or level that will cause toxic effects (increased mortality) after just short-
term exposures (typically four days or less). Chronic lethal limits are those that
affect fish only after longer periods of exposure. In general, the shorter the period
of exposure, the higher the toxic substance concentration, the higher the tempera-
ture, and the lower the oxygen level that fish are able to tolerate.
Lethal limits for water quality parameters vary greatly among fish species and
with fish age (e.g., Fig. 3-5; Boxes 3-C and 3-D). Young fish (eggs, fry, and
juveniles) tend to be much more sensitive to all environmental stresses than older
fish. Thus, these early life stages may be particularly critical times for determining
the impacts of pollutants and natural stresses on fish population success. Relative
species sensitivities vary depending on the type of pollutant or stress. For ex-
ample, brook trout are relatively tolerant of lake acidity compared to other fish
species, but brook trout eggs and fry are relatively sensitive to low levels of dis-
solved oxygen.
Clearly, a fish's lethal limits and preferred ranges of temperature, dissolved
oxygen, and other water quality variables should be carefully considered in select-
ing target species for fisheries management! Water quality conditions are likely to
vary spatially within a lake or reservoir. Thus, assessing a lake's suitability for a
given fish species requires information on the range of water quality conditions
likely to be encountered in the specific areas of the lake inhabited by the species
during each life stage.
Winterkill and Summerkill
High levels of fish mortality occur in some lakes during the summer (summerkill)
and/or winter (winterkill) (see Boxes 3-E and 3-F). Frequently, the cause of death
is suffocation as a result of low levels of dissolved oxygen that tend to occur in the
hypolimnion of eutrophic lakes during summer and in some lakes over winter
during long periods of snow and ice cover (see Chapter 2). High temperatures,
rapid temperature changes during cold or warm spells, and epidemic diseases or
parasites may also cause periodic summerkills.
Fish Population Dynamics
Fish population dynamics is the study of the combined processes of fish growth,
reproduction, and mortality and their impact on the total numbers and biomass of
fish of a given species in a particular ecosystem. The status of a population at any
given time depends on the dynamic balance between the forces of population in-
crease (growth and reproduction) and decrease (mortality). All these processes are
highly interactive with important feedback mechanisms. While fish have an ex-
tremely large reproductive potential, a number of physical and biological checks
act to keep this potential and the population in balance. For example, as popula-
tions increase in abundance, competition for available food increases, increasing
fish mortality and decreasing growth rates that, in turn, cause a delay in sexual
maturity and reduced fecundity. A population subject to increased mortality as a
result of increased fishing mortality may respond by increasing individual fish
42
-------
Chapter 3. Fish Ecology
4.0 5:0 PH 6.0 7.0*
| | | | [ 1 ! 1 ! ! 1 1 [ 1 1 1 1 ! 1 t 1 1 I 1 1 1 1 t ! 1 1
Species • n
1 1 I i i i i i i 1 | I 1 1 ) 1 I I i I | I 1 t f t I i I I |
4.0 5.0 6.0 7.0
PH
Figure 3-5.— Estimated critical pH values for effects on fish populations. Dashed lines
represent the approximate range of uncertainty in the critical pH. Number of studies (n)
used to derive the estimate are noted (source: Baker and Christenson, 1991).
growth, reproduction, and subsequently, survival. As noted earlier, the result of
these compensatory mechanisms are that fish populations in stable environments
generally tend toward some long-term average population biomass that reflects
the carrying capacity of the system.
Population Age Structure
A population's age structure — that is, the numbers of fish in each age or year
class — is determined by the relative magnitudes of the annual birth and death
rates. If birth and mortality rates are constant year to year, then the numbers of
fish in each age class will decline logarithmically with increasing fish age (see
Fig. 11-5, Chapter 11). Unusually large numbers of fish in any given age group in-
dicate either higher than average reproductive success or lower mortality. Miss-
ing year classes or age groups may result from complete. reproductive failure or
mass mortality within a particular year. Populations with only old, large fish
have experienced successive reproductive failures or mass mortalities in recent
Unusually large numbers
offish in any given age
group indicate either
higher than average
reproductive success or
lower mortality.
43
-------
Fish and Fisheries Management In Lakes and Reservoirs
Box|3-C.—Effects of Low Dissolved Oxygen on Fish
Fish and other animals require oxygen to survive, as discussed in Chapter 2. When
levels of oxygen dissolved in the water become too low, fish mortality may increase
dramatically. At moderately low oxygen levels, fish may be sublethally stressed, ex-
periencing decreased growth and increased susceptibility to other causes of mortality.
Table 3-4 summarizes dissolved oxygen concentrations associated with varying levels
of effects on fish. Salmonids, on average, are more sensitive to low levels of dissolved
oxygen than are other fish species (especially warmwater fish species) and thus are
considered separately in Table 3-4. Oxygen solubility is temperature dependent; in
waters at equilibrium with the atmosphere, lower concentrations of dissolved oxygen
occur at higher temperatures (Fig. 3-6). The rate of organic matter decomposition,
which consumes oxygen (see Fig. 2-6), also increases at higher temperatures. Thus in
general, oxygen depletion is more prevalent in warmer waters and during summer. Low
levels of oxygen may also occur, however, during winter in lakes with long periods of
snow and ice cover.
Table 3-4.—Summary of dissolved oxygen concentrations (mg/L) generally as-
sociated with effects on fish in salmonid waters and nonsalmonid waters
(source: U.S. Environment Protection Agency, 1987).
LEVEL OF EFFECT
SALMONID
NONSALMONID
Early Life Stages (eggs and fry)
No production impairment
Slight production impairment
Moderate production impairment
Severe production impairment
Limit to avoid acute mortality
Other Life Stages
No production impairment
Slight production impairment
Moderate production impairment
Severe production impairment
Limit to avoid acute mortality
11 (8)a
9(6)
8(5)
7(4)
6(3)
8.0
6.0
5.0
4.0
3.0
6.5
5.5
5.0
4.5
4.0
6.0
5.0
4.0
3.5
3.0
Values for salmonid early life stages are water column concentrations recommended to achieve the
required concentration of dissolved oxygen in the gravel spawning substrate (shown in parentheses).
161-
14
12
Oxygen
Concentration
(mg/L)
at Saturation 10
30
40
50
60
70
80
90
100
110
Temperature (°F)
Figure 3-6.—Solubility of oxygen in freshwater as a function of temperature (source:
Stand. Methods, 1971). Oxygen levels In lakes are often presented as percent satura-
tion; that Is, the measured oxygen concentration divided by the maximum oxygen
concentration possible (i.e., oxygen solubility) at that temperature times 100.
44
-------
.Chapters. Fish Ecology
Box 3-b.^-Temperature Limits for Fish
As discussed in Chapter 2, fish are cold-blooded vertebrates; their body temperature
and metabolism are determined by the temperature of the surrounding environment.
Thus, temperature directly Influences fish growth rates, activity levels, reproduction,
and most other aspects of fish biology. In addition, temperatures that are too high or
too low can be jethal. A fish's upper and lower temperature limits are not fixed but are
influenced by the temperature to which the fish has been acclimated by being held at
that temperature for several weeks (Fig. 3-7). Some fish are able to tolerate a wide
temperature range (eurythermal species); for example, goldfish with proper acclima-
tion can tolerate a temperature range from 32 to 100°F (0° to 40°C). Other fish species
are stenothermal and have a narrow zone of temperature tolerance. Examples of the
approximate maximum temperatures to which adult and juvenile fish can be exposed
for short periods ,of time during summer (i.e., when fish are acclimated to relatively
high temperatures) without excessive fish mortality are listed in Table 3-5.
40-
30
ce.
X 20
10
Table 3-5.—Calculated short-term
maximum temperature for survival of
juveniles and adults during summer
(source: U.S. Environ. Prot. Agency,
1987).
FISH SPECIES
WATER
TEMPERATURE
0 10
ACCLIMATION
20 30 40
TEMPERATURE (°C)
Figure 3-7.—Relationship between
lethal temperatures (upper and lower)
and fish acclimation temperature for
goldfish, roach (a European rough-
fish), and brown trout (source:
Wootton, 1990; Elliot, 1981).
T (°C)
Channel catfish 95 (35)
Bluegill 95 (35)
Largemouth bass 93 (34)
Northern pike 86 (30)
Lake herring (Cisco) 77 (25)
Coho salmon 75 (24)
Rainbow trout 75 (24)
Atlantic salmon 73 (23)
Sockeye salmon 72 (22)
years. In long-lived fish species, such conditions could continue for several years
with no apparent decline in fishing success. However if the cause of the
reproductive failure or mortality is not corrected, eventually the population will
be lost. Population age structures, therefore, provide important information on
population status and trends. Furthermore, by comparing age structure patterns
to data on year-to-year fluctuations in environmental conditions, it may be pos-
sible to identify factors contributing to variations in population success or long-
term declines (Box 3-G).
Length-Frequency Distributions
Gathering data on fish ages for large numbers of fish can be fairly time-consum-
ing and difficult in some waters and for some species. A quick alternative that
maybe adequate in some cases is the length-frequency distribution (Fig. 3-9). Be-
cause fish age and length are correlated, general information on the population
age structure can be obtained by examining the relative frequency of occurrence
of fish of varying lengths. The absence of very small fish may again be indicative
of reproductive failures in recent years. A truncated age or length distribution
with a sudden decrease in the numbers of fish present above some particular size
suggests a high mortality among older fish; for example, as a result of fishing
mortality. Many methods for sampling fish are less efficient at collecting small
Population age structures,
therefore, provide
important information on
population status and
trends.
45
-------
Fish and Fisheries Management in Lakes and Reservoirs
Box 3-E.—Conditions Associated with Summer
Mortality of Striped Bass in Keystone Reservoir,
j ; Oklahoma (source: Zale et al. 1990)
Striped bass have been introduced into
many inland reservoirs, especially in
the southeastern and southcentral
United States. Although generally these
populations support productive sport
fisheries, summer mortality of adults is
common and widespread (Matthews,
1985). Coutant (1985) hypothesized
that such mortality results from a
temperature-oxygen squeeze. During
summer stratification, the upper waters
in the epilimnion become too hot for
adult striped bass, while the deep, cool
waters lack adequate dissolved oxygen.
Zale et al. (1990) evaluated this
hypothesis in Keystone Reservoir, a
large, 26,000-acre impoundment for
hydroelectric power generation on the
Arkansas and Cimmaron rivers in north-
ern Oklahoma. During the summer,
Keystone Reservoir is characterized by
a strong, chemically induced stratifica-
tion (Fig. 3-8) caused by the differential
total dissolved solids levels in the
Arkansas and Cimmaron river inflows.
Summer mortalities of striped bass fre-
quently occur.
During the period of study, 1986-
88, significant mortality (based on the
occurrence of large numbers of dead
fish found along the shoreline) occurred
in late summer/early fall in both 1987
and 1988, but not in 1986. During sum-
DISSOLVED OXYGEN
CONCENTRATION (mg/L) '
0246
* • I ' f
0
UJ
Q
15
24 26 28
TEMPERATURE (°C)
1000 2000 3000
CONDUCTIVITY (pS)
4000
Figure 3-8.—Water column profiles of
water temperature, dissolved oxygen
concentration, and conductivity (an In-
dicator of the total dissolved solids
content) in the main pool of Keystone
Reservoir, Oklahoma, on July 13, 1988
(source: Zale et al. 1990).
mer, striped bass were restricted to a thin (3 to 6 feet) layer of the stratified water
column consisting of the coolest waters available at which dissolved oxygen con-
centrations exceeded 2 mg/L. Fish stopped feeding when minimum water tempera-
tures in this zone reached about 80°F (27° C). Observations at Keystone Reservoir
indicate that adult striped bass can tolerate exposure to 80 to 82°F (27 to 28°C) for
about one month (as in 1986) but die (probably from malnutrition) when they are ex-
posed to slightly higher temperatures (about 84°F or 29°C, as in 1987) for a similar
period or when exposure to 82° is prolonged (as in 1988).
fish or are selective for certain size classes (see App. B). These size-related differen-
ces in capture efficiency must be accounted for in interpreting fish age or length
distributions in the sample of fish examined.
Because most anglers prefer to catch large fish, the length-frequency distribu-
tion is also of direct interest as an index of the quality of fishing and the relative
balance between small and large fish in the population. For a number of species,
standard length classes have been designated (Table 3-6), based on percentages of
the world record lengths. The percentage of the sample or population falling
within each designated size class is referred to as relative stock density (RSD). Al-
ternatively, the proportional stock density (PSD) index is calculated as follows:
PSD = (number of fish 2= minimum quality length / number a minimum stock length) x 100
Index values range from 0 to 100. For example, if 50 largemouth bass are a 30
cm (12 inches) long (quality size) in a sample of 100 fish a 20 cm (8 inches) long
46
-------
Chapters. Fish Ecology
Box 3-F.—Consequence of Winterkill in Wintergreen
Lake, Michigan (source: Hall and Ehlinger, 1989)
Wintergreen Lake is a small (37-acre), shallow (21 feet maximum depth, 11 feet mean
depth) hypereutrophic, hardwater lake in southern Michigan. Most of the nutrient in-
puts to the lake come from migrant and resident waterfowl feces (Manny et al. 1975).
Runoff from cultivated fields and an intermittent stream from a dairy farm feedlot also
contribute to the large nutrient load.
Currently, nearly 40 percent of the lake's surface is c'overed with macrophytes,
and phytoplankton blooms are common. Historically, fish in the lake were typical of
those in warmwater lakes in the region; the fish community was dominated by centrar-
chids with largemouth bass as the top predator. The lake was subject to an occasional
partial winterkill. But before 1977, individuals of each fish species survived the periods
of low dissolved oxygen or were able to recolonize the lake from downstream Gull
Lake, connected to Wintergreen Lake by an outlet stream during periods of high flow.
The winters of 1977 and 1978, however, were particularly severe in Michigan,
with four months of continuous ice and snow cover. Dissolved oxygen levels in the
lake dropped to below 1 mg/Land massive fish kills resulted. At ice-out in 1977, over
7,000 dead fish were collected along the shoreline; 70 percent of these dead fish were
bluegill and largemouth bass. Since that time (through 1987), no bluegills or lar-
gemouth bass have been caught in any angling or netting surveys in the lake. At the
same time, the golden shiner population has increased dramatically. Golden shiners,
which were relatively rare before 1977-78, are now by far the dominant species. Yel-
low perch, pumpkinseed sunfish, and yellow bullhead also occur. Ail of these species
are more tolerant of prolonged, very low oxygen levels than are bluegill or lar-
gemouth bass (Cooper and Washburn, 1946; Moore, 1942).
Hall and Ehlinger (1989) concluded that (a) the loss of the top predator, large-
mouth bass, was responsible for the explosion in the golden shiner population; and
(b) the increase in golden shiners, a planktivorous fish species, resulted in the ob-
served sharp decline in the abundance of large zooplankton, especially Daphnia
pulex and Daphnia galeata mendotae. Although in some lakes an increased abun-
dance of planktivores has been associated with decreased water clarity (see Chapter
9), no change was evident in the transparency of Wintergreen Lake, based on meas-
urements of Secchi depth transparency in 1971-72 and 1982. Both before and after
the 1977-78 lake winterkill, lake transparency was low (Secchi depth is generally 3 to
6feet or less during the summer).
(stock size), the PSD is 50. Fisheries management goals may then be defined in
terms of the RSD or PSD for target fish species. Changes in the RSD or PSD over
time for one or more species (e.g., Fig. 3-10) can be used to track the progress
towards achieving those goals.
Table 3-6.—Proposed minimum total length (in centimeters, 10 cm equals about 4
inches) for each designated size class: stock, quality, preferred, memorable, and
trophy, for selected fish species (source: Gablehouse, 1984; Anderson and
Gutreuter, 1983).
SIZE DESIGNATION
SPECIES
Largemouth bass
Smallmouth bass
Walleye
Muskellunge
Northern pike
Channel catfish
Bluegill
Black and white crappie
White bass
Common carp
STOCK
20
18
25
51
35
28
8
13
15
28
QUALITY
30
28
38
76
53
41
15
20
23
41
PREFERRED
38
35
- 51
97
71
61
20
25
30
53
MEMORABLE
51
43
63
107
86
71
25
30
38
66
TROPHY
63
51
76
127
112
91
30
38
46
84
47
-------
Fish and Fisheries Management in Lakes and Reservoirs
• Box J3-G.— Factors Influencing Year-Class Strength of •
Walleye in Lake Burton, Georgia (sourbe: Rabern, 1989) ; H
From 1960 to 1968, over six million fry and fingerling walleye were stocked into Lake
Burton, Georgia, and a naturally reproducing population was established. In the 1970s,
Lake Burton supported a strong walleye fishery. By 1 985, however, fishing success
rates for walleye in the lake had declined sharply by nearly 90 percent relative to creel
surveys in 1978-79. In response, the Georgia Department of Natural Resources ini-
tiated a comprehensive study of walleye in Lake Burton to identify the major factors
responsible for the fishery decline. Trends in walleye abundance, size of the spawning
stock, spawning times and locations, age and size distributions, food habits, and
growth rates were evaluated relative to trends in prey abundance, predator abun-
dance, temperature, rainfall, lake discharge, and water levels. The decline in walleye
catch and harvest from 1976 to 1988 was accompanied by an upward shift in the age
and length distribution (Table 3-6) and increased growth rates. During the 1 970s, age-
1 fish dominated the walleye population in the lake, while older age classes (ages 3
and 4) dominated in the 1980s.
Neither food limitations nor excessive losses to predators or fishing could account
for the observed fishery decline. Rather, variations in walleye year class strength were
most strongly correlated with rainfall levels in February (r = 0.90) and the minimum
March water level in the reservoir (r = 0.81). Based on these results, Rabern (1989)
concluded that walleye in Lake Burton were limited primarily by their reproductive suc-
cess and the variable quality of the spawning habitat among years.
Walleye in Lake Burton spawn in tributary streams. However, rising water levels in
the spring following the winter water-level drawdown gradually inundate these areas
so that the spawning habitat shifts from a stream to a lake habitat during egg incuba-
tion and larval development. Favorable conditions for strong year classes occur when
water levels are drawn down 10 feet or more during the winter and heavy winter rains
scour the stream beds, removing the silt and debris accumulated during the preceding
year and exposing significant quantities of rubble/gravel. Recommendations for irrv-
proving the walleye fishery included (a) water-level drawdowns greater than 10 feet
through February, (b) allowing the water level to rise in late February and March to in-
undate all spawning areas, (c) erosion control in the watershed to reduce siltation of
the spawning beds, (d) stocking with fry to supplement natural reproduction in years
when the spawning habitat quality is poor, and (e) creating artificial spawning reefs of
rubble at the mouths of tributary streams to supplement natural spawning areas.
Table 3-7.— Age frequency (%) of walleye collected in November from Lake Bur-
ton, Georgia (source: Rabern, 1989).
AGE
YEAR N 12 3 4 5 6 7 8
1976 4 25.0 0.0 0.0 50.0 25.0
1977 27 22.2 7.4 11.1 7.4 11.1 18.5 14.8 11.1
1978 33 97.0 3.0
1982 22 0.0 13.6 18.2 22.7 13.6 18.2 4.5 9.1
1983 14 0.0 0.0 42.9 14.3 21.4 14.3 0.0 7.1
1984 34 5.9 5.9 17.6 41.2 14.7 2.9 8.8 2.9
1985 27 14.8 0.0 11.1 55.6 11.1 7.4 0.0 0.0 •
1986 30 6.7 10.0 10.0 43.3 3.3 13.3 10.0 3.3
1987 19 0.0 0.0 21.1 73.7 0.0 0.0 5.3 0.0
1988 11 0.0 0.0 27.3 36.4 36.4
The number offish present
in a lake or reservoir at a
given time per unit area or
volume is referred to as
fish density or standing
stock.
Fish Production
The number of fish present in a lake or reservoir at a given time per unit area or
volume is referred to as fish density or standing stock. This number times the
mean weight per fish is the fish population biomass or total weight of fish present
per unit area or volume. The gross or total fish production in a given lake or reser-
voir is the total elaboration of new biomass over a specified period (e.g., one year)
48
-------
Chapter 3. Fish Ecology
Percent
30
25
20
15
10
100
i—i
150
• Age I
M Aae ii
H Age 111
ED Age IV
E3 Age VI
El Age VII
E3 Age VIII
300 350 400
Length Group (25mm)
~i—i—r
450 500
- 1
550
1 - 1
600
Figure 3-9.—Length-frequency distribution of largemouth bass in Lake Eufaula, Alabama,
in spring 1988. Shadings indicate fish age in years (source: Newman et al. 1989).
1967-1973
1974-1976
O
m
A\
*
O
O
CO
O
01
m
40 -
20 -
80
100
BASS STOCK ^ 30 CM (%)
Figure 3-10.—Proportional stock densities of largemouth bass and bluegill In Phillips
Lake, Missouri, 1967-76, plotted on a tic-tac-toe graph. The sequence of points represent
samples collected 3/67, 4/68, 3/69, 5/70, 5/71, 5/72, 6/73, 5/74, 6/75, 10/75, and 5/76. The
zone between the parallel dashed lines defines satisfactory conditions for bass and
bluegill populations in small Missouri impoundments. A 30-cm (12-inch) minimum size
limit on bass was evaluated from 1966-73 and may be responsible for the observed in-
crease in the relative abundance of large bluegills. In 1974, the fishing regulation was
changed to a slot size limit, protecting bass 30 to 38 cm (12 to 15 Inches) (source: Ander-
son, 1976).
49
-------
Fish and Fisheries Management in Lakes and Reservoirs
To ensure the long-term
viability of a population,
the quantity offish
harvested should never
exceed the sustainable
yield.
[MJost of the fish species
sought for recreational
fishing occupy a relatively
high position in the
trophic pyramid.
from both growth and reproduction, regardless of whether or not the biomass
lives through the period under consideration. Net fish production equals the total
production minus losses resulting from mortality; that is, the net change in fish
population biomass between the beginning and end of the time period of interest.
Depending on the relative balance among growth, reproduction, and mortality, the
net production in a lake in any one year may be positive (increase in the popula-
tion biomass), negative (population decrease), or zero (no change in the popula-
tion biomass).
Fisheries Yield
Yield refers specifically to that portion of a fish population (in terms of fish num-
bers or weight) harvested by humans through recreational or commercial fisheries
over some specified period of time and per unit area or volume (e.g., pounds per
year per acre). The yield (Y), or catch from a fishery, is a direct function of the size
of the population (P, population density or biomass), the level of fishing effort (f),
and the "catchability" of the species (q):
Y = q.f-P
An important concept in fisheries management is the optimum sustainable
yield, where sustainable yield refers to any level of yield that could be sustained
indefinitely by the fish population without causing any long-term decline in
population density or biomass. To ensure the long-term viability of a population,
the quantity of fish harvested should never exceed the sustainable yield. An op-
timum sustainable yield is both sustainable and optimal in terms of the benefit
derived from the fishery by humans. Maximum sustainable yield is the maximum
quantity of biomass that could be harvested from a population each year without
causing a long-term population decline. Optimum sustainable yield considers not
only the quantity of fish harvested but also the level of effort and expense required
to collect these fish and, in recreational fisheries, a wide range of other charac-
teristics relating to angler values and the overall quality of the fishing experience
(see Roedel, 1975).
The maximum and optimum sustainable yields for a fishery in a given lake or
reservoir are dependent on the fish population's annual net production, which is
affected in turn by the relative rates of fish growth, reproduction, and mortality.
Lakes with higher productivity can support larger harvests without causing long-
term population declines. Various methods and models exist for estimating fish
production and maximum sustainable yield, some of which are discussed in
Chapter 11. Optimum sustainable yields are difficult to formally quantify, how-
ever, because of the diverse array of variables that must be evaluated simul-
taneously. As a general rule, the optimum sustainable yield is less than the
maximum sustainable yield.
Natural Factors that Influence Fish Production
and Fisheries Yield
All of the factors discussed in previous sections that influence the processes of
growth, reproduction, and mortality also affect fish production and the potential
fishery yield: food availability, temperature, levels of dissolved oxygen, toxic sub-
stances, availability of suitable spawning habitat, competition from other species,
predation, and the occurrence of diseases and parasites. Furthermore, most of the
fish species sought for recreational fishing occupy a relatively high position in the
trophic pyramid. The elements of the trophic pyramid that lead to largemouth
bass production, for example, generally include phytoplankton and/or bacteria,
zooplankton, aquatic insects, and small fish species. Production at each of these
levels and the efficiency of energy transfer between levels will ultimately influence
the production of largemouth bass. Because only a fraction of the available energy
50
-------
Chapters. Fish Ecology
(about 10 to 20 percent) is transferred at each trophic level (see Chapter 2),
generally fish species with the shortest food chains (e.g., plant-feeding fish) have
the highest total production potential.
Fish production and yield are influenced, therefore, by a vast number of
physical, chemical, and biological factors and interactions, most of which are dif-
ficult or impossible to observe or directly measure. Because of these complexities,
several fisheries researchers have attempted to develop relatively simple indices
for estimating potential production or yield as a function of general lake charac-
teristics. Physical characteristics considered have included lake area, mean
depth, maximum depth, shoreline development, littoral-area-to-lake-area ratio,
water residence time, and many others. Physicochemical characteristics of inter-
est include mean temperature, the highest average daily temperature, minimum
oxygen levels, alkalinity, conductivity, and total dissolved solids. Some studies
have also considered biological factors, such as the available biomass of plankton
or benthic invertebrates.
One of the earliest and most widely cited indices was developed in the 1960s
by Richard A. Ryder (1965,1982). Using data for 34 northern temperate lakes sub-
ject to comparable fishing intensities, Ryder found that over 70 percent of the
variability in fishing yield (Y) among lakes could be accounted for by a lake's
mean depth (z) and total dissolved solids (TDS), when combined to form the
morphoedaphic index (MEI):
MEI=-/(TDS/z)
For Ryder's lakes,
Y = 1.4(MEI)0.45
where Y and MEI are in metric units, kg/ha/yr and mg/L/m, respectively.
The morphoedaphic index and various modifications of this index and ap-
proach have been widely applied in fisheries management to provide a quick,
first-order estimate of a lake's potential fisheries yield. The best such predictor of
fisheries yield is dependent, however, on the specific fish species, lake type, and
region of interest. Chapter 11 provides further information on the available em-
pirical models for estimating fish production and potential yield as a function of
a lake's general physical, chemical, and biological characteristics.
Population Genetics
Individual fish within a given species and even within the same population have
a high degree of phenotypic variability; that is, variations in characteristics such
as growth rates, age at sexual maturity, fecundity, and resistance to environmen-
tal stresses. Much of this variability is environmentally determined; as discussed
in earlier sections, fish are very "plastic" and responsive to environmental condi-
tions (e.g., differences in food availability and temperature). However, some por-
tion of this variability is also genetically determined. Heritability is the
proportion of the total phenotypic variation within a species that results from
genetic differences among individuals.
Inherited differences in potential growth rates, resistance to environmental
stresses, and the like have allowed fish populations over many generations to be-
come better adapted to their local environment. Fish species occur over wide
geographic regions with relatively little, if any, natural interbreeding between
populations in lakes separated by large distances. This reproductive isolation can
lead to the development of separate subspecies, strains, or stocks of fish that can
be genetically distinguished within a region or even within an individual lake or
drainage system by using protein electrophoresis and other techniques (see Utter
et al. 1987; Whitmore, 1990). Thus, two individuals from the same species but
Fish production and yield
are influenced, therefore,
by a vast number of
physical, chemical, and
biological factors and
interactions, most of
which are difficult or
impossible to observe or
directly measure.
Fish species occur over
wide geographic regions
with relatively little, if
any, natural interbreeding
between populations in
lakes separated by large
distances.
51
-------
Fish and Fisheries Management In Lakes and Reservoirs
Some lake -populations
spawn only in inlet
streams, while others have
adapted over time to
spawn in lakes or lake
outlets.
Genetic diversity within a
given population offish
increases the likelihood, of
the long-term population
survival....
from different populations (or different stocks, strains, or subspecies) may have
subtle but important differences in their innate characteristics. For example,
hatchery strains of brook trout have distinctly different characteristics (e.g., sur-
vival and growth potential) than do wild strains of brook trout. Even among wild
strains, some populations are adapted to living in lakes, others in streams. Some
lake populations spawn only in inlet streams, while others have adapted over time
to spawn in lakes or lake outlets. Transplants of one population or strain into
another environment for which they are poorly suited (e.g., an inlet-spawning
population into a lake with no inlets) will often fail.
Genetic diversity within a species has two major advantages. First, locally
adapted populations or fish stocks have presumably evolved over multiple
generations to be better suited to survive and reproduce in their immediate en-
vironment. Genetic diversity, therefore, reflects the adaptation of the species to the
variety of environments in which it occurs. Second, environmental conditions fluc^
tuate over time, randomly year to year as well as long-term trends (e.g., long-term
climatic trends). Genetic diversity within a given population of fish increases the
likelihood of the long-term population survival; that is, at least some members of
the population will be able to survive and reproduce given a change in water
quality or periodic extremes in environmental conditions.
Fisheries management activities and fishing can impact fish population
genetics and genetic diversity in several ways:
• Transplants of fish among different lakes and regions, a com-
mon practice historically in fisheries management, break down this sys-
tem of semi-isolated, locally adapted native populations. Genetically
distinct strains or stocks may be lost as a result of interbreeding with
fish of the same species but from different regions or drainage systems.
• Hatchery stocks of fish have often been maintained for generations,
inadvertently selecting fish better adapted for life in the hatchery than
in the wild. Hatchery strains tend to be more docile and less frightened
by humans (and thus easier for anglers to catch). They also feed better
on the pelletized food used in the hatchery than on natural prey and
grow faster but do not live as long as wild strains of fish of the same
species. When stocked, hatchery fish may compete with wild fish for
limited food supplies and also interbreed with native populations,
again resulting in the loss of genetically distinct, locally adapted strains
or fish stocks.
• Anglers prefer large fish. Thus, in heavily fished waters, those fish
that grow faster are more likely to be harvested, while fish that grow
slower tend to live longer, reproduce for more years, and contribute
more offspring to subsequent generations. Heavy fishing pressure may
select, therefore, for slow-growing individuals that become sexually ma-
ture at smaller sizes and may eventually lead to long-term changes in
fish population characteristics. While theoretically sound, relatively few
studies have been conducted to demonstrate the effects of fisheries
selection on fish population genetics (Nelson and Soule, 1987).
• Heavy fishing pressure, especially in small lakes, may greatly reduce
the number of fish in the population at any one time. Very small popula-
tion sizes increase the potential for problems associated with inbreeding
and the ^likelihood of reduced intra-population genetic diversity. As for
the effects of fisheries selection, however, the effects of small population
size on fish population genetics are theoretically sound, but little direct
evidence is available (Nelson and Soule, 1987).
52
-------
Chapters. Fish Ecology
Ryman and Utter (1987) provide additional information on the relationship
between fisheries management and population genetics. Also of interest are
papers from the 1990 International Symposium on The Ecological and Genetic
Implications of Fish Introductions, presented in the Canadian Journal of Fisheries
and Aquatic Sciences (see Hebert, 1991).
Fish Habitat
Mention has been made in many of the previous sections of the importance of a
lake's physical and chemical attributes in determining both the suitability for a
particular fish species as well as the potential total fish production and yield. The
purpose of this section is to reiterate and elaborate on several key points regard-
ing fish habitats. An understanding of fish habitat requirements can serve two
important purposes: (1) to evaluate the degree to which specific habitat features
may be limiting fish population success or productivity within a given lake and
(2) to design and evaluate fish habitat protection and management projects (see
Chapter 8).
Fish require habitats in which they can complete their life cycle and
reproduce. The types of habitats required vary among species and also among
life stages. As a result, assessments of fish habitat suitability must be specific to
species and life stage. The U.S. Fish and Wildlife Service has proposed Habitat
Suitability Indices for many of the common fish species and most sportfish in
fresh waters of the United States. These habitat evaluation approaches and
models are discussed further in Chapter 11.
Some habitats are of critical importance to fish populations because of the es-
sential functions they support and because the availability of these habitats is
often limited. Two common classes of critical fish habitat are
• spawning areas, which are essential for reproduction and survival of
early life stages; and
• nursery areas, which provide cover and feeding areas for young fish.
Tributary streams and wetlands provide critical spawning habitats for many
fish species (see Table 3-3 and App. A). The absence or degradation of these
habitats may limit the types and diversity of species able to maintain self-sustain-
ing populations in the lake or reservoir. Substrate type also is an important deter-
minant of an area's suitability for spawning for many fish. In addition, substrate
type influences the composition and productivity of benthic invertebrate com-
munities and, thus, the availability of food for fish.
A lake's physical features also serve as areas of escape and cover for smaller
fish to avoid or minimize the potential for predation. Extensive beds of aquatic
vegetation are one of the most important refugia for juvenile and small fish in
many lakes and reservoirs. In some waters, overly abundant cover and/or the oc-
currence of too few fish predators may result in relatively high survival rates
among young fish and subsequent overcrowding and stunted populations.
Therefore, as in most management issues, maintaining an appropriate balance
between too little and too much cover and protection is important.
Fish — smaller fish seeking cover as well as larger predatory fish searching
for prey — tend to congregate around areas that provide cover. Adding struc-
tures such as brush piles or cribs to lakes with relatively little natural cover may
serve to attract and concentrate sportfish, thereby improving fishing success. The
potential benefits and use of such "attraction" habitats for fisheries management
are discussed further in Chapter 8.
Changes in water level may have a marked effect on the quantity and quality
of suitable habitat. For example, with a decrease in water level, beds of aquatic
vegetation in the littoral zone may be exposed and no longer available as cover
Some habitats are of
critical importance to fish
populations because of the
essential functions they
support and because the
availability of these
habitats is often limited.
Extensive beds of aquatic
vegetation are one of the
most important refugia for
juvenile and small fish in
many lakes and reservoirs.
Changes in water level
may have a marked effect
on the quantity and
quality of suitable habitat.
53
-------
Fish and Fisheries Management In Lakes and Reservoirs
Managing the quality of
the habitat is a
prerequisite to
maintaining a quality
fishing experience and
productive fisheries.
The abundance and
success of any particular
fish species is clearly
affected by the abundance
o/offer species that
compete with, prey upon,
or are prey for the species
of interest.
for juvenile and small fish. The result may be an increase in predation, benefiting
the larger predatory fish while decreasing the survival of smaller fish. Thus, al-
though somewhat drastic, periodic water drawdowns are one approach to ad-
dressing problems with overcrowded populations of small, stunted fish (see
Chapter 8).
The construction of seawalls, beaches, and docks, and other physical altera-
tions of the shoreline and littoral area environment may also impact the
availability of suitable fish habitat and cover. They are discussed further in Chap-
ter 8.
The colder waters of a lake's metalimnion and hypolimnion provide impor-
tant habitat for coldwater fish species such as brook trout, lake trout, and other sal-
monids (see Table 2-2) and also for coolwater species such as striped bass, alewife,
and blueback herring in southern reservoirs (e.g., see Box 3-E). Lake restoration ac-
tivities that affect the stability of a lake's thermal stratification or the temperature
or levels of dissolved oxygen in these deep waters would directly affect the
suitability of the lake for coldwater or coolwater fisheries and/or the maintenance
of a two-story fishery (with both warm water and cold- or coolwater fish species).
Maintenance of suitable habitats for fish is fundamental to successful fish
management. Yet, many human activities alter or degrade these habitats. Common
threats to fish habitats include increased silt loads as a result of construction, farm-
ing, or lumbering activities within the watershed; dredging; and barriers to migra-
tion, in particular dams on lake inlets and outlets that may block spawning runs.
Threats also include alterations of flow and stream diversions and industrial and
municipal liquid waste discharges and nonpoint sources of nutrients and toxic
substances that may directly and indirectly affect the suitability of the lake or
reservoir for fish survival and reproduction. Managing the quality of the habitat is
a prerequisite to maintaining a quality fishing experience and productive fisheries.
Fish Communities
Historically, fisheries management has focused on managing individual fish
species and populations of greatest interest or value for recreational or commercial
fisheries. However, just as fish cannot be managed in isolation from their environ-
ment and the quality of the fish habitat, individual fish species cannot be effective-
ly managed without considering the broader biological community in which they
coexist. The abundance and success of any particular fish species is clearly affected
by the abundance of other species that compete with, prey upon, or are prey for
the species of interest. Maintaining an optimal yield of the target species requires
appropriate population levels of competitors, predators, and prey species. The ad-
vantages of abundant prey are obvious. Reasonably abundant predators also can
be advantageous because of their selective removal of younger, weaker fish,
decreasing the potential for overcrowding and stunted growth. However, an over-
abundance of predators or competitors may limit the productivity and yield of the
target fish species. '
Chapter 2 provides further discussion on the nature and importance of inter-
actions between fish and other biota and among fish species. Three additional
topics are briefly reviewed here: (1) fish community types, (2) factors that in-
fluence fish species distributions and fish community composition, and (3) the role
of fish community analysis in fish and fisheries management.
Fish Community Types
Some fish species frequently occur together; others are negatively associated.
Based on these patterns, fish communities are often classified into fish community
types, generally denoted by the characteristic or dominant fish species in the com-
munity. For example, Tonn et al. (1983) classified fish communities in small lakes
54
-------
Chapters. Fish Ecology
in northern Wisconsin into three types: mudminnow, bass, and pike. Mudmin-
now lakes typically had populations of stunted yellow perch and one or more
minnow species in addition to the dominant species, the central mudminnow
(Umbra limi). Frequently occurring species in bass lakes included largemouth
bass, yellow perch, and bluegill and/or pumpkinseed sunfish. Lakes dominated
by northern pike typically also contained one or more species of bullhead, white
sucker, pumpkinseed and/or bluegill sunfish, and yellow perch. The composi-
tion and frequency of occurrence of common fish community types vary among
regions.
Two approaches have been used to define fish community types. Many State
fisheries agencies categorize lakes according to their major fishery(ies); for ex-
ample, as walleye lakes, bass-bluegill lakes, lake trout lakes, two-story fisheries,
and so on. Alternatively, fish community types can be determined based on
statistical associations among species (e.g., using ordination analyses; see Gauch
1982; Hill and Gauch, 1980). Examples include the Tonn et al. (1983) study pre-
viously mentioned, Minns (1989), and Hinch et al. (1991).
Factors That Influence Fish Community Composition
Many factors work together to determine the composition of a fish community in
a given lake or reservoir. All of the species that occur must have naturally
emigrated to the lake from waterbodies connected currently or historically or
been introduced, accidentally or on purpose, by human activities. Natural pat-
terns of fish species distribution tend to follow major drainage systems; fish com-
munities in lakes interconnected within the same major drainage system tend to
be more similar to each other than to communities in other systems or regions. In
some areas, especially northern regions influenced by glaciation, historic
drainage patterns were distinctly different from those of today. Large meltwater
lakes formed at the edge of the retreating ice sheet over major portions of Wis-
consin, Ontario, and other areas. Lakes that today are geographically isolated
may have been interconnected during this post-glacial period and, as a result,
have similar species composition. In general, lakes that are geographically iso-
lated (for example, seepage lakes with no inlets or outlets and lakes at high eleva-
tions) tend to support fewer fish species (i.e., have a lower species richness) than
do drainage lakes (with inlets and outlets), reservoirs, and lakes at lower eleva-
tions.
Colonization opportunities and human introductions define the pool of
species that potentially occur in a lake. Habitat characteristics and biotic interac-
tions determine the actual species composition and relative species abundance.
For a species to persist, the lake or reservoir must provide suitable habitat for
reproduction, survival, and growth. Fish species with similar habitat require-
ments (e.g., largemouth bass and bluegill) frequently co-occur, while species that
prefer distinctly different types of habitat (e.g., smallmouth bass and bullheads)
are often negatively associated or occur together only in large lakes with diverse
habitats.
Because large lakes and reservoirs generally provide a greater variety of
habitats, they also tend to support more fish species than do smaller lakes.
Sporadic events, such as winterkill, can also have a long-term impact on fish
community composition (as discussed in Box 3-F) especially if the lake is current-
ly isolated from other waterbodies, preventing or slowing the natural re-
colonization of the lake by fish.-
Predation and competition among fish species also influence fish community
composition. Predation, in particular, may limit species co-occurrence. For ex-
ample, soft-bodied, small fish species (e.g., minnows) that are readily captured
and eaten by predators tend to be absent or rare in lakes with large piscivorous
Natural patterns offish
species distribution tend
to follow major drainage
systems....
Colonization
opportunities and human
introductions define the
pool of species that
potentially occur in a lake.
Predation and competition
among fish species also
influence fish community
composition.
55
-------
Fish and Fisheries Management in Lakes and Reservoirs
species, such as northern pike and largemouth bass (Tonn and Magnuson, 1982;
Jackson, 1988). Inskip and Magnuson (1983) speculated that predation of northern
pike on young-of-the-year muskellunge is the primary reason for the sharp decline
in muskellunge abundance in Big Pine Lake, Wisconsin, following the introduc-
tion of northern pike in the 1940s. Biotic interactions are likely to be of greater im-
portance in small lakes with relatively little fish cover than in larger lakes or those
with abundant macrophytes or other fish cover.
Role of Community Analyses in Fisheries Management
Tonn et al. (1983) and Magnuson (1991) identify several ways in which fish com-
munity analyses may benefit a fisheries management program:
• The delineation of common fish community types in a region identifies
sets of species that commonly co-occur and those that rarely, if ever,
occur together, providing guidelines for reasonable assemblages of
species to target in any given lake or reservoir.
• For regional planning (e.g., State fisheries programs), classification of
lakes by fish-community type facilitates the evaluation and tracking of
available fish resources; the number of lakes within each class provides
an indicator of the types and distribution of fishing opportunities avail-
able.
• Associations between easily measured lake characteristics (e.g., area,
depth, summer temperatures, total dissolved solids) and fish-com-
munity type are more consistent than those for individual fish species.
Multivariate analyses can be used to identify lake characteristics highly
correlated or associated with the occurrence of a particular fish-com-
munity type. Results from these analyses can be used as follows:
» Relatively simple models or dichotomous keys (e.g., Fig. 3-11) can
be developed to predict the type of fish community most likely to
occur in a lake based on measurements of physical and chemical
variables.
• Information on lake characteristics can be used to help establish
reasonable fish management goals, identify lake characteristics that
may be limiting the fish community and fisheries, and avoid inap-
propriate and wasteful management procedure (e.g., stocking fish
into lakes where the fish species is unlikely to survive over the long
term).
1a. Lakes with total watershed size < 10 km2(3.9 square miles)
and surface area < 45 ha (111 acres) 2
1b. Lakes with total watershed size 10-340 km2(3.9-131 sq. miles)
and surface area 45-100 ha (111-247 acres) 3
2a. Lakes with maximum depth < 4 m (13 ft) mudminnow lakes
2b. Lakes with maximum depth 4 to 8 m (13-26 ft) bass lakes
3a. Lakes with pH 5 to 6.5 or conductivity 7 to 50 u.S/cm bass lakes
3b. Lakes with pH 6.5 to 9 or conductivity 51 to 200 uS/cm .. pike lakes
Figure 3-11.—Dichotomous key for predicting fish-community type for small lakes in
forested areas in northern Wisconsin (source: Magnuson, 1991; Tonn et al. 1983).
56
-------
Chapters. Fish Ecology
Special Issues in Reservoirs
The concepts and underlying principles of managing reservoir fisheries are no
different than those for fisheries in natural lakes. Furthermore, most fisheries
management problems and approaches are common to both lakes and reservoirs.
Nevertheless, some features, problems, and approaches are unique or occur more
frequently in reservoirs than in natural lakes. Issues of special concern or interest
for managing fisheries in reservoirs include the following:
• Reservoir design and construction. Unlike natural lakes, reser-
voirs can be designed and constructed specifically with fish habitat re-
quirements and preferences in mind. It may be possible to favor
particular target fish species, enhance productivity, minimize the
potential for certain types of management problems, and also improve
boater and angler access. Factors to consider in the design and con-
struction of reservoirs are discussed further in Chapter 8.
• Fisheries and fish community development. When filled, the
reservoir provides a new lake habitat with little to no pre-existing fish
community. Therefore, both the fish community and fishery must be,
in essence, developed "from scratch." New species must be introduced
and appropriate balances established among prey, predators, and fish
populations.
• Aging. As noted in Chapter 2, new impoundments typically ex-
perience an initial peak in productivity (trophic upsurge) followed by
a trophic depression and longer-term, gradual maturation and aging
process. Fish populations may fluctuate sharply during the trophic
disequilibrium phase but usually stabilize within 5 to 10 years. Chang-
es in target species and management approaches may be warranted
over time in response to changes in the reservoir habitat.
• Water level fluctuations. Water level fluctuations tend to be
greater in many reservoirs than in natural lakes. Periodic exposures of
the littoral zone during water drawdowns may have both positive and
negative effects on the lake ecosystem and fish community. Reservoir
outlet designs that allow for multiple water level discharges facilitate
the use of water level management as a fisheries management tool (see
Chapter 8). To protect the fish community, minimal water levels that
provide a fish conservation pool should be designated.
• Hypolimnetic discharges. Hypolimnetic discharges from reser-
voirs promote subsurface density flows and allow creation of
downstream coldwater fisheries, as discussed in Chapter 2. At the
same time, mainstream reservoirs are frequently constructed in series.
Hypolimnetic discharges from upstream reservoirs may adversely af-
fect the reproductive success and growth of warmwater fisheries in
downstream reservoirs.
• Spatial heterogeneity. Many reservoirs are large, complex, and
diverse systems. This spatial heterogeneity may lead to the develop-
ment of discrete fish stocks with distinct growth and life history char-
acteristics. Variations among fish stocks and the size and spatial
heterogeneity of the reservoir environment increase the difficulty of
obtaining an adequate sample for assessing fish community status and
trends.
[MJost fisheries
management problems
and approaches are
common to both lakes and
reservoirs.
57
-------
Fish and Fisheries Management in Lakes and Reservoirs
• Limited natural cover. Frequent changes in water level together
with the high levels of turbidity that occur in some reservoirs may limit
growths of aquatic macrophytes. As noted in Chapter 2, macrophyte
beds provide important spawning habitats and nursery areas for a num-
ber of fish species. In waters without macrophytes, the addition of struc-
tures to enhance fish cover may be beneficial to the fish community (see
Chapter 8).
• Inergy development. Many reservoirs are constructed specifically
for energy development for hydroelectric power or as cooling ponds for
electrical generating facilities. Both uses introduce a unique set of
problems, including entrainment, impingement, thermal discharges,
and effluents from ash basins. Problems in fisheries management are
discussed further in Chapter 6.
Hall and Van Den Avyle (1986) discuss additional issues and problems relating
to managing fish and fisheries in reservoirs.
58
-------
CHAPTER 4
Key Concepts in
Fish and Fisheries
Management
Chapter Objective
This chapter introduces the major components of and key concepts underlying a
fish or fisheries management program. Subsequent chapters provide further
details on each of these topics and also describe specific management techniques
and approaches.
As discussed in previous chapters, the emphasis is on fish and fisheries
management within the context of an integrated lake management program. Fish-
ing is only one of many human uses of lakes and reservoirs, and fisheries manage-
ment must be viewed within the broader context of managing the quality and
multiple uses of aquatic resources. Water quality management is critical to
fisheries management because (a) sustainable fisheries yields and the types of fish
resources that a lake can support are highly dependent on the quality and charac-
teristics of the lake habitat, and (b) the quality of the lake environment as a whole
(e.g., aesthetics) has a major influence on the level of enjoyment derived from a
fishing experience. Likewise, fish are of interest to water quality managers because
(a) fisheries management activities and fishing can indirectly affect water quality
and other lake uses, and (b) manipulations of the fish community are one of a
number of available tools for water quality management. A joint management
program recognizes the interrelationships among fish, other biota, water quality,
and the physical habitat. Decisions regarding lake management can consider the
full range of effects associated with a proposed action and the potential trade-offs
among all alternative objectives, lake uses, and human values.
Important Underlying Principles
The Lake and Reservoir Restoration Guidance Manual (Olem and Flock, 1990)
presents several underlying principles and conclusions regarding lake restora-
tion efforts. Because of their importance, these major conclusions are repeated
here, modified slightly to better reflect the issues and objectives of primary con-
cern for fish and fisheries management:
• Fisheries or lake management problems have no simple, ready-made
solutions; different situations require different approaches. Applying
the wrong management technique can often make problems worse or
more intransigent, difficult, and expensive to resolve.
A joint management
program recognizes the
interrelationships among
fish, other biota, water
quality, and the physical
habitat.
-------
Fish and Fisheries Management in Lakes and Reservoirs
Management and restoration efforts must treat the cause of the problem,
not the symptom. Actions that address only symptoms are unlikely to
be successful or cost effective over the long-term.
The physical, chemical, and biological components of lake ecosystems
are intricately linked. As a result, identifying causal linkages and causes
of management problems are often difficult. Furthermore, any manage-
ment action is likely to have a series of indirect consequences that must
be anticipated and considered as part of the decision-making process.
Biological communities and fish populations are dynamic and exist in
an environment that is highly variable and largely uncontrollable. These
natural fluctuations must be accounted for in management decisions
and in interpreting the results from lake monitoring programs. Respon-
ses to management actions may occur over a long time frame and re-
quire long-term data sets to detect.
Habitat protection is essential to successful fisheries management;
suitable fish habitat is a prerequisite for productive fisheries. In a similar
manner, a lake and its watershed are tightly coupled. Good manage-
ment practices in the watershed are essential for improving and protect-
ing the physical and chemical quality of the lake environment. Thus,
lake and watershed management must be incorporated within a
fisheries management program.
To be successful, fisheries and lake management objectives must be
compatible with the uses that the natural condition of the lake (and its
watershed) can support most readily. For example, some lakes are
naturally highly productive (eutrophic) because of the types of soils and
geology of their surrounding watershed. To attempt to manage or trans-
form such a system to an unproductive, clear-water (oligotrophic) state
or manage the fisheries in the lake for fish species that do best in
oligotrophic waters would be ill-advised.
Lakes and reservoirs are used for multiple, often conflicting purposes.
Even among the fishing public, conflicting desires, objectives, and fish-
ing preferences frequently arise. Lake management decisions must
reflect the need to set priorities, compromise, and establish an optimal
balance among multiple uses.
Management decisions and actions must be cost effective. Cost con-
siderations must be incorporated directly into fisheries planning and
management decisions.
Because of the complexity of the issues involved and the potential adverse
consequences of making a mistake, professionals trained in fisheries
science and limnology must be involved during each phase of the planning
process, program implementation, and management evaluation. In par-
ticular because the fish in most lakes are pubic resources, personnel from
State fisheries agencies should be contacted before any of the management
activities described in this manual are undertaken. Some of these manage-
ment techniques and fish sampling methods can be conducted only by
State personnel or require State permits (see Chapter 7 and Appendix C for
information on contacting State agencies).
Finally, minimal management is often the best management approach:
protection of the resource rather than intervention. To the degree pos-
sible, management objectives should be achieved by enhancing and
managing native fish populations rather than through large-scale
manipulations and alterations of the existing fish community in the lake
or reservoir.
60
-------
Chapter 4. Key Concepts in Fish and Fisheries Management
Importance of Recreational Fisheries
Fishing is one of the most popular and widespread recreational uses of lakes and
reservoirs. In 1985, 38.4 million individuals 16 years and older participated in an-
gling on fresh waters in the United States (excluding the Great Lakes), for a total
of 786 million angling days (U.S. Fish Wildl. Serv., 1988). In Canada in 1985, 6.5
million active anglers 16 years and older — close to one out of every five
Canadians — fished a total of approximately 69 million days on fresh waters
(Can. Dep. Fish. Oceans, 1988). In the U.S. survey, 15 million people reported
fishing on natural lakes and 22 million on reservoirs, the latter divided fairly
equally among smaller reservoirs (35 percent on waters < 10 acres in size) and
larger systems (45 percent on waters > 40 acres). Fish species and groups
preferred by anglers in the United States and Canada are listed in Table 4-1.
Table 4-1.—Fish species and groups preferred by anglers In the United States and
Canada in 1985 (source: U.S. Fish Wildl. Serv. 1988; Can. Dep. Fish. Oceans, 1988).
PERCENTAGE OF FISHING EFFORT OR CATCH*
FISH SPECIES OR GROUP
UNITED STATES
CANADA
Black bass
White bass
Striped bass and striped bass hybrids
Panfish
Crappie
Catfish and bullheads
Walleye and sauger
Perch
Northern pike and pickerel
Muskie and muskie hybrids
Trout
Salmon
Steelhead
Whitefish
Smelt
Other
Fishing for anything
19
4
4
15
13
16
4
4
1
9
1
1
12
21
10
22
2
1
7
18
* Dashes {—) indicate fish species or groups not listed as a separate category in the U.S. and Canadian .
national survey summary reports.
Direct expenditures on freshwater fishing in 1985 totalled $17.8 billion in the
United States and $2.5 billion in Canada (U.S. Fish Wildl. Serv. 1988; Can. Dep.
Fish Oceans, 1988). Canadian anglers also spent an estimated additional $1.9 mil-
lion for durable goods (e.g., boats, motors, camping gear) related directly to sport
fishing activities; similar data for U.S. anglers were not available.
Since 1955, when the U.S. National Survey of Fishing, Hunting, and Wildlife
Associated Recreation was initiated, the numbers of anglers and angling days
have more than doubled (U.S. Fish Wildl. Serv. 1988). While the number of in-
dividuals participating in angling continues to increase, the total fish resource
and acres of surface waters available for fishing have remained relatively con-
stant in recent years. Thus, sustaining a high level of fishing enjoyment, includ-
ing a reasonable level of fishing returns and fish caught, will require careful
management of the existing resource.
Historical Perspectives
The science and objectives of fisheries management have changed over the years.
In the late 1800s and early 1900s, when many State fisheries agencies were first
established, restrictive fishing regulations and fish stocking were the major
management techniques. Most funding was spent on hatchery operations, with
Fishing is one of the most
popular and widespread
recreational uses of lakes
and reservoirs.
In the late 1800s and early
1900s,... [fjish were
considered a resource to be
exploited.
61
-------
Fish and Rsheries Management in Lakes and Reservoirs
[SJimple approaches to the
management offish
resources have often
caused more harm than
good
[Shocking is no longer
viewed as a panecea
Currently, management
programs recognize the
benefits and role of
managing and protecting
both water quality and the
physical habitat.
[Fisheries management
requires an understanding
of lake ecology as well as
fish biology and fish
population dynamics.
the emphasis on producing the maximum amount of fish biomass for harvest by
anglers. Fish were considered a resource to be exploited. To increase the available
quantity, fish were stocked into waters with relatively little attention paid to the
suitability of the habitat, the potential for long-term survival of the fish popula-
tion, and the impacts on other fish species and biota. Exotic species imported from
other countries or other regions of the United States were widely distributed in an
attempt to increase and diversify fishing opportunities. Examples include the com-
mon carp and brown trout, imported from Europe in the 1800s, and rainbow trout,
which are native to the western United States but have been stocked extensively
throughout much of North America.
Through time, simple approaches to the management of fish resources have
often caused more harm than good, and the science of freshwater fish manage-
ment has developed considerably. Important lessons learned and trends in
fisheries management have included the following (Radonski and Martin, 1985;
Magnuson, 1991):
• Stocking is cost effective only if the stocked fish have a reasonable
chance of survival and the habitat into which they are stocked is
suitable. Stocking programs have become increasingly sophisticated,
developing approaches for optimizing the size, numbers, and types of
fish stocked for the greatest returns and improvement in fishing quality.
• Stocking, especially introductions of non-native species, can cause
serious adverse effects to fishing quality and other lake uses. While still
playing a role in fisheries management as one of a number of manage-
ment options, stocking is no longer viewed as a panacea, the emphasis
on and relative funding of stocking programs have decreased, and the
potential adverse effects of stocking are carefully considered before ini-
tiating any new stocking program.
• Habitat improvement and protection activities can be more effective
than stocking and can result in long-term increases in fishing quality at
relatively low cost. Interest in fish habitat improvements began in the
1930s and primarily involved the installation of physical structures in
streams to stabilize shorelines, deepen pools, and provide fish cover,
and fish attraction features in lakes to concentrate fish for angling. At-
tention shifted to the adverse effects of pollution, especially chemical
pollutants and eutrophication, in the 1960s and 1970s. Currently,
management programs recognize the benefits and role of managing and
protecting both water quality and the physical habitat.
• Many of the fishing regulations used initially — creel limits, minimum size
limits, closed seasons — have been proven ineffective or even
counterproductive in some instances in controlling fish populations. Sub-
stantial research since the 1960s has lead to the development of more tar-
geted and effective regulatory approaches (e.g., slot size limits, discussed in
Chapter 8). Furthermore, current management philosophy is to implement
only those regulations that have a clearly demonstrated need.
• Fisheries management in the 1950s and 1960s, in particular, focused on
individual fish species; fisheries science was largely the study and
modeling of fish population dynamics to estimate maximum sus-
tainable yields. While important, an understanding of fish population
dynamics, by itself, is not sufficient. Fisheries management has ad-
vanced through an appreciation for predator-prey balances to a recogni-
tion of the importance and complexity of the interactions between the
targeted fish species and all other ecosystem components. As discussed
in Chapters 2 and 3, fisheries management requires an understanding of
lake ecology as well as fish biology and fish population dynamics.
62
-------
Chapter 4. Key Concepts in Fish and Fisheries Management
Anglers are interested in more than just maximizing the biomass of
fish caught. In fact in a 1985 survey of Canadian anglers, quality of the
water and beauty of the surroundings were rated as the two most im-
portant factors affecting the enjoyment of a day of fishing. Number of
fish caught, size of fish caught, and fish catch as a source of food were
rated 9,10, and 11, respectively, behind a variety of environmental and
sociological factors such as escape from routine, privacy, and angling
for wild fish (Can. Dep. Fish. Oceans, 1988). While the relative impor-
tance of these factors varies regionally, the scope of fisheries manage-
ment objectives has broadened substantially.
Fish and fishing can affect other lake uses and lake characteristics. The
increasing recognition, starting in the 1960s and 1970s, of the role of
fish predators in the lake ecosystem has lead to (a) a better apprecia-
tion for the indirect effects of fisheries management activities on other
aspects of lake quality and other lake uses; (b) use of biomanipulation
as a tool for water quality management; and (c) increasing emphasis,
as in this manual, on the integration of fisheries and water quality
management programs.
Many of today's environmental problems are regional or global in
scale (e.g., acidic deposition, global climate change) and cannot be ef-
fectively addressed by site-specific research and management
programs.
To better address the diversity of environmental problems and con-
cerns, lake managers must have an increased understanding of the un-
derlying mechanisms of fish response, ecological processes, human
motivations and values, and more sophisticated analysis tools. Studies
of fish physiology, behavior, genetics, community ecology, ecosystem
ecology, and statistics and mathematical modeling have become in-
creasingly important. The science of fisheries management has
evolved from one founded largely in biology to an interdisciplinary
science encompassing biology, chemistry, physics, ecology, mathe-
matics, and statistics as well as economics, sociology, and psychology.
Components of a Management Program
A comprehensive lake management program includes six major components
(Fig. 4-1):
1. Determine the current status of the lake ecosystem and fisheries by
sampling and assessing each of the following (see Appendix B): :
• sportfish in the lake (i.e., the fish populations exploited
directly by recreational fishing);
• other fish species and biota that may prey upon, be prey for,
or compete with the target species;
• other biota that may be indicative of the condition of the
biological community as a whole in the lake or reservoir;
• the fish's habitat, in particular the physical, chemical, and
biological characteristics of the lake that are most critical for
fish survival, reproduction, and growth; and
• the fisheries and fishing success.
2, Characterize the user population; for example, the characteristics and
desires of individuals likely to be involved in recreation (fishing,
63
-------
Fish and Fisheries Management in Lakes and Reservoirs
Assess current status
of lake and fisheries
Characterize lake users
and associated values
Establish priority
management objectives
Identify major problems,
causes, and limiting factors
Select and implement
management approaches
Monitor for results:
program effectiveness and
new problems
Figure 4-1.—Major components of a comprehensive lake management program.
swimming, boating) in the lake or reservoir and also the full range of
environmental values associated with the lake or reservoir by both
users and nonusers (Chapter 5).
3. Establish priority objectives and targets for the management program
that consider the preferences of the fishing public, potential competing
uses, and the environmental characteristics of the lake or reservoir that
may influence or limit the optimal lake uses or target fish species
(Chapter 5).
64
-------
Chapter 4. Key Concepts in Fish and,,Fisheries Management
4. Identify the major factors or problems that may be limiting fisheries
success, the quality of the fishing experience, or other lake uses
(Chapter 6).
5. Select and implement optimal approach(es) to resolving these
problems (Chapters 8 and 9). For fish and fisheries management
problems, actions may include one or more of the following:
» direct manipulation of the fish population or fish community
(e.g., stocking, removing undesirable fish);
• increasing food supplies (e.g., by prey introductions or
increasing lake productivity);
• habitat protection and management (e.g., by modifying a
lake's physical features or improving water quality); and
• fishing regulations and associated activities (e.g., controlling
lake access) to improve the quality of fishing by adjusting
fishing pressure and harvest.
6. Monitor changes in the fish community, fisheries, and lake ecosystem
to determine the effectiveness of the management actions, and iden-
tify any new problems that may arise.
Based on the monitoring data collected, new or modified management ac-
tions may be warranted. In addition, the application of a management action it-
self is a learning process. By observing the response of the lake and lake's
fisheries, further insight can be gained regarding the nature of the problem, the
system constraints, and the optimal management approach to alleviate the prob-
lem. This process, whereby information is gained and management strategies are
improved through direct experience with applying management techniques, is
referred to as "adaptive management" (Walters, 1986). Thus, lake management,
including the six components of a management program in Figure 4-1, is not a
linear process but is highly interactive with multiple feedback loops. Models are
frequently used as part of the adaptive management process to help organize the
accumulated information and evaluate the remaining uncertainties (see Chapter
11).
Regional Perspectives
As noted, in Chapter 1, the object of this manual is to provide useful guidance on
fish and fisheries management appropriate for lakes and reservoirs in the United
States and Canada. To cover such a diverse area in a single manual is a challenge
that, admittedly, can be only partially fulfilled. Priority management objectives,
the types of problems encountered/and optimal management approaches tend to
vary widely among lakes in different regions, of different sizes and lake types,
and with different types of fish communities and fisheries. For example, while
the basic principles and underlying processes are the same, management
strategies commonly used for warmwater fish communities (e.g., bass and
bluegill) differ from those for coldwater fish communities (e.g., trout). Coldwater
and coolwater fish species represent the major sport fish at northern latitudes;
warmwater fish species occur in most areas but are of greater importance at
southern latitudes (see Table 4-1). Many management techniques, especially in-
lake treatments, are more feasible in small lakes than in large lakes. Large lakes
and reservoirs are also more spatially heterogeneous, with a greater diversity of
habitats, fish species, conditions, and problems in any given lake. Winterkill
problems occur predominately in small lakes at northern latitudes or high eleva-
tions, while summerkill is more common in warmer climates or at the southern
edge of the distribution for coolwater species.
By observing the response
of the lake and lake's
fisheries, further insight
can be gained regarding
the nature of problem, the
system constraints, and
the optimal management
approach to alleviate the
problem.
65
-------
Fish and Fisheries Management In Lakes and Reservoirs
Some of these lake-to-lake differences in management strategy can be better
understood by classifying lakes by region, lake type, or fish-community type. State
fisheries agencies, by default, manage by political boundaries. Within a given
State, however, management activities are often organized by subregion and/or
by fish-community type. For example, Omernik (1987) used regional differences in
climate, rainfall, topography (hills, valleys, plains), soils, geology, and land use to
define ecoregions within the United States. A number of States use ecoregions or
other ecologically relevant subregion boundaries to delineate management areas
likely to have relatively similar natural biological communities and lake charac-
teristics and as the basic unit to establish attainable lake uses and biocriteria (i.e.,
numeric or narrative water quality criteria describing the reference biological in-
tegrity of aquatic communities of a given designated use).
This manual attempts to describe management approaches in generic terms.
The discussions are not region-specific for the most part. However, case studies are
provided in Chapter 12 and elsewhere throughout the text to illustrate applica-
tions of these techniques and procedures in different regions and for different
types of lake problems and fish communities.
66
-------
CHAPTER 5
Setting Goals, Specific
Objectives, and
Priorities
Chapter Objectives
Before proceeding, you must first decide what you are trying to achieve and
what actions to take. Thus, the first step in any lake or fisheries management pro-
gram is to establish program goals, specific objectives, and priorities. Goals
describe in general terms what your program is designed to achieve. For ex-
ample, for a fishery in an urban area, important goals may be to provide the max-
imum possible fisheries yield, a high catch rate per unit of angling effort, and
self-sustaining fish populations that can support heavy fishing pressure. Specific
technical objectives should then be defined for each goal, delineating explicit tar-
gets and metrics for tracking progress toward achieving that result. For these
goals, appropriate objectives might include target values for the total number of
angling hours on the lake per year, the average catch per unit effort (e.g., the
number and weight of fish caught per hour fished), and the total yield for one or
more selected target fish species. Often, some goals and specific objectives con-
flict and cannot be optimized simultaneously. Furthermore, funding is frequently
limited, preventing completion of all desirable projects and specific objectives. As
a result, you must make choices and define priorities. Priority setting is an in-
tegral part of establishing a program's goals and specific objectives.
This chapter provides an overview of the process — that is, the activities and
issues associated with defining a program's goals, specific objectives, and
priorities — and briefly describes the types of goals that may be of interest or
value for fish and fisheries management programs in lakes and reservoirs.
Who Should Be Involved?
All too often in the past, fisheries management objectives have been defined
primarily by fisheries biologists working in relative isolation from the user com-
munity (i.e., the fishing public and other groups of lake users). A program's effec-
tiveness and likelihood of success can be greatly enhanced, however, by actively
involving lake users in the planning process. For example, people who currently
fish (or may fish) at the lake can best define factors that contribute to a quality
fishing experience. Moreover, the fishing public is generally keenly aware of ex-
isting problems, user conflicts, and constraints on fishing and other recreational
activities (see Chapter 6).
[T]he first step in any lake
or fisheries management
program is to establish
goals, specific objectives,
and priorities.
A program's effectiveness
and likelihood of success
can be greatly enhanced,
however, by actively
involving lake users in the
planning process.
67
-------
Fish and Fisheries Management in Lakes and Reservoirs
[NJonuser values and
concerns should also be
considered during the lake
planning process.
State fisheries agencies, in
particular, should be
actively involved in
developing and
implementing a fish or
fisheries management
program.
Information on public
values and user
characteristics can help
define and prioritize lake
management goals.
The planning process should include not only anglers but also representatives
from all groups of lake users such as cabin owners, boaters, and swimmers. As dis-
cussed in Chapter 1, the goal is to develop an integrated lake management pro-
gram that considers fisheries, water quality, and all lake uses simultaneously. Even
when the primary topic is fisheries management, many decisions may indirectly
affect other lake uses, and trade-offs may be necessary. Excluding representatives
from any faction can arouse animosity and diminish the broad public support
needed for the program's success. Therefore, it is important to systematically iden-
tify all current and planned lake uses, the interactions between these uses and the
lake's fisheries and fish community, and the associated user populations.
People who currently use the lake for fishing, swimming, or other purposes
generally take the greatest interest in lake management. However, nonusers also
appreciate a lake for its intrinsic values, which can include both option values
(keeping available possible future use of the lake) and existence values (associated
with simply knowing that the lake exists). This applies to future generations or
those with a general concern for nature but with no immediate plans to use the
lake (Bishop et al. 1987). To the degree possible, nonuser values and concerns
should also be considered during the lake planning process.
Finally, State, Federal, and local agencies typically have regulatory or manage-
ment responsibilities that affect the lake or will be affected by the lake manage-
ment program. State fisheries agencies, in particular, should be actively involved
in developing and implementing a fish or fisheries management program. State
water quality agencies should also be contacted because fish and fisheries
management activities may directly or indirectly affect other biota and water
quality. In some instances, multiple agencies may have jurisdiction over the fish in
a lake, with markedly different goals and objectives (e.g., in lakes used for both
recreational and commercial fishing). Although this supplement focuses on en-
couraging public involvement in lake planning together with the appropriate State
agency(ies), many of the same principles and basic approaches can be used to
foster interagency cooperative management programs. Pinkerton (1989) presents
several case studies illustrating the development of co-management plans for
sharing fisheries management authority between two or more agencies.
Gathering Information on User Characteristics
and Public Values
Information on public values and user characteristics can help define and
prioritize lake management goals. Mail surveys, telephone interviews, and per-
sonal contact interviews such as creel surveys can obtain data for a representative
sample of the user population and/or interested nonusers. Questionnaire and in-
terview survey designs and techniques are described in Appendix B.
Various types of information can be collected — for instance, answers to
specific questions regarding possible management goals or approaches; qualita-
tive rankings of the relative merits of different options; or quantitative data on per-
sonal values. Contingent valuation (Bishop et al. 1987; Hoehn, 1987) is frequently
used to assign monetary values to nonmarket goods and services such as recrea-
tional fishing. The respondent's willingness to pay (or assign a value) for such ac-
tivities as better fishing or protecting bald eagles is determined by a series of
"yes-no" questions. Travel cost methods (Talheim et al. 1987) also provide es-
timated monetary values for nonmarket goods and services. Gregory (1987)
presents several nonmonetary approaches to valuing fish resources, including
measures of attitude and social well-being. Talheim and Libby (1987) emphasize
the importance of a total value assessment that considers basic human values (e.g.,
existence values) as well as monetary and assigned monetary values. Finally,
Yarbrough (1987) and Stoffle et al. (1987) discuss the importance of distinguishing
68
-------
Chapters. Setting Goals, Specific Objectives, and Priorities
public attitudes and opinions from underlying public values: the former tend to
be unstable and change in response to a specific situation or concern, while the
latter are generally highly stable and persistent. Simple preference questions may
reveal superficial attitudes rather than underlying values (Talheim et al. 1987; see
also the Social Assessment of Fisheries Resources Symposium published in the
Transactions of the American Fisheries Society, 1987).
Building Consensus and Public Support
Two keys to the planning process are (1) communication and education and (2)
public participation and debate. People involved in the planning process must be
made fully aware of the management options and their consequences so they can
contribute to the decisionmaking process. Public participation and debate can
clarify issues and help people better understand and appreciate alternative
points of view. Open debate often leads to compromise and resolution. The objec-
tive of the planning process is to resolve conflicts and differences of opinion on
appropriate management objectives by building a consensus among competing
interests. This process involves forming an information network to facilitate two-
way communication and education, representing all sides in disputes, channel-
ing debate in fruitful directions, and focusing expert advice on important
problems. Also, always keep the big picture in mind: focus on the whole ecosys-
tem and all lake uses and values to build an integrated management plan (Engel,
1989; Hance et al. 1990).
The best approach to the planning process (in particular, how best to involve
the public in setting goals and priorities) depends on (1) the number and com-
plexity of the various management options and goals; (2) the level of interactions
and conflicts among users; and (3) the size of the affected user community and
the number of persons who want to be actively involved. The following general
guidelines apply to all situations, however:
• Carefully explain the planning process — what you are trying to
achieve, the procedures you will follow, and the program constraints.
• In a clear, straightforward manner, outline the alternative goals,
specific objectives, and approaches for managing the lake, including a
discussion of the likelihood of success, uncertainties, and possible con-
sequences of each alternative.
• Elicit input from all interested parties; recognize each individual's con-
tribution and make everyone feel part of the process. People who are
included in the decisionmaking process are more likely to support the
final decisions and ultimate program plan.
• Maintain a constructive and cooperative atmosphere; remain objective
and avoid confrontation.
• Hold one or more small group workshops (maximum 15 to 20 par-
ticipants) with representatives from each interested user group, or
break down larger meetings into smaller working groups to facilitate
discussions and communication. Face-to-face discussions and interac-
tions in a small group setting are needed to build consensus and define
priorities for the user group as a whole.
• Form a central planning team consisting of lake experts trained in
fisheries management and limnology (see Chapter 7) and a repre-
sentative from each major lake user group, interested nonusers, and
appropriate State, Federal, or local agency. Ad hoc committees or satel-
lite teams can also be useful to deal with specific aspects of the
management program or planning process (Engel, 1989).
Public participation and
debate can clarify issues,
and help people better
understand and appreciate
alternative points of view.
Elicit input from all
interested parties;
recognize each
individual's contribution
and make everyone feel
part of the process.
69
-------
Fish and Fisheries Management in Lakes and Reservoirs
Encourage all interested
parties to express their
opinions and ideas
regarding the proposed
kke management
program.
Although specifics will vary, in general, the planning process consists of six
major steps or phases of activity:
1. Public notification. The public should be notified through an-
nouncements in local newspapers and/or a broad-scale mailing of the
initiation of the planning process and how and when citizens can par-
ticipate.
2. Identification of potential alternatives and their consequen-
ces. A fisheries biologist or limnologist with experience in lake and
fisheries management should prepare a brief written summary of al-
ternative management goals and specific objectives currently being
considered, as well as their possible consequences, and distribute it to
people who expressed an interest in further involvement during Step
1. This initial option summary should be used only to stimulate fur-
ther discussion and debate, not to propose a preferred approach or
goal.
3. Compilation of public opinions, ideas, and responses. En-
courage all interested parties to express their opinions and ideas
regarding the proposed lake management program. The objectives are
to identify the full range and diversity of ideas and priorities and to ac-
tively include and provide a sense of involvement for as large a group
as possible. As noted earlier, each contribution must be formally recog-
nized. For example, for large groups, surveys or questionnaires may be
mailed to each participant together with the option summary dis-
cussed in Step 2. A summary of responses to this questionnaire and the
revised option summary document would then be distributed during
Phase 4. For smaller groups and simpler problems, it may be possible
to combine Steps 3,4, and 5 into one or more group meetings. Sugges-
tions for the meeting format and procedures are presented in Box 5-A.
4. Group communication and exchange of ideas. Having
developed a reasonably complete listing of alternative goals, objec-
tives, and priorities in Step 3, the planning team should initiate active
face-to-face discussions and debates on the various options in a public
meeting or forum — the larger the group, the more formal and struc-
tured this initial meeting. The meeting should be announced publicly,
with separate notices mailed to those who participated in Steps 1 to 3.
The purpose of the meeting is to fully air all points of view regarding
the pros and cons of each alternative goal and objective without at-
tempting to achieve consensus.
5. Group prioritization and consensus building. If conflicts exist
among users or user priorities, the planning team should attempt to
develop a group consensus or compromise. Again, this will require
face-to-face meeting(s) and discussions. At this stage, however, smaller
working groups or workshops with no more than 15 to 20 people are
essential. Several workshops may be needed if the number of inter-
ested participants is large and/or the issues are complex or conten-
tious. Pointers for leading such a workshop are presented in Box 5-A.
6. Final priority goals and objectives. Publish and distribute the
final decisions on program goals and objectives. Follow through and
make sure that these goals and objectives focus the direction of the
program. Invite additional comment and continued input and, as ap-
propriate, request assistance with implementation or other phases of
the planning process (see Chapter 6).
70
-------
Chapters. Setting Goals, Specific Objectives, and Priorities
Box 5-A.—Helpful Hints for Successful Meetings
Small meetings with no more than 15 to 20 participants per group are an effective way
to move toward resolving conflicting opinions and developing consensus on priorities,
goals, and objectives. These meetings should be moderated by a neutral "facilitator"
who ensures that the discussions remain focused, everyone has an opportunity to con-
tribute and be heard, and progress is made toward the specific meeting objective—
developing a set of priority management goals and objectives for the lake. At the
beginning of the meeting, the facilitator should outline the issues/questions to be dis-
cussed as well as the meeting format and schedule. The ground rules for group dis-
cussions and the meeting function and process must be clearly established. To the
degree possible, isolate different issues/questions and deal with them one at a time in
a logical order. As you proceed through each topic, a useful sequence of events is as
follows:
1. Develop a full list of alternatives or opinions.
2. Merge, simplify, and organize participants' options and ideas.
3. Discuss and evaluate each item so that all participants fully understand the
alternatives.
4. Prioritize the alternatives and options.
5. Summarize the group decisions).
First, compile a full list of opinions; for example, a complete list of participants'
ideas on the major goals for the lake management program. Each idea should be listed
on a flip chart to be referred to and discussed later. Discussions on the merits of each
suggestion should be avoided; the objective at this stage is simply to develop the list.
Record all ideas suggested by the group. Overlapping or duplicate items can be iden-
tified and merged during the next stage. Allow sufficient time to extract all relevant
ideas and proposals and try to get everyone to contribute; for example, go around the
table one or more times and ask each participant for his or her suggestions and ideas.
After developing a full list, ask the group to identify similar or overlapping items
and merge any duplicates. If appropriate, establish a hierarchy, listing some items as
subheads under others. As part of this process, discuss and explain each item so that
all participants fully understand it.
Having developed a manageable list of alternatives, ask the group to identify
those with highest priority. It may be useful to open the discussion by simply going
around the table and asking participants to vote on their top three priorities. This ac-
tivity provides a good indication of areas of agreement and disagreement (as well as
the overall level of agreement) and focuses subsequent discussion. The entire group
may rank some goals or specific objectives high priority.
When participants express differences of opinion, ask individuals to fully explain
their viewpoint. Explore the reasons why people think differently to determine whether
some underlying common ground exists. Conceptual models are often useful because
they illustrate interactions and linkages between system components or alternative ap-
proaches and goals. If strong areas of disagreement exist, it may be best to table fur-
ther discussion and reinitiate discussions later in the workshop or even at another
workshop, thereby giving participants and the facilitator a chance to reflect on the dif-
ferent opinions and options for resolution.
Emphasize areas of agreement and consensus. In particular, frequently sum-
marize discussions, group decisions, and the meeting progress. At the end of each
session, the facilitator should summarize the workshop conclusions and identify areas
of consensus, decisions, and the remaining issues to be addressed at future meetings
or through other activities. A written summary of the discussions and meeting outcome
should be distributed to meeting participants no more than one to two weeks after the
meeting.
Additional guidance on organizing and facilitating group meetings can be found in
Delbecqetal. (1975), Doyle and Strauss (1982), Renton (1980), Nathan (1979), Beale
and Fields (1987), and Carpenter (1988).
71
-------
Fish and Fisheries Management in Lakes and Reservoirs
Ecosystem interactions
and potential user
conflicts must be
considered to select a
realistic set of
complementary goals and
specific objectives.
Management goals must
also be consistent with
established water quality
standards for a lake,
including designated
attainable uses and
associated water quality
criteria.
Alternative Goals in Fish and Fisheries
Management
Fish and fisheries management goals can .be grouped into three broad categories:
1. maintaining ecological integrity and protecting natural systems as part
of the public trust;
2. improving and maintaining the quality of the fishing experience
(fisheries management); and
3. improving and maintaining water quality by managing fish.
The list of goals presented for each category is not intended to be comprehen-
sive but only to illustrate the types of management goals of potential interest. In
addition, no goal is necessarily mutually exclusive. In one lake, multiple goals
may be appropriate. Some fish species may be managed for one type of fishery
(e.g., trophy fishing), while others could be managed for increased water clarity or
high angling yields. In many cases, however, trade-offs may be necessary. For ex-
ample, high levels of angling pressure on top predator species may result indirect-
ly in a decrease in water clarity (see Chapters 2 and 9). Ecosystem interactions and
potential user conflicts must be considered to select a realistic set of complemen-
tary goals and specific objectives.
In selecting the management goals for a given lake, one must take into account
not only public preferences but also the lake's physical, chemical, and biological
characteristics that affect the types of fish species, fisheries, and uses for which it is
best suited (see Chapters 2 and 3). Lakes in warmer climates, for example, will
never support self-sustaining coldwater fisheries. Likewise, some fish species
(such as lake trout whose preferred habitat is the deeper, colder waters of the
hypolimnion) will do poorly in shallow lakes that do not thermally stratify. Some
lakes naturally have low levels of dissolved oxygen and periodically experience
winterkill or summerkill. While oxygen levels may be artificially enhanced, it may
make more sense to manage these lakes for fish species that can tolerate relatively
low levels of dissolved oxygen.
Selection of the appropriate target species for fish or fisheries management is
an important element of defining program goals and specific objectives and
developing the lake management plan. Management goals must also be consistent
with established water quality standards for a lake, including designated at-
tainable .uses and associated water quality criteria.
Ecological Integrity and the Public Trust
The primary responsibility of most State fisheries agencies is resource protection
— to preserve for future use all fish community options that we currently enjoy
(Dochoda and Fetterolf, 1987). Fisheries resources are held in trust for society by
government. Only within the constraints of this public trust can managers con-
sider how best to use and allocate the available resources for optimum present-day
social and economic benefit.
Similar goals are incorporated within water quality legislation. The Water
Quality Act Amendments of 1972 explicitly set as a national goal "to restore and
maintain the physical, chemical, and biological integrity of the Nation's waters."
Biological criteria (also called "biocriteria") are now included within EPA's water
quality standards program (U.S. Environ. Prot. Agency, 1988), and all States are re-
quired to adopt narrative biological criteria during fiscal years 1991 to 1993 (U.S.
Environ. Prot. Agency, 1990). Biological criteria are indicators of biological or
ecological integrity compared to some least-disturbed reference site (Karr, 1991).
Karr and Dudley (1981) defined biological integrity as the ability to support and
72
-------
Chapter 5. Setting Goals, Specific Objectives, and Priorities
maintain "a balanced, integrated, adaptive community of organisms having a
species composition, diversity, and functional organization comparable to that of
the natural habitat of the region."
The conservation of genetic diversity has also been identified as an important
fish management goal. As discussed in Chapter 3, intraspecies variations in fish
characteristics, such as resistance to environmental stress and potential growth
rate, increase the likelihood of long-term fish population survival and reflect the
adaptation of populations, over multiple generations, to be better suited to sur-
vive and reproduce in their local environment. Just as the extinction of an en-
dangered species is an irreversible loss, the elimination through extinction or
interbreeding of a genetically unique fish strain or fish stock cannot be reversed.
Conserving genetic diversity, restoring and maintaining ecological integrity, and
protecting and preserving fisheries and other aquatic resources are clearly impor-
tant goals for a lake management program.
Fisheries Management
The overall goal of fisheries management is to improve and maintain the quality
of the fishing experience and to sustain yields. However, the attributes of a
quality fishing experience can incorporate many things, such as a peaceful and
natural fishing environment, easy access, and socializing with family members as
well as catching an adequate number and size of fish (Brown, 1987). Examples of
specific fisheries management goals that may be appropriate in some waters in-
clude the following: - '
• Maximize yield. Provide the maximum level of harvestable fish that
can be sustained over the long term and is optimal in terms of the ef-
fort and expense required to sustain the yield. Although populations
may be supplemented by stocking, the majority of the catch is com-
prised of fish that grow to catchable size in the wild. Management ef-
forts are directed toward providing fishing opportunities of a general
nature, rather than managing for especially large "trophy" fish.
• Maximize catch rates per unit of effort. While similar to the con-
cept of maximum yield, maximizing catch per unit effort also con-
siders the distribution of this yield among anglers and per unit of time
spent fishing. On lakes with very heavy fishing pressure, the total
yield may be high even though the catch per unit effort may be some-
what lower.
• Maximize the "bites per hour." For fisheries that attract large num-
bers of small children, it may be desirable to maximize the level of ac-
tivity. The total quantity, size, and types of fish caught would be of
lesser importance.
• Maximize the number and size of trophy fish. Management ef-
forts in this case are directed primarily toward providing anglers an
opportunity to catch a larger than average fish. In some waters, catch-
and-release fishing regulations may be required to expand the number
of available trophy fish (see Chapter 8).
• Provide fishing opportunities for a particular fish species or
strain that is unique and/or highly desirable. For example, in
western States this may include cutthroat trout in their native range,
golden trout, or grayling. Other examples include heritage strains of
brook trout and other salmonids (i.e., strains of fish native to the region
that have never been commingled with hatchery strains) or rare or ex-
otic species that may be introduced experimentally or permanently.
Conserving genetic
diversity, restoring and
maintianing ecological
integrity, and protecing
and perserving fisheries
and other aquatic
resources are clearly
important goals for a lake
management program.
The overall goal of
fisheries management is to
improve and maintain the
quality of the fishing
experience....
73
-------
Fish and Fisheries Management in Lakes and Reservoirs
Provide a relatively
pristine, natural,
undisturbed environment
for fishing
Provide edible fish, with
little to no health risk from
bioaccumulated toxic
substances....
• Provide fishing opportunities for "wild" fish. Some anglers prefer
to catch fish from populations that are totally supported by natural
reproduction. The goal to catch "wild" fish is often accompanied by the
desire to catch native fish strains (rather than hatchery strains that have
subsequently established a naturally reproducing population) and to
fish in a relatively pristine environment.
• Maximize the diversity of fishing opportunities. Given a highly
diverse fishing community, it may be desirable to purposely diversify
the types of fish and fishing experiences available within the lake (e.g.,
trophy fish of some species, maximum "bites per hour" for others).
More often, however, a high degree of diversity can be better achieved
by managing different waters within a region for different types of
fisheries. Thus, in establishing the goals and specific objectives for any
one lake, the types of fishing opportunities available in other nearby, ac-
cessible waters may be an important consideration.
• Provide a relatively pristine, natural, undisturbed environment
for fishing. For many anglers, being out-of-doors in a natural, undis-
turbed environment, in relative solitude, is an important part of the
quality of a fishing experience. In some regions, this may mean fishing
in remote, high mountain lakes. In others, "relatively pristine" and "un-
disturbed" may be interpreted as free from interference from boaters
and waterskiers, with few to no other anglers in sight. Also implicitly
incorporated within this goal is the satisfaction gained from fishing on
waters with natural, undisturbed ecosystems that support a diversity of
fish species and other biota.
• Maximize the ease and convenience of fishing. Important goals
for some fisheries may be to facilitate lake access, to have stores and
other support facilities conveniently located, and/or to locate the lake
near large concentrations of people who may then take advantage of the
fishing opportunities with minimal difficulty and effort.
• Provide edible fish, with little to no health risk from bioae-
cumulated toxic substances. For some anglers, obtaining fish to
eat is a major reason for fishing. In areas contaminated by toxic chemi-
cals through direct discharges, nonpoint sources in the watershed, or at-
mospheric transport and deposition, toxic substances may
bioaccumulate in fish to levels unsuitable for human consumption.
Management goals for commercial fisheries are not explicitly addressed in this
supplement.
Using Fish Management for Water Quality Management
Additional management goals may be appropriate if fish communities are to be
manipulated and managed for purposes not directly related to the quality of the
fishing experience. Examples of how fish management may be used in lake res-
toration and management include the following:
• Control and reduce the extent of aquatic macrophytes. Grass
carp and a few other fish species that feed on aquatic macrophytes have
been used in some lakes to reduce the extent and density of aquatic
weed beds. Reductions in aquatic macrophytes may be needed to im-
prove fishing, aesthetics, boating, or swimming.
74
-------
Chapter 5. Setting Goals, Specific Objectives, and Priorities
• Reduce water turbidity. Some fish species, such as the common
carp, can extensively disturb the lake bottom as they feed, increasing
water turbidity (i.e., increasing the levels of suspended solids). High
turbidity may make a lake aesthetically unpleasing and reduce its
desirability for swimming. Thus, to control the lake's turbidity
problems, one goal of fish management may be to reduce the abun-
dance of carp or other nuisance fish species.
• Increase water clarity. The potential indirect effects of fish preda-
tion on the aquatic food chain were discussed in Chapter 2. The abun-
dance of planktivorous fish may influence the abundance of
zooplankton, which influences in turn the abundance of phyto-
plankton and water clarity. As a result, reductions in the numbers of
planktivorous fish may indirectly increase water clarity. Reductions in
planktivorous fish may be achieved directly through removal or in-
creased fishing pressure on planktivorous species or indirectly by in-
creasing the abundance of larger fish predators that feed on the smaller
planktivorous fish (see Chapter 9).
Many factors affect the abundance of aquatic macrophytes, water turbidity,
and water clarity and often may override any indirect effects on these lake
parameters resulting from changes in the fish community. Fish management to
control aquatic weeds, reduce turbidity, or increase water clarity will work only
in some circumstances. In addition, fish management may not be the most cost-
effective means of achieving these goals. Potential applications of fish manage-
ment for water quality goals are discussed further in Chapter 9.
75
-------
-------
CHAPTER 6
Problem Identification
and Diagnosis
Chapter Objectives
Having established a reasonable set of lake management goals and specific objec-
tives (Chapter 5), the next step is to determine what factors currently limit or
prevent the achievement of these goals and objectives. A lake problem can be
defined as "a limitation on a desired use of a lake or the inability to attain a
desired goal or objective"; for example, catch rates that are too low or fish that are
uniformly too small. Many lake management problems can be identified simply
by compiling complaints from anglers and other lake users. However, to be suc-
cessful over the long term, lake management must focus on and remedy the un-
derlying cause of a problem, not just treat the symptoms. Thus, problem
diagnosis, which involves a thorough investigation of the cause or causes of an
identified problem, must precede program design and initiation of lake restora-
tion activities.
This chapter discusses the process of problem identification and diagnosis
(Fig. 6-1) and common problems in managing fish and fisheries in lakes and
reservoirs. Potential solutions (lake management techniques) are presented in
Chapters 8 and 9. This manual emphasizes problems associated with the quality
and types of fishing opportunities as well as water quality problems that might
be alleviated by manipulating the fish community. The Lake and Reservoir Restora-
tion Guidance Manual (Olem and Flock, 1990) provides a more general discussion
of the full range of problems that can be encountered in lake management.
Problem Statement
The best starting point for gathering information on lake problems is to ask lake
users (e.g., see Box 6-A). If catch rates or size of desirable fish species have
declined markedly over the years, a lake restoration project might alleviate or
correct the problem. A problem exists if excessive numbers of anglers, boaters,
and waterskiers interfere with the quality of the fishing experience. The types
and quantity of fish caught may be poor relative to other similar lakes in the
region suggesting that conditions in the lake are preventing the lake's fisheries
from achieving their full potential. Lastly, there may not be a problem, per se, but
local anglers may express the desire to improve fishing opportunities — for ex-
ample, by introducing new species or enhancing natural reproduction.
A lake problem can be
defined as "a limitation on
a desired use of a lake or
the inability to attain a
desired goal or objective."
77
-------
Fish and Fisheries Management in Lakes and Reservoirs
Problem Statement
Statement of Problem as
Perceived by Lake Users
- angler complaints
- group meetings
I
Problem Identification
Technical Statement of Problem
Based on Technical Data and Expertise
- status of fish community
- status of fisheries
Problem Diagnosis
Identification of Underlying Causes
- conceptual model
- hypotheses / possible causes
- data compilation / collection
- data analysis / evaluation
i
Possible Solutions
Methods for Lake Restoration and Fisheries Improvement
Lake / Fisheries Management Plan
(Chapters 8 and 9)
Monitoring For Results
Follow-up Monitoring to Determine
Program Effectiveness
(Chapter 10)
Figure 6-1.—Major steps in the process of problem identification and diagnosis as part of
the development of a lake management program.
78
-------
Chapter 6. Problem Identification and Diagnosis
Box 6-A.—Community involvement Program —
Erie and Campbell Lakes, Washington, Restoration
Program (source: Entrance Engineers, 1983 and 1987)
Erie and Campbell lakes are located on Fidalgo Island in Skagit County, Washington.
Both suffered from dense blooms of blue-green algae; Erie Lake also experienced oc-
casional fishkills.
In 1981, a Phase I Diagnostic Study was funded by the EPA Clean Lakes Pro-
gram, State of Washington, and Skagit County to assess the nature and extent of
water quality and fishing problems in the lakes. As part of this effort, a community in-
volvement program was initiated to obtain input from lake users on perceived water
quality problems, fishing problems, and affected beneficial uses, and to invite public
participation in decisions on restoration alternatives. A Lake Study Review Committee
comprised of local residents and interested agency officials met quarterly to review the
status of the project and provide guidance to the technical project team. In addition,
watershed property owners and people attending the first lake study citizens informa-
tion meeting in January 1982 received a questionnaire designed to sample public at-
titudes about lake conditions, recreational uses, fishing, and lake problems.
Lake Erie respondents stated that exposed aquatic plants were the most serious
problem, followed by gradual lake filling (lower water depth), submerged aquatic
plants, algae blooms, swimmer's itch, erosion, and bad odors. Campbell Lake respon-
dents noted that the most serious problems in order were algae blooms, submerged
aquatic plants, lake filling, flooding, exposed aquatic plants, bad odors, and swimmer's
itch. In response to the question of which lake uses were adversely affected by lake
quality deterioration, Lake Erie respondents ranked fishing and swimming as most
seriously impacted; Campbell Lake respondents noted that swimming was the most
adversely affected use, followed by appreciation of the lake's beauty, fishing, and boat-
ing/canoeing.
Subsequent lake sampling and diagnostic analyses identified phosphorus as the
nutrient controlling algal growth and sediment phosphorus release as the most sig-
nificant controllable source of phosphorus to both lakes. Therefore, in 1985, Skagit
County initiated a Phase II Implementation Program, including alum treatments to
reduce internal phosphorus loading from the sediments (see Chapter 8) and mechani-
cal harvesting of aquatic plants.
Compiling a list of problems, concerns, and desired improvements is
generally relatively easy and may be best achieved by incorporating the task
directly into the six-phase planning process described in Chapter 5. Question-
naires and group meetings may also be used to compile, discuss, and prioritize
lake problems as perceived by the lake users. After establishing what the user
community wants (i.e., the priority goals and specific objectives), you can then
ascertain to what degree and in what ways current lake conditions fall short.
These differences between a reasonable set of objectives and current conditions
define the lake's problems, which can then be prioritized using the techniques
described in Box 5-A (also see Appendix 3-A in The Lake and Reservoir Restoration
Guidance Manual).
Actively involving the public will
• facilitate identification and prioritization of lake problems because
lake users have direct, day-to-day experience with fishing quality and
other lake uses and
• help to educate users about the lake ecosystem and their role in con-
tributing to some lake problems (for example, those resulting from
overfishing or lake eutrophication from nutrient-rich urban runoff).
Greater understanding and awareness of problems will generally lead to in-
creased cooperation in their solution and thus a greater likelihood of program
success.
Actively involving the
public will help to educate
users about the lake
ecosystem and their role in
contributing to some lake
problems.
79
-------
Fish and Fisheries Management in Lakes and Reservoirs
While lake users may be
able to identify the
symptoms of a problem or
limitations on lake uses,
tedinical data and
expertise are needed to
confirm and better define
the problem.
Lake probletns need to be
clearly distinguished from
natural constraints on the
types and quality of
fisheries and users that a
lake can support.
Most lake problems result
from human-related
causes.
One type of lake problem cannot be readily detected by anglers and other lake
users; specifically, bioaccumulation of toxic substances in fish that may pose a
health hazard. Early detection of this problem requires routine monitoring of the
contaminant levels in fish tissues, the water, and/or lake sediments. However, be-
cause of the expense of analyzing for the myriad of potential chemical con-
taminants, these monitoring programs are often initiated only if other sources of
information suggest a cause for concern; for example, if a known contaminant
source exists in the watershed or similar problems occur in other nearby lakes. A
supplement on toxic substances in lakes and reservoirs is being prepared for EPA's
Clean Lakes Program that will provide further information on when, where, and
how to monitor for the bioaccumulation of contaminants.
Problem Identification
While lake users may be able to identify the symptoms of a problem or limitations
on lake uses, technical data and expertise are needed to confirm and better define
the problem. Anglers may complain that they catch too few fish, too few large fish,
or not enough fish of a particular preferred species; however, are these real
problems that can be alleviated through lake restoration or management efforts?
Are there really fewer fish than expected for a lake of that size and physical and
chemical characteristics? Are there too few fish, or are anglers just having difficul-
ty catching fish? Only after you clearly define the problem can you develop a
detailed plan for problem diagnosis to determine why fish abundance is low or
why anglers are having trouble catching fish.
A professional fisheries biologist and/or limnologist should assist with prob-
lem identification and diagnosis as well as the subsequent design of a lake
management program. In some cases for publicly owned lakes, State fisheries
agencies and State biologists may be able to provide substantial assistance and
direction. For privately owned lakes, private consultants, local university staff, or
other private organizations may be more appropriate. Chapter 7 discusses the
types of assistance available and offers guidance on selecting a consultant.
Putting Problems in the Proper Perspective
Lake problems need to be clearly distinguished from natural constraints on the
types and quality of fisheries and uses that a lake can support. A lake's natural
physical, chemical, and biological characteristics play a major role in determining
the types of fish species that will survive and reproduce, fish production arid
growth rates, potential fishery yields, and the nature of the fishing experience (see
Chapters 2 and 3). While these natural features can be modified to some degree
(e.g., through habitat management efforts), to attempt to drastically alter a lake's,
basic characteristics would be technically difficult, very expensive, often short-.
lived, and generally unwise. Therefore in this manual, lake problems are defined
specifically as "the failure of a lake to achieve its full natural potential and poten-
tial uses." Most lake problems result from human-related causes.
Regional patterns of lake conditions and fish communities provide an impor-
tant source of information for distinguishing between natural and human-caused
lake problems. If the symptom also occurs in other similar lakes in the region with
undisturbed watersheds or with lower levels of fishing pressure, the perceived
"problem" may actually be a natural constraint or phenomenon. For example,
oligotrophic lakes naturally have relatively low levels of sustainable fisheries yield
because of lower levels of nutrients and productivity. Thus, lakes in northern Min-
nesota, where the soils and bedrock are naturally low in nutrients, generally sup-
port lower fish biomass and yield than lakes in southern Minnesota, where soils
are naturally more fertile. As a result, lakes are naturally more productive.
80
-------
Chapter 6. Problem Identification and Diagnosis
Periodic year-class failures of largemouth bass may result in some cases from
year-to-year fluctuations in weather (such as cold spells or strong winds and
wave action during the reproductive period) rather than from human-related
causes that can be ameliorated through a lake or fisheries restoration program.
Natural constraints are particularly important for fish populations in marginal
habitat or at the edge of their natural range.
Indicators of Fish Community Status and Fisheries
Problems
Identifying fisheries management problems requires technical information on the
status of the fish community and fisheries in the lake. Generally, a routine field
survey of the fish community is warranted, using the methods described in Ap-
pendix B. Data collected in previous lake studies should also be compiled to sup-
plement the field survey data and provide historical perspective.
What, however, should you look for in a fish community or fisheries survey?
What metrics or symptoms indicate a problem? The development of simple,
easy-to-measure, and reliable indicators of fish community "health" and fisheries
condition is being actively researched (see Spigarelli, 1990). While a number of
indicators are available, all have advantages and disadvantages. No single in-
dicator can provide definitive evidence of a problem; rather, multiple indicators
should be evaluated and considered in combination (see Box 6-B) and together
used to judge the current status of a fish community, fish population, or fisheries.
The types of fish community and population characteristics of interest were
introduced in Chapter 3 and involve, for the most part, direct or indirect
measures of important population and fisheries parameters; for example:
• Fish abundance — the density and/or biomass of fish present per
unit area or volume, by species. Because taking absolute measures of
fish abundance can be difficult and time-consuming, especially in
large lakes (see Appendix B), measures of relative abundance (i.e., the
numbers and biomass of fish caught per some standard unit of sam-
pling effort) are often more practical and generally adequate.
• Fishing pressure — the total number of hours (or other suitable
unit) of angling effort.
• Catch per unit and harvest per unit efforts — the number or
biomass of fish caught and harvested, respectively, per unit of angling
effort.
• Fisheries yield — the total numbers or biomass of fish removed from
the lake through angling (per unit area or volume and period of time),
estimated from the measures of fishing pressure and harvest per unit
effort.
Most problems in fisheries management are associated with low or declining
fish abundance, catch per unit effort, and fisheries yield. However, changes in
these parameters are often detectable only when the problem is fairly advanced
and severe. Other parameters may provide an early warning of change or ad-
verse effects before abundance or yield measurably decline. Examples of useful
indicators offish population status include the following:
• Year-to-year variability In fish population abundance — In
some instances, an environmental stressor may initially decrease
population stability and only later, with continued or increased stress,
result in a long-term population decline.
Natural constraints are
particularly important for
fish populations in
marginal habitat or at the
edge of their natural range.
Data collected in previous
lake studies and surveys
should also be compiled to
supplement the field
survey data and provide
historical perspective.
No single indicator can
provide definitive evidence
of a problem; rather,
multiple indicators should
be evaluated and
considered in combination
Most problems in fisheries
management are
associated with low or
declining fish abundance,
catch per unit effort, and
fisheries yield.
[I]n some instances, an
environmental stressor
may initially decrease
population stability and
only later, with continued
or increased stress, result
in a long-term population
decline.
81
-------
Hsh and Fisheries Management in Lakes and Reservoirs
Bpx 6-B.—Framework for detecting the effects of
i chemical contaminants on fish populations
' ' (source: Munkittrick arid Dixon, 1989)
Effects of stressors on fish populations can be direct (acting on growth, reproduction
and/or survival) or indirect (operating through effects on predators or food resources).
Colby (1984) identified five patterns of population response to heavy fishing pressure
based on 10 different indicators offish population status; Munkittrick and Dixon (1989)
adapted this framework for examining fish population responses to chemical stressors
(Tables 6-1 and 6-2). For example, increased adult mortality caused by acutely lethal
toxicant concentrations or heavy fishing pressure would decrease population size and
increase food availability for the fish remaining! presuming that the food base is not ad-
versely affected by the toxicant. Such a change should result in an increased growth
rate for survivors as well as a decreased age at maturation and increased fecundity
and condition factor because of increased food resources (Pattern I, Table 6-2).
Removal of a significant number of adults would also result in a decreased mean
age of the population and a shift in the size distribution toward younger fish. Similar
patterns of response involving multiple interacting population characteristics can be
identified for other ecosystem alterations such as reproductive failure or elimination of
food resources. Munkittrick and Dixon (1989) provided several case histories
demonstrating the applicability of these indicators and indicator patterns for assessing
effects of mining wastes and atmospheric deposition on white sucker populations.
Table 6-1.—Five mechanisms of chemically Induced alterations in ecosystem
quality: consequences on fish populations and food resources (source: Munkit-
trick and Dixon, 1989).
RESPONSE TARGET
PATTERN SOURCE
CONTAMINANT
EVENT
OTHER
COMPARABLE
STRESSORS
EFFECT
ON
POPULATION
EFFECT ON INITIAL
RESOURCE POP.
BASE RESPONSES
Direct on
adults
Acutely lethal
spill away
from nursery
areas or a
response to
chronic
mortality
Fisheries Reduced Increased Increased
exploitation abundance food survivor
of adults availability growth rate
II
Direct on
eggs or
larvae
Spawning
failure or in-
creased larval
mortality
(reproductive
Loss or distur-
bance of
spawning
grounds
Reduced
abundance
of young fish
Decreased
use of
food and
habitat
resources
Gradual
shift in age
distribution
toward
older fish
problems, con-
tamination of
spawning
areas or yolk-
associated
burdens)
Direct on
juveniles
Metabolic
impacts or
restricted food
supply
decrease
energy flow
through
juveniles
Size-
selective
mortality of
small fish
induced by
habitat
change or
loss of food
supply
Reduced Decreased Gradual
abundance replace- shift in age
of young fish ment of distribu-
adult fish tion;
decrease
in fish con-
dition
IV
Indirect,
above
indicator
organism
Predator
removal by
chemical
events or
chronic food
availability
problems
Overstocking
of fish or
overexploita-
tion of
predators
controlling
population
Increased
population
size or
increased
competition
for food
Decreased Decreased
food growth rate
availablity
V
Indirect,
below
indicator
organism
Habitat restric-
tion; reduction
or loss of food
supply
Habitat
destruction or
introduction
of exotic
species
Increased Food web Decrease
food com- restruc- in feeding
petition turing efficiency
82
-------
Chapter 6. Problem Identification and Diagnosis
^••^^•^•i Box 6-B.— Continued ^^^^^^um|
Table 6-2.— Five alternative patterns of fish population response to environ-
mental stressors, depending on the mechanism of effect (see Table 6-1). An
increase in the population characteristic in the stressed population compared
to a reference population In a similar environment but not exposed to the en-
vironmental stressor Is denoted by a plus
(-); and the absence of change by a zero
and Dixon, 1989).
sign (+); a
(0) (source
decrease by a
: Colby, 1984;
minus sign
Munkittrick
CONDI- AGE AT
MEAN AGE GROWTH TION MATURA-
PATTERN AGE DISTRIB. RATE FACTOR*
I + +
II + + 0,+d 0
II + + - -
IV 00--
V 00-0
• Condition factor (K) = 100(wt/length3)
TION RLS"
**(
0 +
+ 0
+• —
+ —
FECUN- EGG
DITY SIZE
+ -,+
0 0
-o
-
-
POP.
CPUE° SIZE
-
-
-
+ +
-,0 -0
b Reproductive life span (RLS) = mean age - (age at maturation)
0 Catch per unit effort
" Change can vary with degree of stress
Population age structure — the numbers of fish in each age group.
Unusually low numbers of older, larger fish may be indicative of high
fishing mortality or other causes of high death rates among older fish.
Unusually low numbers of young fish or missing year-classes are in-
dicative of problems affecting fish reproductive success. Information
on population age structure can also be used to estimate other poten-
tially useful indicators of fish population status, including
• annual total mortality rates,
« mean age of catch, and
• variability in year-class strength.
i Population size structure — the numbers of fish in each length or
weight interval. Length-frequency distributions can be summarized as
proportional stock density (PSD) or relative stock density (RSD) in-
dices, as discussed in Chapter 3.
i Growth rates, condition factors, and relative weight — the
average length and weight of fish in each age group and the relation-
ship between fish length and weight. Low growth rates, condition fac-
tors, and relative weights may be indicative of overcrowded fish
populations, limited food supplies or prey availability, or stresses
caused by toxic substances and other water quality problems that may
adversely affect fish growth.
i Reproductive potential — based on measures of the age at sexual
maturity and fecundity (numbers of eggs per unit weight of female
fish). In some instances, fish populations may respond to stressful
conditions by increasing reproductive potential; the age at which fish
become sexually mature may decline and fecundity increase. Alterna-
tively, adverse conditions may cause a decline in reproductive poten-
tial, primarily by decreasing fish fecundity and delaying sexual
maturation.
83
-------
Fish and Fisheries Management in Lakes and Reservoirs
Fishkills are graphic
evidence of a serious
problem in the lake
ecosystem.
Adverse conditions may
result in the loss of
sensitive species offish in
marginal habitats and,
thus, an overall decline in
species richness.
• Periodic fishkills or periods of high mortality — for example,
during summer or over winter. Fishkills are graphic evidence of a
serious problem in the lake ecosystem. Causes include poor water
quality, such as low levels of dissolved oxygen, high temperatures, or
high concentrations of toxic substances, and infectious agents, including
parasites and viral, bacterial, and fungal agents.
• Physiological or biochemical indicators of stress, such as chan-
ges in body salt content or the levels of various hormones and enzymes,
and associated histological changes (microscopic changes in body tis-
sues) — A wide array of physiological, biochemical, and histological in-
dicators, termed "biomarkers," have been proposed. Some are general
indicators of stress, while others are specific to particular types of stress
or conditions (e.g., lead exposure reduces the activity of the enzyme
delta-ALAD). DiGiulio (1989), Adams (1990), and Niimi (1990) review
the use and types of available biomarkers.
• Incidence of tumors or physical deformities — Some toxic con-
taminants or poor water quality conditions may cause tumors or body
deformities in fish. Standard procedures have been developed to assess
fish health based on external and internal examinations as well as
physiological, biochemical, and histological indicators (Goede, 1988;
Goede and Barton, 1990).
Additional indicators of fish community health or status include:
• Fish species richness — the number of fish species in the lake. Ad-
verse conditions may result in the loss of sensitive species or fish in mar-
ginal habitats and, thus, an overall decline in species richness.
• Species diversity — summary index that reflects both the number of
species in the lake and the relative numbers of fish of each species.
Lakes with numerous species and a more equitable distribution of fish
among species have higher species diversity. As for species richness,
stressful conditions often result in lower species diversity.
• Community composition, especially the status of selected sentinel
species — species that are particularly sensitive to environmental stres-
sors or critical to the maintenance of a healthy fish community. For ex-
ample, Ryder and Edwards (1985) proposed using lake trout and the
invertebrate amphipod, Pontoporeia hoyi, as sentinel species for large
lakes in the Great Lakes basin, providing the basis for the Lake Trout
Ecosystem Health Index (Box 6-C). Rapport (1990) defined two
categories of species expected to change markedly in abundance in
response to environmental stress. Type 1 species are those with narrow
tolerance ranges that are among the first to disappear when conditions
deviate from those found in their natural environment. Exemplary Type,
1 species in oligotrophic lakes include lake trout, deepwater sculpin,
and P. hoyi; for mesotrophic lakes, walleye and the burrowing mayfly,
Hexagenia limbata; and for eutrophic systems, smallmouth bass has been
suggested.
As cultural stress increases, Type 2 species tend to replace Type 1.
Type 2 species are usually present in low numbers in unstressed en-
vironments, but because of their wide tolerance ranges, they rapidly
reproduce and expand in stressed environments. The result is a marked
shift in community composition: a decrease in the abundance of sensi-
tive, Type 1 species and an increase in tolerant, Type 2 species. Type 2
species are often exotics that are not native to the lake or drainage basin.
84
-------
Chapter 6. Problem Identification and Diagnosis
Index of Biotic Integrity (IB1) — a summary index that combines
information on the types of fish species present, their relative abun-
dance, and in some cases, the types and abundance of benthic macro-
invertebrates. The IBI was originally developed by Karr (1981) for
midwestern streams but has since been adapted for streams in other
regions (e.g., Karr et al. 1986; Leonard and Orth, 1986; Miller et al.
1988; Steedman, 1988). To date, applications in lakes are limited, and
specific indices for lakes in most regions are still being developed.
Over the next several years, however, the IBI or other similarly con-
structed indices are likely to play an increasing role in evaluating and
regulating the health of aquatic communities (Karr, 1991).
Box 6-G.-—L.ake Trout E-cbsystem Health Index
(source: Marshall,1992; Edwards et al; 1990)
The Lake Trout Ecosystem Health Index is an update of the Dichotomous Key
developed by Marshall et al. (1987) to assess the health of oligotrophic aquatic
ecosystems in Ontario lakes. The index takes the form of a user-friendly computer
program that functions by posing a series of questions regarding the status of lake
trout, the lake trout environment (e.g., spawning redds and food), and potential stres-
sors that may adversely affect lake trout within the lake of interest (Table 6-3). Lake
trout are used as a sentinel species, serving as a surrogate for the well-being of the
lake ecosystem as a whole (Ryder and Edwards, 1985).
Table 6-3.—Examples of questions Included within the Dichotomous Key,
which has 47 questions in all (Edwards et al. 1990).
Is the annual salmonid harvest less than the long-term mean?
Is the cost/benefit ratio for the fisheries decreasing?
Is the total annual lake trout mortality < 50 percent?
Do lake trout older than 10 years (males) or 11 years (females) represent > 20 percent of
the total standing stocks?
Do Mysis relicta and Pontoporeia hoyi constitute > 80 percent of the diet offshore for lake
trout < 200 mm in length?
Do fish comprise > 50 percent of the diet for lake trout 50 to 60 cm in length?
Is the mean condition factor > 0.90 for lake trout > 50 cm?
Are oxygen levels in the hypolimnion during late summer at 100 percent saturation?
During spring, is the interstitial pH on lake trout spawning beds > 5.0 and aluminum
< 25 ng/L?
Is the ratio of lakewide total spring phosphorus (ng/L) to mean depth (m) < 1 ?
Is the spawning substrate affected by ice scouring?
Is the concentration of PCB in lake trout < 0.1 (*g/g?
Are sperm counts > 10 billion/mL or higher?
The questions are designed to detect deleterious changes in the environment
from those conditions necessary to maintain healthy lake trout stocks. Each question
is answered with a simple "yes," "no," or "I don't know," and a degree of uncertainty is
assigned to each answer. The answers are then processed by the computer, includ-
ing an established ranking scheme that rates the relative importance of each ques-
tion, and an index of ecosystem health is computed. A series of printouts provide
detailed summaries of the stresses detected. In addition, a rationale for each ques-
tion can also be called up within the computer program, including supportive informa-
tion and a list of citations.
Thus, the computer program and index serve several important purposes. The
index provides a quantitative assessment of the relative health of lake trout stocks
and the ecosystem in which they reside and promotes both temporal and interlake
comparisons of values. The program also compels the lake manager to consider a
wide array of possible stressors that may be affecting the ecosystem and helps iden-
tify information inadequacies and data needs. Finally, the computer program is an
educational tool, explaining the current scientific principles and concepts associated
with each question.
Copies of the Ecosystem Health Index are available from Terry Marshall,
Fisheries Research Section, Ontario Ministry of Natural Resources, Box 2089,
Thunder Bay, Ontario P7B 5E7.
Over the next several
years, the IBI or other
similarly constructed
indices are likely to play
an increasing role in
evaluating and regulating
the health of aquatic
communities.
85
-------
Fish and Fisheries Management in Lakes and Reservoirs
To adequately assess all of the above indicators would require an extensive
survey and data collection effort. Therefore generally (at least in the initial stages
of problem identification), a subset of parameters are selected that are likely to
provide the most useful information for a reasonable level of sampling and
analysis.
The best suite of indicators depends on the management objectives and en-
vironmental problems of greatest concern. The indicators listed reflect responses at
various levels of organization, from individual fish (e.g., biomarkers — biochemi-
cal, physiological, or histological indicators), to population-level (e.g., fish popula-
tion abundance, growth rates, reproductive potential), community-level (e.g.,
species richness), and ecosystem-level (e.g., the IBI) responses. Evans et al. (1990)
suggest that monitoring and assessment efforts should focus on the level of or-
ganization at which the stressors of greatest concern act most directly (Fig. 6-2).
TROPHO-ENERGETIC
EFFECTS
STRESSORS
1
ECOSYSTEM
^
Watershed Change
EutrophicatJon
Climate Change
Exotic Species
Toxic Chemicals
Successions!
Processes
FISH COMMUNITY
Species
Interactions
FISH POPULATION
Density -
Dependent
Regulation
INDIVIDUAL FISH
Exotic Species
Stocking
Climate Change
Habitat Change
! Exploitation
Habitat Change
Fish Stocking
Climate Change
L
Toxic Chemicals
Heated Effluents
Entrainment
Contaminants
PREDATION-COMPETITION
EFFECTS
Figure 6-2.—Hierachical structure of levels of organization within aquatic ecosystems. Ex-
amples of external anthropogenic Influences are shown that operate at each level of
organization; homeostatic processes are shown that act at the interfaces between levels
(source: Evans et al. 1990).
Indicators of individual fish response tend to be, on the whole, less expensive
to measure, but their significance relative to effects at the population- or com-
munity-level is often unclear. Indicators at the population-, community-, or
ecosystem-level generally relate more directly to lake management objectives, but
data collection requires more time and effort. Many are also difficult to measure
precisely or are naturally quite variable, and as a result, changes may not be
detected until significant damage has already occurred.
86
-------
Chapters. Problem Identification and Diagnosis
What levels of each indicator signify a^problem or reason for concern? There
are no magic values, only a general principle: observed deviations from expected
norms deserve further investigation. Reference values or ranges can be defined
from historical (pre-disturbance) data for the lake or by comparison to relatively
undisturbed lakes with similar natural features in the same ecoregion. The major
difficulty in interpreting indicators of fish community and fisheries status is dis-
tinguishing between natural variability and deviations from the norm caused by
problems or adverse effects of concern. Models and data analysis approaches that
can aid data interpretation are discussed in Chapter 11.
Problem Diagnosis
Problem diagnosis involves the identification of the underlying cause or causes
of the observed problem or use limitation. In addition to information on fish
community and fisheries status, data are required on the potential sources of
stress or adverse effects, including the physical and chemical characteristics of
the fish habitat and biotic interactions (e.g., the abundance of important
predators and prey).
Most problems are not unique to a particular lake but commonly occur in a
number of lakes in the region. As a result, the general causes and approaches for
solving them are often known. In addition, depending on the nature of the prob-
lem, some causes are likely to be more important than others. Thus, in most
cases, a substantial amount of existing knowledge and expertise are available to
aid in focusing diagnostic analyses and data collection.
Problem diagnosis is an iterative process (Fig. 6-3). Generally, the more com-
plex and unusual the problem, the greater the number of iterations needed to
determine the major cause or contributing factors with a reasonable degree of
confidence.
Before initiating data collection or analysis, three tasks should be completed
that formalize expert understanding of the problem and serve to focus sub-
sequent efforts. First, develop a complete list of the possible causes of the ob-
served problem and the expected symptoms or diagnostic clues of each cause.
Second, develop a conceptual model illustrating the important interactions
among system components that may influence data interpretation (e.g., Fig. 2-
14). Because the physical, chemical, and biological components of lake ecosys-
tems are intricately linked, stressors may have both direct and indirect effects.
Recognizing these system interactions will greatly assist in identifying and
evaluating potential causal linkages. After developing the conceptual model, the
list of possible causes should be reassessed and updated as appropriate. Finally,
based on the list of possible causes and the conceptual model, define specific tes-
table hypotheses regarding likely causes and linkages. Data collection and
analysis activities should then be designed to address and test each of these alter-
native hypotheses.
Having provided a framework for problem diagnosis, the next stage is to
compile and analyze existing data on the lake, watershed, fish community, and
fisheries relevant to the problem(s) of concern. Substantial data may be available
in the files of the State fisheries agency or from previous lake studies. In some in-
stances, the existing information may be sufficient to diagnose the problem and
evaluate alternative hypotheses and potential remediation actions; however, in
most cases, additional data will be required. The results from analyses of existing
data should be used to update, as needed, the conceptual model and hypotheses,
identify important remaining uncertainties and data gaps, and aid in designing a
cost-effective and efficient data collection program. Subsequent data collection
and analysis activities also may be iterative, providing more definitive, quantita-
tive resolution on the sources and causes of the problem at each step (see Fig.
6-3).
What levels of each
indicator signify a
problem or reason for
concern? There are no
magic values, only a
general principle: observed
deviations from expected
norms deserve further
investigation.
Because the physical,
chemical, and biological
components of lake
ecosystems are intricately
linked, stressors may have
both direct and indirect
effects. Recognizing these
system interactions will
greatly assist in
identifying and evaluating
potential causal linkages.
87
-------
Fish and Fisheries Management In Lakes and Reservoirs
List Possible Causes and
Associated Symptoms
Develop Conceptual Model
T
Define Testable Hypotheses
Compile Existing Data
I
Data Analysis and
Hypothesis Testing
Update Conceptual Model,
Possible Causes, and Hypotheses
Collect Additional Data
to Address Data Gaps
and Uncertainties
Identify Data Gaps and
Remaining Uncertainties
Conclusion: Identify Major
Cause(s) and Contributing Factors
I
Propose Possible Solutions
(see Chapters 8 and 9)
Figure 6-3.—Major steps In the iterative process of problem diagnosis.
The types and extent of data required will vary depending on the type and
severity of the problem. Unfortunately, most of the problem symptoms and in-
dicators of fish community and fisheries status are nonspecific; that is, similar
changes occur in response to a broad range of different causes (Table 6-4). In some
cases, substantial investigative work may be needed. For example, six years of in-
tensive study were required to determine that selenium leaching from the fly ash
disposal pond for the Roxboro Steam Electric Plant was the primary cause
of largemouth bass population declines and poor reproductive success observed
in Hyco Reservoir, North Carolina (Woock, 1984; Woock and Summers, 1984). In
88
-------
Chapter 6. Problem Identification and Diagnosis
1
1
V
o
i
•o
c
a
c
"5
o
o.
w
•5
0
_c
"g
to
'u
o
<§
1
CO
a
E
0)
a
E
8
1
c
E
«
£
c
c
i
Table 6-4. — Com
I
DC
ffi
3*
2!
UJ U
ttu.
p
5
o
1
3
i
C/)
uf
sl
u-o
O Z
P O
*"
Z
111 U.
Ss
P 3
O
Ul
u
ii
i
_
|3
COMMON
PROBLEMS
X
^
X
X
X
•1
i!
I'
x
^
X
X
Inadequate spawn-
ing habitat
X
x
^
X
X
Water level
fluctuations
3
X
X
c
c
i
t
o
!
8
X
X
High temperatures
X
X
X
X
Excessive turbidity
X
X
X
X
Entrainment/
impingement
X
X
X
X
X
X
X
.t;
•c
'f.
<
X
X
X
X
X
X
X
X
Toxto substances
*
8
Excessive
macrophytes
*
X
8
;=
<
J*
_C
C
«
X
X
Low prey
availability
X
X
X
Undesirable fish
species
^
x
X
01
c
JC
1
X
Underutilization
i
Q
0)
•8
1v
0
I
0)
1
£
1
•c
g
8
*c
E
i
* XX indicate more c
89
-------
Fish and Fisheries Management In Lakes and Reservoirs
[PJoorly designed
shoreline and watercourse
development can destroy
wetlands and other
nearshore habitats that
may serve as important
spawning and nursery
areas for fish.
Cultural eutrophication
... is one ofthe most
obvious and pervasive
problems that affects lakes.
other instances, expert judgment that relies on analyses of other similar problems
in the region may be sufficient. Several case study examples of the process of prob-
lem identification and diagnosis and the design of fisheries restoration programs
are provided in Chapter 12. In addition, Meyer and Barclay (1990) provide a com-
prehensive how-to manual on investigating and determining the causes of fish-
kills.
Common Causes of Fisheries Management
Problems
Common causes of problems encountered in fisheries management include the
following:
• Loss and degradation of fish habitat. A wide variety of activities in
the watershed and lake proper can result in the general degradation or
loss of important fish habitat. For example, poorly designed shoreline
and watercourse development can destroy wetlands and other near-
shore habitats that may serve as important spawning and nursery areas
for fish. Dam building and stream channeling may eliminate important
spawning areas in tributary streams or lake outlets. Improper logging
and construction practices can increase erosion and sediment transport
into receiving streams and lakes, increasing lake turbidity, altering the
bottom substrate, and potentially smothering fish eggs and fry. Habitat
degradation is an all-encompassing term that includes any adverse
change to the chemical, physical, and biological environment in which a
fish lives. Therefore, many of the other fisheries problems noted in these
paragraphs are actually subsets or special cases of problems associated
with habitat degradation.
• Cultural eutrophication. Cultural eutrophication, caused by marked
increases in nutrient, organic, and/or sediment loadings as a result of
human activities, is one of the most obvious and pervasive problems
that affects lakes (Cooke et al. 1986). Oxygen deficits and high water
temperatures that commonly accompany eutrophication can adversely
impact fish both directly and indirectly. Anglers generally consider the
types of fish that do best in highly eutrophic waters (e.g., carp,
bullhead) less desirable compared to the natural, pre-eutrophication
species. Algal blooms, noxious odors, turbidity, and excessive growths
of rooted aquatic plants, which also typically increase with eutrophica-
tion, decrease the quality of the fishing environment.
• Inadequate or poor spawning habitat. Limitations on the quality
and/or quantity of suitable spawning habitat are often important fac-
tors limiting the productivity of particular fish species within a given
water. Spawning habitat is more likely to be an important limiting factor
for species with fairly specific habitat requirements, such as many sal-
monids (see Appendix A).
• Water level fluctuations. Large fluctuations in water level may in-
crease fish mortality by exposing eggs and fry in nearshore habitats and
also concentrating fish into smaller volumes of water, often with limited
cover, making them more susceptible to predation.
• Low levels of dissolved oxygen. Problems with oxygen depletion
occur principally in the hypolimnion during summer stratification and
over winter under ice and snow cover. Low levels of oxygen also occur
90
-------
Chapter 6. Problem Jcfent/ffeatfon and Diagnosis
periodically in macrophyte beds during summer, at night, or after long
periods of cloud cover. Some lakes naturally experience anoxic condi-
tions or levels of dissolved oxygen too low to support fish in some
habitats. Problems with low dissolved oxygen can be aggravated,
however, by nutrient enrichment and eutrophication. Winterkill
caused by oxygen depletion is relatively common in small, shallow
productive lakes in northern climates (e.g., Box 3-F). Summerkill
generally results from the combined effects of low oxygen and high
temperatures (e.g., Box 3-E).
• High water temperatures. Each fish species has a preferred
temperature range. Temperatures that exceed the fish's upper thermal
tolerance can cause significant fish mortality. On occasion, fishkills
may also result from sudden drops in temperature when temperature
changes occur too rapidly to allow thermal acclimation. Fish species
living in waters at the extremes of their geographic range and near
their upper or lower thermal tolerance limits are more likely to ex-
perience problems associated with water temperature. Large thermal
discharges into waterbodies from electrical generating facilities with
once-through water cooling can create environments where sudden
shifts in temperature are more likely to occur. Finally, decreases in
water transparency resulting from eutrophication or increased tur-
bidity may increase water heating and water temperatures in the
upper surface layers of the lake.
• Excessive turbidity. High levels of turbidity can result from water-
shed disturbances or occur naturally in lakes and reservoirs having
large watersheds with highly erodible soils. As noted, high levels of
turbidity limit light penetration, thereby reducing primary produc-
tivity and increasing temperatures in the upper surface waters. High
turbidity may also alter the bottom substrate and can smother eggs
and fry on the lake bottom. In addition, excessive turbidity may
decrease feeding efficiency of predators that rely on visual cues to cap-
ture prey.
• Entrainment and impingement. Hydroelectric generating
facilities, electric generating units with once-through cooling, pump-
back projects, city water treatment plants, and other similar operations
may withdraw large quantities of water from lakes and reservoirs.
Small fish, especially eggs and larvae with little or no swimming
ability, can be entrained in these water withdrawals and carried direct-
ly into the facility where most or all these organisms die before being
discharged. Larger fish that are caught in the strong currents created
by these water withdrawals and impinged on to water intake screens
also can experience high mortality rates. These problems are of con-
cern principally in lakes and reservoirs where a relatively high per-
centage of the total water volume is withdrawn and discharged daily;
for example, in reservoirs constructed to serve as water storage or
cooling reservoirs for large electrical generating facilities or where
water intakes are located in important fish nursery or spawning
habitats.
• Acidity. High levels of acidity (low pH) are toxic to fish. Different fish
species have varying pH tolerance ranges, although most prefer pH
levels ranging from 6 to 8. High levels of acidity may result from acid
mine drainage and, for waters with relatively low buffering capacity,
from acidic deposition.
91
-------
Fish and Fisheries Management in Lakes and Reservoirs
• Toxic substances. Toxic materials, such as pesticides and heavy me-
tals, may be introduced into waterbodies through point source dischar-
ges of industrial or municipal wastes, nonpoint sources in runoff and
groundwater from agricultural and other activities in the watershed, or
atmospheric transport and deposition. Elevated concentrations of toxic
substances may increase fish mortality rates, especially for early life
stages, decrease fish growth and fecundity, and cause a number of other
sublethal stresses and responses (e.g., physiological and biochemical
changes), resulting eventually in decreased fish abundance and lower
fisheries yield.
i Bioaccumulation of toxic substances in fish tissues. In some
waters, toxic substances may have little direct adverse effect on fish or
the fish community. However, bioaccumulations of toxic substances
within fish tissues may make the fish unsuitable for human consump-
tion.
i Excessive aquatic weeds (macrophytes). Beds of aquatic macro-
phytes provide important cover and nursery areas for young fish and
spawning habitat for some fish species. As a result, the occurrence of
macrophytes is generally advantageous for fish survival and produc-
tion. However, excessive growths of aquatic macrophytes that provide
extensive cover for small fish may severely reduce predation, and thus
mortality, resulting in overcrowding, reduced growth rates, and stunted
populations. In addition, periodic depletion of oxygen in weed beds at
night during summer or in the late summer and fall as quantities of
aquatic weeds die and decompose may kill fish or cause them to leave
the area.
i Low lake fertility and fish production. As discussed earlier, exces-
sive nutrient inputs and eutrophication can cause a variety of adverse
effects on lake ecosystems. However, some lakes are naturally very low
in nutrients and unproductive. If fishing is the primary use in these
lakes, moderate increases in nutrient loads and fertility may be ad-
vantageous, resulting in a significant increase in sustainable fisheries
yield. From the perspective of a lake's fisheries, therefore, conditions of
low fertility and production maybe a problem for some Jakes and reser-
voirs.
i Low prey availability. Inadequate food supplies can limit fish growth
rates. In unproductive lakes, the total quantity and productivity of prey
available are low. However, even in fairly productive systems, fish
growth rates may be less than desired or possible because of the absence
or limited supply of certain preferred prey. For example, many game
species are piscivorous: they feed primarily on smaller fish. When small
fish species such as minnows or other suitable forage fish are lacking or
in short supply, predator growth rates may be slow.
Excessive predation. Heavy losses of desirable fish species to
predators, such as larger fish and piscivorous waterfowl and mammals,
may measurably limit the quantity of harvestable fish. However, both
too little and too much predation can cause population imbalances.
Maintaining an appropriate balance between predators and prey is an
important component of managing the fish community and fisheries
quality.
92
-------
Chapter ft Problem Identification and Diagnosis
• Introduction of undesirable fish species and normative fish
strains. Exotic and nonnative fish species or strains introduced into
surface waters purposely or accidentally may compete with or prey
upon the native species, modify the environment (e.g., carp can in-
crease water turbidity), introduce parasites or diseases, interbreed
with native fish, and cause deterioration of gene pools (see Chapter 3
as well as Billington and Hebert, 1991). The result may be a loss of na-
tive species and wild strains of fish and an overall decline in genetic
diversity.
• Overtishing. Excessive fishing pressure may cause high levels of fish
mortality and subsequently a decline in fish abundance and fishery
yield. Fishing increases fish mortality both directly and indirectly.
Even in a catch-and-release fishery, some fraction of the fish caught
eventually die from the added stress and injuries associated with
hooking and playing the fish on the line.
• Underutilization. Harvest levels substantially below long-term op-
timum sustainable yields may also be viewed as a problem if the
specific objective is to maximize the value and use of the fishery.
• Accessibility. Fishery harvests in some hard-to-access lakes may be
limited not by biological productivity but by low levels of fishing pres-
sure. Improved access by improving roads, trails, or boat launching
facilities or obtaining a right-of-way over private land may increase
the number of anglers and, therefore, the total fishery yield.
• Conflicts among users and stakeholders. People rely on fish
resources to satisfy different needs. They may fish for food or recrea-
tion, they may derive their employment and income from fish, or they
may consider fish an important indicator of the overall health of the
ecosystem. Conflicts may arise among users or stakeholders who do
not have a common set of values and consequently do not agree on
how best to allocate and share the fish resource.
• User expectations not met. Finally, while the lake may be provid-
ing an adequate and productive fishery, it may not be fulfilling specific
expectations of some or all of the lake users; for example, in terms of
the size and number of trophy fish or species available. These per-
ceived fishery inadequacies may result from one or more lake
problems or may simply require redirection of the fisheries manage-
ment program and / or education of the lake users.
Water Quality Problems that Can Be
Alleviated by Fish Management
Chapter 5 discusses three water quality management goals that can be achieved
through a number of viable approaches, including biomanipulation. These same
three topics define water quality problems that may be alleviated through fish
management: (1) excessive growths of aquatic macrophytes; (2) high levels of
water turbidity caused by fish disturbing the lake bottom as they feed or spawn;
and (3) poor water clarity that results from high concentrations of phytoplankton
and periodic algal blooms. The mechanisms by which changes in fish com-
munities affect these lake characteristics are discussed in Chapter 2; specific
management techniques as well as case studies of biomanipulation are presented
in Chapter 9.
93
-------
-------
CHAPTER 7
Who Can Help?
Chapter Objectives
Throughout this manual, we emphasize the need for advice and assistance from
professional fisheries biologists and limnologists in assessing the cause(s) of lake
problems and identifying the most effective solution. Because of the highly inter-
active nature of lake ecosystems, management actions can often have unex-
pected, indirect, and potentially negative side effects. Designing and
implementing a cost-effective and environmentally sound lake management pro-
gram requires substantial expertise and experience. The objectives of Chapter 7
are to provide guidance on how best to obtain this expert assistance as well as in-
formation on specific organizations and government agencies that may be able to
help.
State and Provincial Agencies
State and provincial agencies responsible for fisheries and water quality manage-
ment are the best places to go for advice. Appendix C includes addresses and
telephone numbers for the central office of relevant agencies in the States and
Canadian provinces. Usually, each agency has several regional offices and
separate program offices that deal with various aspects of lake and fisheries
management. The best approach is to contact the central office and ask for recom-
mendations on the most appropriate individual, office, of program for your
specific needs. Requests for information and assistance should be made by a
single representative of the lake association or organized gfoup of concerned
citizens. Before contacting the agency, you should have a dear idea of your
group's needs and goals.
State and provincial agencies must be involved in all lake management
programs. Management objectives and activities must be consistent with State
water quality criteria and designated uses. Furthermore, fish are a public
resource. Landowners can control access to a lake, but control and management
of the fish community are the responsibility of State and provincial fisheries
agencies. Many management actions (e.g., stocking and fish collection) require
permits, and some of the methods described in Chapter 8 such as rotenone treat-
ments and stocking of exotics are prohibited in some States and provinces or in
specific waters or drainage basins. Because water quality and fisheries regula-
tions vary widely among States and provinces, you should obtain an up-to-date
listing of all relevant regulations and permit requirements.
For lakes that are publicly owned or have public access, State and provincial
agencies also can often provide useful background information, including results
from physical, chemical, and biological surveys, fish stocking records, or records
State and provincial
agencies responsible for
fisheries and water quality
management are the best
places to go for advice.
Management objectives
and activities must be
consistent with State
water quality criteria and
designated uses.
95
-------
Fish and Fisheries Management in Lakes and Reservoirs
Some States and provinces
fund lake and fisheries
restoration projects
through community
assistance programs and
should lie asked about the
availability of and
eligibility requirements for
such assistance.
of other lake management activities conducted in the past. At a minimum, State
and provincial biologists should be able to provide general advice on target, fish
species and the types of management efforts that have been successful in similar
lakes in the area. Many agencies distribute pamphlets or handouts on common
problems in local waters and recommended approaches for lake and fisheries
management.
State and provincial biologists oversee activities in many waters and have
many responsibilities; therefore, they usually can devote only limited time to in-
dividual lake management projects. The project's size and nature determine
whether a State or provincial biologist can become actively involved in either the
planning process or project implementation. Nevertheless, the appropriate State or
provincial agency must be informed of the proposed program early in the process.
If State or provincial biologists are unable to assist, they may have lists of or infor-
mation on qualified consultants or other professionals.
Some States and provinces fund lake and fisheries restoration projects through
community assistance programs and should be asked about the availability of and
eligibility requirements for such assistance.
Federal Agencies
Some lakes and reservoirs fall under Federal jurisdiction, are managed by Federal
agencies, or are adjacent to lands or waters managed or regulated by a Federal
agency. In addition, a number of Federal agencies conduct research and technol-
ogy transfer programs relevant to fish and fisheries management. The primary
Federal agencies in the United States involved in research or management ac-
tivities related to freshwater fish are:
• U.S. Fish and Wildlife Service. The lead Federal agency in the con-
servation and management of the Nation's sport fishes as well as
migratory birds, endangered species, and some mammals. Respon-
sibilities include the operation of Federal hatcheries, management of na-
tional wildlife refuges, and an extensive research program on fish and
wildlife conservation and management.
• Army Corps of Engineers. The agency responsible for the manage-
ment, including fisheries management, of the large number of reservoirs
constructed by the Corps.
• Tennessee Valley Authority. The Tennessee Valley Authority is also
responsible for the overall management of a large number of reservoirs,
all in the southeastern United States.
• U.S. Environmental Protection Agency. The Environmental Pro-
tection Agency has a broad range of responsibilities for Federal environ-
mental protection regulations and research and administers the Clean
Lakes Program.
• Bureau of Land Management. The Bureau of Land Management ad-
ministers 48 percent of all federally owned lands — most of them in the
western United States.
• Bureau of Reclamation. This agency is responsible for overseeing a
number of regional reclamation projects, some involving fisheries im-
provements, on arid lands in the western United States.
• U.S. Forest Service. The Forest Service administers national forests
and grasslands and is responsible for the management of these resour-
ces; it also conducts research on forestry and wildlife (including fish)
management and protection.
96
-------
Chapter 7. Who Can Help?
• National Park Service. The National Park Service administers
natural resources on designated, federally protected lands.
In Canada, relevant Federal agencies include:
• Department of Fisheries and Oceans. The agency responsible in
Canada for fisheries development and management and conducting
fisheries and environmental research. DFO administers the federal Fisheries
Act, the prime fisheries legislative tool, but shares many fisheries manage-
ment responsibilities with provincial environmental agencies.
• Environment Canada — This agency's responsibilities include the
acquisition and preservation of natural areas. Conservation and
Protection, part of Environment Canada, includes the Inland Waters
Directorate responsible for planning and managing national and inter-
national water programs, conducting research, and gathering data
relating to the Canada Water Act; the Canadian Wildlife Service, which
administers the Canada Wildlife Act and other regulations and con-
ducts research on migratory birds, endangered species, and other
wildlife; and the Environmental Protection Directorate, responsible for
programs to mitigate toxic chemicals, acid rain, and hazardous wastes,
and assessing environmental impacts.
This manual cannot provide a full listing or discussion of all the offices and
programs that provide useful advice, assistance, or information on designing and
implementating a fish or fisheries management program. Two programs deserve
special note, however.
• The U.S. Fish and Wildlife Service supports cooperative research
units at land grant universities within most States. The leader of the
Fish and Wildlife Service Cooperative Research Unit in your State may
be a useful source of information on researchers and consultants work-
ing in relevant areas.
• The Clean Lakes Program is administered through the U.S. En-
vironmental Protection Agency's regional offices and associated State
programs. This program provides assistance and funding for the
evaluation of lake problems and the implementation of lake restora-
tion programs on waters with public access. Information on the Clean
Lakes Program may be obtained from:
Clean Lakes Program (WH-553)
U.S. Environmental Protection Agency
401 M Street, SW
; Washington, DC 20460
The lake and Reservoir Restoration Guidance Manual (Olem and Flock, 1990: Chap-
ter 8) provides further information on Federal sources of funding and advice.
Private Organizations
A number of private organizations also provide information on organizing
citizens groups, obtaining lists of potential volunteers and interested individuals,
determining angler preferences, establishing fisheries goals and objectives, and
identifying fish and fisheries management techniques and possible funding sour-
ces. Organizations whose primary focus deals with issues relating to freshwater
fish and water quality are listed in Table 7-1; their addresses are provided in Ap-
pendix C. Additional information on these and other organizations can be found
in the Conservation Directory, published periodically by the National Wildlife
Federation, 1400 Sixteenth Street, NW, Washington, DC 20036-2266.
97
-------
Fish and Fisheries Management in Lakes and Reservoirs
Table 7-1.—Selected private organizations Interested in freshwater fisheries and
water quality (source: Natl. Wildl. Fed. 1991).
ORGANIZATION
PRIMARY INTERESTS
American Bass Association,
Inc.
Protecting and enhancing fishery resources and promoting bass
fishing as a major sport
Anglers for Clean Water, Inc.
Educating the general public about water pollution and promoting
the need for conservation of water and fisheries resources
Bass Anglers Sportsman
Society
Conserving water resources, fighting pollution, and teaching young
people good conservation practices
Bass Research Foundation
Encouraging results-oriented research aimed at improving the
quantity and quality of America's bass fishery resources
Clean Water Fund
Environmental Defense Fund,
Inc.
Federation of Fly Fishers
Freshwater Foundation
Izaak Walton League of
America
Helping to build citizen leadership and organizations for more effec-
tive public participation in policy debates regarding environmental
and consumer protection
Involving interdisciplinary teams of scientists, economists, and attor-
neys in the development of economically viable solutions for a
broad range of environmental problems
Promoting fly fishing and preserving all species of fish through local
stream and fishery restoration projects and conservation grants
Supporting research and education on the proper use and manage-
ment of surface and ground waters for human consumption,
industry, and recreation
Educating the public to conserve, protect, and restore the soil,
forest, water, air, and other natural resources
Muskies Inc.
Establishing hatcheries and introducing the muskellunge into
suitable waters, abating water pollution, and promoting
research and a high quality muskellunge sport fishery
National Audubon Society
Promoting science, lobbying, and citizen action to protect air, land,
and water resources
National Wildlife Federation
Encouraging public awareness of the need for the wise use and
proper management of natural resources
Natural Resources Defense
Council, Inc.
Monitoring government agencies, bringing legal action, and dis-
seminating citizen information to protect natural resources and
improve the quality of the environment
North American Native Fishes
Association
Promoting the study and conservation of North American
native fishes and restoring and protecting fish habitat
Sierra Club
Promoting the responsible use of the earth's ecosystems and
resources through public education; exploring and protecting
wild places
Smallmouth Bass, Inc.
Promoting research, education, restoration, and conservation of
smallmouth bass fisheries
Soil and Water Conservation
Association
Advancing the science of good land and water use; conducting
multidisciplinary forums to identify and formulate workable recom-
mendations on land and water management policies and issues
Sport Fishing Institute
Promoting high-quality recreational fishing through an integrated
program of ecological research, fish conservation education, and
aquatic sciences advisory service
Trout Unlimited
Protecting clean water and enhancing trout, salmon, and steel-
head fishery resources
Water Environment Federation
Developing and disseminating technical information on the preser-
vation and enhancement of water quality and water resources
98
-------
Chapter?. Who Can Help?
Professional Societies
Professional societies are private organizations of individuals with advanced
training and experience in specific scientific or technical disciplines. Two profes-
sional societies with particular relevance to fisheries and lake management are
the American Fisheries Society and the North American Lake Management
Society. The membership directories for both organizations serve as a readily ac-
cessible source of names and addresses of knowledgeable experts, some of whom
may be willing to consult and advise on a lake restoration project (see discussion
of private consultants).
The North American Lake Management Society maintains a list of members
who provide such services, sorted by specialty area and region. The American
Fisheries Society supports a certification program for fisheries biologists and can
provide a list of certified fishery biologists as well as all society members and
their area of expertise. Both organizations publish books, journals, and
magazines with useful information; in particular, Fisheries, published by the
American Fisheries Society, and lake Line, published by the North American Lake
Management Society, are designed for a broad audience.
Additional professional organizations involved in lake and fisheries manage-
ment and research are listed in Table 7-2; Appendix C lists their addresses.
Table 7-2.—Selected professional societies relating to lake and fisheries manage-
ment (source: Natl. Wildl. Fed. 1991).
ORGANIZATION
PRIMARY SCIENTIFIC AREAS OF INTEREST
American Fisheries Society
Conservation, development, and wise use of fisheries, both
recreational and commercial
American Society of
Limnology and Oceanography
Physical, chemical, and biological processes in freshwaters
and oceans
American Water Resources
Association
Water resources research, planning, development, and
management to establish a common ground for engineers and
physical, biological, and social scientists
Ecological Society of America
Terrestrial and aquatic ecology; scientific study of organisms in
relation to their environment
North American Benthological
Society
Biotic communities in lake and stream bottoms and their role in
aquatic ecosystems
North American Lake
Management Society
Protection, restoration, and management of lakes and reser-
voirs and their watersheds
Society of Environmental
Toxicology and Chemistry
Environmental toxicology and chemistry and the application of
these sciences to hazard assessment and risk analysis
Environmental Consultants
Some lake management programs may find it necessary to hire an environmental
consultant to perform in-depth analyses of data and assist with field sampling
and project implementation. In some cases, faculty in fisheries or limnology
departments at local universities may be willing to serve as consultants for in-
dividual lake projects. Alternatively, communities can hire environmental con-
sulting firms individually or as teams of experts for complex projects involving a
diversity of disciplines. To get information on candidate consultants, contact
• other lake associations;
• local and State environmental agencies and groups;
99
-------
Rsh and Fisheries Management In Lakes and Reservoirs
• the North American Lake Management Society consultant referral ser-
vice; and
• the American Fisheries Society, which has a listing of certified fisheries
biologists and members in most regions.
The Lake and Reservoir Restoration Guidance Manual (Table 3-3 and pages 42 and
192) discusses how to select a consultant or team of consultants for a lake restora-
tion project; most of these recommendations are relevant for fish and fisheries
management programs. Important criteria for selecting a consultant to assist
specifically with the fisheries management aspects of a lake restoration project in-
clude:
• Expertise
• Demonstrated training and qualifications in the principles of
fishery science and fisheries management (e.g., education, ad-
vanced degrees, certifications).
• Familiar with a broad range of fisheries management problems, the
alternative management approaches discussed in Chapters 8 and 9,
and the ecological consequences of these activities.
« Knowledgeable about relevant local, State, and Federal regulations
and permit requirements.
» Adequate staff and equipment to complete all tasks.
* • Experience
• Prior hands-on experience working with similar management
problems and fish communities in other lakes in the area.
• Demonstrated ability to identify and implement practical cost-
effective solutions to fisheries management problems.
• Prior projects working with a lake association or citizens group
demonstrating the capability to interact effectively with individuals
with diverse backgrounds.
• Past Performance
• References that vouch for the performance of the consultant(s) on
prior projects.
• Prior projects of high quality, completed on time and within
budget.
• Completion of one or more projects that involved the design and
implementation of long-lasting and effective management solu-
tion^) at reasonable cost.
1OO
-------
CHAPTER'S'
Management
Techniques for
Improving and
Maintaining Fisheries in
Lakes and Reservoirs
Chapter Objective
This chapter provides an overview of the various management techniques to im-
prove and maintain fisheries in lakes and reservoirs. It is not intended to be a
how-to guide with step-by-step instructions on implementation but rather a
general description of the types of tools and methods available and their ad-
vantages and limitations. Greater detail on each of these management techniques
can be found in the references cited. Information for some techniques was sum-
marized from EPA's Lake Maintenance Handbook (McComas, in press) and The Lake
and Reservoir Restoration Guidance Manual (Olem and Flock, 1990).
Management methods that use fish to improve water quality are discussed in
Chapter 9. However, Chapters 8 and 9 should be considered as a unit, of interest
to both fisheries and water quality managers. The fisheries management
methods in Chapter 8 involve physical, chemical, and biological manipulations
of the lake and watershed that can not only improve the lake's fisheries but also
affect water quality, other ecosystem components, and other lake uses. The dis-
cussions in Chapter 9 provide insight into the ecological consequences of fish and
fisheries management, which must be evaluated as part of any decision regard-
ing lake management.
Selecting the Appropriate Management
Technique
Managing a fishery is a delicate operation. Mistakes made are often difficult to
correct, and the wrong type of management action may be worse for the fishery
and lake ecosystem than no management at all. To be effective, management ac-
tion must address key limiting factor(s) or major problem(s) affecting the lake's
fisheries; otherwise, money and effort will be expended with little to no positive
[NJone of the methods
described in this manual
should be attempted
without first consulting a
professional fisheries
biologist familiar with fish
communities and fisheries
problems in the area.
1O1
-------
Fish and Fisheries Management in Lakes and Reservoirs
As part of the planning
process, cost estimates
should be obtained for the
subset of management
options being considered.
The size of the lake,
watershed, and associated
drainage system can have
a major influence on the
feasibility and
effectiveness as well as the
cost of various
management techniques.
[SJpecial consideration
must be given to the
potential for effects
downstream or in adjacent
waters.
returns. For these reasons, none of the methods described in this manual should be
attempted without first consulting a professional fisheries biologist familiar with
fish communities and fisheries problems in the area. Furthermore, some activities
(e.g., fish introductions, liming) require permits or are prohibited by State
regulatory authorities (see Chapter 7).
A number of the techniques described are suitable only in limited or certain
circumstances. For example, in many regions of the country, fertilizing a lake to in-
crease fish productivity is considered highly undesirable and therefore not a viable
management option because other lake uses and water quality would be adversely
affected. However, for some waters where fishing is the dominant lake use and
fisheries yields are clearly limited by low nutrients levels, lake fertilization may be
appropriate.
This manual provides a comprehensive review of all possible management ap-
proaches; its scope is not limited by any specific management objective or
philosophy. Nevertheless, in selecting the techniques to apply in any given lake,
careful thought and analysis are necessary to ensure that the management pro-
gram (a) addresses the cause of lake problems and major use limitations to ensure
an effective expenditure of funds and effort, (b) will not result in unexpected ad-
verse effects on other lake uses or ecosystem components, and (c) is consistent
with public values and the long-term management goals for the lake as a whole.
Costs are another important consideration in selecting a management ap-
proach. The cost of implementing a given management technique can vary widely,
depending on the region, lake size, accessibility, and other lake-specific conditions
and factors. Because of this variability, this manual does not provide cost es-
timates, although relative costs are discussed for some techniques. As part of the
planning process, cost estimates should be obtained for the subset of management
options being considered. Both implementation costs and long-term operation and
maintenance costs over the life of the project must be evaluated. How long will the
treatment or beneficial effects last? How often will management actions need to be
repeated? How much effort and expense will be required for routine upkeep and
monitoring?
The size of the lake, watershed, and associated drainage system can have a
major influence on the feasibility and effectiveness as well as the cost of various
management techniques. In-lake treatments such as alum additions to reduce in-
ternal nutrient loads may have relatively little effect in lakes with short hydraulic
residence times and can be very expensive in large lakes. The larger and more
diverse a lake's watershed, the more difficult it may be to control nonpoint source
inputs of nutrients and sediment. For lakes interconnected to other lakes, rivers,
and streams, special consideration must be given to the potential for effects
downstream or in adjacent waters. Stocked fish may migrate to other lakes where
they may not be wanted. Exotic plants and animals may rapidly disperse
throughout a drainage basin, becoming a regionwide nuisance. If undesirable fish
species such as carp also occur in adjacent, connected waters, efforts to reduce or
eliminate them in just one lake are likely to fail. As noted in Chapter 1, a whole-
basin approach is needed for effective fisheries and water quality management.
It is not possible to provide simple rules for designing a management program
— matching specific management techniques to certain types of problems or con-
ditions. The most appropriate method(s) depends on
• the full suite of management goals,
• natural and existing conditions in the lake, watershed, and drainage
basin,
• State regulations,
• available funding, and
• other site-specific factors.
102
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
The types of methods described do, however, correspond generally to the types
of problems discussed in Chapter 6 (Table 8-1) and fall within three major
categories (Fig. 8-1):
1. managing the fish's habitat;
2. manipulating the fish community directly; and
3. managing fishing pressure and harvests.
Table 8-1.—Categories of management approaches used to address common fisheries
management problems.
COMMON FISHERIES MANAGEMENT PROBLEMS
MANAGEMENT
APPROACH
Habitat
protection
Reduce/eliminate
toxicants
Reduce nutrient
loads
Lake fertilization
Aerate/
increase DO
Liming
Spawning habitat
improvements
Aquatic plant
management
Water level
management
Addition of fish
cover
Game fish stock-
ing
Control
undesirable
species
Prey
enhancements
Rshing
regulations
Fishing
tournaments
User
conveniences
c
o
Habitat degradati
X
X
X
X
X
X
X
X
Toxic substancea
X
§
|
ui
X
X
Low lake fertility
X
Low oxygen
X
X
Sf
•a
3
X
?
c
Inadequate spaw
habitat
X
X
X
1
0.
Excessive macro
X
X
o
3=
a
Water level fluctu
X
High temperature
X
X
X
1 Entrapment/
impingement
X
&
Excessive turbid
X
X
a
JO
o
3
a
Undesirable fish
X
X
£•
Low prey avallab
X
Overfishing
X
Underuse
X
X
X
(see Table 6-4)
Habitat Management
• Habitat quality is the single most critical factor that determines the types and
abundance of fish in a lake as well as the quality of a fishing experience. Without
suitable habitat for fish survival, reproduction, and growth, attempts to manage
103
-------
Fish and Fisheries Management in Lakes and Reservoirs
Habitat quality is the
'Single most critical factor
that determines the types
and abundance offish in a
lake as well as the quality
of a fishing experience.
Delineation of
Management Goals
and Objectives
Problem Identification
and Diagnosis
T
Potential Management Approaches and Actions
Managing the Fish's
Habitat
Habitat protection
Reduce/eliminate toxicants
Reduce nutrient loading
Lake fertilization
Aeration/increase DO
Liming
Improve spawning habitat
Addition of fish cover
Aquatic plant management
Water level management
Manipulating the Fish
Community
Game fish stocking, e.g.,
- species introductions
- supplemental stocking
- "put-and-take" fisheries
Control undesirable species
- poisoning
- selective cropping
- spawning disruption
- fish barriers
Prey enhancements
Managing Fishing
Pressure and Harvest
Fishing regulations, e.g.,
- creel limits
- closed seasons
- size limits
- gear restrictions
- catch and release
Fishing tournaments
User conveniences, e.g.,
- improved access
- boat ramps
Quality Fishing
Experience
Figure 8-1.—Potential approaches and management actions for improving and maintain-
ing fisheries In lakes and reservoirs. The appropriate management approach for any given
lake will depend on the nature of the problem and the management goals and objectives.
In addition, monitoring to evaluate the results and success of management actions should
be an Integral part of any fisheries management program.
and sustain a fishery will be expensive and difficult — if not impossible. Many
techniques available for protecting and restoring a lake's habitat have already
been described in The Lake and Reservoir Restoration Guidance Manual (also see
reviews in Cooke et al. 1986; Jorgensen and Vollenweider, 1989). For completeness,
however, relevant information from the aforementioned manual is summarized
briefly in the subsections that follow, emphasizing the usefulness of these ap-
proaches within the context of a fisheries management program. A number of ad-
ditional habitat management activities are also presented that are unique to
fisheries concerns.
The types of activities that may be useful for improving and maintaining a
lake's fisheries include the following (see Fig. 8-1):
• habitat protection,
• methods for reducing or eliminating problems with toxic substances,
• methods for reducing nutrient loads and nutrient availability,
• lake fertilization to enhance fish productivity,
104
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
• lake aeration and other approaches for increasing levels of dissolved
oxygen in critical fish habitats,
• lake liming and associated techniques for decreasing water acidity,
• spawning habitat enhancements or improvements,
• the addition of physical structures to provide increased fish cover and
shelter,
a aquatic plant management, and
• water level management.
Finally, many fisheries management problems for artificial lakes (reservoirs) can
be avoided or reduced if fish habitat requirements are considered during lake
design. Thus, factors to consider in the design and construction of reservoirs are
also summarized.
Habitat Protection
The most cost-effective and long-term approach to habitat management is habitat
protection; that is, preventing the degradation or loss of important fish habitats
through the application of best management practices, controlled watershed and
lake development, and pollution prevention and treatment. Habitat protection
activities should be a top priority for all fisheries management programs.
Fish habitat includes not just the lake proper but also inflowing tributaries,
lake outlet(s), adjacent wetlands, and the shoreline, all of which can provide im-
portant spawning, nursery, and feeding areas for fish. Furthermore, in many
cases, habitat protection begins on the land in the surrounding watershed. Chap-
ter 5 and Appendix D df The Lake and Reservoir Restoration Guidance Manual pro-
vide a detailed discussion on watershed management, including the use of best
management practices to reduce erosion and the export .of sediments, nutrients,
and toxic contaminants to receiving waters. Best management practices have
been developed for agricultural, silviculturai, urban, and construction activities
(U.S. Environ. Prot. Agency, 1987). The effectiveness, cost, and chance of negative
side effects associated with selected watershed best management practices are
summarized in Table 8-2.
Additional habitat protection guidelines for local property owners and
developers include the following (Ontario Ministry of Natural Resources, 1991):
• Disallow dredge and fill operations in or near areas with critical fish
habitat (e.g., wetlands, spawning beds, and tributary streams used for
spawning or nursery areas). Dredge and fill operations not only
destroy fish habitat directly but also can result in increased water tur-
bidity and siltation, which degrade fish habitat.
• Maintain buffer strips of natural vegetation along the banks of streams
and lakes to stabilize the shoreline, reduce sediment inputs, and pro-
vide shading for cooler water temperatures during the summer. In
cases where natural vegetation is not sufficient to stabilize shorelines,
structural devices may be needed. Banks of riprap (carefully arranged
large stones) with shrubs or other vegetation planted over them are
preferable to solid shore walls of steel or cement.
• Boathouses and docks should not disturb river or lake beds or restrict
water movement near the shoreline. Build cantilever, floating, or post-
supported structures where possible. Crib foundations are acceptable
if bridging is constructed between the cribs to allow water to circulate.
All wood preservatives contain compounds toxic to fungi; therefore,
preservatives should be used with caution or avoided.
The most cost-effective
and long-term approach to
habitat management is
habitat protection
1O5
-------
Fish and Fisheries Management in Lakes and Reservoirs
Elevated levels of [toxic]
substances can reduce fish
survival and growth and
may bioaccumulate in fish
tissues, limiting the
suitability of fish for
human consumption.
Table 8-2. — Summary of the effectiveness, cost, and chance of negative side effects
associated with select
Flock, 1990).
watershed
best
management
practices
(source:
!
EFFECTIVENESS
PHOS-
SEDIMENT NITROGEN PHORUS
Agriculture:
Conservation tillage
Contour farming
Contour stripcropping
Range & pasture mgt.
Crop rotation
Terraces
Animal waste mgt.
Urban:
Porous pavement
Street cleaning
Silviculture:
Ground cover maint.
Road & skid trail mgt.
Construction:
Nonveg. soil stabilization
Surface roughening
Multlcategory:
Streamside mgt. zones
Grassed waterways
Interception or diversion
Streambank stabilization
Detention/sedimentation
basins
G-E
F-G
G
G
G
G-E
N/A
F-G
P
G
G
E
G
G-E
G-E
F-G
G
G-E
P
u
u
u
F-G
U
G-E
F-G
P
G
U
P
U
G-E
U
F-G
U
P
F-E
F
F-G
U
F-G
U
G-E
F-G
P
G
U
P
U
G-E
P-G
F-G
U
P
RUNOFF
G-E
F-G
G-E
G
G
F
N/A
G-E
P
G
U
P-G
G
G-E
F-G
P
P
G-E
COST
F-G
G
G
G
F-G
F-G
P
P-G
P
G
P
F-G
F
G
F-G
P-F
P-G
F-G
Olem and
CHANCE
OF
NEGATIVE
EFFECTS
F-G
P
P
P
P
F
F
F
U
P
F
F
P
F
P
P
F
F
E = excellent; G = good; F = fair; P = poor; U = unknown; N/A = no answer.
• Avoid building beaches in areas with critical fish habitat. Alternatives,
such as dry beaches (built above the high water mark) and swimming
platforms are preferable. Instead of sand, consider building beaches
with coarse or pea-sized gravel.
• Maintain a diversity of habitats (e.g., riffles and pools in streams, littoral
areas with a complex physical structure) that can support a wide range
of fish species and sizes. Channelized streams and boat channels in lit-
toral areas are relatively poor fish habitat.
Control of Toxic Contaminants
Toxic contaminants in lakes can include metals, pesticides, oils, and other pol-
lutants in agricultural, industrial, and urban wastes. Elevated levels of these sub-
stances can reduce fish survival and growth and may bioaccumulate in fish
tissues, limiting the suitability of fish for human consumption. Possible corrective
actions include
» eliminating the source of the contaminants by treating effluents (for
point sources) or applying best management practices (for nonpoint
sources);
• dredging and removing contaminated lake sediments;
• isolating contaminants concentrated in the bottom sediments from the
overlying water column by covering the sediments with a relatively im-
permeable layer, such as betonite (a form of clay) or a plastic liner;
106
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
• on-site water treatments — for example, diluting the contaminated
water with "clean" water pumped in from other sources or withdraw-
ing and treating the lakewater (e.g., by chemical precipita-
tion/coagulation and filtration) and then returning the treated water
to the lake;
• the addition of chemicals such as alum (aluminum sulfate) to the lake,
which may accelerate the precipitation of toxic substance(s) out of the
water column into the bottom sediments;
• deepwater aeration, for contaminants (e.g., some metals and am-
monia) that precipitate or become nontoxic in the presence of dis-
solved oxygen;
• controlling changes in water level if the exposure and suspension of
contaminated sediments tend to increase the solubility and mobiliza-
tion of the toxic substance; and
• biomanipulation if the potential for human exposure to bioaccumu-
lated toxics can be reduced by altering the food chain or target fish
species for fisheries management (e.g., avoiding game fish, such as
lake trout, that are top predators and have high levels of body fat).
Relatively few field tests have been conducted to evaluate the long-term ef-
fectiveness of most of these techniques; in addition, a number of techniques can
have potentially serious negative side effects (e.g., dredging operations may
resuspend toxic contaminants and actually increase bioavailability). Not infre-
quently, no action is the most environmentally sound and cost-effective ap-
proach, allowing natural processes, such as sedimentation, to gradually reduce
the concentration and availability of toxic substances after the source of con-
taminants has been eliminated. A technical guidance manual on toxic substances
in lakes and reservoirs for EPA's Clean Lakes Program is currently in preparation
and will provide further details on designing a management program to control
and reduce toxic contaminants.
Reducing Nutrient Loads and Nutrient Availability
As discussed in Chapter 2, eutrophication can adversely affect fish communities
by decreasing dissolved oxygen levels, increasing water temperatures, decreas-
ing water clarity, and altering the types and abundance of phytoplankton,
zooplankton, and other organisms available as fish prey. Increased nutrient load-
ings generally increase lake productivity, in many cases including the total
production of fish. However, the accompanying changes in physical and chemi-
cal habitat often result in an undesirable shift in the types of fish species able to
survive and flourish in these waters. As an indirect effect of high nutrient loads,
lakes may become unsuitable for game species of particular interest to local
anglers.
Much of The Lake and Reservoir Restoration Guidance Manual (Olem and Flock,
1990) is devoted to methods for evaluating and controlling problems with lake
eutrophication. Two basic approaches are described for reducing nutrient inputs
and availability: managing the watershed (Chapter 5, Olem and Flock, 1990) and
various in-lake treatments (parts of Chapter 6, Olem and Flock, 1990). Managing
the watershed may involve the construction or upgrading of wastewater treat-
ment facilities and changes in land use or land use practices in the watershed —
in particular, application of best management practices (see Table 8-2). The rela-
tive merits and effectiveness of best management practices depend on the rela-
tive importance of point and nonpoint nutrient sources to the lake (see "How To
Assess Potential Sources," pages 104 to 106, Olem and Flock, 1990).
Not infrequently, no
action is the most
environmentally sound
and cost-effective
approach, allowing
natural processes, such as
sedimentation, to
gradually reduce the
concentration and
availability of toxic
substances after.the source
of contaminants has been
eliminated.
107
-------
Hsh and Fisheries Management in Lakes and Reservoirs
Watershed management of
both point and nonpoint
sources reduces external
nutrient loadings.
[IJn-lake treatments will
only be effective over the
long-term if accompanied
or preceded by efforts to
reduce external nutrient
loads.
Watershed management of both point and nonpoint sources reduces external
nutrient loadings. In-lake treatment procedures, on the other hand, eliminate in-
ternal nutrient sources or reduce nutrient availability. In general, in-lake treat-
ments will only be effective over the long-term if accompanied or preceded by
efforts to reduce external nutrient loads. In conjunction with a plan for improved
watershed management, in-lake treatments may serve to accelerate the process of
lake recovery.
Many of the in-lake treatments noted previously for reducing toxics also can
reduce nutrients. The following types of in-lake treatments effectively reduce
nutrient availability in at least some circumstances:
• Chemical treatments to precipitate and inactivate phosphorus.
Aluminum salts, such as aluminum sulfate (alum) and sodium aluminate, have a
strong affinity to adsorb and absorb inorganic phosphorus and remove phos-
phorus-containing particulate matter from the water column as part of the floe
(loose precipitate) that forms. After the floe settles, the result is not only a reduc-
tion in phosphorus availability but also generally a substantial increase in water
clarity. Adverse effects may occur, however, if the dosage is too high. Excessive in-
puts of aluminum salts can result in concentrations of dissolved aluminum in the
water column that are toxic to fish and other biota. Example applications of alum
treatments to reduce nutrient levels in lakes include Horseshoe and Snake Lakes,
Wisconsin (Peterson et al. 1973; Garrison and Knauer, 1984); Medical Lake,
Washington (Gasperino et al. 1980; Soltero et al. 1981); Annabessacok Lake, Maine
(Pominie, 1980); and Dollar and West Twin Lake, Ohio (Cooke et al. 1982).
• Sediment removal. Sediments with high concentrations of phosphorus or
nitrogen may serve as an internal nutrient source. If nutrients are concentrated
within the upper sediment layers, dredging and the removal of these nutrient-rich
sediments may substantially reduce nutrient recycling and availability (see Figs.
6-1 and 6-2, Olem and Flock, 1990). At the same time, however, dredging opera-
tions can cause extensive damage to the benthic community, which can be an im-
portant food source for fish, and may disturb fish spawning habitats if not
carefully designed and implemented. Example applications include Lake Trum-
men, Sweden (Andersson et al. 1975; Bengtsson et al. 1975; Cronberg et al. 1975)
and Lilly Lake, Wisconsin (Dunst et al. 1984).
• Dilution and flushing. For small lakes, it may be possible to reduce nutrient
concentrations in the water column by adding sufficient amounts of low-nutrient
waters from other sources, thereby diluting and flushing the high-nutrient water
out of the lake. Applications of this technique are limited, however, by the general
absence of suitable alternative water supplies. Examples include Moses Lake,
Washington (Welch and Patmont, 1980) and Green Lake, Washington (Perkins,
1983).
• Aeration. Phosphorus remobilization from lake sediments is generally higher
in anaerobic waters (with no dissolved oxygen) than in well-aerated waters be-
cause the oxygenated forms of iron and manganese in natural waters form an in-
soluble precipitate with phosphorus. Thus, aeration techniques that increase
oxygen levels in deeper waters may decrease nutrient recycling and availability.
Increases in dissolved oxygen also have a direct positive effect on fish. Specific
aeration methods are discussed later in this chapter.
• Sediment oxidation. Oxidation of the lake's sediments may also reduce the
remobilization of phosphorus into the water column. Rather than air, however, a
solid such as calcium nitrate is added to the sediments as an oxidizing agent. The
procedure is termed "RIPLOX," after its originator (Ripl, 1976) and is considered
still experimental. Example applications include Lake Lillesjon, Sweden (Ripl and
Lindmark, 1978) and Long Lake, Minnesota (Willenbring et al. 1984).
108
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
m Water withdrawals from the hypolimnion. The colder, deeper layers of a
thermally stratified lake or reservoir generally have higher nutrient concentra-
tions than waters in the epilimnion or metalimnion. Selectively withdrawing
these nutrient-rich waters by using a siphon or deepwater outlet in a dam can
decrease the quantity of nutrients stored and recycled in the waterbody. How-
ever, hypolimnetic withdrawals may also trigger thermal instability and lake
turnover. In addition, the discharge of these nutrient-rich, often anaerobic waters
from the hypolimnion of eutrophic lakes may adversely affect downstream
receiving waters. Example applications include Lake Wononscopomuc, Connec-
ticut (Kortmann et al. 1983) and Mauensee in Switzerland (Gachter, 1976; Cooke
et al. 1986).
All these in-lake treatments require significant funding for equipment,
chemicals, and labor and are generally short term. Case studies as well as addi-
tional information on the methods, costs, and potential negative side effects of
each approach can be found in Chapter 6 of The Lake and Reservoir Restoration
Guidance Manual (Olem and Flock, 1990) and Cooke et al. (1986). ,
Lake Fertilization
Lakes and reservoirs that are naturally oligotrophic (i.e., have low nutrient loads)
generally also have relatively low levels of fish production and yield. In some
cases, it may be desirable to increase fisheries yields in these waters through con-
trolled additions of nutrients — in essence, fertilizing the lake to enhance produc-
tivity. However, this increase in nutrient loads will. also alter other lake
characteristics, for example, increasing algal growths and decreasing water
clarity. Thus, while fertilization may be beneficial for fisheries, it is likely to have
detrimental effects on other lake uses. As a result, fertilization as a fisheries
management tool is generally restricted to lakes and reservoirs used only or
primarily for fishing where nutrient additions will not adversely affect
downstream waters. Once a lake is fertilized, returning, the system to its original
oligotrophic, clear-water condition can be difficult, expensive, and a lengthy
process, especially for lakes with long retention times.
Many commercially available fertilizers are suitable for lake fertilization
projects. The optimal application rate and technique depend on current nutrient
loads and concentrations, the desired increase in productivity, the fertilizer type,
and target fish species. As a general rule, McComas (in press) recommends 50
Ib/acre of 8-8-2 emergence fertilizer (8 parts nitrogen, 8 parts phosphorus, and 2
parts potassium). The Georgia Department of Natural Resources recommends
applying approximately 40 Ib/acre of 20-20-5 fertilizer every two to three weeks
beginning in the spring when water temperatures reach 60°F (Ga. Dep. Nat.
Resour. 1988). In waters that are naturally slightly acidic, simultaneous additions
of agricultural limestone (e.g., one to two tons per acre) may further enhance
productivity. Once fertilizer additions are initiated, they must be continued at
regular intervals throughout the growing season. Do not add the total amount of
fertilizer required for an entire season all at one time.
The fertilizer should be spread or dispersed evenly throughout the lake. One
application approach uses submerged wooden platforms anchored about 12 in-
ches below the water surface near the shore. The appropriate quantity of fer-
tilizer is placed on each platform; the fertilizer gradually dissolves and is
distributed through the lake by wave action and water currents. Alternatively,
liquid fertilizer can be used to facilitate mixing.
An increase in phytoplankton productivity is the major, direct effect of fer-
tilizer additions. Thus, fish species that feed on phytoplankton and zooplankton
experience a larger increase in production than do species that feed primarily on
benthic organisms, macrophytes, or other fish. In addition, fertilizer applications
[W]hile fertilization may
be beneficial for fisheries,
it is likely to have
detrimental effects on
other lake uses.
1O9
-------
Fish and Fisheries Management in Lakes and Reservoirs
Low levels of dissolved
oxygen may occur in lakes
as a result of natural
conditions and cultural
eutrophication.
One important option for
lakes with dissolved
oxygen problems is to
manage the fisheries for
species able to tolerate
relatively low levels of
dissolved oxygen or that
do not inhabit areas of the
lake (such as the
hypolimnion) that
experience oxygen
depletion.
During winter, the goal is
not to aerate the entire
waterbody but instead to
create an oxygen-rich
refuge area for fish,
generally near the lake
surface.
will result in a measurable response only if food availability is the major factor
limiting fish production — as opposed to temperature, natural reproduction, or
other variables.
A number of State resource agencies have published guides for lake fertiliza-
tion, including Alabama, Arkansas, Georgia, Illinois, Iowa, Minnesota, New York,
and others (e.g., Iowa Dep. Nat. Resour. undated; Ga. Dep. Nat. Resour. 1988).
State resource agencies are listed in Appendix C.
Lake Aeration and Other Approaches for Increasing
Levels of Dissolved Oxygen in Critical Fish Habitats
Low levels of dissolved oxygen may occur in lakes as a result of natural conditions
and cultural eutrophication. The lowest concentrations tend to occur in the deeper
waters of the hypolimnion during thermal stratification in late summer, during
long periods of snow and ice cover in winter, or in dense macrophyte beds at night
or following long periods of cloud cover (see Chapter 2).
One important option for lakes with dissolved oxygen problems is to manage
the fisheries for species able to tolerate relatively low levels of dissolved oxygen or
that do not inhabit areas of the lake (such as the hypolimnion) that experience
oxygen depletion. For example, many salmonid species require both relatively
high levels of dissolved oxygen and, because of their intolerance of warmer water
temperatures, must reside in the cooler waters of the hypolimnion during summer.
Therefore, to sustain a fisheries for salmonids may require an expensive and con-
tinuing effort to aerate the lake's hypolimnion during some or all of the summer.
Alternatively, if the problems with oxygen depletion are moderate, the lake may
be able to support coolwater or warmwater fisheries without extensive restoration
efforts. Dissolved oxygen and temperature limits for fish are discussed in Boxes 3-
C and 3-D in Chapter 3.
Problems with low dissolved oxygen can also be alleviated by doing one or
more of the following:
• Decreasing the quantity of organic matter decomposing in the lake (the
major process-consuming oxygen) by (a) limiting the export of organic
materials from the watershed to the lake, in particular excessive exports
associated with human activities, such as runoff from feedlots or direct
discharges of wastewaters; (b) dredging to remove organic-rich sedi-
ments; and (c) decreasing in-lake productivity by reducing nutrient
loads and nutrient availability.
• Increasing photosynthesis (an oxygen-generating process) by increasing
light penetration, especially during winter and in areas (deeper waters
of the hypolimnion) subject to oxygen depletion.
• Destratifying the lake (artificial circulation), bringing low oxygen
waters in the hypolimnion in contact with the lake surface and the well-
oxygenated waters of the epilimnion.
• Directly aerating the lake.
The approaches and optimal design criteria for lake aeration projects vary
somewhat for systems installed to alleviate problems with winterkill (oxygen
depletion during winter) as opposed to low levels of dissolved oxygen in the
hypolimnion during summer. During winter, the goal is not to aerate the entire
waterbody but instead to create an oxygen-rich refuge area for fish, generally near
the lake surface. Major design concerns include problems with equipment ice-up
and the need to minimize the loss or weakening of the lake's ice cover for safety
reasons. Hypolimnetic aeration systems must deal with the more difficult problem
110
-------
Chapter 8, Management Techniques for Improving and Maintaining Fisheries
of aerating waters at greater depths. Where the objective is to establish or main-
tain a coldwater fishery, hypolimnetic aeration must be achieved without dis-
turbing the lake's thermal stratification. Otherwise, low levels of dissolved
oxygen may be avoided by preventing thermal stratification through artificially
circulating the water column. In both cases, during both winter and summer,
maximum reliability at minimal cost are important design features.
• Pump and baffle aeration system. One type of winter aeration system is
the pump and baffle. Oxygen-poor water is extracted from a nearshore area of
the lake, pumped to the top of a chute on shore, and then allowed to cascade over
a set of baffles constructed from wooden boards (Fig. 8-2). The turbulence created
as the flow passes over the baffles helps to reaerate the water. The reoxygenated
water is then returned to a different part of the lake away from the intake area to
create a zone of oxygen-rich water.
Generally, approximately 10 percent of the lake's volume should be aerated
(McComas, in press). Thus, for a 100-acre lake with an average depth of 6 feet
(volume of 600 acre-feet), the objective would be to aerate 60 acre-feet or about
19.5 million gallons of water. A typical rig uses a 10 hp motor with a 6- or 8-inch
Figure 8-2.—Photograph of the pump and baffle system used for lake aeration to prevent
winterkill. The aerator pumps lake water to the top of a staircase and then the water cas-
cades down back to the lake (source: McComas, in press).
111
-------
Fish and Fisheries Management in Lakes and Reservoirs
The level of oxygen that
must be maintained
depends on the fish species
in the lake.
The most common cause of
failure in artificial
circulation projects is the
lack of sufficient airflow
to produce satisfactory
mixing.
pump that delivers between 1,600 and 3,000 gallons per minute or 2.3 to 4.3 mil-
lion gallons per day. Thus, a suitable refuge area for this lake could be created
within 5 to 10 days. For larger lakes, multiple rigs may be needed; therefore, the
pump and baffle technique could be too expensive.
The level of oxygen that must be maintained depends on the fish species in the
lake (see Box 3-C). The velocity of water discharged into the lake must be neither
too low nor too high. At low velocities, the amount of water released would be too
small to produce an oxygen-rich zone of sufficient size. At high velocities, the
reoxygenated water discharged will mix too thoroughly with the oxygen-poor
lake water, elevating the entire lake's oxygen level only slightly (and too little to
significantly improve fish survival), rather than creating a smaller refuge area with
higher oxygen levels.
Freeze-up can be a major problem with pump and baffle systems during espe-
cially cold winter days. Freeze-up may occur at the water intake, on the chute, or
at the water discharge. For example, when ice builds up, the chute may become
top-heavy and fall over. Thus, the system must be checked daily to ensure proper
operation.
Pump and baffle systems have several major advantages over other aeration
techniques. In particular, when properly operated, only a small area of the lake's
ice cover is opened. Open areas and thin ice are safety hazards for which the
operator of an aeration system is liable. All of the major pieces of equipment are on
shore. In addition, the chute can be mounted on a trailer and moved from one lake
to another or to different areas of the lake as needed. Generally, to prevent
winterkill, aeration will be required for about two months, depending on winter
conditions. By monitoring dissolved oxygen levels in the lake, the system can be
operated during only those times and winters when needed.
Some lake associations have built their own pump and baffle systems; how-
ever, these systems can be purchased as a unit from a number of manufacturers
(e.g., Crisafulli Pump Company, Glendive, Montana; H&H Pump, Inc., Clarksdale,
Mississippi). McComas (in press) provides further information on the construction
and operation of pump and baffle aeration units.
• Artificial circulation. Artificial circulation eliminates thermal stratification
or prevents its formation either by mechanical pumping or through the injection of
compressed air from a pipe or ceramic diffuser at the lake's bottom (Fig. 8-3). The
rising column of bubbles, if sufficiently powered, will produce lakewide mixing.
As a result, the conditions that create hypolimnetic oxygen depletion (i.e., isolation
of the deeper areas from the atmosphere with little to no primary production in
these darker waters) are eliminated.
The most common cause of failure in artificial circulation projects is the lack of
sufficient air flow to produce satisfactory mixing. On average, about 1.3 cubic feet
per minute of air flow is required per acre of lake surface to adequately mix the
lake and elevate levels of dissolved oxygen (Lorenzen and Fast, 1977). In general,
it is easier and more effective to apply the mixing energy early enough to prevent
stratification, rather than attempting to turn over an already stratified lake (Bums,
1988).
Artificial circulation is one of the most commonly used lake restoration techni-
ques (Cooke et al. 1986). An example of its usefulness for improving fisheries
yields is presented in Box 8-A. Other applications include Parvin Reservoir,
Colorado (Lackey, 1972) and Corbett Lake, British Columbia (Halsey, 1968). The
technique is best used in lakes that are not nutrient limited; nutrient concentra-
tions are often higher in the hypolimnion, and as a result, mixing can stimulate in-
creased algal growth. In addition, artificial circulation is not a viable option for
coldwater fish species, which use the hypolimnion as a thermal refuge during
summer.
112
-------
Chapter 8. Management Techniques for Improving-and Maintaining Fisheries
Figure 8-3.—Artificial circulation system installed at El Capitan Reservoir, California
(source: Lorenzen and Fast, 1977).
• Hypolimnetic aeration. Hypolimnetic aerators may be used to increase
oxygen levels in the hypolimnion without disturbing the lake's thermal stratifica-
tion. An airlift device (see Fig. 6-5, Olem and Flock, 1990) brings cold hypolim-
netic water to the surface. The water is aerated by contact with the atmosphere;
gases such as methane, hydrogen sulfide, and carbon dioxide that may accumu-
late under anaerobic conditions are dispersed; and the water is returned to the
hypolimnion.
Hypolimnetic aerators require a large hypolimnion to work properly and are
generally ineffective in shallow lakes and reservoirs. Costs depend on the
amount of compressed air needed, which is a function, in turn, of the area of the
hypolimnion, the rate of oxygen consumption in the lake, and the degree of ther-
mal stratification (Kortmann, 1989). Example applications include Waccabuc
Lake, New York (Fast et al. 1975), Larson and Mirror Lakes, Wisconsin (Smith et
al. 1975), and Tory Lake, Ontario (Taggart and McQueen, 1981).
Box 8-A.—Effects of Artificial Circulation
on Angling Success (Mosher, 1983)
Pottawatomie State Fishing Lake No. 1 (24 acres, maximum depth 20 feet) in
northcentral Kansas had problems with severe oxygen depletion at depths below 13
feet during thermal stratification. As a result, during summer 89 percent of the fish
were restricted to the upper 10 feet of the water column, in 1976 and 1977, a helixor-
type aeration unit was installed to prevent stratification. Consequently, dissolved
oxygen levels remained above 4 mg/Lthroughout the water column and 64 percent of
the fish occurred in deeper lake waters (below the 10-foot isopleth). Angler days of
fishing increased by 16 percent from 1975 to 1976 and an additional 17 percent in
1977. Channel catfish harvest increased 227 percent from 1975 to 1976, and 48 per-
cent from 1976 to 1977. The aeration unit was removed in 1978 and conditions
returned to those of the pre-circulation period; fishing pressure and harvest of chan-
nel catfish declined. Although circulation increased the channel catfish harvest at
Pottawatomie State Fishing Lake No. 1, no such increase (in fisheries yield or dis-
solved oxygen) was observed when the same operation was transferred to a larger
nearby lake. Apparently, the efficiency of the circulation unit was insufficient for the
larger lake volume (3.7 times larger than Pottawatomie State Fishing Lake No. 1).
113
-------
Fish and Fisheries Management in Lakes and Reservoirs
Even thin layers of snow
can greatly decrease light
penetration, which
decreases primary
productivity and can lead
to oxygen depletion and
winterkill
Waters may be natural
acidic or become acidified
as a result of acid mine
drainage, acidic
deposition, or runoff from
other anthropogenic
sources of acids.
Direct addition of
limestone to the lake
surface is the most
commonly employed
method for decreasing lake
acidity.
• Oxygen injection. Recent studies have shown that it is often more cost effec-
tive and practical to inject pure oxygen into the hypolimnion than to inject air or
aerate the hypolimnion through air-lift systems (Aquat. Syst. Eng. 1990). At
Richard B. Russell Reservoir, Georgia, dissolved oxygen levels in the hypolimnion
have been increased from < 3 mg/L to > 9 mg/L, with an oxygen transfer efficien-
cy of about 75 percent (Gallagher and Mauldin, 1987; Mauldin et al. 1988). Liquid
oxygen is stored in tanks on site and connected to several supply heads sub-
merged and anchored in the reservoir. Flexible membrane diffusers mounted on
the supply heads are used to maximize absorption efficiency and minimize main-
tenance requirements. Flexible membrane systems should last two to six years (or
10 years or more if operated a 6 months per year); the compressor and distribution
system should last substantially longer (an estimated 30-year life).
• Snowplowing to increase light penetration. Snow removal from the lake
surface to increase light penetration and photosynthesis (oxygen generation)
under the ice is a low-tech, low-cost alternative to aerators and maybe sufficient to
prevent winterkill in lakes with marginal levels of dissolved oxygen (McComas, in
press). Snow absorbs light much more effectively than ice. While 85 percent of the
available light will penetrate 5 inches of clear ice, 5 inches of snow over 3 inches of
ice will block out almost all light. Even thin layers of snow can greatly decrease
light penetration, which decreases primary productivity and can lead to oxygen
depletion and winterkill.
If lake associations use volunteers, they can remove snow at relatively low
cost. Snow should be removed from 30 percent or more of the lake surface, alter-
nating between strips of cleared area and snow, rather than clearing the entire
area. In general, snow removal prevents winterkill more effectively in shallow
lakes with abundant rooted macrophytes than in deep lakes where phytoplankton
are the dominant primary producer (McComas, in press).
Additional information on lake aeration systems can be found in Olem and
Flock (1990), Cooke et al. (1986), Lorenzen and Fast (1977), and McComas (in
press). The most cost-effective approach for increasing dissolved oxygen levels
depends on the size (area and depth) of the lake, nature and causes of the problem,
and fisheries management objectives.
JLalce Liming and Other Methods for Decreasing
Water Acidity
Waters may be naturally acidic (e.g., in regions with naturally acidic soils and
large inputs of organic acids) or become acidified as a result of acid mine drainage,
acidic deposition, or runoff from other anthropogenic sources of acids. Extensive
research has been conducted recently to refine and test methods for neutralizing
lake waters, using a variety of neutralizing agents as well as application tech-
niques. The Lake and Reservoir Restoration Guidance Manual (pages 155 to 159, Olem
and Flock, 1990) lists the following five basic approaches to treating acidic lakes:
• Limestone addition to the lake surface. Small limestone particles, lime-
stone powder, or a limestone slurry are dispersed by boat, plane, or helicopter
over the lake. Alternatively during winter, limestone can be spread on the ice by
truck, enabling it to enter the lake in the spring as the ice melts. Direct addition of
limestone to the lake surface is the most commonly employed method for decreas-
ing lake acidity. Because limestone is used for agricultural purposes, it is usually
available at low cost. However, the cost of limestone dispersal can be significant,
particularly for remote lakes without road access. In addition, repeated applica-
tions are needed; lakes with short water retention times may need to be treated an-
nually.
• Injection of base materials into the lake sediment. Limestone, hydrated
lime, or sodium carbonate can be injected into the lake sediments, resulting in a
gradual decrease in lake acidity. This technique is largely experimental, however,
114
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
and limited to small, shallow lakes with soft organic sediments and road access
for transport of application equipment. The treatment may last substantially
longer than surface applications; however, it disturbs the lake's benthic com-
munity, increases turbidity, and costs more.
• Mechanical stream doser. Lake acidity may be decreased by neutralizing
the acidic waters in upstream tributaries. Mechanical dosers are automated
devices that release dry powder or slurried limestone directly into the stream,
with the quantity of material added controlled by monitors of stream flow or
chemistry. The treatment is continuous, expensive, and generally not recom-
mended for lakes unless all other alternatives have been ruled out.
a Limestone addition to the watershed. Limestone is spread on all or
parts of the lake's watershed, decreasing the acidity of runoff and shallow
groundwater flow into the lake. Although the costs of one application are higher,
the overall costs may be lower than for limestone applications to surface waters
because the effects are much more long lasting. Watershed liming may be espe-
cially appropriate for lakes with short retention times (less than six months).
• Pumping of alkaline groundwater. Where abundant supplies of alkaline
groundwater are available, these waters may be discharged directly into lakes or
lake tributaries, decreasing acidity. Applications of this method have been
limited, however, and the costs and effectiveness of this approach are not well
known.
Many reports and books have been published on methods for liming lakes
and streams, including Fraser et al. (1982), Fraser et al. (1985), Olem (1991), and
Brocksen et al. (1992). Additional information can also be found in Olem and
Flock (1990).
Spawning Habitat Management
Fish production in some waters may be limited by the availability of suitable
sites for natural reproduction or the poor quality of available sites, resulting in
relatively low reproductive success. The types of habitats required for spawning
and the factors that influence spawning and reproductive success vary greatly
among species (see Appendix A). Thus, the methods employed for spawning site
management are also, to some degree, species-specific. The types of management
activities fall within three broad categories: (1) efforts to protect existing spawn-
ing habitat, (2) spawning habitat improvements, and (3) construction of new
spawning sites.
The first task required to protect or improve spawning habitat is to locate ex-
isting sites used by target fish species in the lake or associated streams. Some
species spawn in dispersed areas throughout the lake, while others concentrate
activities within fairly localized sites used consistently year after year. Potential
areas should be visited regularly during the spawning season by trained ob-
servers to look for spawning adults, nests, or egg masses. However, finding
spawning areas for species that spawn in deeper waters or that provide little
noticeable evidence of spawning activity (e.g., do not build nests or lay eggs in
visible masses) is much more difficult and time consuming. It will generally re-
quire SCUBA for underwater observations or sampling gear (see Appendix B) to
detect the presence of eggs in the bottom sediments or water column.
• Protection of spawning habitat. Many fish species spawn in relatively
shallow nearshore areas that are subject to disturbance from swimmers, boat traf-
fic, and runoff from the adjacent watershed. It may be necessary to limit con-
struction, land uses, or fertilizer applications in watersheds adjacent to critical
spawning areas, including tributary streams used for spawning, or to divert and
treat runoff that is high in suspended solids (to prevent excessive siltation that
would decrease egg and larval survival).
It may be necessary to
limit construction, land
uses, or fertilizer
applications in watersheds
adjacent to critical
spawning areas....
115
-------
Hsh and Fisheries Management in Lakes and Reservoirs
Silt can be removed from
spawning areas by using a
water pump to blow the
silt and algal growth off
the rocks.
The best time to build the
reef is during winter,
when it can be assembled
on the ice and left until
spring to fall into place as
the ice melts.
Fish species that guard their spawning nest, such as largemouth and
smallmouth bass and most sunfish species, are particularly susceptible to distur-
bances from swimming and boating. If repeatedly disturbed, males may eventual-
ly desert their nests, resulting in poor survival of eggs and fry. During spawning
season, important spawning sites can be identified with buoys, and boat traffic
and swimming should be restricted from these areas.
Waves rebounding off retaining walls may also drive off bass and sunfish
males guarding nests. Shoreline structures that better absorb wave energy, such as
riprap and vegetation, are preferable near important spawning areas.
• Spawning habitat improvements. Siltation is a major cause of degraded
spawning habitat. Some species such as bass, crappies, and bluegill sweep the nest
area off with their tails before spawning; thus moderate siltation is not a major
concern. Other fish such as walleye do not mechanically clean the lake bottom
before spawning; therefore, the buildup of silt in walleye spawning areas can sig-
nificantly decrease egg survival and may limit or prevent spawning activity.
Silt can be removed from spawning areas by using a water pump to blow the
silt and algal growth off the rocks. For example, a three-inch pump can generate
enough force to remove silt from the rock face or turn cobble-sized rocks over to
expose a new face. If mounted on a pontoon or raft, a water pump can clean
several spawning sites in half a day (McComas, in press).
Brook trout have fairly restrictive spawning requirements, and as a result, the
availability of suitable spawning areas is often an important factor limiting brook
trout natural reproduction and productivity. Brook trout prefer to spawn in areas
with upwelling, well-oxygenated groundwater in the littoral zone, tributary
streams, or the lake outlet. Plants and sediments can accumulate on these under-
water springs, obstructing groundwater flow and preventing brook trout spawn-
ing. The locations of underwater springs can be confirmed by inserting a small
diameter pipe, such as two-inch PVC-type pipe, into the lake bottom. If upwelling
groundwater is present, the water level in the pipe will rise above the lake level.
Small-scale dredging techniques may then be used to remove the blanket of
material obstructing the flow (see Chapter 4, Olem and Flock, 1990; McComas, in
press). Carline (1980) provides examples of the success of this technique for
spawning site improvements in Wisconsin lakes.
Finally, some fish species — including muskellunge and northern pike —
spawn in flooded marshes and other heavily vegetated areas in bays or river
floodplains. These heavily vegetated flooded areas also serve as important nur-
series for young fish of many species. Therefore, in lakes and reservoirs with con-
trolled water levels, reproductive success can be increased by raising water levels
in spring to coincide with fish spawning and species' early life stages. The role of
water level management for managing fisheries in lakes and reservoirs is dis-
cussed later in this chapter.
• Construction of new spawning sites. In some instances, it may be
worthwhile to add or construct new sites where important fish species can spawn.
However, even the best-looking spawning habitat is not always used for spawn-
ing. Thus, the construction of new sites alone does not ensure that natural
reproduction will be measurably increased.
Walleye spawn on rocky shoals in lakes or rocky areas in the white water
below impassible falls and dams in rivers. Thus, rock reefs constructed at water
depths of 1.5 to 4 feet may enhance walleye reproduction. The best time to build
the reef is during winter, when it can be assembled on the ice and left until spring
to fall into place as the ice melts (McComas, in press). Areas that receive silt-laden
runoff should be avoided, since siltation will quickly make the reef unusable. In
addition, the lake bottom in the area should be firm so that the added rubble will
not sink. If extra support is needed, first deploy 4 to 6 inches of large-sized gravel
116
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
1/2 to 1 inch in diameter. The reef should be a mixture of rock sizes, with about
10 percent of the reef consisting of rock 3 to 5 inches in diameter, 50 percent 5- to
7-inch rock, and 40 percent 7- to 9-inch rock. In total, the reef should be about 12
inches thick. The Minnesota Department of Natural Resources (1975) distributes
additional information on constructing walleye spawning shoals.
Spawning areas for lake trout have been constructed in a similar manner
with quantities of large rocks at selected sites. The Maine Department of Inland
Fisheries and Game dumped 170 tons of rock in a lake at a depth of 15 feet to pro-
vide a suitable spawning area for lake trout (Everhart and Youngs, 1981). Boxes
of gravel or graveling large areas have been used in warmwater lakes as spawn-
ing aids for nest-building species such as smallmouth bass. To encourage min-
now spawning and production, a variety of devices have been employed,
including cut brush along the shore, spawning slabs, and floating boards for
those species that lay their eggs underneath logs or other debris. Depending on
conditions in the lake and the target fish species, construction of new spawning
sites may be a cost-effective approach for improving fish production and yields.
Addition of Physical Structures for Fish Cover
Some lakes and reservoirs lack sufficient structural features and areas for fish to
hide — in particular, areas where younger, smaller fish can find cover to escape
from larger fish and other predators. Without adequate cover, survival rates of
young fish are often low, and high natural mortality rates can be an important
factor limiting fisheries yields in some lakes. Structural features provide safety
from predators, substrate for food organisms, and in some cases spawning
habitat. Also, predators, which include most game species, tend to concentrate
around structural features in search of prey. By concentrating fish into specific
areas, the addition of fish cover, such as artificial reefs, can increase fishing suc-
cess and angler satisfaction. In fact, the major impact of artificial reefs is often on
fishing success. The effects of increased cover on game fish numbers and growth
are less clear.
Fish cover can be provided by a variety of biological as well as physical
structures. For example, macrophyte beds and flooded marsh areas provide ex-
cellent nursery areas for young fish. For a discussion of aquatic plant manage-
ment for fish cover, see the next subsection.
Common types of physical structural habitat include docks and piers, fallen
logs, brush piles, rock reefs, and drop-offs as well as constructed artificial reefs.
The best reef design depends on the target fish species, available building
materials, and lake morphometry. However, three general design characteristics
should be incorporated:
• Maximum structural complexity to increase the number and variety of
hiding places and attachment surfaces for food organisms.
• Sufficient weight for stability so that the reef stays in place.
• Non-toxic materials that do not deteriorate in a short period of time.
Examples of construction techniques include the following:
• Brush piles. Brush may be held together using a frame constructed of heavy
wood or simply bundled together and weighted down with a concrete block to
sink (Fig. 8-4a). Although easy to construct, brush piles degrade relatively quick-
ly, releasing nutrients into the water column. Piles consisting of green trees and
brush with thicker branches are sturdier and longer lasting. Largemouth bass,
bluegill, and other panfish, in particular, may use brush piles for cover. For ex-
ample, Pierce and Hooper (1979) found 4 to more than 10 times higher densities
and biomass of largemouthbass, channel catfish, bluegill, and white crappie near
brush piles installed in Barkley Lake, Kentucky, than in control areas.
Depending on conditions
in the lake and the target
fish species, construction
of new spawning sites
may be a cost-effective
approach for improving
fish production and yields.
117
-------
Fish and Fisheries Management in Lakes and Reservoirs
(a)
(b)
(d)
CONSTRUCTION OF PYRAMID UNIT
CEMENT
PLUG
PVC PIPE
Figure 8-4.—Construction techniques for artificial reefs: (a) brush pile, (b) crib, (c) stake
bed, (d) piping, and (e) plastic structures (source: Phillips, 1990).
• Cribs. (Fig. 8-4b) Cribs are wooden frames constructed of heavy logs and
generally filled with large rocks and brush. Target fish species include walleye,
bass, panfish, and catfish.
• Stake beds. (Fig. 8-4c) Stake beds, generally constructed of green lumber,
consist of sawmill stakes and two-by-fours weighed down by concrete construc-
tion blocks. Primary target fish are largemouth bass, crappie, and panfish species.
• Piping. (Fig. 8-4d) Suitable fish cover can be made from vitrified clay, PVC, or
corrugated polyethylene pipes bundled together in a pyramid shape with a ce-
ment plug for ballast. Catfish and bullhead, in particular, use reefs made from
pipes.
118
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
m Concrete block/rubble/rock piles. Small piles of rock and broken con-
crete blocks of various sizes attract a variety of fish, including catfish, bass, pan-
fish, and walleye.
• Plastic structures. A variety of structures made of plastic have been
designed specifically to serve as fish cover (see Fig. 8-4e).
Artificial reefs should be placed in areas that lack natural cover where they
will be used by the targeted species of fish and are accessible to anglers. In addi-
tion, the reef must not pose a hazard to boat and skier traffic. Thus, reefs should
be located out of boating lanes and at sufficient depth to allow safe passage. The
reef location should also have a firm substrate such as sand, stone, or clay. Soft
bottoms of silt or mud are not recommended because the heavier reef materials
may eventually subside and disappear. Finally, artificial reefs should not be
placed directly on existing productive bottom habitat, such as natural shoals or
submerged trees or brush. Generally, several smaller reefs at a range of water
depths and locations are preferable to one large unit.
Because artificial reefs increase angler efficiency and can aggravate problems
associated with overfishing, they should not be installed in small or heavily
fished lakes. Furthermore, most of the research on artificial reefs has involved
warmwater or coolwater species; relatively little is known about the response of
trout and other salmonids. Guidelines for constructing and installing artificial
reefs have been prepared by the Sport Fishing Institute (Phillips, 1990) and also
many state fisheries agencies. Brown (1986) provides a review of the use of artifi-
cial structures in reservoirs (also see Box 8-B).
Aquatic Plant Management
While fish and fisheries generally benefit from adequate areas of fish cover, too
much cover can be detrimental. Smaller fish may have too many areas in which
to hide. As a result, survival rates will be high, possibly leading to overcrowding,
slow growth rates, stunted populations, and low yields of piscivorous game fish,
such as largemouth bass (see Chapter 3).
The most common cause of excessive fish cover is extensive growths of
aquatic macrophytes. In lakes and reservoirs where thick beds of macrophytes
cover a high proportion of the lake bottom, an aquatic plant control program
may be needed to improve yields of large predatory game fish and increase the
growth rates of panfish species, such as bluegill and white and black crappie. For
fisheries management, however, the goal is to reduce but not eliminate macro-
phyte growths. More so than for other lake uses such as swimming and boating,
fisheries are enhanced by moderate growths of aquatic plants. The complete
elimination of macrophyte beds maybe as harmful as excessive plant growths.
The specific objective of aquatic plant management, therefore, is to provide
the appropriate amount of aquatic plants, taking into account the effects of mac-
rophytes on fish communities (e.g., Fig. 8-5), other lake uses (e.g., swimming and
boating), nutrient cycles, and aesthetics. Macrophytes and terrestrial vegetation
also help stabilize the lake bed and shoreline, reducing problems with lake shore
erosion and high turbidity.
Excessive plant growths as a result of eutrophication or the inadvertent intro-
duction of an exotic macrophyte species are a common lake problem. The Lake and
Reservoir Restoration Guidance Manual (pages 135-151, Olem and Flock, 1990)
provides a thorough discussion of the various approaches to control nuisance
plant growths:
• Sediment removal and sediment tilling. Lakes can be dredged to remove
sediment and deepened so less of the lake bottom receives adequate light for
macrophyte growth. The maximum depth at which macrophytes can grow
[R]eefs should be located
out of boating lanes and at
sufficient depth to allow
safe passage.
For fisheries management,
however, the goal is to
reduce but not to
eliminate macrophyte
growths.
119
-------
Fish and Fisheries Managemenf'ln Lakes and Reservoirs
Bo;x 8-B>—The Use of Brush ^shelters as Cover by
Spawning Bass in Bull Shoals Reservoir
I (Vogele and» Rainwater, 1975) ;
Black bass, including largemouth, smallmouth bass, and spotted bass, prefer nesting
sites with cover. In some reservoirs with fluctuating water levels, the amount of avail-
able cover varies with the spring water elevation. Often natural cover is scarce in years
when water levels are low but abundant when water levels are relatively high. Suc-
cessful bass reproduction in these reservoirs appears to correlate with high springtime
water levels.
Brush shelters were added to selected areas in coves of Bull Shoals Reservoir in
the spring of 1972, when the water level was low. Observations indicated that spotted
bass consistently preferred to spawn near these sheltered habitats; largemouth bass
preferred nesting sites near the brush shelters early in the spawning season.
Smallmouth bass, on the other hand, exhibited no preference for areas with brush
shelters, but instead spawned primarily in areas with specific substrate types of rock
and gravel. Although the overall effect of the brush shelters on bass abundance was
not assessed, additions of brush piles and other structures may be a useful manage-
ment tool for improving bass reproductive success during years when springtime water
levels are low.
1.0 -
g 0.8 H
2 0.6-
w 0.4 -
1
* 0.2-j
sunfish
largemouth
bass
10
20
30
—I—
40
—I—
50
T—
60
70
80
—I—
90
—1
100
Percent plant cover
Figure 8-5.—Relative production of largemouth bass and sunfish as a function of aquatic
plant cover. Optimal plant cover for bass production is 36 to 40 percent, based on a
trophic model (source: Wiley et al. 1987).
depends on water transparency and the plant species. Hydrilla, a nuisance exotic
plant in southern waters, can grow at lower light intensities than native plants
(Canfield et al. 1985), making control through lake deepening a difficult task.
Reductions in nutrient loads to control eutrophication can increase lake
transparency, increasing the depth at which macrophytes can grow and counter-
ing the effectiveness of dredging to reduce macrophyte growth. Sediment removal
and tilling — e.g., rototilling using cultivation equipment (Newroth and Soar,
1986) — can also be used to disturb the lake bottom and tear out plant roots for
short-term macrophyte control. Both dredging and tilling can have negative side
effects, including destruction of the benthic community and an increase in tur-
bidity and siltation (Olem and Flock, 1990).
120
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
m Water level drawdown. In lakes where water levels can be controlled, lake
levels can be lowered to expose macrophytes in the littoral zone to prolonged
drying and/or freezing. Some species of plants are permanently damaged by
these conditions, which can kill the entire plant including roots and seeds after
exposures of two to four weeks. Other plant species are unaffected or even in-
crease (Table 8-3). Water level management to control macrophyte growths and
for other purposes is discussed further in the next section.
Table 8-3.—Response of common aquatic plants to water drawdown (source: Olem
and Flock, 1990). ___
DECREASE
INCREASE
VARIABLE
coontail
(Ceratophyllum demersum)
Brazilian elodea
(Egeria densa)
watermilfoil
(Myriophyllumspp.)
southern naiad
(Najas guardalupensis)
yellow waterlily
(Nuphar luteum)
waterlily
(Nymphaea spp.)
Bobbin's pondweed
(Potamogeton robbinsil)
alligatorweed
(Atternanthera philoxeroides)
hydrilla
(Hydrilla verticillata)
bushy pondweed
(Najas flexilis)
waterhyacinth
(Eichhornia crassipes)
common elodea
(Elodea canadensis)
cattail
(Typha latifolia)
m Shading and sediment covers. Covers can be placed on the water or sedi-
ment surface as a physical barrier to plant growth or to block light (Engel, 1984).
Sediment covers made of polypropylene, fiberglass, or other similar material can
effectively prevent growths in small areas, such as near docks and swimming
areas, but are generally too expensive to install over large areas. Applications of
silt, sand, clay, or gravel have also been used, but plants eventually root in them.
Shading to reduce growth rates can be provided by floating sheets of
polyethylene (Mayhew and Runkel, 1962) or by planting evergreen trees along
the lake shore (Engel, 1989).
• Introduction of grass carp. Grass carp is an exotic fish species that feeds
on macrophytes. The use of grass carp for aquatic plant management is discussed
in Chapter 9.
• Introduction off insects that infest macrophytes. Several exotic insect
species have been imported to the United States and approved by the U.S.
Department of Agriculture (USDA) for use in macrophyte control. Each insect
species grows and feeds on only select target plant species. In particular, insects
have been used in southern waters to aid control of alligatorweed and water-
hyacinth (Sanders and Theriot, 1986; Haag, 1986). Because insect populations
tend to grow more slowly than the plants, insects work best when used in con-
junction with another plant control technique, such as harvesting or herbicides.
No significant negative side effects from insect infestations have been docu-
mented (Olem and Flock, 1990).
• Mechanical harvesting. Mechanical harvesters constructed on low-draft
barges can be used to cut and remove rooted plants. Cutting rates range from 0.2
to 0.6 acres per hour, depending on machine size; Cooke et al. (1986) provide a
listing of commercially available plant cutters. Harvesters can effectively clear an
area of vegetation, although the benefits are only temporary. Rates of plant
regrowth can be rapid (within weeks) but can be slowed if the cutter blade is
lowered into the upper sediment layer (Conyers and Cooke, 1983). Removing cut
plants eliminates an internal source of nutrients and organics and can have long-
[HJarvesting operations
should precede spawning
periods and/or avoid
important spawning and
nursery areas.
121
-------
Fish and Fisheries Management in Lakes and Reservoirs
term benefits. However, some plant species, such as watermilfoil (Nicholson, 1981)
that can be fragmented and dispersed, actually increase in abundance after har-
vesting operations. Also, small fish can be caught and killed by mechanical har-
vesters. Thus, harvesting operations should precede spawning periods and/or
avoid important spawning and nursery areas.
• Herbicides. Herbicides used to kill aquatic plants include Diquat, endothall,
2,4-D, glyphosate, and fluridone (Olem and Flock, 1990). Although herbicide treat-
ments can rapidly reduce macrophyte growths, the benefits are short term and the
potential for negative side effects is high. Plants are left in the lake to die; decom-
position releases plant nutrients and, in some cases, causes oxygen depletion and
algal blooms. Plants generally regrow after several weeks or months or may be
replaced by other more tolerant macrophyte species.
Most chemicals currently approved are toxic to aquatic organisms and
humans only at relatively high doses. Little information is available, however, on
the long-term ecological consequences of herbicide use. Herbicide applicators
must be licensed, have adequate insurance, wear protective gear, use only EPA-
approved chemicals, and follow label directions exactly. Generally, because they
do not remove nutrients or organics from the lake or address the cause of the
aquatic plant problem, herbicides should be used only where other techniques are
unacceptable or ineffective. Westerdahl and Getsinger (1988) provide guidelines
for herbicide use and application.
Table 8-4.—Comparison of lake restoration and management techniques for control
of nuisance aquatic weeds (source: Olem and Flock, 1990).
TREATMENT (ONE SHORT-TERM
APPLICATION) EFFECTIVENESS
Sediment removal
Drawdown
Sediment covers
Grass carp
Insects
Harvesting
Herbicides
E
G
E
P
P
E
E
LONG-TERM
EFFECTIVENESS
E
F
F
E
G
F
P
COST
P
E
P
E
E
F
F
CHANCE OF
NEGATIVE EFFECTS
F '
F
L
F
L
F
H
E = excellent; F = fair; G = good; P = poor; H = high; and L = low, based on the consensus judgment
of 12 lake restoration experts.
The relative effectiveness, costs, and potential for negative side effects for each
of these techniques is summarized in Table 8-4.
In some lakes, especially newly impounded reservoirs, the problem may be
too few rather than too many macrophytes. In such cases, it may be desirable to in-
troduce (transplant) suitable plants — such as sago pondweed, wildcelery, and lily
pads — or raise water levels to flood vegetated areas. In lakes with fluctuating
water levels, terrestrial plants such as winter wheat or ryegrass can be planted in
the exposed lake bed during periods of water drawdown. These plants provide
both erosion control during drawdown and fish cover when the lake is reflooded,
with no risk of developing nuisance levels or excessive plant growths. Howells
(1986) and Evans (1989) provide guidelines for establishing plants in water fluc-
tuation zones and managing plant communities in southern reservoirs. The joint
use of plant and water level management to improve fish habitat is discussed fur-
ther in the next section.
Wafer Level Management
For many years, large fluctuations in water level were believed detrimental to fish
communities and fisheries. While large, uncontrolled fluctuations may be
detrimental, controlled changes in water level at the right time, place, and mag-
122
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
nitude can be beneficial and provide an important management tool for main-
taining and improving a lake ecosystem and fisheries. Water level management
can be used for a number of purposes:
• Water level drawdowns to control aquatic macrophytes and
periphyton. As noted in the previous section, water level drawdowns are one
of a number of approaches for controlling growths of aquatic plants. Not all
plants are equally susceptible, however, and growths of resistant species may ac-
tually increase (Table 8-3). Generally, both desiccation and freezing are required
to kill the roots and, in some cases, seeds of aquatic plants. Thus, drawdowns for
vegetation control are usually conducted during winter, and programs are con-
sistently successful only in areas where winter temperatures are sufficiently low.
For example, growths of Eurasian watermilfoil were actually more extensive
after a winter drawdown on a lake in Oregon where the mild, wet winter of the
Pacific Northwest did not provide adequate freezing (Geiger, 1983). By contrast,
winter drawdown in Murphy Flowage, Wisconsin, significantly decreased the
extent of macrophyte beds with an associated improvement in fishing. Winter
drawdowns have also been used to reduce growths of periphyton in walleye
spawning areas.
• Water level drawdowns to control overcrowded, stunted fish
populations. Water level drawdowns also may be used to counter the effects of
too much fish cover, which can result in overcrowded, slow-growing fish popula-
tions. When the water level is lowered, fish are forced out of macrophyte beds in
the littoral zone and into the open water. As a result, small fish are more suscep-
tible to predation; increased predation reduces the number of small fish, alleviat-
ing overcrowding problems. In addition, at least in the short term growth rates
and condition factors of predatory fish are improved. Increased feeding immedi-
ately after drawdown has been reported for northern pike, largemouth bass,
smallmouth bass, white bass, walleye, white crappie, and flathead catfish (Willis,
1986). To be most effective, drawdowns for fish control should be conducted
when lake waters are warm (above 55°F) and fish are actively feeding and should
last two to three months. However, after prolonged drawdown, fish growth may
decline as concentrations of prey diminish and invertebrate productivity and fish
reproduction remain low.
• Water level drawdowns to construct or enhance fish cover. In lakes
and reservoirs where the quantity of fish cover is inadequate, fisheries managers
may take advantage of water level drawdowns to enhance fish cover by building
artificial reefs or planting or allowing terrestrial vegetation to grow, which then
serve as spawning and nursery areas when water levels rise. Growths of ter-
restrial vegetation on emerged shoals may be especially useful in reservoirs with
high turbidity and inadequate light penetration for aquatic macrophytes.
• High water levels in the spring to provide increased spawning and
nursery areas. For some fish species, strong year-classes (i.e., high reproduc-
tive success) occur most often in years with rising or high water levels during
and for several months after the spawning season. The flooded vegetation and
marshy areas around the lake provide increased spawning substrate for species
like northern pike and muskellunge and nursery areas for the young of the year
of many fish species. Rapidly rising water levels also often result in at least a tem-
porary increase in food supplies and increased growth rates for opportunistic
fish — such as largemouth bass, sunfish, bullheads, and white catfish — that take
advantage of the influx of terrestrial invertebrates.
• Water level drawdowns during spawning to reduce the reproductive
success of undesirable fish species. If desired, water level management
also can be used to decrease the quantity of spawning substrate and nursery
areas, thus reducing reproductive success. Mortality of eggs and young-of-the-
year fish stranded by water level drawdowns has been reported for many fish
[Controlled changes in
water level at the right
time, -place, and
magnitude can be
beneficial and provide an
important management
tool for maintaining and
improving a lake
ecosystem and fisheries.
123
-------
Fish and Fisheries Management In Lakes and Reservoirs
Drawdowns should be
conducted only in lakes
with a steady water inflow
sufficient to refill the lake
when needed.
species. However, shifts in water level to either reduce or promote reproductive
success will have measurable impacts on fish abundance only if spawning and
early life-stage survival are critical limiting factors for the population. Water level
management as an approach to controlling year-class strength has been successful
only in some cases.
In lakes with a well-maintained outlet structure and drawdown capability, the
dollar costs of a water level management program are minimal, and any or all of
these actions may be useful for fisheries management. However, potential adverse
side effects include
• impacts on other lake uses, such as swimming and boating;
• damage to shore banks, shorelines, and shoreline retaining walls;
• reduced numbers and diversity of benthic invertebrates in the littoral
zone that are important prey items for some fish species; and
• an increased likelihood of winterkill during winter drawdowns.
Drawdowns should be conducted only in lakes with a steady water inflow suffi-
cient to refill the lake when needed. Ploskey (1982,1986) presents additional infor-
mation on the benefits and design of water level management programs.
Reservoir Construction
Physical features that can be altered only slightly once a lake is constructed may
drastically affect the fish community and cost of maintaining quality fishing. Fac-
tors such as watershed area, watershed usage, and the erodibility of soils in the
watershed will impact lakewater quality. Lake volume, mean and maximum
depth, watershed topography, shoreline development, and basin slope will in-
fluence the degree of thermal stratification and other lake characteristics that in-
directly affect the suitability of the lake habitat for fish. For example, Hill (1986)
identified three primary physical characteristics associated with the quality of
fishing in small reservoirs in Iowa:
1. the mean basin slope;
2. the watershed to lake area ratio; and
3. an adjusted siltation index based on the watershed to lake area ratio>
soil erosion rates for soil types in the watershed, and the proportion of
the watershed farmed using approved soil conservation practices.
All of these physical features can be determined before lake construction and
should influence site selection, lake design, and construction methods.
The following factors are relevant specifically to fisheries management and
important to consider when designing and constructing small lakes and reser-
voirs:
• The watershed should be well vegetated to prevent excessive siltation
and free of pesticides and other pollutants. Runoff from row crops, live-
stock operations, and industrial sites (or from areas where erosion can-
not be controlled) should be treated or diverted around the lake.
Limited lakeshore development and no septic discharges into the lake
should be allowed.
• The optimal watershed size and watershed-to-lake-area ratio depends
on the lake volume, rate of rainfall, and topography and land uses in the
watershed. In Georgia, the recommended watershed size for a small,
one-acre lake is about 10 acres of pasture or 25 acres of forested water-
shed (Ga. Dep. Nat. Resour. 1988). Illinois recommends 20 acres of water- -
shed per surface acre of water as a rule of thumb (111. Dep. Conserv.).
124
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
• The amount of timber and brush that should be cleared from the lake
basin before filling depends on the lake's size and planned uses. In
small lakes (< three acres), all trees, stumps, and brush should be
removed to produce the maximum harvestable fish biomass. In larger
reservoirs on the other hand, it is often desirable to leave small blocks
of well-placed timber and brush near the shoreline in coves and em-
bayments to provide fish cover. Timber should be cleared, however, in
the area of the dam in recreational and boating areas. It should be
cleared in the deeper parts of the reservoir where it is unlikely to im-
prove fishing and may aggravate problems with oxygen depletion as
the organic matter left behind gradually decomposes. Too much stand-
ing timber and brush can provide excessive fish cover and should be
avoided.
• If natural spawning areas and fish cover must be supplemented,
spawning sites and artificial reefs can be constructed more easily
before the lake fills than afterward.
• Extensive shallow areas will encourage growths of aquatic macro-
phytes, an undesirable feature in most small lakes designed for fishing
and fish production. Recommended slope ratios along the shoreline
are generally 2:1 or 3:1. Also, sand blankets, gravel beds, or fiberglass
mats maybe used to inhibit rooted plant growth in selected areas.
• Water depths should be sufficient to minimize problems with low
levels of dissolved oxygen in the winter and late summer. Illinois, for
example, recommends that lakes be at least one acre in area and 10 to
12 feet deep in 25 percent of the basin for successful fish management.
• The dam and water overflow should be constructed to allow easy con-
trol of water levels by using a drain pipe or gate valve. In most cases, a
standpipe overflow is recommended to draw water from deeper areas
of the lake.
• Upstream migration of undesirable fish and, to a lesser degree, the
downstream migration of game fish can be hindered by constructing
the emergency spillway with a substantial vertical fall of at least 4 feet
and sufficiently wide so that water depths over the spillway never ex-
ceed 2 inches.
Additional guidelines on the design and construction of small lakes and
reservoirs are available from most State fisheries agencies (e.g., Okla. Dep. Wildl.
Conserv. 1984; 111. Dep. Conserv.; USDA Soil Conservation Service, 1982).
Manipulating the Fish Community
Many fisheries management techniques involve the direct manipulation of the
fish community and other organisms that may serve as prey for or be predators
or competitors with the fish species of interest. Three of these activities are dis-
cussed here: game fish stocking, control of undesirable fish species and stunted
fish populations, and prey enhancements to supplement food supplies.
Game Fish Stocking
Stocking was once considered the panacea of fisheries management. If catch rates
declined or were too low, more fish were stocked. If anglers wanted bigger fish or
different kinds of fish and fishing opportunities, new, larger species were stock-
ed. Unfortunately, as a result of overzealous stocking programs in the past, native
fish communities have been disrupted, wild strains of fish have been lost, genetic
In larger reservoirs ... it
is often desirable to leave
small blocks of well-placed
timber and brush near the
shoreline in coves and
embayments to provide
fish cover.
Recommended slope ratios
^long the shoreline are
generally 2:1 or3:1.
125
-------
Fish and Fisheries Management in Lakes and Reservoirs
Stocking is not a panacea
or remedy for all problems,
but it does have a role in
fisheries management
when used in the right
manner and in the right
locale.
diversity has declined, and what were once considered desirable fish species and
stocked widely (e.g., the common carp) are now nuisance fish difficult to eradicate
in many waters and regions (Hebert, 1991; Allendorf, 1991).
Stocking is not a panacea or remedy for all problems, but it does have a role in
fisheries management when used in the right manner and in the right locale. If
reproductive success is limited by the absence or poor quality of available spawn-
ing habitat, stocking of young fish can supplement those produced naturally,
thereby increasing fish abundance and fisheries yields. If the lake is suitable for
fish survival and growth during only some parts of the year yet demands for fish-
ing opportunities are high, it may be worth the cost to establish a put-and-take
fishery, stocking large, catchable-sized fish each spring. Finally, introductions of
new species through stocking to increase and diversify fishing opportunities may
be appropriate and beneficial in some waters.
Stocking is not always successful, however, and can be an expensive error if
the returns from stocked fish are low and fishing quality is improved little, if at all.
Because of habitat constraints, food limitations, or an abundance of predators and
competitors, few of the fish stocked may survive or growth rates maybe slow. Ad-
ditionally, the fish added to the lake may simply replace an already existing
population and fishery, with no net increase in total yield or fishing opportunities.
Thus, before initiating a stocking program, carefully consider the following:
» Are there other management measures, aside from stocking, that could
achieve the fisheries goals and specific objectives at lower cost, with
longer-term benefits or with less disruption of the existing biological
community?
• What are the characteristics of the fishing demands? What kind(s), sizes,
and abundance of fish are desired?
• What are the characteristics of the species and strain(s) of fish being con-
sidered for stocking—their habitat requirements, growth potential, lon-
gevity, reproductive potential, and vulnerability to angling?
• What species and strains are best suited to the lake environment (physi-
cal, chemical, and biological characteristics of the habitat) and the fish-
ing demands?
• What impact will stocking have on resident wild fish and on other fish
and biological populations in the lake? Fish should never be stocked
where populations of suitable fish are already at the carrying capacity of
the waterbody. In addition, particular care should be taken to avoid in-
troducing species that will prey on desired species already present or
compete with them for food, shelter, or spawning habitat, or where na-
tive wild strains of the species still exist. Potential effects of fish intro-
ductions on other biota and water quality are discussed in Chapter 9.
• Is the introduced species or strain likely to migrate into other waters in
the drainage basin where it is not wanted and may cause harmful effects
to existing fish communities?
• What are the likely returns? What proportion of the stocked fish is likely
to survive and eventually be caught by anglers? By how much will
fisheries yields increase? To what degree will the quality of fishing in-
crease as a result of the stocking? How confident and reliable are these
projections?
• How long will the benefits last? Will the introduced fish reproduce or
must stocking be repeated annually?
» How many fish of what age and size should be stocked for maximum
return at the least cost?
126
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
• When and where should fish be stocked in the lake?
• How much will the stocking program cost, and how do the overall
benefits and costs compare? How do the net benefits (benefits minus
costs) of stocking compare to the net benefits from alternative manage-
ment measures for improving the fishery, such as habitat improve-
ment?
Allendorf (1991) summarized the following concerns regarding the introduc-
tion of normative fish species or strains through stocking programs: (1) Intro-
duced fish can adversely affect native fish and other biota through predation,
competition, hybridization, and the introduction of diseases (see Chapter 3). (2)
All fish introductions involve some ecological costs, and in general, current un-
derstanding of natural systems is not sufficient to accurately predict what these
ecological costs and damages will be. (3) The benefits of fish introductions occur
immediately, while harmful effects are often delayed. Furthermore, (4) most of
the harmful effects, including the loss of native fish populations and decline in
genetic diversity, are irreversible. Therefore, (5) the potential benefits and risks
associated with fish introductions must be carefully weighed.
Li and Moyle (1981) recommended that introductions of nonnative species or
strains be considered only for systems that have been so altered by human ac-
tivity that it is necessary to create a new biological community to take advantage
of the change in environmental conditions (e.g., in reservoirs or eutrophied lakes)
and also are isolated from other bodies of water so that uncontrolled spread of
the species is unlikely. Leach and Lewis (1991), Stanley et al. (1991), and Wingate
(1991) review Federal and State/provincial policies and regulations regarding
fish introductions in the United States and Canada.
Additional guidelines on fish stocking and fish culture can be found in
Stroud (1986).
• Uses. Stocking may be used to
• supplement an existing population (e.g., where natural reproduction
is not sufficient to satisfy angler demands);
• maintain a population that exists in a lake but cannot reproduce itself;
• add a new species to an existing fish community complex;
• restock waters after some natural or human-made catastrophe, such
as winterkill or pollution, or after chemical reclamation (fish
poisoning), discussed later in this chapter; or
• introduce fish into a newly constructed lake that is currently fishless.
Depending on the circumstances, the design of the stocking program and
major factors of concern will vary.
For lakes that are currently fishless, the need for stocking is obvious if a
fishery is desired. The major design objective is simply to select the species or
group of species best suited to the habitat that will best fulfill the fishing
demands (the goals and objectives of the fisheries management program; see
Chapter 5). The introduction of fish will, however, have major implications for
other ecosystem components, causing a shift in the abundance and composition
of amphibian, benthic, zooplankton, and other biological communities.
Likewise, for maintenance stocking of an already established population, the
need is clear (as long as it is desirable to maintain the current fisheries). The
major design concern in this instance is selecting the most cost-effective combina-
tion of how many fish, what size, and when and where to stock to produce the
maximum return at the lowest cost.
[Introductions of
nonnative species or
strains (should) be
considered only for
systems that have been so
altered by human activity
that it is necessary to
create a new biological
community to take
advantage of the change in
environmental conditions
An introduced species or
strain may adversely
affect existing fish
populations, resulting in a
net negative effect.
127
-------
Fish and Fisheries Management in Lakes and Reservoirs
It is preferable to stock
only species and strains
native to the region or
those routinely used in
fisJieries management
programs in nearby
waters.
Box 8-G.— Lake Characteristics Associated
(Bennettanjd McArthur£i990)
Attempts to introduce walleye into lakes and reservoirs where they do not already exist
have met with varying success, ranging from highly successful to complete failure. His-
torically, only about one in three attempts has resulted in the establishment of a self-
sustaining walleye population. Because of the expense and difficulties involved,
walleye should be stocked only into waters with a high probability of success. Analyses
by Bennett and McArthur (1990) identified three lake characteristics that were sig-
nificantly correlated with the success of walleye introductions:
» Larger lake area — The probability of success was higher in larger lakes and
reservoirs. In general, walleyes prefer lakes larger than 1,000 acres.
• Greater maximum depth — Success rates were higher in deeper lakes. Other
researchers have noted that walleye prefer thermally stratified lakes or
moderately shallow waters where shelter, turbidity, or water color shield their
eyes from light. Large, deep waters occlude light and thermally stratify.
" Higher pH — Walleye can successfully reproduce in waters with a pH of 6.0 to
9.0. The correlation between stocking success and higher pH may reflect the
direct effects of lake pH and also serve as a surrogate for other chemical char-
acteristics associated with pH, such as water hardness and calcium levels.
Walleye introductions were also more likely to be successful in older reservoirs
than in newly constructed reservoirs. Older reservoirs tend to have accumulated more
nutrients and generally are more mesotrophic.
Bennett and McArthur (1990) present predictive models to estimate a priori the
likelihood of successful stocking and identify target waters for walleye introductions.
On the other hand, for stocking new species into an existing fish community
and supplemental stocking, the value of stocking may be less certain. An intro-
duced species or strain may adversely affect existing fish populations, resulting in
a net negative effect. Supplemental stocking may or may not increase fish abun-
dance and fisheries yields. Only if stocking addresses key factors currently limit-
ing fish production in the lake will a supplemental stocking program have any
likelihood of success.
Stocking also can be used to introduce fish prey or predators and competitors
that may aid in controlling undesirable fish species. The emphasis in this section,
however, is on stocking target game fish. Stocking programs for prey, predators,
and competitors are discussed later in the chapter.
• How to determine the best species to stock. The species must be well
suited to the lake environment in terms of temperature preferences, oxygen re-
quirements, physical habitats for feeding and spawning, available prey, occur-
rence of predators and competitors, and all of the other physical, chemical, and
biological habitat characteristics that influence fish population success (see Chap-
ter 3 and Box 8-C). In addition, to the degree possible the species should reflect
angler preferences for particular types of fishing opportunities. Species highly
desired by local anglers should only be stocked, however, if they have a high prob-
ability of surviving and growing in the lake's environment without significantly
disrupting other important fish populations and biological communities.
It is preferable to stock only species and strains native to the region or those
routinely used in fisheries management programs in nearby waters. Introductions
of fish species that do not currently occur in other similar waters in the region are
less likely to succeed and more likely to result in unexpected adverse repercus-
sions, including the inadvertent invasion of the species into other waters in the
area. Stocking nonnative species is discouraged and should be done only with cau-
tion and when consistent with the overall lake management goals.
128
-------
Chapter 8. Management Techniques for Improving, and Maintaining Fisheries
Some combinations of species tend to work better than others, and most State
fisheries agencies have a pre-established set of recommended fish combinations
or types. For example, many warmwater fisheries programs rely on the combina-
tion of largemouth bass and bluegill sunfish, sometimes accompanied by channel
catfish and other sunfish species. Fish species may be selected because they fill a
particular niche in the environment or satisfy a specific fishing demand. For ex-
ample, striped bass stocking has been used to create a late fall and winter fishery
in many southern reservoirs. Striped bass and striped bass hybrids also have
produced midsummer pelagic fisheries on large open water reservoirs as well as
deep-Water trolling in mountain reservoirs.
Special hybrids or species strains are stocked in some cases because they are
more robust, faster growing, or have other desirable characteristics (e.g., low
reproductive potential for species that tend to overpopulate waters). Examples
include the striped bass-white bass hybrid, the tiger musky (northern pike-
muskellunge cross), and a variety of sunfish hybrids. The Florida subspecies of
largemouth bass generally grows faster and larger than its northern counterpart
but is also less tolerant of low water temperatures. In southern States as far north
as Oklahoma, Florida largemouth bass have been stocked into high quality bass
waters to provide trophy fishing.
Appendix A provides additional information on the preferred habitats and
characteristics of important game fish that may be used in selecting fish species
for stocking. However, consult a professional fisheries biologist before stocking
any fish. Most State fisheries agencies can provide expert advice on the best types
of fish to stock in a given region and lake type.
• Hatchery versus wild fish strains. Trout species, in particular, have been
raised for many years in hatcheries — so long, in fact, that distinct hatchery
strains of fish have developed. For generation after generation, those fish that
survived and grew best in the hatchery environment were selected for breeding,
eventually resulting in hatchery strains of fish better adapted for life in the
hatchery than in the wild. For example, compared to wild strains, hatchery
strains of brook trout
• feed better on hatchery diets (i.e., food pellets distributed on the sur-
face or sinking through the water column) than on natural diets;
• are more docile, with reduced fright reactions and territoriality (be-
cause hatchery fish are reared in the presence of humans and fed by
them, they are also much more easily caught by anglers);
• have less stamina and less ability to adapt to and withstand environ-
mental stresses (thus, hatchery strains are less robust than wild strains
when exposed to stressful conditions and environmental fluctuations);
and
» are faster growing and mature earlier, which generally means a shorter
life span (while wild strains of brook and rainbow trout often live to be
four to six years old, the maximum age for hatchery strains is typically
two to three years).
Similarly, years of selection in the wild have resulted in resident wild strains of
fish highly adapted for survival in their specific environment. A single species of fish
may have a number of recognizable strains from different regions or different types
of waters, each with subtle but important differences in their basic characteristics
that may affect their survival and growth in a given lake or reservoir.
When hatchery strains are stocked into waters that currently support wild
strains of the species, the added competition and interbreeding may result in the
decline and loss of the native wild strain. The characteristics of the wild strain
that made them especially robust and well adapted to their environment may be
irreversibly lost. Therefore, fish should be stocked into waters with existing
[CJonsult a professional
fisheries biologist before
stocking any fish.
129
-------
Fish and Fisheries Management in Lakes and Reservoirs
[F]ish should be stocked
into waters with existing
populations of the species
only after careful
consideration of the
potential for long-term
detrimental impacts on
native populations and the
loss of fishing
opportunities for unique
wild strains.
Many stocking programs
rely primarily on stocking
fingerlings.
High stocking rates may
lead to interspecies
competition and reduced
growth rates; low stocking
rates may produce fewer
fish of larger size.
populations of the species only after careful consideration of the potential for long-
term detrimental impacts on native populations and the loss of fishing oppor-
tunities for unique wild strains.
• What size fish should be stocked? Fish can be stocked into lakes and reser-
voirs as eggs, fry (1 to 4 months old and less than 1.5 inches), fingerlings (4 to 11
months old, finger length), yearlings (1-year-old fish), or adults. For any given
water and species, the selection of an optimal size for stocking depends on (a) the
availability and cost of obtaining fish of different sizes (some species are easier and
cheaper to rear than others) and (b) the abundance of predators and other factors
likely to result in poor survival of smaller, younger fish.
Many stocking programs rely primarily on stocking fingerlings. Poor survival
rates limit the usefulness of stocking eggs or fry. Fry stocking may be preferable,
however, in lakes that are currently fishless or for fish species that are difficult and
expensive to rear to the fingerling stage. The higher costs per fish often prevent ex-
tensive stocking of yearlings or adults. In some waters, however, the higher return
rates for larger fish more than make up for the higher initial costs per fish, so that
stocking yearlings or young adults may be more cost effective than stocking
fingerlings. It maybe necessary to stock older fish in lakes with poor food supplies
for young fish or very large predator populations. Also, if suitable spawning sites
are available, it may be cost effective to transplant sexually mature adults from
other nearby lakes.
Where fishing pressure is heavy and fishing opportunities are scarce, put-and-
take fisheries may be appropriate. Older fish of "catchable size" (generally 6 to 7
inches) are stocked into waters where they will be caught within a short period of
time. Survival for more than a year or even all of the year is not expected. Most
put-and-take fisheries target trout because of the comparative ease with which
these fish can be raised in the hatchery. The costs per fish are relatively high, how-
ever. Therefore, stocking of catchable-sized trout is justified only when
• a high proportion of the fish planted will be caught by anglers, with
anglers' fees covering the costs; and
• in the absence of a put-and-take fishery, fishing opportunities would
be minimal or inadequate to support the demand because the lake can
support fish during only some parts of the year and/or fishing
pressure is extremely heavy (e.g., lakes near large population centers
or in popular recreational areas).
• How many fish should be stocked? The optimal number of fish stocked
depends on
• the size of fish stocked,
» the size and productivity of the lake or reservoir,
• the fish species,
• the availability of suitable prey and habitat, and
• the objectives of the fisheries management program.
The smaller and younger the fish, the lower the expected survival and, thus,
the greater the number of fish that must be stocked. High stocking rates may lead
to intraspecies competition and reduced growth rates; low stocking rates may
produce fewer fish of larger size. Generally, the more productive the lake, the
greater the number of fish that the lake can reasonably support and the greater the
recommended stocking rate. Easily measured surrogates for lake productivity —
such as mean depth, total dissolved solids, and lake alkalinity — are often used to
estimate lake-specific stocking rates.
130
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
FERTILITY
MAP OF
ILLINOIS IMPOUNDMENTS
BASED ON ALKALINITY
OF THE WATER
Alkalinity
More than 100
PPM*
50 to 100 PPM*
Less than 50 PPM*
Fertility Rating
Good
Average
Fair
Fertility
Key
isMij
^
Approximate
Carrying Capacity
(Lbs/Acre)
LM Bass
100
50
25
Bluegill
400
200
75
*Parts per million
Locate your pond in the black, crosshatched, or clear areas in the map above. Use the
following chart as a guide for its initial stocking.
Initial Fish Stocking Guide
Fertility Key*
Soil Type of Pond
Black
:•• -yi-fSf-i
Light
.&»$••;?$
Forest
x\\\N
Black
\\\\S
Light
\\\\X
Forest
Black
Light
Forest
Number of fingerling fish stocked per surface acre
Largemouth Bass
Channel Catfish
Bluegill
100
100
1000
80
80
700
60
60
500
90
90
800
70
70
600
50
50
400
80
80
700
60
60
500
40
40
300
Bluegill/Redear
Combination
Bluegill
Redear
700
300
560
240
490
210
490
210
420
180
350
150
350
150
310
140
245
105
Figure 8-6.—Recommended fish stocking rates for small lakes in Illinois, based on sur-
face water alkalinity, soil type, and fish species (source: III. Dep. Conserv. 1989).
For many species and regions, general guidelines have been developed for
estimating stocking rates from basic information on the lake's characteristics.
State fisheries agencies are the best source of information on procedures for your
region and target fish species. Figure 8-6 provides an example for stocking fish in
small lakes in Illinois and Box 8-D, a method for calculating stocking rates for
rainbow trout in lakes in west-central North America.
131
-------
Fish and Fisheries Management in Lakes and Reservoirs
Fish should be stocked at
times and locations where
survival rates are likely to
be highest.
The cost-effectiveness of
any stocking program
should be continually
reevaluated.
Bok 8-D.—Stocking Density and Growth of Rainbow
Trout in Mountain Lakes of West-Central
; North America (Donald and Anderson, 1982)
Based on data for 24 small lakes in west-central North America at elevations of 1,000 to
11,000 feet, lake-to-lake variations in the size of age 2 rainbow trout were correlated
with the level of total dissolved solids, fish stocking densities, and the mean depth of the
lake. Total dissolved solids and mean depth are frequently used as indices of potential
fish production (see Chapter 3). Models derived from these analyses can be used to
determine optimal stocking densities for rainbow trout in similar waters to achieve a
given growth rate and size by age 2. For example, for lakes that were historically fish-
less and have little to no capability for natural reproduction, individual rainbow trout
weight (W, in grams) was predicted as follows:
W = -1.20(SD) + 6.34(TDS) - 90.77(MD) + 758
where, SD = stocking density of fingerling rainbow trout, in terms of the number of fish
per hectare; TDS = the concentration of total dissolved solids (mg/L); and MD = the
mean lake depth in meters.
Thus, if the desired weight of an age 2 trout is 1,000 grams (2.2. Ib) and the lake
has a TDS of 200 mg/L and mean depth of 5 meters (16.4 ft), then the recommended
stocking density would be 570 fish/hectare (or 230 fish/acre). Lakes with TDS of less
than 50 mg/L rarely produce large fish and should be stocked with fewer than 100
fish/hectare (40 fish/acre).
• When, where, and how should fish be stocked? Fish should be stocked at
times and locations where survival rates are likely to be highest. Most stockings
occur during the spring or fall when water temperatures are cooler because high
water temperatures combined with handling stress increase fish mortality rates. If
possible, avoid stocking in areas where predators concentrate. Fish can be trucked
to the lake or stocked from the air using a helicopter or fixed-wing aircraft.
The cost-effectiveness of any stocking program should be continually
reevaluated. If the returns do not justify the costs, the stocking program should be
discontinued or modified appropriately. As a general rule, catchable-sized fish
should be stocked only where at least 50 percent of these fish will eventually be
caught by anglers. For smaller fish, their total weight when harvested by anglers
should equal or exceed the initial weight of fish stocked.
Controlling Undesirable Fish Species and
Stunted Fish Populations
Within a given lake, some fish species may be "undesirable" because they interfere
with the survival and growth of "desirable" fish species or with other lake uses.
The term "rough fish" is frequently used to refer to these undesirable species. The
species categorized as rough fish vary from place to place and even over time. For
example, the common carp was originally introduced into the United States in the
late 1800s as a prized food fish. Yet today, carp are ignored by most anglers and
considered a nuisance fish in most waters. Northern pike are generally considered
game fish. However, in some waters pike compete with or prey upon other more
desirable game fish and therefore are considered undesirable rough fish. Many of
today's rough fish are nonnative species introduced inadvertently or purposely
into the drainage system in earlier years.
Fish control programs should be initiated only when clearly demonstrated
that reducing or eliminating rough fish will yield a cost-effective improvement in
the quality of fishing or other lake uses. In many cases, rough fish in reasonable
numbers do little or no harm, and spending time and effort on controls would
132
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
produce little benefit in return. Simply because a species does not contribute
directly to a fisheries does not make it undesirable. Ecological diversity by itself
is an appropriate and beneficial management goal (see Chapter 5).
Fish control programs may be warranted when
• common carp in a lake disturb the lake bottom during feeding and
spawning, increasing suspended solids and decreasing water clarity
(see Chapter 9),
• abundant populations of nongame species (or less desirable game
species) that compete with or prey upon desirable species (game fish
or prey species for game fish) funnel productivity away from target
species and decrease fisheries yields or fishing quality,
• populations of fish ordinarily considered desirable become un-
desirable when they occur in such large numbers and small sizes
(stunted populations) that they are of little sporting value,
• heavy infections of parasites in a species ruin the aesthetic qualities of
a fish population for human consumption, and
• lamprey (Petromyzon marinus) — a parasite on valuable commercial
and sport fishes in the Great Lakes and adjacent waters that can
decrease fisheries yields — are present in large numbers.
Several alternative approaches, which can be used alone or in combination to
control undesirable fish species and stunted fish populations, are:
• fish poisoning,
• extreme water drawdown,
• selective cropping,
• disruption of spawning behavior and reproduction,
• increased predation, and
• barriers to prevent the immigration of rough fish into a lake or reser-
voir.
• Fish poisoning. Poisoning all or most of the fish in the lake and then starting
over by reintroducing only desirable fish species (a process often referred to in
fisheries management as lake "reclamation" or "rehabilitation") is one of the
most extreme approaches to rough fish control. Because of the severity of the
treatment, fish poisoning should be used only as a last resort, only under condi-
tions where adverse side effects can be minimized, and only when it is likely to
successfully restore a quality fisheries over the long term. In all cases, State
authorities require a permit; in some areas fish poisoning is allowed only in spe-
cial circumstances, in others not at all.
Rotenone is most commonly used to poison fish. A natural substance that
comes from the stems and roots of a number of tropical plants, rotenone acts by
inhibiting a biochemical process at the cellular level, making it impossible for fish
to use oxygen. Thus, fish suffocate even though the water contains sufficient dis-
solved oxygen. At recommended doses, it is reasonably specific to fish. Humans
and other animals, with the exception of swine, can drink the treated water with
no ill effects; fish-eating birds and mammals can safely consume rotenone-
poisoned fish, and plants are not harmed. Snails, clams, and crayfish are also
quite tolerant. Rotenone applications do, however, dramatically reduce popula-
tions of zooplankton and aquatic insects. In addition, although adult frogs and
other amphibians are not affected, tadpoles and juvenile salamanders are usually
killed.
Because of the severity of
the treatment, fish
poisoning should be used
only as a last resort....
In all cases, State
authorities require a
permit; in some areas, fish
poisoning is allowed only
in special circumstances,
in others not at all
133
-------
Fish and Fisheries Management In Lakes and Reservoirs
Rotenone is manufactured under several trade names, and application rates are
product-specific. Generally, a concentration of about 2 ppm is toxic to fish, although
sensitivity varies by fish species (Fig. 8-7). Because rotenone is fairly expensive,
larger lakes with water level controls should be drawn down before applications,
reducing water volume and concentrating the fish in the center of the lake.
The most popular way of applying rotenone is spraying the solution from
pumps mounted in boats. Other methods include pouring the toxicant into the
prop wash of an outboard motor, towing bags of toxicant designed to dissolve
slowly, and spraying from planes and helicopters. Backpack pumps are used to
disperse the chemical in vegetated or swampy areas. If the lake is stratified or suf-
ficiently deep, the mixture should be pumped into deep-water areas through hoses
suspended from the boat. The toxicant should be distributed to all areas where fish
may occur or escape, including lake tributaries and marshy shorelines.
Some fish will begin to die within a matter of minutes; most will start showing
effects within an hour. More resistant species, however, may die over several days.
As many fish as possible should be collected and disposed of by burying in
suitable disposal areas (e.g., county landfills).
Rotenone is an unstable compound that breaks down quickly when exposed
to light, heat, oxygen, and alkaline water. At SOT, the water will detoxify in less
than four days; at 45°F, the water may remain toxic to fish for about 30 days. To
detoxify the lake more rapidly, add 5.5 percent potassium permanganate or
chlorinated lime to the water at a concentration approximately equal to the
original rotenone concentration applied. The lake can be restocked after the water
is determined to be no longer toxic, using in situ toxicity tests.
For most fish species, the toxicity of rotenone is greatest between 50° and 75°F.
The rate of detoxification increases with increasing temperature. All else being
equal, late summer may be the optimal time for rotenone applications. However,
for better public relations and to minimize interferences with other lake uses, lake
managers often apply rotenone in September or early October. Because fish eggs
are tolerant of rotenone, it should not be applied when rough fish species are
spawning.
V)
LU
o
W
BLUEQILL
LARGEMOUTH BASS
CHANNEL CATFISH
BLACK BULLHEAD
TOLERANCE
TO ROTENONE
Figure 8-7.—Relative fish species' sensitivity to rotenone, for selected species (source:
Sousa et al. 1991).
134
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
A number of publications provide more detailed guidance on the use of
rotenone for rough fish control, including Sousa et al. (1991), California Depart-
ment of Fish and Game (1985), Eschmeyer (1975), and Illinois Department of
Conservation (undated b). Both rotenone and potassium pemanganate are haz-
ardous substances; therefore, care in handling is required to avoid contact with
the skin and especially with the eyes, nose, and throat. All persons applying pes-
ticides, including rotenone, must be certified.
Various other poisons have also been used in fish control programs, although
none as widely as rotenone. Antimycin, an antibiotic produced in cultures of the
mold Streptomyces, is absorbed through the gills of fish and kills by interfering
with the respiration of the body cells. Concentrations of 2 ppb will kill sensitive
fish species, including most sunfish; higher concentrations (near 15 ppb) kill a
wider array of fish, including carp, suckers, and sunfish as well as most game
fish species (Berger et al. 1969; Gilderhus et al. 1969). Marketed under the trade
name Fintrol, antimycin is somewhat more expensive than rotenone but may be
better for some applications (e.g., thinning stunted populations of sunfish).
A few species-specific chemical fish toxicants have been developed for selec-
tive chemical control programs.
« The lampricide TFM is used to kill larvae and young adults of the
lamprey. At recommended doses, it does not affect1 trout and other
game species, although some species of minnows will show stress.
• Squoxin (l,l'-methylenedi-2-naphthol) is an effective toxicant for
squawfish (Ptychocheilus spp.), a common rough fish in the western
United States. It kills squawfish by acting as a vasoconstrictor, prevent-
ing efficient use of oxygen and the proper functioning of the blood ves-
sels. Applied at the recommended dose (about 0.1 ppm), squoxin will
not harm salmon and trout, although it may kill some nongame
species (e.g., dace and shiners). No effects have been reported on
aquatic insects, other fish foods, humans, or other terrestrial animals;
however, squoxin has not been approved for use by EPA.
Selective chemical treatments also may be achieved by applying general
toxicants such as rotenone only to selected habitats where undesirable fish
species are concentrated. Such partial lake treatments may be used to reduce
rough fish abundance or decrease the density of overpopulated, stunted popula-
tions of fish. For example, in large reservoirs individual bays can be treated to
reduce the numbers of stunted panfish, including bluegill or white and black
crappie. However, most species have a high reproductive potential, and therefore
beneficial effects from such treatments are likely to be short-lived.
Fish poisoning programs are not always successful. Some fish species, such
as bullhead, are especially resistant to chemical poisoning and may survive in
large numbers. Also, in large lakes with many difficult-to-treat refuge areas —
such as lake tributaries and outlets, adjacent marshes and other swampy areas,
and large underwater springs — a large portion of the rough fish population may
be unaffected. Finally, if reintroductions of rough fish species are likely from in-
terconnected waters either upstream or downstream of the lake, then the effec-
tiveness of the lake reclamation will be short-lived. If any of these situations
apply, a fish poisoning program should not be attempted.
State fisheries agencies (see Appendix C) should be contacted for information
regarding local regulations, permit requirements, chemicals approved for use in
certain types of waters, and suppliers and costs of approved fish poisons.
• Extreme water drawdown. A second drastic approach to rough fish control
is extreme water drawdown. Lake levels are dropped to very low levels, leaving
little or no standing water and resulting in substantial fish mortality. As for
rotenone, water level drawdowns affect all fish in the lake and are used primarily
135
-------
Fish and Fisheries Management In Lakes and Reservoirs
[T]he effects of such
selective fish cropping are
likely to be short-lived.
Reproduction will quickly
replace the fish lost unless
harvesting efforts are
repeated regularly and
often.
when fish communities are dominated by rough fish. The specific objective is to
eradicate or drastically reduce existing populations and then restock with
desirable fish species. Water drawdowns also adversely affect other lake uses and
biota and should be used only when such impacts are considered acceptable. Ob-
viously, water drawdowns are a management option only for lakes where water
levels can be controlled.
• Selective cropping. Another direct method for reducing the abundance of
undesirable fish species is simply to selectively harvest them in large numbers
and kill and discard the catch or sell the fish to commercial buyers. Fish can be
caught by using any of the sampling techniques described in Appendix B; choose
the most effective sampling gear, times, and locations (e.g., spawning habitats)
for catching the fish species of concern. Sampling methods that indiscriminately
kill all or most of the catch (e.g., overnight gill net sets) should be avoided, how-
ever.
As for partial fish poisoning, the effects of such selective fish cropping are like-
ly to be short-lived. Reproduction will quickly replace the fish lost unless harvest-
ing efforts are repeated regularly and often. Fish harvesting is also labor-intensive;
to be cost effective, the program must be operated by volunteers or as a commer-
cial fishery. In addition, the species being removed should be easily caught in large
numbers. One approach for encouraging selective cropping is to organize a fishing
derby, with prizes for the greatest numbers and biomass of fish removed. Changes
in fishing regulations also may be a useful part of a selective cropping program.
Fishing regulations and derbies are discussed later in this chapter.
Selective cropping is of little use if the objective is to markedly reduce or eradi-
cate rough fish. It may be a valuable fisheries management tool, however, for deal-
ing with stunted fish populations.
• Disruption of spawning behavior and reproduction. Rather than remov-
ing adults through selective cropping, you can reduce the species' reproductive
success. Projects to disrupt spawning behavior and reproduction are worth con-
sidering, however, only if the fish's spawning activities are reasonably con-
centrated in time and space, obvious, and easy to disturb. For example, yellow
perch lay their eggs in masses loosely attached to vegetation that can be easily
seen and removed in large numbers. Sunfish spawn in shallow littoral areas,
laying their eggs in nests visible from the shore or by boat. If you use a water
pump with sufficient discharge velocity, the eggs can be dislodged and scattered
and soon will be eaten by other fish. Alternatively, sunfish spawning beds can be
destroyed by dragging logging chains over the area behind a rowboat or simply
walking through the nests repeatedly if the water is shallow enough. Sunfish are
resilient, however, and often rebuild their nests and lay more eggs if disturbed.
Therefore, efforts must continue for several weeks throughout the spawning
season to be at all effective.
As for selective cropping, efforts to disrupt spawning and reduce egg survival
will generally have only a short-term effect, must be repeated regularly and often,
and are labor intensive. Thus, this technique is a useful fisheries management tool
only in some circumstances and for some species. Because survival rates of early
life stages are naturally quite low and often density-dependent (see Chapter 3),
measurable reductions in fish abundance are difficult to achieve.
Water level drawdowns during the spawning season also have been used to
reduce the reproductive success of undesirable fish species (see discussion of
water level management earlier in this chapter).
• Increased predation. Rather than attempting to decrease reproductive suc-
cess and increase fish mortality through direct human intervention, increasing
natural predation may be more efficient. Increased predation is often the best solu-
136
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
Box 8-E.—Predator Introductions to Control
Stunted Panfish Populations (Mosner, 1984)
Lyon State Fishing Lake, Kansas, contained an over-abundant, slow-growing popula-
tion of white crappie. In 1975, fingerling walleye were stocked at a density of 75 fish
per acre. Within four years, crappie numbers were reduced, while their total length in-
creased from a maximum of 10 inches to 15 inches. A12- to 15-inch slot length limit
on black bass initiated in 1978 probably also contributed to predation on white crap-
pie. A similar approach was used at Chase State Fishing Lake. However, the white
crappie population in Chase State Fishing Lake is extremely dense, and despite
repeated introductions, walleye have had limited success in establishing a viable
population.
tion for dealing with stunted fish populations. It may be achieved by introducing
a new predator, increasing the abundance of an existing predator population, or
increasing predator efficiency so that the same number of predators capture
larger numbers of prey.
Any species that is an effective predator on the target species can be used for
fish control (e.g., see Box 8-E). Northern pike are voracious predators, and intro-
ductions of pike are frequently considered for controlling stunted panfish
populations. As with any fish introduction, however, inadvertent negative side
effects on other components of the biological community are of potential concern
(see Chapter 9). Increased predator numbers may be achieved through stocking
or other fish enhancement programs or by limiting predator losses. Changes in
fishing regulations, for example, may be used to decrease fishing mortality and
produce more large game fish, which can result in increased predation on small
fish in the lake.
Many game fish are primarily sight-feeders, relying heavily on visual cues to
identify and capture their prey. Thus, increases in water clarity may indirectly
improve predator efficiency. Problems with high turbidity may result from abun-
dant phytoplankton and algal blooms or from heavy loads of suspended particu-
lates. Algal levels may be reduced by limiting nutrient inputs. Suspended solids
may be reduced by controlling watershed disturbances and development.
Methods for improving water clarity are discussed in further detail in The Lake
and Reservoir Restoration Guidance Manual (Olem and Flock, 1990).
Periodic water level drawdowns and reductions in aquatic plants may also
increase predator efficiency, as discussed in the subsections on plant and water
level management earlier in this chapter.
• Fish barriers. Fish barriers can be constructed on lake inlets and outlets to
prevent undesirable fish species from invading lakes in which they do not al-
ready occur or from which they have been eliminated by fish poisoning or water
drawdowns. The effectiveness of such barriers will vary among fish species;
species that are strong swimmers with substantial leaping ability will be more
difficult to exclude. In addition, it is more feasible and less expensive to build ef-
fective barriers on some types of inlets and outlets than others. Fish barriers are
more expensive on larger streams or rivers. They require frequent maintenance
or special, more expensive designs on waters with heavy loads of debris that can
quickly clog a simple fish screen. If screens become clogged during high flows,
the water and fish will simply flow over or around the fish barrier. In streams
with erodible stream banks, currents during high flows may soon cut under or
around the barrier, making it an ineffective impediment to fish movements. In
general, it is easier to prevent fish from moving upstream than downstream.
However, in the right circumstances, fish barriers can be built that will sig-
nificantly delay or prevent the invasion of undesirable fish species, thereby
avoiding future fisheries management problems.
Any species that is an
effective predator on the
target species can be used
for fish control.
Increased predation is
often the best solution for
dealing with stunted fish
populations.
137
-------
Fish and Fisheries Management in Lakes and Reservoirs
One of the simplest barriers is a velocity culvert where outgoing water is chan-
neled to produce high water velocities, preventing poor swimmers such as the
common carp from swimming upstream into the waterbody. A velocity culvert is
basically a stormwater culvert that is set at a steeper angle than usual. For ex-
ample, in Thompson Lake near Cosmos, Minnesota, a 3-foot diameter cement cul-
vert was installed with a 4.5-foot drop over a 142 foot length. This 3 percent slope
resulted in sufficient water velocities to prevent both carp and bullhead from
swimming up the culvert into the lake (McComas, in press). In a similar manner,
dams at a lake's outlet with significant head prevent the upstream movement of
fish species that have little or no jumping ability.
Simple bar screens or metal grates over a culvert or stream (Fig. 8-8) may be ef-
fective in waters with low velocities and where debris is not excessive. These
screens are usually made of narrow round iron bars. They should be installed in a
manner that will facilitate cleaning, especially during high flows when debris
loads are heavier. Often these screens are constructed with removable panels for
repair and easy cleaning. Bar screens have been used with some success to divert
large adult fish but cannot prevent the movement of small fish.
Other more elaborate types of physical barriers are described in Everhart and
Youngs (1981).
Electric screens represent an alternative to physical barriers that can be more
cost effective in some situations (Stewart, 1990). An electrode array, used to create
an electric field in the water column, is a small and inexpensive structure com-
pared with a dam or fence, does not interfere with water flow, and needs relatively
little maintenance. Most electric screens use low intensity fields (1 to 15 Hz)
designed to influence fish behavior (e.g., avoidance of the screen) without harm-
ing or stunning the fish. The design and efficiency of electric screens depend high-
ly on the species and environmental conditions (e.g., natural patterns of fish
behavior at the site). In general, electric fields are more effective (often 70 to 100
percent effective) at preventing upstream fish movements than downstream
migrations. Downstream fish movements can be controlled only at low water
Figure 8-8.—Example of bar screen fish barrier (source: McComas, in press).
138
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
velocities (less than about 1 ft/sec, 0.3 m/sec; Stewart, 1990). Screen efficiency
can also be increased by providing visual or audible cues so that the fish become
aware of the barrier before encountering the electric field.
Electric screens can be a hazard to swimmers, anglers, and boaters and
should be clearly marked with warning signs, lights, and/or buoys.
Prey Enhancement
Substantial quantities of readily available prey are required to support large
populations of stocked or naturally reproducing game fish. Fish growth rates
directly depend on food availability and the energy expended in obtaining suffi-
cient food (see Chapter 3). In addition, most game fish are top predators; that is,
they feed high on the trophic pyramid. Many feed primarily on other, smaller
fish; they have distinctly higher growth rates if small fish are available than if
forced to rely on other types of prey.
In some lakes, the quantity and/or quality (types) of prey available may be a
major factor limiting the numbers and growth of target game fish species. Two
methods for improving prey availability are (1) habitat improvements that can
lead to increased reproductive success and abundance of important prey species
that already occur in the lake and (2) introductions of new prey species to supple-
ment existing food supplies.
Prey introductions can serve to
• increase the total quantity of food available and/or
• increase the efficiency of energy transfers and the proportion of the
total lake productivity converted into game fish growth and
production.
The latter can be achieved by providing prey that (a) feed themselves lower on
the trophic pyramid, thus shortening the length of the food chain to fish, and (b)
are more readily caught and digested by game fish, thus increasing growth ef-
ficiency —that is, the proportion of food energy consumed that ends up as in-
creased fish growth rather than energy expended on prey capture or sustaining
the fish's basic metabolism (see Chapter 3).
• Habitat improvements to enhance prey availability. Most of the habitat
management techniques discussed earlier in this chapter would also directly
benefit game fish prey as well as game fish populations. Two techniques deserve
particular note: (1) efforts to provide sufficient but not excessive areas of fish
cover (either physical structures or macrophyte beds) and (2) spawning habitat
improvements directed specifically at increasing the reproductive success of im-
portant prey species.
Even though prey are abundant, they may not be available to predators if
macrophyte beds (or other structural features) cover all or most of the littoral
zone and lake bottom. With too many areas to hide, a relatively low fraction of
the prey biomass will be caught and converted into game fish biomass. Thus, ef-
forts to control aquatic plants generally benefit game fish growth by increasing
prey availability.
Approaches to increasing the reproductive success of prey, at least for forage
fish, are the same as for game fish species and may involve habitat protection,
improvements (e.g., silt removal), and construction of new spawning sites. Rela-
tively few forage fish species, however, have highly restrictive spawning habitat
requirements. Information for selected species is provided in Appendix A.
• Prey introductions. Introducing a new species into a lake ecosystem can
cause unexpected negative consequences by disrupting the existing biological
community and balances. The same cautionary statements presented earlier in
Most game fish.. .feed
high on the trophic
pyramid.
139
-------
Fish and Fisheries Management In Lakes and Reservoirs
Prey introductions should
proceed only with a high
degree of confidence that
the effort will result in a
significant improvement
in fishing quality and
little or no negative side
effects on other
components of the aquatic
community or other lake
uses.
this section for game fish stocking apply as strongly to prey introductions. All in-
troductions of normative species of fish or other taxa will cause some ecological
damage/ the extent of which can be only poorly predicted (Allendorf, 1991). There-
fore, before initiating a prey introduction program, carefully consider the follow-
ing questions:
» Is prey availability a major factor limiting game fish growth and
production? Would similar or better results be obtained through habitat
improvements or other means?
• Will the introduction of a new prey species significantly improve the ex-
isting prey complex by increasing the total amount of prey biomass
available or providing a preferred food source that will increase energy
transfer and/or growth efficiency?
• Does the lake provide suitable habitat for the prey species that will be
introduced? Is the introduced species likely to survive, reproduce, and
sustain a viable population despite heavy predation? (Only species with
a high probability of establishing a self-sustaining population should be
considered. Populations requiring repeated stockings each year or every
several years are generally not cost effective.)
• Will the total abundance of prey be increased, or will the new species
simply displace an already existing and desirable prey species?
• Will the introduction of a new prey species result in a significant in-
crease in game fish numbers or growth?
• What proportion of the prey biomass and productivity will be con-
verted into game fish production? Preferably, the prey species should be
susceptible to predation throughout all or most of its life cycle. Species
that grow quickly and are soon too large to be consumed by target game
fish should be avoided because much of the species' production would
never be channeled into game fish populations used by anglers. In addi-
tion, the prey species should occur in the same habitats and be readily
captured by game fish predators.
• Is there a chance that the introduced species will become over-abundant
and eventually a nuisance species? Will the new species have indirect,
detrimental effects; for example, by competing for food with other
desirable species?
• Is there a chance that the introduced species will migrate or be
transplanted to other waters in the drainage basin?
Prey introductions should proceed only with a high degree of confidence that
the effort will result in a significant improvement in fishing quality and little or no
negative side effects on other components of the aquatic community or other lake
uses. Li and Moyle (1981) recommended that introductions be considered only for
systems that have been so altered by human activity that it is necessary to create a
new community to take advantage of the change in environmental conditions
(e.g., in reservoirs or eutrophied lakes) and in isolated bodies of water, so that un-
controlled spread of the species is unlikely.
The type of prey best-suited for prey enhancement programs depends on the
target game fish species. Prey organisms that are commonly considered for such
efforts include the following:
» Threadfin shad and gizzard shad have been successfully introduced to
provide forage fish for a diversity of game species, especially in
southern reservoirs. Both feed on phytoplankton and zooplankton and
thus can efficiently transfer energy to piscivorous fish. Each species also
produces large numbers of young and can withstand all but the heaviest
140
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
predation. Gizzard shad, however, grow rapidly and may quickly out-
grow their usefulness as prey for younger fish and for predators with
smaller mouths.
• Silversides and minnow species also feed low on the food chain; how-
ever, they generally do not withstand heavy predation and may be
most useful as initial ("starter") prey when young predators are first
stocked into a lake. These species tend to disappear when predators
become larger and better established.
• Rainbow smelt, cisco, and alewife as well as two crustacean species, Mysis
relicta and Pontoporeia affinis, have been frequently introduced as prey for
lake trout and salmon populations, with varying success (see Box 8-F).
• Bluegill and other sunfish are important prey for largemouth and
smallmouth bass; yellow perch are important prey for northern pike.
All of these panfish species, however, are susceptible to overpopulat-
ing and stunting, can compete with young bass for food, and are
predators on bass eggs and larvae. Crayfish also have been introduced
as prey for black bass in some lakes.
There are as many or more examples of unsuccessful prey introductions as
there are successful programs. In some cases, introductions of new prey species
have had no measurable effect on game fish growth or abundance; in others, sig-
nificant declines or unexpected problems have resulted. Box 8-F provides ex-
amples of both successful and unsuccessful prey introduction projects.
Managing Fishing Pressure and Harvest and
the Fishing Experience
Anglers and fishing regulations play three important roles in fisheries manage-
ment. The success of a fisheries management program is determined largely by
the degree to which the desires and expectations of the fishing public are ful-
filled. Anglers, together with other lake users, define the management goals and
specific objectives (see Chapter 5). If angler expectations are unrealistic, even the
best management program will fail. An important component of all fisheries
management programs, angler education ensures that angler expectations and
quality standards are compatible with the natural conditions and uses that the
lake (and its watershed) can support most readily. Actively Involving anglers and
other lake users in the planning process, as discussed in Chapters 5 and 6, also
serves to better match expectations with cost-effective and realistic solutions.
Second, fishing mortality can have a major effect on the numbers, size, growth
rates, and productivity of fish populations. In combination with the myriad of
other factors that influence fish communities, the level, timing, and nature of fish-
ing mortality today will affect the quantity, sizes, and types of fish available in the
future — in other words, the quality of subsequent fishing experiences. Fishing
regulations, angler education, and controls on lake access are the primary means
of controlling fishing mortality and thus are important fisheries management
tools. Problems result from both overfishing and underuse.
Finally, the quality of a fishing experience is determined by more than just
the numbers and sizes of fish caught. The surrounding environment, the chal-
lenge, the level of effort, and other components of the overall experience all in-
fluence the angler's satisfaction. Many fishing regulations and management
activities serve primarily social objectives — that is, to improve the quality of the
experience rather than alter the fish resource per se. Limits on fishing gear (desig-
nating "fly-fishing only" waters) are one example of a regulation intended to in-
fluence the nature of the fishing experience more than the level of fishing
mortality.
The success of a fisheries
management program is
determined largely by the
degree to which the desires
and expectations of the
fishing public are fulfilled.
Fishing regulations,
angler education, and
controls on lake access are
the primary means of
controlling fishing
mortality and thus are
important fisheries
management tools.
141
-------
Fish and Fisheries Management in Lakes and Reservoirs
;Box 8-R-^-Examples of Successful and Unsuccessful
t ' Prey Introductions to Supplement Food
•j i Supplies for Game Fish Species
Havey (1973): Rainbow smelt were introduced in 1965-67 into Schoodic Lake, Maine,
as a new forage fish for landlocked Atlantic salmon. Within three years following the
initial planting, salmon growth rates had markedly increased. For example, the mean
length and weight of 3-year-old salmon increased from 374 mm, 468 g in 1965-67 to
442 mm, 814 g in 1968-70. Condition factors of salmon, ages 3 to 5 years, increased
from a mean of 0.76 in 1966 to 1.00 in 1969. One disadvantage of smelt as a forage
fish, however, is its extreme population instability. In 1971, as a result of a temporary
collapse of the smelt population, salmon growth rates and condition dropped sharply.
Mosher (1984): In 1974 and 1975 Lake Kahola, Kansas, contained an overabundant,
slow-growing white crappie population, with few individuals larger than 6 to 7 inches
long. In March 1976, the 400-acre lake was stocked with 75 yearling and adult gizzard
shad. By 1977, gizzard shad were numerous throughout the lake, and by 1980 anglers
were reporting 12-inch crappie. White crappie are still abundant in the lake, with many
small crappie, but more larger fish also occur, improving the fishing quality.
DeVrles et al. (1991): Threadfin shad were introduced into Clark and Stonelick lakes'
shallow turbid reservoirs in southwestern Ohio. In Stonelick Lake, abundant popula-
tions of threadfin shad resulted in a marked decline in zooplankton. Survival of young-
of-the-year bluegill also declined, perhaps because of the decreased availability of
zooplankton. In turn, limited survival of bluegill contributed to reduced growth of young-
of-the-year largemouth bass dependent on them for prey. The introduction of threadfin
shad, therefore, appears to have negatively affected growth and recruitment of both
bluegill and largemouth bass. Similar declines in zooplankton and fish growth and sur-
vival did not occur in Clark Lake.
Matuszek et al. (1990): The Cisco (Coregonus artedii) was successfully introduced in
1948 into Lake Opeongo, a 5,860-ha (14,480-square-mile) oligotrophic lake in south-
central Ontario. Data on lake trout growth, abundance, and yields were collected from
1939 to 1979 to assess long-term fisheries trends. Cisco are now the dominant food
item in the diet of lake trout in Opeongo Lake. This shift in diet was accompanied by a
complex array of changes in lake trout growth, fecundity, maturity, and population
abundance. Growth rates of older, piscivorous lake trout (ages 5 to 8) increased initial-
ly as Cisco abundance increased. Cisco abundance decreased as the density of pis-
civorous lake trout increased; the size of ciscos eaten declined as a result of heavy
predation. Growth rates of younger non-piscivorous lake trout (ages 1 and 2) declined
as their abundance increased and the occurrence of their insect prey decreased. As
ciscos became the dominant prey for adult lake trout, cannibalism by adults on
younger lake trout decreased, resulting in higher survival rates. Overall, the Cisco intro-
duction improved the lake trout fishery by raising the maximum sustainable yield from
about 0.18 kg/hectare to about 0.48 kg/hectare. However, model simulations suggest
that the lake trout population also is now more sensitive to possible overexploitation
(see Chapter 12 for further details).
Lasenby at al. (1986): The introduction of the crustacean Mysis relicta have been
shown to modify benthic, phytoplankton, zooplankton, and fish communities, with vary-
ing success relative to fisheries improvements (Table 8-5). Mysis were introduced into
Lake Tahoe, California-Nevada, from 1963 to 1965, and began appearing in large
numbers in lake samples and lake trout stomachs by 1971. The increase in Mysis
resulted in the loss of several cladoceran zooplankton species (Daphnia spp. and Bos-
mina longirostris) on which Mysis feed (Richards et al. 1975) and the eventual collapse
of the kokanee salmon population, which relied heavily on these zooplankton for prey.
Lake trout length and catch per unit effort also declined. Similar declines in kokanee
popujations occurred in Idaho and Montana lakes after Mysis was introduced (Rieman
and Falter, 1981; Rieman and Bowler, 1980).
Continued on next page
142
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
Box 8-F.—Continued
Table 8-5.—Fish population responses to introductions of Mysis rellcta into
British Columbia lakes (adapted from Lasenby et al. 1986).
LAKE
VIABLE
YEAR(S) POPULATION TARGET
INTRODUCED ESTABLISHED SPECIES
APPARENT EFFECT ON
TARGET SPECIES
SIZE
ABUNDANCE
Arrow (upper)
Arrow (lower)
Canim
Christina
Duncan
Grave
Kalamalka
Kootenay
Lac la Hoche
Missezula
Moyle
Okanagon
Otter
Pinaus
Slocan
Whatsam
Wood
1968, 1974
1974
1967-68
1968
1975
1979
1965-66
1949-50
1975-76
1975-76
1970
1966
1975
1965-66
1973-74
1974
1966
yes
yes
yes
yes
?
no
yes
yes
no
no
yes
yes
?
yes
yes
no
' no
kokanee
kokanee
kokanee
kokanee
kokanee
kokanee
kokanee
rainbow
kokanee
mt. whitefish
kokanee
kokanee
kokanee
kokanee
kokanee
rainbow
kokanee
kokanee
kokanee
+
+
?
0
0
0
0
+
+
+
0
0
0
+
0
+
+
?
+
-
—
—
?
0
0
—
—
?
?
?
?
-
—
?
?
?
?
—
? = not determined; + = positive effect; - = negative effect; and 0 = no effect.
Mysis have also been widely introduced into Swedish lakes. In response, benthio
feeding fish, such as brown trout, generally increase in abundance and size while
pelagic fish, such as Arctic char, decrease (Fiirst et al. 1986). As in North America,
Mysis results in a decline of cladoceran zooplankton; the pelagic fish that normally
feed on these zooplankton are unable to switch to a diet of Mysis. Increases in
phytoplankton biomass have also been observed in some Swedish lakes as an in-
direct effect of Mysis introductions and the subsequent decline in cladoceran
zooplankton (Kinsten and Olsen, 1981; also see Chapter 9). Because of these mixed
results, the Mysid Research Group (Morgan, 1982) recommended a moratorium on
further introductions of Mysis rellcta for fisheries management until understanding of
ecosystem responses to these introductions improved.
Regulations and Their Effects
Fishing regulations should be as simple and as few as possible. None should be
implemented unless it will measurably improve the quality of the fishing ex-
perience or long-term sustainability of the fisheries resource. Even more so than
for other management actions, fishing regulations have a direct impact on and
should be closely tied to the pre-established management objectives for the lake.
Some of the regulations widely applied in the past were based on over-
simplified assumptions and theories that subsequent research has found to be
false or inappropriate for many waters. Examples of these often erroneous as-
sumptions include the following:
• If fewer fish are caught now, more fish will be available for future fish-
ing. However, if natural mortality rates are high and density-depend-
ent (see Chapter 3), this assumption will not necessarily hold.
• A fairly large number of mature fish should be protected to allow for
sufficient spawning stock. While true for some species such as salmon,
most fish species are extremely prolific. Each individual female fish
produces large numbers of eggs, and as a result, sufficient numbers of
Fishing regulations should
be as simple and as few as
possible.
143
-------
Fish and Fisheries Management in Lakes and Reservoirs
Regulations can be used to
reduce the total quantity
offish caught and
removed; selectively
harvest, or protect, certain
portions of the population;
influence or control the
type of fishing experience;
and encourage a more
equitable distribution of
the catch among anglers.
Minimum, maximum, and
slot size limits have been
applied, depending on
conditions in the lake and
the management
objectives.
eggs can be produced by relatively few fish. For these species, reproduc-
tive success is determined more by environmental variables than by the
number of spawning fish.
• Fish should be protected from fishing during the spawning season to
ensure adequate reproduction. Again as noted above, for most species
the number of mature fish that successfully spawn is rarely the
dominant factor controlling the number of progeny produced. Closed
fishing seasons during spawning are justified only if the numbers of
spawning fish are very low or if fish are highly vulnerable to capture at
that time.
• Smaller fish should be protected because they will eventually grow into
bigger fish. However, many lakes suffer from overpopulation and too
many small fish; competition for a limited food supply may result in
poor growth rates and stunted fish populations. In these instances, fish-
ing regulations that protect small fish have detrimental effects on fish-
ing quality.
In some instances, controls on fishing pressure and harvest are needed either
to protect and improve the fisheries resource or for social objectives. Regulations
can be used to
• reduce the total quantity of fish caught and removed;
• selectively harvest, or protect, certain portions of the population;
• influence or control the type of fishing experience; and
» encourage a more equitable distribution of the catch among anglers.
The types of regulations used in recreational fisheries include the following:
• Creel limits, which prescribe a maximum number or biomass of fish (or
maximum number of fish of a certain size range) that can be harvested
per angler and per fishing trip. Creel limits may be used to reduce fish-
ing mortality in lakes that are heavily fished and encourage a more
equitable distribution of the catch among anglers.
• Quotas, which define the maximum total number or biomass of fish that
can be removed from the lake over the entire fishing season or by each
individual angler. In both cases, the use of quotas requires some method ,
for tracking and quantifying all fish harvests. In privately owned
waters, quotas may be used as a voluntary means of preventing over-
fishing, especially on small lakes with relatively few large game fish.
• Size limits, where all fish outside of the allowable size range must be
returned unharmed to the water. Generally, the primary objective is to
increase the mean size of the fish caught and/or allow more fish to
grow to reproductive maturity. Minimum, maximum, and slot size
limits have been applied, depending on conditions in the lake and the
management objectives. The role of size limits in fisheries management
is discussed further in Box 8-G.
• Catch and release programs, which require all fish caught (or a percent-
age of the catch) to be returned unharmed to the water; thus, fishing
mortality is greatly reduced. Only some of the fish caught will die as a
result of the stress caused by hooking, playing, and handling. Catch and
release programs may be particularly appropriate for waters that are
heavily fished, during fishing tournaments when lakes are subject to
heavy fishing pressure, or for protected species or strains (e.g., wild
strains or threatened or endangered species) that occur in a mixed
fisheries.
144
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
Box 8-G.—The Role of Size Limits in
Fisheries Management
(adapted from Brousseau and Armstrong, 1987)
Size limits may be used in fisheries regulations for several purposes:
• to maximize yield,
• to prevent overharvest and depletion of stocks,
• to maintain favorable fish population and community structure,
» to maintain favorable fish population dynamics and production (e.g., satisfac-
tory rates of growth, mortality, and reproduction), and
• to sustain the quality of fish and fishing.
These objectives can only be met if size limits are properly applied.
The traditional approach to length-based harvest regulations has been to impose
a minimum size limit. It is generally assumed that, by setting a minimum size limit and
returning small fish, harvest can be maximized and the mean fish size increased.
Generally, the size limit is established so that the majority of fish harvested would
have spawned at least once before capture.
Results from minimum size limit regulations have been mixed, however. When
small fish are protected, the increase in population density can lead to a significant
decrease in fish growth rates. High rates of natural reproduction combined with a
slow growth rate can result in large numbers of under-sized fish and relatively few
legal-sized fish; thus fisheries yield decline. Minimum size limits should be applied
only where
• the fish population has a low natural reproduction potential,
• growth rates are high, especially among younger fish,
• natural mortality rates are low, and
• fishing pressure and fishing mortality rates are high.
Slot size limits protect fish within a specified intermediate size range. Harvests of
smaller fish are allowed to "thin out" large year classes at relatively small sizes and
reduce intraspeeific competition for food, thus improving fish growth rates. As long as
reproductive rates are adequate, the younger, smaller fish caught may be able to
satisfy those anglers fishing mainly for food. At the same time, by protecting fish of in-
termediate size, more fish of "trophy" size should eventually be available. In theory,
slot limits should sustain angling yields and allow increases in fishing effort without
adversely affecting fishing quality in terms of catch rates and the size of fish caught.
Slot size limits are most appropriate for fish populations with the following charac-
teristics:
• good natural reproduction,
• slow growth, especially of young fish,
• relatively high natural mortality of young fish, and
• high angling effort.
Maximum size limits may be useful where protecting brood stock is necessary ,
such as in highly exploited populations with a low density of mature fish, and where
recruitment may be low. Maximum size limits are rarely used, however, largely for so-
cial rather than biological reasons. For both slot limits and maximum size limits,
anglers have resisted regulations that require releasing fish of moderate to large size.
Problems with slot size limits can also occur if anglers release a high proportion of
the small fish caught (resulting in an overabundance of small fish and reduced growth
rates). Both programs, therefore, necessitate an associated user education program
to improve angler compliance.
145
-------
Fish and Fisheries Management in Lakes and Reservoirs
For any regulation to
work, a high degree of
voluntary angler
compliance is essential.
... A positive, intensive,
and well-conducted public
information program is
critical, therefore, to the
successful use of fishing
regulations for fisheries
management....
[I]t may be desirable to
build various user
conveniences that tend to
encourage fishing pressure
... [in] lakes where the
fish resource is currently
underused.
• Restrictions on gear types, either to protect certain sizes or groups of
fish or for social objectives. Examples include fly-fishing only areas,
minimum hook sizes (to reduce the catch of small fish), and restrictions
on the number of hooks per lure. Recreational fisheries are restricted for
the most part to hook and line fishing. Netting and most other capture
techniques, described in Appendix B, may be used for research and
management purposes only.
• Limits on the number or type of fishing units, for example, limiting
anglers to a single rod when trolling or to a set number of tip-ups
during ice fishing. Motorboats may be prohibited or motor sizes
restricted both to limit the total catch and to influence the nature of the
fishing experience.
• Fishing closures, which prohibit fishing in particular areas or during some
seasons; for example, to protect fish during spawning or while migrating
through areas where they may be particularly vulnerable to capture.
For any regulation to work, a high degree of voluntary angler compliance is
essential. If anglers are unaware of or do not understand the need for a regulation,
high noncompliance rates will render the regulation ineffective. A positive, inten-
sive, and well-conducted public information program is critical, therefore, to the
successful use of fishing regulations for fisheries management and especially for
innovative approaches or experimental regulations.
Fishing Derbies and Tournaments
Fishing derbies and tournaments can be an integral part of a fisheries management
program. As noted earlier in this chapter, they are one method for reducing un-
desirable and stunted fish populations. By offering prizes or other incentives, lake
managers can concentrate angler effort on particular fish species or size ranges.
Where fisheries resources are underused, a fishing tournament may result in a
long-term increase in fishing activity and yields. Finally, fishing derbies can be or-
ganized as money-raising events, with the money used to fund other fisheries or
lake management projects. Fishing tournaments, however, are illegal in some
States (e.g., Oregon), strongly objected to by some anglers and conservation
groups, and can interfere with other lake uses. Therefore, these events are ap-
propriate management options only when consistent with the overall, long-term
management goals for the lake.
User Conveniences
Fish may be plentiful in a lake but few caught because of low fishing pressure. As
part of a fisheries management plan, it may be desirable to build (or remove)
various user conveniences that tend to encourage fishing pressure as well as make
fishing more convenient and enjoyable. The addition of user conveniences may be
particularly appropriate for lakes where the fish resource is currently underused.
Three types of user conveniences may be considered:
• improved lake access, through purchases of rights-of-way, trail con-
struction or maintenance, or road construction and improvements;
• construction or upgrading of boat ramps; and
• construction of fishing piers that allow anglers better access to deeper
waters and provide areas for fish cover and concentration, thereby in-
creasing capture efficiency. Earthen piers also effectively increase the
length of the lake's shoreline.
Mosher (1984) presents several inexpensive methods for improving and con-
structing user conveniences.
146
-------
Chapter 8. Management Techniques for Improving and Maintaining Fisheries
Conclusions
Many methods are available, therefore, for maintaining and improving fisheries
in lakes and reservoirs (Fig. 8-1). The best approach for any given lake and situa-
tion will vary depending on the target fish species, nature of the problem,
management goals and objectives, and characteristics of the lake. There are no
cookbook solutions, although experience has demonstrated that some methods
tend to work better in certain situations and for some problems than others (see
Fig. 8-9). Appendix A provides a brief discussion of the most commonly used
management techniques for selected game fish species, and Chapter 12 describes
several case studies of fisheries management programs.
Unnecessary management and overmanagement are as undesirable as no
management at all. Fish communities and fisheries should be monitored routine-
ly to continually assess the effectiveness of management actions and the manage-
ment plan altered appropriately. For example, stocking too many fish in a lake
may not only lead to an overcrowded fish population but is also a waste of
money and resources. The goal should be to select and apply the approach(es)
that will achieve the highest quality fishing possible for the lowest cost and effort
and also ensure the long-term sustainability of the fish resource and lake ecosys-
tem.
Walleye Management Flow Chart
I *
-J Fish
Walleye
Population
Satisfactory
1
i
Population
Not Being Used
1
DOT I
ability |
J Forage ~j
1 Removalj
-[_ Rehabilitation
Reduce
Stocking
Rate or
Frequency
1
Lack of
Public r
Awareness
I Alert 1
| Public |
i
J
r 1 option has limited
[Population 1
[Being Used]
Evaluate
Present
Management
J N° I
"jChangej
Reduce
- Stocking i(
Warranted
No
Management
Walleye
Population
Inadequate
1
J Inadequatel
~j Forage j
Reduce
- Competitor
Abundance
Reduce or
Eliminate
" Competitor
Stocking
1 Forage 1
") Introduction J
Reduce
Walleye
Stocking
Quota
High
_ Predator
Population
Reduce
- Predator
Abundance
Reduce or
Eliminate
" Predator
Stocking
High
._ Fishing
Pressure
J Special j
~] Regulations]
1 Adjust
n Stocking \
-) Rehabilitation |
J Habitat
[Degradation
i-j Aeration""]
I Roughlishj
"| Control |
f Pollution j
"1_cp_n_t_f°l I
Stock Fry
After
Winterkill
-j Rehabilitation j
H
-
Inadequate
Natural
Reproduction
Stocking 1
Water
Level
Managemen
Artificial
Spawning
Areas
Protection
of Brood
Stock
Removal
ol
Migration
Barriers
i 'application
Figure 8-9.—Walleye management flow chart, Identifying the major management options
available for various walleye management problems (from Minn. Dep. Nat. Resour. 1982).
There are no cookbook
solutions...
Fish communities and
fisheries should be
monitored routinely to
continually assess the
effectiveness of
management actions and
the management plan
altered appropriately.
147
-------
-------
CHAPTER 9
Methods for Using Fish
to Improve Water Quality
Chapter Objective
Changes in the fish community directly and indirectly affect other components of
the lake ecosystem, including biological, chemical, and physical lake charac-
teristics (see Chapter 2). Therefore, it may be possible to manipulate the fish com-
munity specifically to improve and maintain water quality. This chapter
describes the current state-of-the-science regarding biomanipulation — that is,
purposely altering the biological community to achieve water quality manage-
ment objectives: methods that have been proposed and tested; their success, ad-
vantages, and limitations; and remaining uncertainties. Only biomanipulation
techniques involving fish management are reviewed.
Biomanipulation is just one of a number of approaches to water quality
management and often works best when applied in conjunction with other
management techniques. Olem and Flock (1990) provide a more comprehensive
discussion of methods for water quality restoration and management.
In addition, biomanipulation — using fish to improve water quality — must
be viewed as complementary to fisheries management (Chapter 8). Fish can be
managed to improve fishing quality (fisheries management) and water quality
(biomanipulation). Often the two conflict, however. A management program
designed to optimize fishing quality may degrade water quality, and vice versa.
Thus, the selection and prioritization of management objectives, as discussed in
Chapter 5, are critical to defining the best overall fish management program to
achieve the appropriate balance between fisheries and water quality and all lake
uses and values.
Background
Biomanipulation, as a distinct field and tool for water quality management, was
first suggested by Shapiro et al. (1975). Since that time, a wide range of experi-
ments and applications have been conducted and the fundamental principles
and usefulness of biomanipulation have been firmly established. Nevertheless,
biomanipulation is still in an early stage of development; it is an active area of re-
search rather than a tried-and-proven management technique (Crowder et al.
1988; Lammens et al. 1990). Ecosystem interactions are complex and only partial-
ly understood. As a result, it is difficult to predict a priori the full suite of out-
comes that will occur in response to a change in the biological community.
Surprises are common, and reliable prescriptions for biomanipulation cannot be
Biomanipulation is just
one of a number of
approaches to water
quality management and
often works best when
applied in conjunction
with other management
techniques.
149
-------
Fish and Fisheries Management in Lakes and Reservoirs
The benefits of
biomanipulation make
efforts to investigate and
implement this technique
worthwhile, given
appropriate controls and
caution.
defined. Despite these limitations, the benefits of biomanipulation — its relatively
low cost, the absence of machinery and toxic chemicals, and its potential effective-
ness — make efforts to investigate and implement this technique worthwhile,
given appropriate controls and caution. The high level of interest in the topic is
evident from the number of recent symposiums and publications on biomanipula-
tion and related fields (e.g., Carpenter, 1988; Benndorf, 1988; Gulati et al. 1990).
The term "biomanipulation" in this manual is used in a broad context to in-
clude any management technique that relies on altering the fish community to im-
prove water quality — to reduce nutrient levels, increase water clarity, reduce
growths of algae or macrophytes, or otherwise achieve water quality management
objectives. Biomanipulation methods are presented within three groups, based on
the types of fish involved and primary lake problem being addressed:
1. introduction of grass carp or other fish species that consume aquatic
plants to control excessive macrophyte growths;
2. reduction of populations of bottom-feeding fish, such as common
carp, that can be a significant internal nutrient source and can physi-
cally disturb the lake bottom, contributing to problems of high lake
turbidity and productivity; and
3. top-down management of the pelagic food web by manipulating the
occurrence and abundance of predatory or planktivorous fish to help
control phytoplankton abundance and improve water clarity.
Grass Carp for Aquatic Plant Control
Excessive macrophyte growth is a common lake problem that adversely affects the
value of a lake for swimming, boating, fishing, and other recreational uses and is
also aesthetically unpleasing. Chapter 8 presented seven different approaches for
controlling plant growth. This section discusses just one of those seven possible
methods: the introduction of grass carp.
Grass carp (Ctenopharyngodon idella, also called white amur) are an exotic fish,
imported originally from Malaysia to the United States in 1962. They are voracious
consumers of macrophytes, grow quickly (as much as 6 pounds per year), and if
stocked at sufficient rates, can completely eradicate all aquatic plants within
several seasons. A genetic derivative, a triploid grass carp (as compared to the nor-
mal diploid grass carp) has been developed that is functionally sterile to minimize
the potential for the uncontrolled spread of the species. In some areas, it is legal to
stock 100 percent triploid grass carp but not diploid grass carp. In many States and
provinces, however, both diploid and triploid grass carp are banned (Table 9-1) be-
cause of concerns regarding the introduction of exotic species and the invasion of
grass carp into nontarget waters. In all cases where grass carp introductions are
legal, appropriate permits and environmental approvals must be obtained from
the State, provincial, or Federal regulatory authority before importing and/or
stocking these fish (see Appendix C).
Grass carp do not consume all types of macrophytes equally. Preferred plant
species include elodea, pondweeds (Potamogeton spp.), naiads (Najas spp.), and
hydrilla; carp generally avoid alligatorweed, waterhyacinth, cattails, spatterdock,
and waterlilies (Olem and Flock, 1990; Cooke and Kennedy, 1989; Wiley et al. 1987;
Van Dyke et al. 1984). Low stocking densities can result, therefore, in selective
grazing on preferred plant species, while less palatable macrophyte species in-
crease in abundance (see Box 9-A, Devils Lake case study). Bonar et al. (1990)
found that grass carp feeding preferences also depend on the plants' chemical
composition, which can vary among lakes.
150
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
Table 9-1.—State and provincial regulations on the possession and use of grass
carp. In all cases, a permit must be obtained from the appropriate State or provincial
regulatory authority.*
A. DIPLOID (ABLE TO REPRODUCE) AND TRIPLOID (STERILE) PERMITTED:
Alabama
Alaska
Arkansas
Hawaii
Idaho
Iowa
Kansas
Mississippi
Missouri
New Hampshire
Oklahoma
Tennessee
B. ONLY 100 PERCENT TRIPLOIDS PERMITTED:
California
Colorado1"
Florida
Georgia
Illinois
Kentucky
Montana
Nebraska
New Jersey
New Mexico
North Carolina
Ohio
South Carolina
South Dakota
Virginia
Washington
West Virginia
C. 100 PERCENT TRIPLOIDS PERMITTED FOR RESEARCH ONLY:
Alberta
British Columbia
Louisiana
New Brunswick
Newfoundland
New York
Northwest Territories
Nova Scotia
Oregon
Prince Edward Island
Quebec
Saskatchewan
Wyoming
Yukon
D. GRASS CARP PROHIBITED:
Arizona
Connecticut
Delaware
Indiana
Maine
Manitoba
Maryland
Massachusetts
Michigan
Minnesota
Nevada
North Dakota
Ontario
Pennsylvania
Rhode Island
Texas
Utah
Vermont
Wisconsin
tiWprOUUUUU Will I eUJUtUJJII CtlO UUVJdlCO II win i no i-cinc? tuiu i iwwui rw« i «VW»*IM»!V« ™.™..—— ..,—. x
and Flock, 1990, pg. 142) and adapted from Allen and Wattendorf (1987).
" Written permission required to stock grass carp in western Colorado.
Appropriate stocking rates for grass carp depend on the amount of plant
biomass to be consumed, the plant species, the size of the grass carp, the relative
length of the growing season for both the fish and plants, and the overall size of
the site. Effective stocking rates vary widely from 2 to 200 fish per acre, although
rates of 10 to 25 fish per acre are generally used (Allen and Wattendorf, 1987). In
most States, specific guidelines or procedures are available for calculating the op-
timal stocking rate for a given lake (see Box 9-B). Grass carp are most effective at
controlling new plant growth, so fish should be stocked preferably in the spring
or following other macrophyte control treatments such as herbicides or mechani-
cal harvesting.
In many cases, grass carp provide a feasible and cost-effective alternative to
other techniques for managing aquatic weeds (see Box 9-A). They are generally
most useful in warmer climates and when the target plant is a preferred food that
can be eaten rapidly. However, it is very difficult to control the level of weed con-
trol by varying the fish stocking rate. In many instances, this is an "all-or-noth-
ing" control technique. When stocking levels are adequate, carp will greatly
reduce or nearly eliminate macrophyte beds, whereas lower stocking rates may
have little impact on macrophyte abundance. In larger bodies of water, grass carp
may eliminate plants from certain areas, leaving problematic quantities of plants
to thrive in others.
Grass carp are not a panacea for plant control. In particular, they may not be
the best approach for plant control efforts directed primarily at improving a
lake's sport fisheries. The total elimination of macrophytes results in the loss of
important nursery areas for small fish and habitat for many invertebrates that are
valuable fish prey (see Chapters 3 and 8).
Furthermore, grass carp introductions and the associated disappearance of
aquatic macrophytes are accompanied in some cases by an increase in turbidity,
nutrient availability, and algal growth (e.g., Leslie et al. 1983; Miller and King,
1984). The cause of this increase is uncertain. Grass carp may convert all or some
of the nutrients previously stored as macrophyte biomass into readily available
forms in the water column, which can stimulate algal growth. Some portion of
Grass carp are most
effective at controlling
new plant growth, so fish
should be stocked
preferably in the spring or
following other
macrophyte control
treatments....
151
-------
Fish and Fisheries Management in Lakes and Reservoirs
Box9-A.-
-iExamples of Grass Carp Introductions
to Control Macrpphytes;
Lake Conroe, Texas (Martyn et al. 1986; Olem and Flock, 1990): Diploid grass carp
were introduced into Lake Conroe, Texas, a water supply impoundment for Houston.
Macrophytes occupied about 44 percent of the 20,000 acres at maximum infestation
levels before the introduction. Most plants were hydrilla (Hydrilla verticillata), although
Eurasian watermilfoil (Myriophyllum spicatum) and coontail (Ceratophyllum demer-
sum) were also abundant. Between September 1981 and September 1982, 270,000
grass carp 8 inches or longer, were stocked. By October 1983, all submersed plants
were gone. Associated with this eradication was an increase in planktonic algae, a
decrease in transparency, and an increase in open-water fish species that feed on
plankton. Populations of fish species associated with macrophyte beds declined.
Lakes Bell, Clear, and Holden, Florida (Van Dyke et al. 1984; Cooke et al. 1986):
Diploid grass carp, each fish weighing 0.5 pounds on average (about 10 Ib/acre), were
stocked in 1974 into Lakes Bell, Clear, and Holden at a stocking rate of 20 fish per acre
(about 10 Ib/acre). Lake Bell had about half of its surface covered with hydrilla in
November 1974. Between 1974 and 1977, vegetation on transects in the lake
decreased by 94 percent, and hydrilla was eliminated. Sawgrass (Cladium
jamaicense) and fragrant waterlily (Nymphaea odorata) were apparently unaffected.
Clear Lake was dominated by hydrilla and coontail, which covered one-third of its sur-
face in 1974. By 1976, both species were eliminated, and by 1977 total vegetation
cover was reduced by 94 percent. In addition to introduction of grass carp, Holden
Lake was treated with herbicide over 13 percent of its area. Hydrilla, which covered
more than one-third of the lake in November 1974, was eliminated.
Devils Lake, Oregon (Thomas et al. 1990; CH2M HILL, 1990): Devils Lake (680
acres, mean depth 10 feet) was stocked in September 1986 with 10,000 triploid grass
carp and an additional 17,000 fish in March 1987, for a combined stocking rate of 2.7
pounds of fish per ton of vegetation. The specific objective was to reduce but not
eliminate macrophytes (from 55 percent cover in 1986 to about 20 percent), thereby
avoiding potential adverse effects on the lake's important sport fishery for largemouth
bass. The introduction, however, has been only partially successful. In 1986, ap-
proximately 55 percent of the lake was covered with macrophytes dominated by
Brazilian waterweed (Elodea densa; 33 percent by weight), coontail (23 percent),
Eurasian watermilfoil (19 percent), and Canadian waterweed (Elodea canadensis; 6
percent). Eurasian watermilfoil, which formed large surface mats during summer, par-
ticularly interfered with boating, fishing, and swimming on the lake. By 1990, following
the introduction of grass carp, macrophyte biomass had increased rather than
decreased by about four times relative to levels in 1986.
Despite this increase in macrophyte biomass, the weed problem in Devils Lake is
generally considered to have lessened because of the marked reduction in the large
mats of Eurasian watermilfoil at the lake surface. The biomass of Brazilian waterweed
and coontail have increased, although neither has formed nuisance mats. It is unclear,
however, to what degree this shift in macrophyte species was caused by the introduc-
tion of grass carp as opposed to a natural succession of plant species. In laboratory
feeding studies, triploid grass carp preferred Eurasian watermilfoil and Canadian
waterweed over Brazilian waterweed. Also, grass carp have been observed feeding at
the lake surface and may have contributed to the decline in surface mats. Finally, mac-
rophyte biomass levels are higher in in-lake enclosures that exclude grass carp than in
the lake proper, suggesting that plant biomass in the lake would be even greater in the
absence of grass carp. Water quality, as measured by nutrient and chlorophyll a con-
centrations, has not changed appreciably since grass carp were introduced. In addi-
tion, no adverse effects are evident on other fish species or the lake's fisheries.
152
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
Box 9-B,—Suggested Stocking Rates,for Triploid
GraSS Carp in Illinois (source: Wiley et al. 1987)
Recommended stocking rates for triploid grass carp in Illinois lakes have been
developed using the computer model, Illinois Herbivorous Fish Stocking Simulation
System. Optimal stocking rates are determined by the following lake characteristics:
• lake area,
• percentage of lake that is less than 8 feet deep,
• percentage of lake that is heavily vegetated when aquatic plant cover is at its
peak, typically in July or August,
• the dominant plant species in the lake or the plant targeted for control, and
• the county in which the lake is located (to account for geographic differences in
climate and water temperatures).
The result is a site-specific stocking rate that will maximize the cost-effective-
ness of using grass carp for aquatic weed control. Examples of recommended stock-
ing rates for a hypothetical lake in northern Illinois are presented in Figure 9-1.
80 -
70 -
60 -
50 -
40 -
30 -
20 •
i
5
CM
I
2
10
Unpalatable Plant Species
Littoral zone
100% vegetated
70% vegetated
50% vegetated
fixed rate
0 100 ' 90 80 70 60 50 ' 40 ' 30 ' 20 ' 10
20 -i _
Palatable Plant Species
fixed rate
^»»^m*^—^^^ m •
0 100 ' 90 ' 80 ' 70 ' 60 ' 50 ' 40 ' 30 20 10
Very Palatable Plant Species
100 ' 90~ ' 80~ '70 ' 60^ ' 50 ' 40
Percent littoral zone
Figure 9-1.—A comparison of fixed-rate (10 fish per acre) recommendations for
grass carp stocking versus estimates based on the procedures in Wiley et al. (1987)
for three categories of plant palatability. Each comparison shows rates for a lake in
northern Illinois when littoral zones are 50, 70, and 100 percent vegetated. Graphs
give the recommended stocking rate, in terms of the number of 10-inch grass carp,
as a function of the percentage of the lake littoral zone (source: Wiley et al. 1987).
153
-------
Fish and Fisheries Management In Lakes and Reservoirs
[G]rass carp introductions
should lie limited to
isolated lakes with little or
no chance offish
migration into other
waterbodies.
the macrophyte nutrients, however, will be tied up in fish biomass. Relatively few
detailed studies have been conducted on the effects of grass carp on nutrient cy-
cling, and the results from the available research are somewhat equivocal (Cooke et
al. 1986). In addition, increases in algal growth following macrophyte reductions
are not limited to control programs using grass carp. Observed increases may be
primarily a response to the loss of a significant competitor (macrophytes) for
nutrients rather than a function of the grass carp per se (Richard et al. 1984).
Grass carp can migrate to other lakes and streams where reductions in plant
growth are not desired. Even though triploid grass carp are functionally sterile,
they can live 10 to 15 years (Allen and Wattendorf, 1987). Bain et al. (1990) observed
significant movement (average 20 miles) of individual adult grass carp stocked into
an open, mainstream reservoir in Tennessee. Such movements must be anticipated
as part of management decisions to introduce this species (Noble et al. 1986). To
prevent its uncontrolled spread, grass carp introductions should be limited to iso-
lated lakes with little or no chance of fish migration into other waterbodies.
All of the available macrophyte control options have disadvantages and ad-
vantages (see Chapter 8). The major advantages of grass carp include its relatively
low cost and long-term effectiveness. For more information on using grass carp for
aquatic plant control, see Chapter 6 of The Lake and Reservoir Restoration Guidance
Manual (Olem and Flock, 1990), Cooke and Kennedy (1989), Cooke et al. (1986),
Allen and Wattendorf (1987), Wiley et al. (1987), and the Illinois Department of
Conservation (1988).
Other fish species, particularly Tilapia zilli (redbelly tilapia) and Tilapia aurea
(blue tilapia), have also been considered for control of macrophytes or filamentous
algae and applied successfully in a few cases (Cooke et al. 1986; Gophen, 1990); ex-
amples include California irrigation canals (Hauser, 1975), a cooling water im-
poundment in North Carolina (Schmiller, 1984), and an Illinois pond (Childers
and Bennett, 1967). Tilapia are intolerant of cooler water temperatures (below 10°C
for extended periods of time) and, thus in most areas, need to be restocked annual-
ly. In addition, blue tilapia may dominate fish communities of lakes into which
they are introduced and compete with native planktivorous fish (Hendricks and
Noble, 1979).
Control of Bottom-Feeding Fish to Reduce
Internal Nutrient Loads and Water Turbidity
Fish that feed on the organisms and detritus in lake sediments can be a significant
internal source of nutrients (Cooke et al. 1986). Nutrients stored in the living and
dead organic matter concentrated in the lake sediments are converted into more
readily available forms through fish digestive processes and excreted into the
water column. Based on experiments in lake enclosures, LaMarra (1975) calculated
that common carp at a biomass of 180 Ib/acre (200 kg/ha) and temperature of 72°F
(22°C) could add about 24 mg of phosphorus to a lake's water column per square
foot per day (2.2 mg/m2/day). Keen and Gagliardi (1981) found similar results in
experiments with brown bullhead, while Smeltzer and Shapiro (1982) calculated
that the carp and bullhead in Union Lake, Minnesota, contributed 0.8 Ib of phos-
phorus/acre/year (88 mg/m2/yr), a phosphorus loading rate approximately
equivalent to that from external sources (Cooke et al. 1986). Brabrand et al. (1990)
estimated that roach (Rutilus rutilus) contributed about 30 percent annually of the
total phosphorus supply to Lake Gjersj0en, Norway, but about 80 percent of the
phosphorus inputs to the lake epilimnion during summer when fish feeding ac-
tivities were at a maximum and inputs from the watershed were low. Roach and
carp feed at the lake bottom and also on zooplankton in the water column. By
migrating between the littoral and pelagic zones, they redistribute nutrients
bound to the lake sediments into the epilimnion, making them available for
phytoplankton uptake and productivity.
154
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
Common carp and other bottom-feeding fish also physically disturb the lake
sediments, contributing directly to problems of high turbidity as well as nutrient
recycling. Carp can reach substantial sizes in eutrophic lakes, 10 to 25 pounds or
more per fish. They feed by sucking up large volumes of soft organic bottom sedi-
ments and then expelling all but the edible particles into the water column (Scott
and Grossman, 1973). In addition especially during the spawning season, carp
concentrate in shallow waters and "roll," splashing and thrashing at the lake sur-
face and stirring up the lake bottom. By loosening the top layer of sediment and
hindering the development of macrophytes, bottom-feeding fish also make the
lake bottom more susceptible to resuspension by winds and waves (Hosper and
Jagtman, 1990). Models developed for shallow lakes in the Netherlands suggest
that 50 percent of the turbidity in these waters results from sediment resuspen-
sion, mainly caused by the activity of bottom-feeding fish (Meijer et al. 1990).
High densities of bottom-feeding fish often accompany eutrophication.
Horppila and Kairesalo (1990), Hosper and Jagtman (1990), Brabrand et al.
(1990), and others have suggested that large populations of bottom-feeding fish
can also substantially delay — or even prevent — lake recovery following reduc-
tion of external nutrient loads. Internal nutrient recycling, primarily from the
lake sediments, is sufficient to maintain a high level of algal productivity. A
reduction in the biomass of bottom-feeding fish can result in decreased water tur-
bidity and nutrient availability and, in some cases, a decrease in phytoplankton
abundance. For example, following a reduction in fish biomass in two shallow
lakes in the Netherlands, lake transparency increased substantially, the result not
only of a decrease in algal biomass but also of a decrease in resuspended sedi-
ment and detritus (Meijer et al. 1990). In enclosure experiments in Lake Vesijarvi,
Finland, lower levels of roach biomass resulted in lower chlorophyll a concentra-
tions (an indicator of phytoplankton abundance) and higher water transparency
(Horppila and Kairesalo, 1990; Fig. 9-2).
Methods for reducing and controlling populations of undesirable fish species
were described in Chapter 8, and include (1) fish poisoning (e.g., using rotenone);
(2) extreme water drawdowns; (3) selective cropping, including establishing
commercial fisheries for the species, where possible; (4) disruptions of spawning
behavior and reproduction through direct disturbance and water level draw-
downs during the spawning season; (5) increased predation; and (6) fish barriers
to prevent the migration of undesirable species into lakes where they do not cur-
rently occur or following eradication of the fish community. Neither carp nor
bullhead spawn in areas where spawning behavior or egg masses can be readily
disturbed, nor are they particularly susceptible to increased predation. Carp are
also extremely prolific. As a result, both species are difficult to control and only
drastic measures, such as rotenone or extreme drawdown, may be effective. Such
measures that impact the entire lake, however, may also interfere with other lake
uses and values. Where possible, the best approach for carp control is to prevent
the species from being introduced or migrating into the lake; for instance, by in-
stalling fish barriers.
Top-Down Management of the Pelagic Food
Web to Reduce Algal Biomass and Improve
Water Transparency
The term "biomanipulation" is frequently used to refer specifically to top-down
management of the pelagic food web; that is, altering populations of fish
predators or planktivores to indirectly control phytoplankton abundance and im-
prove water clarity. The theoretical basis for top-down management was
described in Chapter 2 (see Fig. 2-14):
Common carp and other
bottom-feeding fish also
physically disturb the lake
sediments, contributing
directly to problems of
high turbidity as well as
nutrient recycling.
Where possible, the best
approach for carp control
is to prevent the species
from being introduced or
migrating into the lake...
155
-------
Hsh and Fisheries Management in Lakes and Reservoirs
1. a large biomass of piscivorous (fish-eating) fish will consume large
numbers of smaller, planktivorous (plankton-eating) fish, resulting in
a decline in the abundance of planktivores;
2. lower numbers of planktivores will consume fewer zooplankton, al-
lowing for the development of a large zooplankton biomass, including
large-sized zooplankton taxa such as Daphnia;
CHLOROPHYLL-a mg nr
300
10 20 30
SAMPLING PERIOD (21 TUNS - 1 AUG.) IN DAYS
NO
LO
ME
HI
40
- LAKE
50
WATER TRANSPARENCY cm
250
200 -
150 -
100 -
50-
10 20 30
SAMPLING PERIOD (21 JUNE - 1 AUG.) IN DAYS
NO
LO
HI
40
- LAKE
50
Figure 9-2.—Chlorophyll a concentrations and water transparency In enclosure experi-
ments In Lake Vesljarvl, Finland, with no (NO), low (about 25 g/m2; LO), medium (about 75
g/m2; ME), or high (150 g/m2; HI) biomass levels of roach (a bottom-feeding fish species),
compared to levels in the lake (with a roach biomass of about 50 g/m2) (source: Horpplla
and Kalresalo, 1990).
156
-------
Chapter 9. Methods for Using Fish to Improve Water Quaft'ty
3. large numbers of zooplankton will consume large numbers of
phytoplankton, reducing algal abundance; and
4. lower algal abundance will result in an increase in water transparen-
cy and overall improvement in water quality.
Theoretically at least, top-down management of the food web can have the same
beneficial effects as a reduction in external nutrient loads (referred to as "bottom-
up" management).
Top-down management can be implemented by either increasing piscivore
populations or reducing planktivorous fish populations directly. A variety of
management techniques can be applied for both approaches, including the fol-
lowing:
• Increase the abundance of piscivores through
• introduction, by stocking, of new piscivore species,
• supplemental stocking of existing piscivore populations,
• fishing regulations to restrict angler harvests of piscivores, and
• habitat improvements to enhance piscivore survival and/or
reproduction.
• Reduce the abundance of planktivorous fish through
• fish poisoning,
» extreme water drawdown,
• selective catches and fish removal,
• disruption of spawning behavior and reproduction (e.g., water
level manipulations), and
• fish barriers.
Additional information on each of these fish management techniques is provided
in Chapter 8.
Top-down management can work, as demonstrated by several of the case
studies summarized in Box 9-C. However, in most lakes, food webs are more
complex than the simple food chain just described, with many interspecies inter-
actions (competition as well as predation) and feedback loops. As a result, lake
responses to the application of top-down management are less predictable than
desired. In some cases, fish manipulations have resulted in no measurable effect
on algal biomass or water transparency; in other instances, the benefits have been
short-lived or conditions have actually worsened (see Box 9-C, which also in-
cludes examples of unsuccessful projects). Although the basic principles of top-
down management are sound, the following subsections review some of the
remaining uncertainties and limitations of the approach.
Inedible Phytoplankton
The relative importance of bottom-up (nutrient supply) and top-down (preda-
tion) controls varies with position in the food web (McQueen et al. 1986).
Nutrient inputs have the greatest effect on phytoplankton; other components of
the food web are also affected, but the magnitude of response decreases with
each succeeding step up the trophic pyramid. Likewise, responses to a change in
fish predation are strongest and most predictable near the top of the food web
but weaken and become less predictable with every step down the trophic
pyramid. Thus, the weakest component and major source of uncertainty in top-
down management is the linkage between zooplankton and phytoplankton
(Lampert, 1988; Gulati et al. 1990).
Theoretically at least,
top-down management of
the food web can have the
same beneficial effects as a
reduction in external
nutrient loads.
[RJesponses to a change in
fish predation are
strongest and most
predictable near the top of
the food web but weaken
and become less
predictable with every step
down the trophic pyramid.
157
-------
Fish and Fisheries Management in Lakes and Reservoirs
Box 9-C.—Fish Manipulations to Decrease Algal Biomas
& Imprpve Water Transparency: Examples of Successful &
• Not So Successful Applications of Biomanipulation |
Round Lake, Minnesota (Shapiro and Wright, 1984; Shapiro, 1990): Rotenone was ap-
plied to Round Lake (31 acres) in fall 1980 to eliminate planktivorous and bottom-feed-
ing fish (primarily bluegill, black crappie, and black bullhead). The lake was
subsequently restocked with a high density of piscivores (largemouth bass and walleye)
and smaller numbers (relative to pre-treatment) of bluegills and channel catfish. Daph-
nia, which were rare in 1980, subsequently became the dominant zooplankton genus in
1981 and 1982. Even though total zooplankton numbers declined, zooplankton grazing
rates on phytoplankton were estimated to have doubled because of the large increase
in mean zooplankton size. Chlorophyll a concentrations dropped sharply in 1981 and
1982 relative to values in 1980, and Secchi disk transparency increased (Fig. 9-3). Al-
though highly successful for two years, in year three bluegill increased in abundance
and large-bodied Daphnia decreased, leaving the lake water quality only slightly better
than before biomanipulation. Even though large numbers of piscivores were introduced,
long-term control of the bluegill population was not achieved. This was likely because
larger adult bluegills are not susceptible to predation, and significant numbers of large-
mouth bass were removed from the lake by anglers.
(b)
10-
I 5H
o
I98I
I982
May
June
July
August
Sept.
Figure 9-3.—Secchi depth transparency and epilimnetic chlorophyll a concentrations
in Round Lake, Minnesota, in 1980 before biomanipulation; and in 1981 and 1982 after
treatment (source: Shapiro and Wright, 1984).
Continued on next page
158
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
Box 9-C.—Continued
Lake Michigan (Scavia et al. 1986,1988; Kitchell and Carpenter, 1987): During the
first half of this century, fisheries exploitation coupled with the invasion of sea lamprey
lead to the collapse of the lake trout population, the dominant piscivore in Lake
Michigan. In the absence of significant numbers of piscivores, invading populations of
planktivorous fish flourished. Alewife, in particular, increased dramatically in abundance
during the 1950s and 1960s and was the major component of fish biomass until recent-
ly. In response to this alewife expansion, large-bodied copepods and cladocerans vir-
tually disappeared from the lake during the late 1960s and were replaced by smaller
zooplankton. The development of an effective lampricide and large-scale lamprey con-
trol program in the 1970s allowed for the re-establishment of salmonid populations in
the lake. In addition to lake trout, several Pacific salmonid species (including rainbow
trout and coho salmon) have been stocked and now provide sport fisheries of substan-
tial economic and social value. Also over the last decade, the dominant zooplankton
taxa have shifted from calanoid copepods to Daphnia; filamentous cyanobacteria algae,
which dominated in the late summer, have been replaced by phytoflagellates; and water
transparency has increased. External nutrient loads to the lake have also declined since
the mid-1970s and have contributed to the improved water quality. Model analyses,
however, suggest that the observed changes in the summer plankton community
resulted primarily from the increased abundance of fish piscivores.
Lake Vasng, Frederiksborg Castle Lake, and Lake Sobygard, Denmark (Jeppesen
et al. 1990b): Lake Vaeng (37 acres) and Lake S0bygard (99 acres) are quite shallow
(mean depth about 3 feet) and have high flushing rates (15 to 25 days). Frederiksborg
Castle Lake (52 acres) is stratified in the summer, somewhat deeper (mean depth 10
feet), and has a relatively long hydraulic retention time (4 to 18 years). All three lakes
are eutrophic, although to varying degrees and with different phytoplankton composi-
tion. Less eutrophic Lake Vasnig is dominated by a combination of blue-greens and
diatoms. The removal of 50 percent of the planktivorous fish biomass (roach, bream,
and rudd, Scardinus erythrophthalmus) from Lake Vaanig in 1986 and 1987 by selective
fishing with various gear types (beach seine, electrofishing, and gill, fyke, and pound
nets) resulted in a marked decrease in chlorophyll a and increase in water transparency
(Fig. 9-4). In contrast, only minor changes occurred in Frederiksborg Castle Lake, a
eutrophic lake dominated by blue-greens, after a 78 percent removal of planktivorous
fish in 1986 and 1987 (Fig. 9-4). In hypereutrophic Lake S0bygard, dominated by green
algae, no fish reproduction occurred from 1983 to 1986, probably because of high pH
levels (10 to 11) during the spawning period, and 16 percent of the planktivorous fish
biomass was removed by selective fishing from 1986 to 1988. Over the same period,
chlorophyll a concentrations decreased substantially and water transparency increased.
Differences in lake response appeared to be related to phytoplankton community com-
position — in particular the dominance of bloom-forming blue-greens in Frederiksborg
Castle Lake — and perhaps lake depth and flushing rates.
Bautzen Reservoir, Germany (Benndorf et al. 1988; Benndorf, 1990): Bautzen
Reservoir (1,317 acres) is a multipurpose reservoir used as a cooling water supply for a
power plant, water supply, flood control, and recreation. The major water quality prob-
lem is eutrophication. Biomanipulation began in 1977. Each year, zander (Stizostedion
lucioperca), a piscivore in the same genus as walleye, are stocked as fingerlings. In ad-
dition, restrictions on angler harvests of northern pike, the other major piscivore in the
lake, have been imposed since 1979. Increased predation by pike and zander reduced
the abundance of planktivorous fish in the reservoir (mainly small perch, Perca
fluviatilis). In recent years, the ratio between piscivores and planktivores plus bottom-
feeding fish has stabilized at about 0.3 to 0.5. During the eight years post-manipulation,
zooplankton biomass has increased 21 percent relative to pre-manipulation years; the
biomass of Daphnia galeata, the major large-bodied zooplankton, has increased by 110
percent. The abundance of large predatory invertebrates (Chaoborus flavicans, Lep-
todora klndtii) has also increased, but only to moderate levels because of the continued
presence of some planktivorous fish. Mean Secchi depth transparency increased by 20
percent, with an extended clear water phase in the early summer. Phytoplankton com-
munity composition, however, has shifted to a dominance of inedible cyanobacteria. In
most years, maximum phytoplankton biomass levels have been higher following
biomanipulation than before. The frequency of occurrence of cynobacterial blooms has
also increased. Thus, biomanipulation in Bautzen Reservoir has had both positive and
negative effects on water quality.
159
-------
Fish and Fisheries Management in Lakes and Reservoirs
01
6
Laka Vang .
Fredeflkabofg Castle Lake
Lakt Sobygard
400
300.
250
200
175
ISO-
125
100
75-
50-
25-
25 50 75 100
25 50 75 100
Frequency distribution (%)
25 ,50
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
Table 9-2.—Experiments In lakes (1), reservoirs (2), ponds (3), enclosures (4), and
aquaria (5) that support the hypothesis that planktlvorous fish reduce the blomass
of herbivorous zooplankton (Z), and as a result, Increase the biomass of
phytoplankton and/or decrease water transparency (Ph/T). Positive results that sup-
port the hypothesis are denoted by a plus sign (+), while a zero (0) indicates
indifferent results; lack of a sign indicates no Information (adapted from Persson et
al. 1988).
TYPE
FISH SPECIES/TAXA
Ph/T
REFERENCE
1
1
1
1
1
2
2
3
3
3
3
3
3
3
3
4
4
4
4
Cyprinidae (minnows and carp)
Alewife
Cyprinidae
Cyprinidae
Coregoninae and perch
Cyprinidae
Stickleback
Cyprinidae
Bluegill
Mosquitofish
Cyprinidae
Cyprinidae
Mosquitofish
Pimephales spp. (minnow)
Bluegill
Cyprinidae
Bluegill and Pimephales spp.
Bluegill
Pimephales spp.
+ + Hrbac&k etal. 1961
+ + Brooks and Dodson, 1965
+ + Stenson etal. 1978
+ + Henrikson etal. 1980
+ + Reinertsen and Olsen, 1984
+ + Leah etal. 1980
+ + Olrik etal. 1984
+ 0 Grygierek etal. 1966
+ 0 Hall etal. 1970
+ + Hurlbert etal. 1972
+ + Losos and Hetesa, 1973
+ + Fott etal. 1980
+ + Hurlbert and Mulla, 1981
+ -i- Spencer and King, 1984
+ + Hambright etal. 1986
+ + Andersson etal. 1978
+ + Lynch, 1979
+ Lynch and Shapiro, 1981
+ + Elliot etal. 1983
Most inedible forms of phytoplankton are blue-green algae. Furthermore, in-
edible blue-greens occur most commonly in eutrophic and hypereutrophic lakes
(Davidowicz et al. 1988; di Bernard! and Giussani, 1990; Elser and Goldman,
1991) because large-cell sizes are a disadvantage in nutrient-limited waters. Thus,
zooplankton grazing may be a less effective method for reducing phytoplankton
abundance in eutrophic and hypereutrophic lakes than in meso- or oligotrophic
waters (see the discussion later in this chapter on the influence of trophic status).
Most studies of phytoplankton responses to zooplankton grazing have been
relatively short-term, however. It is possible that, over time, zooplankton com-
munities can adapt to and control even relatively inedible phytoplankton species
by altering their feeding behavior, grazing on them at susceptible stages of the
algal life cycle, or undergoing a shift in zooplankton species composition favor-
ing those species able to handle such food items (Elser and Goldman, 1991). In
addition, a longer "clearwater phase".in the spring brought on by increased
zooplankton grazing on the edible phytoplankton (primarily diatoms) that
predominate at that time may inhibit the proliferation of bloom-forming blue-
green algae later in the summer (Spencer and King, 1986; Elser et al. 1990). How-
ever, additional research is needed on the long-term response of phytoplankton
communities to increased grazing pressure and factors that control the occur-
rence of inedible, blue-green algae.
Zooplankton Composition and Abundance
The objective of top-down management is to maximize the grazing pressure or
"filtration capacity" of herbivorous zooplankton. The best results are achieved
not by maximizing total zooplankton abundance but by increasing the abun-
dance of large-sized zooplankton, such as Daphnia (Benndorf, 1988). Large
zooplankton have higher grazing rates (Peters and Downing, 1984) and can injest
a broader variety of algae, including larger algae (Burns, 1968; Carpenter et al.
161
-------
Fish and Fisheries Management in Lakes and Reservoirs
The method used to
increase the abundance of
large-bodied, herbivorous
zooplankton is to reduce
the biomass offish that
feed on zooplankton.
A reduction in fish
predation intended to
increase the abundance of
herbivorous zooplankton
will also automatically
reduce fish predation on
predacious zooplankton
species,
1985), than do smaller-bodied zooplankton, such as Diaphanosoma or Bosmina.
Smaller zooplankton have relatively restricted diets (e.g., Diaphanosoma and Bos-
mina have difficulty consuming items larger than 15 urn) and, as a result, are
generally unable to control phytoplankton abundance (Kerfoot, 1987).
The method used to increase the abundance of large-bodied, herbivorous
zooplankton is to reduce the biomass of fish that feed on zooplankton — that is,
planktivores, such as alewife and rainbow trout (see Table 2-4). A great deal of re-
search has demonstrated the linkage between planktivorous fish and zooplankton
community composition and abundance (Table 9-2). In the absence of predation
from planktivorous fish, zooplankton communities become dominated by those
species with the greatest competitive advantage. Generally, large-bodied
zooplankton have a competitive advantage over smaller zooplankton because of
their ability to consume a wider array of phytoplankton at faster rates (Kerfoot,
1987).
In some studies, however, reductions in planktivorous fish have not resulted
in zooplankton communities being dominated by large herbivores. For example,
Crisman and Beaver (1990) found that cladoceran assemblages (which include the
genus Daphnia) in subtropical Florida lakes are smaller than those in temperate
lakes. Even though fish reductions result in an increase in total zooplankton abun-
dance, large-bodied zooplankton capable of controlling algal blooms do not occur.
Therefore, top-down management through the zooplankton community may not
be an effective approach for reducing phytoplankton abundance or improving
water transparency in Florida lakes.
Complications may also arise if large predacious zooplankton that feed on
other zooplankton occur in a lake (see Fig. 2-14). A reduction in fish predation in-
tended to increase the abundance of herbivorous zooplankton will also automat-
ically reduce fish predation on predacious zooplankton species. Large invertebrate
predators — such as Leptodora, Chaoborus, Mysis — and some species of Cyclopidae
can feed on relatively large zooplankton, including large Daphnia (Hall, 1964;
Lasenby and Furst, 1981; Barthelmes, 1988; Lunte and Luecke, 1990). Invertebrate
predators, in this case, may simply replace the vertebrate (fish) predators with lit-
tle or no change in zooplankton grazing pressure on phytoplankton.
Invertebrate predation, therefore, has the potential to confound the simple
food web linkages described at the beginning of this section and must be ac-
counted for in designing a top-down management program. Lunte and Luecke
(1990), for example, concluded that the presence of Leptodora kindtii in Lake Men-
dota, Wisconsin, will buffer to some degree lake responses to the ongoing fish
management program where piscivorous fish species have been introduced to
control algal blooms. Edmondson and Abella (1988) concluded that the marked in-
crease in water transparency observed after 1975 in Lake Washington resulted in
large part from the elimination of an invertebrate predator, Neomysis mercedis. In
previous years, high densities of Neomysis had strongly suppressed Daphnia
populations. In the 1960s, the abundance of fish planktivores increased — in par-
ticular, the population of longfin smelt, a fish that feeds selectively on Neomysis.
The subsequent reduction in Neomysis resulted in an increase in Daphnia, an even-
tual decrease in phytoplankton biomass, and an associated increase in water
transparency. Changes in Lake Washington are discussed further in Chapter 12
(Case Studies).
Optimal Biomass of Fish Planktivores
What densities of fish planktivores work best? In many biomanipulation studies,
fish planktivores have been eliminated entirely by using rotenone or extreme
drawdown. Such measures, however, also affect the zooplankton community be-
cause rotenone is toxic to zooplankton as well as fish. In addition, Benndorf (1990)
suggests that moderate levels of fish planktivores should be maintained to control ''
162
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
invertebrate predators and help stabilize Duphnia populations by avoiding over-
population and subsequent starvation and population declines. Benndorf (1990)
denned "minimum fish biomass" as the minimum biomass of zooplanktivorous
fish necessary to avoid such negative side effects and "critical fish biomass" as
the upper limit that cannot be exceeded if populations of large herbivores are to
develop. Minimum and critical biomass levels vary depending on the species
and age of fish and lake conditions. For example, critical biomass levels reviewed
by Benndorf (1990) ranged from 20 to 1,000 kg/ha. Very efficient fish
planktivores (for example, age 0+ yellow perch) had the lowest critical biomass.
Lake conditions that decrease fish feeding efficiency, such as refuge areas for
zooplankton or high turbidity, increase the critical biomass level. The minimum
fish biomass needed to control invertebrate predators can depend on complex in-
terrelationships between the fish, invertebrate predator, and their zooplankton
prey. In some cases, the abundance of invertebrate predators may actually be
greatest at intermediate fish densities and lower at both high and low fish den-
sities (Kerfoot, 1987; Crowder et al. 1988). In general, optimal biomass levels for
fish planktivores cannot be defined with confidence at this time (Benndorf, 1990;
Shapiro, 1990).
Optimal Biomass and Types of Piscivorous Fish
Benndorf (1990) provides the following guidelines for selecting the optimal
biomass and types of piscivores for top-down management programs:
• The proportion of piscivores in the total fish community must be suffi-
ciently high to control populations of planktivorous fish. Generally,
piscivores should comprise approximately 30 to 40 percent of the total
fish biomass; also, the proportion of piscivores must be relatively
stable through time.
• High piscivore diversity increases the stability and reliability of food
web manipulations.
• A sufficiently high proportion of the piscivore population(s) must be
large enough, with a large enough gape, to exert strong predation pres-
sure on adult planktivores, especially large adult planktivores that
have a high reproductive capacity. The occurrence of planktivorous
fish, such as gizzard shad and bluegill that tend to grow too large for
most predators, may prevent implementation of an effective top-down
management program (see Round Lake case study in Box 9-C).
• An adequate number of small piscivore species or age classes must be
present that prefer age 0+ fish as prey and can switch to benthic food
(but not zooplankton) if age 0+ fish are scarce. A wide range and even
distribution of piscivore age classes are important to guarantee high
predation on a broad spectrum of planktivorous fish.
• Many piscivores will switch to other food types, including
zooplankton, if adequate fish for prey are not available. If the pis-
civores consume zooplankton when planktivorous fish are in short
supply, a top-down management program will likely fail. In addition,
some piscivore species feed on zooplankton when young, switching to
a diet of fish only when they reach a certain age or size; therefore, the
full scope of a fish's feeding habits must be considered.
• The piscivore species must be an effective fish predator given the con-
ditions and planktivores in the lake. For example, piscivores that rely
on sight to capture prey and have relatively high light thresholds
below which capture efficiency declines (O'Brien, 1987) would be inef-
fective predators for controlling planktivore populations in a turbid
reservoir.
[MJoderate levels offish
planktivores should be
maintained to control
invertebrate predators and
help stabilize Daphnia
populations....
High piscivore diversity
increases the stability and
reliability of food web
manipulations.
163
-------
Fish and Fisheries Management in Lakes and Reservoirs
Top-down management
should not be attempted in
lakes where a high
proportion of the
planktivore population is
unavailable to predators.
In shallow lakes, even
relatively short-term
improvements in water
transparency may be
sufficient to allow
establishment of
microphytes.
Many planktivores are prolific, with a high reproductive capacity; thus, estab-
lishing adequate control through piscivores or other means can be difficult. If pis-
civores remove only some age or size classes (e.g., only smaller fish), the end result
may be more rather than fewer planktivores because the increased growth and
reproductive success of the remaining planktivores can more than compensate for
predation losses (see Chapter 3). Top-down management should not be attempted
in lakes where a high proportion of the planktivore population is unavailable to
predators (because of their large size or abundant refuge areas) and other
planktivore control methods would be difficult, expensive, and/or effective for
only a short period.
Instability
Two major problems associated with biomariipulation for water quality improve-
ment are (1) making it stable — minimizing year-to-year fluctuations in predator-
prey relations and (2) making it last — sustaining these relations and water quality
improvements over multiple years or decades.
Populations of planktivorous fish that are reduced by intensive fishing, water
level drawdown, or other techniques will generally recover within a relatively
short time (one to three years) through fish growth and reproduction — unless fish
reduction efforts are continued. Even drastic measures such as fish poisoning with
rotenone can be temporary as fish species reinvade the lake from adjacent waters
or are accidentally re-introduced. For example, chlorophyll a concentrations and
water transparency in Round Lake, Minnesota, returned to near pre-manipulation
levels within three years after rotenone treatment (Shapiro and Wright, 1984;
Shapiro, 1990). Even though large numbers of largemouth bass (a piscivore) were
stocked into the lake, bluegill — reintroduced after the rotenone treatment —
recovered sufficiently to suppress large-bodied Daphnia. Failure of the bass
population to adequately control bluegill was attributed to the bluegill's wide-
bodied shape, which made a relatively high proportion of the adult population not
susceptible to bass predation, and removal of bass by anglers.
In shallow lakes, even relatively short-term improvements in water
transparency (e.g., an extended clear water phase during spring) may be sufficient
to allow establishment of macrophytes. Extensive macrophyte growths can stabi-
lize the lake bottom, reducing sediment resuspension, and decrease nutrient
availability for phytoplankton. Hosper and Jagtman (1990), Jeppesen et al. (1990a),
and others have suggested that, once macrophytes are established, this new clear
water state can be relatively stable. Biomanipulation may be essential for switch-
ing from a turbid, algal-dominated system to a relatively clearwater, macrophyte-
dominated system, even with considerable nutrient reduction (Moss, 1990; Hosper
and Jagtman, 1990).
Shapiro (1990) proposed that establishing refuges where prey can escape from
predators may be one method for protecting prey populations from excessive preda-
tion and helping to sustain food web manipulations. Possibilities for refuges include
• regions of low light intensity (e.g., in the deeper parts of a lake or in tur-
bid lakes);
• areas with low temperature or low dissolved oxygen that the prey (such
as herbivorous zooplankton) can inhabit but the predator cannot; and
• macrophyte beds or physical structures where prey can hide.
Relatively few tests have been conducted, however, to evaluate the usefulness of
refuges, and those tests have had equivocal results (Gulati et al. 1990).
Year-to-year fluctuations in the effectiveness of predator controls can be sub-
stantial. Two main contributing factors are variations in climate and time lags in
feedback mechanisms in the food web (Carpenter et al. 1985). Year-class strength
164
-------
Chapter 9, Methods for Using Fish to Improve Water Quality
(a)
| MAN I
Regulations to Optimize Yield
Predation Pressure
Dependent on v, ,.
Growth of Y[eld
Forage Species
Regulates
Recruitment
CGri7he C«^«<»"
j/ Feedback Loop
and Regulator
Size-Selection
Predation
i
Recruitment
(b)
10
9
I 8
| ?
~ 6
taphnia Pulex Den
ej -u m
tj
2
1
Thres
•7K 70
- ^ . »
•78
•
•80
.73
74
"•* '83 79
72 • •
hold
•69
'77 -82 '81 '75 ^ >71
I I ' • * l«« 1 1 1 "»
8 16 -24 32
Number Age-0 Yellow Perch (1OTha)
Figure 9-5.—(a) Trophic level Interactions in the Oneida Lake food web and (b) the as-
sociation between the density of Daphnla pulex (average value for August to October)
and density of age-0 yellow perch in August in the lake (source: Mills et al. 1987).
in fish populations tends to be highly variable (see Chapter 3). Physical factors,
such as cold temperatures or wave action, may cause poor embryo survival in
some years. Weak year-classes are often followed by strong year-classes, and vice
versa, as a result of intra-specific competition for food and cannibalism. The ef-
fects of these variations in year-class strength can be transmitted throughout the
food web and extend over a long time as each year-class cohort develops and
feeding habits change as the fish grow.
Detailed studies over the last 30 years at Oneida Lake, New York, provide in-
sight into the consequences of natural variations in year-class strength and food
web interactions (Mills et al. 1987; Mills and Forney, 1988). Walleye is the
dominant top predator and young yellow perch are the dominant planktivores
(Fig. 9-5a). Walleye feed primarily on young and yearling yellow perch, which
prey on Daphnia pulex (the major large-bodied herbivore) and other zooplankton.
The density of young yellow perch in May is strongly correlated with climatic
conditions during egg incubation. Later in the summer (after the perch reach 18
mm), predation by walleye and adult yellow perch is the major factor controlling
mortality and young perch abundance. In years when the density of age 0+ yel-
low perch exceeds 14,000 /ha in August, Daphnia pulex disappears (Fig. 9-5b) and
smaller zooplankton increase. The loss of Daphnia pulex leads to elevated algal
165
-------
Fish and Fisheries Management In Lakes and Reservoirs
Hitman activities also
contribute to fluctuations
in food web dynamics.
A number of investigators
have concluded that the
importance of top-down
effects varies with trophic
status.
biomass (chlorophyll concentrations nearly two times those in years with low yel-
low perch density), a shift in phytoplankton composition, and a decrease in water
transparency. Seasonal and annual variations in Oneida Lake phytoplankton are
determined, therefore, largely by seasonal and annual variations in the intensity of
yellow perch grazing on zooplankton.
Human activities also contribute to fluctuations in food web dynamics. For ex-
ample, Jassby et al. (1990) concluded that year-to-year variations in primary
productivity in Castle Lake, California, were caused by the weather, specifically
the timing of ice breakup and hydraulic flushing in the spring, and year-to-year
differences in angling pressure on rainbow trout, the primary fish planktivore in-
the lake. Zalewski et al. (1990) found that water levels during May and June in
Sulejow Reservoir, Poland, were closely correlated with the reproductive success
of the dominant fish in the lake (yellow perch and various minnows). In years
with the highest density of fish fry, cladoceran density decreased and
phytoplankton abundance increased. Thus, water levels in the spring indirectly in-
fluenced water quality in the reservoir later in the summer.
Food web interactions are affected, therefore, by a wide array of factors, and
some degree of instability is probably inevitable. Major uncertainties remain, how-
ever, over the degree to which annual variations can be controlled and whether
successful results can be sustained over the long term (Crowder et al. 1988;
Shapiro, 1990).
Importance of Behavioral Responses
Most studies of the effects of predators on prey emphasize the direct lethal effects
of being eaten. However, just as important in determining the success of a top-
down management program can be the sublethal, indirect responses of prey to
predators, including changes in prey behavior, habitat use, activity and movement
patterns, life history, physiology, or morphology (Sih, 1987). He and Kitchell
(1990), for example, found that fish losses resulting from emigration were at least
as great as those from direct consumption following the introduction of a fish
predator (northern pike) to Bolger Bog, Wisconsin. In Peter Lake, Wisconsin, the
minnow population responded behaviorally to even small numbers of largemouth
bass by concentrating in the littoral zone to avoid bass predation; as a result, min-
now grazing on pelagic zooplankton was minimal (Carpenter and Kitchell, 1988).
Some zooplankton also modify their behavior in the presence of fish planktivores,
the most common response being diurnal, vertical migrations through the water
column (Dini and Carpenter, 1991). All these responses effectively change the na-
ture of food web interactions. Behavioral responses can also occur quite rapidly
(within hours or days), more rapidly (in some cases) than predator-caused
mortality.
Influence of Trophic Status
A number of investigators have concluded that the importance of top-down effects
varies with trophic status. In particular, as noted previously, the zooplankton to
phytoplankton linkage tends to be weaker and less consistent in eutrophic and hy-
pereutrophic lakes than in mesotrophic or oligotrophic lakes because of differen-
ces in phytoplankton palatability. Based on enclosure experiments and empirical
data, McQueen et al. (1986) concluded that fish community alterations would have
little to no influence on phytoplankton in eutrophic lakes but could affect
phytoplankton in oligotrophic lakes.
Elser et al. (1990; also Elser and Goldman, 1991) evaluated phytoplankton
responses to variations in zooplankton grazing pressure in three California lakes
with different trophic status: Lake Tahoe (ultraoligotrophic), Castle Lake
166
-------
Chapter 9. Methods for Using Fish to Improve Water Quality
(mesotrophic), and Clear Lake (hypereutrophic). The effects were greatest in
Castle Lake, at an intermediate trophic status, than in either Lake Tahoe or Clear
Lake, at the extremes of the trophic status range. Clear Lake is dominated by in-
edible cynobacteria. Phytoplankton dynamics in Lake Tahoe are controlled
primarily by internal nutrient recycling from deepwaters. The introduction of
Mysis relicta (an invertebrate predator) into Lake Tahoe resulted in the elimina-
tion of Daphnia (see Box 8-F). But no discernible change occurred in primary
productivity, phytoplankton composition or abundance, or water transparency,
supporting the conclusion that water quality in ultraoligotrophic lakes may not
be sensitive to top-down effects.
Fish manipulations to control pelagic food webs and phytoplankton
dynamics may be most successful, therefore, in lakes of moderate productivity or
when implemented in conjunction with a reduction in external or internal
nutrient loads. Benndorf (1990) concluded that top-down management can be ef-
fective only in lakes with phosphorus loading rates below about 0.6 g total
P/m2/year (5.4 Ib/acre/year), although the exact loading threshold depends on
lake characteristics. Lammens et al. (1990) concluded that the chance of success-
ful biomanipulation is variable in lakes with total phosphorus concentrations be-
tween 50 and 200g/L but much less in lakes with higher phosphorus levels.
Successful zooplankton control of algal blooms has been observed, however, in
some strongly eutrophic systems (Schoenberg and Carlson, 1984; Van Donk et al.
1989).
Interactions with Fisheries Management
Fish are an important ecosystem component, and alterations of the fish com-
munity directly and indirectly affect many lake physical, chemical, and biological
characteristics, referred to collectively as "water quality." Fish are also a valued
resource; recreational fishing generates substantial social and economic benefits.
The strong linkage between fisheries and water quality management cannot be
ignored. Changes in the fish community to improve fishing or as a result of fish-
ing can alter water quality. Changes in water quality also directly affect the
quality of habitat for fish and the quality of the fishing experience.
Many examples abound that demonstrate this linkage, some of which have
already been noted in the sections above. The near elimination of macrophytes in
Lake Conroe, Texas (Martyn et al. 1986; Box 9-A) resulted in a decline in fish
species, such as largemouth bass, for which macrophyte beds are important
habitat. Fishing for largemouth bass was suggested as one cause for the inability
to sustain water quality improvements following biomanipulation in Round
Lake, Minnesota (Shapiro 1990). Anglers depleted the bass population to levels
below those required to control bluegill, the dominant planktivore in the lake.
Fishing was also cited by Jassby et al. (1990) as a major factor controlling varia-
tions in primary production in Castle Lake, California. In this case, however, the
target species — rainbow trout — is a planktivore rather than a piscivore. Thus,
high levels of fishing pressure decrease the abundance of planktivores and im-
prove water quality.
Historically, fisheries management has involved extensive fish introductions,
adding new species to lakes and drainage basins to diversify fishing oppor-
tunities or supplement fish prey (see Chapter 8). Such introductions have had
both positive and negative effects on water quality. For example, the introduction
of coho salmon into Lake Michigan to improve the lake's fisheries has caused a
marked decline in the alewife population (a planktivore) and contributed to an
overall improvement in water quality (Scavia et al. 1986; Kitchell and Carpenter,
1987; Box 9-C). In contrast, the introduction of rainbow trout into Medical Lake,
Washington, resulted in a sharp increase in algal biomass and decline in water
Fish manipulations to
control pelagic food webs
and phytoplankton
dynamics may be most
successful, therefore, in
lakes of moderate
productivity....
The strong linkage
between fisheries and
water quality
management cannot be
ignored.... Clearly,
interactions can and will
occur, although the nature
of the final effects -
positive, negative, or
neutral - will vary
depending on the nature of
a lake's food web, the
ecosystem components
and linkages, the target
fish species involved in the
fishery, and the nature of
the fisheries or water
quality management.
167
-------
Fish and Fisheries Management in Lakes and Reservoirs
quality (Scholz et al. 1985). Clearly, interactions can and will occur, although the
nature of the final effects — positive, negative, or neutral — will vary depending
on the nature of a lake's food web, the ecosystem components and linkages, the
target fish species involved in the fishery, and the nature of the fisheries or water
quality management.
168
-------
CHAPTER 10
Designing a
Field Sampling Program
Chapter Objective
Technical data on the status of a lake's fisheries, fish community, and fish habitat
are needed to
• identify existing lake problems and design an effective management
approach,
• establish pre-treatment conditions in the lake,
• quantify the system's response to management techniques and adjust
the management program accordingly, and
• evaluate the long-term success and effectiveness of the management
program (see Figs. 4-1,6-1, and 8-1).
Chapter 10 contains guidance on developing a field sampling and monitor-
ing plan to address these data needs, including sampling and data quality objec-
tives; deciding when, where, what, and how to sample; quality assurance and
quality control; data management; and effective presentation of the sampling
results. Specific sampling methods are described in Appendix B. Water quality
monitoring is discussed in detail in the companion guidance manual on Monitor-
ing Lake and Reservoir Restoration (Wedepohl et al. 1990); therefore, this chapter
focuses on monitoring related to fish and fisheries. For additional information on
field sampling designs for evaluating fish community status and fisheries
problems, see Johnson and Nielsen (1983) and Schreckand Moyle (1990).
Sampling Objectives
The optimal sampling design depends on the sampling objective(s): to assess cur-
rent conditions, diagnose a lake problem, detect before and after changes in
response to a management action, and/or evaluate long-term trends. Therefore,
the first step in developing a field sampling plan is to define specific sampling
objectives (Fig. 10-1).
• What is it that we really want to know when we're done? What are
the key questions to be answered? What lake and fisheries
characteristics are of greatest importance?
The first step in
developing afield
sampling plan is to define
specific sampling
objectives.
169
-------
Fish and Fisheries Management in Lakes and Reservoirs
• How confident do we need to be in our answers? What are the
consequences of an erroneous conclusion? Are we willing to expend
more effort and funds on sampling to increase our confidence in the
final conclusions?
• What level of change do we want to be able to detect? How quickly do
we need to detect this change?
Decisions about the sampling design rely heavily on the answers to each of
these questions. It is impossible to choose among various alternative approaches
as to how, when, where, and what to measure without first defining the sampling
objectives. In particular, data quality objectives must be established that specify
the level of precision and accuracy required to answer important management
questions with an acceptable level of confidence.
Lake Management Plan
- Mgmt. goals and objectives
-- Selected mgmt. techniques
Sampling Objectives
-- Key questions and variables of interest
- Desired level of confidence
Data Analysis Plan
What to measure?
- fishing quality
-- mechanisms
- early warning
indicators
- side effects
How frequently
to sample?
Sampling Plan
How to sample?
(sampling techniques)
Where' to sample?
When to sample?
Quality assurance/
quality control
Figure 10-1.—Major components of a field sampling plan.
170
-------
Chapter 10. Designing a Field Sampling Program
Developing sampling and data analysis objectives should be a top-down
process. Begin with general questions and then move to a more specific delinea-
tion of the types of information needed and level of resolution required. Figure
10-2 provides an example of the top-down planning approach for a diagnostic
study of Lotsa Luck Lake, a hypothetical lake for which fishing quality for
bluegill has reportedly declined in recent years.
Data analysis plans and the sampling design go hand-in-hand. A central part
of designing a sampling program is deciding a priori how the data will be
analyzed and used to address management questions and improve the manage-
ment program. A data analysis plan should be developed concurrently with the
field sampling plan to ensure that the sampling objectives can and will be
achieved. The data analysis plan can also assist in designing the most cost-effec-
tive sampling and monitoring program. Data needs are better defined, thus
avoiding unnecessary expenditures of time and funds to collect information that
will not contribute significantly to achieving the sampling objectives.
The Sampling and Monitoring Plan
A written sampling and monitoring plan should be prepared and in place before
initiating any field activities or management actions. In addition to presenting
the specific sampling and data quality objectives, this plan should address each
of the major components of a field sampling design (Fig. 10-1):
• What variables (lake and fisheries characteristics) will be measured?
• What sampling and analytical techniques will be employed?
• When will samples be collected (at what times of the year)?
• Where in the lake will the sampling take place?
• How many replicate samples will be collected per visit?
• How often will the lake sampling be repeated and for how long?
• How will the quality of the data be assured?
What is the population structure and what are the limiting
factors for bluegill and largemouth bass in Lotsa Luck Lake?
Ill
IV
What Is m What Is H what Is
growth Hfl mortality lj] growth
of bluegill? BNof bluegill?™ of bass?
Figure 10-2.—An example of top-down planning for Lotsa Luck Lake. Recent declines In
the quality of fishing for bluegill have been reported by local anglers. A hierarchical
series of questions Is developed to define the sampling objectives for a diagnostic study
to determine the cause of the fishing decline. The central question (the uppermost box)
can be answered If and on/y if the questions in the second row are answered. The ques-
tions In the second row can be answered if and only if the questions in the third row are
answered, and so on. The numbered boxes are questions that are answerable with estab-
lished methods (source: Johnson and Nielsen, 1983).
A data analysis plan
should be developed
concurrently with the field
sampling plan to ensure
that the sampling
objectives can and will be
achieved.
171
-------
Fish and Fisheries Management in Lakes and Reservoirs
The sampling program
should include all the
necessary elements
measured at the minimum
intensity and frequency
required to achieve the
sampling objectives.
Designing the field sampling program is not a trivial task. The costs of sam-
pling can be substantial; furthermore, future changes in the sampling program can
make trends through time difficult to detect and interpret. Therefore, the field
sampling plan should be well conceived and thoroughly reviewed. The sampling
program should include all the necessary elements (but no more) measured at the
minimum intensity and frequency required to achieve the sampling objectives.
Often, data exist on the lake and fisheries from previous surveys or monitor-
ing efforts. This information should be carefully reviewed for two reasons. First, it
can help you design a better sampling plan. The insight and information gained
from earlier surveys can guide such decisions as what to measure, where to
sample, and how to sample. In addition, in some cases making direct comparisons
between previous and current sampling results to evaluate changes over time may
be desirable. For such comparisons to be valid, the sampling methods (gear, loca-
tion, time, and level of effort) must be comparable.
To diagnose lake problems or assess the effectiveness of a management action,
sampling may be required not only in the lake but also in inflowing tributaries, the
lake outflow, and the watershed as well as other waters in the drainage basin.
Chapter 4 of Monitoring Lake and Reservoir Restoration (Wedepohl et al. 1990) dis-
cusses watershed monitoring. This chapter and Appendix B focus on sampling in
aquatic ecosystems.
What to Measure
The information you gather in the field should be a logical outgrouth of the objec-
tives of the sampling program. Diagnostic studies generally focus on indicators of
fish or fisheries condition — especially those that may be symptomatic of a par-
ticular type of problem — and those factors or conditions most likely to be limiting
or adversely affecting the fish community, fisheries, or fish habitat (see Chapter 6
and Fig. 10-2). To detect changes before and after management actions or long-
term trends, the lake and fisheries characteristics monitored must be sufficient to
assess both the success and effectiveness of the management program. The specific
variables will depend on the program's goals and specific objectives as well as the
management techniques applied.
At a minimum for fisheries management programs, data must be collected on
the key lake and fisheries characteristics that determine the quality of the fishing ex-
perience. If the management objective is to increase the total harvest or the numbers
and size of trophy fish, measures are needed of the numbers, types, and sizes of
fish caught by anglers. Frequently, however, a quality fishing experience and the
management objectives are more broadly defined, including concepts of ecosys-
tem integrity, a wilderness experience, or other aspects of the quality of the en-
vironment in which fishing occurs (see Chapter 5).
In addition to monitoring the program's outcome (i.e., its impact on fishing or
water quality), three other measures should be considered:
1. Information on the underlying mechanismfs) of response. A
better understanding of the mechanism of response and changes in re-
lated variables will allow managers to determine why the manage-
ment program is (or is not) succeeding and better evaluate the
program's effectiveness. For example, if insufficient prey was iden-
, tified as the major problem limiting fishing success, then measures of
. prey abundance and use should be included in the sampling program.
If habitat quality was a problem, these critical habitat features should
be routinely monitored. Generally, information on the status of fish
populations and the fish community in the lake together with direct
measures of fishing success are needed to understand the causes and
underlying mechanisms of response.
172
-------
Chapter 10. Designing a Field Sampling Program
2. Early warning indicators of changes or problems. Generally,
the earlier problems or trends can be detected, the easier they can be
corrected or appropriately adjusted. Thus, careful consideration
should be given to the types of measures and variables most likely to
respond and to the reapid detection of this response. Lake and
fisheries characteristics with a high natural variability may be quite
sensitive but require substantial sampling effort to distinguish be-
tween a management-induced change and the background "noise."
Such variables should be avoided unless the sampling program can
be designed to minimize or account for the effects of this high natural
variability.
3. Potential adverse side effects. As noted in Chapters 8 and 9,
many management techniques can cause undesirable side effects. If
such effects occur and are of sufficient magnitude, changes in the
management program may be warranted. For example, the eradica-
tion of aquatic macrophytes may, in some cases, be accompanied by
an undesirable increase in turbidity and/or phytoplankton blooms
(see Chapter 9). Thus, the sampling plan also should incorporate
measures of the potential side effects of concern for the particular
management techniques applied.
In selecting individual lake and fisheries characteristics to monitor, the fol-
lowing questions should be considered:
• How, specifically, will the measurements be used to evaluate the
program's success and effectiveness?
• Is the variable likely to change or provide valuable information for
assessing the lake's and fisheries' response to the management
program?
• What are the incremental costs (time, effort, and dollars) of
monitoring the variable? (See Box 10-A.)
• Do these costs compare favorably to the incremental benefit and
knowledge gained by including the variable in the sampling
program?
• Could alternative lake or fisheries characteristics be monitored that
would provide similar information at lower cost?
As a group, the suite of variables selected for monitoring should be com-
prehensive, balanced, and cover all of the important aspects and questions to be
addressed without extensive or unnecessary duplication. Conceptual models,
such as Figure 2-14 (Chapter 2), provide a useful check on the completeness of
the sampling plan.
How To Sample
Various methods can be used to collect information on the status of fish, the fish
community, and fisheries in a lake or reservoir. Some methods work better than
others for certain types of fish species, at certain times of the year, and in certain
types of environments and areas. In addition, the information provided varies
somewhat among the sampling methods.
Direct information on the status of a fishery can be obtained by sampling
anglers and evaluating the types, numbers, and sizes of fish caught by anglers ac-
tively involved in recreational fishing on the lake. Creel surveys, angler diaries,
[T]he sampling plan also
should incorporate
measures of the potential
side effects of concern for
the particular
management techniques
applied.
173
-------
Fish and Fisheries Management in Lakes and Reservoirs
Box 10-A.^-A Cost-Benefit Hierarchy for Information
[ about;Fish Populations and Communities
[ ; (source: Johnson and Nielsen, 1983)
The variables measured in a field sampling program should reflect an appropriate
balance between the cost of an activity and the new information provided. Table 10-1
lists selected categories of fish sampling information and the relative costs of each.
The least expensive, but also least informative, is to simply count the number of fish
species present and susceptible to the sampling gear (i.e., number of species caught).
At the other end of the scale is sampling that provides food habit information and
detailed tracking of the movements of individual fish by using radio or sonar tagging.
The metrics included in Table 10-1 are not a comprehensive listing, but an illustration
of some common variables monitored and the large variations in the relative costs.
Table 10-1.—Selected metrics of fish population or community status and the
relative costs of data collection (source: Johnson and Nielsen, 1983).
ACTIVITY
INFORMATION
RELATIVE
COSTS* COMMENTS
Species
enumeration
Number of species present
Easy to collect but depend-
ent on sampling techniques
Numbers of fish
caught of each
species
Relative abudance of the
species present
X2 Usually the minimal level of
information needed
Length of fish
Length distributions can
give relative year-class
strength, growth, and
mortality as well as pro-
portional stock densities
X4 A great deal of information
added, particularly for fast-
growing populations at
temperate latitudes
Weight of fish
Length-weight curves,
condition factors, and rela-
tive weight
X12 Often field scales are not
accurate enough, and special
shelters should be con-
structed
Age determination
More accurate than length
distributions for calcu-
lating year-class strength,
age distribution, growth
history, and mortality
X120 Requires extra handling of fish
and substantial laboratory
time for analysis
Radio or sonar
tagging
Exact information about
fish locations; may be
combined with information
on water depth,
temperature
X1200 Much information gained
about movements of
relatively few fish. Equipment
cost and maintenance can
be quite high
•Relative costs are expressed by comparison to the first activity listed.
and telephone or mail questionnaires are alternative methods for gathering data
on angler catch and use patterns. Such data provide not only insight on the status
of fish populations in the lake but also a direct measure of the quality of fishing
and the fishing experience. Some methods, such as angler diaries, are also relative-
ly inexpensive. At the same time, however, the numbers and types of fish sampled
are limited, focusing on game and large, catchable-sized fish. Little or no informa-
tion is obtained on nongame species and young age classes. Thus, while angler
surveys provide extremely valuable data, they are generally not sufficient for a
comprehensive assessment of fish community status and do not provide an early
warning indicator of change or potential problems.
Methods for sampling the fish community include gill netting, trap netting,
seining, trawling, angling (hook and line fishing), electrofishing, rotenone poison-
ing, hydroacoustics, and visual observations (e.g., by using SCUBA). Each method
174
-------
Chapter 10. Designing a Field Sampling Program
Table 10-2.—Suitable sampling gear for collecting adults and young of the year
(YOY) of selected fish species and groups in lakes. The gear listed are Intended as
examples only; other gear may also be suitable or even better In certain situations
or for specific sampling objectives.
GEAR*
TAXON
Trout, salmon,
whitefish, char
(except lake
trout)
Lake trout
Pike, pickerel,
muskellange
Catfish,
bullheads
Bass, sunfish,
crappie
Minnows, carp,
dace, chub,
shiners
Yellow perch
Walleye
FISH LIFE STAGE
YOY
Adult
YOY
Adult
YOY
Adult
YOY
Adult
YOY
Adult
YOY
Adult
YOY
Adult
YOY
Adult
STANDARD
Electrofishing
Trap nets
Electrofishing (F)
Trap nets (F)
Seine (Su)
Trap nets (S), gill nets (S,F)
Seine
Gill nets, trap netsb
Seine, electrofishing
Electrofishing
Electrofishing
Electrofishing
Seine (Su), electrofishing
Gill net, trap net
Seine (S), electrofishing (F)
Trap nets (S), gil nets (S,F),
electrofishing (S, F)
SUPPLEMENTAL
Gill nets, trawls, seine
Gill nets, electro-
fishing (F)
Seine (F), trawls
Baited traps
Slat nets, angling
Trap nets, angling
Seine
Seine
Trawls (S)
Trawls (S)
"Letter codes indicate seasonal restrictions on gear use to the spring (S), summer (Su), or fall (F).
"Bullheads only.
has its advantages and limitations, as discussed in Appendix B, and frequently,
multiple gear and approaches are employed and compared. The best gear and
sampling methods depend on the target fish species and life stage, the types of
information desired, and the environment to be sampled. Table 10-2 provides an
overview of suitable gear types for sampling selected target fish species and life
stages; further information is given in Appendix B.
One overriding guideline for selecting a sampling technique is the need to
prevent unnecessary fish mortality and stress. Some gear, such as gill nets (espe-
cially if set over-night), can kill all or most of the fish caught. In some cases, how-
ever, gill nets may be the most effective approach for collecting fish and the
optimal technique despite problems with high fish mortality. Sampling-
associated mortality is likely to have a more significant impact in small, low
productivity lakes and on fish populations that are less abundant or already
heavily stressed by other factors.
Often, sampling results are compared among lakes, among sites, or over
time. Because each sampling method has its own biases, these comparisons must
be based on a consistent set of sampling methods and effort. To help assure the
needed uniformity, written sampling protocols should be prepared that
thoroughly describe all aspects of the sampling program. In addition, all infor-
mation related to the specific sampling visit should be recorded in the field — in-
cluding gear types employed, the numbers, locations, and times of each sample,
and general comments and observations — and the log maintained for future ref-
erence.
One overriding guideline
for selecting a sampling
technique is the need to
prevent unnecessary fish
mortality and stress.
175
-------
Fish and Fisheries Management in Lakes and Reservoirs
In many lakes and
regions, the best time to
sample fish is during the
fall overturn period after
thermal stratification
breaks down and the lake
is completely mixed.
Measures of habitat
quality should be
conducted in those areas
and during those times
most critical to fish
population success.
With the proper guidelines and training, volunteers can provide valuable,
high quality monitoring data at minimal costs; therefore, carefully consider using
volunteers to expand the sampling program. Volunteer anglers, in particular, can
assist in monitoring changes in fisheries status.
When and Where to Sample
Typically, fish populations are monitored at least annually and often seasonally,
two to three times per year in the spring, summer, and/or fall. The best time of
year depends on the sampling method, the target fish species, and the type of data
to be collected. In many lakes and regions, the best time to sample fish is during
the fall overturn period after thermal stratification breaks down and the lake is
completely mixed because
» young-of-the-year and age 1+ fish of most target species should be
present and vulnerable to most standard collection gear, including
seines, trap nets, and electroshockers;
» species that dwell in the hypolimnion during the summer may be more
vulnerable to capture during fall overturn; and
• lower water temperatures in the fall can help reduce sampling-related
mortalities.
However, one time is most appropriate for all fish species, gear, and sampling ob-
jectives. Sampling at other times of the year may be necessary or more effective,
particularly for fish species with defined spawning migrations or concentrations
of fish during spawning, when they are more easily captured in large numbers.
Sampling may also be needed at more frequent intervals or other times of the year
to evaluate fish feeding habits or mortality rates relative to special environmental
events, such as winterkill or summerkill.
Sampling locations are also species-, life stage-, and gear-dependent. As with
sampling methods and time, locations should be selected to maximize capture ef-
ficiency for the target species of interest and provide the greatest gain in informa-
tion for the least amount of sampling effort. In addition, some gear types can be
used only in certain types of environments and locales, as discussed in Appendix
B. Within the set of acceptable locations, specific sampling sites should be selected
using a random, stratified, clustered, systematic, or other suitable sampling design
(Fig. 10-3; also see Johnson and Nielsen, 1983; Cochran, 1977; Elliot, 1977).
Measures of habitat quality should be conducted in those areas and during
those times most critical to fish population success. For example, if winterkill is a
major problem, levels of dissolved oxygen should be monitored, at a minimum,
during winters with long periods of snow and ice cover. Early life stages of fish are
often particularly sensitive to effects from toxicants, acidity, temperature, and low
levels of dissolved oxygen. Surface water quality in the times and locations coinci-
dent with the occurrence of these sensitive life stages may be a major factor limit-
ing population abundance and productivity and thus an appropriate focal point
for the sampling program.
For sampling programs designed to assess the success and effectiveness of
management actions, sufficient data must be collected before and after treatment
implementation and continue until the lake's response has stabilized. Pre-treat-
ment data must be collected with the same methods and protocols used for post-
treatment monitoring. Samples should be collected at consistent time(s) and
location(s) year after year to maximize detection of changes and trends. By
measuring the variable consistently at the same point on a seasonal or daily cycle,
in-lake measurement variability can be reduced and trends through time will be
more evident. For many variables, sampling times should be keyed not to a given
calendar day but rather to other environmental factors, such as water temperature,
degree-days, or day length.
176
-------
Chapter 10. Designing a Field Sampling Program
Simple Random Sampling:
Stratified Random Sampling:
Clustered Sampling:
Systematic Sampling:
Figure 10-3.—Example of various sampling designs for the selection of six sites for sein-
ing along a continuous shoreline. All numbers were chosen from a random number table
(source: Johnson and Nielson, 1983).
Number of Replicates and Sampling Frequency
The sampling plan must also specify the number and size of sampling units and
the sampling frequency and duration (how often, for how long). The number of
replicates required depends on the variability among samples, the questions
being addressed, and the desired level of confidence. The more measurements
collected, the easier it is to detect differences between sites or changes through
time. The more variable the characteristic (i.e., the greater the "background
noise"), the more data points are needed to detect a difference or trend of a given
magnitude. Large numbers of replicates and frequent sampling are advantageous
—but expensive; therefore, an optimal sampling design provides the appropriate
balance between costs and the ability to detect statistical differences or trends.
If the sampling and analytical variability are known or can be estimated, then
the numbers of measurements required to detect a statistically significant dif-
ference or trend of a given magnitude and with a given level of confidence can be
calculated using established statistical procedures. Figure 10-4, for example,
provides the results from such calculations for monthly phosphorus measure-
ments collected from the Neuse River, North Carolina. Because of the high
natural variation in phosphorus, over 120 monthly samples would be required to
detect a 23 percent linear decrease in total phosphorus if an error rate of 10 per-
cent is required. Smaller numbers of samples would be needed for larger changes
or for higher acceptable error rates. Many basic statistical texts outline proce-
dures for estimating sample sizes for various types of data analyses (e.g.,
Snedecor and Cochran, 1980; Cochran, 1977; Green, 1979). In addition, some State
agencies have developed standard sampling designs (e.g., Table 10-3) for
monitoring long-term trends in fish communities in the types of lakes and reser-
voirs common within their jurisdiction. Sample sizes of fish required for age,
growth, and condition analyses are discussed in Appendix B.
The more measurements
collected, the easier it is to
detect differences between
sites or changes through
time.
177
-------
Fish and Fisheries Management in Lakes and Reservoirs
120
"j 100
Error=0.20
—_
Error=0.30
PERCENT DECREASE (INCREASE) OF EXPECTED CONCENTRATION
Figure 10-4.—Sample size required to detect a linear trend of the specified magnitude with
a given error probability, based on phosphorus monitoring data for the Neuse River. North
Carolina (source: Wedepohl et al. 1990).
Table 10-3.—Examples of standard sampling designs developed by the Texas Parks
and Wildlife Department for long-term monitoring of fish communities in reservoirs
(source; Johnson and Nielsen, 1983).
SAMPLING
TECHNIQUE
Cove rotenone
poisoning
Gill netting
Seining
Trap netting
SIZE OF
RESERVOIR
(ACRES)
< 10,000
2 10,000
<100
101-5,000
5,001-10,000
> 10,000
< 5,000
5,001-10,000
> 10,000
<100
101-5,000
5,001-10,000
> 10,000
NUMBER OF
SAMPLING
UNITS
3 coves, > 1 acre each
3 coves, > 5 acres total
s 5 net nights
5 net nights
1 0 net nights
15 net nights
5 100-ft stations
10 100-ft stations
15 100-ft stations
5 net nights
5 net nights
10 net nights
15 net nights
WHERE
TO
COLLECT
Randomly
selected
Permanently
selected in
upper, middle,
and lower
section
Permanently
selected,
various habitats
Permanently
selected,
various habitats
WHEN
TO
SAMPLE
Between June and
September, all within
30 days
May
May, July, and Sep-
tember during day-
light
Once between April
and June and once
between September
and November
Quality Assurance/Quality Control
Sampling data must be of known and sufficient quality to achieve the sampling
objectives. Thus, the sampling plan should also include a comprehensive quality
assurance/quality control program.
Quality control involves procedures and protocols to improve the quality of
data collected and decrease the chances of extraneous errors. Examples of quality
control activities include the following:
• Preparation of written protocols for all sampling and analytical
methods to ensure they are consistently and appropriately applied;
178
-------
Chapter 10. Designing a Field Sampling Program
• Sample custody tracking system to minimize problems with the loss or
mislabelling of samples;
• Frequent instrument calibrations and internal quality control checks to
assure accurate measurements;
• Preventive maintenance procedures and schedules; and
• Database verification and validation procedures to identify outliers
and possibly erroneous data points.
Quality assurance involves collecting information to prove that the sam-
pling data are accurate and precise. Examples of quality assurance activities
include:
• Field and laboratory audits to confirm that the sampling and analytical
method protocols are being followed;
• Replicated, independent measurements to quantify sampling and
analytical precision;
• Field blanks and double-blind audit samples to confirm the accuracy
of measurements; and
• Routine quality assurance reports summarizing the results of all
quality control and quality assurance activities.
Quality control and quality assurance requirements for projects funded by
the U.S. Environmental Protection Agency are presented in Interim Guidelines and
Specifications for Implementing Quality Assurance Requirements for EPA Contracts
(EPA QAMS-005/80). State programs may also include written specifications and
requirements for quality assurance/quality control.
Data Management
All data collected should be organized and permanently maintained in a form
that can be easily accessed and analyzed. The voluminous and diverse nature of
the collected data and the variety of persons involved in collecting, recording,
and entering data increase the potential for error, which can have serious nega-
tive implications for any lake management program. Such problems can be
prevented — or at least minimized — however, by setting up a sound and effi-
cient data management system.
When setting up a data management system, several economic, technical,
and managerial components must be considered. Economic components include
the availability of funds to acquire the necessary computer hard ware/software
and training to develop and maintain a data management system or to revert to a
paper file. If economically feasible, technical components involve selecting ap-
propriate computer equipment and software and designing the database, includ-
ing data definition, data standardization, and developing a database dictionary.
The database dictionary provides a written description, including units and
methods of measurement where appropriate, of all variables in the database that
can be easily distributed to database users. The managerial components of data
management include data entry, data validation and verification, and access pro-
cedures for data users.
To assure the integrity of the database, data quality must be controlled and
monitored from collection to the time the information is entered into the
database. Laboratory and field data sheets or a computerized data entry system
may be used to create the initial data record; in either case, care must be taken to
avoid transposing numbers, entering information into the wrong location, or
other errors. For data recorded on laboratory or field data sheets, subsequent
All data collected should
be organized and
permanently maintained
in a form that can be
easily accessed and
analyzed.
179
-------
Fish and Fisheries Management in Lakes and Reservoirs
data entry into a preliminary computerized database file should be made directly
from the original data sheets or photocopies to minimize the potential for
transcription errors. The database design should include automatic range-check-
ing values for all parameters entered into the computer as an initial screening for
errors. Any values outside of the defined ranges should be automatically flagged
and checked and corrected as soon as possible. For some parameters, database
checks that disallow duplicate numbers may be appropriate (e.g., unique codes for
water samples). After a set of values are entered into the preliminary database file,
the information should be printed and verified against the original data sheets to
eliminate any data entry errors.
Additional validation of the data can include expert review to identify suspect
values. To resolve questionable data points, the persons responsible for collecting
and entering the original data should be consulted. After all data are verified and
validated, they can be merged into the master database for the sampling or
monitoring program. To prevent data loss from computer failure, at least one set of
duplicate (backup) copies of all database files should be maintained at a separate
location. Figure 10-5 diagrams a sample data management process.
Effective Presentation of Results
The monitoring results and outcomes from the fisheries management program
should be widely and regularly communicated in an easy-to-understand format to
all those involved in the planning process and program implementation. Especial-
ly for programs involving volunteers or that rely on voluntary compliance with
fishing regulations, the demonstration that the management program has had a
positive impact provides important feedback that encourages continued voluntary
assistance and compliance. Thus, two types of project reports should be routinely
prepared:
1. A technical, detailed analysis of the program results for technical
review by professional fisheries biologists; and
2. An interpretive summary written for a more general, broader
audience.
The latter should present only key findings and explain the significance of the
results with regard to the program's success and future monitoring and manage-
ment activities. Most results can be presented effectively in summary figures or
plots, such as those in Figures 3-1, 3-9, and 3-10. Chambers et al. (1983) and Tufte
(1983) discuss graphical methods for data analysis and ideas for visually display-
ing quantitative information.
This manual cannot provide a discussion of the many statistical techniques
used to analyze environmental data and evaluate the results from a field sampling
program. Chapter 11 discusses the role of modeling in fisheries management, one
method for summarizing and evaluating information. In addition, Chapters 3 and
Appendix B mention a number of commonly used analysis routines for fisheries
data. However, for more detailed and technical reviews of statistical issues and
methods, the reader is referred to Wedepohl et al. 1990 as well as available statis-
tics and fisheries texts, such as Draper and Smith (1966), Ricker (1975), Snedecor
and Cochran (1980), Hollander and Wolfe (1973), Zar (1974), Elliot (1977), Green
(1979), Conover (1980), Everhart and Youngs (1981), Gilbert (1987), and James and
McCulloch (1990).
180
-------
Chapter 10. Designing a Field Sampling Program
FIELD
SAMPLING
LOCATION
DATA ENTRY
FIELD
DATA ENTRY
LABORATORY
DATA ENTRY
UNCORRECTED
RAW DATA
FILES
DATA
VERIFICATION
DATABASE
FILES
MASTER
DATABASE
SYSTEM
DATA ANALYSIS
1
CHAIN OF
CUSTODY
DATA ENTRY
OFFSITE
BACKUP
DATA
VALIDATION
DATABASE
FILES
OFFSITE
BACKUP
OFFSITE
BACKUP
INFORMATION
DISSEMINATION
Figure 10-5.—Common steps in the data management process.
181
-------
-------
CHAPTER 11
Role of Modeling in
Fish and Fisheries
Management
Chapter Objectives
Chapter 11 provides a brief overview of the role of models in fish and fisheries
management, the types of questions models can help address, the types of
models and modeling approaches available, and the uses, advantages, disad-
vantages, and data requirements of each. This chapter does not describe the
process of model development nor any specific model used in managing fish or
fisheries. Citations are included for details on model formulation and example
applications.
Only models relating directly to fish or fisheries management are considered.
Water quality models used to predict changes in water chemistry in response to
alterations in watershed management or pollutant loadings may also be valuable
in addressing some fisheries management concerns. Descriptions and example
applications of water quality models are provided in The Lake and Reservoir Res-
toration Guidance Manual (Olem and Flock, 1990).
Definitions
"A model is a simplified representation of a real object, process, concept, or sys-
tem" (Reckhow and Chapra, 1983; pg. 15). Models can be conceptual or mathe-
matical. "A mathematical model is a mathematical equation or set of equations
that translates a conceptual understanding of a system or process into quantita-
tive terms" (Reckhow and Chapra, 1983; pg. 15). Mathematical models are fre-
quently described or categorized by several criteria:
1. Empirical or mechanistic. Empirical models are developed
primarily from an analysis of data. Mechanistic models, on the other
hand, are mathematical descriptions of theoretical principles. Most
models have elements of each but can be classified according to
which approach dominates.
2. Static or dynamic. Dynamic models describe or predict system
behavior over time, while static or steady-state models are time-inde-
pendent.
3. Deterministic or stochastic. Deterministic models use expected
values for all parameters and yield predictions that are also expected
183
-------
Fish and Fisheries Management in Lakes and Reservoirs
Models provide a means of
synthesizing the available
data and understanding of
these complex
relationships into a more
usableform.
values—that is, single values with no explicit expression of the uncer-
tainty in the prediction. Stochastic models, on the other hand, incor-
porate variability and uncertainty directly into the model by
expressing model parameters and/or outputs as probability density
functions—that is, the distribution of possible values and chance
(probability) that each value will occur. Most fish and fisheries models
used today are deterministic. Stochastic models are computationally
more difficult and time-consuming, although the benefits of explicitly
addressing uncertainties can be substantial, especially for models used
to aid management decisionmaking.
Reckhow and Chapra (1983) and Chapra and Reckhow (1983) provide addi-
tional criteria for model characterization and detailed discussions on model
development and testing specifically for lake management. Walters (1986)
describes the development and use of models for managing renewable natural
resources, such as fisheries.
Why Model?
Lake ecosystems are complex, with many components, interactions, and indirect
effects and substantial spatial and temporal heterogeneity. Models provide a
means of synthesizing the available data and understanding of these complex
relationships into a more usable form.
Models can be developed to learn, to predict, or to evaluate—or to do all of
these functions. Models contribute to the learning process and improved under-
standing of lake ecosystems in two ways:
1. The process of model building—integrating information together into
a representation of the real world — frequently provides new insights,
fosters clear thinking, and helps identify gaps in data and under-
standing.
2. Comparisons of model outputs to expectations and real world data
provide- important feedback that advances learning. Inconsistencies
help to identify misunderstandings, missing components or processes,
erroneous assumptions, or other inadequacies that require additional
thought or research.
Because a major part of the benefits derived from using models is this con-
tribution to learning and improved understanding, lake managers should be
directly involved in model development to the degree possible rather than just as
users of model results. Adaptive environmental management is an approach that
views management as a continual, adaptive learning process, uses models as the
primary means of synthesizing understanding, and actively involves scientists,
managers, policy makers, and other appropriate parties in model development
(Walters, 1986; also see Chapter 4).
Model outputs can also directly aid management decisions. Models can be ap-
plied to predict the outcome of various management options; for example, the ef-
fect of a change in the minimum size regulation on fish growth and fisheries yield.
Models can assist in evaluating lake problems, such as the effects of toxic substan-
ces on fish reproductive success or the relative importance of fishing mortality;
identifying fish species for which the lake provides suitable habitat; estimating the
maximum sustainable fisheries yield; or assessing the nature and magnitude of
user conflicts. All of these model applications can help in selecting the most ap-
propriate and effective management option.
Models are not, however, a substitute for experience, clear and logical think-
ing, or other types of data analysis. Instead, models should be used as an addition-
184
-------
Chapter 11. Role of Modeling in Fish and Fisheries Management
al tool that, together with experience, logical thinking, and other analyses, can
facilitate and improve lake management decisions. Applying models blindly
without understanding their structure, assumptions, and limitations and before
confirming their validity is worse than not using models at all.
Importance of ConceptuaB Models
Conceptual models are qualitative, usually graphical, representations of impor-
tant system components, processes, linkages, and interactions, as in Figures 2-14
and 11-1. They serve several important purposes, many of which have been
noted in earlier chapters. Development of a conceptual model is an initial step in
hypothesis testing and in building mathematical models (Reckhow and Chapra,
1983). Conceptual models, by themselves, can also assist in the following ac-
tivities:
• Designing field sampling and monitoring programs to ensure that all
important system attributes are measured.
• Determining causes of lake problems by delineating system linkages
and possible cause-and-effect relationships.
• Identifying potential conflicts among lake users or management
objectives.
• Anticipating the full scope of lake responses to management actions,
including potential negative side effects.
Conceptual models are relatively easy to develop; therefore, all lake manage-
ment programs should produce a conceptual model of the lake ecosystem as a
framework for all subsequent activities and analyses.
TROPHIC RESOURCES
HABITAT RESOURCES
COVER•
HABITAT
EXPANSION
OPEN
NICHES
HABITAT
QUANTITY
AVAILABLE HABITAT
J
FISH PRODUCTION
Fiaure 11-1 —Conceptual model of factors that influence fish production In reservoirs.
For trophic resources, solid lines indicate organic matter fluxes and dashed arrows rep-
resent nutrient fluxes (source: Kimmel and Groeger, 1986).
Questions that Modeling Can Help Address
The following are examples of the types of management questions and issues
that mathematical models can help address, if existing data are available to
"model" answers to the questions:
1. How does my lake compare, in terms of fish growth, fish abundance,
fisheries yield, or other important attributes, to other similar lakes in
the region?
[AJpplying models blindly
without understanding
their structure,
assumptions, and
limitations and before
confirming their validity
is worse than not using
models at all.
Conceptual models are
relatively easy to develop;
therefore, all lake
management programs
should produce a
conceptual model of the
lake ecosystem as a
framework for all
subsequent activities and
analyses.
185
-------
Fish and Fisheries Management in Lakes and Reservoirs
[A]n important first step
in selecting or developing
a model is to "bound" the
problem: define the
appropriate spatial and
temporal scale and
ecosystem components
and processes that must be
considered to answer the
management questions.
2. Given current conditions in the lake, which fish species are best suited
to the lake habitat and most likely to survive and reproduce?
3. What lake characteristics or factors are currently limiting the survival,
reproduction, or production of fish species in the lake?
4. In how many years will fish in the lake reach a length and weight
suitable for harvesting (e.g., reach the current minimum size limit)?
5. Is fishing a significant contributor to fish mortality? If fishing pressure
is increased or decreased, will the numbers and size of fish available
for harvest change significantly?
6. How many and what biomass of fish can be harvested annually from
the lake or reservoir without adversely affecting the long-term sus-
tainability of the fisheries and fish resource?
7. If the minimum size limit regulation is altered, how will fish growth,
reproduction, abundance, and yield change?
8. If a given number, size, and species of fish are stocked into the lake,
how fast will they grow and how many will survive to reach harves-
table size?
9. If shoreline development destroys five acres of fish spawning habitat,
will fish abundance or the quality of fishing decline? If so, by how
much?
10. Are current levels of toxic substances in the lake causing a measurable
decline in fish survival, growth, abundance, or yield?
11. If nutrient loads to the lake are reduced, how will fish growth and
abundance, fisheries yield, and the quality of fishing be affected?
12. Will introducting fish species "X" into the lake adversely affect the sur-
vival or growth of other fish species or cause a measurable change in
other biotic communities or water quality?
13. If fishing pressure for the top predator in the lake increases, will water
quality be adversely affected?
Types of Models Used in Fish and
Fisheries Management
Modeling approaches and the best type of model to apply depend on the manage-
ment questions being addressed. Thus, an important first step in selecting or
developing a model is to "bound" the problem: define the appropriate spatial and
temporal scale and ecosystem components and processes that must be considered
to answer the management questions.
• Is it necessary to predict changes over time (a dynamic model) or are
predictions of steady-state conditions adequate (static model)?
» If time is important, are we interested in short-term (e.g., daily, seasonal)
changes or long-term trends over years?
• Is the problem best addressed on a regional scale (e.g., comparisons
among lakes) or by modeling specific processes within an individual
lake or watershed?
» Is spatial heterogeneity likely to influence the results, thereby requiring
a model with multiple spatial compartments?
186
-------
Chapter 11. Role of Modeling in Fish and Fisheries Management
• Is modeling a single process (e.g., fish growth or fish mortality) or the
dynamics of an individual fish population (species) in isolation suffi-
cient? Or is considering interactions among species (e.g., predator-prey
relationships) or the influence of habitat characteristics necessary?
This chapter discusses the following six general types of models, each of
which is suitable for addressing one or more of the questions listed previously:
1. Habitat evaluation models
2. Empirical regression models of fisheries yield and other fisheries
attributes
3. Fish mortality models
4. Fish growth models
5. Population dynamics models
6. Ecosystem simulation models
Habitat Evaluation Models
Many factors influence the suitability of a lake or reservoir for fish. Models have
been used to combine these various factors and variables into simple indices of
habitat suitability or quality. The most commonly used habitat evaluation model
is the Habitat Suitability Index (HSI), developed using the U.S. Fish and Wildlife
Service's Habitat Evaluation Procedures (HEP) (U.S. Fish Wildl. 1980). HSI
models are available for 66 species of fish, shellfish, and other aquatic inver-
tebrates (O'Neil and Gray, 1988), including 48 fish species that live at least part of
their life cycle in fresh water (Table 11-1).
Table 11-1.—Fish specios for which Habitat Suitability Indices are available (adapted
from O'Neil and Gray, 1988).
alewife
bigmouth buffalo
blacknose dace
brook trout
Chinook salmon
common carp
cutthroat trout
gizzard shad
lake trout
longnose sucker
paddlefish
redbreast sunfish
shortnose sturgeon
smallmouth buffalo
walleye
white crappie
American shad
black bullhead
blueback herring
brown trout
chum salmon
common shiner
fallfish
green sunfish
largemouth bass
muskellunge
pink salmon
redear sunfish
slough darter
spotted bass
warmouth
white sucker
Arctic grayling
black crappie
bluegill
channel catfish
coho salmon
creek chub
flathead catfish
inland silverside
longnose dace
northern pike
rainbow trout
rock bass
smallmouth bass
striped bass
white bass
yellow perch
The HSI models are generic and applicable over large geographic areas. They
are based largely on literature reviews to identify those habitat characteristics
and conditions most important for the survival, growth, and reproduction of a
species. For each important environmental variable, the levels and conditions
considered suitable for the species are expressed as a suitability index, ranging
from 0.0 (unsuitable) to 1.0 (optimal). Measured values for a given lake or reser-
voir can then be assigned a rating between 0 and 1 for each suitability index.
These individual suitability indices are then aggregated, usually as a geometric
mean, into a composite index, termed the HSI. An example HSI model for brook
trout in lakes is presented in Figure 11-2. Additional guidelines for applying HSI
models in lakes and reservoirs are provided by Terrell et al. (1982).
The most commonly used
habitat evaluation model
is the Habitat Suitability
Index (HSI)....
187
-------
Fish and fisheries Management in Lakes and Reservoirs
1.0
I 0.8
x
| 0.6
jj? 0.4
D 0.2
co
0
Minimum/Maximum pH
I I,
\
I
I I
6 7
pH
10
Average Minimum Dissolved Oxygen
1.0
8 0.8
x
•g 0.6
tO 4
0.2
0
W
1.0
£ 0.8
£
jg 0.6
&
1 °'4
cl 0.2
0
369
Dissolved Oxygen (mg/L)
Average Maximum Temperature -
I
I
Habitat Suitability Index (HSI)
HSI - 0" x DO x pH)1/3
10 20
Temperature (°C)
30
Figure 11-2.—Habitat Suitability Index for brook trout in lakes (modified from Raleigh,
1982)* '
The major assumption of these models is that the aggregated HSI value is
proportional to the carrying capacity or quality of the lake habitat. However, few
of the published HSI models have been field validated. Trial et al. (1984), for ex-
ample, evaluated the performance of HSI models for blacknose dace, common
shiner, fallfish, Atlantic salmon, and brook trout in Maine streams. Both brook
trout and Atlantic salmon standing crops were significantly correlated with the
HSI values. However, Trial et al. (1984) also recommended that the models be sig-
nificantly revised to address important processes not currently included in the HSI
(e.g., the addition of upwelling groundwater and alkalinity to the brook trout
188
-------
Chapter 11, Role of Modeling in Fish and Fisheries Management
model). Most of the HSI models are also quite data-intensive, requiring fairly
detailed assessments of specific habitat features.
Despite these limitations, HSI models provide the best currently available
basis for evaluating habitat quality. Applications of HSI models can provide a
preliminary assessment of the suitability of a lake or reservoir for a particular
fish species (question 2) and insight into major limiting habitat features (ques-
tion 3). For additional information on the HSI, including a list of .available
models and documentation, contact the U.S. Fish and Wildlife Service, National
Ecology Research Center, 4512 McMurry Avenue, Fort Collins, CO 80525-3400,
(303) 226-9311.
Regression Models of Fisheries Yield and Other
Fisheries Attributes
How do fish growth rates, fish biomass, or fisheries yield in my lake compare to
those in other similar lakes in the region (question 1)1 What is the potential
fisheries yield? How many and what biomass of fish can be harvested from the
lake without adversely affecting the long-term sustainability of the fish resource
(question 6)?
These are commonly asked and important questions in fisheries manage-
ment. One approach to addressing these questions is to quantify the individual
processes that contribute to or influence fish population dynamics and yield (e.g.,
growth rates, fecundity and reproductive success, mortality rates). While it is
possible to conduct such a detailed mechanistic analysis, developing and apply-
ing it requires a large amount of site-specific information as well as substantial
experience and expert knowledge. Mechanistic models of this type certainly have
a place in fisheries management and are discussed later in this chapter. However
for most management applications, simpler and easier approaches and models,
such as empirical, regression-based models, can serve this role.
Regression models rely on the observed association between the fisheries at-
tribute of interest (most often, fisheries yield or fish biomass) and selected lake
characteristics measured in a representative sample of lakes or reservoirs within
a particular region. Once calibrated, these models can then be applied to other,
similar lakes in the area. It is assumed that the observed relationship between the
fisheries attribute and lake characteristics in the lakes used to calibrate the model
also holds for any additional lakes to which the model is applied. This is a
reasonable assumption as long as (a) the lake characteristics included as predic-
tor variables in the model are indeed those factors most important in controling
the fisheries attribute or are at least good surrogates for these important factors,
and (b) the model is not applied to lakes or reservoirs with characteristics dis-
tinctly different from those in the calibration data set. A model calibrated on lakes
in a northern temperate region, for example, should not be applied to midr
western or southern waters; a model calibrated for lakes at high elevations is un-
likely to provide accurate predictions of yield in lower elevation lakes.
A wide range of lake and reservoir characteristics may serve as useful predic-
tors of fish biomass and fisheries yield, including physical, chemical, and biologi-
cal variables (Table 11-2). Both single-variable and multiple-variable models have
been developed and in some cases can account for up to 90 percent or higher of
the variation in yield or biomass among the calibration lakes. Aggregated in-
dices, such as the HSI described in the previous subsection, have also been used
as predictors in some models.
One of the most widely used predictors of lake and reservoir fisheries yield is
the Morphoedaphic Index (MEI) (Ryder, 1965,1982; Ryder et al. 1974). The MEI
and MEI models were developed originally for northern temperate lakes (see
Chapter 3) but have been modified and adapted for lakes and reservoirs in many
A wide range of lake and
reservoir characteristics
may serve as useful
predictors offish biomass
and fisheries yield,
including physical,
chemical, and biological
variables.
189
-------
Fish and Fisheries Management in Lakes and Reservoirs
Table 11-2.—Summary of percentages of variation explained by single-variable and
multlvarlate models used to predict fish yield and standing crop in lakes and reser-
voirs from abiotic and blotlc variables (source: Carline, 1986).
INDEPENDENT VARIABLES TESTED*
MODEL %VARIAB.
TYPE" EX- SOURCE
PLAINED
FISHERIES YIELD FROM NATURAL LAKES
Mean depth S 28-92
Mean depth, MEI S 54-73
Phytoplankton production S 57-82
Phytoplankton standing crop and production S 74-84
Benthic biomass, MEI S 62-83
Surface area S 94
Length of growing season S 74
Total P, TDS, MEI, benthic biomass, mean depth S 54-73
Mean depth, MEI M 63-92
Mean depth, TDS M 46-76
Mean depth, TDS M 63-68
Surface area, mean depth, TDS M 95-97
Length of growing season, MEI M 81 -83
Area, mean depth, TDS, total P, benthic biomass M 40-97
Rawson (1952)
Ryder (1965)
Melack(1976)
Oglesby (1977)
Matuszek(1978)
Youngs and Heimbuch
(1982)
Schlesinger and Regier
(1982)
Hanson and Leggett (1982)
Prepas (1983)
Ryder (1965)
Matuszek(1978)
Youngs and Heimbuch
(1982)
Schlesinger and Regier
(1982)
Hanson and Leggett (1982)
FISHERIES YIELD FROM RESERVOIRS
Chlorophyll a, total P S 52-83
Mean depth, MEI S 8-20
Length of growing season, area, reservoir age M 17
Jones and Hoyer (1982)c
Jenkins (1982)
Jenkins and Morals (1971)
Alkalinity
Benthic biomass/mean depth, depth, biomass
Area, mean depth, benthic biomass,
biomass/depth
Length of growing season, area, Secchi disk
depth, macrophyte abundance, panfish index,
rough fish index
STANDING CROP IN NATURAL LAKES
S 27-41
S 20-83
M 35-83
Carlander(1955)
Hanson and Leggett (1982)
Hanson and Leggett (1982)
M
44-56 Schneider (1978)d
STANDING CROP IN RESERVOIRS
Alkalinity
Retention time
Annual outflow volume, retention time, area
MEI
Total P, Secchi disk depth, chlorophyll a
Length of growing season, annual outflow
volume, shoreline development index, TDS
S
S
S
S
S
M
69
72
9-31
21-72
16-41
52
Carlander (1955)
Jenkins (1976)
Aggus and Lewis (1978)
Jenkins (1982)
G.R. Ploskey, undated
Aggus and Lewis (1978)
Abbreviated variables are P = phosphorus, MEI = Morphoedaphic Index, TDS = total dissolved solids.
b S = single-variable model; M = multivariate model. Where more than one single-variable model was tested,
the Independent variable giving the best predictions is listed.
c Some data from lakes were included.
d Some data from reservoirs were included.
other regions and climates (Oglesby, 1982). The MEI predicts fish biomass or
potential yield as a function of mean depth (z) and the concentration of total dis-
solved solids (TDS) (Figs. 11-3 and 11-4):
MEI = (TDS/z)1/2
Jackson et al. (1990) raised concerns, however, about predictive models based
on ratio variables, such as the MEI. Rempel and Colby (1991) refute their concerns
but support the conclusion that multivariate regression models may be preferable
190
-------
Chapter 11. Role of Modeling in Fish and Fisheries Management
100
X
\
D
O)
10
Temperate
. Temperate
10
100
MORPHOEDAPHIC INDEX (ppm/m)
Figure 11-3.—Predicted yield curves as functions of Morphoedaphic Index for six sets of
natural lakes representing six of the world's climatic zones (source: Schlesinger and
Regler, 1982, adapted from Henderson et al. 1973).
50 100
MORPHOEDAPHIC INDEX
Figure 11-4.—Comparisons of regressions of (a) Ryder's (1965) yield (Y) in a sample of
natural lakes, (b) reservoir sportfish harvest (H), and (c) standing crop (C) in kg/hectare
on the Morphoedaphic Index (MEI). Regression formulas are (a) log Y = 0.168 + 0.446 log
MEI (N=23, r2=0.73); (b) log H = 0.925 + 0.563 log MEI - log MEI2 (N=290, ^=0.08); and (c)
log C = 1.498 + 0.677 log MEI - 0.223 log MEI2 (N=290,1^=0.21) (source: Jenkins, 1982).
191
-------
Fish and Fisheries Management in Lakes and Reservoirs
to relying on summary indices. While the MEI and multivariate models produced
similar estimates of yield, multivariate models allow for valid, quantitative es-
timates of model error and confidence limits on model predictions.
Generally, the types of environmental variables significantly correlated with
fisheries yield in reservoirs are the same as in natural lakes. The one exception is
the mean retention time, which is important in reservoirs but of minor significance
in lakes where retention times are often rather long (i.e., several years). The best
MEI-based yield models in reservoirs have been derived when reservoirs were
subdivided into similar operational or chemical groups, such as hydropower
mainstream, hydropower storage, and chemical types of nonhydropower reser-
voirs (Jenkins, 1982). Retention times are similar within groups; hence, the in-
fluence of retention time on productivity is taken into account indirectly by
organizing reservoirs into groups with similar retention times.
The predictive function afforded by empirical regression models should be
adequate for a number of practical purposes where monetary and labor restraints
prevent detailed studies. Quick approximations of yield or fish biomass can be
useful to managers who must make management decisions before obtaining com-
prehensive field data. For the most part, the predictor variables are relatively easy
and inexpensive to measure. On the other hand, collecting accurate data on sus-
tainable yields or fish biomass for a sufficient number of lakes for model calibra-
tion can be difficult and time-consuming (see Chapter 3 and Appendix B).
Mortality Models
Information on fish mortality rates is essential for many management decisions. If
natural mortality rates are high, fish may need to be harvested at relatively young
ages to obtain large fisheries yields. The balance between natural and fishing mor-
tality also influences the magnitude of fisheries yields as well as the maximum
sustainable fisheries yield. Toxic pollutants, habitat destruction, and many other
environmental impacts may affect fish communities primarily by increasing fish
mortality. Models of fish mortality (or that include a mortality component) are
needed to address questions 5, 6, 7, 8, 9, and 10, at a minimum, and potentially
could assist in addressing most of the questions listed earlier.
Most mortality models rely on the same basic equation (Ricker, 1975; Lackey
and Hubert, 1978; Everhart and Youngs, 1981):
Nt = No e'A
where Nt = the number of fish alive at time t,
No = the number of fish alive at the start of the time interval, and
z = the instantaneous mortality rate.
The number of fish dying over a given time interval (often, per year) is as-
sumed to be proportional to the number of fish alive at the beginning of the period
(dN/dt = -zN). If this assumption holds and the mortality rate is constant year to
year, then the numbers of fish in a given cohort (year class) will decline exponen-
tially over time (Fig. ll-5a). The mortality rate can be estimated directly from es-
timates of fish density at each age (Fig. ll-5b) or from changes in catch per unit
effort (CPUE), assuming CPUE is a reasonable indicator of relative fish abundance
(Fig. ll-5c). A single mortality rate can be applied to all fish (or all adult fish), inde-
pendent of fish age, or separate mortality rates can be calculated for each age
group.
If the numbers of fish harvested each year are known or estimated, then the
total mortality rate (z) can be subdivided into fishing mortality (f) and all other
sources of fish mortality, generally referred to as "natural mortality" (m):
z = f + m
192
-------
Chapter 11. Hole of Modeling in Fish and Fisheries Management
(a)
(b)
(c)
o
v.
JO
3
V Slope Z
Time
Age
Figure 11-5.— (a) Exponential decline In the number of fish in a cohort over time If the
number of fish dying is proportional to the initial number of fish and the mortality rate is
constant; (b) on a logarithmic scale, the slope of the line provides an estimate of the in-
stantaneous mortality rate; (c) most sampling methods, however, are less effective at
catching small fish. Thus, the mortality rate should be calculated only from that portion
of a catch curve where fish are equally susceptible to the sampling gear (source: Ever-
hartand Youngs, 1981).
The fishing mortality rate is a function of fishing pressure and can be control-
led, to a large degree, through changes in fishing regulations. In some analyses,
the natural mortality rate is assumed to be constant and independent of fishing
mortality; alternatively, natural mortality rates can be treated as density depend-
ent, varying as a function of fish density. As discussed in Chapter 3, the degree to
which natural mortality is density dependent (and can compensate for changes
in fishing or other human-caused mortality) is a major source of uncertainty in
assessing and modeling fish population responses to environmental stresses.
In most management applications, mortality models are used together with
models of fish growth and reproduction to assess changes in fish population
dynamics (discussed later in this chapter) and fisheries yield. For example, Evans
(1989) and Zagar and Orth (1986) examined the influence of a change in the mini-
mum size regulation, and thus age of fish harvest, on fisheries yield and the size
of fish harvested. Evans and Willox (1991) included a mortality model as part of
their assessment of interactions between native and stocked lake trout, and Muir
(1964) analyzed the effect of fishing on muskellunge in Nogies Creek, Ontario.
Growth Models
The von Bertalanffy (1938) growth equation is one of the most widely used
models for estimating the length or weight of fish at a future point in time.
Length at time t (It) is expressed as a function of the maximum length for the
population (1»), a growth coefficient (K), and the time (t0) when length would
theoretically be zero:
'
Assuming isometric growth, the growth equation stated in terms of weight
(wt)is:
Values for K and loo (or w<») may be obtained by plotting length (or weight) at
time t+1 (y axis) against length at time t (x axis) for each successive age (Fig. 11-
6); the final parameter, to, can then be back-calculated from the growth equation.
Alternatively, computer software is available for estimating all three parameters
directly from data on fish size and age (e.g., Saila et al, 1988).
The basic von Bertalanffy equation assumes that fish growth rates are fixed
and do not vary as a function of food supply or other environmental factors.
[T]he degree to which
natural mortality is
density dependent (and
can compensate for
changes in fishing or other
human-caused mortality)
is a major source of
uncertainty in assessing
and modeling fish
population responses to
environmental stresses.
193
-------
Fish and Fisheries Management in Lakes and Reservoirs
Figure 11-6.—Walford plot (Walford, 1946) of annual increment In fish length. Length at
time t plotted against length at time t+1 (l»= maximum length attainable) (source: Lackey
and Hubert, 1978).
Variations in growth rates can be modeled by applying adjustment factors to the
parameters in the von Bertalanffy equation (e.g., Taylor 1981) or by using alterna-
tive, more mechanistic models of fish growth. In particular, bioenergetics models
have been developed in which fish growth (increase in biomass over time, dB/dt)
is predicted by the difference between the energy value of the prey consumed (C)
and the sum of the specific energy outputs associated with respiration (R), eges-
tion (F), and excretion (U) (Kitchell et al. 1977):
dB/dt = C - (R + F + U)
Fish consumption rates are controlled by the availability of suitable prey and
temperature. Energy expenditures for reproduction can also be considered.
Bioenergetics models are most commonly used within ecosystem models (dis-
cussed later in this chapter) to assess interactive effects among species (e.g.,
predators and prey). Madenjian et al. (1991), for example, used a bioenergetics
model of walleye growth to evaluate walleye stocking strategies as a function of
prey (yellow perch) availability and size distributions. Swartzman and
Beauchamp (1990) modeled the bioenergetics of rainbow trout growth to assess
the effects of trout introduction into Lake Washington on longfin smelt and sock-
eye salmon parr. Because of the large number of parameters that must be quan-
tified, modeling fish bioenergetics is generally practical only in lakes that have
been intensively studied.
194
-------
Chapter 11. Role of Modeling in Fish and Fisheries Management
Models of fish growth are needed to estimate the number of years required
for fish to reach harvestable size (questions 4 and 8) and are a fundamental com-
ponent of estimates of fish production and potential yield. The von Bertalanffy
equation parameters also can be used directly for among-lake comparisons of
fish growth (question 1).
Population Dynamics Models
Many fisheries models have their origin in models of commercial fisheries in the
ocean or anadromous salmon stocks. Generally, these modeling efforts focused
on population-level processes, ignoring species interactions or habitat effects,
and on methods for estimating the maximum sustainable fisheries yield. As a
result, many diverse models of fish population dynamics have been developed.
Two basic types of population-level models can be distinguished: (1) those
that simulate population dynamics by modeling the individual component
processes of mortality, growth, and reproduction, and (2) models that treat
population processes as a "black box" and focus instead on relationships be-
tween integrative indicators, such as changes in fish population abundance and
total fish recruitment. Both approaches as well as models have been applied in
analyses of recreational fisheries and fish populations in lakes.
The Leslie matrix (Leslie, 1945, 1948) was one of the earliest methods for
tracking fish population dynamics as a function of age-specific fish mortality and
growth. Computerized models based on similar concepts have since been
developed, many of which also incorporate fish fecundity and reproduction,
density-dependent growth and mortality, age- and sex-specific exploitation rates,
and stochastic components (e.g., random variability in natural mortality rates;
the general inland fish simulator GIFSIM program developed by Taylor, 1981).
Advantages of these models include their flexibility, diversity of manage-
ment questions that can be addressed (e.g. questions 5 through 10), and basis in
biological principles. Disadvantages include the large number of model
parameters that must be measured or estimated and uncertainties regarding den-
sity-dependent mortality. Christensen et al. (1988) calibrated the outputs from a
Leslie matrix-type model (expressed as relative reproductive potential) to ob-
served fish population responses in the field in an attempt to adjust for density-
dependent mortality and other factors not accounted for in models of fish
population responses to acidification in Adirondack lakes. Other applications of
this mechanistic approach to modeling fish population dynamics have included
environmental assessments of effects from entrainment (Boreman et al. 1982,
Cohen et al. 1983) and toxic substances (Barnthouse et al. 1987), fisheries assess-
ments of the effects of harvest regulations on fish size distributions and yield
(Zagar and Orth, 1986; Evans, 1989), and analyses of the effects of stocking on na-
tive fish strains (Evans and Willox, 1990).
Two examples of black box population models are the stock-recruitment
model (Ricker, 1954, 1975; Beverton and Holt, 1957) and surplus yield models
(Schaefer, 1957; Gulland, 1961; Fox, 1970; Walter, 1973; Schnute, 1985; Ludwig
and Walters, 1989). Both types of models are designed primarily for estimating
the maximum sustainable fisheries yield (Question 6). Deriso (1980) and Schnute
(1985) (and others) have also developed models that combine aspects of the
mechanistic, age-structured models with the concepts of stock-recruitment and
surplus production.
Stock-recruitment models, as the name suggests, relate fish recruitment
(biomass of new fish entering the fishery or added to the population as a result of
fish reproduction) to the biomass of the adult stock. The Ricker (1954, 1975)
model assumes that mortality is density dependent; therefore, recruitment is low
at both low and high levels of adult stock biomass (Fig. 11-7):
195
-------
Fish and Fisheries Management In Lakes and Reservoirs
B
STOCK—*-
Figure 11-7.—The two classical stock-recruitment curves: (A) the Ricker curve and (B) the
Beverton-Holt curve (source: Lackey and Hubert, 1978).
R = alphap-betap
where R = biomass of new recruits,
P = parental stock biomass, and
alpha and beta are positive parameters fit during model
calibration.
The Beverton-Holt model (1957) assumes that density-dependent and density-
independent mortality factors are important; therefore, recruitment levels off at
high adult biomass (Fig. 11-7). In both cases, only the total weight of fish is con-
sidered. Observations of adult biomass and recruitment over multiple years are
used to calibrate the model for any given population. The maximum sustainable
yield is achieved if adult biomass is maintained at a level where the difference
(vertical distance) between new recruits and adult biomass is greatest. Software
for running these models is available in Saila et al. (1988).
Surplus yield models are also single stock models that require no data on the
age structure of either the catch or the stock. The underlying assumption is that
fish population production (increase in biomass over time) follows a sigmoidal or
logistic curve (Fig. 11-8). The maximum rate of population increase (maximum
slope) occurs at the inflection point of the logistic curve, at intermediate levels of
fish abundance. If this is true, then the maximum sustainable yield ("excess
production") also occurs at an intermediate level of fish abundance (also see Fig. 2-
15). In heavily fished populations, fish abundance is controlled largely by the level
of fishing effort; moderate levels of effort result in moderate levels of fish biomass.
Thus, the maximum sustainable (equilibrium) yield occurs at an intermediate level
196
-------
Chapter 11. Hole of Modeling in Fish and Fisheries Management
t
UJ
O
•z.
I
z>
CD
CARRYING CAPACITY
ASYMPTOTIC
LEVEL"
•INFLECTION POINT
TIME—*
Figure 11-8.—Sigmoid growth curve of abundance (N) versus time, the basis of the
surplus yield model (source: Lackey and Hubert, 1978).
Q
LLJ
DC
DO
_J
O
LLJ
INFLECTION POINT
in FIGURE 11-8
FISHING EFFORT (f)
Figure 11-9.—Surplus yield model: equilibrium yield versus fishing effort (source: Lack-
ey and Hubert, 1978).
197
-------
Fish and Fisheries Management in Lakes and Reservoirs
Ecosystem models attempt
to integrate interactions
between multiple species
or trophic levels and
habitat features to predict
effects on fisheries
of fishing effort (Fig. 11-9). A curve, similar to that illustrated in Fig. 11-9, is
calibrated from observations of catch and population abundance over multiple
years for a given fish population.
Ricker (1975), Lackey and Hubert (1978), Everhart and Youngs (1981), and
Walters (1986) explain the underlying mathematics and principles of the surplus
yield, stock recruitment, and related models in greater detail. Because of the re-
quirement for long time series of data for model calibration, neither of these
modeling approaches has been applied as widely for recreational fisheries
analyses as have the mechanistic, age-structured population models described ear-
lier in this section. Most applications have been for commercial fisheries (e.g., Fox,
1970; Welch and Noakes, 1991). In addition, high levels of year-to-year variability
and measurement error often obscure the underlying theoretical relationships.
Ecosystem Models
Ecosystem models attempt to integrate interactions between multiple species or
trophic levels and habitat features (e.g., nutrient loading or temperature) to predict
effects on fisheries (question 11) or the effects of fish on other ecosystem com-
ponents and water quality (questions 12 and 13). Most ecosystem simulation
models are highly mechanistic. Many individual submodels (generally first-order
differential equations) are defined representing specific interactions (e.g.,
zooplankton grazing on phytoplankton) and processes (e.g., fish growth) (see Box
11-A). Each component equation is intended to reflect current understanding of
biological systems as closely as possible.
This manual cannot provide an adequate discussion of the diversity of ecosys-
tem models. The components, processes, and modeling approaches vary depend-
Box 11-A.—Ecosystem Models:
Example Submodel Equations
Scavia et al. (1988) developed a model of the Lake Michigan ecosystem incorporating
the components and pathways presented in Figure 11-11. Model equations for the
phytoplankton and zooplankton compartments are listed below to illustrate how dif-
ferential equations are used to represent biological processes.
Phytoplankton:
dA/dt=(n-s)A-gZ
A = phytoplankton concentration
H = growth rate (see below)
s = settling loss = sinking rate/epilimnion depth
g = zooplankton grazing (see below)
Z = zooplankton concentration
H = Hm * MIN {P/(KP + P), Si/(Ksi + Si)}
where (xm = the maximum growth rate
K = half-saturation constants for phosphorus (P) and silicon (Si)
g = gm * EFC/(K + EFC)
where gm = the maximum weight-specific ingestion rate
K = half-saturation constant
EFC = 2 (W'l * X0. where W is the selectivity coefficient for food source
i with concentration Xi
Zooplankton:
dZ/dT=(g-r)Z-P
r = respiration (see below)
P = fish predation = specific ration * alewife biomass
r=n + r2 * EFC/(K + EFC)
198
-------
Chapter 11, Role of Modeling in Fish and Fisheries Management
Participate
Inorganic P
Non-living
Participates
(e.g.
Organics,
Clays,
CaCO3,
Metal ppt,
feces)
Other
Dissolved
Inorganic P
Carnivore
Zooplankton*
Planktivore Fish*
Sorbed
ConP
Sorbed
P04
Inorganic
& Organic
Condensed P
(Con P)
Ortho-P
(P04)
Piscivores*
(Surplus P)
-i -
Phytoplankton
Dissolved
Organic P
(OOP)*
Figure 11-10.—Conceptual model of phosphorus dynamics indicating major components
and pathways within the water column. Asterisks indicate several functional groups or
life stages within each component (source: Chapra and Reckhow, 1983; reprinted from
Scavia, 1981).
External Load
Sink
Respiration
Figure 11-11.—Schematic of major pathways In model designed to simulate nutrient
cycles and biomass flow among competing phytoplankton and zooplankton groups. Ar-
rows represent major pathways; some are omitted for clarity. Nested boxes are used to
show selective grazing pathways. For example, all algal groups are consumed by Daph-
nla, whereas only flagellates and diatoms are consumed by Dlaptomus (source: Scavia
et al. 1988).
199
-------
Rsh and Fisheries Management in Lakes and Reservoirs
data
4,
Daphnia fuilicaria
biomass
data recr
^ im/iuorat-ion data
chironomid
biomass
predation pr
introduction ingt
I
, 1
* <
rainbow
trout
numbers
/ /
edition . ^ .
f emigrati
stion
I
t
rainbow
trout
weight
1 1 '
T VI
sockeye sockeye
salmon salmon
nt
numbers weignt
on preda :
\
,x
ion emigrat
. . —
ingesfion
\^ data
northern
squawfish
numbers
litment data
ngfin longfin
melt smelt
imbers weight
/
ion
_^^
Figure 11-12.—Flow diagram for the LKWASH model of fish interactions in Lake
Washington (Seattle, Washington). Major model variables are contained in boxes. Arrows
denote flows between compartments and are labeled according to the relevant process.
Multiple cohorts of the same variable are denoted by a stack of boxes. Driving variable In-
puts to model variables are denoted by arrows labeled data (source: Swartzman and
Beauchamp, 1990).
ing on the modeling objectives. Models may be highly complex (e.g., Fig. 11-10) or
model components may be lumped or aggregated by functional group or other
relevant category (e.g., Fig. 11-11). Example applications include (a) modeling of
interspecific interactions in the fish community in Lake Washington to evaluate ef-
fects from the introduction of rainbow trout on other fish species in the lake
(Swartzman and Beauchamp, 1990; Fig. 11-12) and (b) a model-based assessment
of the relative importance of changes in nutrient loading and top-down (fish)
predation on phytoplankton and zooplankton communities in Lake Michigan
(Scavia et al. 1988; Fig. 11-11). Chapra and Reckhow (1983) describe the basic con-
cepts and approaches to mechanistic modeling of food webs and ecosystems.
Johnson et al. (1991) present an alternative approach to ecosystem modeling in
which empirical regression analysis and mechanistic understanding of ecosystem
processes play an equally important role. Conceptual relationships among impor-
tant ecosystem components are defined based on ecosystem theory (Fig. ll-13a)
and then quantified using path analysis (Fig. ll-13b). Traditional path analysis
(Wright, 1968) uses a hierarchical series of linear regression analyses (single or
multiple) to establish the relationships among variables. The path coefficients are
the standard regression coefficients. LISREL (Hayduk, 1987), recommended by
Johnson et al. (1991), however, uses maximum likelihood estimation techniques to
estimate path coefficients rather than least-squares regression. LISREL also incor-
porates measurement error into the modeling process by separating theoretical
concepts (the boxes in Fig. 11-13) from their measured environmental indicator
variables (the ovals in Fig. 11-13). The outputs from LISREL provide a determina-
tion of the total, direct, and indirect effects of the variables in the model on each
other. Ecosystem modeling with LISREL may be particularly useful, therefore, for
identifying the relative importance (strength of relationships) of alternative causes
of lake problems.
To date, ecosystem models have been used primarily for research; manage-
ment applications have been limited. Because of their complexity and the number
of components and processes incorporated, most models are very data-intensive.
Their primary benefit has been improved understanding, although "game play-
ing" (evaluating model responses to perturbations or management actions) can
200
-------
Chapter 11. Role of Modeling in Fish and Fisheries Management
provide new insight on emergent ecosystem properties. As for all models, ecosys-
tem models are a tool that should be used in conjunction with other information
(logical thinking, direct experience, and other data analyses) to aid in manage-
ment decisionmaking.
ECOSYSTEM MODELING WITH LISREL
/'GiRASS CARP\
( PRESENCE/ )
X^ABSENCE/
i
'jlx
A11
GRASS CARP
*.
In
ATRAZINE
CONCENTRATI
AQUATIC
VEGETATION
SUBMERGENT
VEGETATION
/CHLOROPHYLL a A
in —s. XCONCENTRATION/
ZOOPLANKTON A ^---
In
ATRAZINE
CONCENTRATI
GRASS CARP
PRESENCE/
ABSENCE
i
L
1.0
GRASS CARP
*1
V0.363
SUBMERGENT
VEGETATION
AQUATIC
VEGETATION
ZOOPLANKTON
^3
^
1.0
r
In
1.0
In
'CHLOROPHYLL
w CONCENTRATION _
( ZOOPLANKTON J
VABUNDANCEX
Figure 11-13.—Simple pond ecosystem modeled with LISREL. The ecosystem is placed
into a framework of concepts (boxes) and indicator variables (ovals). Causal pathways
proposed among variables are presented in part (a); standard coefficients from LISREL
analysis of data from the Kansas Aquatic Mesocosm Program, indicating the relative ef-
fects of variables, are presented in part (b) (source: Johnson et al. 1991).
2O1
-------
-------
CHAPTER 12
Case Study Examples
Chapter Objective
This chapter presents summaries for seven lake management and restoration
projects that illustrate many of the concepts and techniques discussed in this
manual. These seven projects were selected to represent a diverse array of regions,
different lake types and reservoir systems, a broad sample of problems and objec-
tives, and a wide range of management approaches and techniques (Table 12-1).
Table 12-1.—Summary of case study lakes.
LAKE NAME
Lake Chicot
Cold Springs
Lake
Bear Lake
Lake
Opeongo
Flaming
Gorge
Reservoir
Flathead Lake
Lake
Washington
LOCATION/
SIZE
SE Arkansas
3,500 acres
Iowa
16 acres
N. Wisconsin
300 acres
South Central
Ontario, Canada
14,464 acres
NE Utah and
SW Wyoming
42,000 acres
NW Montana
20,636 acres
Washington
21 ,500 acres
MANAGEMENT
GOALS
(TARGET FISH)
Restore balanced fish
community and
fisheries (largemouth
bass)
Increase fish growth
rates and size (large-
mouth bass, bluegill,
channel catfish,
crappie)
Increase fish growth
rates and size (wall-
eye, largemouth bass,
bluegill)
Increase lake trout
growth and yields
(lake trout)
Provide a diverse,
high quality, sus-
tainable fisheries
(rainbow trout, lake
trout, cutthroat trout,
kokanee salmon)
Protect native fish
assemblages (bull
trout, cutthroat trout,
mountain whitefish);
protect aquatic habitat
and prevent
eutrophication; main-
tain a diverse, high
quality recreational
fisheries (kokanee sal-
mon, rainbow trout,
lake trout, yellow
perch)
Improve water quality;
maitain fisheries
yields (sockeye sal-
mon, rainbow trout)
MANAGEMENT
APPROACHES
— Siltation reduction
— Water level mgmt.
— Reclamation
— Stocking
— Fish cover
— Seeding
— Aeration/ destratifi-
cation
— Selective cropping
— Spawning disruption
— Catch and release
— Game fish stocking
— Prey enhancements
— Fishing regulations
— Game fish stocking
— Rshing regulations
— Reduce nutrient
loading
— Habitat protection
— Water level mgmt.
— Rsh stocking
— Fishing regulations
— Sewage diversion
— Physical habitat
improvement
— Food web
manipulation
INFORMATION
SOURCE
Arkansas Game
and Fish Commission
(Filipeketal. 1989)
Iowa Conservation
Commission (Hill,
1987)
McComas (1988,
1989)
Matuszeketal. (1990)
Wyoming Game and
Fish Department
(Wiley etal. 1976;
Wengert and Wiley,
1987)
Flathead Basin
Commission (1990),
Montana Dept. Fish,
Wildlife and Parks,
and Confederated
Salish and Kootenai
Tribes (1989, 1991)
Edmonson and Leh-
man (1981); Edmon-
son and Abella (1988)
2O3
-------
Fish and Fisheries Management In Lakes and Reservoirs
[TJhe lake was reclaimed
to eliminate or reduce
existing fish populations.
,.. About 3,000 citizens
assisted with the removal
of 155,000 pounds offish.
[TJhe bottom of the lake
was seeded with sorghum
sudan and winter wheat.
Also, 36 fish shelters
constructed. ofPVC pipe
were installed and marked
by buoys.
Lake Ghicot, Arkansas
Background
Lake Chicot is a 3,500-acre natural oxbow lake that was originally created 400
years ago when the meandering Mississippi River changed its course. It has a
maximum depth of 30 feet and a mean depth of 13.8 feet. The lake had an early
history of being prized as scenic and pristine. It served as an untreated water
source for a nearby community and provided an outstanding largemouth bass
fishery.
A series of hydrologjc modification projects implemented in 1926 connected
Lake Chicot to a nearby lake. These projects (and a subsequent failure of as-
sociated levees) expanded the watershed draining into Lake Chicot and lowered
its lake level below that originally intended. Following World War II, agricultural
uses expanded from 10 to 80 percent of the watershed, increasing lake turbidity
and pesticide and nutrient concentrations. In addition, irregular fluctuations in
lake levels caused by inadequate flow control caused severe turbidity problems
and habitat destruction. Consequently, both water quality and the lake's fisheries
deteriorated substantially.
In 1948, the Arkansas Game and Fish Commission constructed a dam that
blocked the channel connecting Lake Chicot to the lake to the north. Water quality
and fisheries in the upper fourth of the lake then returned to near its earlier condi-
tion. The remainder of the lake, however, continued to have severe turbidity
problems, along with uncontrolled water level fluctuations.
The Lake Chicot Project was authorized as part of the Flood Control Act of
1968, which committed the U.S. Army Corps of Engineers (COE) to assist Arkan-
sas in restoring the lake. The Chicot County Improvement District, COE, and
Arkansas Game and Fish Commission contributed funds and resources to the
project. The following information on restoration methods and results is sum-
marized from Filipek et al. (1989).
Restoration Activities
Restoration plans called for reestablishing Lake Chicot's original hydrologic
regime and eliminating the heavy loads of suspended sediments entering the lake.
New outlet structures were constructed that minimized lake-level fluctuations and
restored the lake's original water level. A pumping plant and diversion structures
were constructed to redirect agricultural runoff from areas outside of Lake
Chicof s original pre-1926 watershed. Following these improvements, fisheries res-
toration activities were begun.
Several management actions aimed at restoring a balanced fish community
and fisheries were coordinated by the Arkansas Game and Fish Commission and
COE. First, the lake was reclaimed to eliminate or reduce existing fish populations.
The lake was drawn down to the lowest possible level and fish were further con-
centrated by baiting; these concentrated fish were then killed using rotenone.
About 3,000 citizens assisted with the removal of 155,000 pounds of fish (about 300
pounds per acre). Interestingly, only one largemouth bass was observed in the fish
removed. Subsequently, a comprehensive stocking program was initiated by the
Arkansas Game and Fish Commission to repopulate the reservoir (Table 12-2).
To enhance the quality of the lake's habitat, during the drawdown the bottom
of the lake was seeded with sorghum sudan and winter wheat. Also, 36 fish shel-
ters constructed of PVC pipe were installed and marked by buoys. Hydroacoustic
surveys conducted after stocking and restoration of the lake level revealed that
stocked fish congregated around these shelters almost immediately.
204
-------
Chapter 12. Case Study Examples
Table 12-2.—Corrective fish stockings following restoration of Lake Chicot, Arkan-
sas (source: Filipek et al. 1989).
YEAR
1985
1986
1987
1988
SPECIES
Redear sunfish fingerlings
Florida largemouth bass yearlings
Blue catfish catchables
Channel catfish catchables
Crappie yearlings
Bluegill adults
Bluegill yearlings
Florida largemouth bass fingerlings
Channel catfish catchables
Channel catfish yearlings
Largemouth bass fingerlings
Largemouth bass fingerlings
NUMBER STOCKED
65,000
30,810
19,000
10,475
10,000
100
25,000
43,125
5,000
10,200
10,200
18,000
Table 12-3.—Mean values for eight water quality variables at two stations in Lake
Chicot, Arkansas, before and after lake restoration (source: Filipek et al. 1989).
STATIONS
VARIABLE
Turbidity
Secchi depth
Total solids
Suspended solids
Nitrate
Chorophyll a
Total phosphorus
Orthophosphorus
7PRE-
RESTORATION
182
0.25
347
142
0.534
11.6
0.355
0.082
7 POST-
RESTORATION
12
0.65
189
17.2
0.044
35.7
0.083
0.059
9PRE-
RESTORATION
152
0.20
280
131
0.430 ,
8.9
0.430
0.091
9 POST-
RESTORATION
25
0.45
189
26.1
0.124
30.4
0.102
0.052
To aid in evaluating the effectiveness of the lake restoration, eight water
quality variables were sampled at two stations several years before the renova-
tion of Lake Chicot. Table 12-3 presents mean values from pre-restoration and
post-restoration sampling for turbidity, Secchi depth, total solids, suspended
solids, nitrate, chlorophyll a, total phosphorous, and Orthophosphorus. For each
of these water quality variables, postrestoration concentrations were significantly
different (p z 0.05) from prerestoration samples. Concentrations of chlorophyll a
increased despite the reduction in nutrient concentrations because as turbidity
decreased light penetration increased and, consequently, algal productivity in-
creased.
Fisheries responded positively to the restoration effort. Comparisons of pre-
restoration (1973,1981,1984) and post-restoration (1986,1987,1988) surveys indi-
cated major differences in fish species composition, numbers, weights, and
relative abundances (Table 12-4). Largemouth bass, virtually nonexistent before
lake renovation, became a significant component of the fish community. Dis-
tributions of numbers and biomass among fish species indicated a better
balanced community following renovation. For example, despite increased
predation as a result of the reintroduction of largemouth bass, bluegill increased
10-fold in numbers and weight following restoration.
Several components combined to make the Lake Chicot project a success. The
extensive drawdown exposed much of the lake bottom to the air; thus, nutrients
in the bottom sediments were tied up by oxidation. Drawdown also compacted
the bottom sediments and allowed seeding of much of the lake bottom to help
regulate post-flooding losses of nutrients and sediments to the water column.
Fisheries responded
positively to the
restoration effort....
Several components
combined to make the Lake
Chicot project a success.
205
-------
Fish and Fisheries Management in Lakes and Reservoirs
In 1980, the ICC initiated
a program of lake
destratification to evaluate
its potential for improving
benthic biomass and
production and its effects
on the growth, size
structure, and biomass of
largemouth bass, bluegill,
crappie, and channel
catfish in small stratified
lakes.
Table 12-4.—Numbers and biomass offish in Lake Chicot, Arkansas, before and after
lake restoration; differences before and after restoration were evaluated using a t-test
(source: Flllpek et al. 1989).
SPECIES
Largemouth bass
Bluegill
Gizzard shad
Channel catfish
Total all species
BEFORE
MEAN
NO./ACRE
0
386
2,547
304
6,962
AFTER
MEAN
NO./ACRE
103
5,108
2,414
98
11,055
PROB.
>T'
0.17
0.13
0.86
0.16
0.27
BEFORE
MEAN
LB/ACRE
0
10
92
88
336
AFTER
MEAN
LB/ACRE
26
97
309
83
656
PROB.
a-T1
0.02
0.13
0.04
0.17
0.11
'Probability value from the t-test; probability values less than 0.05 are usually considered indicative of a
statistically significant difference — in this case, between before and after lake restoration.
The low water level during drawdown concentrated fish, permitting efficient
rotenone treatment to thin the overabundant populations of stunted crappie, shad,
sunfish, and catfish. Finally, construction and operation of the pumping plant
diverted much of the turbid and polluted water inputs away from the lake.
Rejuvenation of the largemouth bass population can be attributed to the improved
water quality (especially the increased water clarity needed by these sight-feeding
predators), increased availability of forage fish, and corrective stocking. Changes
in the population structure for most other fish species following restoration can be
partially attributed to increased predation by largemouth bass.
Cold Springs Lake, Iowa
Surveys by the Iowa Conservation Commission (ICC) indicate that the size and
growth of panfish (sunfish and crappie) are unsatisfactory in many small Iowa
lakes and are a function of fish density and the available food supply. Generally,
bluegill in Iowa lakes grow rapidly during the spring and slowly during the sum-
mer. Previous studies by the ICC suggest that this decrease in growth during sum-
mer is caused by increased bluegill densities above the hypolimnion in stratified
lakes. Because of anoxic conditions in the hypolimnion, few fish are found below
the thermocline. Thus, a substantial portion of the lake bottom is inaccessible for
fish feeding on benthic organisms. Furthermore, reduced oxygen levels in deeper
waters can alter the numbers and types of benthos. Hexagenia nymphs, a preferred
prey for bluegill, are intolerant of low oxygen levels, while oligochaetes and
chironomids, which are commonly found in waters with low oxygen, are less
desirable prey.
In 1980, the ICC initiated a program of lake destratification to evaluate its
potential for improving benthic biomass and production an^ its effects on the
growth, size structure, and biomass of largemouth bass, bluegill, crappie, and
channel catfish in small stratified lakes. Years of thermal destratification were al-
ternated with years of stratification in an attempt to control the survival of small
panfish and prevent overcrowding and stunting.. The following paragraphs ex-
tracted from Hill (1987) summarize results from this restoration program for Cold
Springs Lake.
Cold Springs Lake was selected for an initial evaluation of mechanical sum-
mer aeration because of its history of slow-growing panfish and its small size and
close proximity to an ICC research station. Cold Springs Lake, a 16-acre public
recreation lake was reconstructed in 1949 by the ICC specifically for fishing and
swimming. The maximum depth is 14 feet with a mean depth of 5.5 feet. Thermal
stratification occurs at 6.5 feet; during stratification, 50 percent of the lake bottom
is located beneath the hypolimnion and anoxic conditions occur. This severe ther-
mal stratification persists from June through August.
206
-------
Chapter 12. Case Study Examples
Several management techniques had already been employed at Cold Springs
Lake with some success, including (1) chemical reclamations to reduce bluegill
density, (2) grass carp introductions to reduce nuisance aquatic vegetation, and
(3) a minimum length limit to reduce the harvest of smaller largemouth bass. As
a result of these management efforts, fishing improved and fishing pressure in-
creased. Currently, Cold Springs Lake receives more fishing pressure per unit
area than most Iowa lakes.
An axial flow water pump was used to destratify Cold Springs Lake from
June 1 to September 15 in 1981,1982,1983, and 1986. The pump was placed in the
deepest portion of the lake and operated to create a downward flow of water. The
pump's effectiveness in destratifying the lake is illustrated in Figure 12-1 by the
absence of a thermocline during the years when the pump was in operation, as
opposed to the sharp temperature gradient with depth for the months of June,
July, and August during the years when the pump was not in operation.
141
12-
TO-
? 8"
i>
3 2-
0'
5
<
i
t
,
• 14-
T U'
f o 10-.
I I 8-
{ f *
\ a +
I April 2.
V i ^
m W
¥ K
t I'"
TT «• 8-
ft tfr
ft S *
11 May a.
0 *60 70 8*0 90 5*0 60 70 80 9*0 £
Temp Temp
\ ]
\ •
\'
V-
>
i
June ,
i
i
i
l
fk
0 60 7*0 80 90
Temp
»f »f -F
MI
Ta-
w-
s'
2-
O
51
• i
V
V I
\ '
\'
J"«y
3 60 70 80
Temp
i 14.
' ^.t2'
I ^1O
1 f 8-
1-
Q 4-
1 *
n
\
\
\
V
At« |
I 14-
1 Hr
I SflO-
1 £ 8-
' f6'
^ »4-
1 »
L **
1
]
,
1
Sept [
i 14-i
\ -K'
\ I I*
* ^ 8-
i £
•> CL 6-
T »
1 Q 4-
1 2-
f
1
?
f
r o<*
•M (!•
90 50 60 70 80 90 5O 60 7O SO 9O SO 6O 7O 80 9O
Temp Temp Temp
OF- op -F ~f
«
• denotes 1980,1984 & 1985 (stratified)
• denotes 1981,1982,1983 & 1986 (aerated)
Figure 12-1.—Average mid-month temperature profiles in Cold Springs Lake, 1980-86
(source: Hill, 1987).
The biomass and production of benthic invertebrates was significantly
greater (p x 0.05) during the years of destratification (1981,1982,1983, and 1986)
than in the years of stratification (1980,1984,1985) at both deep and shallow sta-
tions (Table 12-5). No significant difference in biomass or production occurred in
years when the lake was allowed to stratify.
A variety of changes also occurred in the fish community in Cold Springs
Lake in response to the destratification/ stratification program:
• Fish reproductive success increased. During three of the four years of
destratification (aeration), the numbers of age 0-t- bluegill were three
times higher than during years of stratification. Numbers of age
0+ largemouth bass also were higher during years of destratification
than when the lake stratified.
The biomass and
production of benthic
invertebrates was
significantly greater
during the years of
destratification than in the
years of stratification
[and] fish reproductive
success increased.
207
-------
Fish and Fisheries Management in Lakes and Reservoirs
Both bluegill and
largemouth bass grew
significantly faster during
the four years of lake
destratification compared
to years when the lake
stratified.
Overall, the
aeration/destratification
program at Cold Springs
Lake resulted in a
significant improvement
in the fisheries at
moderate cost.
Table 12-5.—Estimate of benthos blomass and benthos production at deep and shal-
low water sampling stations In Cold Springs Lake, 1980-86 (source: Hill, 1987).
BIOMASS LB/ACRE (WETWT.)
PRODUCTION LB/ACRE (WET WT.)
YEAR1
1980 (S)
1981 (D)
1982 (D)
1983 (0)
1984(S)
1985 (S)
1986 (D)
SHALLOW
351
550*
1,013*
1,073
475*
368
590*
DEEP
436
742*
696
681
393*
286
715*
SHALLOW
7,581
11,404*
20,426*
21 ,575
10,127*
7,948
12,236*
DEEP
7,255
15,173*
14,034
13,731
6,158*
4,684
14,829*
(D) x Destratifled
* Denotes statistically significant difference with previous year (by station) using a t-test (p * 0.05)
• Destratification, in general, also increased fish survival rates. The mor-
tality of age 0+ bluegill and largemouth bass decreased in years when
the lake was destratified and, conversely, nearly doubled in the follow-
ing period when the lake was allowed to stratify. In three out of the
four years of destratification, bluegill year-classes experienced sig-
nificantly lower mortality than in stratified years. Age 2+ largemouth
bass in all years except for the 1981 year-class also experienced higher
mortality during periods of stratification than during years of
destratification.
» Both bluegill and largemouth bass grew significantly faster (p n 0.05)
during the four years of lake destratification compared to years when
the lake stratified. Panfish growth rates declined, however, during later
years of the aeration program as a result of their increased reproductive
success and subsequent increase in panfish density. Bass growth im-
proved in all years of destratification.
• The overall numbers of fish for all species and most age categories were
substantially higher after initiation of the aeration program at Cold
Springs Lake.
• The expanded environment and increased food supply created by sum-
mer destratification in the first two years (1981,1982) resulted in a sig-
nificant increase (p * 0.05) in bluegill biomass relative to 1980 (stratified
conditions). Bluegill biomass fluctuated in the remaining years of the
study. The fluctuations probably resulted from a combination of (a) in-
creased competition for food with channel catfish, which were stocked
at higher rates during this period; (b) stunted growth for some year-
classes and years as a result of increased recruitment and crowding; and
(c) increased predation by the largemouth bass population.
• Largemouth bass biomass peaked after two years of destratification.
Trends in the biomass and growth of largemouth bass and other fish are
complicated by the coincident increase in fishing pressure and harvest.
The axial pump and installation cost the ICC $1,300 in 1980. The electrical cost
for running the pump for one season averaged $150. One unintended impact was
a moderate to high plankton bloom continuously from June to September during
destratification years. Before destratification, occasional intense algal blooms were
followed by a few weeks of clear water.
Overall, the aeration/destratification program at Cold Springs Lake resulted
in a significant improvement in the fisheries at moderate cost. Problems with pan-
fish stunting might be better controlled through further refinement of the alternate
year stratification/destratification design. During years of stratification, fish are
concentrated within the epilimnion, increasing predation and decreasing the sur-
208
-------
Chapter 12. Case Study Examples
vival rates of small panfish. Thus, the benefits of alternating stratification and
destratification are similar to those of periodic water level drawdown (see Chapter
8) without the adverse effects on other lake uses, such as boating and swimming.
Bear Lake, Wisconsin
Problems associated with too many rough fish, stunted panfish, and too few
game fish may become self-sustaining as anglers continue to harvest scarce game
fish while leaving the abundant, less desirable species to reproduce in excess. The
Bear Lake District in northern Wisconsin instituted a fisheries management pro-
gram to deal with such a problem involving stunted sunfish (pumpkinseed sun-
fish and bluegills) and the decline of walleye from the 300-acre mesotrophic Bear
Lake. In theory, if sunfish densities could be reduced, competition for food in the
shallow nearshore areas would decrease and young walleye inhabiting these
areas would benefit from improved conditions for feeding and survival. Similar-
ly, the sunfish remaining would have more food available, resulting in faster
growth rates and larger sizes. The following overview of the Bear Lake project is
summarized from McComas (1988,1989).
The Bear Lake project demonstrates how fisheries restoration programs can
be promoted and conducted by small groups with a limited budget. A combina-
tion of several small-scale projects were implemented: (a) removal of sunfish and
bullheads using fyke nets and shoreline seining during spawning time; (b) a
volunteer catch and release program for walleye; and (c) continuation of the Wis-
consin Department of Natural Resources (DNR) walleye stocking program.
The collection and removal of stunted sunfish and bullheads using fyke nets
required the greatest amount of effort. The goal was to remove 8 to 12 pounds of
fish per acre of lake surface area each year for three to four years. In support of
this project, the Wisconsin DNR granted permits for fish removal and annually
loaned 10 fyke nets to the Bear Lake District. Volunteer members from the dis-
trict ran the nets and counted, measured, and weighed the sunfish and
bullheads collected. The sunfish were then transported either to nearby muskie
ponds where sunfish provide forage for muskellunges or to nearby Big Bearskin
Lake, which had low sunfish numbers (a permit was required), or to a landfill
for disposal.
During the first year of netting (1985), the district learned that pumpkinseed
spawn first, followed by bluegills. The one week of netting resulted in a catch
dominated by pumpkinseed sunfish with only a few bluegills. Consequently, for
the remaining years of the program, the netting period was increased to two
weeks in June encompassing the end of the pumpkinseed spawning period
during the first week and the beginning of the bluegill spawning period in the
second week. The first two weeks of June is the period in northern Wisconsin
when bluegill and pumpkinseed spawning typically peak.
Fish removal efforts lasted for four years, ending in June 1988. Maintenance
removal continued in 1989 and 1991. During that time, over 12,000 pounds of sunfish
and bullheads (about 40 Ibs/lake surface acre) and over 117,000 fish were removed.
Removing panfish for fisheries improvement is not a new idea. Buchanan et
al. (1974) reported, however, that only about 40 percent of the fish removal
projects conducted have been successful. The Bear Lake project has many of the
characteristics associated with the successful projects described by Buchanan et
al. (1974), as follows:
• lake area 300 acres or less,
• lakes with no permanent surface inflow or outflow,
• low fish species diversity,
• few areas of dense macrophyte growth,
The Bear Lake District in
northern Wisconsin
instituted a fisheries
management program to
deal with such a problem
involving stunted sunfish
(pumpkinseed sunfish and
bluegills) and the decline
of walleye from the
300-acre mesotrophic Bear
Lake.
2O9
-------
Fish and Fisheries Management in Lakes and Reservoirs
m fish removal conducted over multiple years, and
• sunfish removed during their spawning period to disrupt spawning success.
In addition to the fish removal effort, anglers at Bear Lake initiated a catch-
and-release program for walleye and every other year, the Wisconsin DNR stocks
15,000 walleye fry or fingerlings. The Wisconsin DNR has also initiated more in-
tensive sampling of the walleye population.
As of early 1993, the response of the fish community and fisheries to these
management efforts appears to still be changing, and monitoring to assess the
program's success is continuing. Several preliminary observations are encourag-
ing, however.
Data on the length-frequency distributions of bluegill and pumpkinseed sun-
fish for 1985 to 1988 indicate no dramatic shifts in size. However, anglers on the
lake report keeping and eating more sunfish, suggesting an increase in the harvest
of larger fish. Walleye have been observed on their old spawning beds. Although
this is not necessarily indicative of successful reproduction, walleye had not been
observed on these beds since the early 1960s (Table 12.6).
Table 12-6.—Number of gamefish and panfish caught for every fyke net set In Bear
Lake.
DATE
1985*
1986
1987
1988
1989*
1991
WALLEYE
0.3
0.3
0.5
0.1
0.2
0.2
NORTHERN
PIKE
0.2
0.4
0.6
0.5
0.6
1.4
LARGEMOUTH
BASS
1.9
2.1
0.9
1.7
4.0
3.5
YELLOW
PERCH
3.4
1.2
1.0
0.4
0.4
0.4
BLUEGILL
131
246
240
188
169
343
PUMPKIN-
SEED
187
145
116
91
110
81
BULL-
HEAD
—
19
17
40
35
28
* Netting conducted for one week period. Other years netting was conducted for 2 weeks,
The occurance of largemouth bass in test nets has nearly doubled since 1985, the
year the sunfish removal began. Walleye were overfished in the 1960s (leading to col-
lapse of the walleye fishery), and largemouth bass appear to have partly filled their
niche. Competition by bass, crappie, and other larval fish with walleye for prey and
the predation on stocked walleye may contribute to the relatively poor stocking suc-
cess for walleye in Bear Lake (Fig. 12-2). Because of the increasing dominance by
Bluegill sunfish, 4 inches
1-2 years old
Northern Pike, 16.5 inches
6-7 years old, 1.5 pounds
Largemouth Bass, 12.3 inches
3-4 years old, 1 pound
Yellow perch, 5.3 inches
2 years old
Walleye, 21 inches
8 years old, 3 pounds
Figure 12-2.—Relationship (to scale) of predator fish and prey fish In Bear Lake. For
gamefish to control stunted sunfish (4 Inches), a bass must be 12.3 inches; a pike, 16.5
inches; and a walley, 21 inches. This is based on the predator mouth width to prey body
depth relationship. A 5.3 inch perch is equivalent to a 4 Inch bluegill in regard to what can
be swallowed by a gamefish.
210
-------
Chapter 12. Case Study Examples
largemouth bass, the Bear Lake District members are considering asking the
WDNR to shift the fisheries management emphasis from walleye to largemouth
bass as the target species. Additional data on the possible recovery of the walleye
population will help in this decision.
Water clarity also increased in Bear Lake. In 1977 and 1985, the average summer
Secchi depth transparency in Bear Lake was 9.5 feet. By 1986, Secchi depth
transparency had increased to 10.3 feet and to over 11 feet in 1987,1988,1991, and
1992. Manipulation of the fish community may have contributed to this improve-
ment in water clarity. As noted in Chapters 2 and 9, a decrease in the panfish popula-
tion would be expected to increase the abundance of large zooplankton, which
would in turn decrease the abundance of phytoplankton and increase water clarity.
However, while sunfish removal may have helped improve water transparency, the
lower than normal precipitation levels in 1987 and 1988 also may be a factor and
seem to have improved water transparency in many Wisconsin lakes.
Lake Opeongo, Ontario
Lake Opeongo, with a surface area of 22.6 square miles (about 14,500 acres), is lo-
cated in southcentral Ontario, Canada. The lake, which rests on Precambrian
bedrock, is oligotrophic. Annual surveys of lake trout and smallmouth bass an-
gling catches on Lake Opeongo began in 1936 and have operated continuously.
The Lake Opeongo creel survey stands as one of the longest and most complete
sources of information on the dynamics of freshwater fish populations in the
world. This database was used to examine changes in the annual age-specific
growth rates of lake trout 0-8 years old after the 1948 introduction of cisco
(Shuter et al. 1987; Matuszek et al. 1990).
In 1939, the introduction of cisco was first suggested as a management techni-
que for Lake Opeongo (Fry, 1939) to improve the food supply of the resident
population of lake trout, thus improving the lake trout fishery. Researchers
evaluating the lake's survey data were concerned with an apparent slowing of
growth when lake trout switched their diet from small yellow perch and lake
whitefish to larger prey (Fry, 1949). These surveys also found a high percentage of
infertile mature lake trout at the lengths associated with this transition stage (Fry
and Kennedy, 1937). The researchers determined that if a deficiency in the lake
trout diet was responsible, the introduction of cisco might remedy the situation.
It took a few years for cisco populations to increase in abundance and be-
come a significant component of the lake trout diet. From 1948 through 1951,
cisco were rarely seen in lake trout stomachs. They first appeared in significant
numbers in 1952 and rapidly, increased until, by 1960, they had become the
primary fish food resource for Opeongo lake trout (Fig. 12-3a). Three distinct
periods can be identified in the time series trends illustrated in Figure 12-3:1936-
50, the pre-cisco period; 1951-59, the transition period, when cisco increased from
a minor component of the lake trout diet to the primary food source for the pis-
civorous segment of the population; and 1960-79, the period of cisco dominance.
As the importance of cisco increased, the frequency of occurrence of yellow perch
and lake whitefish, which had previously been major components of the pis-
civorous lake trout diet, declined. Likewise, the incidence of insects in the
stomachs of lake trout during spring also declined (Fig. 12-3b).
The transition to cisco as the dominant prey resulted in complex changes in
lake trout growth patterns (Fig. 12-4). Growth rates for older lake trout aged 6 to
8 years increased rapidly and substantially during the transition period but
began to decline gradually after 1960 before leveling off in more recent years.
Shifts in the growth rate of lake trout ages 3 to 5 years have been more erratic,
with an eventual decline below pre-cisco levels. Growth rates of lake trout ages 1
and 2 decreased continually throughout the transition period years and on into
the late 1960s.
In 1939 the introduction
of cisco was first
suggested as a
management technique for
Lake Opeongo to improve
the food supply of the
resident population of lake
trout, thus improving the
lake trout fishery.
It took a few years for
cisco populations to
increase in abundance and
become a significant
component of the lake
trout diet.
211
-------
Fish and Fisheries Management in Lakes and Reservoirs
The transition to cisco as
the dominant prey
resulted in complex
changes in lake trout
growth patterns.
CISCO
80
Figure 12-3.—Annual frequency of occurrence of prey types In the stomachs of (a) pis-
civorous lake trout and (b) all lake trout caught in the Lake Opeongo fishery (source:
Matuszek et al. 1990).
The generally slower growth for all age classes after 1960 is coincident with an
increase in the numbers of lake trout in Lake Opeongo. The introduction of cisco
resulted in a marked improvement in lake trout reproductive success. Fertility,
fecundity, and the abundance of young age classes all increased. As a result of this
increased fish abundance, competition for the available food resource, especially
among young fish, also increased, resulting in a decline in the growth rate of lake
trout ages 1 and 2 and the somewhat erratic patterns for lake trout ages 3 to 5.
Older lake trout that feed primarily on fish/ however, experienced a net increase in
growth. Even though growth rates declined slightly in the 1960s, lake trout ages 6
to 8 in Lake Opeongo still have significantly greater annual growth increments
now than prior to the cisco introduction.
The increase in lake trout abundance occurred despite a simultaneous increase
in fishing pressure and fish harvest from the lake. The primary benefit of the cisco
introduction and lake trout population response was a large increase in the sus-
tainable lake trout yield. The estimated annual maximum sustainable yield in-
creased by about 170 percent, from 0.16 to 0.43 Ib/acre (0.18 to 0.48 kg/ha).
The effectiveness of the cisco introduction at increasing lake trout abundance
and yield results from several key aspects of the lake trout-cisco, predator-prey in-
teraction as follows:
212
-------
Chapter 12. Case Study Examples
Figure 12-4.—Annual growth increments of lake trout in Lake Opeongo by age class
(source: Matuszek et al. 1990).
Within a lake trout size-class, the ciscoes consumed tend to be larger
than the yellow perch that were eaten before the cisco introduction,
resulting in a decrease in lake trout foraging costs (the net energy ex-
pended searching for and capturing prey) and an increase in growth
efficiency (see Chapter 3).
Lake trout and cisco inhabit the same region of the lake during thermal
stratification, while yellow perch do not. Therefore, lake trout en-
counter ciscoes more frequently during critical growth periods.
The primary benefit of the
cisco introduction and
lake trout population
response was a large
increase in the sustainabk
lake trout yield.
213
-------
Fish and Fisheries Management in Lakes and Reservoirs
Data from Flaming Gorge
Reservoir on the Green
River in Wyoming and
Utah provide an
opportunity to review
three decades of fisheries
management
• The introduction of planktivorous ciscoes resulted in an increased trans-
fer of energy from underused zooplankton populations to a fish popula-
tion (cisco) that could then be efficiently and directly used by the lake
trout population.
Although the introduction of cisco into Lake Opeongo had a net positive
benefit, one cautionary note deserves mention. In addition to the changes in lake
trout population dynamics noted above, the age at which lake trout become
sexually mature has increased, while the age at which they are first vulnerable to
angler harvest has declined. These combined characteristics create a situation in
which significant fishing mortality occurs before sexual maturity is attained. As a
result, the population is more sensitive to high fishing pressure and potential over-
exploitation (Fig. 12-5).
3000
o
0-4
0-8
1-2
1-6
20
INSTANTANEOUS FISHING MORTALITY (year'M
Figure 12-5.—Relationship between simulated equilibrium yield and fishing mortality in
Lake Opeongo during the pre-cisco period (solid line) and the period of cisco dominance
(dotted line) (source: Matuszek et al. 1990).
Flaming Gorge Reservoir, Utah and Wyoming
Data from Flaming Gorge Reservoir on the Green River in Wyoming and Utah
provide an opportunity to review three decades of fisheries management. Flaming
Gorge is an especially interesting example because management of the fisheries
evolved over time in response to changing conditions in the reservoir as the reser-
voir aged. Flaming Gorge was originally intended as a rainbow trout fishery and
for the first decade provided a productive and successful fishery. However, as this
case study documents, fish and creel surveys indicated that changing conditions
required a reassessment of management policies. The following paragraphs sum-
marize, by decade, the condition of the fisheries, fishing success, assumptions
regarding the reason for fisheries conditions and problems, management actions,
and the results stemming from these management actions based on Varley et al.
(1971), Wiley et al. (1976), Wengert and Wiley (1990), and Wiley (1991).
214
-------
Chapter 12. Case Study Examples
Flaming Gorge Reservoir is 91 miles long, stores over 3.7 million acre-feet of
water, has a surface area of 42,000 acres, and is characterized by three areas — the
Canyon (lower third), Open (middle third), and Inflow (upper third) areas —
which have unique topographic, limnological, and fisheries characteristics. Water
storage began in 1962, and rainbow trout were introduced almost immediately
thereafter. Several thousand catchable rainbow trout were introduced in the fall
of 1962. This initial introduction was followed by annual stockings of up to four
million (95 per acre) fingerling (3-inch) rainbow trout. Salmonid growth has been
best in the Inflow, Open, and Canyon areas, in that order, and each of the areas
supports a distinct salmonid stock with different growth and forage qualities.
The 1960s
In the 1960s, the primary emphasis was on a family-type fishery for rainbow
trout, which could be caught reasonably easily at a rate of about 0.50 to 0.75 fish
per hour. Fish averaged 0.50 to 0.75 pounds each. Approximately three million
hatchery-reared fingerlings were stocked annually. Competing nongame fishes
appeared in the reservoir during this time, the most numerous being the Utah
chub (Gilo, atraria).
The condition of rainbow trout (see Chapter 3 for a discussion of condition
factors) declined significantly in 1965, and several hundred dead rainbow trout
were discovered in the southern-most half of the reservoir. The cause of the die-
off was never completely identified but appeared to be a combination of effects
from overstocking and an enormous bloom of the toxic blue-green algae,
Aphanizomenonflos aquae. Subsequently, stocking rates were reduced by a half to
two-thirds, resulting in better fish growth and condition.
Fisheries yields during this decade were calculated at about 20 pounds per
acre, remarkable for an inland trout fishery. However, stocks of rainbow trout,
measured by gillnetting, appeared to be declining as populations of nongame
fish increased.
Several additional game fish were introduced to the lake during the 1960s.
Kokanee salmon were stocked in the early 1960s to provide a pelagic fishery and
make use of the extensive zooplankton resource. Kokanee provided only inciden-
tal catches during the decade, however. Toward the close of the decade, brown
trout were stocked as a piscivorous species that could make use of the burgeon-
ing populations of Utah chubs in the upper quarter of the reservoir and offer a
trophy fishery. Smallmouth bass were introduced to provide additional sport
fishing diversity but primarily to prey upon expanding populations of Utah
chub. Although the successful introduction of smallmouth bass provided a
popular but localized fishery, bass growth rates were slow.
The 1970s
During the 1970s, populations of nongame fish continued to expand and
flourish, primarily Utah chub and white sucker. Rainbow trout populations and
sport fishery returns continued to decline. A shift to stocking larger (5-inch) trout
was initiated to improve fish survival and return rates (i.e., the percentage even-
tually harvested by anglers). The program was only partly successful, however,
and gillnet catches of rainbow trout continued to decline.
Brown trout introduced in the late 1960s were very successful; Flaming
Gorge became known across the Nation as an excellent fishery for very large
brown trout. The North American record was harvested from the reservoir.
Lake trout first appeared in the reservoir during the 1970s, apparently
through drift from upstream lakes in Wyoming. Lake trout were harvested infre-
quently during the decade, as were kokanee salmon.
The condition of rainbow
trout declined
significantly in 1965, and
several hundred dead
rainbow trout were
discovered in the
southern-most half of the
reservoir.
215
-------
Fish and Fisheries Management in Lakes and Reservoirs
A study of the
zooplankton resource
indicated a drastic decline
in the abundance of the
types and sizes of
zoopknkton that serve as
preferred food for rainbow
trout. [TJhis reduced
abundance of preferred
prey had resulted in the
poor survival, decreased
growth, and low angler
returns for rainbow trout
observed over the 20-year
period from the 1960s to
1980s.
Threadfin shad from Lake Powell were stocked at the beginning of the decade.
The objective was for the shad to compete with the Utah chub for food, depress the
size of chubs (because of decreased growth), and provide additional forage fish for
rainbow and brown trout. The experiment failed, however, because shad could not
survive in the relatively cold water of the reservoir.
The 1980s
Rainbow trout populations continued to decline while Utah chub stocks increased
and white sucker stocks remained about the same. Creel rates for rainbow trout
declined to less than 0.3 fish per hour, especially in the northern half of the reser-
voir. Lake trout were caught more frequently and began to replace brown trout as
a trophy fish.
The size of rainbow trout stocked was increased to about 8 inches during the
decade and has continued into the 1990s. Return rates have increased from 3 per-
cent of the number planted to about 23 percent, about the same level as in the
1960s. However, harvested rainbow trout still did not meet management objec-
tives for the desired size and weight of the angler harvest.
A study of the zooplankton resource was completed during the 1980s. Sites
sampled originally in the 1960s were sampled again in the 1980s. Results from these
surveys indicated a drastic decline in the abundance of the types and sizes of
zooplankton that serve as preferred food for rainbow trout. Zooplankton densities
were up to 10 times less than those measured in the 1960s. It was concluded that this
reduced abundance of preferred prey had resulted in the poor survival, decreased
growth, and low angler returns for rainbow trout observed over the 20-year period
from the 1960s to 1980s. Rainbow trout stocked at 8 inches continued to be well repre-
sented in the harvest, but were caught by anglers shortly after planting.
Angler interest in trophy lake trout increased through the 1980s. Age-growth
analysis showed that lake trout in Flaming Gorge Reservoir reached trophy size
more rapidly than in other less temperate, less productive lakes.
Kokanee salmon populations increased gradually during the decade. Spawn-
ing populations were documented in several tributaries to the reservoir, the largest
in the Green River upstream. Also, some kokanee stocks spawned along the reser-
voir shore. Gill net and purse seine data suggest that populations of Utah chub
and white suckers were at least static and possibly declining.
The 1990s
The primary sport fishes of interest have become the lake trout and kokanee sal-
mon, both largely self-sustaining. Rainbow trout continue to be stocked and har-
vested, but conditions for long-term survival remain difficult because of depressed
zooplankton abundance and competing predatory trout and nongame fishes.
The long-term management objectives for Flaming Gorge Reservoir are as fol-
lows:
• to discontinue stocking rainbow trout when harvest of kokanee salmon
equals or exceeds that of stocked rainbow trout,
• to manage lake trout as a trophy fishery, and
• to manage kokanee salmon as a self-sustaining sport fishery and as
alternative (to Utah chub) forage for lake trout.
A primary management tool being used to meet these objectives is regulation
of the numbers of trophy lake trout harvested through the use of a "slot" limit:
only two lake trout may be taken per day, all lake trout 26 to 36 inches must be
released, and only one may exceed 36 inches.
216
-------
Chapter 12. Case Study Examples
Flathead Lake, Montana
Background
The Flathead Lake restoration program is somewhat unique because of its
geographic scale, the comprehensive scope of the management activities, and the
number of agencies and people involved. Activities include land use (forestry
and agriculture) management, wastewater treatment, water level control, and
direct management of the fisheries in the Upper Flathead Basin, including
Flathead Lake, its tributaries, and associated watersheds. An ecosystem, whole-
basin approach to resource planning and management is being developed for the
drainage basin and its fisheries. In fact, one very important consideration in
development of the overall management plan for Flathead Lake Basin is the
diversity of fish species that reside in the lake and its surrounding tributaries and
migrate between the two to spawn. Information on the management plan and
program results were summarized from Cross (1987); Flathead Basin Commis-
sion (1990); Montana Department of Fish, Wildlife, and Parks and Confederated
Salish and Kootenai tribes (1989,1991); and Montana Power Company (1990).
The Flathead River basin covers 30,880 square miles and comprises the
northeasternmost basin of the Columbia River drainage, located primarily in
northwestern Montana (Fig. 12-6). The lake is 28 miles long, has a surface area of
20,636 acres, maximum depth of 371 feet, and an average depth of 107 feet, with
the upper 10 feet regulated by Kerr Dam. The steep-sided main basin of the lake
was formed by glacial scouring of underlying soft sedimentary rock, glacial
deposits define the lake's southern boundary, and sediments deposited by the
Flathead River modify its northern shoreline.
Flathead Lake is a relatively cold and unproductive (oligotrophic) lake.
Recent water quality studies suggest, however, that potential problems may be
developing because of increasing phosphate loads from point sources (primary
waste-water treatment plants) plus additional nutrient inputs from nonpoint
source runoff from urban, agricultural, and timber harvest areas. Native vegeta-
tion and land forms within the watershed have been altered by livestock grazing,
agriculture, water diversion and impoundment, logging, mining, and settlement
activities. Periodic blooms of blue-green algae (e.g., Anabaenaflos aquae) also indi-
cate possibly declining water quality and accelerated eutrophication of Flathead
Lake.
Additional concerns for management of the lake's fisheries are changes in the
hydrologic regime and introductions of normative fish species. The annual
hydrographic regime of the Flathead system has been modified by the construc-
tion and operation of hydroelectric and irrigation dams with significant impacts
on kokanee salmon and several species of trout. Native fish assemblages have
been altered by the introduction of normative fish species, which now dominate
parts of the ecosystem and are the management focus for some agencies.
In 1980, Congress enacted the Pacific Northwest Electric Power Planning and
Conservation Act (Public Law 96-501). This act mandated the Northwest Power
Planning Council, composed of representatives from Idaho, Montana, Oregon,
and Washington, to develop a regional energy plan and a fish and wildlife pro-
gram for the entire Columbia River basin. In June 1981, the Council asked the
American Indian tribes and State and Federal agencies located within the basin
to submit recommendations for the fish and wildlife program. In 1983, the Mon-
tana legislature enacted the Flathead Basin Commission Act, which established a
commission to coordinate agency activities, monitor existing environmental con-
ditions, and provide a common forum for activities associated with the water-
shed. The Commission includes the 11 State and Federal agencies, the Montana
Power Company, the Confederated Salish and Kootenai tribes, and agricultural
and other interests.
An ecosystem,
•whole-basin approach to
resource planning and
management is being
developed for the drainage
basin and its fisheries.
Native fish assemblages
have been altered by the
introduction ofnonnative
fish species, which now
dominate parts of the
ecosystem and are the
management focus for
some agencies.
217
-------
Fish and Fisheries Management in Lakes and Reservoirs
Sparwood
Fernie •
BRITISH_COLUMBIA
MONTANA
Figure 12-6.—Flathead River Basin above Flathead Lake (source: Montana Dep. Fish,
Wildlife, and Parks and Confederated Salish and Kbotenai tribes, 1989).
The Fisheries
Twelve game fish species inhabit the Flathead system. Three of these species are
native (cutthroat trout, bull trout, and mountain whitefish), while nine are intro-
duced species (lake trout, rainbow trout, lake whitefish, Yellowstone cutthroat
trout, brook trout, northern pike, grayling, largemouth bass, and kokanee salmon).
With the exception of yellow perch, all of the common nongame fish are native
species.
Average fisheries harvest from Flathead Lake consists of 92 percent kokanee
salmon, 4 percent yellow perch, 2 percent lake trout and bull trout, and 1 percent
cutthroat trout. The average harvest from the mainstem of the Flathead River in-
cludes 86 percent kokanee salmon, 10 percent cutthroat, 2 percent bull trout, 2 per-
cent whitefish, and 0.5 percent rainbow trout. Local anglers comprise 73 percent of
the total angling population on the lake and 88 percent of the anglers on the river.
In 1987, the kokanee salmon fishery collapsed in the lake. Major factors con-
tributing to this appear to be overharvest, hydroelectric operations, and natural
218
-------
Chapter 12. Case Study Examples
predation plus the appearance and increasing abundance of opossum shrimp
(Mysis relicto) in Flathead Lake. Mysis prey mainly on crustacean zooplankton, in-
cluding Daphniu, which also are the primary prey for kokanee salmon. The
presence of Mysis in this system now complicates efforts to manage kokanee and
is likely to increase management costs for the species.
Water Quality
The average annual primary production of phytoplanktori in Flathead Lake has
increased significantly since 1977 (Fig. 12-7), suggesting that nutrient concentra-
tions (phosphorus and nitrogen) in the Flathead Lake drainage are becoming
elevated above natural baseline levels. This trend of increased algal productivity,
however, may also relate to changes in the food web resulting from increasing
populations of Mysis. Additional monitoring data and analyses are needed to bet-
ter clarify the relative importance of these factors in causing productivity changes.
160 •
140
120 •
Grams of ,
Carbon 10°
per Square
Meier 80
per Year
60 ••
40 -
20
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990
Water Year
Figure 12-7.—Annual primary production in the water column of Flathead Lake, 1977 to
1990 water years (source: Flathead Basin Commission, 1990).
Wastewaters are believed to be major sources of phosphorus entering
Flathead Lake. Primary wastewater sources to the lake include discharges from
municipal treatment facilities in Kalispell, Whitefish, Columbia Falls, and Big
Fork upstream from Flathead Lake. Also, other unincorporated areas and many
individual homes have not been included in any of the combined collection and
treatment systems. In attempts to reduce contributions from these latter sources,
the Flathead Basin Commission has promoted improved public understanding of
the present and potential water pollution problems related to continued use of
home septic tank systems. Also, it continues to encourage and support improve-
ments in municipal waste treatment systems throughout the basin. Permit limits
for phosphorus at the wastewater treatment facilities and other point sources
have been restricted to 1.0 mg/L. Additionally, a phosphate detergent ban has
been implemented for the Flathead Basin. However, although these nutrient
reduction programs appear to be working, they have not been operating long
enough for effects to be documented.
In addition to these point sources, an estimated 75 percent of the total phos-
phorus entering Flathead Lake originates from nonpoint sources and activities in
the watershed that increase the runoff of sediments into the lake. Activities of
In 1987, the kokanee
salmon fishery collapsed
in the lake. Major factors
contributing to this
appear to be overharvest,
hydroelectric operations,
and natural predation
plus the appearance and
increasing abundance of
opossum shrimp in
Flathead Lake.
The average annual
primary production of
phytoplankton in Flathead
Lake has increased
significantly since
1977
[T]he Flathead Basin
Commission has promoted
improved public
understanding of the
present and potential
water pollution problems
related to continued use of
home septic tank systems.
219
-------
Fish and Fisheries Management In Lakes and Reservoirs
In addition to promoting
forestry and agriculture
best management
practices, both State and
Federal agencies are
continuing to annually
review 250 to 300 land
use projects within their
jurisdiction that could
physically alter stream or
lake habitats.
special concern include road building, poor logging or agricultural practices,
resource extraction, and other land developments that can increase surface runoff
volumes and sediment movement.
Timber harvest is a major activity in the Upper Flathead Basin. While modern
forest practices can help reduce stream damages, cumulative effects of timber
removal have increased water and sediment yields to excessively high levels in
some drainages, particularly in watersheds where there is mixed public and
private ownership and little coordination of management activities. Road con-
struction accompanying logging activities can also physically alter streams at
crossing points, causing erosion and fish migration barriers if crossings are im-
properly completed. Timber harvest is of particular concern because it often .oc-
curs in the upper reaches of watersheds that provide critical spawning and rearing
habitat for cutthroat and bull trout.
Several efforts are underway to mitigate the effects of logging on fisheries in
the Upper Flathead Basin. The Flathead National Forest has adopted a forest plan
that sets objectives for maintaining fish populations, water quality, and physical
habitat. Several field research and modeling efforts are underway to determine
whether these and related objectives are not only appropriate but also being
achieved. In addition, timber sales in critical areas for fish populations are
reviewed by the Montana Department of Fish, Wildlife, and Parks, the Con-
federated Salish and Kootenai tribes, and the Flathead National Forest.
In addition to promoting forestry and agriculture best management practices,
both State and Federal agencies are continuing to annually review 250 to 300 land use
projects within their jurisdiction that could physically alter stream or lake habitats.
These reviews attempt to eliminate projects or mitigate damage to aquatic habitat.
Hydroelectric Developments
Development and operation of three hydroelectric dams have had a profound ef-
fect on the Flathead fisheries. Hungry Horse Dam blocks access to 42 percent of
the traditional cutthroat and bull trout spawning grounds in the South Fork of the
Flathead, while BigforkDam has eliminated or restricted access to an additional 18
percent of the spawning areas in the Swan drainage. Erratic flow releases from
Hungry Horse Dam have nearly eliminated kokanee salmon spawning in the main
Flathead River. Kerr Dam, which controls the upper 10 feet of Flathead Lake, ad-
versely affects food production and fish spawning around the lakeshore and has
essentially eliminated most kokanee shoreline spawning from Flathead Lake. In
addition, water level fluctuations have increased erosion of not only the lakeshore
but also streambanks of the Flathead River for 22 miles above the lake.
The Northwest Power Planning Act passed in 1980 directed the Bonneville
Power Administration and associated electric utilities to document and mitigate
impacts to fish and wildlife from the construction and operation of hydroelectric
projects in the Columbia River drainage. Studies in the Flathead system have
focused on impacts to cutthroat and bull trout, kokanee salmon, and yellow perch.
A mitigation plan for Kerr Dam has been developed by the Montana Power Com-
pany under a relicensing provision by the Federal Energy Regulatory Commis-
sion. Fisheries mitigation plans to compensate for losses attributed to the
construction and operation of Hungry Horse Dam have been completed by the
Montana Department of Fish, Wildlife, and Parks and the Confederated Salish and
Kootenai tribes. Operational changes, including minimum releases from Kerr and
Hungry Horse dams, have been recommended. However, because optimal flow
for fisheries is not possible given the demands placed by hydroelectric generation
and because of fisheries losses unrelated to current operations regimes, other
mitigation measures are required, including
• improving fish access to spawning grounds,
• additional stocking of hatchery fish,
220
-------
Chapter 12, Case Study Examples
• construction and operation of a small-scale hatchery,
• acquisition and enhancement of off-site habitat, and
• construction of a gravel beach dike to control shoreline erosion on the
north shore of Flathead Lake caused by wave action during periods
of full lake levels.
In addition, Pacific Power and Light will evaluate the feasibility of changing the
design and operation of a fish ladder on Bigfork Dam to facilitate fish migration
to Swan River. Unfortunately, the degree of regulation possible for dam dischar-
ges at Kerr Reservoir will be inadequate to totally eliminate impacts on the
fisheries in Flathead Lake.
Many small hydroelectric projects were proposed in the Upper Flathead Sys-
tem in the early 1980s. Because of changes in hydroelectric rates and present
policies, most of these proposals have been dropped; nevertheless, a number of
other small dams constructed for irrigation continue to have localized but
cumulative effects on fisheries. The Northwest Power Planning Council has
adopted a Protected Areas Program that effectively bans new hydroelectric
development on critical stream reaches used for spawning or as nursery areas for
young fish. This program should significantly reduce the potential for new im-
pacts on western Montana fisheries from hydroelectric developments.
Wafer Quantity
Maintenance of the Flathead drainage fisheries depends on maintaining ade-
quate amounts of water in the streams and reservoirs to allow for spawning, rear-
ing, and feeding. In addition to the considerations discussed previously for
securing flows from existing hydroelectric reservoirs, management strategies
planned to maintain appropriate water flow include
• negotiation and purchase to secure water rights to supplement flows
for the best trout streams,
• purchases of additional water stored in area lakes from local irrigation
districts to maintain fish and wildlife habitat and dilute wastewater
treatment waters from Kalispell treatment plant, and
• maintenance of in-stream flows in the drainage by reviewing water
right applications and other water development projects.
Fisheries Management
Past management of fisheries in Flathead Lake and the upper river system has
centered around the maintenance of wild, self-sustaining fish populations. Much
effort has also focused on protecting and expanding the critical habitat for native
cutthroat and bull trout, two species of special management concern in Montana.
In addition, the public has exerted considerable pressure to restore the kokanee
salmon fishery or develop some comparable replacement fishery.
Three primary fisheries goals established by the Montana Department of
Fish, Wildlife, and Parks and the Confederated Salish and Kootenai tribes guide
fisheries management in the Flathead Basin, with the lake, river, and tributaries
now managed as a single, interconnected system.
1. Populations of native fish species living in the basin will be
preserved, protected, and enhanced. Species of special concern, such
as bull trout and westslope cutthroat trout, shall receive top priority
for protection activities.
Populations of native fish
species living in the basin
will be preserved,
protected, and enhanced.
221
-------
Fish and Fisheries Management in Lakes and Reservoirs
Lake Washington is one of
the best known examples
of recovery from cultural
eutrophication.
2. A diverse recreational fisheries will be maintained in the Flathead
Basin to provide a variety of opportunities for fishing during all
seasons of the year for a variety of fish species and sizes, with trophy,
sport, and harvest-oriented fishing available to the angler.
3. The existing water quality and aquatic habitat will be maintained or
enhanced.
Individual species management plans have been developed for 10 species of
game fish, including bull trout, westslope cutthroat trout, kokanee salmon, lake
trout, yellow perch, lake whitefish, mountain whitefish, rainbow trout, northern
pike, and largemouth bass. These management plans emphasize development of
naturally reproducing wild stocks of a diverse array of species. The highest
priority in the management plan is to ensure the survival and genetic integrity of
native bull and westslope cutthroat trout populations. Table 12-7 summarizes the
individual fishery management issues, goals, and strategies for 8 of the 10 target
species. (Northern pike and largemouth bass were excluded because of their rela-
tive unimportance in the overall fisheries plan for the Upper Flathead Basin.)
With the collapse of the kokanee salmon fishery, other fisheries will receive in-
creased angler interest and will have to provide a larger share of the annual har-
vest. Therefore, several game fish species will receive supplemental stocking until
natural populations are sufficiently abundant and natural reproduction can sus-
tain the increased harvest pressure.
The fisheries management program is integrally tied to the water quality and
habitat improvement programs; thus, population increases may occur for a num-
ber of formerly less abundant fish species. To date, only preliminary data are avail-
able to assess the benefits of these restoration efforts, but this information is
encouraging. Substantive data to evaluate the success of these efforts will probably
not be available until 1994—the last year of this management cycle.
Lake Washington, Washington
Lake Washington is one of the best known examples of recovery from cultural
eutrophication. Over the last 30 years, it has reverted from a eutrophic lake to its
more natural mesotrophic-oligotrophic condition. Located adjacent to Seattle (Fig.
12-8), Lake Washington (area, 33.6 square miles; maximum depth, 213 feet)
provides a diversity of fishing and other recreational opportunities. The following
paragraphs provide a brief summary of eutrophication control efforts and the role
of fish in lake improvements as compiled from Eggers et al. (1978), Edmondson
(1979), Edmondson and Lehman (1981), Edmondson and Litt (1982), Edmondson
and Abella (1988), Swartzman and Beauchamp (1990), and the National Research
Council (1991).
Lake Washington was first affected by raw and treated sewage from Seattle in
the early 1900s; however, diversion of Seattle's effluent from the lake to Puget
Sound in the mid-1930s ended this initial period of pollution. Water pollution
problems in the lake again became apparent in the 1940s, when suburban growth
from Seattle spread along the lakeshore north and south of the city. By 1955, the
first bloom of the blue-green alga, Oscillatoria rubescens, was observed. By 1963, ef-
fluents from 11 sewage treatment plants were being discharged into the lake or its
tributaries, contributing 63 percent of its total phosphorus load.
Diversion of this sewage effluent away from Lake Washington began in 1963;
by March 1967,99 percent of the sewage effluent had been diverted. Phosphorus
inputs dropped from a high of about 450,000 Ib/yr (204,000 kg/yr) in 1964 to a low
of 95 Ib/year (43 kg/yr) in 1973 and 1976. The lake promptly responded with
decreases in nutrient concentrations, phytoplankton abundance, and the propor-
tion of blue-green algae in the phytoplankton community (Fig. 12-9). Secchi disk
222
-------
Chapter 12. Case Study Examples
Table 12-7.—Individual species management concerns, objectives, and strategies
for the Flathead Basin (compiled from Montana Dep. Fish, Wildlife, and Parks and
Confederated Salish and Kotenai tribes, 1989).
SPECIES
MANAGEMENT
ISSUES
MANAGEMENT
OBJECTIVES
MANAGEMENT
STRATEGIES
Bull
trout
International coordination
required; some fish spawn
in British Columbia
Very sensitive to streambed
habitat degradation and angling
pressure
Predatory fish that may
compete with lake trout and
may also eat cutthroat trout
Hatchery production is
experimental; return rate to
creel is unknown
Genetic integrity of native
population high priority
Increase use and
harvest by 20 to 25
percent
Increase levels of
spawning fish beyond
existing counts in
most productive
tributaries
Increase enforcement
activities in spawning areas
and at the river mouth
fishery
Increase agency coordina-
tion and habitat monitoring;
increase available spawning
and rearing habitat by
opening blocked areas
Plant 260,000, 8" bull trout
directly into Flathead Lake
through an experimental
hatchery program
If hatchery program is
successful in increasing
population, daily bag limit
may be increased. If
population doesn't respond,
shorten angling season for
river or close additional
spawning streams from
fishing
Encourage voluntary catch
and release through public
education campaign
Westslope
cutthroat
trout
Maintenance of genetic purity
and diversity of stocks
Spawning and rearing habitat
threatened
Very vulnerable to anglers in
rivers; requires suitable catch
restrictions
Difficult to monitor populations
in lake and river
Substantial fishing pressure
increase possible with loss of
kokanee
salmon fishery
Increase harvest and
use of cutthroat by 20
percent
Increase populations
substantially to buffer
impact of increased
harvest
Improve fish passage in
blocked areas. Increase
agency coordination, habitat
protection, and monitoring
Increase enforcement to
ensure compliance with
fishing regulations
Stock Flathead Lake with
1 million 4- to 6-inch fish
annually
Initially set lakewide daily
limit of 2 to standardize limit
and prevent over harvest
until hatchery fish enter
fishery. Limits increased if
plants successful. Tailor
other restrictions for other
sections of watershed
Encourage voluntary catch
and release with education
program
Kokanee
salmon
Impact of Mysis shrimp on
survival of kokanee
Spawning areas greatly
reduced because of
hydroelectric operations
Hatchery facilities inadequate
to producenecessary egg
supplies; costly and time-
consuming to remedy
Plants of fingeriings
experimental; success unknow
1 Lake trout predation may limit
kokanee recovery
Restore kokanee
population to levels
required to sustain a
harvest of 60,000
fish/15,000 angler
days (small fraction o'
pre-crash harvest)
Continue annual ex-
perimental stocking of 3-5
million fish, which may
produce 60,000 adults
Continue current manage-
ment efforts to protect
kokanee in lake and river
system (size, catch, and
season limits)
continued on next page
223
-------
Fish and Fisheries Management in Lakes and Reservoirs
Table 12-7—Continued
SPECIES
MANAGEMENT
ISSUES
MANAGEMENT
OBJECTIVES
MANAGEMENT
STRATEGY
Lake
trout
Maintain trophy segment of
population in spite of loss of
kokanee food base
Limit overharvest offish
that take 15 years to reach
trophy size
Potential for increased
predation on kokanee if
lake trout population
Increases
Competition with other large
predators (bulltrout) if favored
prey (kokanee) decreases
Maintain trophy
fishery
Reduce overall lake
trout biomass by
increasing harvest of
small fish
Increase angler use
to 15,000 angler
days/year; harvest to
8,000 fish/year
Public education
program on methods to catch
smaller (3-8 Ib) lake trout
Survey public; modify
regulations. Options include
increase in size limit, a slot
limit, increase in daily bag
limit, or some combination.
Yellow
perch
Receives little management
attention despite occupying
portion of lake underused by
other game fish and anglers
Not classified as game fish;
no harvest restrictions
Yellow perch populations
expanding in warmer,
shallower portion of lake
Increase harvest to
100,000 fish annually;
maintain catch rate
and average length
Provide better public
access for anglers to
portion of lake occupied by.
yellow perch
Increase public awareness
of fishing opportunities for
yellow perch
Develop fishing guide
describing fishing
techniques, seasons, and
locations
Introduce artificial
structural enhancement to
provide structural diversity
at low pool to improve
recruitment and minimize
overwinter predation
Lake
whitefish
Lake whitefish may compete
with other species for
zooplankton forage (i.e.,
kokanee and westslope
cutthroat)
Underused by anglers despite
good fishing experience and
taste qualities
Increase use to
10,000 angler
days/year and
harvest to 20,000
fish/year
Publicize fishing quality,
fishing techniques, locations,
and seasons in the lake
through brochures and the
media
Mountain
whitefish
Greatly underused relative to
abundance; small average size
discourages more harvest
May compete for food and
space with other game fish
that are more popular with
anglers
Increase use and
harvest to 10,000
fish/year
Publicize fishing tech-
niques, seasons, locations,
and cooking tips through
brochures and the media
Rainbow
trout
May compete for food and
space with native cutthroat
trout
May hybridize with westslope
cutthroat trout, reducing genetic
integrity of native stocks
Returns from past plants have
been poor
Increase use and
harvest to 1,000
fish/year
Publicize identification of
rainbow and cutthroat trout,
encourage angler harvest of
rainbow and voluntary catch
and release of cutthroat
224
-------
Chapter 12. Case Study Examples
transparency increased from about 3 to 13 feet (1 to 4 meters), total phosphorus
decreased from 70 to 16 fig/L, and epilimnetic chlorophyll decreased from 35 to 4
ug/L. By 1975, the lake was considered to have largely recovered from
eutrophication.
Lake Washington supports about 30 species of fish, many of them intro-
duced. Fisheries management concerns focus on interactions among four species:
1. Rainbow trout. Introduced into the lake in 1981, this species is
stocked annually (average 250,000 young fish stocked per year).
2. Juvenile sockeye salmon. This species resides in the lake for
about 15 months before migrating to sea.
3. Northern squawfish (Ptychocheilus oregonens/s). Native to
Lake Washington, these voracious piscivores feed heavily on juvenile
sockeye salmon but are not an important game or sport fish.
4. Longfin smelt (Spirinchus thaleichthys). This species currently
dominates the pelagic zone of the lake along with juvenile sockeye
salmon.
Rainbow trout support a put, grow, and take fishery that averages 20,000 angler-
caught fish per year. In addition, Lake Washington has the largest sockeye sal-
mon run in the State of Washington, supporting a commercial and sport fishery
that averaged about 80,000 adults per year from 1971 to 1984.
Changes in Lake Washington's water quality have continued to occur since
1975 and are attributed largely to changes in the fish and zooplankton com-
munities in combination with reduced nutrient loads. In 1976, Daphnia (which
had occurred in the lake only sporadically and in modest numbers) suddenly be-
came the dominant zooplankton (Fig. 12-10). Coincidently, the mean summer
transparency doubled (Fig. 12-11). Secchi disk transparency had increased from
about 3 to 13 feet (1 to 4 meters) in response to nutrient diversions in the 1960s
but increased even further to approximately 23 feet (7 meters) in the late 1970s in
response to the explosion in the Daphnia population. The effects of Daphnia on
phytoplankton abundance and composition and indirectly on water transparen-
cy are well documented (see Chapter 9).
Two factors contributed to the increased abundance of Daphnia: a sharp
decrease in the abundance of the predatory zooplankton Neomysis mercedis in the
mid-1960s and a decrease in the abundance of Oscillatoria, a filamentous blue-
green algae, in 1975. The reduction in Neomysis was caused, most likely, by an in-
crease in the abundance of longfin smelt, a planktivore that feeds selectively on
this zooplankton. (During 1962-64, Neomysis accounted for 85 percent of smelt
gut contents.) Although native to the system, before 1960 longfin smelt were
quite rare. Increases during the 1960s were attributed primarily to the following
physical improvements in smelt spawning habitat in Cedar River, the major
tributary to Lake Washington: cessation of the annual stream dredging program,
installation of shoreline stabilization structures (banks of large stones), and initia-
tion of low flow regulations.
Although the Neomysis population declined in the mid-1960s, increases in
Daphnia did not occur until 1975. Thus, the decrease in Neomysis, although essen-
tial, was not sufficient in itself to permit Daphnia to flourish. As long as Oscz7-
latoria were abundant, Daphnia remained scarce. The mechanical interference of
Oscillatoria with Daphnia feeding is considered the most likely cause for the
delayed success of Daphnia. As noted above, the decline in Oscillatoria and other
blue-greens (see Fig. 12-9) was a direct result of sewage diversions and reduced
nutrient inputs.
The introduction of rainbow trout into Lake Washington in 1981 raised con-
cerns about adverse effects on both Daphnia and sockeye salmon. Rainbow trout
have elastic feeding habits that range from planktivory and benthic feeding to
225
-------
Fih and Fiherfes M anagera entii Lakes and Reserwois
SWAMP CREEK
BEAR CREEK
IZ5Z
SAMMAMISH RIVER
'.'.'.'..'.I LOCKS ff.v
: . •.••'.• \ LAKE UNION
5 KM
CEDAR RIVER
Figure 12-8.—Lake Washington and its tributaries. Arrows numbered 1-11 show sewage
treatment plants. Four-digit numbers are U.S. Geological Survey gauging stations
(source: Edmondson and Lehman, 1991).
piscivory; their diet depends primarily on prey availability. Bioenergetics models
were developed to evaluate the interactions among rainbow trout, sockeye sal-
mon, longfin smelt, Daphnia, and other species (see Fig. 11-12 in Chapter 11).
Model results suggest that an increase in rainbow trout abundance as a result of
either increased stocking (by 10-fold) or decreased fishing pressure (by 50 percent),
could decrease (by 50 percent or more) the abundance of both sockeye salmon and
longfin smelt. Although not explicitly modeled, increases in rainbow trout could
also depress populations of Daphnia, an important prey for young trout, and
potentially reverse recent improvements in water transparency.
226
-------
Chapter 12. Case Study Examples
250-1
PARTICULATE P
I I .. I _- I — ' .- i .- i --. ' ... i -~ '
62 ' 63 ' 64 ' 65 ' 66 ' 67 ' 68 ' 69 ' 70 ' 71 ' 72 73 74 75 76 77 78
62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78
62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78
YEAR
Figure 12-9.—Total mass of phosphorus (P) and of particulate P in Lake Washington
plotted by months, concentrations of chlorophyll a in surface samples, and proportion of
total phytoplankton blomass represented by filamentous blue-green algae in surface
samples (source: Edmonson and Lehman, 1981).
227
-------
Fish and Fisheries Management in Lakes and Reservoirs
Daphnia
NO./I
0-
0-
10-
0-
30-
20-
10-
O-
10-
ambigua
schjdleri
Ihorai
a
A
pulicaria
galeata
o
1972
1973
1974
1975
A
/\
A
JL
(I
• }\
I
\
A
J\
i
i
V A
f\
\
./I
1976 1977 1978 1979
Figure 12-10.—Abundance of various species of Daphnia in the top 10 meters of Lake
Washington from 1972-79. Bars above baseline indicate presence of males, ephlppla (egg
cases), or both (source: Edmondson and Litt, 1982).
1950 1955
1960
1-
2-
3-
4-
6-
7-
8-
9-
_ 100
>»
en
50-
1965
i
1970
-J—S 1_
1975
. i •
SECCHI TRANSPARENCY
JULY - AUGUST
MEAN AND RANGE
t-
SEWAG
\.
E DIVERSION
.}
-5Kr3.4rri
100%-
50
0—I
DISSOLVED PHOSPHORUS
1950 1955
1960
1965
1970
1975
Figure 12-11.—Mean and range of summer Secchi disk transparency for each year (mean
values for 1971-75 and 1976-79 shown to the right); schedule for diversion of sewage ef-
fluent; and total loading rate of dissolved phosphorus and loading rate contained in
sewage effluent (source: Edmondson and Litt, 1982).
228
-------
APPENDIX A
Background Information
on Selected
Fish Species
Appendix Objective
This appendix contains brief descriptions of the habitat requirements and
management concerns for selected fish species widely distributed in lakes and
reservoirs in the United States and Canada. Its objective is to provide introduc-
tory information that can assist managers in selecting target species, evaluating
lake problems, and designing a fish or fisheries management program. A number
of good reference books are available for further details as well as information on
species not covered in this appendix. General reference books include Scott and
Grossman (1973), Carlander (1969, 1977), Kendall (1978), Nelson (1984), and
Hocutt and Wiley (1986). Region-specific fish guides have also been prepared for
many States and geographic areas (e.g., Becker, 1983; Manooch, 1984; Miller et al.
1982; Robinson and Buchanan, 1988; Sigler and Sigler, 1987; Smith, 1985; Sublette
et al. 1990; Tomelleri and Eberle, 1990; Trautman, 1981; and Wydoski and Whit-
ney, 1979). In addition, many State agencies prepare species-specific management
plans that include basic information on fish biology and habitat needs (e.g.,
Minn. Dep. Nat. Resour. 1982; La. Dep. Wildl. Fish. 1990; Me. Dep. Inland Fish.
Wildl. 1986). The information summarized here is extracted from Scott and
Grossman (1973) and Carlander (1969,1977) as well as the other references noted
for each species or fish group.
Threatened and Endangered Species
Special care and management approaches are needed for fish species or strains
classified as threatened or endangered. Most States and provinces regularly
publish and update lists of threatened and endangered species as well as species
or strains of special concern. Williams et al. (1988,1989), Johnson (1987), and Ono
et al. (1983) review threatened and endangered fish species in broader
geographic areas. The occurrence — or potential occurrence — of protected or
rare species must be carefully assessed before any lake management activities are
initiated.
Special care and
management approaches
are needed for fish species
or strains classified as
threatened or endangered.
229
-------
Fish and Fisheries Management in Lakes and Reservoirs .
Largemouth bass... occur
most often in the upper
levels (warmer waters) of
small, shallow lakes or
shallow bays of larger
lakes, in association with
soft bottoms, stumps, and
extensive growths of
emergent and. submergent
aquatic vegetation.
Adult bass feed primarily
on forage fishes, such as
sunftsh and shad, and are
top predators in most
waters.
Largemouth Bass, Smallmouth Bass,
and Spotted Bass
Largemouth bass (Micropterus salmoides), smallmouth bass (M. dolomieu), and
spotted bass (M. punctulatus) are all important game fish. Largemouth bass, in par-
ticular, are widely distributed throughout much of the United States and Canada,
the primary game fish managed in many warmwater lakes and reservoirs, and
often the focus of fishing tournaments. Two subspecies are recognized: the north-
ern largerriouth bass, M. salmoides salmoides, and the Florida largemouth bass, M.
salmoides floridanus. Spotted bass are native to the southcentral United States, but
have been introduced into California, Nebraska, South Carolina, and several other
States. Smallmouth bass occurred originally from southern Canada as far south as
Oklahoma and Alabama, although they have also been widely introduced in other
areas. All three black bass species have a number of common habitat needs and
management concerns.
Habitats
Largemouth bass are highly adaptable to a wide range of environmental condi-
tions and inhabit a variety of aquatic habitats. They occur most often in the upper
levels (warmer waters) of small, shallow lakes or shallow bays of larger lakes, in
association with soft bottoms, stumps, and extensive growths of emergent and
submergent aquatic vegetation. They can tolerate moderate turbidity and warm
water temperatures (up to 97°F if fish are acclimated to warmer water). Preferred
summer temperatures are in the upper 70s(°F), while feeding is restricted below
50°F. Florida largemouth bass and spotted bass are less tolerant of low tempera-
tures than are northern largemouth, while smallmouth bass prefer slightly cooler
waters (preferred temperature range in the low 70s(°F) during summer). Both
smallmouth and spotted bass are also less tolerant of high turbidity and prefer
waters with firmer substrate (e.g., rocky or gravel substrate) than largemouth bass.
Reproduction
All three species spawn in the late spring, early summer. Spawning is keyed
primarily to water temperature, rather than a specific date, and therefore generally
progresses from south to north following the seasonal warming trend. Spawning
begins as temperatures reach around 55° to 60°F, and activity peaks at 65° to 70°F
for largemouth and spotted bass and 61° to 65°F for smallmouth bass.
The male develops the nest site and guards the eggs and schools of fry for
several weeks after emergence. In lakes and reservoirs, nests are usually con-
structed at water depths of 1 to 4 feet but can occur as deep as 15 feet. The depth
selected in any given lake can vary directly with water clarity. Largemouth bass
reproduce successfully on almost any type of bottom as long as a firm, silt-free
nest bed can be created; sites with rocky or gravelly substrate and adequate cover,
in the form of logs, stumps, or vegetation, are preferred. Smallmouth bass and
spotted bass, on the other hand, reproduce successfully only in waters with
suitable areas of shoreline gravel or rocky substrate for nest construction. For all
three species, reproductive success may be reduced by sudden drops in tempera-
ture or water level, high winds and wave action, heavy predation on eggs and fry
by other fish (e.g., sunfish), or silt deposits on the eggs after a heavy rainfall.
Food Habits
Adult bass feed primarily on forage fishes, such as sunfish and shad, and are top
predators in most waters. Crayfish are also often an important component of adult
diets. Fry feed primarily on zooplankton, while fingerlings feed on aquatic insects
and other small organisms. All three species become piscivorous at a fairly young
age and small size (when individuals reach about four inches in length).
230
-------
Appendix A. Background Information on Selected Fish Species
Management Concerns
Black bass are "net shy" and difficult to sample quantitatively with gill nets, trap
nets, or other nets commonly employed to sample fish in lakes. Better informa-
tion can be obtained using one or more of the following:
• night electrofishing,
» seining, especially for adult bass in the spring or young-of-the-year
bass later in the year,
• angler reports and creel censuses, and
• visual observations of male bass on spawning beds in the spring.
Common problems encountered in largemouth bass management include
the following:
• Inadequate forage. Other predators, such as walleye and northern pike,
may compete with bass for forage fish. If forage is scarce and bass are considered
the primary target fish of interest, stocking of other predators should be reduced
or discontinued and other control measures considered. Stocking of forage fish is
unlikely to be effective.
• High predator population. Northern pike may, in some cases, consume ex-
cessive numbers of young, small bass. Methods for controlling or eliminating
northern pike may be worth considering in these instances.
• Habitat degradation. The shallow, fairly productive lakes generally in-
habited by largemouth bass may be subject to periodic oxygen depletion (e.g.,
winterkill) and eutrophication. Methods for countering these problems were dis-
cussed in Chapter 8. If the entire population of bass is lost from winterkill, for ex-
ample, the easiest methods for reintroducing the species are (a) transplants of
sexually mature fish from other nearby waters or (b) stocking of fry, collected at
the time of swim-up. Aquatic vegetation provides essential cover for young bass;
watershed or lake disturbances that markedly reduce the extent of macrophyte
beds can also be detrimental to largemouth bass populations.
• Inadequate natural reproduction. Largemouth bass have a high
reproductive potential and insufficient natural reproduction is seldom a prob-
lem. If maintenance stocking is necessary to provide a bass fishery, managing the
lake for bass is probably not cost effective nor appropriate. Poor year classes can
occur, however, because of sudden changes in water temperature during spawn-
ing, excessive wind and wave action, or limited availability of food for newly
rising fry. Heavy cannibalism of older bass on young-of-the-year bass can also
occur in waters with high fish density.
• Fishing pressure. High fishing pressure generally does not significantly
reduce bass reproduction and recruitment but can result in a decline in fishing
quality. Large harvests of fish greater than some minimum size limit (e.g., longer
than 12 inches) also can adversely affect the predator/prey balance by decreasing
bass predation on other smaller fish, increasing the possibility of a stunted pan-
fish population. Slot length limits may be one possible solution to excessive har-
vests of larger fish.
Management concerns for smallmouth and spotted bass are generally
similar. However, spotted bass tend to grow slower and to have shorter life spans
(often, few fish live longer than three years) than largemouth bass, requiring
quite different length limits and other fishing regulations for optimal fisheries
management.
Aquatic vegetation
provides essential cover
for young bass; watershed
or lake disturbances that
markedly reduce the
extent of macrophyte beds
can also be detrimental to
largemouth bass
populations.
If maintenance stocking is
necessary to provide a bass
fishery, managing the lake
for bass is probably not
cost effective nor
appropriate.
231
-------
Fish and Fisheries Management in Lakes and Reservoirs
[SJunfish and crappie...
can occur in large
numbers and represent a
valued fisheries
component in many
waters. Both groups,
however, have a tendency
to overpopulate and stunt
if the numbers of small
fish are not adequately
controlled by predators or
other means.
Most sunfish species
prefer well-vegetated
habitats, which provide
protection from predators.
References
In addition to Scott and Grossman (1973) and Carlander (1977), the following ref-
erences provide useful information on black basses: Minnesota Department of
Natural Resources (1982), Louisiana Department of Wildlife and Fisheries (1990),
Morrison and Tilyou (1991), and Boyle (1980).
Sunfish and Crappie
Like black bass, sunfish and crappies are members of the sunfish family, Centrar-
chidae. Common sunfish species include bluegill (Lepomis macrochirus), pumpkin-
seed (L. gibbosus), and redear (L. microlophus). Two species of crappie occur in
North America: the white crappie (Pomoxis annularis) and black crappie (P.
nigromaculatus). Collectively, sunfish and crappie are often referred to as panfish;
that is, smaller fish caught primarily for their food value rather than for fishing
sport. They can occur in large numbers and represent a valued fisheries com-
ponent in many waters. Both groups, however, have a tendency to overpopulate
and stunt if the numbers of small fish are not adequately controlled by predators
or other means.
Habitat
Sunfish and crappie are generally classified as warmwater fish. They are usually
found in quiet warm waters of small lakes and bays and shallower areas of larger
lakes and reservoirs. Most sunfish species prefer well-vegetated habitats, which
provide protection from predators. Maximum growth rates for bluegill occur at
summer temperatures in the low 70s (°F), although fish still actively feed and grow
at higher temperatures (up to about 80°F); pumpkinseed prefer somewhat cooler
waters, while redear sunfish grow better in warmer waters. The black crappie
prefers clearer, deeper, and cooler lakes than the white crappie, and its range ex-
tends further north. Abundant cover, such as inundated timber or submerged
vegetation, and clear water are the black crappie's primary habitat requirements.
The white crappie is quite tolerant of turbidity and siltation and often occurs in
lakes where aquatic vegetation is lacking.
Reproduction
As for black bass, sunfish and crappie spawn in relatively shallow waters (general-
ly 1 to 5 feet) in quiet areas and bays. Males develop the nest sites and guard the
eggs during incubation and schools of fry for a period of time after emergence.
Most sunfish and crappie will spawn in a variety of substrates including mud,
gravel, or sand, although nests are usually located near some type of cover, such as
macrophytes, stumps, or brushpiles. Depending on the location, crappie spawning
occurs from mid-March to early summer (June to mid-July), when water tempera-
tures rise above about 60°F. Most sunfish species spawn for extended periods,
often from late spring through mid- to late-summer, and in some cases in early fall.
Food Habits
Primary food items include aquatic insects, crustaceans, and snails. Adult bluegills
and crappie also feed in some lakes on small forage fish. Young fish feed almost
solely on small zooplankton during their first year.
Management Concerns
Information on the relative abundance and population characteristics of sunfish
and crappie can be obtained most readily by trapnetting during the spawning
season, observing spawning sites, and conducting creel censuses in early or late
winter or early spring.
232
-------
Appendix A, Background Information on Selected Fish Species
Major management problems include the following:
• Stunting. Overcrowded and therefore stunted fish is the most common
management problem. To improve fish growth rates, the numbers of small fish
must be reduced substantially. Management approaches for stunted populations
were discussed in Chapter 8 and include water level management, aquatic
vegetation control, introductions of predators or increased predator efficiency,
and selective cropping and reclamation.
• Habitat degradation. Crappies are relatively tolerant of low levels of dis-
solved oxygen, and are among the most winterkill-resistant species. Yet, a variety
of habitat problems may limit crappie survival and production, including exces-
sive eutrophication or pollution. Bluegills and other sunfish may also be adverse-
ly affected by eutrophication, toxic contaminants, increased turbidity, and low
levels of dissolved oxygen. Maintaining appropriate covers of aquatic vegetation
is an important component of habitat management for sunfish.
• Inadequate natural reproduction. Crappie and sunfish have a high
reproductive potential; inadequate natural reproduction is seldom a problem.
However, low levels of recruitment may occur in the absence of emergent and
submerged vegetation to provide protective cover and feeding areas for young
fish.
• Poor fishing. If the lake lacks adequate structures to provide cover and con-
centrate fish, crappies may distribute themselves throughout the midwater
pelagic zone and be difficult to locate. Thus, crappie may be abundant in a lake,
yet few caught by anglers. Additions of artificial reefs or other structural features
may improve fishing success.
References
Useful references include' Arnoldi et al. (1991) and Minnesota Department of
Natural Resources (1982) as well as the many general and region-specific refer-
ences listed at the beginning of this appendix.
Striped Bass and White Bass
Striped bass (Morone saxatilis) and white bass (M. chrysops) are members of the
temperate bass family in the order Perciformes.
Habitat
In their natural habitat, striped bass are anadromous, moving from the ocean up
rivers into fresh water to spawn. In recent years, however, striped bass as well as
striped bass/white bass hybrids have been widely introduced into large reser-
voirs, particularly in the southern United States. White bass inhabit coolwater
lakes and reservoirs from Canada to the Gulf of Mexico. Both species occur
primarily in pelagic regions and can be an important component of open-water
fisheries in lakes and reservoirs.
Reproduction
Sexually mature white bass form schools and move onto shoals for spawning in
the spring. Spawning commences in April in the southern United States and late
May/early June in northern areas, at a water temperature of 50° to 65°F. A given
population may spawn over a period of 5 to 10 days. Eggs and sperm are
released simultaneously into the water, near the lake surface, or in mid-water.
Overcrowded and
therefore stunted fish is
the most common
management problem.
Maintaining appropriate
covers of aquatic
vegetation is an important
component of habitat
management for sunfish.
[SJtriped bass as well as
striped bass/white bass
hybrids have been widely
introduced into large
reservoirs, particularly in
the southern United
States.
233
-------
Fish and Fisheries Management in Lakes and Reservoirs
The most frequently cited
management problem for
reservoir populations of
striped bass is summerkill
caused by high
temperatures and low
levels of dissolved oxygen.
The second most
commonly cited problem is
an inadequate forage base.
The eggs sink and become attached to gravel, boulders, or vegetation on the bot-
tom. Egg survival depends on the availability of silt-free surfaces. Eggs hatch in a
relatively short period of time (generally two to three days); adults provide no
parental care to either the eggs or fry.
Striped bass also spawn in the spring, when water temperatures reach 60° to
70°R Like white bass, the eggs and sperm are released simultaneously into the
water column. However, striped bass eggs are semibuoyant. Unless suspended by
water currents, they will settle to the bottom and perish. Thus, striped bass spawn
in rivers; sexually mature fish can migrate long distances upriver to spawn.
Food Habits
Both white and striped bass are piscivores; important forage fish include threadfin
and gizzard shad, alewifes, silversides, blueback herring, and yellow perch.
Adults also consume insects and crayfish. Younger fish feed on insect larvae and
zooplankton.
Management Concerns
The most frequently cited management problem for reservoir populations of
striped bass is summerkill caused by high temperatures and low levels of dis-
solved oxygen (see Box 3-E). Eleven of the 30 State agencies that manage one or
more striped bass populations reported having problems with high-temperature,
low-oxygen stress (Axon and Whitehurst, 1985). Likewise, 27 of the 80 reservoirs
(34 percent) reviewed had some summer mortality of striped bass (Matthews,
1985). For populations in more northern waters (e.g., Minnesota and Oregon) low-
temperature stress during long winters may also be a problem. Although of con-
cern, periods of high mortality (summerkill or winterkill) do not usually prevent
the establishment of a quality fishery for striped bass or striped bass/white bass
hybrids.
The second most commonly cited problem is an inadequate forage base. Giz-
zard or threadfin shad are often stocked coincidently with striped or white bass in-
troductions into reservoirs. However, heavy predation by adult bass may deplete
the supply of available forage, aggravated by problems with high mortality
(winterkill) of gizzard or threadfin shad. Food supplies may be inadequate, even
in some waters with a high biomass of forage fish, if a substantial fraction of the
fish are too large to be readily eaten.
Concerns have been raised regarding potential adverse effects of striped
bass/white bass introductions on other game fish populations. Several States have
reported problems with striped bass predation on rainbow trout in reservoirs with
a "two-story" trout fishery (Axon and Whitehurst, 1985). Studies of striped bass-
largemouth bass interactions, however, have found no significant negative effects
on largemouth bass growth rates or population structure (Turner, 1986; Harper
and Namminga, 1986).
Finally, losses of striped bass through emigration can be an important problem
in some systems. Spillway escapement, high discharge rates, or extreme water-
level fluctuations were reported to cause emigration of striped bass from reser-
voirs in eight States (Axon and Whitehurst, 1985).
References
Publications with useful information on striped bass, white bass, and hybrid
populations in freshwaters include Scott and Grossman (1973), Manooch (1984),
Axon and Whitehurst (1985), Matthews (1985), and Coutant (1985).
234
-------
Appendix A. Background Information on Selected Fish Species
Bullheads and Catfish
In the family Ictaluridae, a number of bullhead and catfish species can be impor-
tant components of fish or fisheries management programs. Channel catfish (Ic-
talurus punctatus) grow to large sizes (up to 25 to 30 pounds) and provide highly
valued commercial as well as recreational fisheries, particularly in the southern
United States. Blue catfish (I. furcatus) and flathead catfish (Pylodictis olivaris)
occur primarily in large rivers, although they have also been stocked into a few
reservoirs with varying success. Several bullhead species are widely distributed
in central and eastern North America: brown bullhead (Ameiurus nebulosus),
black bullhead (A. melas), and yellow bullhead (A. natalis). Bullheads are general-
ly smaller than catfish. Depending on angler preferences, the region, and size dis-
tribution of the population, bullheads may be viewed as a nuisance species or a
prized game fish.
Habitats
As a group, catfish and bullhead are highly adaptable, occur in almost all types
of habitats from southern Canada to Florida and Texas, and are quite tolerant of
environmental stresses, including low levels of dissolved oxygen, high tempera-
tures, and toxic pollutants. Brown bullhead prefer cooler, northern lakes, and are
one of the most common fish in high elevation lakes in the Adirondack Moun-
tains of New York and widely distributed across northern Michigan, Wisconsin,
and Minnesota. Black and yellow bullhead occur predominantly in warmwater
lakes and reservoirs; black bullhead in particular are common in warm, turbid,
eutrophic waters. Channel catfish occur as far north as southern Canada but are
of greater importance in southern warmwater lakes and reservoirs.
Reproduction
Spawning occurs in late spring and early summer as water temperatures' warm to
70° to SOT. The male — or for brown bullhead, the male and female — fish select
a nest site in shallow waters, generally in a secluded area under logs> brush, or
banks or in patches of vegetation. Less often, nests may be constructed in the
open as a shallow depression in a sand or mud bottom. Eggs are laid in large ad-
hesive, gelatinous masses that the male guards through incubation and, in some
species, for a short period after fry emergence.
Feeding Habits
Bullhead and catfish are primarily bottom feeders, feeding on insects, crayfish,
amphipods, mollusks, algae, fish eggs, and to a lesser degree, other fish.
Management Concerns
Because of their adaptability and tolerance of a wide range of environmental con-
ditions, bullhead and catfish populations often need little direct management or
manipulation. Natural reproduction is generally adequate. However, in waters
with few predators, populations can overcrowd and stunt. In many regions,
bullhead populations are underused by anglers. In eutrophic waters, bullheads
and catfish may contribute to internal nutrient recycling and high algal produc-
tivity (see Chapter 9). In such cases, a fish control program, as discussed in Chap-
ter 8 (reducing undesirable fish populations), may be warranted.
References
This information was summarized from Scott and Grossman (1973), Carlander
(1969), and Manooch (1984).
As a group, catfish and
bullhead are highly
adaptable, occur in almost
all types of habitats from
southern Canada to
Florida and Texas, and are
quite tolerant of
environmental stresses....
In many regions, bullhead
populations are underused
by anglers.
235
-------
Fish and Fisheries Management in Lakes and Reservoirs
Walleye are an important
coolwater game fish
They ...are most
abundant in large, shallow
lakes that are moderately
turbid but also frequently
occur in large, deep,
clearwater lakes with
rocky bottoms.
Walleye and Yellow Perch
Walleye (Stizostedion vitreum) and yellow perch (Perca flavescens) are members of
the family Percidae. Walleye are an important coolwater game fish, particularly in
northern areas. Scott and Grossman (1973) describe walleye as probably the most
economically valuable species in Canada's inland waters. Yellow perch are har-
vested by anglers in some waters and serve as important prey for many valued
sport fish species, including walleye. High quality walleye fishing is frequently as-
sociated with fairly large populations of perch.
Habitat
Walleye can survive at extreme temperatures (32° to 90°F), but prefer waters with a
maximum temperature of 77°F (coolwater). They occur primarily in medium to
large lakes (greater than about 1,000 acres), are most abundant in large, shallow
lakes that are moderately turbid (Secchi depth 3 to 6 feet) but also frequently occur
in large, deep clearwater lakes with rocky bottoms.
Yellow perch can adapt to a wide range of lake habitats and occur in a greater
diversity of environments than walleye, including both small and large lakes and
warm and cool waters. They tend to be most abundant in the upper pelagic region
at a temperature of 66° to 70°F in lakes with moderate vegetation, clear water, and
bottoms of muck, sand, or gravel.
Reproduction
Both walleye and yellow perch spawn in early spring. Normally, walleye spawn-
ing begins shortly after the ice breaks up, at a water temperature of 42° to 48°F.
Spawning occurs in rocky areas in the white waters below impassible falls or dams
or along boulder to coarse gravel shoals in lakes. Eggs are dispersed in shallow
waters along the shoreline, falling into crevices in the rocky/gravel substrate.
Yellow perch spawn slightly later, when water temperatures range between
45° and 55°F. Adults migrate shoreward into the shallows of lakes and sometimes
tributary streams. Spawning usually takes place near rooted vegetation, sub-
merged brush, or fallen trees. Eggs are laid in a long, semibuoyant gelatinous
strand that adheres to submerged surfaces or the lake bottom. Neither walleye nor
yellow perch develop nests or provide any parental care of eggs or fry.
Feeding Habits
Walleye are piscivores, feeding predominantly on other fish after reaching about
three inches in length. Walleye populations can also be highly cannibalistic if other
small fish are not available. Young walleye feed on small, planktonic crustaceans
and insects. Yellow perch diets are more diverse and include benthic insect larvae,
leeches, amphipods, crayfish, and small fish. In some lakes, yellow perch mainly
prey on fish eggs of yellow perch as well as other fish species.
Management Concerns
Figure 8-9 in Chapter 8 presents a flow chart for managing walleye in Minnesota
lakes, identifying major problems as well as potential management approaches for
resolving these problems. Factors that frequently limit walleye success or produc-
tivity include the following:
• Inadequate forage. Poor growth rates and low condition factors may indi-
cate that food supplies are inadequate as a result of low prey abundance, excessive
competition from other top predators (e.g., northern pike or largemouth bass) or
236
-------
Appendix A. Background Information on Selected Fish Species
rough fish (e.g., white sucker), or excessive numbers of walleye. Possible
management methods for improving growth include reducing the abundance of
competitors, introductions or enhancement of prey (effective in some circumstan-
ces only), or reduced stocking of walleye to decrease intraspecific competition.
• Large predator population. Young walleye are highly susceptible to
predation, and almost any fish-eating fish can become a significant walleye
predator. Predation is a common cause of unsuccessful walleye stocking or
reproduction in waters with existing, abundant populations of piscivores.
Management approaches for reducing predatory losses include cessation of
predator stocking, netting programs to reduce predator abundance, and in small
lakes, chemical reclamation with rotenone. Northern pike, in particular, frequent-
ly co-occur with walleye and can be important predators as well as competitors.
• High fishing pressure. Indicators of excessive harvests of walleye include a
reduction in catch rates over time, decrease in average size, and decrease in the
number of walleye year-classes represented in the fishery. Management alterna-
tives include fishing regulations (e.g., size limits or closed seasons or areas to
protect spawning fish), increased walleye stocking, or adjustments in other fish
populations that may enhance walleye productivity (e.g., increase in abundance
of yellow perch or other forage fish). Brousseau and Armstrong (1987) discuss the
role of size limits in walleye management.
• Habitat degradation. Winterkill is a problem in some walleye lakes. In ad-
dition, walleye can be adversely affected by eutrophication or increased levels of
toxic contaminants.
• Inadequate natural reproduction. Poor reproductive success may be
countered by means of supplemental stocking, water level management to en-
sure stable or rising water levels during egg incubation, development of artificial
or enhanced spawning areas, fishing regulations to protect spawning adults, or
removal of barriers to spawning migrations into tributary streams and rivers.
Yellow perch are highly prolific, with a high reproductive potential and vora-
cious appetites. Thus, problems with yellow perch generally relate to overcrowd-
ing. High fish densities resulting in poor growth rates and stunted populations
make them of little interest to anglers. In addition, large numbers of perch can
lead to detrimental effects on other more valued fish species, such as bass or
trout, as a result of competition or perch predation on fish eggs.
References
The information above was summarized from Minnesota Department of Natural
Resources (1982), Scott and Grossman (1973), Manooch (1984), and Bennett and
McArthur (1990). Ebbers et al. (1988) compiled a bibliography of references on
walleye and sauger (Stizostedion canadense). Craig (1987) discusses the biology of
perch and related fish.
Pike, Pickerel, and Muskellunge
Members of the family Esocidae in North America include muskellunge (Esox
masquinongy), northern pike (E. Indus), chain pickerel (E. niger), redfin pickerel
(E. americanus americanus), and grass pickerel (E. americanns vermiculatus). Redfin
and grass pickerel occur primarily in slow moving streams and rivers, rather
than lakes, and are not discussed further. Muskellunge are the largest of the
esocids, growing commonly to 28 to 48 inches and 5 to 36 pounds, and provide
prized trophy fishing. Northern pike and chain pickerel are viewed as valued
game fish in some waters but rough fish in others. All esocids are highly efficient
predators that can compete with and/or prey upon other fish species in a lake or
Predation is a common
cause of unsuccessful
walleye stocking or
reproduction in waters
with existing, abundant
populations of piscivores.
[PJroblems with yellow
perch generally relate to
overcrowding.
237
-------
Fish and Fisheries Management in Lakes and Reservoirs
Esocids... are most
common and abundant in
relatively shallow, warm
bodies of water or coves in
larger lakes with extensive
growths of aquatic
vegetation.
In some lakes and regions,
pike and pickerel are
considered undesirable
fish species because of
their predation on or
competition with other,
more valued game fish —
reservoir. Muskellunge and northern pike occur only in Canada and the northern
United States. Tiger muskie, a cross between northern pike and muskellunge, are
also stocked in some areas. Chain pickerel are widely distributed throughout the
eastern edge of North America.
Habitats
Esocids tolerate a broad spectrum of water quality and habitats but are most com-
mon and abundant in relatively shallow, warm bodies of water or coves in larger
lakes with extensive growths of aquatic vegetation. For muskellunge, maximum
water temperatures of 78°F are optimal, although the species can withstand
temperatures as high as 90°F. Chain pickerel prefer waters with summer tempera-
tures of 70° to 86°F. Esocids, in general, are relatively tolerant of low levels of dis-
solved oxygen. However, because they are sight feeders, feeding efficiency as well
as fishing are adversely affected by high turbidity.
Reproduction
Spawning occurs in the early spring, immediately after ice out for northern pike
(at water temperatures of 40° to 52°F) and shortly thereafter for chain pickerel and
muskellunge (at temperatures of 47° to 52°F and 49° to 59°F, respectively). North-
ern pike and muskellunge spawn in shallow (15 to 20 inches) weedy bays, adjacent
marshes connected by small tributary streams or in heavily vegetated floodplains
of rivers; chain pickerel generally spawn in somewhat deeper water (usually 3 to
10 feet) over flooded vegetation. Eggs are scattered at random, are slightly to very
adhesive, and remain attached to the vegetation in the spawning area. No parental
protection or care is provided.
Food Habits
Pike, muskellunge, and pickerel are all highly efficient predators and strongly pis-
civorous (after reaching about 1.5 inches in length). Adult esocids will consume
most any living vertebrate within the size range that they can engulf, including
frogs, muskrats, mice, and ducklings.
Management Concerns
In some lakes and regions, pike and pickerel are considered undesirable fish
species because of their predation on or competition with other, more valued game
fish, such as trout or walleye. In such cases, populations may be reduced or
eliminated by netting and fish removal, building barriers (where feasible) to block
migrations into spawning areas, or applying fish poisons, such as rotenone, as part
of a chemical reclamation project. It may also be desirable to increase angler ex-
ploitation of pike and pickerel resources through angler education and com-
munication programs.
Common factors limiting muskellunge production and fisheries yield include
the following:
• Inadequate forage. Muskellunge growth rates are low in lakes with inade-
quate numbers of suitable-sized (including larger) prey, in particular yellow perch
and minnows. Possible management methods for improving growth include
reducing the abundance of northern pike (which compete with muskellunge) by
netting and removal or interfering with pike reproduction; when appropriate, in-
troducing new forage fish; or in infertile waters where populations are supported
or supplemented by stocking, reducing the rate or frequency of muskellunge
stocking.
238
-------
Appendix A. Background Information on Selected Fish Species
m High predator population. Northern pike is the most common and serious
predator on muskellunge. Control methods for northern pike were previously
noted.
• High fishing pressure. Waters with a relatively small number of large, old
muskellunge may suffer from overfishing. Fishing pressure can be reduced by in-
creasing the minimum size limit or closing the fishery until the population
recovers.
• Habitat degradation. Problems with periodic winterkill can be alleviated
through aeration or other techniques for increasing winter oxygen levels (see
Chapter 8) or restocking in the spring. Esocid populations can also be adversely
affected by decreased water clarity and by draining adjacent marshes and
floodplains that provide important spawning and nursery areas.
• Inadequate natural reproduction. Reproductive success can be enhanced
by removing barriers (e.g., beaver dams, log jams, or silted channels) to fish
migration into suitable spawning areas; improving the spawning habitat by
removing brush, trees, and silt to encourage growths of desirable vegetation; and
managing water levels, increasing areas of flooded vegetation during spawning,
and maintaining stable water levels through egg incubation, fry emergence, and
early feeding. Supplemental stocking may also be effective in some instances.
Similar management concerns apply to northern pike and chain pickerel,
where populations are managed as a fisheries resource. Common problems in-
clude inadequate forage, inadequate natural reproduction, and habitat degrada-
tion. Anglers often have difficulty distinguishing among muskellunge, northern
pike, and hybrids where they co-occur (Casselman et al. 1986). Thus, implement-
ing distinct fishing regulations for each species will be ineffective without an ac-
companying angler education program.
References
Information on pike, pickerel, and muskellunge was compiled from the Min-
nesota Department of Natural Resources (1982), Maine Department of Inland
Fisheries and Wildlife (1986), and Scott and Grossman (1973). Hall (1986) also dis-
cusses the management of muskellunge.
Trout and Salmon
Many members of the family Salmonidae are highly valued game and sport fish,
supporting important fisheries in coldwater lakes. Only six are reviewed briefly
here, however: brook trout (Sdvelinus fontinalis), rainbow trout (Oncorhynchus
mykiss), brown trout (Salmo trutta), cutthroat trout (O. darki), lake trout (Salvelinus
namaycush), and kokanee salmon (O. nerka).
The wide distribution of these species reflects, in part, the historical
popularity of salmonid transplants and stocking. Brook trout are native to north-
eastern North America, from Canada to the southern Appalachians in Georgia
and west to Minnesota. They have been introduced, however, into many
coldwater lakes in western regions, especially high elevation lakes in the Rocky
Mountains. Rainbow and cutthroat trout are native to western North America, al-
though rainbow trout, in particular, have been widely stocked throughout
northcentral and northeastern North America. Brown trout are native to Europe
and western Asia but were transplanted to the United States initially in 1883 and
now occur in coldwater lakes scattered throughout Canada and the northern
United States. Lake trout also occur throughout northern North America.
Kokanee, the landlocked form of the anadromous sockeye salmon, are native to
the northwest, but like most salmonids, have been introduced into a diversity of
coldwater habitats and regions.
Waters with a relatively
small number of large, old
muskellunge may suffer
from overfishing.
Many members of the
family Salmonidae are
highly valued game and
sport fish, supporting
important fisheries in
coldwater lakes.
239
-------
Fish and Fisheries Management in Lakes and Reservoirs
All salmonids require or
prefer dear, cool,
zoell-oxygenated lakes and
streams.
Mature fish may travel
many miles upstream to
reach suitable spawning
areas.
Habitat
All salmonids require or prefer clear, cool, well-oxygenated (> 5-6 mg/L dissolved
oxygen) lakes and streams. Brook and cutthroat trout occur most commonly in
small headwater lakes, often at high elevations (above 8,000 feet). Both species are
able to survive and grow in very cold lakes with short growing seasons and are
relatively intolerant of warm water, seeking out temperatures below 68°F (in the
hypolimnion) when surface waters warm up during summer. Rainbow trout are
usually found in moderately deep to deep cool lakes with adequate shallows and
vegetation to support good food production. They are most successful in habitats
with temperatures of 70°F or slightly lower available, but they grow slowly in cold
alpine lakes. The optimum temperature range for brown trout is 65° to 75°F. Brown
trout remain active and can thrive at slightly higher temperatures than brook
trout, but otherwise they have very similar habitat requirements. Kokanee salmon
and lake trout prefer even colder waters (50° to 59°F and SOT, respectively),
moving into deep hypolimnetic waters during summer stratification. Both species
occur, therefore, primarily in large, deep lakes; typical lake trout habitat consists of
a large, deep coldwater lake with irregular bottom contours and shorelines
covered with rock and gravel. In cold climates (e.g., Canadian Northwest Ter-
ritories), however, lake trout can also persist in shallow lakes.
Reproduction
For lakes to support self-sustaining salmonid populations, habitat suitable for
spawning and survival of eggs and fry must be available. Brook, rainbow, brown,
and cutthroat trout and kokanee salmon all spawn over gravel beds in small
streams. Mature fish may travel many miles upstream to reach suitable spawning
areas. Brook trout, brown trout, and kokanee salmon can also spawn on gravelly
shallows in lakes, although brook trout require groundwater upwelling and a
moderate current for successful reproduction. Lake trout spawning occurs most
often in lakes over a large boulder or rubble bottom at depths of less than 40 feet
and sometimes as shallow as 1 foot.
Brook, brown, and lake trout and kokanee salmon are fall spawners. Brook
trout eggs are deposited in late summer (August) in northern regions and as late as
December in the southern portion of the range. Brown trout spawn in late autumn
to early winter, at a temperature of 44° to 48°F; kokanee generally spawn between
September and December at 41° to 51°F. Lake trout spawn in the fall, but the exact
date varies from lake to lake and depends on latitude, weather, and the size and
topography of the lake as well as water temperature. For all four species, eggs
hatch in midwinter and swim-up fry emerge from the gravel in very early spring,
just before ice breakup.
Rainbow trout and cutthroat trout are primarily spring spawners. Cutthroat
trout spawn about three to five weeks after ice breakup at a water temperature of
about 50°F. Rainbow trout spawn between mid-April and late June in most areas
at temperatures between 50° and 60°F. Eggs incubate for four to seven weeks
before hatching, and fry emerge from the gravel after another five days to two
weeks.
All six species spawn in nests, referred to as "redds," prepared primarily by
the female. Lake trout clean the spawning area by brushing the rocks with their
body or tail or rubbing them with their snout. The fertilized eggs fall into the
crevices between the large rocks. The remaining species clear away debris and silt
from the redd by turning sideways and beating the bottom substrate using a series
of rapid fanning movements of the caudal fin. When the spawning process is com-
pleted, the female covers the redd with loose gravel using a similar motion. No
further parental care or protection is provided.
240
-------
Appendix A. Background Information on Selected Fish Species
Kokanee salmon (like most Pacific salmon) generally die a few days to
several weeks after spawning. Kokanee mature, spawn, and die at about four
years (range: two to eight years). Atlantic salmon and trout, on the other hand,
do not die after spawning and generally spawn in multiple years.
Food Habits
Brook, rainbow, brown, and cutthroat trout are carnivorous and feed on a wide
range of organisms, including aquatic and terrestrial insects, crayfish, leeches,
large zooplankton, mollusks, frogs, and small fish. In general, fish play a less im-
portant role in the diet of these species than for most other important game fish,
such as largemouth bass, walleye, and muskellunge. Brown trout and rainbow
trout tend to reach larger sizes than either brook or cutthroat trout. Fish and
crayfish figure more prominently in the diet of very large brown and rainbow
trout.
Lake trout also feed on a broad range of organisms, including freshwater
sponges, crustaceans, aquatic and terrestrial insects, many species of fish, as well
as small mammals. The food consumed depends on availability and lake trout
size. Like brown and rainbow trout, lake trout can grow to large sizes. Lake trout
commonly live to be 15 to 25 years old and can grow to be 30 to 40 inches and 10
to 25 pounds or more. The importance of fish in the lake trout diet tends to in-
crease with increasing size. In lakes without suitable forage fish, lake trout grow
slowly and do not live as long as trout feeding primarily on other fish.
Kokanee salmon feed mainly on zooplankton, although bottom organisms
can represent a significant diet component in some lakes. They are not known to
prey on other fish.
Management Concerns
In general, trout and salmon fisheries require more intensive management than
do many warmwater or coolwater fisheries. Management problems and concerns
frequently encountered include the following:
• Habitat degradation. Poor forestry or other land use practices can lead to
siltation of spawning areas. Salmonids can reproduce successfully only in clean
gravel substrate; egg and fry survival can be decreased dramatically by even
small to moderate silt loads. Land clearing can also increase water temperatures.
Eutrophication can deplete oxygen levels in the hypolimnion, eliminating
suitable habitat for trout and salmon during summer. Brook, cutthroat, and to a
lesser degree, rainbow trout also occur in habitats susceptible to winterkill (small
lakes in cold climates with long winters and heavy snow cover).
• Inadequate natural reproduction. Because of their fairly specific spawn-
ing habitat requirements, salmonid populations are generally limited by inade-
quate natural reproduction. Suitable spawning areas may be unavailable or
migrations into spawning streams may be blocked by beaver dams, log jams, or
construction of dams or roads. Lake trout can experience high egg and fry mor-
tality if spawning occurs in shallow waters and water levels drop during egg in-
cubation overwinter. Reproductive success may also be low as a result of fish
predation on salmonid eggs, fry, and juveniles. Often, populations with inade-
quate reproduction are supplemented or supported by stocking. As discussed in
Chapter 8, however, stocking should occur only if it is cost effective and if native
strains of the species are not endangered.
• Excessive predators or competitors. Young trout and salmon are highly
susceptible to predators, such as chain pickerel, northern pike, walleye, or fish-
eating waterfowl. Yellow perch may compete with juvenile salmonids and also,
In general, trout and
salmon fisheries require
more intensive
management than do
many warmwater or
coolwater fisheries.
Poor forestry or other land
use practices can lead to
siltation of spawning
areas.
[SJalmonid populations
are generally limited by
inadequate natural
reproduction.
241
-------
Fish and Fisheries Management in Lakes and Reservoirs
The alewife, gizzard shad,
and threadfin shad... can
be important forage fish
for game species.
potentially, feed on salmonid eggs. Historically, the common solution to problems
with predators or competitors was chemical reclamation, poisoning all fish in the
lake and re-stocking with only salmonids.
• Slow growth. Slow growth rates may occur naturally in highly oligotrophic
lakes. However, in some cases growth rates can be increased by eliminating or
reducing populations of competitors, reducing salmonid stocking rates, increasing
forage fish availability (for lake, rainbow, and brown trout), or eliminating stress-
ful environmental conditions (e.g., water temperatures above optimal levels
during part of the growing season). As noted in Chapter 8, forage introductions
are often unsuccessful, with negative side effects, and should be considered only
in limited circumstances. Chapter 12, however, presents a successful case study of
introducing cisco as a forage fish to increase lake trout growth rates and fishery
yields in Lake Opeongo, Ontario.
• Overfishing. Trout, in general, are highly catchable and susceptible to over-
fishing during some seasons of the year. In addition, brook and cutthroat trout, in
particular, tend to occur in small unproductive lakes that support relatively few
fish; therefore, populations can be easily depleted. Possible remedies for overfish-
ing include fishing regulations and stocking. Lake trout typically mature at 6 or 7
years old, but may mature as late as 13 years old in some lakes. Slow-growing,
late-maturing populations may require relatively long minimum size regulations
to sustain adequate numbers of sexually mature, reproducing fish.
• Loss of wild, native strains and genetic diversity. Extensive stocking of
hatchery strains of trout and salmon in previous years has resulted in the loss of
many native strains and decreased genetic diversity (see Chapter 3). In many
States, wild strains and naturally reproducing populations are legally protected.
Stocking these waters is prohibited and fishing pressure may be limited by special
regulations.
References
Information on trout and salmon management was compiled from Scott and
Grossman (1973), Carlander (1969), Minnesota Department of Natural Resources
(1982), Maine Department of Inland Fisheries and Wildlife (1986), and Nelson
(1988). Olver and Martin (1984) compiled a bibliography of publications and
reports on lake trout. Other references of potential interest include Willers (1981),
Trotter (1987), Gresswell (1988), and Mills (1989).
Threadfin Shad, Gizzard Shad, and Alewife
The alewife (Alosa pseuddharengus), gizzard shad (Dorosoma cepedianum), and
threadfin shad (D. petenense) are members of the herring family, Clupeidae. None
of these species is of any major recreational or commercial importance in fresh-
waters, although they all can be important forage fish for game species.
Habitats
The alewife is primarily an anadromous fish on the Atlantic coast of North
America from the St. Lawrence River to North Carolina, but it has also been
stocked into a number of lakes and reservoirs. The gizzard and threadfin shad
occur primarily in southern regions, the northern extent of their range being the
Great Lakes for gizzard shad and Oklahoma/Tennessee for threadfin shad.
Threadfin shad cannot tolerate temperatures below about 7°F.
242
-------
Appendix A. Background Information on Selected Fish Species
Reproduction
Landlocked alewife inhabit the open waters of lakes during most of the year but
move onto shallow beaches and into ponds to spawn in late spring and early
summer. The eggs, which are essentially nonadhesive, are broadcast at random
over sandy or gravelly bottoms.
Gizzard shad also spawn in spring to early summer (mid-March to mid-
August) generally at water temperatures of 63° to 73°F. The eggs are highly ad-
hesive. After being released near the lake surface, they sink slowly to the bottom
or are carried with the current until attaching to any object with which they come
in contact.
Threadfin shad generally spawn in the spring and early summer (April to
early July, temperatures 57° to 70°F), but some populations have two spawning
peaks in spring and fall. They spawn in schools in open water or under brush
and floating logs, where the eggs adhere through incubation and hatching.
Food Habits
All three species feed primarily on plankton, both as young and as adults. Giz-
zard and threadfin shad consume both phytoplankton and zooplankton, while
alewifes are basically zooplankton feeders.
Management Concerns
Shad and alewife are eaten by a wide range of fish predators and can provide im-
portant forage to sustain good fish growth rates and high fisheries yields. Game
fish that consume these fish when available include lake trout, rainbow trout,
northern pike, muskellunge, smallmouth and largemouth bass, and walleye. Giz-
zard shad, however, grow rapidly and are too large for most piscivorous fish by
two years of age. Thus, a substantial portion of gizzard shad production may be
unavailable for conversion into harvestable fisheries biomass.
All three species are subject to periodic die-offs, generally caused by sudden
temperature changes. Large fish die-offs can be a serious nuisance, causing heath
concerns and problems with odors and aesthetics. Each of these species is highly
prolific, can increase to nuisance densities, and is difficult to eradicate once estab-
lished. Therefore, new introductions should be attempted only after careful study
and review of the potential negative consequences (see Chapter 8).
References
This information was compiled from Scott and Grossman (1973) and Carlander
(1969).
All three species are
subject to periodic die-offs,
generally caused by
sudden temperature
changes.
243
-------
-------
APPENDIX B
Methods for Assessing
Fisheries Status
Appendix Objectives
This appendix describes specific sampling and analytical techniques that can be
applied as part of a field sampling program to collect information on the status of
a lake's fisheries and related variables. It supplements the information in Chapter
10 on the overall design of a field sampling plan. The sections that follow review
techniques for surveying anglers and fish communities, methods for measuring
fish characteristics (such as length, age, and fecundity), and methods for assess-
ing the food base, water quality, and physical habitat. Much of the material
presented is summarized from Fisheries Techniques (Nielsen and Johnson, 1983),
published by the American Fisheries Society.
This appendix provides only an introductory summary of the principles, ad-
vantages, and limitations of each sampling technique. However, many good ref-
erence materials are available on fish and fisheries sampling techniques,
including books edited or written by Nielsen and Johnson (1983), Schreck and
Moyle (1990), and Everhart and Youngs (1981) as well as sampling manuals
prepared by most State and provincial fisheries agencies (e.g., Ontario Ministry
of Natural Resources, 1989; Minnesota Department of Natural Resources, 1970,
1978,1985; Texas Parks and Wildlife Department, 1991).
As noted in Chapter 10, a field sampling program for managing fish or
fisheries in lakes and reservoirs may involve sampling in not only the lake but
also adjacent streams, other lakes in the drainage basin, and the watershed.
Watershed monitoring techniques and methods for measuring lake physical and
chemical characteristics are discussed in other supplements in this series:
Wedepohl et al. (1990), and Olem and Flock (1990). This appendix focuses, there-
fore, on sampling fisheries, fish, fish prey, and fish habitat in lakes and, to a lesser
degree, streams.
Techniques for Surveying Anglers
Creel Surveys
One common complaint from anglers is that fish catch rates or sizes have
declined in recent years or are less than expected, based on catches in other
similar waters in the area. Creel surveys are one approach for verifying or
evaluating trends in angling success.
[M]cmy good reference
materials are available on
fish and fisheries sampling
techniques
[A] field sampling
program for managing
fish or fisheries in lakes
and reservoirs may
involve sampling in not
only the lake but also
adjacent streams, other
lakes in the drainage
basin, and the watershed.
Creel surveys are one
approach for verifying or
evaluating trends in
angling success.
245
-------
Fish and Fisheries Management in Lakes and Reservoirs
Basically, creel surveys entail direct contacts with anglers by creel "clerks" on
the lake or reservoir of interest. Each angler is asked the number of anglers in the
party, the total number of hours and times fished during the visit, angling
methods (e.g., shore, boat still-fishing, trolling, casting, ice), and the total numbers
of fish caught (including those released) and harvested by species and fish size
(numbers of legal-sized versus undersized fish caught). The creel clerk may also
measure fish in the angler's creel for length and weight and collect a scale sample
for aging. Additional information on angler expenditures or other characteristics
may also be useful. A sample creel survey form is presented in Figure B-l.
SPECIES
CAUGHT
Brook
Trout
Rainbow
Trout
Brown
Trout
Large-
mouth
Bass
Small-
mouth
Bass
Bluegills
Sunfish
Yellow
Perch
Pike
Perch
(Walleye)
Northern
(Grass)
Pike
Rock
Bass
Grapples
(Speckled
Bass)
Carp
Catfish
Bullheads
LEGAL
SIZE
(NUMBER)
UMDER-
SIZE
(NUMBER)
FISH KEPT
(NUMBER)
FISH
RELEASED
(NUMBER)
FREQUENCY
OF FISHING
HOURS
FISHED
METHOD
USED
NUMBER
IN PARTY
Figure B-1.— Example form used In creel surveys.
Creel clerks should interview all anglers fishing the lake during the sampling
interval or, alternatively, should count or otherwise estimate (e.g., by counts from
aircraft) the total number of active anglers and then collect creel survey data from
a representative subset. Sampling intervals should be conducted on weekdays,
weekends, and holidays, both morning and evening. Clerks can contact all or a
defined frequency of the anglers fishing along shorelines or in boats (roving
246
-------
Appendix B. Methods for Assessing Fisheries Status
method), contact anglers as they return to boat launch areas or along access
routes (point of access method), or employ a combination of roving and point of
access methods.
Creel surveys can be designed to sample anglers at random or during regular
sampling intervals (days or parts of days) over specific period(s) of interest (a
month, season, or year). It is generally best to include three or more sampling in-
tervals in each period of interest. Larger sample sizes are needed when the period
of interest is longer. Larger sample sizes also tend to reduce error and uncertainty
associated with using samples to estimate population parameters.
Sampling intervals and survey times must be standardized. Because fishing
pressure tends to be heavier during weekends than weekdays, the sampling ef-
fort can be stratified (split) to provide comparable information for weekday and
weekend anglers. Sampling could also be stratified among morning, mid-day,
and evening hours to provide a better estimate of total angling effort and success.
Based on the creel data collected for anglers interviewed during each sam-
pling interval, estimates of the total angling effort can be derived for the period
of interest, total numbers of fish caught and harvested by species or angling
method, and numbers of fish caught per hour fished or other unit of effort. Fish
population status can also be inferred from information on relative catch rates
(catch per unit effort) as well as fish size and age distributions.
Further details on the design and implementation of creel surveys and the
analysis of creel survey results can be found in Malvestuto (1983), Van Den Avyle
(1986), and Guthrie et al. (1991).
Angler Diaries
Information on fishing success also can be obtained by asking individual anglers
who frequent the lake or reservoir to maintain a diary or written log of fishing ef-
fort and fish caught. Generally, the cooperating anglers are volunteers. Angler
diaries, therefore, can be an inexpensive way to collect data on fisheries and the
fish community. Drawbacks, however, include (a) less control over the quality
and completeness of data recorded and (b) lack of data or estimates for all anglers
and inability, therefore, to quantify total angling effort and harvest. Anglers' fish-
ing effort and skills vary greatly, and these factors are difficult to account for
when analyzing and interpretating angler diaries. Furthermore, success rates
may improve over time as the angler learns more about where, when, and how to
fish in a given lake. Nevertheless, because of the ease of data collection, angler
diaries should be seriously considered as at least a supplemental data collection
technique.
Typically, anglers are given individual copy(ies) of the diary (often a pocket-
sized booklet) to be used for the survey. Anglers can be instructed to maintain
separate diaries for different fish species or groups of fish. Figure B-2 shows
sample record pages from an angler diary for largemouth bass. All information
requested about each fishing trip is entered by the angler keeping the diary.
The opening pages of an angler's diary should include a place for the
angler's name and address, an address and person to whom the completed diary
should be returned, the starting and ending dates for diary entries, a contact (and
telephone number) for additional information, and a brief introduction on how
the information will be used. Instructions for making diary entries must also be
provided. The following should be noted:
• The diary should be taken on all fishing trips so information can be
recorded accurately as it is obtained.
• Information for each fishing trip should be recorded on a separate
page whether or not fish are caught.
Information on fishing
success also can be
obtained by asking
individual anglers who
frequent the lake or
reservoir to maintain a
diary or written log of
fishing effort and fish
caught.
247
-------
Fish and Fisheries Management in Lakes and Reservoirs
Name:
Address:
. Weather:
.Time:
Date:
Record Individual Lengths
LENGTH
(INCHES)
HARVESTED
FIN CLIP
CODE
TAG
NUMBER
CATCH/RELEASE ONLY
LENGTH
(INCHES)
FIN CLIP
CODE
TAG
NUMBER
I
Remarks:
Figure B-2.—Example form used in angler diaries (adapted from the Illinois Department of
Conservation).
Information for each fish caught should be recorded as required on the
form. When information on fish length is requested, the diary should in-
clude a diagram illustrating the specific points on a fish that define the
desired length measurement: Diaries can also include drawings or
photographs of important fish species to help anglers identify species
accurately.
248
-------
Appendix B. Methods for Assessing Fisheries Status
tc
I 0.1
u
t-
<
o
o.o
eo
2 40
20
20 i
o
M
ff
10
78
80
82
84
YEAR
Figure B-3.—Changes in catch rate (20-cm and longer fish per angler hour), proportional
stock density (PSD), and relative stock density (RSD) for smallmouth bass caught by
tournament anglers at Wilson Reservoir, Kansas, 1978-84. Smallmouth bass were stock-
ed Into Wilson Reservoir from 1978 to 1981 (source: Willis and Hartmann, 1986).
• Any markings (e.g., clipped fins, tags) on the fish should be recorded.
The types and locations of management markings used in the lake
should be explained and illustrated. If requested, fish tags may be
returned with the diary.
• The importance of maintaining accurate and complete records should
be emphasized.
Organized tournaments on a lake or reservoir provide a special opportunity
to compile a large database on angler catch rates and success. While tournament
anglers, on average, have higher success rates than do nontournament anglers,
the biases in catch rates and length distributions are consistent. Therefore, long-
term trends in fishery characteristics can be assessed (see Figure B-3). By involv-
ing local fishing clubs and tournaments, the numbers of cooperating anglers can
be increased substantially. Angler diaries, in general, provide data for more fish
and anglers at lower cost than can be obtained using creel surveys. Sztramko et
al. (1991) present an example application of angler diaries to monitor fisheries
trends and use in Lake Erie from 1984 to 1989.
Questionnaires to Obtain Angler Use or Opinion Data
Questionnaires are particularly useful for obtaining general information on lake
use patterns, angler expectations and preferences, and fishing success because
data can be compiled from a large number of lake users at relatively low cost.
These surveys do not, however, provide reliable, quantitative information on
specific fishery characteristics, such as catch rates or fish sizes.
Methods for questionnaires include volunteer response surveys (e.g, box-on-
post surveys), personal contact interviews, telephone interviews, and mail sur-
veys. To acquire accurate information requires considerable planning and a
Organized tournaments
on a lake or reservoir
provide a special
opportunity to compile a
large database on angler
catch rates and success.
Questionnaires are
particularly useful for
obtaining general
information on lake use
patterns, angler
expectations and
preferences, and fishing
success....
249
-------
Fish and Fisheries Management in Lakes and Reservoirs
Tb acquire accurate
information requires
considerable planning and
a comprehensive survey
design.
comprehensive survey design. Babbie (1973) provides a good general introduction
to survey methods. Dillman (1978) presents "The Total Design Method" for mail
and telephone surveys, which is followed by many of the most successful surveys
now conducted. Important considerations from these texts are highlighted in the
paragraphs that follow.
When designing a questionnaire survey, the first step is to carefully define the
information needed, the populations) from whom this information is needed, and
any subpopulations (subsets) of interest. Then develop the questions, the ques-
tionnaire, introductory materials for the survey, and the sampling design. Ques-
tionnaires must be succinct, the layout should be eye-appealing, and the format
and questions should be simple and clear. A short explanation should be provided
on why the information is needed, how to complete the questionnaire, and where
to submit the completed form and request additional information. For mail sur-
veys, special consideration must also be given to writing and designing the cover
letter(s), supplemental materials to accompany each package, and any pre-
notification or post-mailing follow-up to the survey mailings.
The least demanding approach to collecting survey information is a volunteer
response survey. Boxes containing copies of questionnaires can be placed at access
locations (e.g., boat launches, picnic areas, or trail heads) with a sign requesting
users to complete the form and noting briefly why the information is needed. User
response rates can sometimes be increased by providing a space on the question-
naire form for respondents to (a) contribute any additional information and/or (b)
enter his or her name and address to request copies of summary information or
reports resulting from the survey.
Personal or telephone interviews allow more rigorous control on the quality of
data collected and can provide a more accurate and statistically defensible data set.
Personal interviews can be conducted door-to-door with lakeshore residents or
anglers entering or leaving fishing access trails or boat sites. Phone interviews can
be used to contact somewhat larger numbers of respondents more economically. In
either case, to obtain high quality information, procedures for introducing the sur-
vey, interview techniques, and questionnaire forms must be standardized. The most
successful phone surveys are those that can be completed in 10 minutes or less.
While telephone interviews can be used to survey more dispersed groups or
large populations of interest, mail surveys are more commonly used for this pur-
pose. For example, estimates of the total fishing pressure or of angler attitudes
within a region or across a State are generally obtained through mail surveys.
For surveys of large populations of interest, whether by telephone or mail,
contacting all members of the group is often impossible . Statistical procedures are
then applied to select one or more representative samples or subsets of the group
to be surveyed. A sample for a fishing pressure mail survey, for example, could be
drawn from the fishing license receipts issued within the area where the informa-
tion is desired.
Intuitively, one might assume that the larger the population of interest, the
larger the sample size needed to accurately estimate population characteristics.
This is not always the case, however, especially for very large populations.
Generally, a sample size of 400 randomly selected persons is sufficient to estimate
population parameters with reasonable accuracy and precision no matter how
large the population. Where separate estimates are required for two or more
similar groups (such as anglers in the northern and southern halves of a State), a
sample of up to 400 people must be surveyed from each subpopulation. For
smaller populations, sample sizes can be smaller. In general, less than 10 percent of
any population must be randomly sampled to obtain accurate population es-
timates. Most introductory statistical texts present procedures for determining ap-
propriate sample sizes and for selecting random samples (e.g., Cochran, 1977;
Snedecor and Cochran, 1980).
250
-------
Appendix B. Methods for Assessing Fisheries Status
To obtain data from 400 respondents, more than 400 questionnaires must be
distributed. Questionnaire response rates will determine the number of question-
naires that are needed. If, for example, the expected response rate is 65 percent, at
least 923 (400/0.65) questionnaires must be mailed to ensure that 400 completed
questionnaires are returned.
Response rates can vary from 10 percent to 90 percent. However, using
Dillman's (1978) procedures for the Total Design Method, response rates are com-
monly greater that 65 percent and frequently greater than 85 percent. In addition
to paying careful attention to the survey and mail-out package design, Dillman's
approach includes substantial follow-up efforts to increase response rates. One
week after the surveys are mailed, a postcard reminder/thank-you is sent to the
entire survey sample. Three weeks later, a letter of encouragement/thank-you is
sent to all non-respondents, and a final letter and replacement questionnaire is
sent to all non-respondents seven weeks after the first mailing. Thus, to be suc-
cessful and provide accurate results, mail surveys require a substantial commit-
ment of money and personnel. Meiers et al. (1992) present an example
application of this method to estimate fishing pressure in Wyoming waters.
Techniques for Surveying Fish Populations
and the Fish Community
Firsthand information on the status of the fish community is often required to
evaluate fisheries problems and the effectiveness of management programs.
Direct sampling can be used to determine, for example, fish growth rates, the fre-
quency of reproductive failures, fish feeding habits, and fish mortality rates. A
variety of methods are available to directly sample fish populations. These can be
loosely classified into passive capture methods, active capture methods, fish
toxicants, and observational methods. This section briefly describes some of
these methods and the factors important in selecting the most appropriate gear
or method for sampling a specific fish population or community. Further details
on fish sampling techniques can be found in Nielsen and Johnson (1983) as well
as most introductory fisheries texts (e.g., Lagler, 1956; Everhart and Youngs,
1981).
Passive Capture Methods
Passive capture techniques include both entanglement (gill and trammel nets)
and entrapment methods (hoop nets, fyke nets, trap nets, pound nets, minnow
traps, and weirs) (Hubert, 1983). All of these sampling methods use equipment
with relatively simple designs and construction that requires little training to use.
Each technique, when deployed correctly, can capture large numbers of fish and
provide reasonably precise data on relative fish abundances.
Passive capture methods are not without limitations, however. Most are size-
and species-selective; that is> they catch some sizes and types of fish more effec-
tively than others. Catches are also biased toward fish with greater daily move-
ments, and numbers of fish caught depend on the duration of the set (length of
time the net is left in the lake), times of day they are fished, season, water
temperature, light, turbidity, and sometimes unpredictable changes in fish be-
havior. To help reduce the influence of some of these factors, the fishing effort
should be standardized, especially if results will be compared among different
periods. In general, passive capture techniques tend to be most efficient when the
nets are set overnight and emptied each day.
Entanglement methods
• Gill nets, the most common fishing gear that depends on fish entanglement,
'' are generally fished as a single layer web wall (Fig. B-4). Often, experimental gill
Direct sampling can be
used to determine, for
example, fish growth
rates, the frequency of
reproductive failures, fish
feeding habits, and fish
mortality rates.
251
-------
Fish and Fisheries Management in Lakes and Reservoirs
Gill nets have one major
disadvantage. Unkss
tended at frequent
intervals, they generally
result in the death of all or
most of the fish caught.
Trammel nets are best for
fish that have external
spines or rough surfaces
An important advantage
of entrapment sampling
techniques is that most of
the fish caught are not
harmed.
nets are made up of multiple panels, with each panel comprised of ,a different size
of mesh. Plastic or wooden floats are used to support the net on the top, with lead
weights attached on the bottom to maintain the net in a vertical orientation. Gill
nets are relatively light and easy to transport and deploy.
Commonly, gill nets are set to be stationary on the bottom, but they also can be
floated on or near the surface or hung vertically through the water column with
anchor ropes extending to the bottom or the shore. Depending on how they are
deployed, gill nets can sample littoral or pelagic areas at a variety of depths. Nets
are generally set while traveling or drifting downwind to keep them from tan-
gling. In turn, net retrieval is usually done while traveling into the wind and fish
are removed as the nets are pulled out of the water. Gill nets are commonly fished
in lakes and reservoirs with minimal currents and bottoms free of snags.
Mesh sizes should be appropriate for the size of fish sought. Too large a mesh
opening allows small fish to swim through, while small mesh sizes do not capture
large fish effectively. Gill nets capture fish whose girth is about 1.25 times the size
of the mesh perimeter most efficiently. Experimental gill nets (with multiple
panels of varying mesh size) are useful for collecting a wide variety of species and
fish size classes. Independent of the mesh sizes used, however, gill nets are less ef-
ficient at collecting small fish, which do not have the power to swim far enough
into the mesh to become entangled.
Gill nets have one major disadvantage. Unless tended at frequent intervals,
they generally result in the death of all or most of the fish caught. Frequent tend-
ing (e-S-/ every one to two hours) to release fish caught in the net can reduce but
not eliminate fish mortality. Thus, these nets must be used with caution in most
lakes and may not be suitable in some. Shorter set durations, careful removal of
the entangled fish, and cooler water temperatures can all help reduce mortality
rates.
• Trammel nets are made from three panels of nets: two larger mesh nets on the
outside and a single, finer-mesh, looser-hanging net on the inside. While this type
of net can be fished in many of the same ways as gill nets, a particularly effective
approach is to surround concentrations of fish, such as can occur in weed beds,
and then scare the fish into the nets. Fish swimming into the net pass through the
first outer netting and then push the inner netting through the second outer net-
ting, trapping themselves in pouches of the protruding inner netting (Fig. B-4).
Trammel nets are best for fish that have external spines or rough surfaces, such
as catfish, sturgeon, yellow perch, and largemouth and smallmouth bass. Trammel
nets have two advantages over gill nets: they tend to leave the fish in better shape
following removal from the net, and they are less size-selective. Otherwise, tram-
mel nets have many of the same uses and biases as gill nets.
Entrapment methods
A variety of common entrapment methods are available for sampling, including
hoop nets, fyke nets, trap nets, and minnow traps (Hubert, 1983). An important
advantage of entrapment sampling techniques is that most of the fish caught are
not harmed.
• Hoop nets consist of circular hoops ranging from 0.5 to over 3 meters (11/2 to
10 feet) in diameter that are connected by netting to form a long cylinder (Fig. B-5).
The netting rnesh size is small enough to prevent all but the smallest fish from
passing through (10- to 100-mm mesh; 1/3- to 4-inch). Additional netting in the
mouth of these nets forms a funnel-like throat opening into the first hoop. The fish
enters the net at the larger end of this funnel opening, while the small diameter of
the funnel inside the net prevents captured fish from escaping. Often, the interior
of the net includes one or more additional funnel throats that can help concentrate
captured fish in the closed "cod end" or "pot" of the net (see Fig. B-5). When the
252
-------
Appendix B. Methods for Assessing Fisheries Status
Gill Net Trammel Net
Figure B-4.—Examples of entanglement nets — gill and trammel (source: Hubert, 1983).
first one to three circular hoops at the mouth end are replaced with rectangular
frames, the net is called a frame net. Frame nets are less inclined to roll on sloping
bottoms or in currents than hoop nets.
While hoop nets are commonly used in rivers and can be fished in fairly
strong currents without damage, they can also be fished along lakeshores. They
may be especially effective near weed beds to capture the fish attracted to this
cover. When setting hoop nets, the cod ends are often anchored to posts driven
into the lake bottom. Generally, the nets are baited with cheese or pressed
soybean cakes and fished overnight or for 24 hours. When retrieving the nets, the
cod ends are retrieved first, the drawstrings closing the net are untied, and the
fish are removed and sorted.
Hoop nets share the common biases of the other passive sampling methods
discussed previously. As with other entrapment methods, some fish species are
better able to escape from the net than others and capture efficiency can depend
largely on net size.
• Fyke nets are essentially hoop nets (or frame nets) with a "leader" and/or
"wing" net(s) attached to the hoop at the mouth. The leader net extends perpen-
dicularly from the mouth generally toward the shore, while the two wing nets ex- •
tend out from the mouth at 45° angles (Fig. B-5). Because of their design, fyke
nets are most commonly fished in lakes and reservoirs near weedy cover to cap-
ture highly mobile, cover-seeking fish species, including sunfish, crappie, bass,
and pike. They can also be used to successfully capture trout and salmon species
in more open areas of lakes and reservoirs during the spawning season. As fish
travel along the shore in search of prey or spawning sites, the leader net deflects
their path of travel outward and the wing nets help funnel the fish into the
mouth of the net for capture.
• Trap nets are very similar to fyke nets in design and use. Both net designs in-
clude a leader and/or wing nets (Fig. B-5). The principal difference is that, in-
stead of using hoops to maintain the inner circular integrity of the net from the
mouth to the cod end, the rectangular interior of a trap net is maintained by
means of spreader rods, floats, and anchors. As a result, trap nets are less bulky
[FJyke nets are most
commonly fished in lakes
and reservoirs near weedy
cover to capture highly
mobile, cover-seeking fish
species....
253
-------
Fish and Fisheries Management in Lakes and Reservoirs
HOOPNET
SMALL TRAP NET
leader
Outside Heart
Inside Heart
FYKE NET
Figure B-5.—Examples of entrapment nets — hoop, trap, and fyke (source: Hubert, 1983).
and easier to transport than other styles of entrapment nets. Thus, trap nets may
be.especially appropriate in waters with more difficult access (for example, remote
lakes with no road access).
• Minnow traps are one example of "pot gear," which also includes lobster, eel,
and slat traps used to capture a variety of small fish and shellfish (Fig. B-6). Like
hoop nets, which they resemble in general appearance, pot gear is generally baited
with dried bread crumbs, cheese, or pressed soybean meal. Wire or plastic min-
now traps can be very useful for assessing the presence of small fish in lakes, reser-
254
-------
Appendix B. Methods for Assessing Fisheries Status
American Lobster Pot
Slat Trap
L_ ,
\
'•"•"r1'^-—-'
ff^'-.- ~ -~ ~
"**iC^.-_-.
V ^M\';H
Bait
Figure B-6.—Examples of pot gears — American lobster pot, minnow trap, slat trap, eel
pot, and crab pot (source: Hubert, 1983).
voirs, and quiet areas of streams. Fish captured in these traps can provide valu-
able information on the age structure and condition of small-sized fish species as
well as supplemental information on the reproductive success of populations of
larger species. The capture efficiency of most pot gears is highly variable. As a
result, these gear types are relatively poor indicators of fish abundance or fishing
catch rates.
Because most of the fish captured can be returned to the water alive, entrap-
ment methods may serve as the primary sampling gear (rather than gill or tram-
mel nets) in waterbodies where it is important to minimize fish mortality—for
example, in very small lakes or lakes with small numbers of fish or threatened or
endangered fish species.
255
-------
Fish and Fisheries Management in Lakes and Reservoirs
Angling is the simplest, at
times the most effective,
and potentially the most
fun collection technique
Active Capture Techniques
Active capture methods include angling, various kinds of seines and trawls that
sieve fish from the water, and electrofishing techniques (Hayes, 1983).
• Angling is the simplest, at times the most effective, and potentially the most
fun collection technique, but it is often overlooked as an appropriate approach for
collecting technical information on fish community status. Angling can be one of
the best methods for collecting some fish species and sizes (e.g., adult bass and cat-
fish) that are less vulnerable to many of the other sampling techniques. To provide
comparable information among samplers and sampling periods, the angling tech-
niques employed (i.e., gears, effort, times) must be standardized. In the absence of
sufficient anglers for a creel survey, standardized angling can also be used to
generate data on the recreational fishing potential.
• Beach or haul seines are one of the most commonly used active capture
techniques in lakes and reservoirs. Seines are constructed of mesh panels and
some include a bag in the middle portion, which can increase catch rates in long
seines and facilitate fish removal (Fig. B-7). Generally, floats support the top of the
seine at the water surface, while lead weights help hold the seine on the lake bot-
tom. Sticks or poles attached at each end of the seine are used to haul the net
through the water. Beach or haul seines may range from a few feet to 90 feet (or
more) long.
Seines are generally fished by one or more persons holding each end of the
seine and wading through the water. Often one end of the seine is held stationary
on or near the shore while the other end is swept out from and then back to the
Haul Seine with Taper
and Graduated Mesh
Detail of Mesh
Figure B-7.—Two examples of seines (source: Hayes, 1983).
256
-------
Appendix B. Methods for Assessing Fisheries Status
shore in a wide closing arc. Sometimes, the shore end of the seine is moved paral-
lel to the shore to increase the area of the arc sieved. In deeper waters, a small
boat may be used to help drag the outer end of the seine, after anchoring the
other end on shore. The boat end of the seine must be attached to a paddle or
stick to keep it submerged. In all cases, the depth of the water should be less than
the height of the seine. In addition, the area seined should have a relatively
smooth bottom, free of any extensive weed cover, so that the lead line glides
smoothly over the bottom without riding up on obstructions that would permit
fish to escape beneath the seine.
Beach seines are most effective for capturing near-shore spawners and small,
slow moving or schooling fish that live in shallow waters in both lakes and
streams. Field experience indicates that long (90-foot) seines cause less distur-
bance and provide better estimates of the numbers and types of fish within the
sampled area than do shorter seines. Small mesh sizes (i.e., 6.4-mm or 1/4-inch
mesh) allow capture of small fish, which may provide an indication of fish
reproductive success or the available forage base. The number of fish caught rela-
tive to the area of the lake bottom included within the arc circumscribed by the
i seine haul provides a quantitative estimate of fish abundance in the littoral
habitat or stream.
• Trawls are bag nets that are generally towed behind one or two boats to sieve
fish from the bottom, midwater, or surface layers of the water column (Fig. B-8).
Catches from trawls can be quantified based on the volume or surface area of
water sieved during the time of the haul. Large trawls for capturing adult fish are
used primarily in marine environments or larger lakes, reservoirs, or slow-
moving rivers. One of the most common applications of trawls for freshwater
fisheries assessments, however, is to sample larval and juvenile fish in the pelagic
region with a small-mesh trawl to estimate year-class strength and young-of-the-
year survival.
Floats.
Headrope
Intermediate
Belly (bottom panel)
Codend
Lazy Line
Bobbin or Rollers Footrope
Figure B-8.—Example of trawl net (source: Hayes, 1983).
• Electrofishing involves the use of electricity to immobilize fish, which are
then captured by dip nets. Subsequently, fish are usually returned to the water
unharmed. Electricity can also be used to guide or block fish movements or to
anesthetize or quickly kill fish for eradication or human consumption. Three
types of electrofishing units are commonly used to capture fish: (1) boat-mounted
units that are usually generator powered, (2) backpack-mounted units powered
by a generator onshore, and (3) backpack-mounted units powered by either 12V
batteries or small generators mounted on the backpack frame. Reynolds (1983)
and Cowx and Lamarque (1990) provide detailed discussions on the use of
electricity for fish sampling. Information from these documents is summarized in
the next paragraphs.
Beach seines are most
effective for capturing
near-shore spawners and
small, slow moving or
schooling fish that live in
shallow waters in both
lakes and streams.
Electrofishing involves the
use of electricity to
immobilize fish, which are
then captured by dip nets.
257
-------
Fish and Fisheries Management in Lakes and Reservoirs
The art of effective
electrofishing is selecting
the best current type
(usually pulsed DC) that
will capture the greatest
number offish with the
least injury or mortality,
given the specific
environmental conditions
in the field.
Working with electricity
near water can be
hazardous. However, with
appropriate precautions,
electrofishing can be
conducted safely.
Fish react to electric fields in several ways, depending on the type of current
and voltage gradient they encounter. Current densities are highest near the
electrode and decrease rapidly with increasing distance away from the electrode.
The higher the current density, the higher the voltage gradient and the greater the
effect. High current densities kill fish, moderate densities stun them, and low den-
sities produce a "fright" reaction, allowing the fish to escape.
Current types include unmodified direct current (DC), unmodified alternating
current (AC), and a number of modifications of DC and AC, including pulsed DC
(with different pulse shapes, durations, and frequency), quarter-wave rectified
AC, fully rectified AC. Each current type produces a somewhat different fish
response. Fish exposed to DC in the "stun" field are attracted to the anode (posi-
tive electrode); fish swim toward the anode, where they roll over and are easily
captured. In an alternating current (AC) field, by contrast, fish tend to orient per-
pendicularly to the electric field, show no directed movement toward the anode,
and tetanus (state of muscle rigidity) occurs at a greater distance from the
electrode than with DC. Unmodified AC also causes the greatest damage to fish
and can result in hemorrhaged tissue, ruptured swim bladders, and fractured ver-
tebrae. Fish responses to pulsed DC and modified AC are generally intermediate
between those for unmodified DC and AC. The art of effective electrofishing is
selecting the best current type (usually pulsed DC) that will capture the greatest
number of fish with the least injury or mortality, given the specific environmental
conditions in the field.
Water conductivity (i.e., its ability to conduct an electric current) can have a
substantial effect on electrofishing efficiency. At high conductivities (> 500
umhos/cm) water is less resistant than fish and electric currents tend to flow
around rather than through the fish, producing little to no electroshock. For this
reason, electrofishing is not widely used in brackish or salt waters. In waters with
very low conductivity (< 100 nmhos/cm), the electric field is limited to the imme-
diate area of the electrodes. Higher voltage gradients can be produced by increas-
ing the circuit voltage or, within limits, the electrode size. Increasing the voltage,
however, requires a larger generator, which may be expensive and unwieldy. In
small streams, salt blocks added upstream can be used to increase water conduc-
tivity but may be illegal in some areas.
Electrofishing efficiency is also affected by other environmental conditions as
well as operating conditions and the target fish species. Because of the physical
limitations of the electrical field, electrofishing is effective only in relatively shal-
low water (less than about 10 to 12 feet). At night, large predatory fish can often be
found inshore feeding. Fish are attracted by the lights used during sampling and
seem less apt to avoid capture. Thus, night electrofishing generally catches more
fish, more species, and larger fish than electrofishing during the day. High tur-
bidity and dense macrophyte beds can make it more difficult to see and collect fish
that have been stunned. High water transparency, on the other hand, can shift fish
distributions into deeper waters, where they are less susceptible to capture. At a
given voltage gradient, larger fish receive a greater electroshock than smaller fish.'
Large fish are also more visible and maybe inadvertently selected during fish col-
lections. Finally, fish species that inhabit littoral areas in lakes are more vulnerable
to capture than are pelagic or benthic species.
Working with electricity near water can be hazardous. However, with ap-.
propriate precautions, electrofishing can be conducted safely. Goodchild (1990,
1991) and Reynolds (1983) discuss guidelines for equipment construction, main-
tenance, and safe operations. In addition, many States and provinces conduct
training and certification courses to ensure that electrofishing is used safely and
reliably.
258
-------
Appendix B. Methods for Assessing Fisheries Status
Fish Toxicants
The use of rotenone and other fish poisons to remove populations of undesirable
fish species was discussed in Chapter 8. The same principles and methods can be
applied to fish sampling. Small areas of a lake, reservoir, or stream (e.g., coves or
stream reaches) are blocked off with nets and treated with rotenone. Fish killed
by the rotenone treatment are then collected over the next several days using
hand-held or boat-mounted scoop nets. It is essential, especially in standing
waters, that rotenone be applied over the entire sample area. Generally, the
rotenone is applied as an emulsifiable liquid. A weighted hose can be used to en-
sure complete mixing throughout the water column. Potassium permanganate or
another detoxifying agent (e.g., chlorinated lime) can be applied outside the
boundary of the blocking nets to reverse the action of the rotenone.
The toxicity of rotenone varies with fish species and size, water temperature,
pH, and concentrations of dissolved oxygen and suspended matter. At water
temperatures of 50 to 75°F, 1.0 to 2.0 mg/L (ppm) of rotenone are usually applied
to assure a complete kill of all fish species. Treatments in streams tend toward the
lower limit of this range, while the upper limits are more common in larger,
warmer, turbid lakes and reservoirs. These concentrations are also lethal to
zooplankton and many other aquatic invertebrates.
Toxicants are particularly efficient for obtaining a nearly complete sample of
the fish within a particular area for detailed information on population biomass
and age structure. Potential problems can arise, however, where high densities of
macrophytes occur. Such growths can trap affected fish and prevent their
retrieval. Recovery percentages of marked fish introduced before treatment or
underwater SCUBA surveys can be used to evaluate collection efficiencies and
develop correction factors to account for the proportion of fish not retrieved.
Davies and Shelton (1983) provide additional details on fish sampling with
rotenone and other toxicants; Booth and Holtz (1988) review the available
literature on rotenone effects.
Note: Since both rotenone and potassium permanganate are hazardous sub-
stances, their use requires care in handling to avoid contact with the skin and
especially with the eyes, nose, and throat. All individuals applying pesticides, in-
cluding rotenone, must be certified.
Observational Techniques
Two common observational techniques can be used to aid in detecting fish and
quantifying fish abundance in lakes: hydroacoustics (sonar) and visual under-
water surveys conducted by swimmers using snorkeling or SCUBA.
• Hydroacoustical methods have advanced greatly in the past decade. "Fish
finders" are now commonly used by anglers. More sophisticated devices that can
accurately estimate fish density and biomass and monitor fish behavior have
been successfully applied in both small and large lakes (Thorne, 1983; Brandt and
Unger, 1986). Two advantages of hydroacoustics are (1) the measurements are not
affected by most environmental conditions and (2) data on fish communities can
be collected without disrupting fish behavior or requiring their removal. Disad-
vantages include poor discrimination among fish species, poor ability to detect
fish on or very near either the lake bottom or surface, and the lack of fish samples
for determining length, weight, and age distributions. In addition, sophisticated
hydroacoustic equipment can be expensive and requires specialized training and
expertise. Once the equipment is purchased and training completed, however,
the costs of data collection per sampling trip are relatively low compared to
many other fish sampling techniques. Sonar may be especially useful for evaluat-
ing capture efficiencies associated with other gear; for example, by estimating
fish abundance just before trawl passage.
Toxicants are particularly
efficient for obtaining a
nearly complete sample of
the fish within a
particular area for detailed
information on population
biomass and age structure.
Two advantages of
hydroacoustics are (1) the
measurements are not
affected by most
environmental conditions
and (2) data on fish
communities can be
collected without
disrupting fish behavior or
requiring their removal.
259
-------
Fish and Fisheries Management In Lakes and Reservoirs
When there are particular
concerns about
populations of genetically
unique fish species within
a lake or reservoir, the
nondisruptive and
nondestructive aspects of
these observational
techniques are
particularly important
attributes.
Fish marks can be
biological, chemical, or
physical.
Fin clipping and external
body tags are the most
common methods for
markingfish.
• Underwater survey is the second common observational technique of fish in
lakes or streams using snorkel- or SCUBA-equipped divers (Helfman, 1983).
Snorkeling has the advantages of requiring less equipment, limited training, and
consequentially, lower costs. SCUBA, on the other hand, allows for longer con-
tinuous underwater sessions. The efficiency of both methods can be limited by
poor visibility. Diving at night, in areas with strong currents, or under ice is poten-
tially dangerous and should be avoided.
The numbers, species, length, behavior, and locations of fish observed can be
used to estimate fish species composition, approximate size distributions, and
relative abundance as well as fish distribution and behavior patterns. Actual
population estimates can be made using transect methods, where divers count fish
while swimming or being pulled behind a boat, or grid count techniques, where
divers swim to set locations or for set distances before stopping to count fish. Data
can be recorded underwater on special underwater paper and scrolls, erasable
slates, or writing cuffs made from roughened plastic pipes.
When there are particular concerns about populations of genetically unique
fish species (e.g., fish species listed as threatened or endangered) within a lake or
reservoir, the nondisruptive and nondestructive aspects of these observational
techniques are particularly important attributes. Other fish observation methods
include underwater cameras and glass- or plexiglass-bottom boats and lookboxes.
Marking Fish for Identification
Fish tags and other marks are used to uniquely identify individual fish or groups
of fish. Data on marked fish collected using one or more of the above sampling
techniques can then be used to
• study the movement and locations of individual fish in their natural
environment over extended periods,
• identify individual stocks of fish of special interest,
• assess the success of fish stocking programs,
• estimate fish population abundance, mortality, or angler harvests, and
• validate fish age and growth assessments.
Wydoski and Emery (1983) provide a comprehensive review of the methods, uses,
and advantages and limitations of alternative techniques for marking fish.
Fish marks can be biological, chemical, or physical. Biological marks have
natural origins, including marks caused by parasites, morphological differences,
and genetic differences among individual fish or groups of fish. Chemical marks
can be applied by immersion, injection, tattooing, or feeding fish foods containing
dyes. Physical marks include various fin clips, internal and external tags, cold
branding, and spray (dye) marking. Table B-l presents general criteria for selecting
appropriate fish marks.
Fin clipping and external body tags are the most common methods for mark-
ing fish. Fin dipping can be used to identify specific fish stocks or groups of fish.
However, the number of marking combinations is limited by the number of fins.
Thus, fin clips are inappropriate for tracking individual fish. Partial fin clips or
punches may be used when fish need only be recognized over a short time, as with
mark-recapture studies conducted over a few days (discussed further ,later in this
chapter). Otherwise, the entire fin is removed by clipping close to the body. Even
these fins can regenerate, however, although the regenerated fins are often
deformed (Fig. B-9). Permanent records should be maintained of all fin clip com-
binations used in a given water.
Some special studies may require tagging of individual fish. Many kinds of ex-
ternal and internal body tags are available from a variety of sources (Fig. B-10,
260
-------
Appendix B. Methods for Assessing Fisheries Status
^
f
£?
«
1
^5
(0
1
"§,
E
£
I
t£>
V
O
4>
CT
'E
i
O)
IS
S
ra
O)
_c
8
"3
(0
o
«
£
~
Table B-1.— General c
lYSICAL
£
i
i
u
1
z
g
3
i
111
£
<9
1
1
a
§
2
i
2
U)
i
jj
<3"
u <
§~ oc
c
it
CHARACTERISTICS
xxxx
xxxx
XXX
xxxx
X X
X X
Duration of Mark
Days
Weeks
Months
Years
X
X
X
X
X
X
Individuality of Mark
Very Low
Low
High
X X X X X
xxxx
X X X X X
X X X X X
X X
X X X X X
Size of Organism at
Marking
Very Large
Large
Medium
Small
Very Small
xxxx
xxxx
xxxx
xxxx
XXX
X
Numbers to be Marked
Low (<59)
Medium (>50-<200)
High (>200-<1, 000)
Very High (>1, 000)
x«x
X
"x
*x
X
"x
Recovery Method
Visual
Nonvisual
X
X
X
1
X
X
-x
,jif
JC
CO
tf=
•5
E
i s
i g>
t3 ffl •£
¥| i
Q Q § .
11 s
'i"l 1
0) E o
|f|
2 2 -S
||l
|||
C m c
"May be necessary to use a
"Personnel must have speci
"Ultraviolet light (black light)
261
-------
Fish and Fisheries Management in Lakes and Reservoirs
Radio and sonar tags are
used to monitor remotely
the location, behavior,
and/or physiology of
individual fish in their
natural environment.
Figure B-9.—Appearance of generated fins — (A) fins clipped close to body usually have
little generation; (B) fins clipped away from body often regenerate with deformed rays; (C)
fins clipped further from the body often regenerate to normal size with Irregularities where
clip occurred; (D) fins with multiple clips often will show multiple irregularities (source:
Wydoskl and Emery, 1983).
ibcutaneous
Bachtlor Button
Strip (Opercle)
Figure B-10.—Example of the various tags and body locations on or in fish used for mark-
Ing fish (source: Wydoski and Emery, 1983).
Table B-2). Individually coded tags can be used to identify individual fish and
most tags are highly visible. However, fish tags cost substantially more than fin
clips and may work lose and be lost over time. Before purchasing physical body
tags, the manufacturer or distributor should be requested to supply information,
on the long-term persistence of their tags on or in fish. Tag loss rates reported
range from a low of 13 percent over 12 months (Keefer, 1988) to a high of 79 to 90
percent over 9 months (Prichard et al. 1974; reviewed by Evans, 1989) and vary
with tag design, quality control during manufacture, quality of attachment, and
other factors. Fish handling and tagging, if not conducted with care, can also cause
substantial fish mortality after release.
Radio and sonar tags are used to monitor remotely the location, behavior,
and/or physiology of individual fish in their natural environment. Generally,
radio tags work better than sonar tags for tracking fish in waters that are shallow,
thermally stratified, low conductivity, or turbulent, and where large areas need to
be searched to track highly mobile species. Tags can be attached externally, surgi-
262
-------
Appendix B, Methods for Assessing Fisheries Status
Table B-2.—Manufacturers and distributors of fish marking materials, equipment,
and related supplies (modified from Wydoski and Emery, 1983).
Carolina Biological Supply Company
2700 York Road
Burlington, NC 27215
919-584-0381
FAX 919-584-3399
Biological stains and chemicals
Fisher Scientific Company
1600W. Glenlake Avenue
Itasca, IL60143
708-773-3050
FAX 708-773-5916
Biological stains and dyes
Floy Tag & Manufacturing, Inc.
4616 Union Bay Place, NE
Seattle, WA 98105
206-524-2700
FAX 206-524-8260
Dart tags, spaghetti tags (tying or locking), anchor
tags, stream tags, Petersen tags, applicators
National Band and Tag Co.
721 York Street
P.O. Box 430
Newport, KY41072
606-261-2035
FAX 606-261-8247
Monel strap tags, magnetic internal tags, vinyl
subcutaneous tags
Northwest Marine Technology
Shaw Island, WA 98286
206-468-2340
FAX 206-468-3844
Coded wire tags and related equipment
Philips Process Co., Inc.
20 Magnolia Street
Rochester, NY 14608
716-436-2310
No FAX
Industrial inks for all purposes
Pilgrim Plastic Products Co.
278 Babcock Street
Boston, MA 02215
617-782-9300
FAX 617-782-4740
Internal tags, messages printed on
white plastic for capsule tags
• Salt Lake Stamp Co.
380 West Second South, Box 2399
Salt Lake City, UT 84101
801-364-3200 or 800-677-6809
FAX 801-364-6809
Circular strap tags
Scientific Marking Materials
Box 24122
Seattle, WA 98121
206-524-2695
No FAX
Fluorescent pigments and equipment to
apply to fish
Sigma Chemical Company
P.O. Box 14508
St. Louis, MO 63178
314-771-5765
FAX 800-325-5052
Biological stains and dyes
Wildlife Supply Company
301 Cass Street
Saginaw, Ml 48602
517-799-8100
FAX 517-799-8115
Aquatic sampling equipment
cally implanted, or inserted into the fish's stomach. After a suitable period of
recovery and tag testing, the fish is released into the environment. Information is
then relayed from the tag through ultrasonic or radio signals to a remote receiv-
ing system. Tags may be set to unique signal frequencies to identify individual
fish. Sensor tags are also available commercially that monitor temperature or
water depth, although sensor tags and the associated recording equipment are
expensive. Winter (1983) reviews telemetry systems, equipment needs, methods
for tag attachment, fish tracking, and data collection and analysis.
Fish Measurements
Fish collected using the sampling techniques described previously can be
measured for length and weight; aged; examined to determine their sex, sexual
maturity, and fecundity; and used to estimate the density and biomass of the fish
population in the lake, reservoir, or stream. Methods for each of these tasks are
described in the following subsections, compiled from information presented in
Living Lakes, Inc. (1989), Lagler (1956), Everhart and Youngs (1981), Anderson
and Gutreuter (1983), and Jearld (1983).
263
-------
Fish and Fisheries Management in Lakes and Reservoirs
Generally, all fish caught
in the field should be
counted, by species. Data
on fish length, weight, and
age can be collected for all
fish caught or for a
representative subset of
the total samples.
Assessing Fish Size, Age, Growth, and Condition
Processing fish in the field
Generally, all fish caught in the field should be counted/by species. Data on fish
length, weight, and age can be collected for all fish caught or for a representative
subset of the total samples.
Total length is the distance from the anterior-most part of the fish to the end
of the longest caudal fin ray when the fin is compressed for maximum extension
(Fig. B-ll). Length measurements should be to the nearest millimeter or 1/8 inch.
Length measurements should be obtained for all target game fish caught or a
large (> 100) representative sample of the fish caught for length-frequency
analyses.
Individual fish should be weighed on the most sensitive scale available. When
a large number of fish are captured at a single location, only a subsample (30 to 100
fish per species) must be weighed individually. The fish weighed should be
selected to cover the full range of fish length. As a general rule of thumb, up to five
fish should be measured in each one-inch length class. This results in ap-
proximately 30 individual fish weights for small species, such as bluegill, and
about 100 for large species (with more length classes), such as largemouth bass.
The remaining fish may be weighed as a group, sorted by species.
To assess the general health of the collected fish, examine each fish for signs of
physical deformity, wounds, injuries, and external parasites. The presence of
marks (e.g., fin clips or tags) should also be noted. Additionally if appropriate, fish
Scale Sample Area
Lateral Line \
Standard Length
Fork Length
Total Length
Scale Sample Area
Figure B-11.—Locations included In various length measurements used for fish and loca-
tions used for sampling scales described in text (source: Lagler, 1956). Top: spiny-rayed
fish (perch, sunfish, bass); bottom: soft-rayed fish (trout, salmon, pike).
264
-------
Appendix 8. Methods for Assessing Fisheries Status
sex and sexual maturity can be determined by examining adult fish during the
spawning period (discussed in the next subsection). All information should be
recorded on field sheets.
If fish are to be aged, calcified structures for age estimation should also be
collected from a representative sample of fish. As for fish weights, preferably
about five fish per one-inch length class should be aged, for a total of 30 to 100
fish per species. Lagler (1956), Bagenal and Tesch (1978), Jearld (1983), and Cas-
selman (1987) provide detailed discussions of methods for determining fish age.
Fish scales are the most commonly used, structure for fish aging. For soft-
rayed fish species (e.g., trout, salmon, and pike), scale samples should be col-
lected from the left side below the forward-most portion of the dorsal fin and
above the lateral line (Fig. B-ll). For spiny-rayed fish (e.g., perch, sunfish, and
bass), scales should be obtained from the left side of the fish in the region below
the lateral line and behind the pectoral fin, with the pectoral fin pressed against
the body. Areas of obvious scale regeneration should be avoided. If necessary, the
scale sample can be collected from the right side of the fish; it may be necessary
to skip scale sampling if excess scarring is present on both sides.
Remove dirt and mucus in the area where the scales are to be sampled by
gently scraping in the direction of the tail with a knife. The scales can then be
removed by placing the blade of the knife on the scales in the cleaned area and
carefully moving the blade with downward pressure toward the tail of the fish.
When several scales are obtained, they should be placed within a small folded
piece of paper and the paper inserted into a labeled scale envelope. The scale
removal instrument should be cleaned after each sample is taken. Scale en-
velopes should be labeled with the name of the waterbody, location, date, collec-
tion method, fish species, number, length, weight, and collector information.
These samples and accompanying field sheets are then returned to the laboratory
for analysis.
All other calcified structures used for age determination require that the fish
be sacrificed. Often, however, these structures provide more reliable age es-
timates than scales for certain species, age classes, or environmental conditions.
Otoliths (earstones) can be used to determine fish age in days for juvenile fish or
improved age estimates for adult fish from waters where the annual marks on
fish scales are poorly defined. Otoliths are removed by cutting open the top of the
fish skull, from slightly behind the eyes back to the upper edge of the gill cover.
The head is then opened by pressing down quickly on the nose, and the large sac-
culus Otoliths should be visible behind the brain. After removal, Otoliths can be
stored dry in an envelope or in alcohol or glycerin. Storing otoliths in a medium
of 2:3 glycerine to alcohol helps to dear thicker otoliths and facilitate fish aging at
a later date.
For catfish (Ictaluridae), spines from the left pectoral fin should be obtained
by grasping the spine with a forceps or pliers, and pulling and twisting the spine
outward to remove it at the point it enters the body (articulation). The spine
should then be placed in a labeled scale envelope. Similarly for suckers (Catos-
tomidae), fin rays may be better for age determinations than scales. Fin rays can
be severed at or below their articulation using cartilage scissors or cutting pliers.
Finally, the cleithrum bone is frequently used for more accurate aging of esocids
(pike, pickerel, and muskellunge).
Laboratory procedures for aging fish
using anatomical structures
After being removed from the scale envelopes, scales are soaked in water to
separate them and remove debris. A small, fine-bristle brush or ultrasonic cleaner
can facilitate this process. Six to eight scales are mounted on a single cellulose
acetate slide and rolled through a scale press. These acetate impressions are then
If fish are to be aged,
calcified structures for age
estimation should also be
collected from a
representative sample of
fish.
Fish scales are the most
commonly used structure
for fish aging.
265
-------
Fish and Fisheries Management in Lakes and Reservoirs
[I]t is also assumed that
the distance between each
scale annuli is
proportionally equal to the
increase in the fish's total
length for that year.
examined to estimate the fish's age. A diamond pencil or other suitable implement
should be used to etch a code to identify the scale mounts from each individual
fish into the upper right-hand corner of each acetate slide.
With trout and small fish, acetate impressions can be difficult to interpret. In
these cases, scales should be mounted between two glass slides. The slides are
taped at each end and labeled in the same manner used to identify the acetate im-
pressions. All mounts and acetate impressions should be stored in their respective
envelopes with their original scales.
Pectoral spines, fin rays, and cleithra should be sectioned perpendicular to the
longitudinal axis just above the basal recess or groove for spines and fin rays. It
may be necessary to dry some spines and rays in an oven before sectioning. Sec-
tions 0.4-0.6 mm thick generally are cut using a fine (70 teeth per inch) jewelers'
saw. Cut sections can then be polished, if necessary, with an extra fine (#180 or
finer) grit silicone carbide paper. A clear mounting cement can be used to mount
sections onto glass or plastic slides. Typically, two or three sections from a single
fish should be mounted onto a single slide, with each slide labeled as noted above.
Otoliths may be examined directly in glycerin or alcohol; larger otoliths may
require thin sectioning using a jeweler's saw.
After the scales, otoliths, spines, fin rays, or cleithra from a sampling trip have
been processed, the samples should be sorted by species and size. Examinations to
estimate fish ages should proceed one species at a time, beginning with the smal-
lest (i.e., youngest) fish. Since members of a species from the same lake should ex-
hibit similar growth patterns, working from the smallest to the largest can help to
avoid overlooking annuli and reduce errors in fish aging.
The impressions or mounts of the scales or other structure are examined using
a microprojector or microscope. These structures each show growth patterns
similar to tree growth rings. During cold weather, growth slows and the ringed
patterns grow close together, at times appearing as a single dark ring. Generally,
the interval between dark rings represents the growth between one winter and the
next (Fig. B-12). However, factors other than winter can cause growth to slow and
dark "false annuli" to form. These factors can include unseasonably cold weather,
chemical stress, disease; or spawning, factors not uncommonly encountered in
natural populations. Therefore, when estimating fish ages, it is critical to watch for
such problems and to obtain expert assistance. Lagler (1956), Bagenel and Tesch
(1978), Jearld (1983), Casselman (1987), or other fisheries management texts should
be consulted for more information on fish aging.
Back calculation of length at age
While a variety of formulae and techniques are available for assessing fish growth,
only one approach—using a modified direct-proportionality formula—is dis-
cussed here. It is assumed that there is a direct linear relationship between the total
length of a fish and its total scale, otolith, spine, or fin ray radius. Furthermore, it is
also assumed that the distance between each scale annuli is proportionally equal
to the increase in the fish's total length for that year. Using these relationships, a
graph of body length against scale radius can be produced for each group of fish
(Fig. B-13). Male and female fish often have distinctly different growth rates and
thus require separate scale-body length relationships.
Frequently, rather than a strict 1:1 relationship between scale radius and fish
length that passes through the origin (as in line A in Fig. B-13), body growth begins
before scale formation, as in line C, or the relationship between scale and body
length may best match line B. If the y-axis is crossed at some positive or negative
length, then a correction factor is needed, requiring use of a modified direct-
proportionality formula:
U-C+ -
266
-------
Appendix B. Methods for Assessing Fisheries Status
B
Figure B-12. — Typical enlarged appearances of structures used to age fish: (A) trout
scale showing three annuli; (B) sunflsh scale showing one annul); (C) madtom catfish
vertebra showing two annuli; (D) yellow perch opercle showing five annual marks
(source: Lagler, 1956).
where:
L'
S'
S
L
C
length of fish when annulus "n" was formed,
radius of annulus "n" (at length L),
total scale radius,
length of fish at time scale sample was obtained, and
intercept of the line on the y-axis.
Standard intercept values are available in the literature for many species
(Carlander, 1982) and may be preferable to use when sample sizes are small
rather than calculating the y-intercept by regression analysis. Digitized pads and
computer programs are also available that can facilitate fish scale measurements
and back-calculation of fish lengths (Frie, 1982).
Length-frequency analysis
Length-frequency analyses often can aid in the assessment of fish ages, as
long as each age group has a unimodal size distribution and there is little
overlap in fish lengths among age classes. Plots are prepared showing the
numbers of fish caught in each length interval (see Fig. 3-9, Chapter 3).
Various graphical and computer-assisted statistical methods can be applied to
compile individual lengths for a large number of fish from a population. Ac-
curate estimates of fish age based on length measurements are generally pos-
267
-------
Fish and Fisheries Management in Lakes and Reservoirs
Fish length and weight
measurements can be used
as the basis for a number
of indices of fish
well-being....
Rarely for late
management programs is
the need for information
on fish sex sufficient to
justify destroying large
numbers offish.
0
Ox
10 20
Scale length
30
Figure B-13.—Example relationships showing relation of body length and scale radius
(source: Everhart and Youngs, 1981). Explanation of lines A, B, and C appears in text.
sible, however, only for younger age classes or for fish species with relatively
short life spans (less than five years). In addition as noted above, male and female
fish often have distinctly different growth rates and may require separate length-
frequency analyses.
Condition factors and relative weight
Fish length and weight measurements can be used as the basis for a number of in-
dices of fish well-being, including Fulton's condition factor (C or K), the relative
condition factor (Kn), and relative weight (Wr). Calculation methods for each of
these indices are presented in Chapter 3.
Sex, Maturation Rate, and Fecundity
The eggs of most fish species are fertilized outside of the body, and because of this,
most fish do not have specialized external reproductive structures. Without such
morphological characteristics, it is impossible to distinguish between males and
females during most of the year without dissecting the fish and examining the
reproductive organs. Rarely for lake management programs is the need for infor-
mation on fish sex sufficient to justify destroying large numbers of fish.
F9r a period before, during, and following spawning, however, some species
develop sexually dimorphic characteristics. For example, some male trout and sal-
mon develop hooked jaws and humped backs. Tubercles form on the heads of the
males of some suckers, chubs, and minnows. Some fins of certain fish species elon-
gate, and in a number of species, males and occasionally females become more
colorful. Female fish may also have visibly distended body cavities when they are
filled with eggs. General references on fish taxonomy (Eddy, 1957) and regional
guides to fishes (Baxter and Simon, 1970; Phillips et al. 1982) provide descriptions
268
-------
Appendix B. Methods for Assessing Fisheries Status
of these species-specific morphological differences between the sexes during
spawning times. In addition in some species, males and females can be distin-
guished during spawning by applying gentle front-to-rear pressure on the ab-
domen to extrude gametes (eggs or sperm).
Lake problems that result in poor reproductive success may cause missing
year classes and fish population declines, as discussed in Chapter 3. The popula-
tion sampling and assessment procedures discussed in earlier sections of this
chapter can reveal missing age classes. In particular, the absence of small, young
fish in samples collected using beach seines or minnow traps can provide an
early warning of year-class failures. Such observations may trigger the need for
more comprehensive evaluations of specific reproductive functions, such' as
sexual maturation and fecundity (number of eggs per female).
Sexually mature fish can be identified using the sexual characteristics
described above or by dissecting the fish and examining the condition of the
reproductive organs. In combination with age estimates, the average age at
which fish reach sexual maturity can be determined. The gonadosomatic index
(GSI) — the weight of the gonads expressed as a percentage of body weight—
may also be monitored as an indicator of gonad development and maturity.
Fecundity is determined by counting, weighing, or measuring the volume of
eggs per fish in a representative sample of females from the lake. Larger fish
generally have more eggs. Thus, analyses of fish fecundity must account for dif-
ferences related to fish size. Synder (1983) provides additional information on
methods for studying fish fecundity.
If the ages at which fish sexually mature or levels of fish fecundity are sig-
nificantly higher or lower than expected based on data from similar lakes in the
region, then further study of fish population dynamics in the lake may be war-
ranted.
Estimating Fish Population Size
Commonly used approaches for estimating fish density or biomass in a lake or
stream include catch per unit effort, mark-recapture, and depletion methods. Es-
timates of absolute fish abundance can require considerable technical expertise
and resources, especially in large lakes and reservoirs. As a result, absolute
population estimates may be practical only in streams and small-to-moderate
sized lakes. Furthermore, for many management purposes, information on rela-
tive fish abundance is sufficient and more cost effective. ,
Catch per unit effort (CPUE) is the most commonly used index of relative
abundance. The basic assumption is that CPUE is related directly to population
size:
where:
C = qfP
or
C/f = qP
C =
f =
C/f=
q
p
the numbers (or biomass) of fish caught,
the fishing effort applied, for example, the number of hours fished,
the catch per unit of sampling effort (CPUE),
the catchability coefficient, which is species- and gear-specific, and
the population density or biomass.
For CPUE to be proportionally related to population abundance, the
catchability coefficient must be constant, at least for a given fish species, gear
type, and sampling protocol. Because of uncontrolled variations in catchability,
CPUE is only an approximate index of relative fish abundance. Despite this,
trends in angling success (e.g., the catch rates in Figure B-3) or catches obtained
from routine sampling programs may provide important information at relative-
ly low cost on the year-to-year status of a fishery and fish population.
Lake problems that result
in poor reproductive
success may cause missing
year classes and fish
population declines
Estimates of absolute fish
abundance can require
considerable technical
expertise and resources,
especially in large lakes
and reservoirs [F]or
many management
purposes, information on
relative fish abundance is
sufficient and more cost
effective.
269
-------
Fish and Fisheries Management in Lakes and Reservoirs
If absolute estimates of
fish abundance are
required, one of the
simplest approaches is the
Petersen mark-recapture
method.
If absolute estimates of fish abundance are required, one of the simplest ap-
proaches is the Petersen mark-recapture method. In the Petersen method, a sample
of fish is collected, marked, and released. Then, at a later time (commonly, later in
the same day or the next day), a second sample is collected that includes both
marked and unmarked fish. It is assumed that the proportion of fish that are
marked in the recapture sample is the same as the proportion marked in the total
population. Therefore, since the number of marked fish is known, the total
population size can be estimated as follows:
, N = MC/R
where: N = the estimate of the population size,
M = the total number of marked fish,
C = the number of fish in the second sample, and
R = the number of marked fish in the second sample.
The validity of the Petersen method depends on the following assumptions:
• marked fish have the same mortality and behavior as unmarked fish,
• marks are not lost,
• marked fish are caught at the same rate as unmarked fish,
• marked fish are randomly distributed, and
• the population size is constant over the sampling period.
Many refinements and improvements on the basic Petersen mark-recapture
technique have been developed (e.g., adjustments for tag loss rates, when known)
and are described in Ricker (1975), Everhart and Youngs (1981), and other fisheries
texts. Mark-recapture studies can also be used to estimate fish mortality and ex-
ploitation rates (e.g., Robson, 1963; Seber, 1972; Ricker, 1975).
For depletion methods of population estimation, the population is sampled
repeatedly. The fish caught are removed, at least temporarily, from the population.
As developed originally (Leslie and Davis, 1939; DeLury, 1947), CPUE is plotted
against the cumulative catch. The number of fish in the original population is es-
timated by extrapolating this regression line to the point at which it would inter-
sect with the x-axis (cumulative catch) (Fig. B-14). Presumably, when CPUE equals
0, all fish would have been captured and the cumulative catch would equal the
original population size. To work, the sampling effort must be sufficiently intense
to measurably reduce the population size, an impossible task in most large lakes
and reservoirs but possible in some smaller lakes and also streams. The relation-
ship between CPUE and cumulative catch is assumed to be linear; that is, it is as-
sumed that fish catchability remains constant. Additional assumptions include:
• the population is totally available to the sampling effort,
• no natural mortality or recruitment occurs during the sampling period,
and
• the method is constant in its effectiveness.
More sophisticated adaptations of the Leslie and DeLury method have also
been developed. The Zippen maximum likelihood model (Zippen, 1958) is one of
the most satisfactory and easy-to-use estimation techniques when the proportion
of the population taken in consecutive catches remains constant throughout the
sampling. When this is not the case, the more robust maximum weighted
likelihood model developed by Carle and Strub (1978) produces more statistically
.reliable estimates. Further information on depletion methods can be found in
Ricker (1975) and Cowx (1983).
270
-------
Appendix B. Methods for Assessing Fisheries Status
Initial Abundance
Figure B-14.—Example regression line calculated for the relationship between catch per
unit effort (C/f) and cumulative catch (sum C); the x-axis intercept gives an estimate of
the initial fish abundance (source: Lackey and Hubert, 1978).
Computerized programs are available for a number of population estimation
routines, both depletion and mark-recapture, and for estimating fish mortality
rates from mark-recapture data (e.g., Brownie et al. 1985; Saila et al. 1988).
Fish Genetics
For some management objectives, it is necessary to distinguish genetically diver-
gent populations, strains, or stocks within the same species (see Chapters 3 and
5). Historically, fisheries biologists relied on morphological and meristic differen-
ces; that is, variations in body shape, the number or geometric relation of body
parts, or other visible external characteristics. Such an approach, however, has
poor discriminatory power at the subspecies level, is subject to environmental in-
fluences, and does not directly assess the degree of genetic divergence between
individuals or groups of fish.
A second approach, which is now fairly widely employed, relies on
electrophoresis, a process in which the genetically controlled structure of proteins
is displayed. Fish tissues, frequently from the liver or muscle, are homogenized;
an electric field is then applied during electrophoresis to separate the proteins in
the tissue based primarily on their charge. Differences in protein patterns provide
the basis for distinguishing among fish stocks. Methods for electrophoresis are
described in Utter et al. (1974), Harris and Hopkinson (1976), and Aebersold et al.
(1987); example applications include Clayton et al. (1974), Philipp et al. (1983),
Leary et al. (1987), Ihssen et al. (1988), and White and Shaklee (1991).
In recent years, techniques have been developed that examine the structure
of DNA directly. Analyses of differences in DNA among fish stocks are highly
sensitive. While protein separation techniques are limited in terms of the number
of genetically distinct stocks that can be detected, the number of DNA-level
markers is almost infinite. Disadvantages of DNA analyses, however, are the ex-
pense and high level of technical expertise required. Hallerman and Beckmann
(1988) review the advantages and disadvantages and different methods for ex-
amining DNA variations. Billington and Hebert (1991) review the results of
studies of mitochondrial DNA for over 40 fish species. Ryman and Utter (1987)
provide an overview of fisheries management and population genetics, includ-
ing methods for studying fish genetics.
For some management
objectives, it is necessary
to distinguish genetically
divergent populations,
strains, or stocks within
the same species.
271
-------
Fish and Fisheries Management in Lakes and Reservoirs
Evaluating the quantity
and quality of food
available for target fish
species is an important
aspect of assessing
fisheries status and
potential fisheries
problems.
Any differences in prey
digestibility or
recognizability must be
accounted for in
interpreting the results
from fish stomach analyses.
Assessing the Food Base
Evaluating the quantity and quality of food available for target fish species is an
important aspect of assessing fisheries status and potential fisheries problems.
Quantitative information is needed on both the composition of the fish's diet (food
consumed) and the availability of alternative prey items in the fish's environment.
Very brief discussions are presented for both activities. Additional information oh
techniques for evaluating fish diets can be found in Bowen (1983). Prey organisms
may include algae, zooplankton, littoral and benthic macroinvertebrates, and fish.
Methods for sampling fish populations, including forage fish species, were
described earlier in this chapter. Detailed sampling methods for other aquatic or-
ganisms are presented by Standard Methods (1989), American Society for Testing
and Materials (1991), Lind (1985), and Wetzel and Likens (1979).
Quantitative Description of Diet
To quantitatively describe the diet of a fish population requires
• collecting a representative sample of fish,
• removing, fixing, and preserving the gut contents,
• identifying the food items in the gut, and
• quantifying the absolute or relative amount of each food type in the
diet (Bowen, 1983).
Techniques for collecting representative samples of fish were described else-
where in this chapter. Sampling should consider the daily and seasonal variations
in fish feeding and the effects of fish size, territoriality, and differential digestion
rates on the types of food organisms consumed and identifiable in the gut,
Gut contents can be removed from live fish using stomach pumps or, if the fish
is sacrificed, by dissection. Ten percent formalin is generally used to fix the
sample. After removal of the formalin by washing, the samples can be preserved
in 70 percent ethanol.
Because of digestion, many of the items in the fish's stomach may be difficult
or impossible to identify. Furthermore, some types of prey, such as those with
hard-to-digest body parts (e.g., shells or spines), may be more readily identifiable
than others. Any differences in prey digestibility or recognizability must be ac-
counted for in interpreting the results from fish stomach analyses. Prey should be
identified to the lowest taxonomic unit practical, although generally identifica-
tions to order or family are adequate.
The results from stomach analyses may be expressed in terms of the frequency
of occurrence of different food items, percent composition by number, and/or per-
cent composition by weight or volume. Frequency of occurrence is the fastest ap-
proach to quantitatively describe the diet. A list is made of all likely food types and
the presence or absence of each food type in each specimen is recorded. The fre-
quency of occurrence is the proportion of the fish examined that contained one or
more representatives of a given food type. The percent composition by number is
the number of items of a given food type divided by the total number of food
items counted in a given stomach, multiplied by 100. Percent composition by
weight or volume is the weight or volume of items of each food type expressed as
a percentage of the total weight or volume of ingested food for an individual fish.
Diet Indices
The electivity index developed by Ivlev (1961) is used to compare the composition
of food items observed in the fish's stomach to the relative abundance of prey
available in the fish's environment. The index value indicates the extent to which
the observed diet differs from a diet selected at random. A number of indices have
272
-------
Appendix B. Methods for Assessing Fisheries Status
also been proposed that quantify diet overlap between fish species (Schoener,
1970; Wallace, 1981; Bowen, 1983; Crowder, 1990), although opinions vary
regarding which, if any, index is most biologically relevant and statistically reli-
able. Other types of diet indices are described by Bowen (1983) and Crowder
(1990).
Phytoplankton
Phytoplankton (free-floating, microscopic algae) are eaten by the early life stages
of many fish species and by adults of a few species. Phytoplankton composition
and abundance are also useful indicators of specific water quality conditions.
Because phytoplankton distributions can be patchy, several water samples
should be collected at discrete depth intervals in the epilimnion and then com-
posited or an integrated water sample drawn from throughout the epilimnetic
water column. Samples can be collected with a pump or sampling bottle similar
to that illustrated in Figure B-15. Samples should be collected at several times
during the growing season because plankton communities change seasonally
and often rapidly.
Typically, 250 to 1,000 mL of water are preserved per sample. By examining
samples under the microscope and weighing a filtered subsample, data can be
generated on the total phytoplankton biomass per unit volume of water, the
numerical density (number of organisms per unit volume) of each
phytoplankton taxon identified, relative abundance by numbers or biomass of
each taxon, and the presence and abundance of indicator species.
Chlorophyll« is the pigment that gives primary producers their green color.
Chlorophyll concentrations in water, therefore, provide an indirect measure of
phytoplankton abundance. Water for chlorophyll analysis can be subsampled
Figure B-15.—Two common water sample bottles — horizontal plexiglass Van Dorn (top)
and a brass Kemmerer (bottom) (source: Wildlife Supply Co.).
Phytoplankton
composition and
abundance are also useful
indicators of specific water
quality conditions.
Chlorophyll
concentrations in water,
therefore, provide an
indirect measure of
phytoplankton abundance.
273
-------
Fish and Fisheries Management in Lakes and Reservoirs
Ztiolarikton provide a
critical food resource for
most young fish and are
important prey for the
adults of many fish species.
Populations ofbenthic and
littoral
macroinvertebrates,
particularly aquatic
insects and crustaceans,
are important food sources
for fish and widely
recognized as useful
indicators in aquatic
monitoring programs.
from the samples described above for phytoplankton community analysis. Each
chlorophyll sample must be filtered through a separate glass fiber filter. The filters
are then placed on ice or frozen in the dark immediately following filtration to
minimize sample degradation. Typically, the samples are extracted in the
laboratory using 90 percent acetone. Frequently, to aid in extraction, the filter con-
taining the sample is ground using a tissue grinder to disrupt the algal cells on the
filter. After clarification, the samples are analyzed using a spectrophotometer or
fluorometer.
Methods for assessing algal biomass and phytoplankton community composi-
tion are discussed further in Olem and Flock (1990), Standard Methods (1989), and
Wetzel and Likens (1979).
Zooplankton
Zooplankton are microscopic animals that live suspended in the water column.
They provide a critical food resource for most young fish and are important prey
for the adults of many fish species. Zooplankton communities, like
phytoplankton, can change rapidly and must be sampled multiple times during
the year.
One simple method to collect zooplankton is to tow a Wisconsin plankton net
(Fig. B-16) though a known volume of water. This volume can be measured using
a flowmeter set into the mouth of the towed net or estimated using the measured
diameter of the net mouth times the measured or estimated distance that the net is
towed vertically through the water column or horizontally behind a boat. After the
net is retrieved, the sides should be washed from the outside, using lake water, to
concentrate the plankton into the removable collection bucket at the bottom of the
net. This concentrate is then rinsed from the collection bucket into an appropriate
sized (often 125 mL) sample bottle, where preservatives are added (see Wetzel and
Likens, 1979; Standard Methods, 1989).
Individual zooplankton can be identified and measured in the laboratory
under a microscope. As for phytoplankton, the results from these analyses can be
expressed as
• the total zooplankton biomass per unit volume of water,
• the numerical density of each zooplankton taxon identified,
• relative abundance of each taxon by numbers or biomass, and
• the presence and abundance of specific indicator species.
Benthie and Littoral Macroinvertebrates
Populations ofbenthic and littoral macroinvertebrates, particularly aquatic insects
and crustaceans, are important food sources for fish and widely recognized as use-
ful indicators in aquatic monitoring programs. In lakes, the benthic macroinver-
tebrate community is generally sampled using the dredges shown in Figure B-17.
Samples are brought to the surface and either preserved in their entirety in
polyethylene bags or other suitable containers or washed using a fine sieve (e.g.,
with 500-um screening) and then preserved in a suitable container. Samples are
analyzed to determine the total benthic invertebrate biomass, the biomass and/or
numerical density (numbers per substrate area) of each taxon identified, relative
abundances for each taxon by numbers or biomass, and/or the abundance of in-
dicator species and taxa.
Littoral invertebrate communities in lakes can be sampled with D-frame dip
nets, sweeping the lake bottom, water column and water surface, and macrophyte
beds in as many different habitats as possible (e.g., shallow weedy coves, tributary
274
-------
Appendix B. Methods for Assessing Fisheries Status
Wisconsin Plankton
Bucket
Wisconsin Net with new SS
Bucket and Adaptor, assembled
Figure B-16.—Wisconsin-style plankton net, which can be used as a horizontal, vertical,
or diagonal tow net or as a filter net through which water is poured (source: Wildlife
Supply Co.).
Ponar grab
Figure B-17.—Three common styles of dredges used to collect bottom sediment and
benthic invertebrates (source: Standard Methods, 1989).
275
-------
Fish and Fisheries Management in Lakes and Reservoirs
mouths). Sampling times (total minutes spent searching and sweeping) per lake or
unit lake area should be standardized. Clams, snails, and leeches can be preserved
in 10 percent formalin; insects, crayfish, and sponges should be preserved in 70
percent ethyl alcohol. Hard-bodied forms can be dropped directly into the pre-
servative. If time permits, soft-bodied insects, such as mayflies, should be dropped
live into hot (not boiling) water for 30 seconds and then transferred into the pre-
servative. The numbers of organisms collected per unit sampling effort provide a
qualitative index of relative macroinvertebrate abundance by taxon.
In streams, benthic macroinvertebrates can be sampled qualitatively, using
kick samples, or quantitatively with a Surber sampler, to collect organisms from a
standard known area of the stream bottom. The open frame of the Surber sampler
is placed on a suitable area of stream substrate with the mouth of the net facing
upstream. Substrate within the frame is then thoroughly disturbed, rocks are
removed from the bottom, and the associated animals and debris are carefully
washed into the mouth of the net. The collected sample may be sorted to separate
macroinvertebrates from the debris, either in the field or laboratory. Most samples
can be preserved in 10 percent formalin, although samples with large amounts of
organic debris require 15 to 20 percent formalin. Alternatively, samples can be
preserved in the field with 80 percent ethanol but must be sorted within two days
or drained and fresh 80 percent ethanol added to the sample within 24 hours of
collection.
As for lake benthic invertebrates, results from Surber samplers can be used to
estimate the total benthic invertebrate biomass, the biomass and/or numerical
density (numbers per substrate area) of each taxon identified, relative abundances
for each taxon by numbers or biomass, and/or the abundance of indicator species
and taxa. Standard protocols and indices have also been developed for stream in-
vertebrates that form the basis for EPA and State biocriteria. Rapid bioassessment
protocols for use in streams and rivers are described in Plafkin et al. (1989), and
Barbour et al. (1992) provide a review of EPA's benthic metrics based on these
rapid bioassessment protocols.
Assessing Wafer Quality
Methods for assessing water quality are discussed in detail in The Lake and Reser-
voir Restoration Guidance Manual (Olem and Flock, 1990) and the technical supple-
ment on Monitoring Lake and Reservoir Restoration (Wedepohl et al. 1990). Only
methods for those variables that may directly impact fish are briefly reviewed
here: toxic chemicals, dissolved oxygen, temperature, pH, salinity (total dissolved
solids), and suspended solids.
Toxic Chemicals
Problems caused by toxic chemicals can be identified by several means:
• Routine monitoring of toxic chemicals in water, fish, and/or sediments
may indicate concentrations elevated above background levels.
• The presence of a source of toxic chemicals in the watershed (e.g., pes-
ticide spraying) may alert lake managers and users to a potential prob-
lem.
• An impairment of lake uses may occur (e.g., decline in fishing success or
increase in the incidence of tumors on fish) that may be related to toxic
chemicals.
* Routine biological monitoring may identify a pattern or trend (e.g.,
reduced fish abundance) potentially attributable to toxic chemicals.
276
-------
Appendix B. Methods for Assessing Fisheries Status
Because a large number and diversity of toxic chemicals may adversely affect fish
communities and fisheries, comprehensive chemical-specific monitoring can be
expensive.
Once a potential problem is identified, the identity and source of the chemi-
cal or chemicals causing the problem must be determined, and the linkage be-
tween the chemical source and problem must be established. Three approaches
are available for identifying causes and sources of toxic effects in lake ecosys-
tems: chemistry-based, biology-based, and toxicity-based approaches. The
chemistry-based approach relies on analytical chemistry to detect specific toxic
chemicals; the biological approach relies on measurements of population or com-
munity level parameters and effects; and the toxicity approach relies on in situ
and laboratory toxicity tests. Details of these approaches will be presented in the
EPA Clean Lakes Program technical supplement, Toxic Substances in Lakes and
Reservoirs, in preparation. Often, toxic contaminants are concentrated in lake
sediments. Forstner (1989) and Baudo et al. (1990) discuss methods for assessing
the chemistry and toxicity of pollutants in sediments.
Dissolved Oxygen
Dissolved oxygen can be measured using chemical methods (U.S. Environ. Prot.
Agency, 1983 [EPA Method 360.2]) or with a dissolved oxygen electrode and
meter (U.S. Environ. Prot. Agency, 1983 [EPA Method 360.1]). Dissolved oxygen
meters are generally used when numerous determinations are necessary. The
meter must be regularly calibrated by comparison to chemical measurements,
however, because some meters have a tendency to drift. Lethal limits of dissolved
oxygen for fish are discussed in Chapter 3, Box 3-C.
Temperature
Temperature can be measured with simple, liquid-filled, or electronic ther-
mometers. Multiple readings at various depths through the water column are
used to determine the degree and extent of thermal stratification. Lethal tempera-
ture limits and preferred temperatures for fish are discussed in Box 3-D, Chapter 3.
pH
Water pH can be determined in the field using a field pH meter and probe, or a
water sample can be collected and returned to the laboratory. For the most ac-
curate measurement of in situ pH, which can be affected by changes in aqueous
CO2 following contact with the atmosphere, water samples can be collected at
the lake or stream station in syringes and sealed. In the laboratory,, the syringe
contents are injected into a closed chamber surrounding a highly sensitive pH
probe. For most fisheries management projects, however, field pH meters, ac-
curate to 0.1 to 0.2 pH units, are adequate. Details on pH measurements in the
field and laboratory are provided in handbooks from the U.S. Environmental
Protection Agency (1987,1989). Critical pH levels for effects on fish were sum-
marized in Figure 3-5.
Salinity
Most freshwater fish can tolerate waters with salinities up to 1,000-2,000 mg/L
total dissolved solids. Some fish, including some salmonid species, can tolerate
and thrive in waters with even higher salinity, up to and including seawater.
Total dissolved solids are measured by filtering a water sample through a
0.45 um filter, evaporating the filtrate (water that passes through the filter), and
Three approaches are
available for identifying
causes and sources of toxic
effects in lake ecosystems:
chemistry-based,
biology-based, and
toxicity-based approaches.
277
-------
Fish and Fisheries Management in Lakes and Reservoirs
Although suspended
solids rarely attain lethal
levels in lakes and
reservoirs, they can
smother eggs and fry and
depress lake productivity
by inhibiting
photosynthesis.
then weighing the residue. An indirect measure of total dissolved solids in fresh
waters is conductivity, which can be easily measured with a conductivity meter.
Conductivity and total dissolved solids are positively correlated. Based on pub-
lished empirical relationships between conductivity and total dissolved solids for
specific types of waters, conductivity can be used to quantitatively estimate total
dissolved solids. Further information on measuring conductivity and' total dis-
solved solids is provided in Standard Methods (1989).
Suspended Solids
High levels of suspended solids sometimes occur in lakes and more often in reser-
voirs. Although suspended solids rarely attain lethal levels in lakes and reservoirs,
they can smother eggs and fry and depress lake productivity by inhibiting
photosynthesis. Suspended solids are measured by filtering a water sample
through a 0.45 um filter (pre-weighed), drying, and then weighing the filter and
associated residue. The original filter weight is then subtracted from the combined
weight to determine the weight of the solid residue. Methods for sampling and
monitoring suspended solids are provided in Standard Methods (1989).
Assessing the Physical Habitat
Important components of lake and reservoir habitat for fish include lake area,
depth, morphometry, shoreline contours, flushing rate, water level, cover, struc-
tures, substrate, and vegetation (Orth, 1983). Habitat Suitability Indices (HSI)
developed by the U.S. Fish and Wildlife Service provide one means for using these
physical measurements to assess habitat quality for particular fish species (see
Chapter 11). Hamilton and Bergerson (1984) describe procedures for measuring
the specific habitat features used to define each HSI. Additional information on
appropriate methods for assessing physical habitats are contained in EPA's The
Lake and Restoration Guidance Manual (Olem and Flock 1990) and Monitoring Lake
and Reservoir Restoration (Wedepohl et al. 1990), Lind (1985), and the lake inventory
manuals developed by many State and provincial fisheries agencies (e.g., Ontario
Ministry of Natural Resources, 1989; Minnesota Department of Natural Resources,
1970, 1978, 1985; Texas Parks and Wildlife Department, 1991).
Morphometric Measurements
Common morphometric habitat measurements include lake area, depth, volume,
and shoreline development. Lake area can be determined using a polar planimeter,
tracing the boundaries of the lake from a topographical map or aerial photograph
of known scale. Depth is most easily measured with an electronic echosounder or
fish finder. A continuous record of depth along transects can be obtained using a
depth sounder moved across the lake at a constant speed. Contour maps can be
made by interpolating the spatial data to connect lines of equal depth. Computer
software is available for digitizing map depth data to produce contour maps.
Lake volume can be approximated by multiplying the mean depth times the
surface area. More precise estimates of volume require a good contour map. First,
determine the surface area at each contour, then, estimate the volume of water in
the stratum between contour lines (Vs) as
where: h = the height of each stratum,
Al = the area of the upper surface of the stratum, and
A2 = the area of the lower stratum.
278
-------
Appendix B. Methods for Assessing Fisheries Status
The total volume is the sum of the volumes for each stratum. Mean depth is
estimated simply by dividing the volume by the surface area.
The shoreline development index (SDI) is an indicator of the potential
amount of littoral zone development and is the ratio of the shoreline length (L) to
the circumference of a circle of the same area as the lake:
SDI-— L
Shoreline length and area must be expressed in comparable units (e.g., miles
and square miles). A circular lake will have a SDI of 1, and the greater the ir-
regularity of the shoreline, the greater the SDI.
Flushing Rate and Water Levels
The flushing rate is equal to the proportion of the lake or reservoir volume dis-
charged per unit time and is calculated as the discharge divided by the volume
(see Chapter 2). Staff gauges or continuous recorders can be installed for measur-
ing fluctuations in water level, which in streams can be related to stream dis-
charge.
Cover
In shallow and clear lakes and reservoirs, cover — such as logs, boulders, brush
piles, and vegetation — can be quantitatively mapped using grids, transacts, or
point sampling methods. In deep waters, cover can be detected using
echosounders to map locations and extent of cover. Transect sampling is recom-
mended (Platts et al. 1983).
Substrate
Substrate type can be classified using the modified Wentworth scale (see Table 2-
1, Chapter 2) and spatial distribution can be determined using a point sampling
method. Substrate samples can be collected using the same methods described
for benthic macroinvertebrates, as discussed earlier in this chapter. Subsurface
analysis of the substrate can be completed on samples collected using a McNeil
or freeze-core sampler (Platts et al. 1983).
Vegetation
In shallow waters, aerial photography or shoreline surveys with boats can be
used to map the distribution of aquatic macrophytes. Macrophytes are usually
surveyed once or twice during the growing season. Information collected should
include species, area covered, relative abundance (e.g., abundant, common, or
sparse) or density (stems per unit area), and depth.
The shoreline development
index (SDI) is an
indicator of the potential
amount of littoral zone
development....
279
-------
-------
APPENDIX C
Addresses and
Telephone Numbers
State Agencies
Alabama
Division of Game and Fish
Department of Conservation and
Natural Resources
64 N. Union Street
Montgomery, Alabama 36130
205/242-3465
FAX 205/242-3032
Alabama Department of Environmental
Management
1751 Congressman W.L. Dickinson Drive
Montgomery, Alabama 36109
205/271-7700
FAX 205/270-5612
Alaska
Department of Fish and Game
P.O. Box 25526
Juneau, Alaska 99802-5526
907/465-4100
FAX 907/465-2332
Department of Environmental
Conservation
410 Willoughby Ave., Suite 105
Juneau, Alaska 99801-1795
907/465-5000
FAX 907/465-5097
Arizona
Arizona Game and Fish Department
2221W. Greenway Road
Phoenix, Arizona 85023-4312
602/942-3000
FAX 602/789-3920
Department of Environmental Quality
3033 North Central Ave.
Phoenix, Arizona 85012
602/207-2300
FAX 602/207-2218
Arkansas
Game and Fish Commission
#2 Natural Resources Drive
Little Rock, Arkansas 72205
501/223-6300
FAX 501/223-6425
Department of Pollution Control and
Ecology
8001 National Drive
P.O. Box 8913
Little Rock, Arkansas 72219
501/562-7444
FAX 501/562-4632
California
Department of Fish and Game
1416 Ninth Street
Sacramento, California 95814
916/653-7664
FAX 916/653-1856
Water Resources Control Board
901 P Street
P.O. Box 100
Sacramento, California 95801-0100
916/657-1155
FAX 916/657-1747
281
-------
Fish and Fisheries Management in Lakes and Reservoirs
Colorado
Division of Wildlife
Department of Natural Resources
6060 Broadway
Denver, Colorado 80216
303/297-1192
FAX 303/294-0874
Division of Water Resources
Department of Natural Resources
1313 Sherman, Room 818
Denver, Colorado 80203
303/866-3581
FAX 303/866-3589
Connecticut
Wildlife Division
Department of Environmental Protection
State Office Building
165 Capitol Avenue, Room 254
Hartford, Connecticut 06106
203/566-4683
FAX 203/566-6024
Bureau of Water Management
Department of Environmental Protection
165 Capitol Avenue
Hartford, Connecticut 06106
203/566-3245
FAX 203/566-8650
Delaware
Division of Fish and Wildlife
Department of Natural Resources and
Environmental Control
89 Kings Highway
P.O. Box 1401
Dover, Delaware 19903
302/739-5295
FAX 302/739-6157
Division of Water Resources
Department of Natural Resources and
Environmental Control
89 Kings Highway
P.O. Box 1401
Dover, Delaware 19903
302/739-4860
FAX 302/739-3491
Florida
Game and Fresh Water Fish Commission
620 S. Meridian Street
Tallahassee, Florida 32399-1600
904/488-1960
FAX 904/488-6988
Department of Environmental
Regulation
Division of Water Management
2600 Blair Stone Road
Tallahassee, Florida 32399-2400
904/488-4805
FAX 904/488-6579
Georgia
Game and Fish Division
Department of Natural Resources
2070 U.S. Hwy 278 S.E.
Social Circle, Georgia 30279
404/918-6400
FAX 404/656-2285
Environmental Protection Division
Department of Natural Resources
Floyd Towers East
205 Butler Street
Atlanta, Georgia 30334
404/656-4713
FAX 404/656-2285
Hawaii
Division of Aquatic Resources
Department of Land and Natural
Resources
1151 Punchbowl Street, Room 330
Honolulu, Hawaii 96813
808/587-0100
FAX 808/587-0115
Division of Water and Land
Development
Department of Land and Natural
Resources
P.O. Box 373
Honolulu, Hawaii 96809
808/587-0230
FAX 808/587-0219
Commission on Water Resource
Management
Department of Land and Natural
Resources
P.O. Box 621
Honolulu, Hawaii 96809
808/587-0214
FAX 808/587-0219
Idaho
Idaho Department of Fish and Game
600 S. Walnut
P.O. Box 25
Boise, Idaho 83707
208/334-3700
FAX 208/334-2114
282
-------
Appendix C. Addresses and Telephone Numbers
Community Program Division of
Environmental Quality
IDHW
1410 N.Hilton
Boise, Idaho 83706
208/334-5860
FAX 208/334-0576
Illinois
Fisheries Division
Illinois Department of Conservation
600 N. Grand Ave. West
Springfield, Illinois 62706
217/782-6424
FAX 217/785-8262
Illinois Environmental Protection
Agency
2200 Churchill Road
Springfield, Illinois 62706
217/782-3397
FAX 217/782-9891
Indiana
Division of Fish and Wildlife
Department of Natural Resources
402 W.Washington St.
Room W 273
Indianapolis, Indiana 46204
317/232-4080
FAX 317/232-8150
Indiana Department of Environmental
Management
105 S. Meridian Street
P.O. Box 6015
Indianapolis, Indiana 46206-6015
317/232-8603
FAX 317/233-3257
Iowa
Fish and Wildlife Division
Department of Natural Resources
E. Ninth and Grand Avenue
Wallace State Office Bldg.
Des Moines, Iowa 50319-0034
515/281-5145
FAX 515/281-6794
Environmental Protection Division
Department of Natural Resources
E. Ninth and Grand Avenue
Wallace State Office Bldg.
Des Moines, Iowa 50319-0034
515/281-5145
FAX 515/281-8895
Kansas
Kansas Department of Wildlife and
Parks
900 Jackson Street, Suite 502
Topeka, Kansas 66612-1233
913/296-2281
FAX 913/296-6953
State Department of Health and
Environment
Landon State Office Bldg., Room 901
Topeka, Kansas 66612-1290
913/296-1522
FAX 913/296-7119
Kansas State Water Office
109 SW Ninth Street, Suite 300
Topeka, Kansas 66612-1249
913/296-3185
FAX 913/296-0878
Kentucky
Department of Fish and Wildlife
Resources
#1 Game Farm Road
Frankfort, Kentucky 40601
502/564-3400
FAX 502/564-6508
Natural Resources and Environmental
Protection Cabinet
Department for Environmental
Protection
14ReillyRoad
Frankfort, Kentucky 40601
502/564-2150
FAX 502/564-4245
Maine
Department of Inland Fisheries and
Wildlife
284 State Street, Station #41
Augusta, Maine 04333
207/289-2766
FAX 207/287-6395
Department of Environmental Protection
State House, Station #17
Augusta, Maine 04333
207/289-2811
FAX 207/287-7826
Maryland
Department of Natural Resources
Tawes State Office Bldg.
Annapolis, Maryland 21401
410/974-3041
FAX 410/974-5206
283
-------
Fish and Fisheries Management in Lakes and Reservoirs
Department of the Environment
2500 Broening Highway
Baltimore, Maryland 21224
410/631-3000
Massachusetts
Department of Fisheries, Wildlife, and
Environmental Law Enforcement
100 Cambridge Street
Boston, Massachusetts 02202
617/727-3194
FAX 617/727-7988
Department of Environmental
Management
100 Cambridge Street, Room 1905
Boston, Massachusetts 02202
617/727-3163
FAX 617/727-9402
Michigan
Fisheries Division
Department of Natural Resources
Box 30028
Lansing, Michigan 48909
517/373-1280
FAX 517/373-0381
Surface Water Quality Division
Department of Natural Resources
Box 30028
Lansing, Michigan 48909
517/373-1949
FAX 517/373-9958
Minnesota
Department of Natural Resources
Division of Fisheries
500 Lafayette Road
St. Paul, Minnesota 55155-4012
612/296-6157
FAX 612/297-4916
Minnesota Pollution Control Agency
Water Quality Division
520 Lafayette Road
St. Paul, Minnesota 55155
612/296-6300
FAX 612/297-8683
Mississippi
Department of Wildlife, Fisheries, and
Parks
2906 State Street
P.O. Box 451
Jackson, Mississippi 39205
601/362-9212
FAX 601/364-2125
Bureau of Pollution Control
Department of Environmental Quality
P.O. Box 10385
Jackson, Mississippi 39289-0385
601/961-5171
FAX 601/354-6612
Missouri
Fisheries Division
Department of Conservation
P.O. Box 180
Jefferson City, Missouri 65102-0180
314/751-4115
FAX 314/893-6079
Division of Environmental Quality
Department of Natural Resources
P.O. Box 176
Jefferson City, Missouri 65102
314/751-4810
FAX 314/751-9277
Montana
Department of Fish, Wildlife, and Parks
1420 East Sixth Avenue
Helena, Montana 59620
406/444-2535
FAX 406/444-4952
State Department of Health and
Environmental Sciences
Cogswell Bldg.
Helena, Montana 59620
406/444-2544
FAX 406/444-1804
Nebraska
Game and Parks Commission
2200 N. 33rd Street
P.O. Box 30370
Lincoln, Nebraska 68503
402/471-5515
FAX 402/471-5528
Department of Environmental Quality
1200 N Street, Suite 400
P.O. Box 98922
Lincoln, Nebraska 68509-8922
402/471-2186
FAX 402/471-2909
Department of Water Resources
Box 94676
Lincoln, Nebraska 68509-4676
402/471-2363
FAX 402/471-2900
284
-------
Appendix C. Addresses and Telephone Numbers
Nevada
Department of Wildlife
Box 10678
Reno, Nevada 89520
702/688-1500
FAX 702/688-1595
Department of Conservation and
Natural Resources
Division of Environmental Protection
Capitol Complex
333 W.Nye Lane
Carson City, Nevada 89710
702/687-4670
FAX 702/687-5856
New Hampshire
Fish and Game Department
2 Hazen Drive
Concord, New Hampshire 03301
603/271-3421
FAX 603/271-1438
Department of Environmental Services
Water Supply and Pollution Control
Division
6 Hazen Drive
P.O. Box 95
Concord, New Hampshire 03302-0095
603/271-3503
FAX 603/271-2867
New Jersey
Division of Fish, Game, and Wildlife
Department of Environmental Protection
501E. State Street, CN 400
Trenton, New Jersey 08625-0400
609/292-2965
FAX 609/984-1414
Division of Water Resources
Department of Environmental Protection
401 E. State Street
Trenton, New Jersey 08625-0402
609/292-1637
New Mexico
New Mexico Game and Fish Department
P.O. Box 25112
Santa Fe, New Mexico 87504
505/827-7899
FAX 505/827-7915
New Mexico Environment Department
Surface Water Quality Bureau
1190 St. Francis Drive
P.O. Box 26110
Santa Fe, New Mexico 87502
505/827-2792
FAX 505/827-0160
New York
Division of Fish and Wildlife
Department of Environmental
Conservation
50 Wolf Road, Room 518
Albany, New York 12233-4753
518/457-5420
FAX 518/485-5827
Division of Water
Department of Environmental
Conservation
50 Wolf Road, Room 306
Albany, New York 12233-3500
518/457-6674
FAX 518/485-8991
North Carolina
Division of Boating and Inland Fisheries
Wildlife Resources Commission
Archdale Building
512 N. Salisbury Street
Raleigh, North Carolina 27604-1188
919/733-3633
FAX 919/733-7083
Division of Water Resources
Department of Environment, Health,
and Natural Resources
P.O. Box 27687
Raleigh, North Carolina 27611
919/733-4064
FAX 919/733-3558
North Dakota
State Game and Fish Department
100 North Bismarck Expressway
Bismarck, North Dakota 58501
701/221-6300
FAX 701/221-6352
State Department of Health and
Consolidated Laboratories
Department of Health
1200 Missouri Avenue
Bismarck, North Dakota 58502-5520
701/221-5210
FAX 701/221-5200
285
-------
Fish and Fisheries Management in Lakes and Reservoirs
Ohio
Division of Wildlife
Department of Natural Resources
1840 Belcher Drive
Columbus, Ohio 43224
614/265-6300
FAX 614/262-1143
Environmental Protection Agency
1800 Watermark Drive
Columbus, Ohio 43215
614/644-3020
FAX 614/644-2329
Oklahoma
Fisheries Division
Department of Wildlife Conservation
1801N. Lincoln
P.O. Box 53465
Oklahoma City, Oklahoma 73152
405/521-3721
FAX 405/521-6535
State Department of Health
1000 Northeast Tenth
Oklahoma City, Oklahoma 73117-1299
405/271-5601
FAX 405/271-2865
Oregon
Oregon Department of Fish and Wildlife
P.O. Box 59
Portland, Oregon 97207-0059
503/229-5400
FAX 503/229-5602
Department of Environmental Quality
811 SW Sixth Avenue
Portland, Oregon 97204
503/229-5630
FAX 503/229-6124
Pennsylvania
Fish and Boat Commission
P.O. Box 6700
Harrisburg, Pennsylvania 17106-7000
717/657-4518
FAX 717/657-4549
Department of Environmental Resources
Public Liaison Office
P.O. Box 2063
Harrisburg, Pennsylvania 17105-2063
717/783-8303
FAX 717/783-8926
Puerto Rico
Department of Natural Resources
P.O. Box 5887
Puerta de Tierra Station
San Juan, Puerto Rico 00906
809/724-8774
FAX 809/722-2785
Rhode Island
Division of Fish, Wildlife, and Estuarine
Resources
Department of Environmental
Management
Stedman Government Center
4808 Tower Hill Road
Wakefield, Rhode Island 02879
401/789-3094
FAX 401/783-4660
Division of Water Resources
Department of Environmental
Management'
291 Promenade Street
Providence, Rhode Island 02908
401/277-3961
FAX 401/521-4230
South Carolina
Wildlife and Marine Resources
Department
Division of Game and Fresh Water
Fisheries
Rembert C. Dennis Bldg.
P.O. Box 167
Columbia, South Carolina 29202
803/734-3889
FAX 803/734-3951
Water Resources Commission
1201 Main Street, Suite 1100
Columbia, South Carolina 29201
803/737-0800
FAX 803/765-9080
South Dakota
Game, Fish and Parks Department
523 East Capitol
Pierre, South Dakota 57501-3182
605/773-3381
FAX 605/773-6245
Environment and Natural Resources
Joe Foss Office Bldg.
523 East Capitol
Pierre, South Dakota 57501-3181
605/773-3151
FAX 605/773-6035
286
-------
Appendix C. Addresses and Telephone Numbers
Tennessee
Wildlife Resources Agency
Fish Management Division
P.O. Box 40747
Ellington Agricultural Center
Nashville, Tennessee 37204
615/781-6500
FAX 615/741-4606
Division of Water Pollution Control
Department of Environment and
Conservation
401 Church Street
6th Floor L & C Annex
Nashville, Tennessee 37243-1534
615/532-0625
FAX 615/532-0614
Texas
Parks and Wildlife Department
Fisheries
4200 Smith School Road
Austin, Texas 78744
512/389-4800
FAX 512/389-4894
Guadalupe-Blanco River Authority
P.O. Box 271
Sequin, Texas 78156-0271
210/379-5822
FAX 210/379-9918
Texas Water Development Board
1700 N. Congress Avenue
P.O. Box 13231
Austin, Texas 78711
512/463-7847
FAX 512/475-2053
I/tali
Division of Wildlife Resources, Fisheries
Management
State Department of Natural Resources
1596 W. North Temple
Salt Lake City, Utah 84116-3154
801/538-4700
FAX 801/538-4709
Division of Water Resources
State Department of Natural Resources
1636 W. North Temple
Salt Lake City, Utah 84116-3156
801/538-7230
FAX 801/538-7315
Vermont
Department of Fish and Wildlife
Agency of Natural Resources
103 South Main, 10 South
Waterbury, Vermont 05671-0501
802/244-7331
FAX 802/241-3295
Agency of Natural Resources
Department of Environmental
Conservation
Center Building
103 South Main Street
Waterbury, Vermont 05671
802/244-7347
FAX 802/244-5141
Virgin Islands
Department of Planning and Natural
Resources
Suite 231, Nisky Center
St. Thomas, U.S. 00802
809/774-3320
FAX 809/775-5706
Virginia
Department of Game and Inland
Fisheries
4010 W. Broad Street
Box 11104
Richmond, Virginia 23230
804/367-1000
FAX 804/367-9147
Department of Conservation and
Recreation
Division of Soil and Water Conservation
203 Governor Street
Suite 206
Richmond, Virginia 23219
804/786-2064
FAX 804/786-1798
Washington
Department of Wildlife
Fisheries Management Division
600 Capitol Way North
Olympia, Washington 98501-1091
206/753-5700
FAX 206/586-0248
Department of Ecology
P.O. Box 47600
Olympia, Washington 98504-7600
206/459-6000
FAX 206/459-6077
287
-------
Fish and Fisheries Management In Lakes and Reservoirs
West Virginia
Warmwater Fisheries
Department of Natural Resources
1900 Kanawha Blvd., East
Charleston, West Virginia 25305
304/558-2771
FAX 304/558-3147
Coldwater Fisheries
Department of Natural Resources
P.O. Box 67
Elkins, West Virginia 26241
304/637-0245
FAX 304/637-0250
Water Resources
Department of Natural Resources
1201 Greenbrier Street
Charleston, West Virginia 25311
304/558-2107
FAX 304/558-5905
Wisconsin
Bureau of Water Resources Management
Department of Natural Resources
Box 7921
Madison, Wisconsin 53707
608/267-7610
FAX 608/267-2800
Bureau of Fisheries Management
Department of Natural Resources
Box 7921
Madison, Wisconsin 53707
608/266-1877
FAX 608/267-7857
Wyoming
Game and Fish Department
5400 Bishop Blvd.
Cheyenne, Wyoming 82002
307/777-4600
FAX 307/777-4610
Environmental Quality Department
122 W. 25th Street
4th Floor West, Herschler Bldg.
Cheyenne, Wyoming 82002
307/777-7937
FAX 307/777-7682
Provincial Agencies
Alberta
Fish and Wildlife Division
Fisheries Management
Department of Environmental Protection
5th Floor, Bramalea Bldg.
9920108 Street
Edmonton, Alberta T5K 2M4
403/427-6730
FAX 403/422-9559
British Columbia
Fisheries Branch
Ministry of Environment, Lands, and
Parks
780 Blanchard Street, 2nd Floor
Victoria, British Columbia V8V1X4
604/387-9711
FAX 604/387-9750
Water Management Division
Ministry of Environment
765 Broughton Street, 6th Floor
Victoria, British Columbia V8V1X4
604/387-9396
FAX 604/954-3603
Manitoba
Department of Natural Resources
Legislative Bldg., Room 314
Winnipeg, Manitoba R3C OV8
204/945-3730
FAX 204/945-3586
New Brunswick
Fish and Wildlife Branch
Department of Natural Resources, and
Energy
P.O. Box 6000
Fredericton, New Brunswick E3B 5H1
506/453-2433
FAX 506/453-6699
N& wfoundland
Department of Environment and Lands
P.O. Box 8700
St. John's, Newfoundland A1C 4J6
709/729-2574
FAX 709/729-0112
288
-------
Appendix C. Addresses and Telephone Numbers
Northwest Territories
Department of Renewable Resources
Government of the Northwest Territories
P.O. Box 1320
Yellowknife, Northwest Territories
X1A2L9
403/873-7128
FAX 403/873-0110
Nova Scotia
Department of Fisheries
Scotia Fundy Region
P.O. Box 550
Halifax, Nova Scotia B3J 2S7
902/426-2373
FAX 902/426-3479
Ontario
Ministry of Natural Resources
Whitney Block
99 Wellesley St. West, Room 6301
Toronto, Ontario M7A1W3
416/314-2301
FAX 416/314-2216
Prince Edward Island
Department of the Environment
P.O. Box 2000
Charlottetown, Prince Edward Island
C1A7N8
902/368-4689
FAX 902/368-5830
Quebec
Department of Recreation, Fish, and
Game
Place de la Capitale
150 Rene-Leuesque E. Blvd., 17th Floor
Quebec City, Quebec G1R 4Y3
418/643-6527
FAX 418/643-9588
Saskatchewan
Saskatchewan Natural Resources
Fisheries Branch
3211 Albert Street, Room 338
Reginia, Saskatchewan S4S 5W6
306/787-2884
FAX 306/787-0737
Yukon Territory
Department of Renewable Resources
Fisheries Section
Box 2703
Whitehorse, Yukon Territory Yl A 2C6
403/667-5110
FAX 403/668-4263
Professional Societies
American Fisheries Society
5410 Grosvenor Lane
Suite 110
Bethesda, Maryland 20814
301/897-8616
FAX 301/897-8096
American Society of Limnology and
Oceanography
Biological Oceanography Division
Bedford Institute of Oceanography
P.O. Box 1006
Dartmouth, Nova Scotia B2Y 4A2
902/426-3793
FAX 902/426-9388
American Water Resources Association
5410 Grosvenor Lane, Suite 220
Bethesda, Maryland 20814
301/493-8600
FAX 301/493-5844
North American Benthological Society
Business Office
P.O. Box 1897
Lawrence, Kansas 66044
913/843-1221
FAX 913/843-1274
North American Lake Management
Society
1 Progress Blvd., Box 27
Alachua, Florida 32615-9536
904/462-2554
FAX 904/462-2568
Society of Environmental Toxicology
and Chemistry
1010 North 12th Avenue
Pensacola, Florida 32501-3307
904/469-1500
FAX 904/469-9778
289
-------
Fish and Fisheries Management in Lakes and Reservoirs
Private Organizations
American Bass Association, Inc.
2810 Trotters Trail
Wetumpka, Alabama 36092
205/567-6035
FAX 205/567-8632
BASS, Inc.
Anglers for Clean Water, Inc.
P.O. Box 17900
Montgomery, Alabama 36141
205/272-9530
FAX 205/279-7148
Bass Anglers Sportsman Society
5845 Carmichael Road
Montgomery, Alabama 36117
205/272-9530
FAX 205/279-7148
Clean Water Action
132018th Street, NW, Suite 300
Washington, DC 20036
202/457-1286
FAX 202/457-0287
Environmental Defense Fund, Inc.
257 Park Avenue South
New York, New York 10010
212/505-2100
FAX 212/505-2375
Federation of Fly Fishers
P.O. Box 1088
West Yellowstone, Montana 59758
406/646-9541
FAX 406/646-9728
Freshwater Foundation
725 County Road Six
Wayzata, Minnesota 55391
612/449-0092
FAX 612/449-0592
Izaak Walton League of America, Inc.
1401 Wilson Blvd., Level B
Arlington, Virginia 22209-2318
703/528-1818
FAX 703/528-1836
Muskies, Inc.
2301 7th Street, North
Fargo, North Dakota 58102
701/239-9540
FAX 701/239-9540
National Audubon Society
700 Broadway
New York, New York 10003-9501
212/979-3000
FAX 212/979-3188
National Wildlife Federation
1400 Sixteenth Street, NW
Washington, DC 20036-2266
202/797-6800
FAX 202/797-6646
Natural Resources Defense Council, Inc.
40 West 20th Street
New York, New York 10011
212/727-2700
FAX 212/727-1773
North American Native Fishes
Association
123 West Mt. Airy Avenue
Philadelphia, Pennsylvania 19119
Sierra Club
730 Polk Street
San Francisco, California 94109
415/776-2211
FAX 415/776-0350
Soil and Water Conservation Society
7515 NE Ankeny Road
Ankeny, Iowa 50021-9764
515/289-2331
FAX 515/289-1227
Sport Fishing Institute
Suite 320
1010 Massachusetts Avenue, NW
Washington, DC 20001
202/898-0770
FAX 202/371-2085
Trout Unlimited
800 Follin Lane, Suite 250
Vienna, Virginia 22180
703/281-1100
FAX 703/281-1825
Water Environment Federation
601 Wythe Street
Alexandria, Virginia 22314-1994
703/684-2400
FAX 703/684-2492
290
-------
GLOSSARY
Adaptive management. The process whereby information is gained and
management strategies are improved through direct experience with applying
management techniques.
Aerobic. Describes life or processes that require the presence of molecular oxygen.
Algae. Small aquatic plants that occur as single cells, colonies, or filaments.
Alloehthonous. Materials (e.g., organic matter and sediment) that enter a lake
from the atmosphere or a drainage basin (see autochthonous).
Anaerobic. Describes processes that occur in the absence of molecular oxygen.
Anoxia. A condition of no oxygen in the water. Often occurs near the bottom of fer-
tile stratified lakes in the summer and under ice in late winter.
Autochthonous. Materials produced within a lake (e.g., autochthonous organic
matter from plankton versus allochthonous organic matter from terrestrial
vegetation).
Bathymetric map. A map showing the bottom contours and depth of a lake; can
be used to calculate lake volume.
Benthos. Macroscopic (seen without aid of a microscope) organisms living in and
on the bottom sediments of lakes and streams. Originally, the term meant the
lake bottom, but it is now applied almost uniformly to the animals associated
with the substrate.
Biochemical oxygen demand (BOD). The rate of oxygen consumption by or-
ganisms during the decomposition (respiration) of organic matter, expressed as
grams oxygen per cubic meter of water per hour.
Biological criteria. Indicators of biological or ecological integrity compared to
some least-disturbed reference site.
Biomanipulation. Any management technique that relies on altering the fish com-
munity to improve water quality.
Biomass. The weight of biological matter. Standing crop is the amount of biomass
(e.g., fish or algae) in a body of water at a given time. Often measured in terms of
grams per square meter of surface.
Biota. All plant and animal species occurring in a specified area.
Catch per unit effort and harvest per unit effort. The number or biomass of
fish caught and harvested, respectively, per unit of angling effort.
Chemical oxygen demand (COD). Nonbiological uptake of molecular oxygen
by organic and inorganic compounds in water.
Chlorophyll. A green pigment in algae and other green plants essential for the con-
version of sunlight, carbon dioxide, and water to sugar (i.e., photosynthesis)
bugar is then converted to starch, proteins, fats, and other organic molecules
291
-------
Fish and Fisheries Management In Lakes and Reservoirs
Chlorophyll a. A type of chlorophyll present in all types of algae, sometimes in direct
proportion to the biomass of algae.
Decomposition. The transformation of organic molecules (e.g., sugar) to inorganic
molecules (e.g., carbon dioxide and water) through biological and nonbiological
processes.
Detritus. Nonliving dissolved and particulate organic material from the metabolic
activities and deaths of terrestrial and aquatic organisms.
Ecosystem. A system of interrelated organisms and their physical-chemical en-
vironment. In this manual, an ecosystem includes the lake and surrounding land
as well as streams that drain into the lake.
Epilimnion. Uppermost, warmest, well-mixed layer of a lake during summertime
thermal stratification. The epilimnion extends from the surface to the thermocline.
Eutrophic. From Greek for "well-nourished," describes a lake of high photosynthetic
activity and low transparency.
Eutrophlcation. The process of physical, chemical, and biological changes as-
sociated with nutrient, organic matter, and silt enrichment and sedimentation of a
lake or reservoir. If the process is accelerated by human influences, it is termed
"cultural eutrophication."
Evaporation. The direct conversion of liquid water into water vapor by the addition
of heat. ,
Evapotranspiration. The combined conversion of water to water vapor, and loss
resulting from both evaporation and transpiration.
Fall overturn. The autumn mixing, top to bottom, of lake water caused by cooling
and wind-derived energy.
Fecundity. The number of eggs produced by a single female fish.
Fish abundance. The density and/or biomass of fish present per unit area or
volume, by species.
Fish community. The collection of all fish populations (i.e., all fish species).
Fish population. A group of fish of the same species that occurs within a given lake
or reservoir.
Fisheries yield. The total number or biomass of fish removed from the lake through
angling (per unit area or volume and period of time), estimated from the measures
of fishing pressure and harvest per unit effort.
Fishery. The act or occupation of fishing — the harvesting of fish from waterbodies
for either commercial or recreational purposes.
Fishing pressure. The total number of hours (or other suitable unit) of angling ef-
fort.
Flushing rate. The rate at which water enters and leaves a lake relative to lake
volume, usually expressed as time needed to replace the lake volume with inflow-
ing water.
Food chain. The general progression of feeding levels from primary producers, to
herbivores, to planktivores, to the larger predators.
Food web. The complex of feeding interactions existing among the lake's organisms.
Forage f Ssh. Fish, including a variety of panfish and minnows, that are prey' for
game fish.
292
-------
Glossary
Groundwater. Water that infiltrates into the soil and underlying rock layers.
Groundwaters eventually flow into lakes and other surface waters through seeps
and springs, although some deep groundwaters can remain underground for
hundreds of years.
Habitat. The place or type of area where a plant or animal normally lives and
grows.
Hybrids. The offspring of parents of different species) for example, a cross between
bluegill and green sunfish.
Hydraulic residence time. The average time required to completely renew a
lake's water volume.
Hypereutrophic. Describes a lake that often experiences pea-soup conditions be-
cause of high concentrations of algae and/or excessive densities of rooted
aquatic plants.
Hypolimnion. Lower, cooler layer of a lake during summertime thermal stratifica-
tion.
Internal nutrient cycling. Transformation of nutrients such as nitrogen or phos-
phorus from biological to inorganic forms through decomposition, occurring
within the lake itself.
Internal nutrient load. Nutrients that reenter the water column from sediments.
Lake. A considerable inland body of standing water, either naturally formed or
human-made.
Lake management. A comprehensive program that incorporates both protection
and restoration activities to effectively improve and maintain the quality of the
lake ecosystem.
Lake morphometry. The physical configuration and shape of the lake basin.
Lake reclamation or rehabilitation. An extreme approach to rough fish control
whereby all or most fish in the lake are poisoned and desirable fish species are
reintroduced.
Limnology. The scientific study of the physical, chemical, geological, and biological
factors that affect aquatic productivity and water quality in freshwater ecosys-
tems — lakes, reservoirs, rivers, and streams. Also termed freshwater ecology.
Littoral zone. That portion of a waterbody extending from the shoreline lakeward
to the greatest depth occupied by rooted plants.
Loading. The total amount of material (e.g., sediment, nutrients, oxygen-demand-
ing material) brought into the lake by inflowing streams, runoff, direct discharge
through pipes, groundwater, the air, and other sources over a specific period of
time, often annually.
Macroinvertebrates. Aquatic insects, worms, clams, snails, and other animals
visible without aid of a microscope that may be associated with or live on sub-
strates such as sediments and macrophytes. They supply a major portion of fish
diets and consume detritus and algae.
Macrophytes. Rooted and floating aquatic plants, commonly referred to as water-
weeds. These plants may flower and bear seed. Some forms, such as duckweed
and coontail (Ceratopkyllum), are free-floating forms without roots in the sedi-
ment.
Maximum sustainable yield. The maximum quantity of biomass that could be
harvested from a population each year without causing a long-term population
decline.
293
-------
Fish and Fisheries Management in Lakes and Reservoirs
Meromictic lakes. Lakes that are permanently stratified as a result of differences in
total dissolved solids.
Mesotrophic. Describes a lake that has intermediate nutrient availability and
biological productivity.
Metalimnion. Layer of rapid temperature and density change in a thermally
stratified lake. Resistance to mixing is high in the region.
Microbes. Term used to refer collectively to bacteria, fungi, and other microscopic or-
ganisms involved in organic matter decomposition.
Morphometry. Relating to a lake's physical structure (e.g., depth, shoreline length).
Oligotrophic. From Greek for "poorly nourished," describes a lake of low plant
productivity and high transparency.
Ooze. Lake bottom accumulation of inorganic sediments and the partially decom-
' posed remains of algae, weeds, fish, and aquatic insects. Sometimes called muck;
see sediment.
Optimum sustainable yield. The quantity of fish harvested and the level of effort
and expense required to collect these fish and, in recreational fisheries, a wide
range of other characteristics relating to angler values and the overall quality of
the fishing experience.
Pelagic zone. This is the open-water area of a lake, from the edge of the littoral zone
to the center of the lake, not directly influenced by the shore or the bottom.
Periphyton. Organisms associated with submerged substrates, such as bottom sedi-
ments, aquatic vegetation, docks, and other surfaces.
Photic zone. The lighted region of a lake where photosynthesis takes place. Extends
down to a depth where plant growth and respiration are balanced by the amount
of light available.
Photosynthesis. The biological process by which light energy is converted into
chemical energy and stored as organic compounds, which can then be used to sup-
port biological growth and production.
Phytoplankton. Microscopic algae and microbes that float freely in the open water
of lakes and oceans:
Piscivores. Fish that feed primarily on other fish, often referred to as forage fish.
Planktivores. Plankton-eating fish.
Plankton. Planktonic algae float freely in the open water. Filamentous algae form
long threads and are often seen as mats on the surface in shallow areas of the lake.
Primary productivity. The rate at which algae and macrophytes fix or convert light,
water, and carbon dioxide to sugar in plant cells. Commonly measured as mil-
ligrams of carbon per square meter per hour.
Profundal zone. Mass of lake water and sediment occurring on the lake bottom
below the depth of light penetration.
Reservoir. A human-made lake where water is collected and kept in quantity for a
variety of uses, including flood control, water supply, recreation, and hydro-
electric power.
Respiration. Process by which organic matter is oxidized by organisms, including
plants, animals, and bacteria. The process releases energy, carbon dioxide, and
water.
294
-------
Glossary
Rough fish. Undesirable fish species that interfere with the survival and growth of
desirable fish species or with other lake uses.
Sediment. Bottom material in a lake that has been deposited after the formation of
a lake basin. It originates from remains of aquatic organisms, chemical precipita-
tion of dissolved minerals, and erosion of surrounding lands (see ooze).
Stratification. Layering of water caused by differences in water density. Thermal
stratification is typical of most deep lakes during summer. Chemical stratification
can also occur.
Surface runoff. Excess precipitation or snowmelt that does not infiltrate into the
soil but flows over the land surface before reaching a defined stream channel or
other surface water. Large quantities of surface runoff are most common in arid
regions and in humid regions where the natural vegetation and soils have been
disturbed.
Surface water. Standing or flowing water on top of the land surface, such as
streams, rivers, lakes, and oceans.
Transpiration. The conversion of water to water vapor by plants and loss of the
water vapor from plant surfaces. <
Trophic level. A step or level within the trophic pyramid, that is, a hierarchical
classification of organisms based on the types of organisms that they eat and that
eat them. Plants are eaten by herbivores, which are eaten in turn by predators,
which may be consumed by other predators. Each of these'groups represents a
level on the trophic pyramid.
Trophic state. The degree of eutrophication of a lake. Transparency, chlorophyll
levels (as an indicator of algal abundance), phosphorus concentrations, amount
of rooted aquatic vegetation, and quantity of dissolved oxygen in the hypolim-
nion can be used to assess a lake's trophic state.
Watershed. A drainage area or basin in which all land and water areas drain or
flow toward a central collector such as a stream, river, or lake at a lower eleva-
tion.
Yield. That portion of a fish population, in terms of numbers or weight, harvested
by humans through recreational or commercial fisheries over some specified
period of time and per unit area or volume.
Zooplankton. Microscopic animals that float freely in lake water, graze on detritus
particles, bacteria, and algae, and may be consumed by fish.
295
-------
-------
REFERENCES
Chapter 1
Creager, C.S., and J.P. Baker. 1991. North Carolina's Whole Basin Approach to Water
Quality Management: Program Description. Rep. N. Carolina Div. Environ. Manage.
and U.S. Environ. Prot. Agency. Western Aquat., Durham, NC.
National Research Council. 1991. Restoration of Aquatic Ecosystems: Science, Technology,
and Public Policy. Natl. Acad. Sci., Washington, DC.
Olem, H., and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Wedepohl, R.E. et al. 1990. Monitoring Lake and Reservoir Restoration. EPA 440/4-90-007.
U.S. Environ. Prot. Agency, Washington, DC.
Chapter 2
Carpenter, S.R., ed. 1988. Complex Interactions in Lake Communities. Sprineer-Verlae,
New York, NY.
Carpenter, S.R., and J.R Kitchell. 1988. Introduction. Pages 1-8 in S.R. Carpenter, ed. Com-
plex Interactions in Lake Communities. Springer-Verlag, New York, NY.
Carpenter, S.R., J.R Kitchell, and J.R. Hodgson. 1985. Cascading trophic interactions and
lake productivity. BioScience 35:634-39.
Davis, R.B. et al. 1978. Descriptive and Comparative Studies of Maine Lakes. Life Sci.
Agric. Exp. Sta. Tech. Bull. 88. Univ. Maine, Orono, ME.
Eilers, J.M. 1991. Are lakes in the Cascade Mountains receiving high ammonium deposi-
tion? Northw. Sci. 65:238-47.
Hecky, R.E. and P. Kilham. 1988. Nutrient limitation of phytoplankton in freshwater and
marine environments: A review of recent evidence on the effects of enrichment. Lim-
nol. Oceanogr. 33:796-822.
Hunter, M.L. Jr., J.J. Jones, K.W. Gibbs, and J.R. Moring. 1986. Duckling responses to lake
acidification: Do black ducks and fish compete? Oikos 47:26-32.
Hutchinson, G.E. 1957. A Treatise on Limnology. Vol. I, Part 1 in Geography and Physics
of Lakes. John Wiley & Sons, New York, NY.
Jordan, M., and G.E. Likens. 1975. An organic carbon budget for an oligotrophic lake in
New Hampshire, U.S.A. Verh. Int. Ver. Limnol. 19:994-1003.
Kairesalo, T. 1980. Comparison of in situ photosynthetic activity of epiphytic, epipelic and
planktonic algae communities in an oligotrophic lake, southern Finland. J. Phycol.
16:57-62.
Likens, G.E. and F.H. Bormann. 1972. Nurtrient cycling in ecosystems. Pages 279-85 in
Ecosystem Structure and Function. Oregon State Univ. Press, Corvallis, OR.
Magnuson, J.J. 1991. Fish and fisheries ecology. Ecol. Appl. 1:13-26.
Magnuson, J.J., L.B. Crowder, and P.A. Medvick. 1979. Temperature as an ecological
resource. Am. Zool. 19:331-43.
Morris, D.P., and W.M. Lewis, Jr. 1988. Phytoplankton nutrient limitation in Colorado
mountain lakes. Freshw. Biol. 20:315-27.
Olem, H., and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Ruttner, F. 1963. Fundamentals of Limnology. Univ. Toronto Press, Ontario, Can.
Schindler, D.W., V.E. Frost, and R.V. Schmidt. 1973. Production of epilithiphyton in two
lakes of the Experimentals Lake Area, Northwestern Ontario. J. Fish. Res. Board Can
30:1511-24.
297
-------
Fish and Fisheries Management in Lakes and Reservoirs
Scott, W.B. and E.J. Grossman. 1973. Freshwater Fishes of Canada. Bull. 184. Fish. Res.
Board Can., Ottawa, Can.
Shapiro, J., V. Lamarra, and M. Lynch. 1975. Biomanipulation: An ecosystem approach to
lake restoration. Pages 85-96. in P.L. Brezonik and J.L. Fox, eds. Proc. Symp. Water
Qual. Manage, through Biolog. Control. Univ. Florida Press, Gainesville, PL.
Sondergaard, M., and K. Sand-Jensen. 1978. Total autotrophic production in oligotrophic
Lake Kalgaard, Denmark. Verh. Int. Ver. Limnol. 20:667-73.
Thornton, K.W., B.L. Kimmel, and F.E. Payne. 1990. Reservoir Limnology: Ecological
Perspectives. John Wiley & Sons, New York, NY.
Wetzel, R.G. 1975. Limnology. W.B. Saunders Co., Philadelphia, PA.
. 1983. Limnology. 2d ed. W.B. Saunders Co., Philadelphia, PA.
For Further Reading
Many basic texts are available on the ecology of lakes and reservoirs. Good examples in-
clude the following:
Goldman, C.R., and A.J. Home. 1983. Limnology. McGraw-Hill, New York, NY.
Moss, B. 1980. Ecology of Freshwaters. Blackwell Publ., Oxford, England.
Thornton, K.W., B.L. Kimmel, and F.E. Payne. 1990. Reservoir Limnology: Ecological
Perspectives. John Wiley & Sons, New York, NY.
Wetzel, C.G. 1983. Limnology. W.B. Saunders Company, Philadelphia, PA.
Wetzel, R.G., and G.E. Likens. 1990. Limnological Analyses. Springer-Verlag, New York,
NY.
Useful reference books on specific topics include the following:
Jorgenson, S.E., and R.A. Vollenweider. 1989. Guidelines of Lake Management. Vol. 1, Prin-
ciples of Lake Management. Int. Lake Environ. Comm., United Nations Environ. Prog.,
New York, NY.
Merritt, R.W., and K.W. Cummins, ed. 1983. An Introduction to the Aquatic Insects of
North America. Kendall/Hunt Publ. Co., Dubuque, I A.
Pennak, R.W. 1978. 2d ed. Fresh-water Invertebrates of the United States. John Wiley &
Sons, New York, NY.
Prescott, G.W. 1969. How to Know the Aquatic Plants. Wm. C. Brown Co., Dubuque, IA.
Ward, H.B., and G.C. Whipple. 1959. Fresh Water Biology. John Wiley & Sons, New York,
NY.
Chapter 3
Anderson, R.0.1976. Management of small warm water impoundments. Fisheries l(6):5-7;
26-8.
Anderson, R.O., S.J. Gutreuter. 1983. Length, weight, and associated structural indices.
Pages 283-300 in L.A. Nielsen and D.L. Johnson, eds. Fisheries Techniques. Am. Fish.
Soc., Bethesda, MD.
Baker, J., and S. Christensen. 1991. Effects of acidification on aquatic biota. Pages 83-106 in
D.F. Charles, ed. Acidic Precipitation and Surface Water Acidification: Regional Case
Studies. Spring-Verlag, New York, NY.
Champeau, T.R., and K.W. Denson. 1989. Effectiveness of a catch-and-release regulation for
largemouth bass in a Florida lake. Pages 241-52 in R.A. Barnhart and T.D. Roelofs, eds.
Catch-and-Release Fishing: A Decade of Experience. Humboldt State Univ., Arcata,
CA.
Chapman, P., and W.V. Fish. 1985. Largemouth bass tournament catch results in Florida.
Proc. Annu. Southe. Ass. Fish Wildl. Agencies 37:495-505.
Cone, R.S. 1989. The need to reconsider the use of condition indices in fishery science.
Trans. Am. Fish. Soc. 118:510-14.
. 1990. Comments: Properties of relative weight and other condition indices. Trans.
Amer. Fish. Soc. 1991; 1048-58.
298
-------
References
Cooper, G.P., and G.N. Washburn. 1946. Relation of dissolved oxygen to winter mortality
in fish in Michigan lakes. Trans. Am. Fish. Soc. 76:23-33.
Coutant, C.C. 1985. Striped bass, temperature, and dissolved oxygen: A speculative
hypothesis for environmental risk. Trans. Am. Fish. Soc. 114:31-61.
Elliot, J.M. 1981. Some aspects of thermal stress on freshwater teleosts. Pages 209-45 in
A.D. Pickering, ed. Stress and Fish. Academic Press, London, England.
Gablehouse, D.W. Jr. 1984. A length-categorization systein to assess fish stocks. N. Am J.
Fish. Manage. 4:273-85.
Gauch, H.G. Jr. 1982. Multivariate Analysis in Community Ecology. Cambridge Univ.
Press, England.
Gustaveson, A.W., R.S. Wydoski, and G.A. Wedemyer. 1991. Physiological response of
largemouth bass to angling stress. Trans. Am. Fish. Soc. 120:629-36.
Hall, D.J., and TJ. Ehlinger. 1989. Perturbation, planktivbry, and pelagic community struc-
ture: The consequence of winterkill in a small lake. Can. J. Fish. Aquat Sci. 46:2203-09.
Hall, G.E., and M.J. Van Den Avyle, eds. 1986. Reservoir Fisheries Management: Strategies
for the 80s. Am. Fish. Soc., Bethesda, MD.
Hebert, P.D.N. 1991. Introduction. Symposium on the Ecological and Genetic Implications
of Fish Introductions (FIN). Can. J. Fish. Aquat. Sci. 48:5-6.
Hill, M.O., and H.G. Gauch, Jr. 1980. Detrended correspondence analysis, an improved or-
dination technique. Vegetation 42:47-58.
Hindi, S.G., N.C. Collins, and H.H. Harvey. 1991. Relative abundance of littoral zone
fishes: Biotic interactions, abiotic factors, and postglacial colonization. Ecology
72:1314-24.
Inskip, P.O., and J.J. Magnuson. 1983. Changes in fish populations over an 80-year period:
Big Pine Lake, Wisconsin. Trans. Am. Fish. Soc. 112:378-89.
Jackson, D. A. 1988. Fish communities in lakes of the Black and Hollow River watersheds,
Ontario. Thesis. Univ. Toronto, Ontario, Can.
LeCren, E.D. 1951. The length-weight relationship and seasonal cycle in gonal weight and
condition in perch (Percaflavescens). J. Animal Ecol. 20:201-19.
Lee, D.P. 1989. Mortality of tounament caught and released black bass in California. Pages
207-16 in R.A. Barnhart and T.D. Roelofs, eds. Catch-and-Release Fishing: A Decade of
Experience. Humboldt State Univ., Arcata, CA.
Magnuson, J.J. 1991. Fish and fisheries ecology. Ecol. Appl. 1:13-26.
Manny, B.A., R.G. Wetzel, and W.C. Johnson. 1975. Annual contribution of carbon,
nitrogen, and phosphorus by migrant Canada geese to a hardwater lake. Verh. hit.
Ver. Theor. Angew. Limnol. 19:949-51.
Matthews, W.J. 1985. Summer mortality of striped bass in reservoirs of the United States.
Trans. Am. Fish. Soc. 114:62-66.
McComas, S. In press. Lake Maintenance Handbook. Terrene Inst., Washington, DC.
Minns, C.K. 1989. Factors affecting fish species richness in Ontario lakes. Trans. Am. Fish.
Soc. 118:533-45.
Moore, W.G. 1942. Field studies on the oxygen requirements of certain freshwater fishes;
Ecology 23:319-29.
Murphy, B.R., D.W. Willis, and T.A. Springer. 1991. The relative weight index in fisheries
management: Status and needs. Fisheries 16:30-8.
Nelson, K., and M. Soule. 1987. Genetic conservation of exploited fishes. Pages 345-68 in
N. Ryman and F. Utter, eds. Population Genetics and Fisheries Management. Univ.
Washington Press, Seattle, WA.
Newman, M.J., M.L. Merril, and F. Hamilton. 1989. Eufaula Reservoir Management Report
1988. Game Fish Div., Alabama Dep. Conserv. Nat. Resour., Montgomery, AL.
Ontario Ministry of Natural Resources. 1983. The Identification of Overexploitation:
Strategic Planning for Ontario Fisheries. Rep. SPOF Working Group No. 15. Toronto,
Can.
Rabern, D.A. 1989. Factors Influencing Year-Class Strength of Walleye hi Lake Burton,
Georgia. Proj. N. F-25, Georgia Dep. Nat. Resour., Atlanta, GA.
Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish popula-
tions. Bull. Fish. Res. Board Can. No. 191:1-382.
299
-------
Fish and Fisheries Management in Lakes and Reservoirs
Roedel, P.M., ed. 1975. Symposium on optimum sustainable yield as a concept of fisheries
management. Spec. Publ. No. 9. Am. Fish. Soc., Bethesda, MD.
Ryder, R. A. 1965. A method for estimating the potential fish production for north-temperate
lakes. Trans. Am. Fish. Soc. 94:214-18.
. 1982. The morphoedaphic index: Use, abuse, and fundamental concepts. Trans.
Am. Fish. Soc. 111:154-64.
Ryman, N., and F. Utter, eds. 1987. Population Genetics and Fisheries Management. Univ.
Washington Press, Seattle, WA.
Scott, W.B., and E.J. Grossman. 1973. Freshwater Fishes of Canada. Bull. 184. Fish. Res.
Board Can., Ottawa, Can.
Shelton, W.L., W.D. Davies, T.A. King, and T.J. Timmons. 1979. Variantion in the growth of
the initial year class of largemouth bass in West Point Reservoir, Alabama and Georgia.
Trans. Am. Fish. Soc. 108:142-49.
Standard Methods for the Examination of Water and Wastewater. 1971, 13th ed. Joint
Editorial Board, Am. Pub. Health Ass., Am. Water Works Ass., and Water Pollut. Con-
trol Fed., Washington, DC.
Tonn, W.M., and J.J. Magnuson. 1982. Patterns in the species composition and richness of
fish assemblages in northern Wisconsin lakes. Ecology 63:1149-66.
Tonn, W.M., JJ. Magnuson, and AJ. Forbes. 1983. Community analysis in fishery manage-
ment: An application with northern Wisconsin lakes. Trans. Am. Fish. Soc. 112:638-77.
U.S. Environmental Protection Agency. 1987. Quality Criteria for Water 1986. EPA 440/5-86-
001. Off. Water Reg. Stand., Washington, DC.
Utter, F., P. Aebersold, and G. Winans. 1987. Interpreting genetic variation detected by
electrophoresis. Pages 21-46 in N. Ryman and F. Utter, eds. Population Genetics and
Fisheries Management. Univ. Washington Press, Seattle, WA.
Wege, G.J., and R.Q. Anderson. 1978. Relative weight (Wr): A new index of condition for
largemouth bass. Pages 79-91 in G.D. Novinger and J.G. Dillard, eds. New Approaches
to the Management of Small Impoundments. N. Central Div. Spec. Publ. 5, Am. Fish.
Soc., Bethesda, MD. . „. v
Whitmore, D.H., ed. 1990. Electrophoretic and Isoelectric Focusing Techniques in Fisheries
Management. CRC Press, Boca Raton, FL.
Wootton, R.J. 1990. Ecology of Teleost Fishes. Chapman and Hall, New York, NY.
Zale, A.V., J.D. Wiechman, R.L. Lochmiller, and J. Burroughs. 1990. Limnological conditions
associated with summer mortality of striped bass in Keystone Reservoir, Oklahoma.
Trans. Am. Fish. Soc. 119:72-6.
For Further Reading
A number of general texts are available on fish ecology and fisheries management that pro-
vide further detail on the topics discussed in this chapter. Examples include the following:
Bennett, G.W. 1971. Management of Lakes and Ponds. Van Nostrand Reinhold Co., New
York, NY. ,,
Cairns, V.W., P.V. Hodson, and J.O. Nriagu. 1984. Contaminant Effects on Fisheries. John
Wiley & Sons, New York, NY.
Everhart, W.H. and W.D. Youngs. 1981. Principles of Fishery Science. Cornell University
Press, Ithaca, NY.
Gerking, S.D. 1978. Ecology of Freshwater Fish Production. Blackwell Sci. Publ.,
Cambridge, MA.
Hall, G.E., and M.J. Van Den Avyle, ed. 1986. Reservoir Fisheries Management: Strategies
for the 80s. Am. Fish. Soc., Bethesda, MD.
Lackey, R.T., and L.A. Nielson. 1980. Fisheries Management. John Wiley & Sons, New York,
NY.
Pitcher, T.J. and P.B. Hart. 1983. Fisheries Ecology. AVI Publ., Westport, CT.
Schreck, C.B., and P.B. Moyle. 1990. Methods for Fish Biology. Am. Fish. Soc., Bethesda, MD.
Wootton, R.J. 1990. Ecology of Teleost Fishes. Chapman and Hall, New York, NY.
300
-------
References
Chapter 4
Canadian Department of Fisheries and Oceans. 1988. Sport Fishing in Canada, 1985.
DFO/3823, Commun. Directorate Bull., Ottawa, Ontario, Can.
Magnuson, J.J. 1991. Fish and fisheries ecology. Ecol. Appl. 1:13-26.
Olem, H., and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Omernik, J.M. 1987. Ecoregions of the conterminous United States. Freshw. Am. Ass. Am.
Geogr. 77(l):118-25. . ,
Radonski, G.C., and R.G. Martin. 1985. Fisheries advances since the thirties. Fisheries
10(3):2-4.
U.S. Fish and Wildlife Service. 1988. National Survey of Fishing, Hunting, and Wildlife As-
sociated Recreation. U.S. Dep. Int., Washington, DC.
Walters, C. 1986. Adaptive Management of Renewable Resources. Macmillan, New York,
NY. . . ,
Chapter 5
Beale, L., and R. Fields. 1987. The Win/Win Way. Harcroft, Brace, Jovanovich, Orlando, FL.
Bishop, R.C., K.J. Boyle, and M.P. Welsh. 1987. Toward total economic valuation of Great
Lakes fishery resources. Trans. Ani. Fish. Soc. 116:339-45.
Brown, T.L. 1987. Typology of human dimensions information needed for Great Lakes
sport-fisheries management. Trans. Am. Fish. Soc. 116:320-24.
Carpenter, S. 1988. Managing Public Disputes. Jossey-Bass Publ., San Francisco, CA.
Delbecq, A., A. VanDeVer, and D. Gustafson. 1975. Group Techniques for Program Plan-
ning: A Guide to Nominal Group and Delphi Processes. Scott, Foresman, and Co.,
Glenview, IL.
Dochoda, M.R., and CM. Fetterolf, Jr. 1987. Public purpose of Great Lakes fishery
management: Lessons from the management experience. Trans. Am. Fish. Soc.
116:302-08.
Doyle, M., and D. Strauss. 1982. How To Make Meetings Work. Berkley Publ. Group, New
York, NY.
Engel, S. 1989. Lake use planning in local efforts to manage lakes. Pages 101-05 in Proc.
Natl. Conf. Enhancing States' Lake Management Programs. Northe. 111. Plann.
Comm., Chicago, IL.
Gregory, R. 1987. Nonmonetary measures of nonmarket fishery resource benefits. Trans.
Am. Fish. Soc. 116:374-80.
Hance, B.J., C. Chess, and P.M. Sandman. 1990. Improving dialogue with communities: A
risk communication manual for government. New Jersey Dep. Environ. Prot., New
Brunswick, NJ.
Hoehn, J.P. 1987. Contingent valuation in fisheries management: The design of satisfactory
contingent valuation formats. Trans. Am. Fish. Soc 116:412-19.
Karr, J.R. 1991. Biological integrity: A long neglected aspect of water resource manage-
ment. Ecol. Appl. 1:66-84.
Karr, J.R., and D.R. Dudley. 1981. Ecological perspective on water quality goals. Environ.
Manage. 5:55-68.
Nathan, E.D. 1979.24 Questions in Group Leadership, 2nd ed. Addison-Wesley Publ. Co.,
Reading, MA.
Pinkerton, E. 1989. Co-operative Management of Local Fisheries. Univ. of British Colum-
bia Press, Vancouver, BC, Can.
Renton, M. 1980. Getting Better Results from the Meetings You Run. Research Press,
Champaign, IL.
Stoffle, R.W., F.W. Jensen, and D.L. Rasch. 1987. Cultural basis of sport anglers' response to
reduced lake trout catch limits. Trans. Am. Fish. Soc. 116:503-09.
Talheim, D.R., and L.W. Libby. 1987. In search of a total value assessment framework:
SAFR symposium overview and synthesis. Trans. Am. Fish. Soc. 116:293-301.
301
-------
r
Fish and Fisheries Management in Lakes and Reservoirs
Talheim, D.R., J.E. Hanna, and P. Victor. 1987. Product travel cost approach: Estimating acid
rain damage to sportfishing in Ontario. Trans. Am. Fish. Soc. 116:420-31.
U.S. Environmental Protection Agency. 1988. WQS Draft Framework for the Water Quality
Standards Program. Off. Water, Washington, DC.
. 1990. Biological Criteria: National Program Guidance for Surface Waters. Off. Water,
Washington, DC.
Yarbrough, C.J. 1987. Using political theory in fishery management. Trans. Am. Fish. Soc.
116:532-36.
Chapter 6
Adams, S.M., ed. 1990. Biological Indicators of Stress in Fish. Am. Fish. Soc. Symp. 8,
Bethesda, MD. (
Billington, N., and P.N. Hebert, eds. 1991. Internat. Symp.: The Ecological and Genetic Im-
plications of Fish Introductions (FIN). Can. J. Fish. Aquat. Sci. 48:1-181.
Colby, P.G. 1984. Appraising the status of fisheries: Rehabilitation techniques. Pages 233-57
in V.W. Cairns, P.V. Hodson, J.O. Nriagu, eds. Contaminant Effects on Fisheries. Advan-
ces in Environmental Sciences and Technology, Vol. 16. John Wiley and Sons, New
York, NY.
Cooke, G.D., E.B. Welch, S. A. Peterson, P.R. Newroth. 1986. Lake and Reservoir Restoration.
Butterworth Publ., Stoneham, MA.
DiGiulio, R. 1989. Biomarkers. Chapter 7 in W. Warren-Hicks, B. Parkhurst, and S. Baker, Jr.,
eds. Ecological Assessment of Hazardous Waste Sites: A Field and Laboratory Refer-
ence. EPA/600/3-89/013. U.S. Environ. Prot. Agency, Corvallis, OR.
Edwards, C.J., R.A. Ryder, and T.R. Marshall. 1990. Using lake trout as a surrogate of
ecosystem health for oligotrophic waters of the Great Lakes. J. Great Lakes Res. 16:591-
608.
Entrance Engineers. 1983. Water Quality Analysis and Restoration Plan for Erie and
Campbell Lakes. Bellevue, WA.
. 1987. Erie and Campbell Lakes, Final Report Restoration and Implementation.
Kirkland,WA.
Evans, D.O., G.J. Warren, and V.W. Cairns. 1990. Assessment and management of fish com-
munity health in the Great Lakes: Synthesis and recommendations. J. Great Lakes Res.
16:639-69.
Goede, R.W. 1988. Fish Health/Condition Assessment Procedures. Utah Div. Wildl. Resour.,
Fish. Exp. Sta., Logan, UT.
Goede, R.W., and B.A. Barton. 1990. Organomismic indices and an autopsy based assess-
ment as indicators of health and condition of fish. Pages 93-108 in Vol. 8. Am. Fish. Soc.
Symp., Bethesda, MD.
Karr, J.R. 1981. Assessment of biotic integrity using fish communities. Fisheries 621-7.
. 1991. Biological integrity: A long-neglected aspect of water resource management.
Ecol. Appl. 1:66-84.
Karr, J.R., K.D. Fausch, P.O. Angermeier, P.R. Yant, and I.J: Schlosser. 1986. Assessing
biological integrity in running waters: A method and its rationale. 111. Nat. History
Surv. Spec. Pub. 5., Champaign, IL.
Leonard, P.M., and DJ. Orth. 1986. Application and testing of an index of biotic integrity in
small, coolwater streams. Trans. Am. Fish. Soc. 115:401-14.
Marshall, T. 1992. Personal communication. Productivity Unit. Ontario Ministry Nat.
Sesour., Thunder Bay, Ontario, Can.
Marshall, T.R., R.A. Ryder, C.J. Edwards, and G.R. Spangler. 1987. Using the lake trout as an
indicator of ecosystem health — Application of the Dichotomous Key. Great Lakes Fish.
Comm., Tech. Rep. 49. Ann Arbor, MI.
Meyer, P.P., and L.A. Barclay, eds. 1990. Field Manual for the Investigation of Fish Kills.
Resour. Pub. 177, Fish Wildl. Serv., U.S. Dep. Int., Washington, DC.
Miller, D.L. et al. 1988. Regional applications of an index of biotic integrity for use in water
resource management. Fisheries 13:12-20.
302
-------
References
Munkittrick, K.R., and D.G. Dixon. 1989. Use of white sucker (Catostomus commersoni)
populations to assess the health of aquatic ecosystems exposed to low-level con-
taiminant stress. Can. J. Fish. Aquat. Sci. 46:1455-62.
Niimi, A.J. 1990. Review of biochemical methods and other indicators to assess fish health
in aquatic ecosystems containing toxic chemicals. J. Great Lakes Res. 16:529-41.
Olem, H., and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Rapport, D.J. 1990. Challenges in the detection and diagnosis of pathological change in
aquatic ecosystems. J. Great Lakes Res. 16:609-18.
Ryder, R.A., and C.J. Edwards, eds. 1985. A conceptual approach for the application of
biological indicators of ecosystem quality in the Great Lakes basin. Rep. Great Lakes
Sci. Advisory Board, Int. Joint Comm,, Great Lakes Fish. Comm., Windsor, Ontario,
Can.
Spigarelli, S.A., ed. 1990. Fish community health: Monitoring and assessment in large
lakes. J. Great Lakes Res. 16:493-669.
Steedman, R.J. 1988. Modification and assessment of an index of biotic integrity to quan-
tify stream quality in Ontario, Can. J. Fish. Aquat. Sci. 45:492-501.
Woock, S.E. 1984. Accumulation of Selenium in Golden Shiner (Notemigonus crysoleucas)
Hyco Reservoir, NC, Cage Study 1981-1982. Rep. Carolina Power Light, New Hill,
NC.
Woock, S.E., and P.B. Summers, Jr. 1984. Selenium monitoring in Hyco Reservoir, NC,
waters (1977-1981) and biota (1977-1980). Pages 6-1 to 6-27 in Workshop Proc. Effects
of Trace Elements on Aquatic Ecosystems. EA-3329. Electric Power Res. Inst., Palo
Alto,CA.
Chapter 7
National Wildlife Federation. 1991. Conservation Directory. Washington, DC.
Olem, H. and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC
Chapter 8
Allendorf, F.W. 1991. Ecological and genetic effects of fish introductions: Synthesis and
recommendations. Can J. Fish. Aquat. Sci. 48:178-81.
Andersson, G., H. Berggren, and S. Hambrin. 1975. Lake Trummen restoration project. III.
Zooplankton macrobenthos and fish. Verh. Int. Ver. Limnol. 19:1097.
Aquatic Systems Engineering. 1990. Assessment and guide for meeting dissolved oxygen
water quality standards in hydroelectric plant discharges. EPRI GS-7001. Electric
Power Res. Inst., Palo Alto, CA.
Bengtsson, L., S. Fleischer, G. Lindmark, and W. Ripl. 1975. Lake Trummen restoration
project. I. Water and sediment chemistry. Verh. Int. Ver. Limnol. 19:1080-87.
Bennett, D.H., and T.J. McArthur. 1990. Predicting success of walleye stocking programs in
the United States and Canada. Fisheries 15:19-23.
Berger, B.L., R.E. Lennon, and J.W. Hogan. 1969. Laboratory studies on antimycin as a fish
toxicant. Invest, in Fish Control No. 26, U.S. Bur. Sport Fish. Wildl., Washington, DC.
Brocksen, R., M. Marcus, and H. Olem. 1992. Practical Guide to Managing Acidic Surface
Waters and their Fisheries. Lewis Publ. Inc., Chelsea, MI.
Brousseau, C.S., and E.R. Armstrong. 1978. The role of size limits in walleye management.
Fisheries 12:2-5.
Brown, A.M. 1986. Modifying reservoir fish habitat with artificial structures. Pages 98-102
in G.E. Hall and M.J. Van Den Avyle, eds. Reservoir Fisheries Management: Strategies
for the 80s. Am. Fish. Soc., Bethesda, MD.
Burns, F.L. 1988. Aeration of lakes and reservoirs in Australia. Pres. N. Am. Lake Manage.
Soc. Annu. Meet., St. Louis, MO.
California Department of Fish and Game. 1985. Rotenone Use for Fisheries Management.
Environ. Serv. Branch, Pesticide Invest. Unit, Rancho Cordova, CA.
303
-------
Fish and Fisheries Management in Lakes and Reservoirs
Canfield, D.E. Jr., K.A. Langeland, S.B. Linda, and W.T. Haller. 1985. Relations between
water transparency and maximum depth of macrophyte colonization in lakes. J. Aquat.
Plant Manage. 23:25-8.
Carline, R.F. 1980. Features of successful spawning site development for brook trout in Wis-
consin ponds. Trans. Am. Fish. Soc. 109:453-7.
Conyers, D.L., and G.D. Cooke. 1983. A comparison of the costs of harvesting and her-
bicides and their effectiveness hi nutrient removal and control of macrophyte biomass.
Pages 317-21 in Lake Restoration, Protection, and Management. EPA-440/5-83-001. U.S.
Environ. Prot. Agency, Washington, DC.
Cooke, G.D., R.T. Heath, R.H. Kennedy, and M.R. McComas. 1982. Change in lake trophic
state and internal phosphorus release after aluminum sulfate application. Water Res.
Bull. 18:699-705.
Cooke, G.D., E.B. Welch, S.A. Peterson, and PR. Newroth. 1986. Lake and Reservoir Res-
toration. Butterworth Publ., Stoneham, MA.
Cronberg, G., C. Gelin, and K. Larsson. 1975. Lake Trummen restoration project, n. Bacteria,
phytoplankton, and phytoplankton productivity. Verh. Int. Ver. Limnol. 19:1088-96.
DeVries, D.R., R.A. Stein, J.G. Miner, and G.G. Mittelbach. 1991. Stocking threadfin shad:
Consequences for young-of-year fishes. Trans. Am. Fish. Soc. 120:368-81.
Dominie, J.R. 1980. Hypolimnetic aluminum treatment of softwater Annabessacook Lake.
Pages 417-23 in Restoration of Lakes and Inland Waters. EPA-440/5-81-010. U.S. En-
viron. Prot. Agency, Washington, DC.
Donald, D.B., and R.S. Anderson. 1982. Importance of environment and stocking density for
growth of rainbow trout in mountain lakes. Trans. Am. Fish. Soc. 111:675-80.
Dunst, R.C., J.G. Vennie, R.B. Correy, and A.E. Peterson. 1984. Effect of dredging Lilly Lake,
Wisconsin. EPA-600/3-84-097. EPA Coop. Agree. No. R804875, Environ. Res. Lab., Cor-
vallis, OR.
Engel, S. 1984. Evaluating'stationary blankets and removable screens for macrophyte con-
trol hi lakes. J. Aquat. Plant Manage. 22:43-8.
. 1989. Lake use planning in local efforts to manage lakes. Pages 101-105 in Enhanc-
ing States' Lake Management Programs. N. Am. Lake Manage. Soc., Washington, DC.
Eschmeyer, P.D., ed. 1975. Symposium on Rehabilitation of Fish Populations with Fish
Tqxicants. N. Central Div., Am. Fish. Soc., Bethesda, MD.
Evans, J.W. 1989. Objectives and guidelines for aquatic plant management in Georgia. Geor-
gia Dep. Nat. Resour., Game Fish Div., Forf Valley, GA.
Everhart, W.H., and W.D. Youngs. 1981. Principles of Fishery Science. Cornell Univer. Press,
Ithaca, NY.
Fast, A.W., V.A. Dorr, and R.J. Rosen. 1975. A submerged hypolimnion aerator. Water
Resour. Res. 11:287-93.
Fraser, J.E., et al. 1985. Acid Precipitation Mitigation Program (APMP) Guidance Manual.
Vol. H, Liming Materials Methods. Biol. Rep. 80(40.25). U.S. Fish & Wildl. Serv.,
Washington, DC.
Fraser, J.E., et al. 1982. Feasibility Study to Utilize Liming as a Technique to Mitigate Surface
Water Acidification. EPRI EA-2362, Project 1109H-14. Electric Power Res. Inst., Palo
Alto, CA. ^,_
Fiirst, M., J. Hammar, and C. Hill. 1.986. The introduction of My sis relicta in SweedertTEfiects
on fish species in impounded lakes. EIFAC Symp. Habitat Modification and Freshw.
Fish., Aarhus, Den.
Gachter, R. 1976. Die Tiefenwasserableitung, ein Weg zur Sanierung von Seen. Schweiz Z
Hydrol. 38:1-28.
Gallagher, J.W., and G.V. Mauldin. 1987. Oxygenation of releases from Richard B. Russell
Dam. Pages 121-24 in Proc. CE Workshop on Reserv. Releases. U.S. Army Corp. Eng.,
Vicksburg, MS.
Garrison, P.JV and D.R. Knauer. 1984. Long-term evaluation of three alum treated lakes.
Pages 513-17 in Lake and Reservoir Management. EPA-440/5-84-001, U.S. Environ.
Prot. Agency, Washington, DC.
Gasperino, A.F. et al. 1980. Medical Lake improvement project: Success story. Pages J424-28
in Restoration of Lakes and Inland Waters. EPA-440/5-81-010. U.S. Environ. Prot.
Agency, Washington, DC.
304
-------
References
Geiger, N.S. 1983. Winter drawdown for the control of Eurasian watermilfoil in an Oregon
oxbow lake (Blue Lake, Multnomah County). Pages 193-97 in Lake Restoration,
Protection, and Management. EPA-440/5-83-001. U.S. Environ. Prot. Agency,
Washington, DC.
Georgia Department of Natural Resources. 1988. Management of Georgia Fish Ponds.
Game Fish. Div., Atlanta, GA.
Gilderhus, P.A., B.L. Berger, and R.E. Lennon. 1969. Field Trials of Antimycin A as a Fish
Toxicant: Investigations in Fish Control 27. U.S. Bur. Sport Fish. Wildl., Washington,
DC.
Haag, K.H. 1986. Effective control of waterhyacinth using Neocketina and limited herbicide
application. J. Aquat. Plant Manage. 24:70-5.
Halsey, T.G. 1968. Autumnal and overwinter limnology of three small eutrophic lakes with
particular reference to experimental circulation and trout mortality. J. Fish. Res. Board
Can. 25:81-99.
Havey, K.A. 1973. Effects of a smelt introduction on growth of landlocked salmon at
Schoodic Lake, Maine. Trans. Am. Fish. Soc. 102:392-7.
Hebert, P.D.N. 1991. Intro. Int. Symp. on the Ecological and Genetic Implications of Fish
Introductions (FIN). Can. J. Fish. Aquat. Sci. 48:5-6.
Hill, KR. 1986. Classification of Iowa lakes and their fish standing stock. Lake Reserv.
Manage. 2:105-9.
Howells, R.G. 1986. Guide to techniques for establishing woody and herbaceous vegeta-
tion in the fluctuation zones of Texas reservoirs. Fed. Aid in Spot Fish Restor. Proj. F-
31-R-12, Texas Parks Wildl. Dep., Austin, TX.
Illinois Department of Conservation. Undated a. Small Lakes and Ponds: Their Construc-
tion and Care. Fish. Bull. No. 3. Div. Fish., Springfield, IL.
. Undated b. Rotenone for Eradication of Undesirable Fish in Management of Lakes
and Ponds. Leaflet No. 5. Fish Wildl. Resour. Div. Springfield, IL.
1989. Management of Small Lakes and Ponds in Illinois. 2d ed. Div., Fish.,
Springfield, IL.
Iowa Department of Natural Resources. Undated. Iowa's Farm Ponds. Des Moines, IA.
Jorgensen, S.E., and R.A. Vollenweider. 1989. Guidelines of Lake Management. Vol. 1,
Principles of Lake Management. Int. Lake Environ. Comm., U.N. Environ. Progv New
York, NY.
Kinsten, B., and P. Olsen. 1981. Impact of Mysis relicta introduction on the plankton of two
mountain lakes. Sweden Inst. Freshw. Res. Drottningholm 59:64-74.
Kortmann, R.W. 1989. Aeration: Technologies and sizing methods. Lake Line 9:6-7 and 18-
19.
Kortmann, R.W., E. Davis, C.R. Frink, and D.D. Henry. 1983. Hypolimnetic withdrawal:
Restoration of Lake Wonoscopomuc, Connecticut. Pages 46-55 in Lake Restoration,
Protection and Management. EPA-440/5-83-001. U.S. Environ. Pro. Agency,
Washington, DC.
Lackey, R.T. 1972. Response of physical and chemical parameters to eliminating thermal
stratification in a reservoir. Water Res. Bull. 8:589-99.
Lasenby, D.C., T.G. Northcote, and M. Furst. 1986. Theory, practice, and effects of Mysis
relkta introductions to North American and Scandinavian lakes. Can. J. Fish. Aquat.
Sci. 43:1277-84.
Leach, J.H., and C.A. Lewis. 1991. Fish introductions in Canada: Provincial views and
regulations. Can. J. Fish. Aquat. Sci. 48:156-61.
Li, H.W., and P.B. Moyle. 1981. Ecological analysis of species introductions into aquatic
systems. Trans. Am. Fish. Soc. 110:772-82.
Lorenzen, M.W., and A.W. Fast. 1977. A Guide to Aeration/Circulation Techniques for
Lake Management. EPA-600/3-77-004. U.S. Environ. Pro. Agency, Washington, DC.
Matuszek, J.E., B.J. Shuter, and J.M. Casselman. 1990. Changes in lake trout growth and
abundance after introduction of Cisco into Lake Opeongo, Ontario. Trans. Am. Fish.
Soc. 119:718-29.
Mauldin, G., R. Miller, J. Gallagher, and R.E. Speece. 1988. Injecting an oxygen fix. Civil
Eng. March 1988:54-6.
3O5
-------
Fish and Fisheries Management In Lakes and Reservoirs
Mayhew, J.K., and S.T. Runkel. 1962. The control of nuisance aquatic vegetation with black
polyethylene plastic. Proc. Iowa Acad. Sci. 69:302-7.,
McComas, S. In press. Lake Maintenance Handbook. Terrene Inst., Washington, DC.
Minnesota Department of Natural Resources. 1975. Evaluation of an Improved Walleye
Spawning Shoal with Criteria for Design and Placement. Invest. Rep. 340. St. Paul, MN.
. 1982. Lake Management Planning Guide. Spec. Publ. No. 132. Div. Fish Wildl., St.
Paul, MN.
Morgan, M.D., ed. 1982. Ecology of Mysidacea. W. Junk Publ., The Hague, The Neth.
Mosher, T.D. 1983. Effects of artificial circulation on fish distribution and angling success for
channel catfish in a small prarie lake. N. Am. J. Fish. Manage. 3:403-9.
Mosher, T.D., ed. 1984. A Guide to the Management of Community Sport Fisheries. Kansas
Fish Game Comm., Emporia, KS.
Newroth, P.R., and R.J. Soar. 1986. Eurasian watermilfoil management using newly
developed technologies. Lake Reser. Manage. 2:252-7.
Nicholson, S.A. 1981. Changes in submersed macrophytes in Chautauqua Lake, 1937-75.
Freshw. Biol. 11:523-30.
Oklahoma Department of Wildlife Conservation. 1984. Pond Management in Oklahoma.
Fish Div., Oklahoma City, OK..
Olem, H. 1991. Liming Acidic Surface Waters. Lewis Publ., Inc., Chelsea, MI.
Olem, H., and G. Flock eds. 1990. The Lake and Reservoir Restoration Guidance Manual. 2d
ed. EPA 440/4-90-006. U.S. Environ. Pro. Agency, Washington, DC.
Ontario Ministry of Natural Resources. 1991. Working around water? What you should
know about fish habitat. Fact sheets. Toronto, Ontario, Can.
Perkins, M.A. 1983. Limnolpgical characteristics of Green Lake: Phase I restoration analysis.
Dep. Civil Eng., Univ. Washington, Seattle, WA.
Peterson, J.O., J.T. WaU, T.L. Wirth, and S.M. Born. 1973. Eutrophication control: Nutrient in-
activation by chemical precipitation at Horseshoe Lake, Wisconsin. Tech. Bull. 62. Wis-
consin Dep. Nat. Resour., Madison, WL
Phillips, S.H. 1990. A Guide to the Construction of Freshwater Artificial Reefs. Artificial Reef
Dev. Center, Sport Fishing Inst., Washington, DC.
Pierce, B.E., and G.R. Hooper. 1979. Fish standing crop comparisons of tire and brush fish
attrartors inBarkley Lake, Kentucky. Proc. Annu. Conf. S.E. Assoc. Fish Wildl. Agencies
33:688-91.
Ploskey, G.R. 1982. Effects of water-level changes on reservoir ecosystems, fish, and fishing,
with guidance on reservoir operations to enhance fisheries. Tech. Rep. 81. U.S. Fish
Wildl. Serv., Washington, DC. ~~~
. 1986. Effects of water-level changes on reservoir ecosystems, with implications for
fisheries management. Pages 86-97 in G.E. Hall and M.J. Van Den Avyle, eds. Reservoir
Fisheries Management: Strategies for the 80s. Am. Fish. Soc., Bethesda, MD.
Richards, R.C., C.R. Goldman, T.C. Frantz, and R. Wickwire. 1975. Where have all the Daph-
nia gone? The decline of a major cladoceran in Lake Tahoe, California-Nevada. Int. Ver.
Theor. Angew. Limnol. 19:835-43.
Rieman, B.E., and B. Bowler. 1980. Trophic ecology of kokanee and limnology in Pend
Orielle Lake. Bull. 1. Idaho Fish Game Fish., Boise, ID.
Rieman, B.E., and C.M. Falter. 1981. Effects of the establishment of Mysis relkta on the mac-
rozooplankton of a large lake. Trans. Am. Fish. Soc. 110:613-20.
Ripl, W. 1976. Biochemical oxidation of polluted lake sediment with nitrate: A new restora-
tion method. Ambio 5:132-35.
Ripl, W., and G. Lindmark. 1978. Ecosystem control by nitrogen metabolism in sediment.
Vatten 34:135-44.
Sanders, D.R. Sr., and E.A. Theriot. 1986. Large-scale operations management test (LSOMT)
of insects and pathogens for control of waterhyacinth in Louisiana. II. Results for 1982-
83. Tech. Rep. A-85-1. U.S. Army Corps Eng., Vicksburg, MS.
Smith, S.A., D.R. Knauer, and T.L. Wirth. 1975. Aeration as a lake management technique.
Tech. Bull. No. 87. Wisconsin Dep. Nat. Resour., Madison, WL
Soltero, R.A., D.G. Nichols, A.F. Gasperino, and M.A. Beckwith. 1981. Lake restoration:
Medical Lake, Washington. J. Freshw. Ecol. 1:155-65.
306
-------
References
Sousa, R.J., EP. Meyer, and R. A. Schnick. 1991. Better Fishing Through Management: How
Retenone is Used to Help Manage Our Fishery Resources More Effectively. U.S. Fish
Wild. Serv., Washington, DC.
Stanley, J.G., R.A. Peoples, Jr., and J.A. McCann. 1991. U.S. federal policies, legislation, and
responsibilities related to importation of exotic fishes and other aquatic organisms.
Can. J. Fish. Aquat. Sci. 48:162-66.
Stewart, P.A.M. 1990. Electric screens and guides. Pages 140-56 in I.G. Cowx and P.
Lamarque, eds. Fishing with Electricity. Applications in Freshwater Fisheries
Management. Blackwell Sci. Publ., Cambridge, MA.
Stroud, R.H., ed. 1986. Fish Culture in Fisheries Management. Proc. Symp. Role of Fish
Culture in Fish. Manage. Lake Ozark, MO. Am. Fish. Soc., Bethesda, MD.
Taggart, C.T., and D.J. McQueen. 1981. Hypolimnetic aeration of a small ertrophic kettle
lake: Physical and chemical changes. Arch. Hydrobiol. 91:150-80.
U.S. Department of Agriculture, Soil Conservation Service. 1982. Ponds: Planning, Design,
and Construction. Agric. Handbook No. 590. U.S. Govern. Printing Off., Washington,
DC.
U.S. Environmental Protection Agency. 1987. Guide to Nonpoint Source Pollution Control.
Off. Water, Washington, DC.
Vogele, L.E., and W.C. Rainwater. 1975. Use of brush shelters as cover by Spawning black
basses (Micropterus) in Bull Shoals Reservoir. Trans. Am. Fish. Soc. 104:264-69.
Welch, E.B., and C.R. Patmont. 1980. Lake restoration by dilution: Moses Lake,
Washington. Water Res. 14:1317-25.
Westerdahl, H.E., and KD. Getsinger, eds. 1988. Aquatic Plant Identification and Her-
bicide Use Guide, Vol. 1 and Vol. II. Aquat. Plant Control Res. Prog. Tech. Rep. A-89-9.
U.S. Army Corp. Eng., Vicksburg, MS.
Wiley, M.J., P.P. Tazik, and S.T. Sobaski. 1987. Controlling aquatic vegetation with triploid
grass carp. Circular 57. 111. Nat. History Surv., Champaign, IL.
Willenbring, P.R., M.S. Miller, and W.D. Weidenbacher. 1984. Reducing sediment phos-
phorus release rates in Long Lake through the use of calcium nitrate. Pages 118-21 in
Lake and Reservoir Management. EPA-440/5-84-001. U.S. Environ. Prot. Agency,
Washington, DC.
Willis, D.W. 1986. Review of water level management of Kansas reservoirs. Pages 110-14 in
G.E. Hall and M.J. Van Den Avyle, eds. Reservoir Fisheries Management: Strategies
for the 80s. Am. Fish Soc., Bethesda, MD.
Wingate, P.J. 1991. U.S. State's view and regulations on fish introductions. Can. J. Fish.
Aquat. Sci. 48:167-70.
Chapter 9
Allen, S.A., and R.J. Wattendorf. 1987. Triploid grass carp: Status and management im-
plications. Fisheries 12:20-24.
Andersson, G., H. Berggren, G. Cronberg, and C. Gelin. 1978. Effects of planktivorous and
benthivorous fish on organisms and water chemistry in eutrophic lakes.
Hydrobiologia 59:9-15.
Bain, M.D., D.H. Webb, M.D. Tangedal, and L.N. Mangum. 1990. Movements and habitat
use by grass carp in a large mainstream reservoir. Trans. Am. Fish. Soc. 119:553-61.
Barthelmes, D. 1988. Fish predation and resource reaction: Biomanipulation background
data from fisheries research. Limnologica 19:51-60.
Benndorf, J. 1990. Conditions for effective biomanipulation: Conclusions derived from
whole-lake experiments in Europe. Hydrobiologia 200/1:187-204.
. 1988. Objectives and unsolved problems in ecotechnology and biomanipulation:
Preface. Limnologica 19(1):5-10.
Benndorf, J., H. Kneschke, K. Kossatz, and E. Penz. 1984. Manipulation of the pelagic food
web by stocking predacious fishes. Int. Revue Ges. Hydrobiologia 69:407-28.
Benndorf, J. et al. 1988. Food-web manipulation enhancement of piscivorous fish stocks:
Long-term effects in the hypereutrophic Bautzen Reservoir. Limnoligica 19:97-110.
307
-------
Fish and Fisheries Management in Lakes and Reservoirs
Bergquist, A.M., S.R. Carpenter, and J.C. Latino. 1985. Shifts in phytoplankton size structure
and community composition during grazing by contrasting zooplankton assemblages.
Limnol. Oceanogr. 30:1037-45.
Bonar, S.A., H.S. Sehgal, G.B. Pauley, and G.L. Thomas. 1990. Relationship between the
chemical composition of aquatic maorophytes and their consumption by grass carp,
Ctenophuryngodon idelh. J. Fish Biol. 36:149-58.
Brabrand, A., B.A. Faafeng, and J.P.M. Nilssen. 1990. Relative importance of phosphorus
supply to phytoplankton production: Fish excretion versus external loading. Can J.
Fish. Aquat. Sci. 47:364-72.
Brooks, J.L., and S.I. Dodson. 1965. Predation, body size and composition of plankton.
Science 150:28-35.
Burns, C.W. 1968. The relationship between body size of filter-feeding Cladocera and the
maximum size particle ingested. Limnol. Oceanogr. 13:675-78.
Carpenter, S.R., ed. 1988. Complex Interactions in Lake Communities. Springer-Verlag, New
York, NY.
Carpenter, S.R., and J.F. Kitchell. 1988. Consumer control of lake productivity. BioScience.
38:764-69.
Carpenter, S.R., J.F. Kitchell, and J.R. Hodgson. 1985. Cascading trophic interactions and
lake productivity. BioScience. 35:634-39.
Childers, W.F., and G.W. Bennett. 1967. Experimental vegetation control by largemouth
bass-Tilapia combinations. J. Wildl. Manage. 31:401-07.
CH2M Hill. 1990. Devils Lake Monitoring Progress Report No. 3. Devils Lake Water Im-
prove. Distr., Lincoln County. Corvallis, OR.
Cooke, G.D., and R.H. Kennedy. 1989. Water Quality Management for Reservoirs and Tail-
waters. In-lake Reservoir Water Quality Management Techniques. Tech. Rep. E 89-1.
U.S. Army Corps Eng., Vicksburg, MS.
Cooke, G.D., E.B. Welch, S.A. Peterson, and P.R. Newroth. 1986. Lake and Reservoir Res-
toration. Butterworth Publ., Stoneham, MA.
Crisman, T.L., and J.R. Beaver. 1990. Applicability of planktonic biomanipulation of manag-
ing eutrophication in the subtropics. Hydrobiologia 200/1:177-86.
Crowder, L.B. et al. 1988. Food web interactions in lakes. Pages 141-60 in S.R. Carpenter, ed.
Complex Interactions in Lake Communities. Springer-Verlag, New York, NY.
Davidowicz, P., Z.M. Gilwicz, and R.D. Gulati. 1988. Can Daphnia prevent a blue-green algal
bloom in hypereutrophic lakes: A laboratory test. Limnologica 19:21-26.
de Bernardi, R., and G. Giussani. 1990. Are blue-green algae a suitable food for
zooplankton? An overview. Hydrobiologia 200/1:29-42.
Dini, M.L., and S.R. Carpenter. 1991. The effect of whole-lake fish community manipula-
tions of Daphnia migratory behavior. Limnol. Oceanogr. 36:370-76.
Edmondson, W.T., and S.E.B. Abella. 1988. Unplanned manipulation in Lake Washington.
Limnologica 19:73-80.
Elliott, E.T., L.G. Castanares, D. Perlmutter, and KG. Porter. 1983. Trophic-level control pf
production and nutrient dynamics in an experimental planktonic community. Oikds
41:7-16.
Elser, J.J., H.J. Carney, and C.R. Goldman. 1990. The zooplankton-phytoplankton interface
in lakes of contrasting trophic status: An experimental comparison. Hydrobiologia
200/1:69-82.
Elser, J.J., and C.R. Goldman. 1991. Zooplankton effects on phytoplankton in lakes of con-
trasting trophic status. Limnol. Oceanogr. 36:64-90.
Fort, J.L., L. Pechar, and M. Prazakova. 1980. Fish as a factor controlling water quality in
ponds. Pages 255-61 in L. Mur and J. Varica, eds. Hypereutrophic Ecosystems. Develop-
ments in Hydrobiology 2. Dr. W. Lunk, The Hague, The Neth.
Gliwicz, Z.M 1977. Food size selection and seasonal succession of filter-feeding
zooplankton in an eutrophic lake. Ekol. Pol. 25:179-225.
Gophen, M. 1990. Biomanipulation: Retrospective and future development. Hydrobiologia
200/1:1-12.
Grygierek, E., A. Hillbricht-Ilkowska, and I. Spodniewska. 1966. The effect of fish on
plankton community in ponds. Verh. Int. Ver. Limnol. 16:1359-66.
308
-------
References
Gulati, R.D. E.H.R.R. Lammens, M.-L. Mejer, and E. van Donk, eds. 1990. Water Manage-
ment. Developments in Hydrobiology 61. Kluwer Academic Publishers, Dordrecht.
Reprint. Hydrobiology 200/1:1-627.
Hall, D.J. 1964. An experimental approach to the dynamics of a natural .population of
Daphnia galeata niendotae. Ecology 45:94-111.
Hall, D J., W.E. Cooper, and E.E. Werner. 1970. An experimental approach to the produc-
tion dynamics and structure of freshwater animal communities. Limnol. Oceanogr.
15:839-928.
Hambright, K.D., R.J. Trebatoski, and R.W. Drenner. 1986. Experimental study of effects of
bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides) on pond
community structure. Can. J. Fish. Aquat. Sci. 43:1171-76.
Hauser, W.J. 1975. Tilapia as biological control agents for aquatic weeds and noxious
aquatic insects in California. Proc. Papers. Annu. Conf. Calif. Mosquito Contr. Ass.
43:51-53.
He, X., and J.R Kitchell. 1990. Direct and indirect effects of predation on a fish community:
A whole-lake experiment. Trans. Am. Fish. Soc. 119:825-35.
Hendricks, M.K., and R.L. Noble. 1979. Feeding interactions of three planktivorous fishes
in Trinidad Lake, Texas. Proc. Annu. Conf. S.E. Ass. Fish Wildl. Agencies 33:324-30.
Henrikson, L., H.G. Nyman, H.G. Oscarson, and J.E. Stenson. 1980. Trophic changes
without changes in the external nutrient loading. Hydrobiologia 68:257-63.
Horppila, J., and T. Kairesalo. 1990. A fading recovery: The role of roach (Rutilus rutilus L.)
in maintaining high phytoplankton productivity and biomass in Lake Vesijarvi,
southern Finland. Hydrobiologia 200/1:153-66.
Hosper, S.H., and E. Jagtman. 1990. Biomanipulation additional to nutrient control for res-
toration of shallow lakes in The Netherlands. Hydrobiologia 200/1:523-34.
Hrback, J., M. Dvorakova, V. Korinek, and L. Prochazkova. 1961. Demonstration of the ef-
fect of the fish stock on the species composition and the intesity of the metabolism of
the whole plankton association. Verh. Int. Verein. Limnol. 14:192-95.
Hurlbert, S.H., and M.S. Mulla. 1981. Impacts of mosquitofish (Gambusia affinis) predation
on planktonic communities. Hydrobiologia 83:125-51.
Hurlbert, S.H., J. Zedler, and D. Fairbanks. 1972. Ecosystem alteration of mosquitofish
(Gambusia affinis). Science 175:639-41.
Illinois Department of Conservation. 1988. Aquatic Weeds: Their Identification and
Methods of Control. Fish. Bull. No. 4. Div. Fish., Springfield, IL.
Infante, A., and S.E. Abella. 1985. Inhibition of Daphnia by Osdllatoria in Lake Washington.
Limnol. Oceanogr. 30:1046-52.
Jassby, A.D., T.M. Powell, and C.R. Goldman. 1990. Interannual fluctuations in primary
production: Direct physical effects and the trophic cascade at Castle Lake, California.
Limnol. Oceanogr. 35:1021-38.
Jeppesen, E., et al. 1990a. Fish manipulation as a lake restoration tool in shallow, eutrophic,
temperate lakes. 2: Threshold levels, long-term stability and conclusions. In R.D.
Gulati et al., eds. Biomanipulation: Tool for Water Management. Developments in
Hydrobiology 61. Kluwer Academic Publishers, Dordrecht. Reprint. Hydrobiology
200/1:219-28.
Jeppesen, E., et al. 1990b. Fish manipulation as a lake restoration tool hi shallow,
eutrophic, temperate lakes. l:Cross-analysis of three Danish case-studies. In R.D.
Gulati et al., eds. Biomanipulation: Tool for Water Management. Developments in
Hydrobiology 61. Kluwer Academic Publishers, Dordrecht. Reprint. Hydrobiology
200/1:219-28.
Keen, W.H., and J. Gagliardi. 1981. Effect of brown bullheads on release of phosphorus in
sediment and water systems. Prog. Fish-Cult. 43:183-85.
Kerfoot, W.C. 1987. Cascading effects and indirect pathways. Pages 57-70 in W.C. Kerfoot
and A. Sih, eds. Predation: Direct and Indirect Impacts on Aquatic Communities.
Univ. Press New England, Hanover, NH.
Kitchell, J.F., and S.R. Carpenter. 1987. Piscivores, planktivores, fossils, and phorbins.
Pages 132-148 in a W.C. Kerfoot and A. Sih, eds. Predation: Direct and Indirect Im-
pacts on Aquatic Communities. Univ. Press New England, Hanover, NH.
309
-------
Fish and Fisheries Management in Lakes and Reservoirs
LaMarra, V.J. Jr. 1975. Digestive activities of carp as a major contributor to the nutrient load-
ing of lakes. Verh. Int. Ver. Limnol. 19:2461-68.
Lammens, E.H.R.R., R.D. Gulati, M.-L. Meijer, and E. van Donk. 1990. The first
biomanipulation conference: A synthesis. Hydrobiologia 200/1:619-27.
Lampert, W. 1981. Inhibitory and toxic effects of blue-green algae on Dophnia. Int. Rev.
Gesamten Hydrobiol. 66:285-98.
. 1988. The relationship between zooplankton biomass and grasing: A review. Lim-
nologica 19:11-20.
Lasenby, D.C. and M. Fiirst. 1981. Feeding of Mysis relkta Loven on Macrozooplankton.
Rep. Ins. Freshw. Res. Drottningholm 59:75-80.
Leah, R.T., B. Moss, D.E. Forrest. 1980. The role of predation in causing major changes in the
limnology of a hyper-eutrophic lake. Int. Revue Gesamten Hydrobiol. 65:223-47.
Leslie, A.J. Jr., L.E. Nail, and J.M. Van Dyke. 1983. Effects of vegetation control of grass carp
on selected water-quality variables in four Florida lakes. Trans. Am. Fish. Soc. 112:777-
87.
Losos, B., and J. Hetesa. 1973. The effect of mineral fertilization and of carp fry on the com-
position and dynamics of plankton. Pages 173-218 in ]. Hrb^ck and M. Straskraba, eds.
Hydrobiological Studies, Vol. 3. Academia, Prague.
Lunte, C.C., and C. Luecke. 1990. Trophic interactions of Leptodora in Lake Mendota. Lim-
nol. Oceanogr. 35:1091-1100.
Lynch, M. 1979. Predation, competion and zooplankton structure: An experimental study.
Limnol. Oceanogr. 24:253-72.
Lynch, M., and J. Shapiro. 1981. Predation, enrichment, and phytoplankton community
structure. Limnol. Oceanogr. 26:86-102.
Martyn, R.D., R.L. Noble, P.W. Bettoli, and R.C. Maggio. 1986. Mapping aquatic weeds with
aerial color infrared photography and evaluating their control by grass carp. J. Aquat.
Plant Manage. 24:46-56.
McQueen, D.G., J.R. Post, and E.L. Mills. 1986. Trophic relationships in freshwater pelagic
ecosystems. Can. J. Fish. Aquat. Sci. 43:1571-81.
Meijer, M.-L, M.W. de Haan, A.W. Breukelaar, and H. Buiteveld. 1990. Is reduction of the
benthivorous fish an important cause of high transparency following biomanipulation
in shallow lakes? Hydrobiologia 200/1:303-16.
Miller, A.C., and R.H. King. 1984. Large-scale operations management test of use of the
white amur for the control of problem plants. Tech. Rep. A-78-2. Aquat. Plant Control
Prog., U.S. Corps Eng., Vicksburg, MS.
Mills, E.L., and J.L. Forney. 1988. Trophic dyanamics and development of freshwater pelagic
food webs. Pages 11-30 in S.R. Carpenter, ed. Complex Interactions in Lake Commun-
ties. Springer-Verlag, New York, NY.
Mills, E.L., J.L. Forney, and K.J. Wagner. 1987. Fish predation and its cascading effect on the
Oneida Lake food chain. Pages 118-31 in W.C. Kerfoot and A. Shi, eds. Predation: Direct
and Indirect Impacts on Aquatic Communities. Univ. Press New England, Hanover,
NH.
Moss, B. 1990. Engineering and biological approaches to the restoration from eutrophication
of shallow lakes in which plant communities are important components. In R.D. Gulati
et al., eds. Biomanipulation: Tool for Water Management. Developments in Hydrobiol-
ogy 61. Kluwer Academic Publishers, Dordrecht. Reprint. Hydrobiology 200/201:367-
78.
Noble, R.L., P.W. Bettoli, and R.J. Betsill. 1986. Considerations for the use of grass carp in
large, open systems. Pages 46-48 in G. Redfield, J.F. Taggart, and L.M. Moore, eds. Lake
and Reservoir Management, Vol. 2. N. Am. Lakes Manage. Soc., Merrifield, VA.
O'Brien, W.J. 1987. Planktivory of freshwater fish: Thrust and parry in the pelagia. Pages 3-
16 in W.C. Kerfoot and A. Sih, eds. Predation: Direct and Indirect Impacts on Aquatic
Communities. Univ. Press New England, Hanover, NH.
Olem, H. and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual. 2d
edition. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Olrik, K., S. Lunder, and K. Rasmussen. 1984. Interactions between phytoplankton,
zooplankton, and fish in the nutrient rich shallow Lake Hjarbaek Fjord, Denmark. Int.
Revue Gesamten Hydrobiol. 69:389-405.
31O
-------
References
Persson, L., G. Andersson, S.F. Hamrin, and L. Johansson. 1988. Predator regulation and
primary production along the productivity gradient of temperate lake ecosystems.
Pages 45-68 in S.R. Carpenter, ed. Complex Interactions in Lake Communities.
Springer-Verlag, New York, NY.
Peters, R.H., and J.A. Downing. 1984. Empirical analysis of zooplankton filtering and feed-
ing rates. Limnol. Oceanogr. 29:763-84.
Porter, KG., and J.D. Orcutt. 1980. Nutritional adequacy, manageability, and toxiciry as
factors that determine food quality of green and blue-green algae for Daphnia. Am.
Soc. Limnol. Oceanogr. Spec. Symp. 3:268-81.
Reinertsen, H., and Y. Olsen. 1984. Effects of fish elimination on the phytoplankton com-
munity of a eutrophic lake. Verh. Int. Ver. Limnol. 22:649-57.
Richard, D.I., J.W. Smith, Jr., and J. A. Osborne. 1984. Phytoplankton responses to reduction
and elimination of submerged vegetation by herbicides and grass carp in four Florida
lakes. Aquat. Bot. 20:307-19.
Scavia, D. et al. 1986. Influence of salmonid predation and weather on long term water
quality trends in Lake Michigan, Can. J. Fish. Aquat. Sci. 43:435-43.
Scavia, D., G.A. Lang, and J.F. Kitchell. 1988. Dynamics of Lake Michigan plankton: A
model evaluation of nutrient loading, competion, and predation. Can. J. Fish. Aquat.
Sci. 45:165-77.
Schmiller, D.H. 1984. A major utilities program to manage aquatic weeds. Pages 179-82 in
Proc. 18th Annual Meeting. Misc. Pap. A-84-4. Aquat. Plant Contr. Res. Prog., U.S.
Army Corps Eng., Vicksburgh, MS.
Schoenberg, S.A., and R.E. Carlson. 1984. Direct and indirect effects of zooplankton graz-
ing of phytoplankton in a hypereutrophic lake. Oikos 42:291-301.
Scholz, A.T. et al. 1985. Biomanipulation of a trout fishery and its effect on zooplankton
composition, phytoplankton biovolume and water quality of Medical Lake, Spokane
County, Washington, following restoration by treatment with alum. Pages 48-56 in
Lake and Reservoir Management: Practical Applications. N. Am. Lake Manage. Soc.,
Merrifield, VA.
Scott, W.B., and E.J. Grossman. 1973. Freshwater Fishes of Canada. Bull. 184. Fish. Board
Can., Ottawa, Can.
Shapiro, J. 1990. Biomanipulation: The next phase — making it stable. Hydrobiologia
200/1:13-28.
Shapiro, J., V. Lamarra, and M. Lynch. 1975. Biomanipulation: An ecosystem approach to
lake restoration. Pages 85-96 in P.L. Brezonik and J.L. Fox, eds. Proc. Symp. Water
Quality Management through Biological Control. Univ. Florida Press, Gainesville, FL.
Shapiro, J., and D.I. Wright. 1984. Lake restoration by biomanipulation: Round Lake, Min-
nesota, the first two years. Freshw. Biol. 14:371-83.
Sih, A. 1987. Predators and prey lifestyles: An evolutionary and ecological overview. Pages
203-224 in W.C. Kerfoot and A. Sih, eds. Predation: Direct and Indirect Impacts on
Aquatic Communities. Univ. Press New England, Hanover, NH.
Smeltzer, E., and J. Shapiro. 1982. Biological effects on the size of the nutrient pool. The
role of benthivores in Lake Marion, Minnesota. Pages 12-29 in J. Shapiro, et al., eds.
Experiments and Experience in Biomanipulation. Interim Rep. No. 19, Limno. Res.
Center, Univ. Minnesota, Minneapolis, MN.
Spencer, C.N., and D.L. King. 1984. Role of fish in regulation of plant and animal com-
munities in eutrophic ponds. Can. J. Fish. Aquat. Sci. 41:1851-55.
. 1986. Regulation of blue-green algal buoyancy and bloom formation by light, inor-
ganic nitrogen, COz, and trophic level interactions. Hydrobiologia 144:183-92.
Stenson, J.A.E. et al. 1978. Effects of fish removal from a small lake. Verh. Int. Verein. Lim-
nol. 20:794-801.
Thomas, G.L. et al. 1990. Short-term Effects of Triploid Grass Carp (Ctenopharyngodon idel-
la) on the Plant Community, Fish Assemblage, and Water Quality of Devils Lake,
Oregon. Rep. Devils Lake Water Improve. Disrr. Wash. Coop. Fish Wildl. Res. Unit,
Univ. Washington, Seattle, WA.
Van Donk, E., R.D. Gulati, and M.P. Grimm. 1989. Food web manipulation in Lake'Zwem-
lust: Positive and negative effects during the first two years. Hydrobiol. Bull. 23:19-34.
311
-------
Fish and Fisheries Management In Lakes and Reservoirs
Van Dyke, J.M., A.J. Leslie, Jr., and L.E. Nail. 1984. The effects of grass carp on the aquatic
macrophytes of four Florida lakes. J. Aquat. Plant Manage. 22:87-95.
Webster, K.E., and R.H. Peters. 1978. Some size-dependent inhibition of larger cladoceran
filterers iri filamentous suspensions, Limnol. Oceanog. 23:1238-45.
Wiley, M.J., P.O. Tazik, and S.T. Sobaski. 1987. Controlling aquatic vegetation with tripolid
grass carp. Ore. 57. 111. Nat. Hist. Surv., Champaign, IL.
Zalewski, M., B. Bresinska-Zara, P. Frankiewicz, and S. Kalinowski. 1990. The potential for
biomanipulation using fry communities in a lowland reservoir: Concordance between
water quality and optimal recruitment. Hydrobiologia 200/1:549-56.
Chapter 10
Chambers, J.M., W.S. Cleveland, B. Kleiner, and P.A. Tukey. 1983. Graphical Methods for
Data Analysis. Duxbury Press, Boxton, MA.
Cochran, W.G. 1977. Sampling Techniques. 3rd ed. John Wiley and Sons, New York, NY.
Conover, WJ. 1980. Nonparametric Statistics. John Wiley and Sons, New York, NY.
Drapper, N.R., and H. Smith. 1966. Applied Regression Analysis. John Wiley and Sons,
New York, NY.
Elliot, J.M. 1977. Some Methods for the Statistical Analyses of Benthic Invertebrates. Freshw.
Biolog. Ass. Sci. Publ. 25,2d ed: The Ferry House, Ambleside, England.
Everhart, W.H., and W.D. Youngs. 1981. Principles of Fishery Science. Cornell University
Press, Ithaca, NY.
Gilbert, R.O. 1987. Statistical Methods for Environmental Pollution Monitoring. Van
Nostrand Reinhold, New York, NY.
Green, R.H. 1979. Sampling Design and Statistical Methods for Environmental Biologists.
John Wiley and Sons, New York, NY.
Hollander, M., and D.A. Wolfe. 1973. Nonparametric Statistical Methods. John Wiley and
Sons, New York, NY.
Janies, EC., and C.E. McCulloch. 1990. Multivariate statistics in ecology and systematics:
Panacea or Pandora's box. Annu. Rev. Ecol. System. 1990:129-66.
Johnson, D.L., and L.A. Nielsen. 1983. Sampling considerations. Pages 1-21 in L.A. Nielsen
and D.L. Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Ricker, W.E. 1975. Computation and Interpretation of Biological Statistics of Fish Popula-
tions. Bull. 191. Fish. Res. Board Can., Ottawa, Can.
Schreck, C.B., and P.B. Moyle, eds. 1990. Methods for Fish Biology. Am. Fish. Soc., Bethesda,
MD.
Snedecor, G.W., and W.G. Cochran. 1980. Statistical Methods. Univ. Iowa Press, Ames, IA.
Tufte, E. 1983. The Visual Display of Quantitative Information. Graphics Press, Cheshire,
CT.
U.S. Environmental Protection Agency. 1980. Interim Guidelines and Specifications,for
Preparing Quality Assurance Project Plans. QAMS-005/80, EPA-600/4-83-004. Office of
Monitoring Systems and Quality Assurance, Quality Assurance Management Staff,
Washington, DC.
Wedepohl, R.E., et al. 1990. Monitoring Lake and Reservoir Restoration. EPA 440/90-007i
U.S. Environ. Prot. Agency, Washington, DC.
Zar, J.H. 1974. Biostatistical Analysis. Prentice-Hall, Englewood Cliffs, NJ.
Chapter 11
Aggus, L.R., and S.A. Lewis. 1978. Environmental conditions and standing crops of fishes in
predator-stocking-evaluation reservoirs. Proc. Annu. Conf. Southe. Ass. Fish Wildl.
Agencies 30:131-40. ,
Barnthouse, L.W., G.W. Suter II, A.E. Rosen, and J.J. Beauchamp. 1987. Estimating responses
of fish populations to toxic contaminants. Environ. Toxicol. Chem. 6:811-24.
Beverton, R.J.H., and S.J. Holt. 1957. On the dynamics of exploited fish populations. UJC
Ministry Agric. Fish. Food Fish. Invest. (Ser. 2) 19.
312
-------
References
Boreman, J. et al. 1982. Entrainment impact estimates for six fish populations inhabiting
the Hudson River estuary. ORNL/NUREG/TM-385/V1. Oak Ridge Natl. Lab., Oak
Ridge, TN.
Carlander, KD. 1955. The standing crop of fish in lakes. J. Fish. Res. Board Can. 12:543-70.
Carline, R.R 1986. Indices as predictors of fish community traits. Pages 46-56 in G.E. Hall
and M.J. Van Den Avyle, eds. Reservoir Fisheries Management: Strategies for the 80s.
Reserv. Comm. South. Div., Am. Fish. Soc., Bethesda, MD.
Chapra, S.G., and K.H. Reckhow. 1983. Engineering Approaches for Lake Management.
Vol. 2: Mechanistic Modeling. Butterworth PubL, Boston, MA.
Christensen, S.E., J.E. Breck, and W. Van Winkle. 1988. Predicting acidification effects on
fish populations using laboratory data and field information. Environ. Toxicol. Chem.
7:735-47.
Cohen, J.E., S..W. Christensen, and C.P. Goodyear. 1983. A stochastic, age-structured
population model of striped bass (Morone saxatilis) in the Potomac River. Can J. Fish.
Aquat. Sci. 40:2170-83.
Deriso, R.B. 1980. Harvesting strategies and parameter estimation for .an age-structured
model. Can. J. Fish. Aquat. Sci. 37:268-82.
Evans, D.O., and C.C. Willox. 1991. Loss of exploited, indigenous populations of lake
trout, Salvelinus namaycush, by stocking of non-native stocks. Can. J. Fish. Aquat. Sci.
48:134-47.
Evans, J.W. 1989. A survey of the largemouth bass fishery on Lake Sinclair. Dingell-
Johnson Project F-33. Game Fish Div., Georgia Dep. Nat. Resour., Atlanta, GA.
Everhart, W.H., and W.D. Youngs. 1981. Principles of Fishery Science. Cornell Univ. Press,
Ithaca, NY.
Fox, W.W. 1970. An exponential surplus-yield model for optimizing exploited fish popula-
tions. Trans. Am. Fish. Soc. 99:80-88.
Gulland, J.A. 1961. Fishing and the stocks of fish at Iceland. U.K. Ministry Agric. Fish.
Food Fish. Invest. (Ser. 2) 23(4).
Hanson, J.M., and W.C. Leggett. 1982. Empirical prediction of fish biomass and yield.
Can. J. Fish. Aquat. Sci. 39:257-63.
Hayduk, L.A. 1987. Structural equation modeling with LISREL. The John Hopkins Univ.
Press, Baltimore, MD.
Henderson, H.F., R.A. Ryder, and A.W. Kudhongania. 1973. Assessing fishery potentials of
lakes and reservoirs. J. Fish. Res. Board Can. 30:2000-09.
Jackson, D.A., H.H. Harvey, and K.M. Somers. 1990. Ratios in aquatic sciences: Statistical
shortcomings with mean depth and the morphoedaphic index. Can. J. Fish. Aquat.
Sci. 47:1788-95.
Jenkins, R.M. 1976. Prediction of fish production in Oklahoma reservoirs on the basis of
environmental variables. Ann. Oklahoma Acad. Sci. 5:11-20.
. 1982. The morphoedaphic index and reservoir fish production. Trans. Am. Fish.
Soc. 111:133-40.
Jenkins, R.M., and D.I. Morais. 1971. Reservoir sport fishery effort and harvest in relation
to environmental varibles. Pages 381-84 in G.E. Hall, ed. Reservoir Fisheries and Lim-
nology. Spec. Publ. No. 8. Am. Fish. Soc., Bethesda, MD.
Johnson, M.L., D.G. Huggins, and F. deNoyelles, Jr. 1991. Ecosystem modeling with
LISREL. Ecol. Applic. 1:383-98.
Jones, J.R., and M.V. Hoyer. 1982. Sportfish harvest predicted by summer chlorophyll-a
concentration in midwestern lakes and reservoirs. Trans. Am. Fish. Soc. 111:176-79.
Kimmel, B.L., and A.W. Groeger. 1986. Limnological and ecological changes associated
with reservoir aging. Pages 103-9 in G.E. Hall and M.J. Van Den Avyle, eds. Reservoir
Fisheries Management: Strategies for the 80s. Reserv. Comm. South. Div., Am. Fish.
Soc., Bethesda, MD.
Kitchell, J.F., D.J. Stewart, and D. Weininger. 1977. Applications of a bioenergetics model to
yellow perch (Perca flavescens) and walleye (Stizostedion vitreum vitreum). J. Fish. Res.
Board Can. 34:1922-34.
Lackey, R.T., and W.A. Hubert, eds. 1978. Analysis of exploited fish populations. Virginia
Polytechnic Inst. and State Univ., Blacksburg, VA.
313
-------
Fish and Fisheries Management in Lakes and Reservoirs
Leslie, P.H. 1945. On the use of matrices in population mathematics. Biometrika 33:183-212.
Leslie, P.H. 1948. Some further notes on the use of matrices in mathematics. Biometrika
35:213-45. ;
Ludwig, D., and C.J. Walters. 1989. A robust methods for parameter estimation from catch
and effort data. Can. J. Fish. Aquat. Sci. 46:137-44.
Madenjian, C.P., B.M. Johnson, and S.R. Carpenter. 1991. Stocking strategies for fingerling
walleyes: An individual-based model approach. Ecol. Appl. 1:280-88.
Matuszek, J.E. 1978. Empirical predictions of fish yields of large North American lakes.
Trans. Am. Fish. Soc. 107:385-94.
Melack, J.M. 1976. Primary productivity and fish yields in tropical lakes. Trans. Am. Fish.
Soc. 105:575-80.
Muir, B.S. 1964. Vital statistics of Esox mosquinongy in Nogies Creek, Ontario. II. Population
size, natural mortality, and effect of fishing. J. Fish. Res. Board Can. 21:727-46.
Oglesby, R.T. 1977. Relationships of fish yield to lake phytoplankton standing crop produc-
tion, and morphoedaphic factors. J. Fish. Res. Board Can. 34:2271-79.
Oglesby, R.T. 1982. The MEI symposium-overview and observations. Trans. Am. Fish. Soc.
111:171-75.
Olem, H., and G. Flock, eds. 1990. The Lake and Reservoir Restoration Guidance Manual.
2d ed. EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
O'Neil, L.J., and H.K. Gray. 1988. Availability of habitat models and literature reviews. In-
house Report. Waterw. Exp. Sta., U.S. Army Corps Eng., Vicksburg, MS.
Ploskey, G.R. Undated. Personal communication with R.F. Carline. Aquat. Ecosyst.
Analysts, Fayetteville, AR.
Prepas, E.E. 1983. Total dissolved solids as a predictor of lake biomass and productivity.
Can. J. Fish. Aquat. Sci. 40:92-95.
Raleigh, R.F. 1982. Habitat suitability index models: Brook trout. FWS/OBS-82/10.24. West.
Energy Land Use Team, U.S. Fish. Wildl. Serv., Fort Collins, CO.
Rawson, D.S. 1952. Mean depth and the fish production of large lakes. Ecology 1:513-21.
Reckhow, K.H., and S.C. Chapra. 1983. Engineering Approaches for Lake Management. Vol.
1: Data Analysis and Empirical Modeling. Butterworth Publ., Boston, MA.
Rempel, R.S., and P.J. Colby. 1991. A statistically valid model of the morphoedaphic index.
Can. J. Fish. Aquat. Sci. 48:1937-43.
Ricker, WE. 1954. Stock and recruitment. J. Fish. Res. Board Can. 11:559-623.
. 1975. Computation and interpretation of biological statistics of fish populations.
Bull. Fish. Res. Board Can. 191:382.
Ryder, R. A. 1965. A method for estimating the potential fish production of north-temperate
lakes. Trans. Am. Fish. Soc. 94:214-18.
. 1982. The morphoedaphic index: Use, abuse, and fundamental concepts. Trans. Am.
Fish. Soc. 111:154-64.
Ryder, R.A., S.R. Kerr, K.H. Loftis, and H.A. Regier. 1974. The morphoedaphic index: A fish
yield estimator — review and evaluation. J. Fish. Res. Board Can. 31:663-88.
Saila, S.B., C.W. Recksiek, and M.H. Prager. 1988. Basic fishery science programs: A compen-
dium of microcomputer programs and manual of operation. Devel. Aquacul. Fish. Sci.
18.
Scavia, D. 1981. Conceptual model of phosphorus cycling. In D. Scavia and R. Moll, eds.
Nutrient Cycling in the Great Lakes: A Summarization of Factors Regulating the Cy-
cling of Phosphorus. Great Lakes Res. Div. Spec. Rep. No. 83. Univ. of Michigan, Ann
Arbor, MI.
Scavia, D., G.A. Lang, J.F. Kitchell. 1988, Dynamics of Lake Michigan plankton: A model
evaluation of nutrient loading, competition, and predation. Can. J. Fish. Aquat. Sci.
45:165-77.
Schaeffer, M.B. 1957. A study of the dynamics of the fishery for yellowfin tuna in the eastern
tropical Pacific Ocean. Inter.-Am. Trop. Comm. Bull. 2:245-85.
Schlesinger, D.A., and H.A. Regier. 1982. Climatic and morphoedaphic indices of fish yields
from natural lakes. Trans. Am. Fish. Soc. 111:141-50.
Schneider, J.C. 1978. Predicting the standing crop of fish in Michigan lakes. Fish. Res. Rep.
No. 1860, Michigan Dep. Nat. Resour., Lansing, MI.
314
-------
References
Schnute, J. 1985. A general theory for analysis of catch and effort data. Can. J. Fish. Aquat.
Sci. 42:419-29.
Swartzman, G.L., and D.A. Beauchamp. 1990. Simulation of the effect of rainbow trout in-
• troduction in Lake Washington. Trans. Am. Fish. Soc. 119:122-34.
Taylor, M.W. 1981. A generalized inland fishery simulator for management biologists. N.
Am. J. Fish. Manage. 1:60-72.
Terrell, J.W. et al. 1982. Habitat suitability index models: Appendix A. Guidelines for
riverine and lacustrine applications of fish HSI models with the habitat evaluation
procedures. FWS/OBS-82/10.A. U.S. Fish Wildl. Serv., Washington, DC.
Trial, J.G., C.S. Wade, and J.G. Stanley. 1984. HSI models for northeastern fish. Pages 17-56
in J.W. Terrell, ed. Proc. Workshop on Fish Habitat Suitability Index Models. Biolog.
Rep. 85(6). Western Energy Land Use Team, U.S. Fish Wildl. Serv., Fort Collins, CO.
U.S. Fish and Wildlife Service. 1980. Habitat as a basis for environmental assessment. 101
ESM. Div. Ecol. Serv., U.S. Fish Wildl. Serv., Washington, DC.
von Bertalanffy, L. 1938. A quantitative theory of organic growth: Inquiries on growth
laws, H. Hum. Biol. 10:181-213.
Walford, L. A. 1946. A new graphic method of describing the growth of animals. Biol. Bull.
90(2):141-47.
Walter, G.G. 1973. Delay-differential equation models for fisheries. J. Fish. Res. Board Can.
30:939-45.
Walters, C. 1986. Adaptive Management of Renewable Resources. MacMillan, New York,
NY.
Welch, D.W., and D.J. Noakes. 1991. Optimal harvest rate policies for rebuilding the
Adams River sockeye salmon (Oncorhynchus nerka). Can J. Fish. Aquat. Sci. 48:526-35.
Wright, S. 1968. Evolution and Genetics of Populations. Vol. 1. Genetic and Biomedical
Foundations. Univ. of Chicago Press, IL.
Youngs, W.D., and D.G. Heimbuch. 1982. Another consideration of the morphoedaphic
index. Trans. Am. Fish. Soc. 111:151-53.
Zagar, A.J., and D.J. Orth. 1986. Evaluation of harvest regulations for largemouth bass
populations in reservoirs: A computer simulation. Pages 218-26 in G.E. Hall and M.J.
Van Den Avyle, eds. Reservoir Fisheries Management: Strategies for the 80s. Am. Fish.
' Soc., Bethesda, MD.
Chapter 12
LAKECHICOT
Filipek, S.P. et al. 1989. Effect of Lake Chicot Renovation Project/ Pumping Plant on the
Fisheries of Lake Chicot. Proj. No. F-42-C23L Arkansas Game Fish Comm., Little
Rock, AR.
COLD SPRINGS LAKE
Hill, K. 1987, Destratification-Stratification as a Method of Improving Fish Populations in
Cold Springs Lake. Proj. No. F-90-R-10. Iowa Conserv. Comm., Des Moines, IA.
BEAR LAKE
Buchanan, A. et al. 1974. Evaluation of effects of thinning on panfish populations. Pres.
Wisconsin Chap. Am. Fish. Soc., Bethesda, MD.
McComas, Steve. 1988. Improving gamefish and panfish fisheries with small-scale
projects. Lake Line 8(6):4-13.
. 1989. Improving game and pan fish: Sunfish and walleye on Bear Lake. Lake Line
LAKEOPEONGO
Fry, F.E.J. 1939. A comparative study of lake trout fisheries in Algonquin Park, Ontario.
Biolog. Ser. 45. Ontario Fish. Res. Lab. 58, Univ. Toronto, Can.
- . 1949. Statistics of a lake trout fishery. Biometrics 5:27-67.
Fry, F.E.J., and W.A. Kennedy. 1937. Report on the 1936 lake trout investigation, Lake
Opeongo, Ontario. Biolog. Ser. 42. Ontario Fish. Res. Lab. 54, Univ. Toronto, Can.
315
-------
Fish and Fisheries Management in Lakes and Reservoirs
Matuszek, J.E., BJ. Shuter, and J.M. Casselman. 1990. Changes in lake trout growth and
abundance after introduction of cisco into Lake Opeongo, Ontario. Trans. Am. Fish.
Soc. 119:718-29.
Shuter, B.J., J.E. Matuszek, and H.A. Regier. 1987. Optimal use of creel survey data in assess-
ing population behavior: Lake Opeongo lake trout (Salvelinus namaycush) and
smallmouth bass (Micropterus dolomieui), 1936-83. Can. J. Aquat. Fish. Sd. 44:229-38.
FLAMING GORGE RESERVOIR
Varley, J.D., A.F. Regenthal, and R.W. Wiley. 1971. Growth of rainbow trout in Flaming
Gorge Reservoir during the first six years of impoundment. In G.E. Hall, ed. Reservoir
Fisheries and Limnology. Spec. Publ. No. 8. Am. Fish. Soc,, Bethesda, MD.
Wengert, W., and R. Wiley. 1990. Perspectives on fishery management at Flaming Gorge
Reservoir, including evaluation of three strains of rainbow trout. Proc. 1990 and 1991
Meet. Colorado-Wyoming Chap. Am. Fish. Soc., Bethesda, MD.
Wiley, R. 1991. Resume on fishery management strategies employed on Flaming Gorge
Reservoir. Memo, to C. Creager and J. Baker. Wyoming Game Fish Dep., Laramie, WY.
Wiley, R., DJ. Dufek, and R. Stone. 1976. Flaming Gorge Reservoir, Its History, The Fishery,
and Management. Rep. Wyoming Game Fish Dep., Utah Div. Wildl. Res., Cheyenne,
WY.
FLATHEADLAKE
Cross, D. 1987. An Opportunity for Integrated Management of the Flathead River-Lake
Ecosystem, Montana. Fisheries 12(2):17-22.
Flathead Basin Commission. 1990.1989-1990 Biennial Report. Flathead and Lake counties,
MT.
Montana Department of Fish, Wildlife, and Parks and Confederated Salish and Kootenai
tribes. 1989. Upper Flathead System Fisheries Management Plan 1989-1994. Helena,
MT.
. 1991. Fisheries Mitigation Plan for Losses Attributable to the Construction and
Operation of Hungry Horse Dam. Helena, MT.
Montana Power Company. 1990. Kerr Project Mitigation and Management Plan. Butte, MT.
LAKE WASHINGTON
Edmondson, W.T. 1979. Lake Washington and predictability of limnological events. Arch.
Hydrobiol. 13:234-41.
Edmondson, W.T., and J.T. Lehman. 1981. The effect of changes in the nutrient income oh
the condition of Lake Washington. Limnol. Oceanogr. 26:1-29.
Edmondson, W.T., and A.H. Lift. 1982. Daphnia in Lake Washington. Limnol. Oceanogr.
27:272-93.
Edmondson, W.T., and S.E.B. Abella. 1988. Unplanned biomanipulation in Lake
Washington. Limnologica 19:73-79.
Eggers, D.M. et al. 1978. The Lake Washington ecosystem: The perspective from the fish
community production and forage base. J. Fish. Res. Board Can. 35:1553-71.
Montana Department of Fish, Wildlife, and Parks and Confederated Salish and Kootenai
tribes. 1989. Upper Flathead System Fisheries Management Plan 1989-1994. Helena,
MT.
National Research Council. 1991. Restoration of Aquatic Ecosystems: Science, Technology,
and Public Policy. Natl. Acad. Sci., Washington, DC.
Swartzman, G.L., and D.A. Beauchamp. 1990. Simulation of the effect of rainbow trout in-
troduction in Lake Washington. Trans. Am. Fish. Soc. 119:122-34.
Appendix A
Arnoldi, D.C., C.E. Hoenke, K.E. Lantz, and M.G. Wood. 1991. Crappie Management Plan.
Louisiana Dep. Wildl. Fish., Baton Route, LA.
Axon, J.R., and D.K. Whitehurst. 1985. Striped bass management in lakes with emphasis on
management problems. Trans. Am. Fish. Soc. 114:8-11.
Becker, G.C. 1983. Fishes of Wisconsin. Univ. Wisconsin Press, Madison, WI.
Bennett, D.H., and T.J. McArthur. 1990. Predicting success of walleye stocking programs in
the United States and Canada. Fisheries 15(4):19-23.
316
-------
References
Boyle, R.H. 1980. Bass. W.W. Norton & Co., New York, NY.
Brousseau, C.S., and E.R. Armstrong. 1987. The role of size limits in walleye management.
. Fisheries 12(l):2-5.
Carlander, K.D. 1969. Handbook of Freshwater Fishery Biology. Vol. 1. Life History Data
on Freshwater Fishes of the United States and Canada, Exclusive of the Perdformes.
Iowa State Univ. Press, Ames, IA.
1977. Handbook of Freshwater Fishery Biology. Vol. 2. Life History Data on
Centrachid Fishes of the United States and Canada. Iowa State Univ. Press, Ames, IA.
Casselman, J.M. et al. 1986. Biology and life history: Identification of muskellunge, north-
ern pike, and their hybrids. Am. Fish. Soc. Spec Publ. 15:14-46.
Coutant, C.C. 1985. Striped bass, temperature, and dissolved oxygen: A speculative
hypothesis for environmental risk. Trans. Am. Fish. Soc. 114:31-61.
Craig, J. 1987. The Biology of Perch and Related Fish. Timber Press, Portland, OR.
Ebbers, M.A., P.J. Colby, and C.A. Lewis. 1988. Walleye - Sauger Bibliography. Investiga-
tional Rep. No. 396. Minnesota Dep. Nat. Resour., St. Paul, MN.
Gresswell, R.E. 1988. Status and Management of Interior Stocks of Cutthroat Trout. Am.
Fish. Soc., Bethesda, MD.
Hall, G.E. 1986. Managing Muskies. Am. Fish. Soc., Bethesda, MD.
Harper, J.L., and H.E. Namminga. 1986. Fish population trends in Texoma Reservoir fol-
lowing establishment of striped bass. Pages 156-65 in G.E. Hall and M.J. Van Den
Avyle, eds. Reservoir Fisheries Management: Strategies for the 80s. Am. Fish. Soc.
Bethesda, MD.
Hocutt, C, and E. Wiley. 1986. The Zoogeography of North American Fresh-Water Fishes.
John Wiley & Sons, New York, NY.
Johnson, J.E. 1987. Protected Fishes of the United States and Canada. Am. Fish. Soc.,
Bethesda, MD. '
Kendall, R.L. 1978. Selected Coolwater Fishes of North America. Am. Fish. Soc., Bethesda,
MD,
Louisiana Department of Wildlife and Fisheries. 1990. Louisiana Black Bass Management
Plan. Fish. Manage. Plan Ser.'No. 1, Prop. Baton Rouge, LA.
Maine Department of Inland Fisheries and Wildlife. 1986. Planning for Maine's Inland
Fish and Wildlife: Species Assessments and Strategic Plans 1986-1991. Vol. II.
Fisheries, Part 1. Augusta, ME.
Manooch, C.S. m. 1984. Fisherman's Guide: Fishes of the Southeastern United States.
North Carolina State Mus. Nat. Hist., Raleigh, NC.
Matthews, W.J. 1985. Summer mortality of striped bass in reservoirs of the United States.
Trans. Am. Fish. Soc. 114:62-66.
Miller, W.H., et al. 1982. Fishes of the Upper Colorado System: Present and Future. Am.
Fish. Soc., Bethesda, MD.
Mills, D. 1989. Ecology and Management of Atlantic Salmon. Chapman & Hall,
Gaithersburg, MD.
Minnesota Department of Natural Resources. 1982. Lake Management Planning Guide.
Spec Publ. No. 132. Fish. Div., St. Paul, MN.
Morrison, T., and G. Tilyou. 1991. Spotted Bass (Micropterus punctulatusfPre-management
Plan. Louisiana Dep. Wildl. Fish., Baton Rouge, LA.
Nelson, J.S. 1984. Fishes of the World. John Wiley & Sons, New York, NY.
Nelson, W.C. 1988. High lake research and management in Colorado. Spec. Rep. No. 64.
Aquat. Res., Colorado Div. Wildl., Denver, CO.
Olver, C.H., and N.V. Martin. 1984. A Selective Bibliography of the Lake Trout, Salvelinus
namaycush (Walbaum), 1784-1982. Ontario Fish. Tech. Rep. Ser. No. 12. Ontario Min.
Nat. Resour., Toronto, Ontario, Can.
Ono, R.D., J.D. Williams, and A. Wagner. 1983. Vanishing Fishes of North America. Stone
Wall Press, Ventura, CA.
Robinson, H.W., and T.M. Buchanan. 1988. Fishes of Arkansas. Univ. Arkansas Press,
Fayetteville, AR. ;
Scott, W.B., and E.j. Grossman. 1973. Freshwater Fishes of Canada. Bull. 184. Fish. Res.
Board Can., Ottawa, Can. , *
317
-------
Fish and Fisheries Management In Lakes and Reservoirs
Sigler, W., and J.W. Sigler. 1987. Fishes of the Great Basin: A Natural History. Univ. Nevada
Press, Reno, NV.
Smith, C.L. 1984. The Inland Fishes of New York State. New York Dep. Environ. Conserv.,
Albany, NY.
Sublette, J.E., M.D. Hatch, and M. Sublette. 1990. The Fishes of New Mexico. Univ. New
Mexico Press, Albuquerque, NM.
Tomelleri, J.R., and M.E. Eberle. 1990. Fishes of the Central United States. Univ. Press Kan-
sas, Lawrence, KS.
Trautman, M. 1981. The Fishes of Ohio. Ohio State Univ. Press, Columbus, OH.
Trotter, P.C. 1987. Cutthroat, Native Trout of the West. Univ. Press Colorado, Boulder, CO.
Turner, WM. 1986. Evaluation of the striped bass x white bass hybrid in Montrose Lake,
Missouri. Page 311 in G.E. Hall and M.J. Van Den Avyle, eds. Reservoir Fisheries
Management: Strategies for the 80s. Am. Fish. Soc., Bethesda, MD.
Williams, J.E., D.W. Sada, and CD. Williams. 1988. American Fisheries Society guidelines
for introductions of threatened and endangered fishes. Fisheries 13(5):5-11.
Williams, J.E. et al. 1989. Fishes of North America endangered, threatened, or of special con-
cern: 1989. Fisheries 14(6):2-20.
Willers, W.B. 1981. Trout Biology: An Angler's Guide. Univ. Wisconsin Press, Madison, WI.
Wydoski, R.S., and R.R. Whitney. 1979. Inland Fishes of Washington^ Univ. Washington
Press, Seattle, WA.
Appendix B
Aebersold, P.B. et al. 1987. Manual for Starch Gel Electrophoresis: A Method for the Detec-'
tion of Genetic Variation. Tech Rep. Natl. Ocean. Atmos. Admin., Washington, DC.
American Society for Testing and Materials. 1991. Standard Guide for Conducting Sediment
Toxicity Tests with Freshwater Invertebrates. ASTM E-1383-94. Philadelphia, PA.
Anderson, R.O., and S.J. Gutreuter. 1983. Length, weight, and associated structural indices.
Pages 283-300 in L.A. Nielsen and D.L. Johnson, eds. Fisheries Techniques. Am. Fish.
Soc., Bethesda, MD.
Babbie, E.R. 1973. Survey Research Methods. Wadsworth Publ. Co., Belmont, CA:
Bagenal, T.B., and F.W. Tesch. 1978. Age and growth. Pages 101-36 in T.Bi Bagenal, ed.
Methods for Assessment of Fish Production in Freshwater. 3rd ed. Blackwell Sci. Publ.,
Oxford, England.
Barbour, M.T. et al. 1992. Evaluation of EPA's rapid bioassessment benthic metrics: Metric
redundancy and variability among reference stream sites. Environ. Toxicol. Chem.
11:437-49.
Baudo, R., J.P. Geisy, and H. Muntau. 1990. Sediments: Chemistry and Toxicity of In-Place
Pollutants. Lewis Publ., Inc., Ann Arbor, MI.
Baxter, G.T., and J.R. Simon. 1970. Wyoming Fishes. Bull. No. 4. Wyoming Game Fish Dep.,
Cheyenne, WY.
Billington, N., and P.D.N. Hebert. 1991. Mitochondrial DNA diversity in fishes and its im-
plications for introductions. Can. J. Fish. Aquat. Sci. 48:80-94.
Booth, G.M., and K.E. Holtz. 1988. Review of U.S. Fish and Wildlife Service Information
regarding Rotenone. Rep. Ontario Min. Natl. Resour., Toronto, Can..
Bowen, S.H. 1983. Quantitative description of the diet. Pages 325-36 in L.A. Nielsen and
D.L. Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Brandt, S.B., and P. Unger. 1986. Development of a Bioacoustic System to Assess Fish Stocks
in Small Lakes and Ponds in Relation to Acid Precipitation. Tech. Rep. CR-812663-01-0.
Corvallis Environ. Res. Lab., U.S. Environ. Prot. Agency, Corvallis, OR.
Brownie, C, D.R. Anderson, K.P. Burnham, and D.S. Robson. 1985. Statistical Inference from
Band Recovery Data: A Handbook. 2nd ed. Resour. Publ. No. 156. U.S. Fish Wildl. Serv.,.
Washington, DC.
Carlander, K.D. 1982. Standard intercepts for calculating lengths from scale measurements
for some centrachid and percid fishes. Trans. Am. Fish. Soc. 111:332-36.
Carle, F.L., and M.R. Strub. 1978. A new method for estimating population .size from
removal data. Biometrics 34:621-30.
318
-------
References
Casselman, J.M. 1987. Determination of age and growth. Pages 209-42 in A.H. Weatherley
and H.S. Gill, eds. The Biology of Fish Growth. Academic Press, London, England.
Clayton, J.W., R.E.K. Harris, and D.N. Tretiak. 1974. Geographical distribution of alleles
for supernatent malate dehydrogenase in walleye (Stizostedion vitreum vitreum)
populations from western Canada. J. Fish. Res. Board Can. 31:342-45.
Cochran, W.G. 1977. Sampling Techniques. 3rd ed. John Wiley and Sons, New York, NY.
Cowx, I.G. 1983. Review of the methods for estimating fish population size from survey
removal data. Fish. Manage. 14:67-82.
Cowx, I.G. and P. Lamarque. 1990. Fishing With Electricity: Applications in Freshwater
Fisheries Management. Fishing News Books, Blackwell Sci. Publ. Ltd., Cambridge,
MA.
Crowder, L.B. 1990. Community ecology. Pages 609-32 in C.B. Schreckand P.B. Moyle, eds.
Methods for Fish Biology. Am. Fish. Soc., Bethesda, MD.
Davies, W.D., and W.L. Shelton. 1983. Sampling with toxicants. Pages 199-213 in L. A. Niel-
sen and D.L. Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
DeLury, D.B. 1947. On the estimation of biological populations. Biometrics 3:145-47.
Dillman, D.A. 1978. The Total Design Method. John Wiley & Sons, New York, NY.
Eddy, S. 1957. The Freshwater Fishes. Wm. C. Brown Co. Publ., Dubuque, IA.
Evans, J.W. 1989. A survey of the largemouth bass fishery on Lake Sinclair. Proj. No. F-33.
Georgia. Dep. Natl. Resour., Atlanta, GA.
Everhart, W.H., and W.D. Youngs. 1981. Principles of Fishery Science. Cornell Univ. Press,
Ithaca, NY.
Forstner, U. 1989. Contaminated Sediments. Springer-Verlag, New York, NY.
Frie, R.V. 1982. Measurement of fish scales and back-calculation of body lengths using a
digitizing pad and microcomputer. Fisheries 7:5-8.
Goodchild, G.A. 1990. Electric fishing and safety. Pages 157-75 in I.G. Cowx and P.
Lamarque, eds. Fishing with Electricity: Applications in Freshwater Fisheries
Management. Fishing News Books, Blackwell Sci. Publ. Ltd., Cambridge, MA.
. 1991. Code of Practice and Guidelines for Safety with Electric Fishing. Qccas. Pap.
No. 24. European Inland Fish. Advisory Comm., U.N. Food Agric. Organ., Rome,
Italy.
Guthrie, D. et al., eds. 1991. Creel and Angler Surveys in Fisheries Management. Symp. 12.
Am. Fish. Soc., Bethesda, MD.
Hallerman, E.M., and J.S. Beckmann. 1988. DNA-level polymorphism as a tool in fisheries
science. Can. J. Fish. Aquat. Sci. 45:1075-87.
Hamilton, K, and E.P. Bergerson. 1984. Methods to Estimate Aquatic Habitat Variables.
Colorado Coop. Fish Wildl. Unit, U.S. Fish Wildl. Serv., Colo. State Univ., Fort Collins,
CO.
Harris, H., and D.A. Hopkinson. 1976. Handbook of enzyme electrophoresis in human
genetics. Am. Elsevier Publ. Co., New York, NY.
Hayes, M.L. 1983. Active fish capture methods. Pages 123-45 in L.A. Nielsen and D.L.
Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Helfman, G.S. 1983. Underwater methods. Pages 349-69 in L.A. Nielsen and D.L. Johnson,
eds. Fisheries Techniques. Am. Fis. Soc., Bethesda, MD.
Hubert, W.A. 1983. Passive capture techniques. Pages 95-111 in L.A. Nielsen and D.L.
Johnson, eds. Fisheries Techniques. Am. Fis. Soc., Bethesda, MD.
Ihssen, P.E., J.M. Casselman, G.W. Martin, and R.B. Phillips. 1988. Biochemical genetic dif-
ferentiation of lake trout (Salvelinus namaycush) stocks of the Great Lakes region. Can.
J. Fish. Aquat. Sci. 45:1018-29.
Ivlev, V.S. 1961. Experimental Ecology of the Feeding of Fishes. Yale Univ. Press, New
Haven, CT.
Jearld, A. Jr. 1983. Age determination. Pages 301-24 in L.A. Nielsen and D.L. Johnson, eds.
Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Keefer, L.C. 1988. A Survey of the Sport Fishery of Four Major Reservoirs in Southwest
Georgia. Final Rep. Proj. F-28. Georgia Dep. Natl. Resour., Atlanta, GA.
Lackey, R.T., and W.A. Hubert, eds. 1978. Analysis of Exploited Fish Populations. Virginia
Polytechnic Inst. State Univ., Blacksburg, VA.
319
-------
Fish and Fisheries Management irt Lakes and Reservoirs
Lagler, K.F. 1956. Freshwater Fishery Biology. Wm. C. Brown Co., Dubuque, IA.
Leary, R.F., F.W. Allendorf, S.R. Phelps, and K.L. Knudsen. 1987. Genetic divergence and
identification of seven cutthroat trout subspecies and rainbow trout. Trans. Am. Fish.
Soc. 116:580-87.
Leslie, P.H., and H.S. Davis. 1939. An attempt to determine the absolute number of rats in a
given area. J. Anim. Ecol. 8:94-113.
Living Lakes, Inc. 1989. Field Operations Program Implementation Manual for Aquatic
Liming and Fish Restoration Demonstration Program. Washington, DC.
Lind, O.T. 1985. Handbook of Common Methods in Limnology. Kendall/Hunt Publ. Co.,
Dubuque, IA.
Malvestuto, S.P. 1983. Sampling the recreational fishery. Pages 397-419 in L.A. Nielsen and
D.L. Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Meiers, VJP., M.D. Marcus, and L.E. Noel. 1992. Fishing in Wyoming: Results of the 1991
Fishing Pressure Survey. Wyoming Game Fish Dep., Laramie, WY.
Minnesota Department of Natural Resources. 1970. Manual of Instructions for Lake Sur-
veys. Spec. Publ. No. 1. Div. Fish and Wildl., St. Paul, MN.
. 1978. Minnesota Stream Survey Manual. Spec. Publ. No. 120. Div. Fish and Wildl.,
St. Paul, MN.
. 1985. Large Lake Sampling Guide. Spec. Publ. No. 140. Div. Fish and Wildl., St.
: Paul,MN.
' Nielsen, L.A., and D.L. Johnson, eds. 1983. Fisheries Techniques. Am. Fish. Soc., Bethesda,
MD.
Olem, H. and G. Flock, eds. 1990. Lake and Reservoir Restoration Guidance Manual. 2d ed.
EPA 440/4-90-006. U.S. Environ. Prot. Agency, Washington, DC.
Ontario Ministry of Natural Resources. 1989. Manual of Instructions: Aquatic Habitat In-
ventory Surveys. 8th ed. Official Procedure Manual Policy Fl.2.03.01 Ontario, Toronto,
Can.
Orth, D.J. 1983. Aquatic habitat measurements. Pages 61-84 in L.A. Nielsen and D.L.
Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Philipp, D.P., W.F. Childers, and G.S. Whitt. 1983. A biochemical genetic evaluation of the
northern'and Florida subspecies of largemouth bass. Trans. Am. Fish. Soc. 112:1-20.
Phillips, G.L., W.D. Schmid, and J.C. Underhill. 1982. Fishes of the Minnesota Region. Univ.
Minn. Press, Minneapolis, MN.
Plafkin, J.L. et al. 1989. Rapid Bioassessment Protocols for Use in Streams and Rivers: Ben-
thic Macroinvertebrates and Fish. EPA 444/4-89-001. U.S. Environ. Prot. Agency,
Washington, DC.
Platts, W.S., W.F. Megahan, and G.W. Minshall. 1983. Methods for Evaluating Stream,
Riparian, and Biotic Conditions. GTR INT-138. Intermountain Forest Range Exp. Sta.,
U.S. Forest Serv., Ogden, UT.
Pritchard, D.L., N.E. Carter, and B. Rutledge. 1974. Cold Brands and Anchor Tags as Mark-
ing Techniques for Blue Catfish (Ictalurus furcatus) and Largemouth Bass (Micropterus
salmoides). Heart of the Hills Res. Sta. Proj. No. F-23-R-3. Texas Parks Wildl. Dep., Aus-
tin, TX.
Reynolds, J.B. 1983. Electrofishing. Pages 147-63 in L. A. Nielsen and D.L. Johnson, eds.
Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish popula-
tions. Bull. Fish. Res. Board Can. 191.
Robson, D.S. 1963. Maximum likelihood estimation of a sequence of annual survival rates
from a capture-recapture series. Int. Comm. Northw. Atl. Fish. Spec. Publ. 4:330-35.
Ryman, N. and F. Utter, eds. 1987. Population Genetics and Fisheries Management. Univ.
• Washington Press, Seattle, WA.
Saila, S.B., C.W. Recksiek, andM.H. Prager. 1988. Basic fishery science programs, a compen-
dium of microcomputer programs and manual of operation. Dev. Aquacul. Fish. Sci.,
18. Elsevier, Amsterdam.
Schreck, C.B., and P.B. Moyle, eds. 1990. Methods for Fish Biology. Am. Fish. Soc., Bethesda,
,MD. i"
320
-------
References.
Schoener, T.W. 1970. Non-synchronous spatial overlap of lizards in patchy habitat. Ecol-
ogy 51i408-18.
Seber, G.A,F. 1972. Estimating time-specific survival and reporting rates for adult birds
from band returns. Biometirika 57:313-18.
Snedecor, G.W., and W.G. Cochran. 1980. Statistical Methods. Univ. Iowa Press, Ames, IA.
Snyder, D.E. 1983. Fish eggs and larvae. Pages 165-97 in L.A. Nielsen and D.L. Johnson,
eds. Fisheries Techniques. Am. Fish. Soc.; Bethesda, MD.
Standard Methods for the Examination of Water and Wastewater. 1989. 17th ed. Joint
Editorial Board, Am. Public Health Ass., Am. Water Works Ass., and Water Pollut.
Control Fed., Washington, DO--.
Sztramko, LJC, W.I. Dunlop, S.W. Powell, andR.G. Sutherland. 1991. Applications and
Benefits of an Angler Diary Program on LakeiBrie.-Am. Fish. Soc. Symp. 12:520-28.
Texas Parks and Wildlife Department.. 1991. Texas Inland Fishery Assessment Procedures,
Inland Fish. Branch, Austin, TX.
Thorne, R.E. 1983. Hydroacoustics. Pages 239-59 in L.A. Nielsen and D.L. Johnson, eds.
Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
U.S. Environmental Protection Agency. 1983. Methods for Chemical Analysis of Water and
Wastes. EPA/006/4-79/020. U.S. Environ. Prot. Agency, Cincinnati, OH.
. 1987. Handbook of Methods for Acid Deposition Studies: Laboratory Analysis for
Surface Water Chemistry. EPA 600/4-87/026. Off. Res. Dev., Washington, DC.
-. 1989. Handbook of Methods for Acid Deposition Studies: Field Operations for Sur-
face Water Chemistry. EPA 600/4-89/020. Off. Res. Develop., Washington, DC.
Utter, F.M., H.O. Hodgins, and F.W. Allendorf. 1974. Biochemical genetic studies of fishes:
Potentialities and limitations. Pages 213-38 in D.C. Malins and J.R. Sargent, eds.
Biochemical and Biophysical perspectives in Marine Biology. Vol. 1. Academic Press,
New York, NY.
Van Den Avyle, MJ. 1986. Measuring angler effort, success, and harvest. Pages 57-64 in
G.E. Hall and M.J. Van Den Avyle, eds. Reservoir Fisheries Management: Strategies
for the 80s. Reserv. Comm., Southern Div. Am. Fish. Soc, Bethesda, MD.
Wallace, R.K., Jr. 1981. An assessment of diet-overlap indices. Trans. Am. Fish. Soc. 110:72-
76.
Wedepohl, R.E. et al. 1990 Monitoring Lake and Reservoir Restoration. EPA 440.4-90-007.
-Off. Water, U.S. Environ. Prot. Agency, Washington, DC.
Wetzel, R.G., and G.E. Likens. 1979. Limnological Analyses. W.B. Saunders Co., New York,
NY.
'White, B.A. and J.B. Shaklee. 1991. Need for replicated electrophoretic analyses in multi-
agency genetic stock identification (GST) programs: Examples from a pink salmon
- .(Oncorhynchus gorbuscha) GSI fisheries study. Can. J. Fish. Aquat. Sci. 48:1396-1407.
Willis, D.W., and R.F. Hartmann. 1986. The Kansas Black Bass Tournament Monitoring
Program. Fisheries 11:7-10.
Winter, J.D. 1983. Underwater biotelemetry. Pages 371-98 in L. A. Nielsen and D.L.
Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Wydoski, R. and L. Emery. 1983. Tagging and marking. Pages 215-37 in L. A. Nielsen and
D.L. Johnson, eds. Fisheries Techniques. Am. Fish. Soc., Bethesda, MD.
Zippen, C. 1958. The removal method of population estimation. J. Wildl. Manage. 22:82-90.
•U.S GOVERNMENT PRINTING OFFICE 1 99 3. 7 1 5-o 03, 87079
321
-------
-------
-------
------- |