PB85-217669
Reproduction and Distribution of Fishes in a
Cooling Lake: Wisconsin Power Plant Impact Study
Wisconsin Univ.-Madison
Prepared for
Environmental Research Lab.-Duluth, MN
Jun 85
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA/600/3-85/049
3. RECIPIENT'S ACCESSION NO.
5 217669/1$
4. TITLE AND SUBTITLE
REPRODUCTION AND DISTRIBUTION OF FISHES IN A COOLING
LAKE: Wisconsin Power Plant Impact Study
5. REPORT DATE
June 1985
6. PERFORMING ORGANIZATION CODE
7. AUTHORISI
8. PERFORMING ORGANIZATION REPORT NO.
Dennis W. Rondorf, and James F. Kitchell
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Water Resources Center
University of Wisconsin-Madison
Madison, WI 53706
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
803971
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Research Laboratory
U.S. Environmental Protection Agency
Office of Research and Development
Duluth, MN 55804
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA-600/03
15. SUPPLEMENTARY NOTES
16. ABSTRACT Spatial and temporal patterns during reproduction and early life history
of fishes were studied in a manmade cooling lake. Lake Columbia, impounded in 1974,
near Portage, Wisconsin, has an area of 190 ha, a mean depth of 2.1 m, and a 15 C
temperature gradient derived from the thermal effluent of a 527-MW fossil-fueled
generating station which began operating in 1975. The lake was initially colonized by
fishes when filled with Wisconsin River water. Observations suggest a decline of
species diversity of the fish community due U> direct action of upper lethal tempera-
tures, absence of colonization by warm-water, lake-dwelling species, and lack of
recruitment for certain species. Spatial and temporal patterns of spawning of black
crappie were altered by a rapid rise in water temperatures following plant start-up
after a threer-week shutdown. Water temperatures above expected spawning temperatures
reduced available spawning area and induced aggregation of sexually mature black
crappie at coolest available temperatures. Elevated temperatures subsequently
shortened the spawning season, induced resorption of ova, and caused loss of secondary
sexual characteristics. A second generating unit began operating in February 1978.
Spawning of black crappie and white bass occurred 1 month earlier during the spring of
1978 than in 1977. Species abundance of larval fish catches was greater in 1978 when
the spawning season was not unusually abbreviated, as in 1977. After initially
drifting with water current, juvenile stages of sunfish and gizzard shad responded to
changes in the thermal gradient by horizontal and vertical shifts in abundance.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
3. DISTRIBUTION STATEMENT
Release to public
19. SECURITY CLASS (This Report!
Unclassified
21. NO. OF PAGES
69
20. SECURITY CLASS (Thispage)
Unclassified
22. PRICE
EPA Form 2220-1 (Re». 4-77)
PREVIOUS EDITION IS OBSOLETE
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NOTICE
This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication. Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.
11
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FOREWORD.
Ths U.S. Environmental Protection Agency (EPA) was designed to
coordinate our country's efforts toward protecting and improving the
environment. This extremely complex task requires continuous research in a
multitude of scientific and technical areas. Such research is necessary to
monitor changes in the environment, to discover relationships within that
environment, to determine health standards, and to eliminate potentially
hazardous effects.
One project, which the EPA is supporting through its Environmental
Research Laboratory in Duluth, Minnesota, is the study "The Impacts of Coal-
Fired Power Plants on the Environment." This interdisciplinary study,
centered mainly around the Columbia Generating Station near Portage, Wis.,
involves investigators and experiments from many academic departments at the
University of Wisconsin and is being carried out by the Environmental
Monitoring and Data Acquisition Group of the Institute for Environmental
Studies at the University of Wisconsin-Madison. Several utilities and State
agencies are cooperating in the study: Wisconsin Power and Light Company,
Madison Gas and Electric Company, Wisconsin Public Service Corporation,
Wisconsin Public Service Commission, and Wisconsin Department of Natural
Resources.
Spatial and temporal patterns during reproductive and early life
history of fish were studied in a man-made cooling lake. Fish initially
colonized the lake when it was filled with water from the Wisconsin River.
Observations suggest a decline of species diversity in the fish community
caused by upper lethal tempertures, absence of colonization by warm-water,
lake-dwelling species, and lack of recruitment for certain species.
Norbert A. Jaworski
Director
Environmental Research Laboratory
Duluth, Minnesota
iii
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ABSTRACT
Spatial and temporal patterns during reproduction and early life
history of fishes were studied in a manmade cooling lake. Lake Columbia,
impounded in 1974, near Portage, Wisconsin, has an area of 190 ha, a mean
depth of 2.1 m, and a 15 C temperature gradient derived from the thermal
efluent of a 527-MW fossil-fueled generating station which began operation
in 1975.
The lake was initially colonized by fishes when filled with Wisconsin
River water. Observations suggest a decline of species diversity of the
fish community due to: (1) direct action of upper lethal temperatures,
(2) absence of colonization by warm-water, lake-dwelling species, and
(3) lack of recruitment for certain species.
Spatial and temporal patterns of spawning of black crappie (Pomoxie
nigromaculatus') were altered by a rapid rise in water temperatures following
plant start-up after a 3-week shutdown. Water temperatures above expected
spawning temperatures reduced available spawning area and induced
aggregation of sexually mature black crappie at coolest available
temperatures. Elevated temperatures subsequently shortened the spawning
season, induced resorption of ova, and caused loss of secondary sexual
characteristics.
A second generating unit began operation in February 1978. Spawning of
black crappie and white bass Qdorone ahrysops) occurred 1 month earlier
during the spring of 1978 than in 1977.
Species abundance of larval fish catches was greater in 1978 when the
spawning season was not unusually abbreviated, as in 1977. After initially
drifting with water current, juvenile stages of sunfish (Lepomie sp.) and
gizzard shad (Dorosoma aepedianum) responded to changes in the thermal
gradient by horizontal and vertical shifts in abundance.
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CONTENTS
Foreword ill
Abstract • iv
Figures... .. vi
Tables viii
Acknowledgments ix
1. Introduction .... 1
2. Study Site . 2
3. Relative Abundance of Fishes 6
Introduction 6
Methods 6
Results 7
Discussion 10
4. Reproduction of Fishes 15
Introduction 15
Methods 15
Results 17
Discussion 26
5. Distribution of Larval Fishes 30
Introduction 30
Methods 30
Results 32
Discussion 45
6. Conclusions 49
7. Recommendations 50
References 52
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FIGURES
Number Page
.1 Map of Lake Columbia,.Wisconsin. 3
2 Water current velocity and thermal gradient > 4
3 Mean dally power plant water intake, outfall, and air
temperature during the first 6 months of 1977 and 1978 5
4 Shannon-Weaver diversity index and percent similarity
to first sample of quarterly fyke net catches 8
5 Mean catch per effort in fyke nets during quarterly
sampling periods 9
6 Length frequency distributions of black crappie and white
bass, 1975-7 7... 11
7 Percent increase or decrease in abundance of selected
fishes 12
8 Mean gonadosomatic index of female white bass during the
springs of 1977 and 1978 18
9 Mean gonadosomatic index of female black crappie during
the springs of 1977 and 1978 20
10 White bass distribution during presence and absence of
thermal gradient during the spring of 1977 21
11 Black crappie distribution during presence and absence of
thermal gradient during the spring of 1977 22
12 Mean gonadosomatic index of female black crappie during the
springs of 1977 and 1978 and the percent of surface area of
Lake Columbia with water temperatures in the range of
expected spawning temperatures of black crappie -.. 24
13 Minimum and maximum water temperatures during the spring
1977 and expected spawning temperatures of selected
species 25
vi
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14 Number of.larval and early juvenile fishes per cubic meter
of water sampled by Miller sampler during the springs of
1977 and 1978 33
15 Expected median and interquartile limits of water
temperature based on distribution of sampling effort and
the observed temperature at location of capture of larval
and early juvenile periods of Lepomie sp. and gizzard
shad during 1977 35
16 Abundance and temperature at location of capture in light
traps for larval and early juvenile Lepomis sp. during the
spring of 1977 36
17 Abundance and temperature at location of capture in
Miller samplers for larval and early juvenile gizzard
shad during the spring of 1977 38
18 Length frequency of gizzard shad captured at warm stations
and cool stations on 19 and 29 May 1977 39
19 Percent of gizzard shad caught at 0.5 and 1.2 m at different
times of day on 18 to 20 and 29 to 30 May 1977 41
20 Percent of gizzard shad catch at each station for 0.5 m
depth with evening Miller tows and for sum of catches at 0.5
and 1.2 m during a 24-h period on 18 to 20 and 29 to 30 May
1977 43
21 Abundance of larval gizzard shad at time, location, and
temperature of capture on 24 May 1978 44
22 Number of gizzard shad caught at 0.5, 1.0, and 1.5 m depth
at cool temperatures on 17 May and warm temperatures on
18 May 1978 46
vii
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TABLES
Number
Expected spawning temperatures based on values in
literature and observed spawning temperature for black
crappie 26
Number of larval and juvenile fishes caught in light traps
and Miller samplers, 1977-78 34
The G-statistic values partitioned according to the
hypothesis tested for three factor diel vertical migration
observations 40
The G-statistic values partitioned according to the
hypothesis tested for three factor observations on thermal
suppression of vertical migration 45
viii
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ACKNOWLEDGMENTS
The U.S. Environmental Protection Agency is gratefully acknowledged for
providing financial support through the Environmental Research Laboratory in
Duluth, Minnesota. Financial support was also received from the U.S.
Department of the Interior, Office of Water Research and Technology through
the Water Resources Center, University of Wisconsin-Madison. We would also
like to thank the faculty, staff, and students of the Laboratory of
Limnology, University of Wisconsin-Madison.
ix
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SECTION 1-
INTRODUCTION
Impoundment of a man-made cooling lake provides an opportunity for
development of a recreational fishery. Thermally elevated areas of a cool-
ing lake can increase angler utilization by concentrating fishing effort and
extending seasonal angler use in temperate climates (McNurney et al.
1977). Because the cooling lake is a relatively small man-made system it
has greater potential and flexibility for recreational fishery management
than many systems.
Fish management strategies of stocking or fish harvest for temperate
lakes based on surface area or morphoedaphic characteristics will not be
valid for lakes substantially altered by thermal input. The elevated
thermal conditions of cooling lakes create temporal and spatial limiations
for organisms native to nearby lakes. Growth (Bennett and Gibbons 1974),
distribution (Merriman and Thorpe 1976), and reproduction (Bennett and
Gibbons 1975, Kaya 1977) are modified in thermally altered areas. Lake
Columbia, located at the Columbia Generating Station near Portage,
Wisconsin, provides an opportunity for research and development of manage-
ment strategies specifically for cooling lakes in the Great Lakes region.
As a subproject of an assessment of a developing cooling lake ecosystem
(Lozano et al. 1978), this study of fishes concerned the reproductive
responses of adults and distributional patterns of adult, larval, and early
juvenile forms in Lake Columbia. . The objectives were: (1) determine
changes in species composition of the fish population; (2) delineate
temporal and spatial limits of fish reproduction; and (3) determine distri-
butional patterns of larval and early juvenile fishes.
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SECTION 2
STUDY SITE
Lake Columbia, Columbia County, Wisconsin, is a 190-ha closed-cycle
cooling reservoir for a fossil-fuel generating plant owned by Wisconsin
Power and Light Co. The cooling reservoir was created within dikes over a
peat sedge meadow. The lake was first filled in June 1974, but the water
levels gradually declined until the lake was refilled in November 1974.
Water levels were then maintained through March 1975 when testing of the
527-megawatt (MW) Columbia I unit began. Columbia II, a second 527-MW unit,
began operating in February 1978.
A central baffle dike constructed of gravel separates the east and west
arms of the reservoir (Figure 1). Dike slopes are covered with rock rip-
rap. Water depth is between 1.9 and 2.4 m, with an average depth of 2.1
m. To compensate for leakage and evaporative loss, water from the Wisconsin
River is pumped at rates up to 52 m /min into a settling basin before
entering the main body of the reservoir.
Water is removed from the reservoir at the intake channel and pumped
through the power-plant condensers where temperatures are raised about 15
C. Effluent water flows from the outfall channel and circulates around the
center baffle dike back to the intake channel in approximately 5 days .
Water is pumped through the power plant condensers at a rate of 750
m /min. Current velocity and water temperature decline exponentially as
water flows from outfall to intake channel (Figure 2). Current velocity
increases as flow is constricted near the settling basin and intake. During
periods of power-plant shutdown, isothermal conditions exist. Water
temperatures measured in the settling basin were 5 to 6 C cooler than intake
temperature. January to July variations in water temperature between
outfall and intake are shown in Figure 3.
Lake configuration and shallow depth causes vertical mixing and results
in little thermal or chemical stratification. Except for temperature and
current (Figure 2), there are no consistent horizontal gradients of physical
and chemical parameters (Andren et al. 1976).
Partially decomposed peat and detrital material cover the bottom of the
lake except near the south end where it was removed during construction.
Macrophyte surveys during 1975 indicated that production declined rapidly
during the first summer of operation and was restricted to areas near the
intake in subsequent summers (Lozano et al. 1978).
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-N-
0 0.1
I I
0.5
I
kilometers
Baffle Dike
Outfall
Intake
Settling
Basin
1 2
DISTANCE FROM PLANT (km)
Circulation
Figure 1. The cooling lake at the Columbia Generating Station.
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40-
a
o
20-
w
H
Z
0-
15-
2 10-
w
l-l
o
5-
0-
0 '
-" .00162 + .02452X - .0009 X2
Y = 18.51e--089X
r2 - .87
20
40
DISTANCE FROM OUTFALL (100 m)
60
Figure 2. Water current velocity and thermal gradient in the cooling lake.
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50
40
30
20
10
0
-10
-20H
! 50H
w
H
40H
30-
20-
10-
0-
-10-
-20-
1977
Outfall
1978
•• #
f: /
A A :'\:
V': ••" "'
»•* •.%•
I r~F
M - ' - J - ' - j
MONTH
Figure 3. Mean daily power plant water intake, outfall, and air
temperature during the first 6 months of 1977 and 1978.
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SECTION 3
RELATIVE ABUNDANCE OF FISHES
INTRODUCTION
New Impoundments are known foe the dramatic changes they cause In fish
communities after filling. Studies suggest these changes can be attributed
to changes of biotlc and abiotic characteristics of the impoundment (Jenkins
and Morais 1971). In the cooling lake environment, the effects of the
unique thermal regime are imposed on these expected changes in the fish
community. Therefore, the first objective was to determine if changes in
species composition of the fish population occurred with time.
The fish community was initially established in Lake Columbia by colo-
nization from the Wisconsin River and its backwaters. A drain culvert
connected the lake with an adjacent marsh and permitted fish to enter during
construction. Following.the filling of the lake in 1975 the Wisconsin
Department of Natural Resources (WDNR) introduced largemouth bass in an
effort to establish a warm-water sport fishery.
METHODS
Composition of the fish community and the relative abundance of adults
at locations in Lake Columbia were assessed using fyke nets. Fyke nets were
constructed with 32-mm stretch mesh nylon webb, and equipped with a 15.2-m
lead, 1.8-m frames, and five 0.75-m diameter hoops. Nets were set perpen-
dicular to shore for 24 h with regular sampling stations at 0.5, 1.3, 2.2,
3.8, 4.5, and 5.5 km from the outfall (Figure 1). Fish were identified,
measured for total length, and weighed.
Water temperatures were measured at 0.5, 1.0, 1.5, and 2.0-m depths
when nets were set and raised. Recording thermographs were used during
spring and summer in 1977 and 1978 to continuously monitor diel temperature
changes. Current velocities were measured using an electromagnetic water
current meter.
The number of fish per fyke net set—catch per effort (CPE)—was used
as a measure of the relative abundance of fish species over time. Two
hundred thirty-four fyke net sets were completed on 49 sampling dates from
July 1975 through May 1978. Mean quarterly CPE was calculated from monthly
catches from December to February, March to May, June to August, and
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September to November. Species diversity of the fish population in
quarterly fyke net catches was calculated using the Shannon and Weaver
(1963) general index of diversity (H) . Percent similarity was calculated
between each quarterly catch and the catch from the first quarter of 1975
using the following formula:
2 - IP. . -.P. . x 100
where
1 = tJie Pr°P°rtion °f species i in the first quarter;
= the proportion of species i in the k-th quarter.
RESULTS
During the sampling period, 24,403 fish were caught in fyke nets.
Thirty species of fish were represented in the catch.
The Shannon-Weaver diversity index suggests a decline in diversity of
quarterly catches that started in the winter of 1975-76 and continued
through the fall of 1976 (Figure 4). In fall 1976 only 34% of the catch was
similar to that of summer quarter 1975. In the fall quarter of 1976 black
bullhead (Ictalurus melae) made up 71.5% of the catch, the highest percent
for a single species of all quarterly samples. Pumpkinseed sunfish (Leporrtis
gibboeus) and black crappie (Pomoxis nigrormculatus') were at low levels in
fall 1976, while northern pike (Esox luaius") were absent from catches
following a die-off in summer 1976. Species diversity did not return to
1975 levels.
Changes in the diversity of fyke net catches can be attributed to a
decline of CPE for some species and numerical dominance by others. The mean
quarterly CPE of centrarchids in Lake Columbia (Figure 5A) indicates that
the abundance of pumpkinseed sunfish declined somewhat between July 1975 and
August 1977. The mean CPE for white bass Q4orone chrysops) (Figure 5B) was
high in the winter quarter samples and decreased during the study period.
Bluegill (Lepomis macrochirus) catches increased dramatically, showing the
first peak during fall 1976 and a second during summer 1977. Gizzard shad
(Doroeoma cepedianum) CPE increased from none caught during the first
quarter to a CPE >5 in 1977 (Figure 5B).
Bluegill and gizzard shad length frequencies indicate successful growth
and reproduction in the new lake environment, as evidenced by increased
CPE. Length frequencies of bluegill suggested an increase of fish <150 mm
in length by June 1976. The increased contribution from bluegill <150 mm
corresponds with the quarter in which bluegill CPE began to increase (Figure
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00
2.0n
Q
z
CO
Q£
LU
1.0-
Pecent similar to first sample
I I
I. I
rlOO
73
n
-50
S FWS S FWS S
1975 1976 1977
Figure 4. Shannon-Weaver diversity index (H) and percent similarity to first
sample of quarterly fyke net catches in Lake Columbia.
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H
OT
H
Px
a!
H
, Bluegill
•••
s&. crappie
•Pumpklnseed
6. shad
W. bass
1.5H
0.5-1
Quillback
SFWSSFWSS
1975
1976
1977
Figure 5. Mean catch per effort in fyke nets during quarterly
sampling periods in Lake Columbia.
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5A). Length frequencies of gizzard shad show an increasing abundance of
smaller shad in January 1977 that also corresponds with dramatic increases
in CPE during the winter quarter of 1977 (Figure 5B).
Length frequencies of black crappie and white bass suggest limited
recruitment (Figure 6). Examination of scale samples showed that the length
frequency modes were different year classes (Lozano et al. 1978). Black
crappie length frequency modes were made up of the 1973 and 1974 year
classes. The largest mode of white bass was the 1974 year class (Figure
6B). Year classes strongly represented in length frequencies of black
crappie and white bass were from years prior to power plant operation.
Other fish species common to the Wisconsin River were found in Lake
Columbia. The relationship between changes in relative abundance, final
temperature preferenda, and upper incipient lethal temperatures of the most
abundant species in fyke net catches is shown in Figure 7. Yellow perch
(Perca flavescene) and walleye (Stizostedion vitreum) made up <0.5X of the
catch in all quarters. Species at low abundance that have decreased in CPE
Include qulllback (Carpoides cyprinus), smallmouth buffalo (Ictiobue
bubalue), and carp (Cyprinue c&rp-io) (Figures 5C,7). Minnow trap catches
indicated fathead minnows (Pimephales promelas) and mud minnows (Umbra lirrri)
were abundant when the plant began operation in March 1975, but abundance
was reduced by July. The mean quarterly CPE of northern pike declined 99%
between the first and third year of the study. Northern pike disappeared
from catches during the summer quarter of 1976 (Figure 5B). On 17 July
1976, 97 dead northern pike were found along the middle dike of the lake.
Water temperatures were high (>29.6 C at all depths), dissolved oxygen was
low (2.5 ppm), and wind conditions were calm prior to the time that the dead
fish were observed. Bluegill abundance increased more than eight-fold
between the first and third years (Figure 7).
DISCUSSION
The decline in species diversity of fyke net catches can be attributed
to: (1) an absence of colonization by warm-water, lake-dwelling species;
(2) direct action of upper lethal temperatures; and (3) lack of recruitment
for certain species. The lack of colonization by warm water fishes is
expected since the cooling lake is similar to the biological communities of
an island. In this case its geographic isolation from other warm water
communities reduces the chance of natural colonization. In addition, colo-
nizing species must survive water temperatures near 30 C in summer and be
able to acclimate to water temperatures near 0 C in winter during shutdowns.
Thermal characteristics of Lake Columbia were important in structuring
the fish community through the direct action of upper lethal temperatures.
The rapid disappearance of fathead minnows can also be attributed to high
water temperatures. Fathead minnows acclimated to 30 C prefer high
temperatures of 26.5 to 30.3 C, but exposure to 33 C has been found to be
lethal (Cherry et al. 1977). The observed kill of northern pike eliminated
a large piscivorous mesotherm that is an important predator in temperate
10
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Black crappie
40
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40
0
40
0
40
. 0
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se
£ 0
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Aug. 75
Jan. 76
June 76
Jan. 77
Mav 77
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® White bass
1 I Aue.75
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June 76
Jan. 77
rrTHlTU
rf
r-m
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r*i 1-1
h«
20 30
TOTAL LENGTH (cm)
40
Figure 6. Length frequency distributions of black
crappie and white bass, 1975-77.
11
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PREPERRED TEMPERATURE ± S.D.
INCIPIENT LETHAL TEMPERATURE
Gizzard shad
Bluegill
Black bullhead
Black crappie
Yellow perch
White bass
Pumpkinseed
Carp
Carpsucker sp.
Buffalo sp.
Northern pike
20 30 40
TEMPERATURE (C)
N = nonguardlng spawners
G = guarding spawners
PERCENT
DECREASE/INCREASE
50
0 400
PERCENT
800
REPRODUCTIVE
GUILD
N. Lltho-pelagophil
G. Lithophil
G. Lithophil
G. Phytophil
N. Phyto-Lithophil
N. Phyto-Llthophil
G. Polyphll
N. Phytophil
N. Psammophil
N. Phytophil
N. Phytophil
REFERENCE
PREFERRED, LETHAL
a, b
a, c
a, d, e
a. b
a, c
a. e
a. b
a. b
a, e
Figure 7. Percent increase or decrease in abundance of selected fishes in Lake Columbia.
Preferred and upper incipient lethal temperatures of fish are from other
sources (Reutter and Herendorf 1974, Brungs and Jones 1977, Cherry et al.
1977, Coutant 1977, Cvancara et al. 1977). Reproductive guilds are from Balon
(1975a).
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lakes with similar morphometric characteristics. Northern pike have a
laboratory final preferendum of approximately 24 C and an upper incipient
lethal temperature of 30.8 C LD^Q (Cvancara et al. 1977), approximately
equal to 29.6 C observed prior to the fish kill. . Bluegill, which have a
final preferendum of 30.5 C and a 7-day upper lethal temperature of 36 C
(Cherry et al. 1977), increased more than eight-fold. Species that
increased in abundance had final preferenda ranging from 20.5 to 30.5 C and
upper lethal temperatures ^?3 C. Other species with relatively high upper
lethal temperatures, such as white bass (LD^Q = 33.5 C; Cvancara et al.
1977) and carp (LD.JQ = 36 C; Brungs and Jones 1977) decreased in
abundance. This suggests that other factors were Important in determining
the abundance of some species.
The lake habitat changed rapidly with increased water temperature,
water depth, and the disappearance of macrophytes when the power plant began
operation. Subsequent recruitment of bluegill and the apparent lack of
success by pumpkinseed changed the centrachid complex from numerical domina-
tion by pumpkinseed to numerical domination by bluegill. Bluegill feed
higher in the water column and in many cases the major components of the
diet are chironomid larvae and zooplankton, while pumpkinseed feed on
benthic prey such as mollusks and isopods associated with macrophytes
(Werner et al. 1977, Keast 1978). The abundance of chironomid larvae
(Krornery 1976), lack of macrophytes (Lozano et al. 1978), and minimum summer
water temperatures near 30 C indicate that the bluegill is well adapted to
the cooling lake habitat.
The lack of recruitment by black crappie, white bass, and other species
with decreases in CPE is not readily explained by final preferenda or upper
incipient lethal temperatures (Figure 7). Rapid growth (Lozano et al. 1978)
of black crappie (final preferendum 21.7 C), northern pike (Eeox sp.; 24 to
26 C), pumpkinseed (27.7 C), and white bass (28 to 30 C) (Coutant 1977)
suggests that species with a wide range of optimal growth temperatures were
able to find adequate food and temperature suitable for growth in the
heterothermal lake. The lack of recruitment may result from natural
variation in year class strength or inhibited reproduction due to exposure
to high temperature, such as observed for trout (Kaya 1977) and yellow perch
(Hokanson 1977).
Species which increased in abundance tended to have reproductive
characteristics in common (Figure 7). The reproductive guilds described by
Balon (1975a) Indicate that species with increasing CPE tended to be nest
guarding lithophlls, species utilizing gravel or sand spawning substrates.
Species such as carp, buffalofish, and northern pike declined more than 50%
in abundance and belong to the nonguarding phytophil guild which utilizes
flooded vegetation as a spawning substrate (Figure 7). The spawning of carp
and northern pike is inhibited by the lack of flooded vegetation (Balon
1975a, June 1978). In this case, in Lake Columbia, water temperatures would
indirectly inhibit spawning by causing macrophytes to disappear in areas of
higher temperatures.
In conclusion, the decline of species diversity resulted from a lack of
colonization by warm-water fish species, mortality caused by water tempera-
13
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Cures exceeding upper lethal temperatures of some species, and a lack of
recruitment by other species. Bluegill are well adapted for the cooling
lake because of their relatively high thermal preferendum, planktivorous
diet, ability to forage in open water habitat and presence of suitable
spawning habitat. Species with limited recruitment tended to belong to
similar reproductive guilds, usually nonguarding phytophils.
14 ' !
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SECTION 4
REPRODUCTION OF FISHES
INTRODUCTION
Thermal requirements for reproduction of a species are one of the
primary limits to distribution and abundance (Alderdice and Forrester 1968,
Hokanson 1977). Temperature and photoperiod are environmental factors
Important in the recrudesence of gametogensis of many teleosts (De Vlaming
1972, 1974, Schrech 1974, Hokanson 1977). The unique thermal regime in the
cooling lake creates temperatures during winter and early spring at or above
those associated with the initiation of spring spawning. The thermal
gradient was expected to determine the spatial and temporal location of
spawning within limits of photoperiod control. Thus, the second objective
was to study the temporal and spatial limits of reproduction within Lake
Columbia. White bass and. black crappie were selected for study because
adults were growing well but did not appear to be producing young.
METHODS
Temporal Patterns of Reproduction
Temporal patterns of reproduction were determined by monitoring the
maturity of white bass and black crappie from the initiation to the
completion of spawning during the springs of 1977 and 1978. The percent
gonad weight of total body weight or gonadosomatic index (GSI = gonad
wt/total fish wt x 100) was calculated as a measure of maturity at 2-week
intervals starting in February 1977. Sampling intervals were shortened as
fish became more sexually mature. Fish were removed from 24-hr fyke net
sets, subsampled within specific size classes, and frozen on dry ice.
During 1977, length strata were 200 to 300 and 250 to 350 mm for black
crappie and white bass, respectively. During 1978 the lengths were 250 to
350 and 300 to 400 mm for black crappie and white bass, respectively.
Samples of 10 to 15 fish of each sex per date were frozen for dissec-
tion. Remaining fish were classified according to eight stages of maturity
(Bagenal and Braum 1971) and released. Specimens were taken to the labora-
tory where total length and total weight were measured. Gonads were then
removed, blotted for 1 min on an absorbent towel, and weighed to the nearest
0.01 g. When fish were abundant, equal numbers, were selected from stations
15
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0.1 to 2.9 km (warm side) and 3.0 to 6.0 km (cool side) from the outfall
(Figure 1).
Spatial Patterns of Reproduction
Spatial limiations of spawning relative to the thermal gradient were
examined during the springs of 1977 and 1978. Relative abundance of
sexually mature fish at various locations in Lake Columbia was determined by
fyke nets as previously described. Abundance of adults recorded as CPE was
regressed on mean water temperature at station of capture and station loca-
tion in km from the outfall. Differences between distributions described by
least square linear regression were tested by comparing slopes of the lines
(Snedecor and Cockran 1967). For nonlinear distributions, observed CPE in
0.5 C intervals was compared to the expected CPE using the two sample
Kblmorgorov-Smironov test (Siegel 1956).
Thermal exposure of adult black crappie was estimated from equations
describing distribution of adults and the thermal gradient. The least
squares linear regression of log mean water column temperature (N - 4) on
station location (N = 20) was used to describe the decline in water tempera-
ture. The regression equation was then used to generate predicted mean
water column temperature (f) for station locations at 0.1 km intervals on a
daily basis. Predicted mean water temperature values of each station (T)
were then adjusted by adding the difference between the mean intake tempera-
ture of a given day and the mean intake temperature predicted by the regres-
sion.
Mean intake temperatures were calculated by integration of water
temperatures recorded by Ryan thermographs located 0.5 km from the intake.
Temperature records were integrated using a Hewlett-Packard model 9107A
calculator and digitizer. Missing data during 1977 were replaced by daily
mean intake temperatures provided by the Columbia Generating Station and
Wisconsin Power and Light, Inc. .Daily mean intake temperatures were
calculated from readings taken at 4-h intervals at the Columbia I intake.
The regression fit of mean water temperature on station was an
exponential function:
T = 14.16e - 0.049X
r2 = 0.98
where
f = predicted mean water column temperature at the station;
X = a given station (1 to 60) at 0.1 km intervals from 0.1 to 6.0
km from the outfall.
16
-------
Median and interquartile limits of the thermal exposure are those mean
water column temperatures corresponding with 25, 50 (median), and 75% levels
of the black'crappie distribution. Percent levels of distribution were
calculated by the summation of predicted values from equations describing
fyke net catches of sexually mature fish.
Gamete Viability
Black crappie gamete viability was tested. Testes of three males were
removed, blotted dry, and held in petri dishes floating in a water bath at
22 C in an insulated ice chest. Ova of three females were then stripped
separately into petri dishes and fertilized with spermatozoa from two
different fish. Several drops of water were added and ova were allowed to
sit 5 tain. Embryos were then moved to floating incubation cups with nitrex
mesh bottoms for transport to the laboratory. At the laboratory embryos
were incubated at room temperature (19 to 20 C). Water from Lake Columbia
was replaced in the incubation bath twice daily. Microscopic examination of
selected embryos was made during incubation. When hatching began, ova were
fixed for 5 min in a 4% glacial acetic acid and 0.7% NaCl solution and
preserved in 5% buffered formalin for later examination of embryos (Bagenal
and Braum 1971). About half of the ova in one incubation chamber were
allowed to hatch and held in an aquarium. The randomness of hatching
success in each of 10 incubation cups was tested using the multiple runs
tests (Siegel 1956).
RESULTS
Temporal Patterns of Reproduction
From 10 to 30 April 1977, the Columbia I generating unit shut down for
maintenance. This resulted in a rapid decrease followd by an increase in
water temperatures, which in turn altered the temporal placement and dura-
tion of spring spawning. During the shutdown water temperatures in the lake
were isothermal; Although the Columbia I generating unit did shut down
between 6 and 16 April 1978, changes in water temperature and its effects on
the temporal placement of spawning were minimized by the operation of the
Columbia II generating unit (Figure 3).
Mean GSI of female (Figure 8A) and male white bass increased steadily
during spring 1977 until power plant shutdown in early April and then
declined slightly between 3 and 29 April. During the shutdown a slight
decline in GSI suggested spawning was occurring prior to plant start-up, but
no running ripe females, spent females, or spawned ova were found in the
nets. When power plant operation resumed 1 May 1977 the decrease in mean
female GSI from 12.2 on 29 April to 1.9 on 11 May coincided with an increase
in water temperatures (Figure 8A). By 11 May, only 12 days later, white
bass ovaries were completely spent, and in an advanced stage of resorption.
17
-------
20-
H 10
X
UJ
Q
O
5
O
CO
O 20
Q
O
O
10
[Mean and 95% Confidence Interval
—-Outfall Water Temperature
1977
1978
F M A
MONTH
M
40
20
•40
-20
HI
GC
UJ
Q.
UJ
H
Figure 8. Mean gonadosomatic index (GSI) of female white
bass during the spring of 1977 and 1978.
18
-------
During the spring of 1978 a decline of female white bass GSI began at
least 36 days earliet and lasted 28 days longer than during 1977. Mean GSI
of female white bass decline from 13.1 on 25 February to 2.4 on 3 May 1978,
(Figure 8B). Mean GSI of male white bass also declined from 4.7 on 15 March
to 0.5 on 3 May 1978.
The GSI of black crappie during the spring of 1977 increased and
declined similar to the GSI of white bass in 1977. Male black crappie mean
GSI was highest on 16 April and declined to a low on 11 May after resumption
of plant operation. Mean GSI of female black crappie continued to increase
during April shutdown to 6.4 and then declined sharply to 3.9 after the
power plant resumed operation (Figure 9A). The decline of female mean GSI
coincided with a rise in lake water temperatures when the generating plant
returned to operation 1 May. The resulting decrease in GSI accounted for
only 38% loss of mean ovary weight while most of the remaining ovarian
weight was resorbed. Ovaries of most black crappies contained atretic ova
and yolk material in which ova were not readily discernable. Between 29
April and 11 May male black crappies lost most of the melanistic color
pattern typical of breeding adult male crappies.
The decline of mean GSI of female black crappie in 1978 began 30 days
earlier in the spring and lasted 25 days longer than in 1977. Mean GSI of
female black crappie was highest on 28 March at 8.2 and subsequently
declined to 2.2 on 3 May 1978 (Figure 9B). Mean GSI of male black crappie
was highest on 1 April 1978 at 0.98 and lowest at 0.42 on 3 May 1978.
Spatial Patterns of Reproduction
Shutdown and resumption of power plant operation did not significantly
affect white bass distribution. The mode of distribution at 3.8 km from the
Intake accounted for 85% of the total catch prior to the shutdown (Figure
10A), 58% of the total during the shutdown (Figure 10B), and 43% of the
total after shutdown (Figure IOC). The mean CPE at stations sampled during
shutdown and after resumption of plant operation was not significantly
different using the Kblmorgorov-Smironov two sample frequency test
(p > 0.05). White bass did not aggregate at spring or summer final
preferenda temperatures (Reutter and Herdendorf 1974), but remained most
abundant 3.8 km from the intake (Figure 10). The distribution of sexually
mature white bass was similar during the spring of 1978, with a mode 3.8 km
from the Intake and fewer fish near the intake and outfall.
Black crappie distributions responded to water temperature changes
caused by power plant shutdown and the return of the plant to operation.
Prior to the shutdown black crappie aggregated in warmer water 6 km from the
power plant intake (r = 0.34, p < 0.05, Figure 11A). During the 3-week
power plant shutdown the aggregation of black crappie dispersed under
ambient water temperature conditions. A regression of number of black
crappie caught during the shutdown on station location did not have a slope
significantly different from zero (r2 = 0.003, p > 0.05, Figure 11B). The
return of the thermal input into Lake Columbia on 1 May 1977 following a 3-
19
-------
—Outfall Water Temperature
J Mean and 95% Confidence Interval
B-
6-
4-
55 ~
o
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Figure 9.
Mean gonadosomatic index (GSI) of female black
. crappie during the springs of 1977 and 1978.
20
-------
MEAN WATER TEMPERATURE (C)
14 16 18 20 24
80
20-
5-
18
80<
z
W
20-
U.
o
DC 5-
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22
i
Final Preferendum
®
March,1977
'km
thermal gradient \8
(km
24
I
28
I
32
_J C
I I
024
DISTANCE FROM INTAKE (km)
Figure 10. White bass distribution during presence
and absence of thermal gradient during the
spring of 1977. Final temperature preferenda
for spring (a) and summer (b) are from Reutter
-and Herdendorf (1974).
21
-------
6-
MEAN WATER TEMPERATURE (C)
14
16
18 20 24
Final Preferendum
I
km
March, 1977
ra«.34
P<0.05
18
18
VJ 80-
\L
s «••
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April, 1977
ra».003
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20-
22
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24
28
32
i km
May, 1977
ra*.55
P&.05
DISTANCE FROM INTAKE (km)
Figure 11. Black crappie distribution during presence and
absence of thermal gradient during the spring of
1977. Final temperature (+ 1 standard deviation)
preferenda for spring (a) and summer (b) are from
Reutter and Herdendorf (1974).
22
-------
week power plant shutdown resulted In a rise of water temperatures and the
spatial redistribution of spawning black crappie. As indicated by the
negative slope of the regression, fish were more abundant near the intake at
cool water temperatures after the shutdown (r = 0.55, p < 0.05, Figure
11C). Black crappie were more abundant during March at water temperatures
included in the spring final preferendum ± 1 SD and during April at summer
final preferendum ± 1 SD.
In constrast to the 1977 distribution of black crappie the 1978
distribution had a single mode with little change throughout the reproduc-
tive period. The mode of black crappie remained 2.5 to 3.0 km from the
intake.
The 1977 movement of sexually mature black crappie toward cooler
temperatures coincides with a rapid Increase in temperature, decrease in
GSI, and decline In available spawning area. Available spawning area was
identified as lake surface area with water temperatures ranging from 14.4 to
20.0 C. Black crappie are expected to spawn at these temperatures (Goodson
1966; Schneberger 1972). The surface area of the lake with water tempera-
tures suitable for spawning declined precipitously after the resumption of
power plant operation (Figure 12A). During 1978 when thermal input was not
Interrupted, the percentage of area within expected spawning temperature
fluctuated near 50% for 20 days and then declined as seasonal temperatures
increased (Figure 12B).
The precipitous decline of available spawning area during 1977 resulted
because water temperatures rose rapidly above expected spawning temperatures
(Figure 13). The rising water temperatures and declining available spawning
area ultimately resulted in exposure of the black crappie population to
temperatures above expected spawning temperatures. The thermal exposure of
a black crappie population distributed as described are shown in Table 1.
Thermal exposure during 9 to 13 May 1977—9 days after the resumption of
thermal input—had median and interquartile limits (25%, median, 75%) of
24.8, 25.2, and 26.0 C, respectively. These temperatures are substantially
above the range of expected spawning temperatures of 14.4 to 20.0 C.
Despite the movement of black crappie into cooler water in response to
Increased thermal input, interquartile limits of thermal exposure exceeded
the range of expected spawning temperatures.
Gamete Viability
Relatively high thermal exposure of black crappie before and during
197.8 spawning (Table 1) did not result in reduced gamete viability when
tested by artificial fertilization. Of the 5,746 black crappie embryos
incubated to test gamete viability, 74% reached the near-hatch stage. A
check of sperm viability in water under a microscope indicated > 90% of
sperm were highly mobile. The percent hatch in each of 10 incubating
chambers did not deviate significantly (p < 0.05) from random when tested
using a one sample runs test (Siegel 1956). Much of the embryo mortality
could be attributed to fungal growth among the large number of embryos
23
-------
GSI
Percent area
100i
75-
£ 501
Q_
I- 25-
O
Z c
I
00
1-1001
1977
UJ 75
UJ
uu 25-i
CL.
1978
/ \
M A
MONTH
M
r8
•6
-4
-6
^-4
O
2 X
UJ
Q
Z
8 8
o
Q
O
o
Figure 12. Mean gonadosomatic index (GSI) of female black crappie
during the springs of 1977 and 1978 and the percent of
surface area of Lake Columbia with water temperatures
in the range of expected spawning temperatures of black
crappie (14.4 to 20.0 C).
24
-------
50,
40-
§30-
I
20-
10-
bluegill
*»,y black crapple
white bass
maximum
temperature
5 ' A ' M~
MONTH 1977
Figure 13. Minimum and maximum water temperatures in Lake Columbia during
the spring of 1977 and expected spawning temperatures of
selected species.
25
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incubated in a confined system such as that used. A portion of the embryoes
were allowed to hatch. Swim-up fry developed that did not appear deformed.
TABLE 1. EXPECTED SPAWNING TEMPERATURES BASED ON VALUES IN LITERATURE AND
OBSERVED SPAWNING TEMPERATURES FOR BLACK CRAPPIE IN LAKE COLUMBIA
Temperature (C) Reference/Date
Expected (Range)
17.8 20.0 Schneberger (1972)
14.4 17.8 Goodson (1966)
Observed (25% interquartile, median, 75% interquartile) (1977)
14.9-18.0-21.6 Before shutdown (19 March to 8 April)
20.6-21.0-21.8 After shutdown (3 to 8 May)
24.8-25.2-26.0 After shutdown (9 to 13 May)
Observed (25% interquartile, median, 75% interquartile) (1978)
19.8-21.1-23.0 Before spawning (13 to 30 May)
18.6-19.8-21.5 During spawning (31 March to 16 April)
22.6-23.8-25.3 After spawning (17 April to 3 May)
DISCUSSION
Spatial limitations were imposed by the heterothermal environment of
the cooling lake on the spawning distribution of black crappie, but the
response of white bass was not as well defined. The observed aggregation
during spawning of black crappie at median temperatures of 21.0 and 19.8 C
during 1977 and 1978 (Table 1), respectively, was near the spring final
preferendum (Figure 11) of 21.0 C (Reutter and Herdendorf 1974). The
aggregation at a spring final preferendum that approximates optimum
temperatures for reproduction (17.8 to 20 C) (Schneberger 1972) would be a
reproductive advantage. However, in the cooling lake a subsequent rise in
water temperature stimulated spawning, reduced available spawning area, and
induced aggregation of black crappie at coolest available water
temperatures.
The observed distribution of black crappie before spawning in 1977 and
early in the spawning season of 1978 resulted in an estimated thermal
exposure at the upper limits of expected spawning temperatures. Spawning
was initiated at higher temperatures than expected based on literature
values. Yellow perch held at elevated thermal regimes in the laboratory
initiate spawning earlier and at higher temperatures (Hokanson 1977). The
slightly higher spawning temperatures observed may be the stimulus needed to
overcome the inhibiting effects of slighly shorter photoperiods of early
26
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spring and an elevated thermal exposure. Spawning at low temperatures can
be inhibited by insufficient gonadotropin levels (Hoar 1969). Perhaps a
similar inhibition due to low levels of gonadotropin may occur as a result
of an elevated thermal exposure. Plasma levels of gonadotropin and
spermatogenesis in the goldfish (Caraesuis auratus) are maximal at 17 to
24 C and inhibited at water temperatures near 30 C (Gillet et al. 1977).
Gonadotrophic hormones are associated with the production of gonadal
sex steroids which are involved in the development of secondary sexual
characteristics (DeVlaming 1974). Melanistic pigmentation, a secondary
sexual characteristic of male black crappies, was well developed during
spawning. The rapid loss of melanistic pigmentation observed in male black
crappie at elevated temperatures was analogous to the reduced male secondary
sex characteristics of male fathead minnows held at an elevated water
temperature of 30 C (Brungs 1971).
Female black crappies exhibited resorption of ova during 1977,
indicating that thermal limits of spawning were exceeded. The relative
importance of spawning and resorption of white bass ovaries could not be
evaluated for white bass because ovaries changed from partially spent to an
advanced stage of resorption within 12 days. Resorption of residual ova
amounted to about 50% of total fecundity of white bass in a thermally
unaltered reservoir (Ruelle 1977). Shrode and Gerking (1977) found the
thermal limits of oogenesis of the eurytherm Cyprinodon ns. nevadenis, a
desert pupfish, were even narrower than the limits for successful hatching
of eggs exposed to temperature stress after spawning. The observed
physiological changes of black crappie, and white bass were similar to those
described for golden shiner (Notemigonus cryeoleucas) exposed to elevated
temperatures under laboratory conditions (DeVlaming and Paquette 1977).
Female golden shiner had atretic oocytes and significantly smaller GSI after
11 days of continuous exposure to 27 C. Partial loss of gonad weight and
resorption of remaining ova in female black crappie were similar to
observations by Kaya (1977) for brown trout (Salmo trutta) inhabiting a
thermally elevated environment.
Expected spawning temperatures of black crappie were exceeded by
minimum water temperatures during 1977, but spawning temperatures of more
thermally tolerant bluegill were not exceeded (Figure 13). A review of
percid temperature requirements (Brungs and Jones 1977, Hokanson 1977)
revealed that the range of expected spawning temperatures in percids
corresponded closely with embryo tolerance limits. If a similar relation-
ship exists for black crappie, embryos incubating at temperatures above
expected spawning temperatures would be above upper tolerance limits.
Developing embryos of bluegill, a species with successful reproduction in
the cooling lake, would be more temperature tolerant based on their broad
range of spawning temperatures (Figure 13). Large temperature increases
induced spawning and at the same time reduced the area having temperatures
below expected upper lethal temperatures of embryo and larval stages.
Upon hatching, fry metabolize the yolk sac and subsequently become
sufficiently mobile to move into the water column and limnetic zone (Faber
1967, Werner 1969, Amundrud et al. 1974). Grunion (Leureethee term-is)
27
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larvae were not able to metabolize the yolk at 27 C. Ehrlich and Muszynski
(1981) suggested that this was due to breakdown of proteolytic enzymes.
Such ultimately lethal effects of an elevated thermal history experienced by
larvae may be more important than directly lethal effects of high
temperatures (Rosenthal and Alderice 1976).
Temporal patterns of reproduction were modified by thermal input to the
cooling lake. Spawning of black crappie occurred approximately 1 month
earlier in 1978 than in 1977. In 1978, the decline of GSI and presence of
black crappie fry indicated spawning was initiated by the end of March, 30
days earlier than in 1977. In a heated reservoir black crappie fry were
captured 44 days earlier under conditions of themal input (Ruelle et al.
1977) than under ambient conditions. The GSI of white bass was at a maximum
36 days earlier in 1978 than in 1977. June (1978) found little year-to-year
variability between peak spawning dates of 17 species of fish in Lake Oahe,
South Dakota, a thermally unaltered reservoir. The mean calendar day of
peak white bass spawning activity in Lake Oahe, South Dakota, had a standard
deviation of only 4.1 days from 1964 to 1971 (June 1978). Earlier spawning
in Lake Columbia in 1978 can be attributed to a further elevated thermal
regime due to the operation of the Columbia II generating unit which began
in February 1978 (Figure 3).
Following resumption of power plant operation in the spring of 1977
there was rapid warming. This resulted in an unusually abbreviated duration
of spawning activity for white bass because this species may not be adapted
to the warmer water temperatures. The rapid warming restricted white bass
spawning to < 11 days. Mean duration of white bass spawning has been
reported as 25 to 28 days (Horrall 1961, Ruelle 1977). The eurythermal
bluegill, which spawns intermittently during early spring and summer (Breder
and Rosen 1966), showed continued recruitment during the spring of 1977.
Fox (1978) found that the English bullhead (Cottus gobio L.) spawned only
once per year In northern England and intermittently in the longer spawning
season available in southern England. In this case, the adaptive advantages
of temporally intermittent and one-time reproductive strategies hypothesized
by Pianka (1976, 1978) may be extended to spring spawning strategies.
Although there are advantages to both strategies, the extreme abbreviation
of spawning season for a species that is adapted to spawn for a mean
duration of 25 to 28 days might considerably reduce the chances of having a
number of individually successful cohorts.
The increase in water temperatures during 1977 induced spawning in many
species and temporally compressed the successional appearance of larval
fish. Spawning and subsequent dispersal of larval fish into the limnetic
zone results in the successional appearance of predator and prey species
(Amundrud et al. 1974). A shortened spawning period, Induced by sharply
increasing water temperature, disrupted seasonal succession and may modify
predator-prey relationships and change competitive interactions.
In summary, a rapid rise in water temperatures following a 3-week power
plant shutdown during 1977 stimulated spawning, reduced available spawning
area, and induced aggregation of black crappie at coolest available water
temperatures. Elevated water temperatures subsequently induced resorption
28
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of black crappie ova, loss of secondary sexual characteristics, and were
probably near upper lethal temperatures of embryo and larval stages. A
temporally shortened spawning season was associated with a rapid rise in
water temperatures, while additional thermal input by the Columbia II
generating unit caused spawning to occur 30 days earlier in the spring.
29
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SECTION 5
DISTRIBUTION OF LARVAL FISHES
INTRODUCTION
Larvae of many spring spawning fishes initially disperse into limnetic
waters (Faber 1967, Werner 1969, Netsch et al. 1971, Amundrud et al. 1974,
Kelso and Ward 1977) and later aggregate as juveniles in littoral areas
which have higher water temperatures• Juvenile fishes exhibit thermo-
regulatory behavior in the laboratory (Cherry et alt 1977) and after
reviewing temperature preference data of fish Coutant (1977) concluded that
laboratory and field results were reasonably consistent. During the
development of thermoregulatory behavior, increasing mobility probably
facilitates the ability of individual juveniles to thermoregulate. However,
little is known about the thermal responsiveness of pelagic larvae and early
juveniles of fish when distributed in the limnetic zone. Therefore, an
objective of this study was to describe distributional responses of pelagic
larvae and juvenile fish to changes in the thermal gradient. Certain
abiotic factors—i.e., temperature—are correlated with year-class strength
of some fish populations (Kramer and Smith 1962, Koonce et al. 1977).
Larval white bass and black crappie were not captured in sufficient
numbers to interpret distribution patterns. Gizzard shad and bluegill, two
species whose populations increased in the cooling lake, were studied to
determine how the larval forms respond to the dynamic heterothermal
environment of the cooling lake. Gizzard shad are surface spawners, their
ova settle to rock and gravel substrates, while bluegill are a nest guarding
species that utilize sand and gravel substrates (Balon 1975a). The larvae
of both species have pelagic behavior soon after hatching.
Additional observations were designed to investigate factors affecting
the relative abundance of larval fish. The time of capture, depth of
capture, station location, and diel movement patterns were examined.
METHODS
Distribution of Larval Fishes
Abundances of larvae and early juveniles in Lake Columbia were used to
measure reproductive success of fishes in the cooling lake. The limnetic
area of the lake was sampled from May to July 1977 using paired Miller
30
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samplers (Miller 1961) Cowed from the ends of a 6.6-m boom mounted across a
6.1-m flat-bottom aluminum boat. Samplers were towed along transects marked
by lights. Samplers were equippped with collecting cups and conical nets
90 cm in length with 0.25, 0.59, or 0.96-mm aperature mesh nitrex, depending
on the date and the size of fish. Miller samplers were assumed to filter
all water encountered (Miller 1961, Noble 1970).'
Tows to assess horizontal distribution patterns were made at a depth of
0.5 m between 1900 and 2400 h central standard time (CST). Towing began
approximately 0.5 h after sunset in 1977 and 1 h after sunset in 1978.
Sampling transects in 1977 were 1.0 km long for sampling dates between 12
and 20 May and 2.0 km thereafter. All transects completed in 1978 were
1.0 km in length.
.Clear plexiglass traps equipped with lights, a modification from
previous designs (Breder 1960, Casselman and Harvey 1973), were used to
collect larval fish in 1977. The traps were 30 x 30 x 15 cm with two
funnels opening to an area of 30 x 27.7 cm. The traps had a 0.1 amp light
bulb in a 270 ml jar mounted on the trap with electrical wiring to a 6 volt
dry cell on a styrofoam float. The traps were set at 30 cm depth for 2 h
between 2100 and 2300 h.
Larval and juvenile fish were preserved in the field in 10% formalin
and later placed in 5% buffered formalin. In the laboratory, specimens were
counted and identified under a binocular dissecting scope according to
larval keys and descriptions (May and Gassaway 1967, Siefert 1969, Meyer
1970, Hogue et al. 1976). Salon's (1975b) developmental terminology was
used. Random subsamples of not more than 60 specimens per sample in 1977
and not more than 30 specimens per sample in 1978 were measured for total
length. Larvae <_15 mm were measured to the nearest 0.1 mm with an ocular
micrometer and those > 15 mm were measured to the nearest mm on metric graph
paper.
Horizontal distributions of Lepomis sp. and gizzard shad are reported
with respective mean water temperature at capture and by location of capture
in km from outfall. Logarithmic transformations of data were performed to
normalize variances (Cassie 1971). Least squares linear regression and
second order polynomial fit of number of fish on station location (km) and
temperature were.used to describe horizontal distribution patterns.
Abundance of larval and early juvenile fish per m on different dates
illustrates the relative abundance over time. Water temperatures at which
fish were captured were compared to all water temperatures sampled to
determine whether fish aggregated in respect to temperature on each sample
date. Median and interquartile ranges of the temperature at which fish were
captured are compared to the median, interquartile range and range of water
temperatures where sampling took place on the sample date. Median total
length of larval and early juvenile fish between two groups of one or more
stations were compared using the Mann-Whitney U test (Sokal and Rohlf 1969).
31
-------
Factors Affecting Relative Abundance
Factorial designs were used to analyze the diel vertical movements of
larval and early juvenile fish. On 18 to 20 May 2x4x4 factorial design
observations were conducted with two depths, four stations, and four times
of day during a 24-h sampling period to determine the importance of these
factors. Samples were collected at 0.5 and 1.2 m depth using methods
described earlier. Sampling times were noon, 1200 h; evening, 2100 h;
midnight, 2400 h; and morning, 0500 h (GST). Similar factorial observations
with two depths, three stations, and three times of day were conducted on 29
to 30 May to examine the behavior of larger early juvenile fish. Gizzard
shad catches collected at various strata were tested for heterogeneity using
the G-test (Sokal and Rohlf 1969).
Gizzard shad catches were examined to determine whether 0.5-m deep
samples collected 0.5 h after sunset were adequate to describe the hori-
zontal distribution. Evening catches at 0.5 m depth were compared to total
number caught at 0.5 and 1.2 m at each station during the 24-h sampling
period. Comparisons were made to determine whether different conclusions
could be drawn with the additional information.
Effects of water temperature on diel vertical movements were examined
using a factorial design with 2 days, three depths, and four time periods.
Samples were collected between 1.5 and 2.0 km from the outfall on two
consecutive dates with different water temperatures. Samples were collected
with Miller samplers at 0.5, 1.0, and 1.5-m depths. Midpoints of sampling
times were 1700, 1900, 2100, and 2400 h CST. Results of the factorial
design were tested for heterogeneity using the G-test (Sokal and Rohlf
1969). Two regression lines fitted to subsets of the data were compared
according to Snedecor and Cochran (1967).
RESULTS
Distribution of Larval Fishes
Species abundance was greater in 1978 than in 1977 (Table 2). The mean
number of taxa per sample date in 1978 was 5.4 and 2.1 in 1977. The 1977
larval fish catches were dominated by Lepomie sp., accounting for 24%, and
gizzard shad, accounting for 76% of the total catch (Table 2). The number
of larval fish/m declined throughout the 1977 sampling period (Figure
14A). Larval fish sampling was initiated within 12 days of the resumption
of power plant operation. Resumption of operation induced rapid gonad
weight loss in adult black crappie and white bass, but no larval or early
juvenile stages of either species were captured. During 1978, larval fish
increased to 24.2 larval fish/m^ by 14 April and then declined (Figure
14B). In 1978 gizzard shad dominated all samples and accounted for 96% of
the total catch (Table 2). Although sampling extended from 28 March to
5 June 1978, 97% of the Mprone sp. captured during 1978 were captured
32
-------
oc
UJ
I
oc
UJ
UJ
S
O
m
o
cc
UJ
a. 20
MAY
JULY
25
u,
o
UJ
CD
2
3
10
5-
r,
MARCH APRIL MAY JUNE
1978
Figure 14. Number of larval and early juvenile.fishes
per cubic meter of water sampled by Miller
sampler during the springs of 1977 and 1978.
33
-------
between 28 March and 16 April. Eighty-six percent of the black crappie were
caught between 4 and 24 April 1978.
TABLE 2. NUMBER OF LARVAL AND JUVENILE FISHES CAUGHT IN LIGHT TRAPS AND
MILLER SAMPLERS, 1977-78
Species
Morane sp.
LeporntB sp .
Pomoxis sp.
Miaropterue sp.
D. aepedianwn
I. natdl-is
I. punetatus
C. aarpio
N. spilopterus
Cyprinidae
Catostomidae
Atherinidae
Unknown
Light Trap Miller Tow
(1977) (1977)
6,727a 1,627
2
1 .
644 5,246D
47
11 2
18
1
Miller Tow
(1978)
119
232
160
16
16,298C
1
3
28
7
33
18
17
f67% captured between 10 and 15 June.
b62% captured between 12 and 21 May.
C68% captured between 14 and 26 April.
The median water temperature at locations where Lepomis sp. and gizzard
shad were caught during 1977 was near 30 C. The median temperature of
capture for Lepomis sp. ranged from 28.1 to 30.9 C during the spring of
1977, while the temperatures during sampling ranged from 24.5 to 40.0 C
(Figure 15A). The median temperature of capture of gizzard shad ranged from
29.6 to 31.3 C, while temperatures of effort ranged from 25.1 to 40.2 C
(Figure 15B). Median temperature of capture of Leponri.8 sp. and shad during
June 1977 was below 30 C. This reflects a lower thermal preference at later
stages of development or increased ability to avoid temperatures > 30 C.
Spatial patterns of distribution of juvenile fish changed as ambient
temperatures influenced the thermal gradient of the lake. On 25 to 27 May
1977, when the temperature gradient ranged from 29.9 to 42.8 C, Lepomis sp.
were more abundant 5.0 to 6.0 km from the outfall where the coolest
temperatures were available (Figure 16A,B). Under conditions of lower
ambient temperatures on 10 June, when the gradient ranged from 24.6 to 37.5
C, the mode of distribution moved to 1.5 to 2.0 km from the outfall (Figure
16C). Location of the mode coincided with water temperatures between 29 and
31 C (Figure 16D). A mid-June rise in air temperatures resulted in lake
34
-------
40n
30-
UJ
cc
<
CC
UJ
Q.
5
UJ
cc
UJ
20-
40H
I
range of effort
median, interquartiles of effort
imedian,interquartlies at capture
Lepomis sp_.
30-
D. cepedlanum
jf
tt
20'
15.
MAY
25
DATE 1977
15
JUNE
Figure 15. Expected median and interquartile limits of water
temperature based on distribution of sampling ef-
fort and the observed temperature at location of
capture of larval and early juvenile periods of
Lepomis sp. and gizzard shad during 1977.
35
-------
210
140
70.
o-
j" 450'
Eh
g 300-
«J
w 150-
§
§ 0-
3000.
400-
20-
1-
r2 = .64
©r2
ns
.95
r
.5
2 4 24
DISTANCE FROM OUTFALL (km)
May 25,27 1977
June 10
r2 - ns
June 15
.89
28 32 36
WATER TEMPERATURE (C)
40
Figure 16. Abundance and temperature at location of capture
in light traps for larval and early juvenile
Lepomis sp. during the spring of 1977.
36
-------
temperatures of 27.4 to 40.6 C and a concurrent reduction of juvenile
Lepomis sp. abundance in areas near the outfall (Figure 16E). The mode then
returned to an area at a greater distance from the outfall (3.0 to 5.0 km)
with 28.1 C water temperature (Figure 16F).
Changing distribution patterns may reflect increasing mobility at more
advanced stages of development. Median length of Lepomie sp. was greater at
warm stations near the outfall for 10 of 11 dates when significant differ-
ences existed (Mann-Whitney 0 test, p < 0.05). The one exception was 27 May
1977 when recruitment of smaller larvae to catches occurred. Median length
of Lepomie sp. was greater at warm stations near the outfall for 10 of 11
dates when significant differences existed (Mann-Whitney U Test, p < 0.05).
The one exception was May 27, 1977 when recruitment of smaller larvae to
catches occurred. Median length of Lepomis sp. at warm stations signifi-
cantly decreased from 5.6 mm on 18 May to 4.8 mm on 27 May (Mann-Whitney U
test, p < 0.05). During periods of recruitment to light traps, signifi-
cantly greater abundance (Figure 16A) and larger median lengths at greater
distance from the outfall (Mann-Whitney U test, p < 0.05) indicate an
initial down-current drift. Subsequent changes in modes of abundance and
larger median length near the outfall indicate movement by Lepomie sp. in
the pelagic stage.
Early juvenile gizzard shad responded to temperature changes in the
cooling lake environment by changing relative abundance. The mode of
relative abundance of gizzard shad caught in Miller samplers was located .
further from the outfall on 17 and 18 May (Figure 17A, B) and then shifted
to the outfall on 29 May. The shift of abundance mode to warm stations near
the outfall on 29 May (Figure 17C, D) coincided with a change from signifi-
cantly larger shad at cool stations on 19 May to significantly larger shad
near the outfall on 29 May (Mann-Whitney 0 test; p < 0.01) (Figure 18). On
19 May 46% of the total shad catch was ^ 10 mm length, suggesting recent
hatching and recruitment to the gear (Figure 18A). On 29 May 96% of the
shad catch near the outfall was >_ 30 mm length, while only 29% of the cool
station shad catches were >_ 30 mm (Figure 18B). Samples of 7 to 14 June
Indicated that the mode of abundance of juvenile gizzard shad had returned
to stations toward the middle of the lake (Figure 17E). Shad distribution
observed during June, similar to that described for Lepomis sp. (Figure
16E), was most abundant 2.0 to 4.0 km from the outfall, an area of low
surface current velocities (2 to 4 cm/sec) and temperatures of 28 to 31 C
(Figure 17F).
The median length of gizzard shad caught in 1978 was greater at down-
current stations during the peak reproductive period, suggesting that drift
was an important factor in determining distribution patterns of early larval
stages. The period of peak reproductive activity occurred between 14 and 16
April 1978 when 68% of the gizzard shad were caught (Table 2). Median
length of gizzard shad ranged from 4.8 mm on 4 to 6 April to 5.1 mm on 24 to
26 April, with significantly larger fish at down-current stations for three
groups of 32 Miller samples (Mann-Whitney U test, p < 0.05). Approximately
1 month after peak reproductive activity, larval gizzard shad had a median
length of 5.1 mm with significantly larger fish at warm stations (Mann-
Whitney U test, p < 0.05). The median length at warm stations was 5.3 mm
37
-------
w
M
en
w
400 _
100-
10-
1-
300-
200-
100-
1-
80-
20-
5-
1-
.35
.33
.61
0 2 4 24
DISTANCE FROM OUTFALL (km)
.42
I
.52
.58
May 17,18 1977
May 29,June 1
June 7,14
iii
28 32 36
WATER TEMPERATURE (C)
Figure 17. Abundance and temperature at location of capture
• in Miller samplers for larval and early juvenile
gizzard shad during the spring of 1977.
38
-------
20
10-1
30
20
co
w
20-
10-
20-
10 -
D 0-2.9 km DISTANCE FROM OUTFALL
| 3.0-6.0 km
May 19, 1977
i i
May 29, 1977
LuiL
20 40
TOTAL LENGTH (mm)
60
Figure 18. Length frequency of gizzard shad captured at warm
stations (0.1 to 2.9 km from outfall) and cool
stations (3.0 to 6.0 km from outfall) on 19 and
29 May 1977.
39-
-------
with 20.5% > 10 mm. Only 1.9% of the fish caught at cooler down-current
stations were > 10 mm length.
Factors Affecting Relative Abundance
Several factors influenced the distribution of larvae and early
juveniles and therefore the validity of results. Field observations were
conducted to test the effects of depth, station, and time of day at which
the samples were collected.
The number of gizzard shad caught on 18 to 20 May was not independent
of depth, station, or time of day. The observations had highly significant
G-test statistics for combinations of depth, station, and time of day (p <
0.01, Table 3). The median length of gizzard shad caught on 19 May was 12.0
mm (N = 358) for all stations. The time x depth independence term was
significant (Table 3), indicating that the abundance of gizzard shad at 0.5
and 1.2 m was not independent of time of sampling. Gizzard shad were more
abundant during the evening (2100 h) at 0.5 m depth than at 1.2 m depth
(Figure 19A). Seventy-three percent of the gizzard shad caught in the
evening were caught at 0.5 m depth. Fourteen percent of the catch at noon
were at 0.5 m depth, while the remaining 86% were caught at 1.2 m depth
(Figure 19A). The time x station independence term was significant,
indicating that abundance at stations changed with time of sampling.
Abundance at all stations was low during the noon (1200 h) sample, composing
only 10% of the total catch. The lack of Independence between depth and
station was influenced by the large percentage (30%) of total catch captured
TABLE 3. THE G-STATISTIC VALUES PARTITIONED ACCORDING TO THE HYPOTHESIS
TESTED FOR THREE FACTOR DIEL VERTICAL MIGRATION OBSERVATIONS, 18
TO 20 AND 29 TO 30 MAY 1977
Date Hypothesis tested df G Significance
18 to 20
May 1977
29 to 30
May 1977
Time x depth independence
Time x station independence
Depth x station independence
Time x depth x station interaction
Time x depth x station independence
Time x depth independence
Time x station independence
Depth x station independence
Time x depth x station interaction
Time x depth x station independence
3
9
3
9
24
2
4
2
4
12
101.22
8307.98
135.18
8001.68
542.10
79.80
98.80
3.60
27.60
209.80
**
**
**
a
**
**
**
V
nsb
**
**
**p < 0.01.
aSee Sokal and Rolf (1969, p. 607) and Kullback (1959, p. 171).
bns Not significant at p < 0.05.
40
-------
00.5m
D1.2m
100-j
50-
I
O
^
O
a. °
O
\G/
3
X
X
X
X
x
x
x
X
X
X
__.
X
J
s
X
^
i i
M
x
x
X
X
X
^
f
May 18-20,1977
HI 100-1
O
DC
LU
OL
50-
0-
\s/
xl
X
X
X
X
x
X
(1
a>
X
X
X
X
X
^s
X
x
X
X
X
X
X
X
X
X
^
•
1—
II 1
—
x
x
X
x
x
X
X
^
S*
X
1
1
May 29-30,1977
1200 2100 2400 0500
TIME CST
Figure 19. Percent of gizzard shad caught at 0.5 and
1.2 m at different times of day on 18 to
20 and 29 to 30 May 1977.
41
-------
In 0.5-m depth samples at the station located at the greatest distance from
outfall. The significant time x depth x station interaction term indicates
that the abundance of gizzard shad at a given depth can be expected to
differ with station and the time of day the sample was collected.
Observations with a similar factorial design were conducted on 29 to 30
May to determine if early juvenile stages responded to depth, station, and
time factors in the same pattern. The median total length of gizzard shad
during the study was 32.0 mm (N = 290). Observations had significant G-
values for time x depth, time x station, and the interaction term (p < 0.01,
Table 3). Eighty-six percent of the total catch occurred during the evening
to midnight sampling and 3% were captured during the noon sample. Fish
caught at the 0.5-m depth accounted for 91% of the evening to midnight
sample (Figure 19B).
To examine the effects of using shad abundance at a depth of 0.5 m as a
measure of relative abundance, catches were compared to distribution
patterns determined by summation of 0.5 and 1.2-m samples. Evening samples
on 18 May 1977 at the 0.5-m depth indicated greater abundance as distance
increased from the outfall. A similar pattern of abundance emerged when the
percentages of catch collected at 0.5 m depth during the evening were
compared to percentages of total catch collected at 0.5 and 1.2 m depth in a
24-h period (Figure 20A). The same conclusion was reached for 29 May after
two depths and three time periods were pooled (Figure 20B). Therefore,
relative abundance, as determined by 0.5-m deep samples, appeared to
adequately describe horizontal distribution.
Although 0.5-m deep samples collected during the evening minimized the
effects of diel vertical movements and adequately described horizontal
distributions they were not adequate during thermal stratification with
elevated surface temperatures. For example, samples collected during the
evening of 24 May 1978 (Figure 21A) indicated consistently low abundance
near the outfall (Figure 21B). Two 1.5-m depth samples collected near the
outfall had a higher abundance (Figure 21B). The 1.5-m samples shown by
open circles in Figure 21B taken near the outfall at 30.4 C had catches
similar to other samples taken at that temperature (Figure 21C), although
the samples were spatially separated by 1 km.
The lower abundance of larval fish observed at the 0.5-m depth at warm
stations was partially due to reduced abundance of larval gizzard shad
completing upward vertical migration. A total of 2,400 larval gizzard shad
and 28 other specimens, including Pomoxie sp., Mioropterus sp., Cyrinidae,
and Catostomidae, were caught during the study of vertical migration on 17
and 18 May 1978. Due to declining ambient air temperatures from late
afternoon through the night, the 0.5-m deep water temperatures ranged from
28.0 to 30.8 C on the cool day (17 May) and 31.5 to 34.9 C on the warm day
(18 May).
Partitioning of the G-test statistic used to analyze the factorial
design for vertical migration indicated gizzard shad catches were not
independent of 2 days, three depths, and four time periods of collection
(Table 4). The significant time x depth term (p < 0.01, Table 4) indicates
42
-------
100-1
50^
X
o
K
u
H-
Z
HI
O
ff
UJ
o.
100 i
50-
• May 18 at 0.5m evening
O May 18-20 at 0.5m and 1.2m
• May 29 at 0.5m evening
O May 29-30 at 0.5m and 1.2m
I i i
0246
DISTANCE FROM OUTFALL (km)
Figure 20. Percent of gizzard shad catch at each station
for 0.5 m-depth in the evening using Miller
tows and for sum of catches at 0.5 and 1.2 m
during a 24-h period on 18 to 20 and 29 to 30
May 1977.
43
-------
I
12 400-1
u.
u. 100-
O
cc 10
UJ
m
1-
r2=.003
P>.OS
r2=.91
P<.06
o abundance at 1.5m
r2=.84
P<.05
50
150
250
26
I
30
34
MINUTES AFTER SUNSET DISTANCE FROM OUTFALL (km) WATER TEMPERATURE (C)
Figure 21. Abundance of larval gizzard shad at time (minutes after sunset), location
(km from outfall), and temperature of capture on 24 May 1978.
(.Sample at 0.5 m unless otherwise noted.)
-------
the abundance at three depths sampled changed during the sampling times
(Figure 22). Lack of independence between time x day and depth x day
indicates a significant difference (p < 0.01) between catches on the cool
day and warm day. Shad catches at the 0.5 and 1.0-m depths increased more
rapidly oh the cool day (black dots) after 1900 h than on the warm day
(regression slope, p < 0.05; Figure 22A, B). Water temperatures at the 0.5
and 1.0-m depths declined to 31.5 C on the warm day, but abundance did not
increase at the 2400-h sampling period (open circles, Figure 22A, B). The
number of larvae captured on the warm day at the 1.5-m depth during the 1700
and 1900-h sampling times was less than the number captured on the.cool day
(Figure 22C). Catches collectd at 2100 and 2400 h at 1.5 m depth with
temperatures ranging from 29.6 to 30.3 C appeared similar to catches from
the cool day (Figure 22C). Warm day catches of gizzard shad were 35 to 55%
of total catches collected at respective depths on the previous cool day.
Abundance of larval gizzard shad completing upward vertical migration was
reduced when water temperatures were > 31 C.
TABLE 4. THE G-STATISTIC VALUES PARTITIONED ACCORDING TO THE HYPOTHESIS
TESTED FOR THREE FACTOR OBSERVATIONS ON THERMAL SUPPRESSION OF
VERTICAL MIGRATION, 17 TO 18 MAY 1978
Hypothesis tested
df
**
p < 0.01.
Significance
Time x depth independence
Time x day independence
Depth x day independence
Time x depth x day interaction
Time x depth x day Independence
6
3
2
6
17
259.2
28.2
12.4
120.0
419.8
**
**
**
**
**
DISCUSSION
Miller samples were expected to be effective in sampling larval forms
of fish inhabiting open water in Lake Columbia. Larval stages of bluegill
(Werner 1969), pumpkinseed sunfish (Faber 1967), black crappie (Amundrud et
al. 1974), white bass, and gizzard shad (Netsch et al. 1971) inhabit the
limnetic zone of a lake. Largemouth bass fry were not expected to be
effectively sampled since they inhabit the nearshore area during larval and
juvenile stages (Elliot 1976).
The vertical distribution pattern of gizzard shad in May 1977 suggests
that gizzard shad undergo diel vertical migration and are more abundant near
the surface at night. This observation could be partially explained by gear
avoidance of gizzard shad during the day. Noble (1970) found that visual
45
-------
0.5m depth
• May 17, 30.3-28.0 C
O May 18, 34.9-31.5 C
x
U.
U.
O
OC
UJ
CO
2
3
•z.
150-
00-
50-
0-
150-
00-
50-
0-
150-
100-
50-
0-
^
^
^^ •
^At
\ |^—--^ 8
i i i 1
1.0m depth
(§) • May 17, 27.6-25.8 C
OMay 18,33.9-31.5 C
.X*
• X^
8 1/^8- — 5
© LSmdepth
• May 17, 24.2-21.8 C
* 0 May 18, 31.0-29.6 C
• • '. I ;
O
8 8
1 1 1 1
1700 1900 2100 2400
TIME CST
Figure 22. Number of gizzard shad caught at 0.5, 1.0, and 1.5 m
depth at cool temperatures (30.3 to 21.8 C) on 17 May
and warm temperatures (34.9 to 29.6 C) on 18 May 1978.
Samples were collected, 1.5 to 2.0 km from the power
plant outfall in Lake Columbia, Wisconsin.
46.
-------
cues were an important factor in the ability of yellow perch fry to avoid
Miller samplers. The greater percentage of the total catch of each station
taken at noon at 1.2 m depth indicated diel vertical migration (Figure
19). Storck et al. (1978) found gizzard shad to be concentrated at the
surface during the day and dispersed at night in the turbid upper parts of a
reservoir. Acoustic records, trawl catches, and meter net catches of
gizzard shad in a reservoir with low turbidity showed abundant but widely
dispersed gizzard shad in the upper 10 m at night and tightly schooled
concentrations at a 10-m depth during the day (Netsch et al. 1971).
The vertical migration of larval and early juvenile fish in lentic and
lotic waters is common for a number of fish species, but the adaptive value
is unknown. McLaren (1963) hypothesized that diel vertical movements in
zooplankton have a bioenergetic advantage. Zooplankton achieve improved
growth efficiency when they feed in surface waters and digest at deeper,
cooler water. An analogous hypothesis was proposed by Brett (1971) to
explain the diel movement of young sockeye salmon (Oncorhynohue nerka) from
the thermocline to the surface at night. Diel movements may be advantageous
under conditions such as those shown in Figure 22 when temperature differ-
ences as great as 6.2 C exist between 0.5 and 1.5 m depth. Thermal strati-
fication was usually limited because even slight winds vertically mixed the
shallow lake.
Suppression of vertical migration by elevated temperatures during
thermal stratification reduced abundance of gizzard shad at 0.5 and 1.0m
after 1900 h. Marcy (1976) found that caged juvenile American shad (Alosa
sapidiseima) migrated downward (40 cm) as temperatures increased to near
30 C. The reduced abundance observed at elevated temperatures in Lake
Columbia may be due to suppression of vertical migration, direct action of
lethal temperatures, or thermally Induced emigration from the area.
Horizontal patterns of distribution of gizzard shad at the 0.5-m depth
were similar to those found by summation of 0.5 and 1.2-m samples during the
24-h periods sampled in May 1977 (Figure 20). The greater relative
abundance at the 0.5-m depth after sunset justifies the sampling design
starting after sunset. This allows maximum numbers to be captured with
minimal effects from clustered distributions (Cassie 1971) and vertical
movements induced by light and temperature.
Horizontal patterns of abundance and median lengths of Lepomis sp. and
gizzard shad indicate intitial downstream drifting by larvae in the cooling
lake. Downstream drift of larval fish occurs mainly during the night and is
common in a number of fish families, including Catostomidae (Clifford 1972),
Percidae, and to a lesser extent in Centrarchidae (Gale and Mohr 1978).
Gale and Mohr (1978) suggested an adaptive value in dispersing at night when
larvae are less visible to predators. Downstream drift of larval capelin
Q4allotus villosus) in the St. Lawrence River resulted in the transport of
larval fish into the region of maximum primary production in the Gulf of
St. Lawrence (Jacquaz et al. 1977). Downstream drift during the night may
have evolved as a mechanism to transport larval fish to areas of higher food
density. In areas of higher food density travel rates were reduced to
anchovy larvae (Engraulie mordax) because larvae changed swimming direction
47
-------
more often (Hunter, and Thomas 1974). Continued immigration and reduced
exodus in areas of high food abundance would result In aggregation of larvae
and, perhaps, enhanced survival. However, in the unique cooling lake
environment larvae initially aggregated in the power plant intake, an area
of potential entrainment.
Lepomis sp. and gizzard shad responded to water temperature changes
while in the pelagic juvenile stages. The greater abundance of gizzard shad
near the outfall may be the result of rheotactic behavior, such as has been
reported for the aggregation of the alewife (Alosa pseudobarengus) in
thermal plume areas (Romberg et al. 1974). The importance of thermal
preference in aggregation of adult fish in thermal plumes has been reported
(Neill and Magnuson 1974, Marcy 1976). Thermal preference and the avoidance
of potentially lethal temperatures was important in determining the spatial
location of the mode of abundance in the cooling lake environment. Movement
of the mode of abundance resulted in fish maintaining a position at water
temperatures of 28 to 31 C. Distribution changes that showed the presence
of larger fish at warm stations could be partially attributed to the
movement of larger and more mobile juveniles into the warmer areas. Petty
and Magnuson (1974) found this for juvenile bluegills in a power plant
outfall area on Lake Monona, Wisconsin. In the cooling lake however, the
effects of increased growth at warm temperatures cannot be discounted.
The ability of pelagic early juveniles to respond to thermal gradients
has evolved under ambient thermal regimes and may or may not be of value in
the cooling lake environment. Under ambient conditions pelagic early
juveniles of spring spawning fishes appear in aquatic systems when thermal
gradients are small, but rapid spring warming occurs. Early mobility and
thermal responsiveness may enhance aggregation in nursery areas at
temperatures where growth and other physiological processes are optimal.
Resulting spatial separation of young-of-the-year and adults of lower
thermal preference might serve to partition resources and minimize predation
(Brandt 1980). The observations that such behavior occurs and that
juveniles of other species respond to temperature differentials as small as
0.1 C (Marcy 1976) suggest that it may be important even at ambient
temperatures.
In summary, species diversity of larval fish catches was low in 1977
when water temperatures increased rapidly. The median temperature of
capture of larval Lepomis sp. and gizzard shad was near 30 C. Temperatures
> 31 C during thermal stratification reduced the abundance of gizzard shad
completing diel vertical movements. After initially drifting with current
Lepomis sp. and gizzard shad responded to water temperature changes by
horizontal shifts in abundance with a mode at 28 to 31 C.
48
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SECTION 6
CONCLUSIONS
Observations suggest that the species diversity of fish in Lake
Columbia, Wisconsin declined during the first year of thermal input by the
plant. Habitat modification, such as reduced vegetation as a direct result
of thermal input, may be the reason for the decrease in abundance of some
species. The decline in species diversity was accentuated by fish mortality
from temperatures exceeding upper lethal limits, an absence of colonization
of warm-water, lake-dwelling species, and limited reproductive success.
Thermal inputs by the power plant modified temporal and spatial
characteristics of spawning white bass and black crappie. Resumption of
plant operation following a 3-week shutdown resulted in a rapid increase in
water temperatures that stimulated spawning, reduced available spawning
area, and induced aggregation of sexually mature black crappie at coolest
available water temperatures. Water temperatures above expected spawning
temperatures induced partial resorption of ovaries, loss of secondary sexual
characteristics, and abbreviation of spawning duration. The combined
operation of the Columbia I and II generating units induced spawning about 1
month earlier than when only Columbia I was operating.
The rapid increase in water temperatures that Induced spawning and
subsequent gonadal resorption in 1977 was associated with a lower number of
species of larval fishes. If a number of species were stimulated to spawn,
as indicated by Figures 8 and 9, then a greater number of ichthyoplankton
species would be expected at that time, but this was not observed.
Therefore, factors associated with the increase in temperatures must have
been responsible for reducing ichthyoplankton species abundance. The number
of species of larval fishes was lower during 1977 when water temperatures
increased rapidly and reproductive responses were aberrant. This may
explain the limited reproductive success observed for some species
successful as adults in the cooling lake environment.
Larval and early juvenile stages of bluegill and gizzard shad were
responsive to temperature changes within the thermal gradient. Larval forms
initially drifted downstream. Pelagic larval and juvenile stages of
bluegill and gizzard shad were most abundant at 28 to 31 C and were capable
of responding to changes in the thermal gradient induced by changing air
temperatures. Larval gizzard shad exhibit reduced diel vertical movements
when temperatures are > 31 C. Pelagic larval and early juvenile forms
responded to thermal dynamics of the cooling lake by modifying horizontal
and vertical distribution patterns.
49
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SECTION 7
RECOMMENDATIONS
1. The disappearance of aquatic vegetation should be expected in cooling
lakes with heavy thermal loading. Management to enhance fish popula-
tions of species that require vegetation to spawn should not be
attempted.
2. Initiation of spawning was approximately 1 month earlier with the
thermal input of two 527-MW generating units. If fishery management
agencies protect spawning adult fish during spring by closed season, the
regulations may not be applicable to cooling lake fisheries. The
accelerating of spawning during spring can provide the opportunity to
open a fishery while other temperate lake fisheries are closed during
normal reproductive season.
3. Power plant shutdowns are often scheduled during spring but rapid
temperature increases when plants resume operation can cause aberrant
reproductive responses in spring-spawning fish. The operation of more
than one generating unit may be beneficial because addition units buffer
the effects of rapid changes in temperature of a single unit.
4. Successful reproduction of fish in a cooling lake is spatially limited
to water temperatures within the thermal tolerance limits of reproduc-
tion. Cooling lake water temperatures and corresponding areas can be
estimated during planning. Design should provide adequate area with
water temperatures within the thermal tolerance limits of oogenesis,
spawning, and incubation during spring.
5. Pelagic larval stages drift downstream in a recirculating cooling lake
and will subsequently be entrained by the power plant if cooling lake
turnover time is not adequate to permit metamorphosis into.the more
mobile early juvenile stages. Entrainment should be accepted as a part
of the cooling lake environment, however, careful design can minimize
entrainment of larval and early juvenile stages. Additional generating
units should be augmented by increasing cooling lake area and volume or
by providing cooling towers to increase lake turnover time.
50
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6. Early juvenile fish in pelagic stages are mobile and respond to thermal
gradients and water currents by congregating in preferred habitats.
Cooling lake design can increase juvenile nuersery areas and species
diversity by providing heterogeneous habitats with a diversity of water
depths, substrates and shoreline configurations. These design modifica-
tions would not inhibit the cooling capacity of the lake because cooling
is most dependent on surface area.
7. After power plant operation began species diversity declined as a few
eurythermal species increased in abundance and other species declined.
Sport fish should be stocked early in the operation of the lake so that
juveniles can utilize forage species likely to become abundant after
the power plant begins operation. Thermally-tolerant nest-guarding
Centrarchids and Ictalurids, such as largemouth bass and channel
catfish, are likely to be the most successful native species in cooling
lakes and should be preferred for initial stocking.
8. After the power plant begins operation water temperatures of the
cooling lake may exceed the upper lethal limits of popular cool water
sport fish resulting in fish kills. Design can create thermal refugia
using water depth and circulation patterns. Fishery managers and the
public should anticipate fish kills as a part of starting the long term
management of a cooling lake, but recurrent fish kills can be avoided
through careful design.
9. Largemouth bass, a species susceptible to over-harvest, was caught at
the highest rate by angling near the outfall in winter (0.28 bass/cast)
and in cool water near the intake in late spring (0.27 bass/cast:
Lozano et al. 1978). Thus, the area near the intake and outfall should
be permanently closed to fishing to protect summer and winter aggrega-
tions of fish under seasonally extreme thermal conditions.
10. Small reservoirs are often subject to over-exploitation of sport fish
populations, particularly .when fish are spatially limited by tempera-
ture or lake morphometry. Thus, when power plant security is designed,
consideration should be given to minimize over-harvest of fish in out-
fall and intake areas and reduce potential conflicts between power
plant security and fisherman.
51
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