siM*
United States
Environmental Protection
Agency
Environmental Research
Laboratory
Corvallis, OR 97330
Research and Development
EPA-600/S3-81-021 July 1981
Project Summary
Natural Variation in
Abundance of Salmonid
Populations in Streams
and Its Implications for
Design of Impact Studies
James D. Hall and Ned J. Knight
This project was an extensive
literature review relating to stock size
and production of salmonid
populations in streams. The objective
was to bring together data on thd
magnitude of natural variation in
population size and to relate this
variability to environmental
conditions wherever possible.
Recommendations are presented for
the use of this information in
designing studies to estimate the
impact of nonpoint source (NPS)
pollution. A partially annotated
bibliography of 260 references is
included in the Project Report.
A number of long-term studies,
some up to 15-20 years, have
provided useful data on temporal
variation in population abundance.
Other studies have examined spatial
variation. Data from the best
examples of both kinds of variation are
presented. Temporal and spatial
variation may be as high as several
orders of magnitude in the extreme
and, even at the least, are sufficient to
mask significant pertubations caused
by NPS pollutants. Environmental
variables most closely associated with
spatial variation are those relating to
the quality of salmonid habitat,
particularly physical characteristics
such as cover in its many forms.
Streamflow and food abundance have
been associated with both temporal
and spatial variation. In general,
physical characteristics of habitat
appear to be the most promising as
descriptors of variability.
Considerable emphasis should be
placed upon systems of rating habitat
quality in attempts to. minimize the
effects of natural variation when
evaluating the impact of NPS
pollutants. First priority should be
placed on the assessment of physical
features. Thus far, this approach has
been used mainly to explain spatial
variation, but also has promise in
explaining temporal variation. The
other major emphasis should be in
further development of systems of
stream and watershed classification.
The most useful of these systems
devised to date take a perspective
from geomorphology and focus on the
potential of a stream system for
biological production. As a means of
more clearly separating natural
variation from damage caused by NPS
pollutants, more emphasis should be
placed upon the study of basic
processes in stream ecosystems and
more extensive use should be made of
paired comparisons in the design of
impact studies.
This Project Summary was
developed by EPA's Environmental
Research Laboratory, Corvallis. OR,
-------
to announce key findings of the
research project that is fully
documented in a separate report of the
same title I see Project Report ordering
information at back).
Introduction
Assessment of impacts on streams
caused by nonpoint source pollutants is
now receiving increasing attention.
Salmonids are the principal fish species
of economic importance affected by
pollution in the western United States.
Assessment of damage to these fish
populations cannot be undertaken
without some understanding of the
natural variation in abundance within
and between populations. Strategies of
analysis must be devised that will
separate natural variations from those
effects due to man-made disturbances.
The purpose of this review is to bring
together literature and unpublished
data on the natural variation in
abundance of salmonid populations in
streams and to attempt to relate this
variation to physical, chemical and
biological variables.
There are two kinds of variability to be
considered, spatial and temporal.
Spatial variation can be studied at
several levels of resolution, ranging
from microhabitat preferences to that
variability occurring within and
between streams. Temporal variation
can occur on a die), seasonal, or annual
scale.
This report concentrates on studies of
salmonid species during that part of
their lives spent in the stream
environment. These species include the
coho salmon (Oncorhynchus kisutch),
Chinook salmon (0. tshawytschaj, pink
salmon (0. gorbuscha), chum salmon
(0. ketal, brown trout (Salmo trutta),
rainbow trout (S. gairdneri), steelhead
trout (S. gairdneri gairdneri), cutthroat
trout (S. clarki), Atlantic salmon (S.
salar), brook trout (Salvelinus
fontinalis), and Dolly VardenfS. malmaj.
This review was begun with the
emphasis on studies carried out on the
West Coast of North America. However,
it was found that most of the
quantitative data on variability in
resident salmonid populations came
from other areas. Therefore, much of
that information has been included in
this report.
Much less information is available on
population levels of the other fish
species associated with salmonids.
Though not included in this report, the
importance of this element of the
aquatic system should be emphasized
and steps taken to fill this gap in our
knowledge of fish communities.
Conclusions and
Recommendations
The standing stock biomass of
salmonid fishes in streams shows great
natural variation, both in time and
space. Reported levels of biomass vary
from zero, or just above, to over 60
g/m2. This variation is sufficient to
mask large-scale perturbations caused
by NFS pollutants such as those
resulting from logging and agricultural
practices. Among the most important
causes of variation are differences in
the physical characteristics of streams,
including streamflow and habitat
quality, particularly cover. Biological
factors, such as food abundance and
predation, may sometimes influence
abundance. However, their mode of
action is less clear andthe case for their
involvement more equivocal than that of
the physical elements of the habitat.
Several courses of action are
recommended that will help minimize
the effects of this natural variation
when attempts are made to evaluate
impacts of a particular NFS pollutant.
Habitat quality rating systems are being
developed that show promise for
explaining much of the spatial variation
in salmonid populations in streams.
These rating systems are based
primarily on the assessment of physical
features. They may also help to explain
temporal variation caused by changes in
streamflow, but other influences on
temporal variation need further study.
The other major approach that may aid
impact assessment is the development
of schemes of stream and watershed
classification. One appears to be
particularly promising in that it focuses
upon the potential of a system for
biological production, rather than a
particular value of the moment and
takes a biogeoclimatic perspective.
Continuing emphasis on the study of
basic physical and biological processes
that lead to growth, mortality and
production of stream salmonids is
another promising approach to
understanding natural variation in
abundance. New approaches to the
design of impact studies are suggested
that may aid in more clearly separating
natural variation from that caused by
NFS pollutants and in monitoring the
time required for biological systems to
recover from perturbation.
Table 1 summarizes the advantages
and disadvantages of four major
approaches to watershed stream
analysis. Studies may be grouped
according to whether they bracketed
(before-after) or followed (post)
treatment. The other level of
classification was based on whether
detailed studies were made on one or
very few streams (intensive) compared
to less detailed study on many streams
(extensive). This two level classification
results in four categories, which are
evaluated for efficiency and sensitivity
of impact detection. This listing of
advantages and disadvantages of each
type reveals that no one design is
optimum. The best approach appears to
be a combination of post treatment
analysis with carefully designed
process studies carried out at one or
more locations.
-------
Table 1. Summary of A dvantages and Disadvantages of the Four Major Approaches to Watershed Stream Analysis
A. Intensive Before-After (10-15 years; 5-7 years before and after treatment).
Advantages Disadvantages
1) Possible to assess year-to-year variation and 1) No replication; results must be viewed as a case study.
place size of impact in context of that variation.
2) Results not necessarily applicable elsewhere (areas
2) Can assess short-term rate of recovery (ca. 5 years). of different soils, geology, fish species, etc.).
3) No assumptions required about initial conditions. 3) Results vulnerable to unusual climatic events
(e.g. high or low rainfall season(s) immediately following
4) Possible to monitor whole watershed impacts (provided treatment).
substantial investment in facilities such as flow
and sediment sampling wiers, fish traps). 4) Final results and management recommendations require
exceptionally long time to formulate - up to 15 years
5) Long time frame provides format for extensive after initial planning stage.
process studies.
5) Difficult to maintain intensity of investigation and
continuity of investigators over such a long period.
6) Must rely on outside agencies or firms to complete treatments
as scheduled - considerable coordination required.
B. Extensive Before-After (2-4 years; 1 year before treatment, 1 year after).
Advantages Disadvantages
1) Provides broader perspective across geographical 1) Lack of long-term perspective-- little opportunity
area than (A). to observe year-to-year variation.
2) Larger number of streams examined lessens 2) Able to assess only immediate results, which may not be
danger of extreme case. representative of longer time sequence.
3) Increased generality of results allows some extrapo- 3) Treatment vulnerable to unusual weather (if all treatments
lation to other areas. in same year).
4) Relatively short time to achieve results (3-4 years 4) Must rely on outside agency (see (A) above).
from planning stage).
C. Intensive Post-Treatment (One Watershed-Paired Sites) (4-5 years, following treatment).
Advantages Disadvantages
1) Shorter time for results than (A). . 1) Provides no strict control-requires assumption that upstream
control was identical to treated area prior to treatment.
2) Moderate ability to assess year-to-year variation.
2) "Control" most logically must be located upstream of treatment.
3) Provides opportunity for moderate level of effort on Strong downstream trend in any feature would confound
process studies. analysis.
3) Provides no spatial perspective-results of limited
application elsewhere. application elsewhere.
3 « US GOVERNMENT PHINTINOOFFICE: 1«61 -757-012/7183
-------
Table 1. {Continued)
D. Extensive Post-Treatment. 10-30 Watersheds (or more); all observations in 1-2 years (variable time after treatment).
Advantages Disadvantages
1) Wide spatial perspective allows extrapolation to other
areas.
2) Long temporal perspective is possible-can assess
recovery for as many years as past treatments have
occurred.
3) Provides ability to assess interaction of physical setting
and treatment effects (e.g., effects of sediment input
at different stream gradients).
4) Requires least time of all four designs to get results—
as little as 2 years.
5) Probably most economical of all four approaches per
unit of information.
1) No data available on pre-treatment conditions-forces
assumption that control and treatment were identical
(on average).
2) Control predominantly upstream.
3) Total cost concentrated in very short period—requires
extensive planning.
4) Not as effective as (A) in assessing whole watershed effects.
5) Methods used in early treatments may not be comparable
to later ones.
James D. Hall and Ned J. Knight are with the Department of Fisheries and Wild-
life, Oregon State University, Corvallis, OR 97331.
Jack H. Gakstatter is the EPA Project Officer (see below).
The complete report, entitled "Natural Variation in Abundance of Salmonid
Populations in Streams and Its Implications for Design of Impact Studies,"
(Order No. PB 81-163 214; Cost: $9.50, subject to change) will be available
only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22J61
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Corvallis, OR 97330
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
RETURN POSTAGE GUARANTEED
PS 0000329
U S ENVIR PROTECTION AGENCY
REGION 5 LIBRARY
230 S DEARBORN STREET
CHICAGO IL 60604'
------- |