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DISTRIBUTION, DIET, AND GROWTH OF TWO COEXISTING
POPULATIONS OF YELLOW PERCH (PEBCA FLAVESCENS)

AND WHITE SUCKER (QATOSTOMQS COMMERSONI)

BY

Daniel Brian Hayes

A THESIS
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Fisheries and Wildlife

1988

Copyright by
DANIEL BRIAN HAYES

1988

ABSTRACT

DISTRIBUTION, DIET, AND GROWTH OF TWO COEXISTING
POPULATIONS OF YELLOW PERCH (PERCA FLAVESCENS)
AND WHITE SUCKER (CATOSTOMUS COMMERSONI)

BY

Daniel Brian Hayes

The objectives of this study were to determine the
growth, diet, and distribution of two coexisting
populations of yellow perch (Perca flavescens) and white
sucker (Catostomus commersoni) in order to assess potential
axes of competition between the two species.

Perch in both little Bear Lake and Douglas Lake were
"stunted" with 4-year old perch averaging less than 130 mm
in length. The diet of young-of-the-year perch shifted
from zooplankton to benthos in July. Adult perch shifted
back to a diet of zooplankton during the second summer of
life. Suckers initially fed on zooplankton, but quickly
shifted to a diet of benthos. The low diet overlap
observed may be an indication of little competition between
the two species, or it may indicate depletion of benthos by
sucker predation to the point where perch are competitively

excluded from utilizing this resource.

ACKNOWLEDGEMENTS

This research was sponsored by the Institute for
Fisheries Research, Michigan Department of Natural
Resources, and funded. through the Federal Aid in Fish
Restoration (Dingell-Johnson) Project Number F-35-R,
Michigan. This material is also based upon work sponsored
under a National Science Foundation Graduate Fellowship.
Any opinions, findings, conclusions or recommendations
expressed in this thesis are those of the author and do not
necessarily reflect the views of the National Science
Foundation.

I would first like to thank James Schneider and the
members of my thesis guidance committee, Dr. William
Taylor, Dr. Darrell King, Dr. Donald Hall, and Dr. W. C.
Latta fOr the support and instruction they have provided
me throughout this project. I feel most fortunate in
having had such good teachers and role models to guide me
on my endeavors to become a scientist.

Throughout this project, Dr. William Taylor has been
most generous in providing me with interns to aid with
field and lab work. The Michigan Department of Natural

Resources also provided a great deal of help through their

1...
H.

summer temporary employment program. I can't express
enough thanks to Kathy Brewer, Jim Sherbonda, Russ Hanshue
and Mark Feltner who all spent many sleepless nights and
rainy days in the field, and endured long tedious days in
the lab. Similar gratitude is expressed toward my fellow
graduate students and Gary E. Whelan. Their help is much
appreciated as is their friendship.

Finally, I would like to thank my family and loved
ones for their unending support throughout my endeavors.
Thanks Mom and Dad. I love you both for all you've done.
Teresa, I love you dearly. I only hope someday I can

repay your patience and support.

iii

TABLE OF CONTENTS
Page
LIST OF TABLES....................................Vi
LIST OF FIGURES.................................Xiii
INTRODUCTION.......................................1
STUDY AREA.........................................6
METHODS............................................7
Young-of-the-year Fish........................7
Adult Fish...................................ll
Prey Populations.............................15
Limnological Parameters......................l6
RESULTS.................................... ....... l7
Young-of—the-year Fish.......................l7
Perch Growth..............................l7
Perch Density.............................23
White Sucker Density and Growth...........29
Diet and Overlap..........................34
Adult Fish...................................38
Abundance.................................38
Spatial Distribution......................39
Daily Activity Pattern....................56
Diet......................................62

Adult Yellow Perch.....................62

iv

Page

Larger Yellow Perch....................68

Adult White Sucker.....................71
Stomach Fullness and Feeding Rate.... ..... 71
Adult Yellow Perch.....................71
Adult White Sucker.....................80
0ver1ap...................................80
Growth....................................80
Prey Resources...............................83
Zooplankton...............................83
Benthos...................................90
DISCUSSION............................. ..... . ..... 94

Diet Ontogeny, Resource Limitation
and GrOWthoooooooooooooooooooooooo0000000000095

Intraspecific Competition.......... ....... ...98
Competition with White Suckers...............99
Limnological Characteristics.................99

Potential for Competition Between Perch
and SUCkers...OOOOOOOOOOOOOOOOOOOO0.0.0.0...100

Spatial Distribution........................101
SUWRYOCOO'OOOOCCOCOOOOOOOOOOO0.0.0.0000000000000104
LIST OF REFERENCES 0 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 106

APPENDIX A

Diet composition of young-of—the-year
yellow perch.......................... ...... 113

APPENDIX B

Diet compostition of young-of-the-year
white sucker................................120

Table

Table

Table

Table

LIST OF TABLES
Page

Mean length (millimeters) of young-

of—the-year yellow perch in Little

Bear Lake in 1985 and 1986. The

dashed lines separate samples taken

by ichthyoplankton trawling (above)

and seining (below). Standard error

is denoted by SE, and sample size is

denoted by N.................................18

Mean length (millimeters) of young-

of-the-year yellow perch in Douglas

Lake in 1985 and 1986. The dashed

lines separate samples taken by

ichthyoplankton trawling (above) and

seining (below). Standard error is

denoted by SE, and sample size is

denoted by N..................... ......... ...19

Mean weight (grams) of young-of-the-

year yellow perch in Little Bear

Lake. The dashed lines separate

samples taken by ichthyoplankton

trawling (above) and seining (below).

Standard error is denoted by SE, and

sample size is denoted by N..................20

Mean weight (grams) of young-of-the-
year yellow perch in Douglas Lake.
The dashed lines separate samples

.taken by ichthyoplankton trawling

(above) and seining (below).
Standard error is denoted by SE, and
sample size is denoted by N..................21

vi

Table 5.

Table

Table

Table

Table

Page
Mean catch of young-of-the-year
yellow perch in Little Bear Lake and
Douglas Lake, 1985-1986.
Ichthyoplankton trawls are above the
dashed line, and are expressed as
number/cubic meter. Seine hauls are
below the dashed line and are
expressed as number/139.4 square
meters. Standard errors are in
parentheses...................... ........... .27

Mean catch, length, and weight of
young-of-the-year white sucker in

Little Bear Lake, 1985. The dashed

lines separate samples taken by

ichthyoplankton trawling (above) and

seining (below). Standard errors are

denoted by SE. Sample sizes apply to

both length and weight.......................30

Mean catch, length, and weight of
young-of—the-year white sucker in

Douglas Lake, 1985. The dashed

lines separate samples taken by

ichthyoplankton trawling (above) and

seining (below). Standard errors are

denoted by SE. Sample sizes apply to

both length and weight............... ........ 31

Mean catch, length, and weight of
young-of-the-year white sucker in

Little Bear Lake, 1986. The dashed

lines separate samples taken by

ichthyoplankton trawling (above) and

seining (below). Standard errors are

denoted by SE. Sample sizes apply to

both length and weight............ ......... ..32

Mean catch, length, and weight of
young-of—the-year white sucker in

Douglas Lake, 1985. The dashed

lines separate samples taken by

ichthyoplankton trawling (above) and

seining (below). Standard errors are

denoted by SE. Sample sizes apply to

both length and weight.......................33

vii

Table

Table

Table

Table

Table

Table

Table

Table

Table

10.

11.

12.

13.

14.

15.

16.

17.

18.

Page

Schoener's diet overlap index between
young-of—the-year yellow perch and
young-of-the-year white sucker in

Little Bear Lake and Douglas Lake

1985-1986. The dashed line separates

samples taken by ichthyoplankton

trawling (above) and seining (below).. ....... 35

Schoener's diet overlap indices

between young-of—the-year white

suckers and yellow perch and adult

yellow perch and white suckers in

Little Bear Lake, 1985-1986..................36

Schoener's diet overlap indices

between young-of-the-year white

suckers and yellow perch and adult

yellow perch and white suckers in

Douglas Lake, l985-l986................ ...... 37

Temperature (°C) profiles on dates of
24-hr studies in Little Bear Lake and
Douglas Lake, 1985.00.00.0000000000000.0.0.0053

Temperature (°C) profiles on dates of
24-hr studies in Little Bear Lake and
Douglas Lake, 1986.....OCCOCOOOCOOOIOOOO00.0.54

Mean number of items found in adult
yellow perch (95-135 mm TL) stomachs
during 24-hr studies in Little Bear
Lake, 1985...................................63

Mean number of items found in adult

yellow perch (95-135 mm TL) stomach

during 24-hr studies in Little

Bear Lake, 1986..............................64

Mean number of items found in adult

yellow perch (95-135 mm TL) stomach

during 24-hr studies in Douglas

Lake, 1985..................... .............. 65

Mean number of items found in adult

yellow perch (95-135 mm TL) stomach

during 24-hr studies in Douglas

Lake, 1986...................................66

viii

Table

Table

Table

Table

Table

Table

Table

Table

19.

20.

21.

22.

23.

24.

25.

26.

Page

'Strauss's linear electivity indices

for zooplankton taxa eaten by adult
yellow perch (90-135 mm TL)..................67

Stomach contents of large adult

yellow perch (>140 mm TL) in Douglas

Lake, June to August 1985, and May to

August 1986. Sample sizes are

enclosed in parentheses below the

length class designations. Standard
deviations of the mean number of each

food item are enclosed in parentheses

after the mean...............................69

Stomach contents of large adult

yellow perch (>140 mm TL) in Little

Bear Lake, June to August 1985, and

May to August 1986. Sample sizes are

enclosed in parentheses below the

length class designations. Standard

deviations of the mean number of each

food item are enclosed in parentheses

after the mean...............................70

Mean number of items found in adult
white sucker guts obtained during
24-hr studies in Little Bear Lake, 1985......72

Mean number of items found in adult
white sucker guts obtained during
24-hr studies in Little Bear Lake, 1986......73

Mean number of items found in adult
white sucker guts obtained during
24-hr studies in Douglas Lake, 1985..........74

Mean number of items found in adult
white sucker guts obtained during
24-hr studies in Douglas Lake, 1986..........75

Comparison of mean stomach fullness
(expressed as percenmt of fish's body
weight) of fish caught on the 2, 4,
and 8-meter contours for Little Bear

_and Douglas Lakes, 1985-1986.

Standard deviations are enclosed in
parentheses below the means..................76

ix

Table

Table

Table

Table

Table

Table

Table

Table

Table

27.

28.

29.

30.

31.

32.

33.

34.

35.

Page
Diel pattern of stomach content
weight (% of wet body weight) of

-adult yellow perch (95-140 mm TL) in

Little Bear Lake and Douglas Lake,
1985 and 1986.00.00.00000000.000000000000000078

Mean stomach fullness, gastric

evacuation rate, and feeding rate

estimated from 24-hr studies,

Little Bear and Douglas Lakes, 1985-

1986. Feeding rates are expressed as

wet weight of food eaten per day as a
percentage of the wet body weight of

the fish........................ ............. 79

Schoener's diet overlap indices

between adult yellow perch (95-140 mm

TL) and adult white suckers (>95 mm

TL) caught during 24-hr studies in

Little Bear Lake and Douglas Lake,
1985-1986....................................81

Length at age of yellow perch and
white sucker as determined by scales
or fin ray sections..........................82

Mean length and weight of adult

yellow perch caught during 24-hr
studies. Standard errors are

in parentheses. Sample sizes are
denoted by N.................................84
Weighted mean number of zooplankton

per liter from vertical plankton

hauls taken on the 2, 4, and 8-meter

contours in Little Bear Lake, l985...........86

Weighted mean number of zooplankton

per liter from vertical plankton

hauls taken on the 2, 4, and 8-meter

contours in Douglas Lake, l985...............87

Weighted mean number of zooplankton

per liter from vertical plankton

hauls taken on the 2, 4, and 8-meter

contours in Little Bear Lake, 1986...........88

-Weighted mean number of zooplankton

per liter from vertical plankton
hauls taken on the 2, 4, and 8-meter
contours in Douglas Lake, l986...............89

X

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

Table

36.

37.

38.

39.

40.

41.

42.

43.

44.

45.

46.

Page
Mean number of items per square foot
(929 square cm) in Ekman dredge
samples taken from Little Bear Lake
and Douglas Lake, 1985.......................91

Mean number of items per square foot

(929 square cm) in Ekman dredge

samples taken from Little Bear Lake

and Douglas Lake, l986.......................92

Mean number of items in the stomach

of young-of-the-year perch caught

with ichthyoplankton trawls in Little

Bear Lake, 1985.............................113

Mean number of items in the stomach

of young-of-the-year perch caught

with ichthyoplankton trawls in

Douglas Lake, 1985..........................1l4

Mean number of items in the stomach

of young-of-the-year perch caught

with ichthyOplankton trawls in

Little Bear Lake, 1986......................115

Mean number of items in the stomach

of young-of-the-year perch caught

with ichthyoplankton trawls in

Douglas Lake, l986............... ........... 116

Mean number of items in the stomach
of young-of-the-year perch caught
with seine hauls in Douglas Lake, 1985......117

Mean number of items in the stomach
of young-of-the-year perch caught
with seine hauls in Little Bear Lake, 1985..118

Mean number of items in the stomach
of young-of-the-year perch caught
with seine hauls in Douglas Lake, 1986......119

Mean number of items in the stomach
of young-of-the-year perch caught
with seine hauls in Little Bear Lake, 1986..120

Mean number of items in the stomach

of young-of-the-year white suckers

caught with ichthyoplankton trawls in

Douglas Lake 1985-1986......... ............. 121

xi

Table

Table

Table

Table

47.

48.

49.

50.

Page
Mean number of items in the stomach
of young-of-the-year white suckers
caught with ichthyoplankton trawls in
Little Bear Lake 1985-1986..................123

Mean number of items in the stomach

of young-of-the-yearwhite suckers

caught with seine hauls in Douglas

Lake 1985-1986..............................124

Mean number of items in the stomach

of young-of-the-year white sucker

caught with seine hauls in Little

Bear Lake 1985..................... ..... ....125

Mean number of items in the stomach

of young-of-the-year white sucker

caught with seine hauls in Little

Bear Lake l986...................... ...... ..126

xii

Figure

Figure

Figure

Figure

Figure

Figure

Figure

LIST OF FIGURES
Page

Mean length (millimeters) of young-

Of-the-year yellow perch in Little

Bear and Douglas Lake, 1985-1986. In

most cases one standard error of the

mean is contained within the symbol..........22

Instantaneous growth rate of young-
of-the- year yellow perch in Little
Bear and Douglas Lakes, 1985-1986............24

Mean density (number/cubic meter) of
young-of-the-year yellow perch

sampled with ichthyoplankton trawls

in Little Bear and Douglas Lakes,

1985-1986. Vertical bars indicate

+/- 1 standard error of the mean.............25

Natural logarithm of catch

(number/139.2 square meters) of
young-of-the-year yellow perch

sampled with seine hauls in Little

Bear and Douglas Lakes, 1985-1986............26

Mean proportion of gillnet catch of
adult yellow perch within a period
occurring on the 8, 4, and 2-meter
contours in Little Bear and Douglas
Lakes, June to August l985...................41

Mean proportion of gillnet catch of
adult yellow perch within a period
occurring on the 8, 4, and 2-meter
contours in Little Bear and Douglas
Lakes, May to August l986....................42

Mean proportion of day's gillnet

catch of adult yellow perch at each

contour occurring within each period

in Little Bear Lake, June to August 1985.....43

xiii

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

10.

ll.

12.

13.

14.

15.

16.

Page
Mean proportion of day's gillnet
catch of adult yellow perch at each
contour occurring within each period
in Douglas Lake, June to August 1985.........44

Mean proportion of day's gillnet

catch of adult yellow perch at each

contour occurring within each period

in Little Bear Lake, May to August 1986......45

Mean proportion of day's gillnet
catch of adult yellow perch at each

‘contour occurring within each period

in Douglas Lake, May to August l986..........46

Vertical distribution (mean distance

from lake surface) of adult yellow

perch caught in gillnets set on the

8-meter contour in Little Bear Lake,

June to August 1985..........................47

Vertical distribution (mean distance

from lake surface) of adult yellow

perch caught in gillnets set on the

8-meter contour in Douglas Lake,

June to August l985..........................48

Vertical distribution (mean distance

from lake surface) of adult yellow

perch caught in gillnets set on the

8-meter contour in Little Bear Lake,

May to August 1986.1.........................49

Vertical distribution (mean distance

from lake surface) of adult yellow

perch caught in gillnets set on the

8-meter contour in Douglas Lake,

May to August 1986...........................50

Mean depth of capture of adult yellow

perch caught in gillnets set on the

8-meter contour in Little Bear and

Douglas Lakes, June to August 1985,

and May to August 1986.......................52

Mean proportion of gillnet catch of

adult white sucker within a period

occurring on the 8, 4, and z-meter

contours in Douglas Lake, June to

August 1985, and May to August 1986..........55

xiv

Figure

Figure

Figure

Figure

Figure

17.

18.

19.

20.

21.

Page
Activity pattern of adult yellow
perch caught in gillnets in Little
Bear and Douglas Lakes, June to
August 1985..................................57

Activity pattern of adult yellow

perch caught in gillnets in Little

Bear and Douglas Lakes, May to

August 1986..................................58

Mean proportion of day's gillnet

catch of adult white sucker at each

contour occurring within each period

in Douglas Lake, June to August 1985.........59

Mean proportion of day's gillnet

catch of adult white sucker at each

contour occurring within each period

in Douglas Lake, May to August 1986..........60

Activity pattern of adult white

sucker caught in gillnets set in

Douglas Lake, June to August 1985,

and May to August 1986................ ...... .61

XV

INTRODUCTION

Yellow perch (Perca flavescens) are a highly valuable

 

sportfish in Michigan, providing approximately 20% of the
catch from inland lakes and 72% of the non-salmonid catch
from the Great Lakes (Jamsen 1985). Growth of yellow perch
in inland lakes is sometimes poor, producing fisheries of
relatively low quality. In a recent workshop sponsored by
the Michigan Department of Natural Resources, slow growth
or "stunting" of bluegills (Lepomis macrochirus) and yellow
perch ranked second behind insufficient public access among
key problems identified by fishery managers. and fishery
user groups (Scott et a1. 1985).

Stunted populations of yellow perch (including the
closely related European perch, Pgrca fluviatilis) are
thought to be the result of food limitation; especially in
the availability of benthic invertebrates (Schneider 1972:
Persson 1986). In lake systems where perch growth is
relatively rapid, they often show an ontogeny of diet from
zooplankton to benthos and finally fish or crayfish
(Schneider 1972; Clady 1974: Elrod et a1. 1981). When
benthic food resources are scarce, perch are unable to

switch to larger food items and a bottleneck in the growth

2

of yellow perch may occur, with stunting the result.
Intra- and inter-specific exploitative competition (Pielou
1974) have been commonly implicated as factors controlling
the availability of benthic prey resources to yellow perch
(Persson 1983; Alm 1946; Hanson and Leggett 1985: Schneider
1972). Some of the species that have been observed to
compete with yellow perch or the closely related European
perch are white sucker (Catostomus commersoni) (Schneider
and Crowe 1980; Johnson 1977), pumpkinseed sunfish (Lepomis
gibbosus) (Hanson and Leggett 1985), and roach (Rutilus
rutilus) (Persson 1983). The mechanisms causing decreased
growth, abundance, or reproduction of perch are only well
known in the study by Persson, where removal of 70% of the
roach present resulted in increased zooplankton abundance
and increased yellow perch growth in Lake Sovdeborg,
Sweden.

In order for exploitative competition to ocCur, the
presence of one species (or individual) must decrease the
availability' of resources for’ another' species (or
individual) (Pielou 1974). In order for this to occur,
predation must be able to exert some control over the prey
populations being co-utilized. The ability of fish to
regulate zooplankton communities has been well documented
(see McQueen et a1. 1986 for review), but the impact of
fish on benthic invertebrate communities has been studied

less and is in general less well known. Several studies

3
(Hall et a1. 1970; Hayne and Ball 1956) provide clear
evidence that predation can decrease the abundance of
benthic invertebrates. Hall et a1. (1970) found that
predation by fish had little effect on the biomass of the
benthic community, but some individual species were greatly
impacted. Predation affected larger individuals to a
greater degree, especially the late instar and pupal stages
of Chironomus tentans, late instar zygopteran larvae, and
amphipods. Hayne and Ball (1956) found that biomass
decreased in response to predation by a centrachid fish
community, but apparent production increased. Schneider's
(1972) results are less clear on 'the ability of fish
predation to limit the biomass of benthic invertebrates.
After stocking yellow perch into two lakes that had
previously been treated with rotenone to remove the
existing fish communities, one lake showed a decrease in
the abundance of the benthic invertebrates whereas the
other showed an increase. Thorp and Bergey (1981) using in
situ exclosures found no appreciable differences in benthic
density or taxon richness between control and treatment
plots. Johnson (1977) found no persistent changes in the
abundance of benthic invertebrates after the removal of
adult white suckers from Wilson Lake, Minnesota. The
results of these studies indicate that fish predation can
strongly impact the benthic community under certain

conditions, but the conditions which mediate the strength

4
of this control are virtually unknown. In terms of the
potential for competitive interaction, this means that
exploitative competition can occur only under those
conditions where predation can exert at least some control
over the benthic community, thereby limiting the abundance
of these prey items.

White suckers, being perceived as food competitors,
are sometimes removed in order to improve yellow perch
populations” -Two studies (Johnson 1977; Schneider' and
Crowe 1980) document a strong positive response by yellow
perch to white sucker removal. However, in other lakes this
management technique has not proven to be very effective
(James Schneider, Michigan Department of Natural Resources,
personal communication). Schneider and Crowe (1980)
observed yellow perch harvest to increase from 500
fish/year to over 12,000 fish per year following a sucker
removal program in Big Bear Lake, Otsego Co. In Wilson
Lake, Minnesota, 85% of the adult white sucker population
was removed by trapnetting, resulting in a 15-fold increase
in yellow perch recruitment, and a 40 ndllimeter increase
in mean length of age V and VI yellow perch. Neither of
these studies was effective in determining the mechanisms
producing the responses observed. In order to be able to
predict the response of yellow perch to white sucker
removal, it is necessary to understand the mechanisms

controlling the interactions between the two species.

5
The goal of this study was to examine the life-history
of two sympatric populations of yellow perch and white
suckers in order to identify potential axes of competition.
Specifically, I examined the distribution and abundance of
zooplankton and benthos, and the growth, abundance, diet,

feeding rate, daily activity and distribution of perch and

suckers.

STUDY AREA

Little Bear Lake, Otsego Co., Michigan is 51.8
hectares in size, has a mean depth of 4.5 meters and a
maximum depth of 10 meters. Douglas Lake, Otsego Co.,
Michigan is 38.1 hectares in area, has a mean depth of 4.7
meters and a maximum depth of 11 meters. These lakes were
chosen because they are morphometrically similar, and
preliminary netting indicated that the fish communities of
both lakes contained white suckers and populations of
small-sized perch. Both lakes are mesotrophic per Carlson's
(1977) criteria, with Secchi disk transparencies ranging
from 2.1 to 8.0 meters. The alkalinity of lakewater in
Little Bear Lake on 4/27/87 was 117 mg CaC03/1 and the pH
was 8.26. The alkalinity and pH of Douglas Lake on this
date were similar, with an alkalinity of 93 mg CaCO3/l and
a pH of 7.98. The water temperature on both of these dates
was 12° C. Thermal stratification generally occured only in
the bottom 1-2 meters, and oxygen concentrations of less
than 4 ppm ‘were not observed” Little Bear Lake has
approximately 150 cottages around its shoreline, while
Douglas Lake has about 75. The shorelines of both lakes
generally have a sand, gravel or cobble substrate, with few

aquatic macrophytes evident.

METHODS

Young-of-the-Year Fish

Young-of-the-year (YOY) fish were sampled for
evaluation of growth rate, mortality rate, relative
abundance, and diet using ichthyoplankton trawls and
seines. Surface trawls were conducted both before and
after dark with a 0.5-meter diameter, 760-micron mesh
ichthyoplankton net with a flow meter mounted at the net's
mouth. The net was towed at approximately 1 meter/second
for 5 minutes, thereby sampling approximately 59 cubic
meters per trawl. Surface trawls were taken because perch
larvae tend to concentrate near the lake surface (Clady
1976), and to provide results comparable with other
studies of larval fish (Corbett and Powles 1983: Faber
1967) . Since most feeding occurs during daylight hours
(Noble 1972), samples were taken before dark to provide
fish for stomach analyses. Catch rates of larval fish are
generally higher after dark, and fish caught after dark
were used to estimate relative density and growth. Three
trawl samples were taken on each of the 2, 4 and 8 meter
contours. Trawl samples were taken from the time of
hatching in mid- to late-May‘ until the YOY perch and
suckers were vulnerable to beach seines in late-June to
early-July when they reached a size of about 25

millimeters. Trawl samples were taken at weekly intervals

8
with one exception in the spring of 1985 when one sample
was missed.

Shore seine samples were taken weekly from the time
YOY perch and suckers became vulnerable to this gear to the
end of August. Nine sites were sampled on Douglas Lake
and seven sites on Little Bear Lake using a seine with
0.48-centimeter mesh 7.6 meters in length and 1.2 meters in
depth. These sites were selected to represent a variety
of bottom types, including sand, cobble, vegetation, and
mixtures of the above. At each site 15.2 meters of
shoreline were seined, with the width of the seine haul
dependent on the depth of the site. Catch was
standardized to number caught per 139.4 square meters (1500
square feet). Mortality rates were estimated by regressing
the natural logarithm of catch against date for the
descending limb of the catch curve (Ricker 1975).

All YOY perch and suckers caught in ichthyoplankton
trawls, and a subsample of 25 YOY fish from each site
seined were preserved in 90% ethanol. The total length of
preserved fish was measured to the nearest 0.01 millimeter
using a digitizing pad. The preserved wet weight of a
subsample of 5 fish per day from fish caught in
ichthyoplankton trawls was measured to the nearest 0.00001
gram with a Mettler analytical balance. Regressions
between the logarithm of total length and the logarithm of

preserved wet weight were used to estimate the preserved

9
wet weight for each fish measured for length that had not
been measured for weight. Young-of-the-year perch and
suckers caught in shore seines were weighed with an Ohaus
electronic balance to the nearest 0.001 gram. During 1985,
the preserved wet weight of a subsample of 5 fish perch day
was obtained, and these data were used to develop length-
weight regressions in the same manner as for fish caught
with ichthyoplankton trawls. During 1986 the entire
subsample of fish measured for length were also measured
for weight. Since preliminary data analysis using analysis
of variance indicated that there are sometimes significant
(p<0.05) differences in. the 'mean length and. weight of
young-of-the-year yellow perch caught on the same day at
different sites, population mean length and weight were
calculated using a mean weighted by the catch at each site.
The mean length and weight from each site were assumed to
be independent, and variance of the population mean was

calculated using the formula (Mendenhall et al. 1971):

1
N2
where,

N = total catch
nr = catch at site r

52r = variance of mean at site r

10
Growth in terms of length was estimated by linear
regression, and was expressed as millimeters/day.
Instantaneous growth (day'l) in terms of weight (u) was

calculated by the formula (Ricker 1975):

ln(weight2) - 1n(weight1)

u = (2)

 

time in days

Stomach contents were identified and enumerated under
a dissecting microscope. Diet overlap indices were
estimated between the following groups: YOY yellow perch,
YOY white suckers, adult yellow perch, and adult white
suckers, where all fish age I and older are considered to
be adults. These indices were calculated on the average
of the proportion that each prey taxon made up of
individual fish's stomach contents using Schoener's (1970)

index:
Overlap- 1 - (0.5 X In“ - p“ I) (3)

where,
Pxi a proportion of food i in the diet of species x
Pyi = proportion of food i in the diet of species y
Index values can range from 0.0 indicating no diet overlap,

to 1.0 indicating complete diet-overlap.

11

Adult Fish

The term "adult fish" is used here to refer to all age
I and older fish whether they were sexually mature or not.

Horizontal monofilament gill nets were set in 2 and 4
meters of water, and vertical gill nets in 8 meters of
water to evaluate daily activity, spatial distribution,
and diet of adult perch and suckers. Horizontal nets were
1.8 meters in depth, 15.2 meters in length, and had 3-
meter panels of 2.54, 3.81, 5.08, 6.35, and 7.62-
centimeter stretched mesh monofilament netting. Vertical
gill nets were constructed in each of the above mesh
sizes, and were 1.8 meters in width and 8 meters in length.

In order to estimate daily activity patterns and
spatial distribution of yellow perch and white sucker, 8
nets were set at each of two sites for a period of 24
hours, and were checked every 3 hours. The start and end
of the periods were timed such that periods 3 and 8 would
be centered on sunrise and sunset, respectively. Since the
time of sunrise and sunset is variable, the beginning time
and ending time for each period were also variable. As
such, results concerning daily activity patterns and
spatial distributions will be reported using only a period
designation. The approximate initial time for each period
is as follows: Period 1= 2300 hr; Period 2= 0200 hr:

Period 3= 0500 hr; Period 4= 0800 hr; Period 5= 1100 hr;

12
Period 6= 1400 hr; Period 7= 1700 hr; and Period 8= 2000
hr. Each site contained one horizontal net set
approximately on the 1.8-meter contour, a surface and a
bottom horizontal net approximately on the 3.7-meter
contour, and a vertical gill net in each of the above
meshes approximately on the 8-meter contour. The
proportion of catch on each contour was weighted by the
proportion of the lake area that each contour represented.
In Little Bear Lake, 30.6% of the lake area was contained
between the 0-and 2.7-meter contour: 18.6% was contained
between the 2.7-and 5.2-meter contour; and 50.8% of the
lake area was contained in water greater than 5.2 meters in
depth. In Douglas Lake, these percentages were 28.5% from
0-2.7 meters, 21.1% from 2.7 to 5.2 meters, and 50.3% in
water greater than 5.2 meters in depth. Samples were taken
at 3-week intervals from mid-June to the end of August
during 1985, and at 5-week intervals from mid-May to the
end of August during 1986. A subsample, consisting of 5
fish per top and bottom half of the horizontal nets and 5
fish per vertical meter within the vertical gill nets was
preserved in 10% formalin for stomach analysis. The
contents of the stomach and intestine were weighed
separately .to the nearest 0.001 gram wet weight with an
Ohaus electronic balance and stomach contents were
identified and counted. Stomach fullness was expressed as

the percent that the wet weight of the stomach contents

13
occupied of the fish's wet body weight.

The mean stomach fullness (S) for the day was
estimated from the unweighted mean of the the mean stomach
fullness from each period, following the method outlined by
Elliott and Persson (1978). Instantaneous gastric
evacuation rate was estimated by the instantaneous rate of
decrease of mean stomach fullness during non-feeding
periods. Gastric evacuation rate was also estimated by
Persson's (1979) formula derived from laboratory data.
Persson found that the evacuation rate of adult perch fed
on zooplankton (including Chaoborus) was strongly

temperature dependent, and could be described by the

formula:

0.14T
R= 0.0182 * e (4)

where,

R = instantaneous gastric evacuation rate (hr-1)

T = temperature in °C

Feeding rates were calculated using each of the
estimates for gastric evacuation rate following equation

14 of Elliott and Persson (1978):

l4
Feeding rate = 24 * S * R (5)
where,
S = mean stomach fullness for the entire day

R

instantaneous gastric evacuation rate (hourly)

and were expressed in terms of wet weight of food as a
percentage of the wet body weight.

Electivity indices were calculated for zooplankton
species eaten by adult yellow perch. Indices were not
calculated for adult white suckers because chydorid
cladocerans, which made up a large proportion of their
diet, were not found in either plankton tows or benthos
samples. Electivities were calculated using Strauss's

(1979) index (Li):

Li = ri - Pi (5)
where,
ri = proportion of food 1 in fish's diet

Pi = proportion of food i in the environment.

Growth rate of adult yellow perch was estimated in two
ways. First, scales were taken from just above the lateral
line at a point below the 3rd dorsal spine from fish
collected during the spawning period. Annuli measurements
were taken from a image of the scale projected. on a

digitizing pad. Due to the difficulty of accurately

15

reading scales from fish growing so slowly, another
estimate of growth was obtained from adult perch collected
for stomach analysis. The mean length and weight were
estimated for fish caught during each of the 24-hr
studies, and increments estimated between these dates.
This estimate of growth applies to the dominant size class,
and includes members of several age classes. This method
does not permit calculation of mean length at age, but is
not dependent on the accuracy with which scales can be
read. One problem with this method is that recruitment of
fish into the dominant size class will decrease the
estimate of growth increment.
Prev Populations

Zooplankton was sampled with a 20-cm diameter, 80-
micron mesh Wisconsin net towed vertically from 0.5 meter
off the bottom to the surface. All tows were taken
between 0900 hr and 1600 hr. Two samples were taken on
each of the 2-, 4- and 8-meter contours. Zooplankton
samples were preserved in a sucrose-formalin solution
(Haney and Hall 1973), and were subsampled using a
Hensen-Stemple pipette. Zooplankton samples were taken
at 2-week intervals during 1985, and on or near the dates
of the 24-hr gill netting samples during 1986.

Benthos samples were collected using a 15.24 x 15.24
centimeter Ekman dredge, strained through a 250-micron

benthos bucket, and fixed in the field with formalin.

16

These samples were picked in the lab using sugar
flotation. Three random samples were taken on each of the
2-, 4-, and 8-meter contours. Benthos samples were taken
at 3-week intervals during 1985, and on or near the dates
of the 24-hr gill netting samples during 1986.
Limnological Parsmeters

Water temperature profiles were taken at midday on
each of the 24-hour sampling dates using a Yellow Spring
Instrument Co. meter. Dissolved oxygen concentrations were
also measured with a Yellow Spring Instrument Co. meter

which was calibrated against a Winkler titration.

RESULTS
Young-of-the-vear Fish
Perch Growth

Young-of-the-year (YOY) yellow perch were first caught
on 5/21 in 1985 and 5/12 in 1986. The mean total length of
larval yellow perch on the first date of capture ranged
from 5.27 'mm to 7.40 mm for the two years. There were
significant differences (t-test, p<0.05) in mean length and
weight of YOY perch between years and lakes on the first
sampling date, however this may be due to differences in
the time of hatching relative to the first sampling date.
By the second sampling date length and weight were greater
(t-test, p<0.05) in Little Bear Lake and this difference
persisted both years until the eighth or ninth week after
hatching (Tables 1 - 4). After this time, mean length and
weight of YOY perch were greater in Douglas Lake until the
end of August.

Growth in length was approximately linear throughout
the entire sampling period in both lakes both years (Figure
1). Fits to linear regression lines were very good (R2=
0.97 to 0.99; p<0.001), and inspection of standardized
residuals did not show any departures from the assumptions
of linear regression. The rate of increase estimated by
linear regression was 2.83 mm/week and 3.12 mm/week in

Little Bear Lake during 1985 and 1986, respectively.

17

18

 

 

Table 1. Mean length (millimeters) of young-of-the-year
yellow perch in Little Bear Lake in 1985 and
1986. The dashed lines separate samples taken by
ichthyoplankton trawling (above) and seining
(below). Standard error is denoted by SE, and
sample size is denoted by N.

Week
sfter 1985 1986
hatching

Mean SE N Mean SE N
l 6.55 0.08 48 5.53 0.03 89
2 - - - 9.15 0.09 44
3 14.54 0.13 40 11.25 0.06 91
4 19.04 0.14 27 14.18 0.07 83
5 21.39 0.26 43 17.28 0.10 65
6 24.50 0.12 60 - - -
7 25.51 0.89 6 28.15 0.18 89
8 29.71 0.09 464 30.61 0.11 150
9 35.83 0.10 503 30.81 0.11 175
10 37.68 0.13 450 35.41 0.17 161
11 37.53 0.07 348 38.27 0.17 160
12 40.90 0.14 354 40.84 0.26 132
13 40.78 0.16 146 43.73 0.27 141
14 48.24 0.24 199 43.63 0.22 121
15 45.60 0.25 167 50.00 0.28 134
16 - - - 51.98 0.20 149

19

Table 2. Mean length (millimeters) of young-of-the-year
yellow perch in Douglas Lake in 1985 and 1986.
The dashed lines separate samples taken by
ichthyoplankton trawling (above) and seining
(below). Standard error is denoted by SE, and
sample size is denoted by N.

 

 

 

 

week
after 1985 1986
hatflfing
Mean SE N’ Mban SE N
1 7.40 0.07 102 5.27 0.02 81
2 - - - 8.10 0.09 61
3 11.31 0.24 32 10.50 0.05 81
4 11.59 0.77 5 12.70 0.10 29
5 18.25 0.21 15 17.67 0.93 7
6 _ _ _ _ - _
7 - - - 25.59 0.19 77
8 29.65 0.69 6 30.16 0.27 73
9 37.05 0.20 56 34.15 0.40 22
10 41.26 0.34 36 40.13 0.48 22
11 45.91 0.52 20 44.32 0.91 13
12 47.44 9.34 4 43.63 0.62 16
13 52.08 1.95 8 46.08 - 1
14 57.85 - 2 52.14 0.89 8
15 61.89 - 2 - - -

16 - - - 55.99 1.21 10

20

 

 

Table 3. Mean weight (grams) of young-of-the-year yellow
perch in Little Bear Lake. The dashed lines
separate samples taken by ichthyoplankton
trawling (above) and seining (below). Standard
error is denoted by SE, and sample size is
denoted by N.

Week
after 1985 1986
hatching

Mean SE N Mean SE N

1 0.00116 0.00006 48 0.00088 0.00001 89

2 - - - 0.00521 0.0002 44

3 0.0235 0.0008 40 0.0102 0.0002 91

4 0.0719 0.0021 27 0.0237 0.0004 83

5 0.1116 0.0050 43 0.0485 0.0010 65

6 0.1879 0.0039 60 - - -

7 0.2167 0.0308 6 0.158 0.003 89

8 0.166 0.002 464 0.189 0.002 150

9 0.276 0.002 503 0.186 0.002 175
10 0.316 0.003 450 0.303 0.004 161
11 0.306 0.002 348 0.395 0.005 160
12 0.393 0.003 354 0.504 0.010 132
13 0.385 0.004 146 0.636 0.012 141
14 0.597 0.008 199 0.612 0.010 121
15 0.533 0.009 167 0.854 0.015 134
16 - - - 0.963 0.012 149

21

 

 

Table 4. Mean weight (grams) of young-of-the-year yellow
perch in Douglas Lake. The dashed lines separate
samples taken by ichthyoplankton trawling (above)
and seining (below). Standard error is denoted
by SE, and sample size is denoted by N.

Week
after 1985 1986
hatching
Mean SE N Mean SE N
1 0.00429 0.00011 102 0.00041 0.00001 81
2 - - - 0.00262 0.00009 61
3 0.0126 0.0005 32 0.00642 0.0001 89
4 0.0143 0.0027 5 0.0133 0.0004 29
5 0.0532 0.0016 15 0.0455 0.0084 7
6 _ _ _ .. _ .-
7 - - - 0.107 0.003 77
8 0.155 0.022 6 0.182 0.005 73
9 0.296 0.005 56 0.232 0.007 22
10 0.424 0.011 36 0.389 0.013 22
11 0.526 0.020 20 0.515 0.029 13
12 0.597 0.388 4 0.513 0.017 16
13 0.757 0.114 8 0.580 - 1
14 0.991 - 2 0.961 0.055 8
15 1.183 - 2 - - -
16 - - - 1.052 0.049 10

LENGTH Onnfi

LENGTH Onnfl

Figure 1.

22

1985

80

 

+ DOUGLAS LAKE

70" - UTTLE BEAR

60- *

40— + - -
30- c
20" I .

10_ '0 4

 

 

 

0 I I I l I I I I I I I I I

0 2 4 6 8 1'0 1'2 14 16
WEEK AFTER HATCHING

1986

I

 

80 ~—
T + DOUGLAS LAKE

70‘ - LITTLE BEAR

60~
50- ” - '
40-
30- I -
20—

10" . I

 

 

 

O I I I I I I I I I I I I I I I I
0 2 4 6 8 10 12 14 16
WEEK AFTER HATCHING

Mean length (millimeters) of young-of-the-year
yellow perch in Little Bear and Douglas Lake,
1985-1986. In most cases one standard error of
the mean is contained within the symbol.

23
The growth rate of YOY perch was higher in Douglas Lake
each year, averaging 4.14 mm/week in 1985 and 3.63 mm/week
in 1986.

Attempts to fit an exponential curve to observed
growth resulted in serious violations of the assumptions‘
of the regression model used. Von Bertlanffy equations
(Ricker 1975) did not aptly fit the data either, as growth
in weight did not approach an asymptote during the sampling
period. In general, instantaneous growth rates in terms
of weight were highest just after hatching, and decreased
as the summer progressed (Figure 2). An exception to this

was in Douglas Lake during 1985, when initial growth was

relatively slow.

Perch Density

The density of larval yellow perch just after hatching
was significantly greater in Douglas Lake during 1985 (t-
test, p<0.05) and similar to the density measured in Little
Bear Lake during 1986 (t-test, p>0.1). By the third or
fourth week after hatching, however, catch rates dropped
below those in Little Bear, and remained so throughout the
remainder of the summer (Figures 3 and 4: Table 5). Total
loss rate calculated from the first sampling date (5/21/85
and 5/12/86) to the last ichthyoplankton sampling date

(7/2/85 and 6/9/86) was 97.4 and 90.2% in Little Bear Lake

24

1985

 

 

 

 

 

 

03
+ + DOUGLAS LAKE
f: 0.25 - I LITTLE BEAR
I
g 0.2 -
O
V 0 15 -
E3 .
§ 0.1 -»
3:
E 0.05 -
8
o 0 V \,
—0.05 W I I I I I I I I I I I I I
0 2 4 6 8 10 12 14
WEEK AFTER HATCHING
03
+ DOUGLAS LAKE
f: 025 ... I LITTLE BEAR

0.2 7

 

GROWTH RATE (DAY -
o o
o o -
m a m

0

 

 

 

l
P
0
0|

 

I I I r I —I I F

2 4 6 a 1'0 12 ' 14
WEEK AFTER HATCHING

0

Figure 2. Instantaneous growth rate of young-of-the-year
yellow perch in Little Bear and Douglas lakes,
1985-1986.

NUMBER PER CUBIC METER

NUMBER PER CUBIC METER

Figure 3.

25

1985

1.0

 

4' DOUGLAS LAKE

0'9 ' - LITTLE BEAR

0.8 -

0.7 ~ '*

 

0.6 ~ I
0.5 ~
0.4 ~
0.3 -
0.2 -

0.1 '-

 

 

 

”—K
o I I I I I I I

0 2 4 6 8
WEEK AFTER HATCHING

1986

2.0

 

1 8 .. + DOUGLAS LAKE
' 1 - LITTLE BEAR
1.6 -

1.4-1

1.2-1

 

1.0 -‘

0.8 c

0.6 d

0.4 -

0.2 —

 

 

 

o I I I I I

0 2 4 6 8
WEEK AFTER HATCHING

-l
—

Mean density (number/cubic meter) of young-of-
the-year yellow perch sampled with
ichthyoplankton trawls in Little Bear and
Douglas Lakes, 1985-1986. Vertical bars
indicate +/- 1 standard error of the mean.

LOGe CPE

LOGe CPE

Figure 4.

26
1985
+ DOUGLAS LAKE

6‘ uIJnLEEfilR

 

5—4

4—4

2—4
1- ///k\‘\k\\\‘\

° /
_1"

 

 

 

 

1 I I I I I

1'0 12 14 16
WEEK AFTER HATCHING

1986

6 - I LITTLE BEAR

_3 'JI'"‘ I I1 I
8

 

1 ~ /’
0

-... \/
-3 “IE—“‘1’“ I I I ' ' I

6 8 1'0 I 1'2 1 4 1 6
WEEK AFrER HATCHING

 

 

 

 

Natural logarithm of catch (number/139.4 square
meters) of young-of-the-year yellow perch
sampled with seine hauls in Little Bear and
Douglas Lakes, 1985-1986.

27

 

Table 5. Mean catch of young-of-the year yellow perch in
Little Bear Lake and Douglas Lake, 1985-1986.
Ichthyoplankton trawls are above the dashed line,
and are expressed as number/cubic meter. Seine
hauls are below the dashed line and are expressed
as number/139.4 square meters. Standard errors
are in parentheses.

little Bear Douglas

week

after 1985 1986 1985 1986
hatdhing

1 0.235 (0.084) 1.543 (0.442) 0.719 (0.178) 1.690 (0.457)
2 - - 0.199 (0.066) - - 0.103 (0.019)
3 0.039 (0.009) 0.024 (0.008) 0.034 (0.017) 0.374 (0.051)
4 0.045 (0.013) 0.424 (0.119) 0.009 (0.003) 0.076 (0.023)
5 0.291 (0.209) 0.181 (0.036) 0.021 (0.008) 0.013 (0.004)
6 0.213 (0.072) 0.002 (0.002)

7 0.006 (0.003) 100.7 (67.00) 0.000 - 94.5 (59.50)
8 193.7 (42.7) 99.4 (21.23) 0.4 (0.24) 61.8 (43.25)
9 500.0 (179.9) 153.0 (29.24) 6.2 (3.14) 8.2 (3.27)

10 254.9 (110.4) 416.8 (168.20) 4.2 (2.18) 7.2 (3.05)

11 163.7 (42.7) 86.2 (17.64) 2.2 (1.21) 3.1 (2.08)

12 225.9 (85.6) 86.3 (31.64) 0.1 (0.12) 6.2 (4.26)

13 47.9 (19.7) 146.2 (67.64) 0.9 (0.77) 1.4 (1.16)

14 65.4 (30.8) 53.1 (15.86) 0.4 (0.25) 3.2 (1.66)

15 48.1 (15.8) 174.0 (63.35) 0.2 (0.15) 0.3 (0.25)

16 - - 143.1 (65.80) - - 2.9 (1.45)

 

 

 

 

28

and 99.7 and 99.2% in Douglas Lake during 1985 and 1986,
respectively. These figures are probably overestimates of
mortality rate for ‘the entire larval period, since net
avoidance generally increases over time (Noble 1970).
However, differences in the initial catch rates of seine
samples support the claim that mortality rates were higher
during the early life stages in Douglas Lake. Mortality
rates for the period of ichthyoplankton trawling could not
be estimated using catch curve analysis (Ricker 1975) due to
a bimodal distribution of catch rates (Figure 3). Catch
curves showed an initial peak on the first day of
ichthyoplankton trawling, and a second peak near the middle
of the sampling period in both years in both lakes. Since
length-frequency distributions did not show a bimodal
distribution, the second peak was not due to a second
spawning period.

Catch per effort of YOY perch in seine hauls was much
higher in Little Bear Lake than in Douglas Lake during both
years (Table 5; Figure 4). During 1985, peak catch rates of
young perch in seine hauls were nearly 80 times greater in
Little Bear. As the summer progressed, this difference
increased to over 100 fold. During 1986, initial catch
rates in seine hauls were similar, but in Little Bear Lake,
catch decreased little during the summer, whereas in
Douglas Lake catch rates decreased to a small percentage of

their initial values (Figure 4). Mortality estimates

29

obtained by regressions of natural logarithm of catch versus
time for the descending limb of the catch curve (Ricker
1975) show higher' mortality rates in Douglas Lake both
years. Instantaneous weekly mortality rates in Douglas Lake
were estimated to be 0.518 and 0.410 in 1985 and 1986,
respectively. The corresponding values in Little Bear were
0.361 and 0.082. The value obtained for Little Bear Lake
during 1986 is very low, and a plot of ln(catch) versus time
does not show a clear downward trend (Figure 4).
White Sucker Density and Growth

The catch rate of juvenile white suckers in both lakes
was relatively low during 1985 and 1986. Consequently,
estimates of average length, weight, and. mortality' rate
could not be obtained for many dates during each year. From
the data available, it appears that young suckers were
vulnerable to ichthyoplankton trawls approximately 1 week
after the young perch. Initial growth was slower than young
perch, especially in terms of weight. After the young
suckers became demersal in habits and were recruited to
seine nets, growth rate increased, and their size at the end

of summer was equal to or greater than that of young perch

(Tables 6 - 9).

30

 

 

Table 6. Mean catch, length, and weight of young-of-the-

year white sucker in Little Bear lake, 1985. The

dashed lines separate samples taken by

ichthyoplankton trawling (above), and seining

(below). Standard errors are denoted by SE.

Sample sizes apply to both length and weight.

Catchl length (mm) Weight (g) 6.5111616

Date Mean SE Mean SE Mean SE Size
5/21 0.015 0.007 12.37 0.35 0.00504 0.00023 8
6/4 0.002 0.002 12.23 - 0.00420 - 1
6/11 0.000 0.000 - - - - 0
6/18 0.000 0.000 - - - - 0
6/25 0.000 0.000 - - - - 0
7/2 0.004 0.004 14.84 - 0.0255 - 2
7/9 1.1 0.8 25.72 0.89 0.143 0.014 8
7/16 2.3 0.4 32.23 1.22 0.302 0.031 16
7/23 1.3 0.8 34.26 1.35 0.355 0.045 9
7/30 0.9 0.9 38.42 0.88 0.501 0.036 6
8/6 0.0 0.0 - - - - 0
8/14 0.3 0.3 37.65 - 0.461 - 2
8/20 0.0 0.0 - - - - 0
8/27 0.0 0.0 - - - - 0

1 Mean catch per cubic meter of trawling or per 139.4 square meters
of seining.

31

Table 7 . Mean catch, length, and weight of young-of-the-year
white sucker in Douglas Take, 1985. The dashed
lines separate samples taken by ichthyoplankton
trawling (above), and seining (below). Standard
errors are denoted by SE. Sanple sizes apply to
both length and weight.

 

 

catchl length.(mm) Weight (g) Sample
Date mean SE 1220: SE MBan SE Size
5/21 0.000 0.000 - - - - 0
6/4 0.000 0.000 - - - - 0
6/11 0.002 0.002 8.76 - 0.00527 - 1
6/18 0.000 0.000 - - - - 0
6/25 0.002 0.002 16.11 - 0.0321 - 1
7/2 0.000 0.000 - - - - 0
7/9 2.7 1.3 21.34 0.46 0.081 005 24
7/16 0.1 0.1 32.68 - 0.232 - 1
7/23 0.0 0.0 - - - - 0
7/30 0.0 0.9 - - - - 0
8/6 0.0 0.0 - - - - 0
8/14 0.0 0.0 - - - - 0
8/20 0.0 0.0 - - - - '0
8/27 0.0 0.0 - - - - 0

1 Mean catch per cubic meter
of seining.

of trawling or per 139.4 square meters

32

 

 

Table 8 . Mean catch, length, and weight of young-of-the-year

white sucker in Little Bear lake, 1986. The dashed

lines separate samples taken by ichthyoplankton

trawling (above), and seining (belm). Standard

errors are denoted by SE. Sample sizes apply to

both length and weight.

Catch1 length (mm) Weight (g) Sample

Date Mean SE Mean SE Mean SE Size
5/12 0.000 0.000 - - - - 0
5/20 0.004 0.004 12.57 - 0.00700 - 2
5/27 0.024 0.008 13.10 0.40 0.00883 0.00089 11
6/2 0.002 0.002 10.49 - 0.00436 - 1
6/9 0.016 0.011 11.87 0.61 0.00746 0.00131 9
6/23 11.0 10.3 26.72 0.85 0.086 0.009 77
6/30 6.6 3.4 20.73 1.02 0.038 0.009 24
7/7 0.3 0.3 36.69 - 0.485 - 2
7/15 8.1 5.3 38.28 0.83 0.507 0.109 30
7/22 6.6 4.6 46.63 2.04 0.974 0.134 46
7/29 0.7 0.5 58.27 2.01 1.500 0.266 3
8/6 6.0 5.5 54.93 2.37 1.735 0.187 33
8/11 4.8 3.4 58.62 1.77 2.135 0.189 28
8/18 2.1 1.3 62.00 5.70 1.929 0.464 12
8/27 0.4 0.3 64.00 - 2.003 - 2

1 Mean catch per cubic meter of trawling or per 139.4 square meters

of seining.

33

 

 

Table 9 . Mean catch, length, and weight of young-of-the-year

white sucker in Douglas lake, 1986. The dashed

lines separate samples taken by idithyoplarflcton

trawling (above), and seining (helm). Standard

errors are denoted by SE. Sanple sizes apply to

both length and weight.

Catchl Length (m) Weight (g) Sample

Date Mean SE Mean SE Mean SE Size
5/12 0.000 0.000 - - - - 0
5/20 0.006 0.006 12.07 - 0.00466 - 3
5/27 0.065 0.032 11.42 0.17 0.00561 0.00076 33
6/2 0.000 0.000 - - - - 0
6/9 0.000 0.000 - - - - 0
6/23 0.7 0.4 21.29 0.85 0.058 0.012 6
6/30 0.0 0.0 - - - - 0
7/7 0.3 0.3 27.21 0.64 0.143 0.008 3
7/15 0.0 0.0 - - - - 0
7/22 0.0 0.0 - - - - 0
7/29 0.0 0.0 - - - — 0
8/6 0.0 0.0 - - - - 0
8/11 0.0 0.0 - - - - 0
8/18 0.0 0.0 - - - - 0

1 Mean catch per cubic meter
of seining.

of trawling or per 139.4 square meters

34
Diet and Overlap

The diet of YOY perch and suckers varied greatly among
sampling periods and lakes, but diet overlap between the
two species was consistently low during all time periods
(Table 10). Copepods and copepod nauplii were numerically
predominant in the diet of young perch during the time they
were sampled with ichthyoplankton trawls. Also present in
their diet at this time were Da hnia, Ch dorus,
Ceriodaphnia, Bosmina, and rotifers (Appendix A). During
the larval phase of life, white suckers fed predominantly
on Bosmina and chydorid cladocerans. A number of other
items were also eaten, including rotifers, copepods,
Scaphloberis, and chironomid larvae (Appendix B).

Near the beginning of July, the diets of both suckers
and perch showed a shift toward benthic items. The most
numerous items in the sucker's diet were chydorid
cladocerans, harpacticoid copepods and ostracods, all
generally' benthic meiofauna (Appendix: B). ‘Young jperch
generally consumed a more varied diet including both
planktonic micro-crustaceans as well as benthic meio- and
macrofauna (Appendix A).

In general, diet overlap between adult yellow perch
and the young-of-the-year of both species was low (Tables
11 and 12). Overlap between YOY of both species and adult

suckers were generally much higher (Tables 11 and 12).

35

 

Table 10. Schoener's diet overlap index between young-of-
the-year yellow perch and young-of-the-year
white sucker in Little Bear Lake and Douglas
Lake, 1985-1986. The dashed line separates
.samples taken by ichthyoplankton trawling
(above) and seining (below).

Lfliielkmm' Dmxflas

Waflc

after 1985 1986 1985 1986
haUflfing

1 _ - _ _

2 — ... _. _.

3 0000 0020 - 0002

4 - _ .. —

5 - 0000 - -

6 - ...- .. ..—

7 0.10 0.05 0.00 0.04

8 0.21 0.19 0.15 -

9 0.16 0.05 0.04 -
10 0.32 0.01 - 0.58
11 0.44 0.07 - -
l3 - 0.01 - -
14 0.07 0.01 - -
15 - 0.13 - -
16 - 0.28 - -

36

 

Table 11. Schoener's diet overlap indices between young-
of-the-year white suckers (WS) and yellow perch
(YP) and adult yellow perch and white suckers in
Little Bear Lake, 1985-1986.
Dates Interacting groups Overlap
1985
Jul 9-11 YOY WS and adult YP 0.035
Jul 30-31 YOY WS and adult YP 0.003
1986
Jun 23-25 YOY WS and adult YP 0.010
Jul 29-30 YOY WS and adult YP 0.013
Aug 25-Sep 3 YOY WS and adult YP 0.004
1985
Jul 9-11 YOY WS and adult WS 0.278
Jul 30-31 YOY WS and adult WS 0.478
1986
Jun 23-25 YOY WS and adult WS 0.653
Jul 29-30 YOY WS and adult WS 0.155
Aug 25-Sep 3 YOY WS and adult WS 0.277
1985
Jun 18-19 YOY YP and adult YP 0.290
Jul 9-11 YOY YP and adult YP 0.032
Jul 30-31 YOY YP and adult YP 0.014
Aug 20-21 YOY YP and adult YP 0.054
1986
May 20-22 YOY YP and adult YP 0.233
Jun 23-25 YOY YP and adult YP 0.092
Jul 29-30 YOY YP and adult YP 0.049
Aug 25-Sep 3 YOY YP and adult YP 0.014
1985
Jun 18-19 YOY YP and adult WS 0.054
Jul 9-11 YOY YP and adult WS 0.537
Jul 30-31 YOY YP and adult WS 0.633
Aug 20-21 YOY YP and adult WS 0.210
1986
May 20-22 YOY YP and adult WS 0.001
Jun 23-25 YOY YP and adult WS 0.108
Jul 29 YOY YP and adult WS 0.327
Aug 25-Sep 3 YOY YP and adult WS 0.376

37

 

Table 12. Schoener's diet overlap indices between young-
of-the-year white suckers (WS) and yellow perch
(YP) and adult yellow perch and white suckers in
Douglas Lake, 1985-1986.
Ixmes Intenxxfingqpxmps meflap
1985
Jun 25-26 YOY WS and adult YP 0.000
Jul 16-17 ' YOY WS arrl adult YP 0.000
1986
Jun 23-18 YOY WS and adult YP 0.015
Jul 7-23 YOY WS and adult YP 0.029
1985
JUn 25-26 YOY WS and adult.WS 0.516
Jul 17-16 YOY WS and adult WS 0.735
1986
Jun 23-18 YOY WS and adult WS 0.457
Jul 7-23 YOY WS and adult WS 0.578
1985
Jul 16-17 YOY YP and adult YP 0.052
Aug 6-8 YOY YP and adult YP 0.053
Aug 27 YOY YP and adult YP 0.002
1986
Jun 23-18 YOY YP and adult YP 0.234
Jul 22-23 YOY YP and adult YP 0.002
Aug 25-27 YOY YP and adult YP 0.005
1985
Jul 16-17 YOY YP and adult WS 0.215
Aug 6-8 YOY YP and adult WS 0.395
An927 YOY YP and adult.WS 0.220
1986
Jun 23-18 YOY YP and adult 95 0.107
Jul 22-23 YOY YP and adult WS 0.370
Aug 25-27 YOY YP ard adult 98 0.431

38
Adult fish

Abundance

During 1985 and 1986, over 99% of the adult yellow
perch catch was made in l-inch stretched mesh gill
netting. Fish caught in the l-inch netting generally
ranged in size from 95 to 140 millimeters TL. During 1985,
the mean catch of yellow perch in 1-inch mesh netting
during the 24-hour samples was similar in Little Bear and
Douglas Lakes (t-test, p>0.1), averaging 1092 perch/day in
Little Bear, and 1123 perch/day in Douglas Lake. Catch
rates for the same time period during 1986 were lower in
both lakes (t-test. p<0.05), averaging' 717 perch/day' in
Little Bear and 644 perch/day in Douglas Lake. Catch rates
in May 1986 were lower than during the summer with 353
perch caught in Little Bear on 5/22/86 and 413 perch caught
in Douglas Lake on 5/14/86. These differences are
presumably due to lower water temperature and perch
activity on these sampling dates. Catch rates of large
adult yellow perch with total lengths greater then 140
millimeters were very low, averaging 0.75 per day during
1985 and 13.50 per day during 1986 at Little Bear, and 1.25
per day both years at Douglas Lake. The catch of large
yellow perch was significantly greater (t-test, p<0.05) at
Little Bear during 1986 than at Douglas Lake either year,
and was significantly greater (t-test, p<0.05) than the

catch at Little Bear during 1985.

39

There were large differences in the catch rate of
suckers in the two lakes (t-test, p<0.05). Average catch
of suckers was 1.5/day each year in little Bear, whereas
catch averaged 17/day and lO/day in Douglas Lake during
1985 and 1986, respectively. In 1984, during our
preliminary netting, catch rate of suckers in Little Bear
Lake was much higher than during 1985 and 1986. Catch of
suckers in 76.2-meter experimental mesh gill nets set
perpendicular to shore averaged 3.6/day during 1984, but
catch dropped to 0.7/day in 1985 and 0.8/day in 1986. These
differences are not statistically (significant (t-test,
p>0.1), but may represent real biological differences
between 1984 and the subsequent years.
Spatial Distribution

The catch rate of fish in gill nets is dependent on
both the activity level and the abundance of fish in the
vicinity of the net. Since no literature data to the
contrary could be found, I have assumed that the proportion
of active fish is the same at all sites, and the relative
distribution and activity of fish is directly related to
catch rates. In these analyses, catch rates have also been
weighted in proportion to the area of the lake each net
represents using the proportion presented in the methods.

Catch rates of adult yellow perch in gill nets were
highest during the daylight hours (periods 4-7), with 90-

99% of the catch within a period occurring at the 8-meter

40

sites (Figures 5 and 6). At the 2- and 4-meter sites,
catches were generally very low, making 10% or less of the
total catch within each period. At night (periods 1 and 2),
catch rate decreased dramatically at the deep sites, but
catch rates of perch at the shallow sites (1.8- and 3.7-
meters) increased at dusk (period 8), and remained above
daytime levels throughout the night (Figures 7-10).
Although the contribution of the deeper sites decreased
during the night, 60% or more of the catch within a night
periods still occurred at these sites.

The average percentage of the catch during the
daytime occurring at the 8-meter sites during 1985 and 1986
were 96.8% and 95.8% in Little Bear Lake, and 91.3% and
91.5% in Douglas Lake. The difference between lakes is
statistically significant (Wilcoxon's signed rank. test,
p<0.05), but the magnitude of this difference is small and
may not be ecologically important. Differences were also
noted between the lakes for other times of day and netting
sites, but the extent of these differences was small in all
cases. I

The vertical distribution of yellow perch caught in
vertical nets was quite different between lakes. Perch in
Little Bear Lake were concentrated near the bottom, whereas
in Douglas Lake they were distributed more evenly
throughout the water column (Figures 11 - 14). The

difference in vertical distribution is also illustrated by

PROPORTION OF CATCH

PROPORTION OF' CATCH

Figure 5.

41

LITTLE BEAH LAKE

09- I‘E‘fl\\\\~
0.8 -‘
0.7 - o B—METER CONTOUR

0.5 .. + 4—METER CONTOUR
. 2-METER CONTOUR

 

 

 

 

 

0.5 '4
0.4 ..
0.3 -'
02-

0.1 "' \ J

O I I I ; I" Y I

2 4 6 8

PERIOD

DOUGLAS LAKE

0'9 ‘ M
0.8 ‘
0.7 "

0.6 .. . a-IIEIER CONTOUR

+ 4—METER CONTOUR
0.5 - - 2-METER CONTOUR

0.4 -
0.3 '-
0.2 4
0.1 ~

 

 

 

 

 

 

 

 

PERIOD

Mean proportion of gillnet catch of adult yellow
perch Within a period occurring on the 8, 4, and
2-meter contours in Little Bear and Douglas
Lakes, June to August 1985.

PROPORTION OF CATCH

PROPORTION OF CATCH

Figure 6.

42

 

0.9 -
0.8 -
0.7 -
0.6 a
0.5 -
0.4 «
0.3 -
0.2 -
0.1 4

 

 

LTTTLE BEAH LAKE
L:;;\.

o B—METER CONTOUR

4' 4-METER CONTOUR
I 2—METER CONTOUR

 

 

2 4 6 8
PERIOD

DOUGLAS LAKE

 

0.9 -
0.8 ~
0.7 -
0.6 ~
0.5 '1
0.4 -
0.3 ~
0.2 ~
0.1 -

 

o B-METER CONTOUR

+ 4—MEI'ER CONTOUR
I 2—METER CONTOUR

  

 

 

 

Mean proportion of gillnet catch of adult yellow
perch within a period occurring on the 8, 4, and

     

I I I Y T

2 4 6
PERIOD

mu:

2-meter contours in Little Bear and Douglas
Lakes, May to August 1986.

43

B-METER CONTOUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1;...
E \\
V m§§§§§\

-4

”I!
'u a.
g d

 

4-METER CONTOUR

 

 

 

 

 

 

 

 

 

PERCENT 30F DAY‘S CATCH
- W

a

1 2 a 5 I

4
PERIOD

E-METER CONTOUR

 

 

 

 

 

 

 

 

?‘ \ N
0 go. \\\ \\\
m°1$5453g$

g .
8

Figure 7. Mean proportion of day's gillnet catch of adult
yellow perch at each contour occurring within

T332 period in Little Bear Lake, June to August

PERCENT OF DAY'S CATCH

PERCENT OF DAY'S CATCH

PERCENT OF DAY'S CATCH

Figure 8.

44

B-METER CONTOUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2% V
\
\ § \ \
\ \
.exx\§§\9
‘ 2 3 RERIO; . 7 a
50’ 4-METER CONTOUR

 

 

 

 

 

 

8
“f /////7////

 

 

 

 

~1/////

 

 

 

 

 

 

. \Q

0‘ T\ ERG . qu .

1 2 4 5 0 7
PERIOD

2-METER CONTOUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q:

///////
'-////////A

\
,§\ m m
I

i i 5 a
PERIOD

“-

Mean proportion of day's gillnet catch of adult
yellow perch at each contour occurring within
each period in Douglas Lake, June to August
1985.

PERCENT OF DAY'S CATCH PERCENT OF DAY’S CATCH

PERCENT OF DAY‘S CATCH

Figure 9.

45

B-METER CONTOUR

50

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

204 \
\ \
. 5%? r N
.. 4—METER CONTOUR
..; R

N
”I N \
i: a a
01?§?§-§>
w 2—METER CONTOUR

20"

10"

 

 

 

 

 

“TA/533333232229f/
/é??22222/

 

 

 

ESE .
4 5 o 7
PERIOD

 

an.
'9"
I

Mean proportion of day's gillnet catch of adult
yellow perch at each contour occurring within

each period in Little Bear Lake, May to August
1986.

46

B-METER CONTOUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.3...

\
g \\ \
Hee§§Q§x

I 3
PERIOD

4-METER CONTOUR

 

 

20“

10"

.1618 m

1 2 3 4 6 o T
PERIOD

PERCENT OF DAY'S CATCH

 

 

 

-'////////////

 

 

 

2-METER CONTOUR

 

 

 

 

//////

 

 

PERCENT OF DAY'S CATCH

\

 

 

 

 

 

~-////////

10‘ \

 

 

 

 

 

 

 

“a

I i I
4 5 6
PERIOD

“1

I

Figure 10. Mean proportion of day's gillnet catch of adult
yellow perch at each contour occurring within

each period in Douglas Lake, May to August
1986.

47

LITTLE BEAR LAKE 1985

 

 

 

0-1
1-2-
2-3—
g 3-44
E
E
o 4-5"
Figure 11.

 

 

 

 

 

 

 

Vertical distribution (mean distance from lake
surface) of adult yellow perch caught in
gillnets set on the 8-meter contour

in Little Bear Lake, June to August 1985.

48

DOUGLAS LAKE 1985

 

 

DEPTH (m)

 

 

 

Figure 12. Vertical distribution (mean distance from lake
surface) of adult yellow perch caught in
gillnets set on the 8-meter contour
in Douglas, June to August 1985.

49

LITTLE . BEAR LAKE 1986

I

 

 

 

 

 

DEPTH (m)
A
I
a

 

 

   

Figure 13. Vertical distribution (mean distance from lake
surface) of adult yellow perch caught in
gillnets set on the 8-meter contour
in Little Bear Lake, May to August 1986.

oeflH(m)

50

DOUGLAS LAKE 1986

 

 

 

Figure 14.

 

 

Vertical distribution (mean distance from lake
surface) of adult yellow perch caught in
gillnets set on the 8-meter contour

in Douglas Lake, May to August 1986.

51

the mean depth of capture of perch in the two lakes (Figure
15). These differences do not appear to be related to lake
thermal stratification, as neither lake showed any strong
thermal discontinuity except for the bottom 1 to 2 meters
(Tables 13 and 14). During the night hours, perch in
Little Bear showed distinct modes of catch near the surface
and near the bottom, whereas perch in Douglas Lake were
more evenly distributed throughout the water column
(Figures 11-14)

The catch rate of adult white suckers in Little Bear
Lake was too low to obtain estimates of their spatial
distribution. In Douglas Lake during 1985, adult suckers
tended to be caught in greater numbers at the 8-meter
contour at all times of day. The proportion of individuals
located in shallow water was generally under 50% (Figure
16), but this proportion was usually higher than the
proportion of perch caught in shallow water. During the
daytime, few adult suckers were caught in nets set on the
1.8-meter contour, but during the twilight and evening
hours, up to 30% of the adult suckers caught within a
period were caught at this depth. In 1986, the catch rate
of suckers was lower' than in 1985, and ‘the resulting
estimates of spatial distribution were influenced much more
by individual fish, especially during the daytime when few

or no suckers were caught.

METERS FROM SURFACE
l

METERS FROM SURFACE
I.

Figure 15.

52

1985

 

+ DOUGLAS LAKE
I UTflEEfilR

 

 

 

I I r I I

2 4 6 8
PERIOD

1986

d
d
-

 

4" DOUGLAS LAKE
I UHLEEEAR

 

 

 

I I I

4
PERIOD

N-I
m-I
(:1

Mean depth of capture of adult yellow perch
caught in gillnets set on the 8-meter contour
in Little Bear and Douglas Lakes, June to
August 1985, and May to August 1986.

53
Table 13. Temperature (°C) profiles on dates of

24-hr studies in Little Bear Lake and
Douglas Lake, 1985.

Lflnnelxarlzme

 

 

1985
temuifnan
surface (111) Jim 19 Jul 11 Jul 31 Aug 21 Oct 27
1 18.0 21.0 21.8 20.8 9.9
2 17.5 21.0 21.8 20.5 9.9
3 17.1 21.0 21.8 20.5 9.9
4 17.0 21.0 21.8 20.5 9.8
5 17.0 20.9 21.8 20.2 9.8
6 16.8 20.0 21.8 20.2 9.7
7 16.2 19.3 21.5 20.0 9.7
8 16.0 19.0 21.2 20.0 9.7
Damnaslame
1985

[EPUJfTUD
surface (m) Junzs 00117 Aug? Aug27

1 19.0 22.0 24.0 20.0

2 19.0 22.0 23.8 20.0

3 19.0 22.0 23.0 20.0

4 18.5 22.0 23.0 19.9

5 18.0 22.0 22.8 19.9

6 17.9 20.8 22.3 19.2

7 16.1 16.5 22.0 19.0

8 12.0 16.0 21.2 19.0

54
Table 14. Temperature (°C) profiles on dates of

24-hr studies in Little Bear Lake and
Douglas Lake, 1986.

Lumielherlame

 

 

1986

Depth from

surface (m) May 22 Jun 25 .3111 30 Sep 3
1 14.3 19.0 23.5 20.4
2 14.0 19.0 23.5 20.0
3 13.9 19.0 23.5 19.9
4 13.7 19.0 23.0 19.9
5 13.2 19.0 23.0 19.5
6 13.0 19.0 23.0 19.0
7‘ 13.0 17.0 22.8 18.9
8 13.0 15.5 21.2 18.9

DurflaleMe
1986

039th than

surface (m) May 14 Jun 18 Jul 23 Aug 27
1 15.0 18.5 24.9 18.2
2 15.0 18.0 24.9 18.0
3 15.0 18.0 24.4 18.0
4 15.0 17.0 24.0 18.0
5 13.0 17.0 23.0 18.0
6 12.0 17.0 20.9 18.0
7 11.0 13.0 18.1 18.0

8 10.1 12.0 14.9 18.0

55

1985

 

o B-MEI'ER CONTOUR

4- 4—METER CONTOUR
e 2—METER CWT”

   
 
   

PROPORTION OF CATCH
O
J.

 

 

 

A
Y

 

 

 

 

1 3 6 ' 7
PERIOD
1986
1 1 A _
_ .Oemnncmnmm
I: 09 +44mnncmflmm
Q 0 8_ - 2-uETER CONT -
F_ .
1<
o 0.7- '
D.
O 0.5“
2 0.5-3
.9
P— . ~
g; 04+
% 0.3- ,
0: 0.2“
n- 1
Q1—
0 Y T Y I Y
1 3 5 7
PERIOD

Figure 16. Mean proportion of gillnet catch of adult white
sucker within a period occurring on the 8, 4,
and 2-meter contours in Douglas Lakes, June to
August 1985, and May to August 1986.

56
The pattern of catch during 1986 showed a much smaller
proportion of suckers caught in deep water than in 1985
(Figure 16).

Most suckers were caught within 1 meter of the
bottom, but during the night suckers were occasionally
caught up to 5 meters off the bottom in offshore sites.
Daily Activity Pattssg

The overall population activity pattern is difficult
to determine since nets set on different depth contours
show differing patterns of catch rate (Figures 7-10). This
disparity may be due to subpopulations of perch at the
different _depth contours having different daily activity
patterns, or it may be due to movement of fish between
depths. If the latter possibility is true, then the
population activity pattern can be estimated by using catch
rates from nets on each of the depth contours, weighed by
the proportion of the lake area each net represents. The
general activity pattern calculated in this manner shows
nearly constant activity levels throughout the daylight and
twilight hours, with very low activity levels at night
(Figures 17 and 18). Note that most of this activity
pattern is determined by catches from the deeper sites,
where most of the adult perch reside.

Suckers in Douglas Lake were most active during the
twilight and evening hours and least active during the day
(Figures 19 - 21).

57

LITTLE BEAR LAKE 1985

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Ezo- \§\

2 X \

w- N\\\N‘

go.m\\\§\\\§
1 2 3 HERIUD 6 7 8
DOUGLAS LAKE 1985

g; 304

u. 1 T\

32° \ \

6.. \R R

8 §\\\\\

3f 0‘ . é;:\ \T\\ ::\V EEE: SEE: EET: ;:>N

PERIOD

Figure 17. Activity pattern of adult yellow perch caught

'in gillnets in Little Bear and Douglas Lakes,
June to August 1985.

58

LITTLE BEAR LAKE 1986

50

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

E \\ V\\
we \\ \\\
.. AREAS
DOUGLAS LAKE 1985

\
\ a
ma \§\\
.ts§e§§§§

PERIOD

Figure 18. -Activity pattern of adult yellow perch caught
in gillnets in Little Bear and Douglas Lakes,
May to August 1986.

50

59

B-METER CONTOUR

 

PERCENT OF OAY'S CATCH

40-
30a
20~

10'-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

50

 

-/////

 

‘\

4~METER CONTOUR

 

PERCENT OF OAY'S CATCH

50

4o-

30‘

20‘

10‘

 

 

 

 

//

 

 

 

 

 

 

 

 

 

 

 

2-METER CONTOUR

 

10

PERCENT OF OAY'S CATCH

4o~
30~

20‘

\

 

 

 

//////////

 

 

 

 

 

 

 

 

Figure 19.

”-1

i 1 5
. PERIOD

Mean proportion of day's gillnet catch of adult
white sucker at each contour occurring within

each period in Douglas Lake, June to August
1985.

60

B-METER CONTOUR

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

§4°+
230-
320. \ \
g \ \ \
fl§\ §\\
T i Pga'oos s 7 a
so 4-METER CONTOUR
.3404
%::§ \ \
m , \\ . ‘ >1 x
1 2 Famous a 7 .6
so 2-METER CONTOUR
é N
2 40- §§§
E 30‘ SSS
2%: § Q
RN 1 N r N
1 2 3 PERIODS 6 7 8

Figure 20. Mean proportion of day's gillnet catch of adult
white sucker at each contour occurring within

each period in Douglas Lake, May to August
1986.

61

DOUGLAS LAKE 1985

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

T

2 3 4 5 is 5
PERIOD

:20- §

§‘°J\\\\ \§—§
1 2 3 pgpmn)£5 6 7 8
DOUGLAS LAKE 1986

(2’30“

520_§

a\

§W§\\ \ g
o.\.\\.m\ NA

Figure 21. Activity pattern of adult white sucker caught
in gillnets set in Douglas Lake, June to August
1985, and May to August 1986.

62

Diet

 

Adult yellow perch

Crustacean zooplankton were numerically predominant in
the diet of adult yellow perch, 90-140 mm TL, on all
sampling dates except 7/11/85 (Tables 15 - 18).
Zooplankton taxa found included: Da hnia, Cerioda hnia,
Bosmina, Le todor , golopegigm, piaphanosoma, Chydorgs,
Latona, calanoid copepods, and cyclopoid copepods.
Chaoboru§_ was also frequently eaten, but will be
considered separate from the zooplankton due to its low
vulnerability to daytime Wisconsin net tows. 0f the above
taxa, Da hnia, Le todo , and Holopedium were positively
elected for (Table 19) on all sampling dates with one
exception. Cyclopoid and calanoid copepods and
Qiaphanosoma showed negative electivities on nearly all
sampling dates. The electivities of Ch dorus, Bosmina, and
C_eriodaphnia were more variable, with each taxon having
days with positive electivities and other days with
negative electivities of similar magnitude. The electivity
of Latona was not calculated as none were collected in
Wisconsin net samples and it was not identified as Latona
from diet samples until 1986.

Of the other items commonly found in adult perch
stomachs, Chaoborus pupae and larvae was numerically pre-
dominant. On 7/11/85 in Little Bear Lake, they made up

over 67% of the perch's diet by numbers, but more commonly

63

 

Table 15. Mean number of items found in adult yellow perch
(95-135 mm TL) stomachs during 24-hr studies
in Little Bear Lake, 1985.
1985
Organian Jun 19 Jill 11 Jul 31 Aug 21 Oct 27
Chmkxzma
Dagflnia 20.45 5.48 33.43 43.50 112.26
Cerioda a 1.00 0.00 17.89 8.59 6.98
Bosmina 0.07 0.00 0.19 1.18 0.18
mgr: 2.35 0.17 0.61 0.62 0.23
H01 ium 0.00 0.01 0.27 2.76 0.56
.Qiaphangggma 0.00 0.01 0.72 4.16 0.08
(hygoms mericus 0.00 0.00 0.01 0.02 0.02
Latona - - - - -
Chydorids 0.00 0.00 0.00 0.00 0.00
Macrothricids 0.00 0.00 0.00 0.00 0.00
Cyclopoids 0.18 0.64 0.80 0.18 0.32
Calamids 0.59 0.00 3.52 3.70 0.82
Inaxta
Chaoborus pupae 2.37 13.22 0.22 2.39 0.00
Chadborus larvae 0.04 0.38 0.29 1.00 0.00
Chironanid pupae 0.09 0.01 0.02 0.01 0.00
Chironauid larvae 0.05 0.01 0.00 0.00 0.00
Ephemeropteran.nymphs.0.01 0.01 0.00 0.00 0.00
Gastropoda 0.00 0.00 0.00 0.00 0.00
Pflxxs
YOY yellow perch 0.22 0.13 0.03 0.10 0.00
Other 0.93 0.00 0.24 0.42 0.01

64

Table 16. Mean number of items found in adult yellow perch

(95-135 mm TL) stomachs during 24-hr studies
in Little Bear Lake, 1986.

 

 

1986
Organism May 22 am 25 Jul 30 Sep 3
Cnaaxxma
Daphnia 110.02 16.63 23.25 130.95
ceriodanhnia 32.76 22.62 10.59 29.74
Bosmina 2.55 0.00 0.00 0.20
Lgptgggra 0.06 0.59 0.70 0.73
Eclgpggium 7.40 3.36 0.76 0.55
Luggzggxzzgma 0.05 4.87 28.73 0.00
Chygorus gggaericus 0.17 0.05 0.00 0.01
Latona - - - -
Chydorids 0.00 0.00 0.00 0.00
Macrothricids 0 . 00 0 . 00 0 . 00 0 . 00
cyclopoids 2.60 0.45 1.99 2.26
calanoids 44.50 2.40 5.08 1.46
Insaxa
Chadborus pupae 0.00 0.66 0.05 0.06
Chaoborus larvae 0.20 0.05 0.03 0.00
Chironomdd.pupae 0.02 0.20 0.30 0.09
Chironomid.larvae 0.12 0.09 0.30 0.11
Ephemeropteran nymphs 0.01 0.01 0.01 0.00
Gastropoda 0.00 0.00 0.00 0.00
Pnuxs
YOY yellow perch 0.01 0.36 0.04 0.01
Other 0.84 1.10 1.66 0.63

65

 

Table 17. Mean number of items found in adult yellow perch
(95-135 mm TL) stomachs during 24-hr studies
in Douglas Lake, 1985.
1985
Organism Jim 26 Jul 17 Aug 8 Aug 27
Cladooera
Daflia 115 . 89 54 . 82 55 . 22 101 . 75
Ceriodagmia 0.06 0.12 0.38 0.02
Bosmina 0.01 0.00 0.33 0.03
My; 3.57 1.70 2.94 0.69
H01 imn 5.67 18.11 0.40 0.24
w 2.17 8.93 3.13 2.14
Chygorus mericus 0.01 0.77 0.09 0.07
Latona - - - -
Chydorids 0.00 0.00 0.00 0.00
Macrothricids 0.00 0.00 0.00 0.00
Cyclopoids 0.93 1.34 9.71 0.46
Calamids 3.53 3.83 4.22 0.32
Insecta
Chaoborus pupae 0.80 0.43 1.58 0.04
Chaoborus larvae 0.31 0.11 1.43 0.87
Chironanid pupae 0.00 0.01 0.09 0.02
Chironanid larvae 0.03 0.17 0.03 0.10
manempteran nynphs 0.01 0.00 0.05 0.00
Gastropoda 0.00 0.00 0.00 0.00
Pisces
YOY yellow perch 0.03 0.01 0.02 0.00
Other 0.07 0.82 1.96 3.75

66

 

 

 

Table 18. Mean number of items found in adult yellow perch
(95-135 mm TL) stomachs during 24-hr studies
in Douglas Lake, 1986.
12§§
Organism May 14 Jun 18 Jul 23 Aug 27
Cladooera
Daplirga 2.23 79.44 120.32 28.33
Cerioda ia 0.00 0.43 2.63 1.65
Bosmina 161.34 0.41 0.10 0.00
I_.gp_t9§9_r§ 0.00 3.28 0.47 0.18
Holfl'mn 0.25 8.56 0.40 0.03
Diaphanosom_a 0.00 1.47 9.26 0.43
Chflorus mericus 42.71 0.07 0.48 0.00
Latona - - - -
Chydorids 0.00 0.00 0.00 0.00
Macrothricids 0.00 0.00 0.00 0.00
cyclopoids 4.81 0.84 1.50 0.68
Calamids 0.64 0.81 0.17 11.65
Insecta
Chaoborus pupae 0.00 0.58 0.75 0.00
Chaoborus larvae 0.10 1.53 1.18 0.31
Chironomid pupae 0.46 0.08 0.01 0.27
Chironomid larvae 1.00 0.13 0.02 0.00
Wei-an nynphs 0.00 0.01 0.00 0.00
Gastropoda 0.00 0.00 0.00 0.00
Pisces
YOY yellow perch 0.71 0.07 0.01 0.03
Other 0.47 0.21 1.43 0.03

(57

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68

made up 0-9% of their diet. Benthic items such as chiro-
nomid larvae and pupae, and ephemeropterans generally made
up less than 1% of the adult perch's diet. Electivities
were not calculated for benthic food items because very
small items such as chydorid cladocerans and harpacticoid
copepods were not observed in Ekman dredges. The fish
species most commonly eaten by adult perch was young-of-
the-year perch. Young-of—the-year yellow perch were preyed
upon most often soon after hatching, and the mean number of
YOY perch in the stomachs of adult perch decreased through
the summer. In general, the mean number of YOY perch eaten
was higher in Little Bear than in Douglas Lake, ekcept in
May of 1986 when this average was much higher in Douglas
Lake.
Larger Yellow Perch

Perch greater than 140 mm TL were caught in low
numbers, and their diet can. not. be typified for each
sampling date. There are some trends in the data avail-
able, however. Generally, fish occurred in the diet of a
relatively small proportion of adult perch 140 to 160 mm TL
(Table 20 and 21). Adult perch greater than 160 mm It.
frequently fed on fish, and in adult perch greater than 170
mm TL fish were the predominant food item. Benthos,
including crayfish, Chaoborus, chironomids and. mayflies
were eaten more by perch greater than 140 mm TL in Little

Bear Lake than Douglas Lake (Tables 20 and 21).

Table 20.

69

Stomach contents of large adult yellow perch
(>140 mm TL) in Douglas Lake, June to August
1985, and May to August 1986. Sample sizes
are enclosed in parentheses below the length
class designations. Standard deviations of
the mean number of each food item are enclosed
in parentheses after the mean.

Inapmhcflass Cummflsm Peaxmm Manlnmuxm'

(mm)

 

140-159
(6)

160-169
(0)

170-195
(2)

Zooplankton. 66.0 66.0 ( 85)
BaMins OJ) 0JJ(OJD
F001 3343 0.3 «L5)
mmxflankUII - -
Iaamhas - -
Fhfl: - -
mmxflankUJ1 0.0 0J)(0.0)
lkamhos 0.0 OJJ(0.0)
Fidh 1004) lJ)(0.0)

70

Table 21. Stomach contents of large adult yellow perch
(>140 mm TL) in Little Bear Lake, June to August
1985, and May to August 1986. Sample sizes
are enclosed in parentheses below the length
class designations. Standard deviations of
the mean number of each food item are enclosed
in parentheses after the mean.

 

IsmgdmcflaSs Onfindsm Penxmm Manxnmmxa'
(mm) (xrurnare insflnmde
Zooplankton 71.4 183.0 (262)

140-159 Benthos 14.2 1.5 (4.4)
(14) Fish 14.2 0.2 (0.5)
Zooplanktm 13.5 50.0 (186)

(22) Phil 4302 045(05”
mmxflank011 0A) 0.0 «L0)

170-195 Benthos 40.0 0.6 (0.8)
(10) Fish 60.0 0.7 (0.6)

71
Zooplankton made up a large portion of the diet of perch
between 140 and 159 mm TL, but its occurrence in the diet

of adult perch declined with increasing size (Tables 20
and 21).

Adult White Sucker

Chydorid cladocerans and chironOmid larvae, both of
which are benthic items, were numerically predominant in
the diet of adult white suckers (Tables 22 - 25). os na
and cyclopoid copepods were regularly observed in the diet
of adult suckers, and occassionally were numerically
predominant in their diet. Electivities were not
calculated for prey eaten by white suckers because small
benthic items such as chydorids cladocerans (other than
Chydorus sphaericus) were not observed in either bottom
dredge samples or plankton tow samples.
Stomach Fullness and Feeding Rate
Adult Yellow Perch

Before calculating mean stomach fullness for the
entire adult perch population, it is necessary to compare
stomach fullness across the three depth contours that were
sampled. One pattern that is apparent in both lakes is
that the contour having the greatest stomach fullness was
the 2-meter contour during the day, the 4-meter contour

during the twilight hours, and the 8-meter contour at night
(Table 26).

72

Table 22. Mean number of items found in adult white
sucker guts during 24-hr studies in
Little Bear Lake, 1985.

 

1255
Organism Jun 19 Jul 11 Jul 31 Aug 21 Oct 27
Camixxma
Daggnia 0 0 0 0 0
Cerioda ia 0 0 0 0 0
Baafina 0 0 (J O 0
1391590913 0 0 0 0 0
Hdkxggbmn 0 0 O 0 0
W 0 0 0 0 0
Chflorus mericus - - - - -
ngma 0 0 56 C) 0
Chydorids 1037 300 1019 2743 1651
Mmmxmhrflfids 0 0 () 0 0
cupaxda .
Cyclop01ds 375 1200 380 118 323
Chlamids 0 0 81 0 0
Ihaafia
cmmxxmuslmmae 0 0 0 0 O
Chadmnuslkuwae O 0 0 0 0
Chinmxmddlmmae 0 0 0 0 0
Chironomid.larvae 775 592 220 784 44
EpMmenxfienminwmhs O (J 2 0 O
Gamquxh. 0 0 (3 0 0
Prams 0 0 0 0 O

Other 63 0 144 13 1

73

Table 23. Mean number of items found in adult white sucker
guts during 24-hr studies in Little
Bear Lake, 1986.

 

 

1986
Organism May 22 Jun 25 Jul 30 Sep 3
Ciaaxxma
Dagmia 0 0 15 0
Cerioda a 0 0 294 0
Bosmina 42450 0 37 0
1159mm! 0 0 0 0
Hbl 1mm 0 O 0 0
01m 0 0 0 0
Chflimnmsgggyaficus - - - -
Laxma O 81 3 0
Chydorids o 1729 90 143
Mbcnmfludchks O 0 0 0
cyclopoids 37 212 37 10
Cahmtdds 0 0 0 0
Inaxxa
cmmflxmuslmmae 0 4 4 6
Chmixmusiuuwae () 0 4 0
Chinmxmddzamae 0 15 O 0
Chironanid larvae 375 465 200 337
Ephemnnphaanlmmphs 0 0 0 0
(Emmrqxda 0 0 0 0
Phase 0 0 0 0

Other 0 109 15 38

74

 

Table 24. Mean number of items found in adult white sucker
guts during 24-hr studies in Douglas
Lake, 1985 .
1985

Organism Jun 26 Jul 17 Aug 8 Aug 27

Cladooera
mimia 0 18 5 5
Carl ia 9 0 20 0
Bosmina 442 O 0 0
Mrs D 0 0 0
Holggfiium 0 0 0 0
DEM 0 0 0 0
Chmoms mericus - - - -
Latona 283 54 352 40
Chydorids 4447 11113 2106 1129
Macrothricids 33 53 0 O
Cyclopoids 30 33 33 142
Calanoids A 1 0 12 0

Insecta
Chaoborus pupae 7 0 4 0
(haoborus larvae 0 0 0 0
Chironomid pupae 7 18 4 2
Chironanid larvae 565 96 830 463
Ephemeropteran nymphs 198 126 8 3

Gastropoda 21 8 75 42

Pisces 0 0 0 0

Other 9 13 23 42

75

Table 25. Mean number of items found in adult white sucker
guts during 24-hr studies in Douglas
Lake, 1986.

 

 

1255
Organism May 14 Jun 18 Jul 23 Aug 27
Cfladaxna
‘Dmigfia 0 0 1 1
ggrmthhnra O O O l
Bosmina 489 1649 26 O
leggkaa O 0 O 0
thzgghmt 0 0 0 0
0120M 0 0 0 0
cmgkmusggflgadcus - - - -
Latona 5 80 12 83
Chydorids 169 699 914 375
Manxkhrkfids 0 6 O 0
copqxda .
cyclopo1ds 24 40 33 59
Chdmmfids O 2 0 O
Inmxxa
cmmixmusgmpae 11 l 3 22
Chmdxmusiknwae 0 9 3 0
Chinmxmddlamae 0 1 l. 9
Chironanid larvae 1222 788 326 670
Ephemeropteran.nymphs 26 115 0 0
Gasunzxdb 6 35 1 55
Phxms 0 0 0 0

Other 44 14 7 343

76

Table 26. Oauparison of mean stanach fullness (expressed as
percent of fish's body weight) of fish caught on
the 2, 4, and 8-meter oontmrs for Little Bear
and Douglas lakes, 1985-1986. Standard deviations
are in parentheses below the means.

II'I'I'LEBEARLAKE

any DUSK NIGHT
2m moon 1.378 0.186 0.120
4 (0.811) (0.152) (0.156)
4m mm 0.400 0.453 0.088
(0.339) (0.648) (0.127)
8-METER 001mm 0.219 0.231 0.267
(0.111) (0.233) (0.325)

DOUGLAS LAKE
DAY DUSK NIGHT
2+METER.00NIOUR. 0.195 0.166 0.064
(0.170) (0.173) (0.036)
4-MEI‘ER comm 0.098 0.211 0.119
(0.066) (0.192) (0.104)
84MBTER.00NTOUR 0.140 0.126 0.178

(0.046) (0.056) (0.097)

77

Results of the Friedman test, however, indicate that there
were no statistically significant differences between the
three contours for any time of day in either lake. The
power of this test to detect these differences is limited,
however, by the small number of instances where fish were
caught on all three contours during the same time period on
the same date. Because of the lack of statistical
differences between stomach fullness between the three
contours, data from each contour were grouped in the
calculation of the population's mean stomach fullness.

Relative stomach fullness showed a similar diel
pattern on. all sampling dates except July 11, 1985 in
Little Bear Lake (Table 27). Generally, peak stomach
fullness was observed in the late afternoon or dusk periods
(periods 6-8), and minimum stomach fullness during late
evening or at dawn (periods 2-3). In order to estimate
feeding rate, two basic pieces of information are needed.
First, the mean stomach fullness over the day determined
from stomach fullness obtained at regular intervals, and
second the gastric evacuation rate. Mean stomach fullness
(in percent of body weight) was determined for all 24-hr
sampling dates (Table 28) except for August 27, 1985 in
Douglas Lake where fish were not caught from 2 of the 8
periods. Gastric evacuation rates (R) were estimated for
each of the 24-hr studies from the water temperature on

that date using equation (4) , and from the instantaneous

78

 

 

Table 27. Diel pattern of wet stomach content weight
(percent of wet body weight) of adult yellow
perch (95-140 mm TL) in Little Bear Lake and
Douglas Lake, 1985 and 1986.

IIITIE BEAR.LAKE
200300
Date 1 2 3 4 5 6 7 8
1985
Jun 19 0.033 0.067 0.206 0.230 0.190 0.180 0.273 0.143
J01 11 0.060 0.620 0.786 0.463 0.118 - 0.056 0.061
J01 31 0.052 0.000 0.049 0.046 0.138 0.076 0.599 0.140
Aug 21 - - 0.098 0.175 0.079 0.075 0.441 0.081
Oct 27 0.037 0.005 0.003 0.044 0.235 0.102 0.378 0.090
1986
May 22 0.145 0.065 0.049 0.258 0.074 0.284 0.606 0.512
Jun 23 0.161 0.610 0.414 0.426 0.121 0.341 0.227 0.051
J01 30 -. 0.002 0.123 0.060 0.165 0.099 0.168 0.171
Sep 3 0.024 - 0.014 0.125 0.071 0.147 0.208 0.185
DJKHASIJKE
Enrica
Irma 1 2 3 4 5 6 7 8
1985
J0n 26 0.144 0.070 0.112 0.211 0.302 0.364 0.225 0.303
J01 17 0.185 0.057 0.146 0.177 0.164 0.097 0.190 0.148
Aug 7 0.149 0.113 0.143 0.129 0.068 0.234 0.112 0.114
Aug 27 - - 0.179 0.090 0.154 - - 0.107
1986
May 14 0.229 0. 149 0.278 0. 190 0.018 0. 168 0. 199 0.212
J0n 18 0.109 0.186 0.130 0.135 0.161 0.155 0.140 0.304
Jul 23 0.130 - 0.107 0.266 0.078 0.100 0.099 0.119
Aug 27 - 0.000 0.080 0.077 0.178 0.109 0.037 0.027

79

Table 28. Mean stomach fullness, gastric evacuation rate,
and feeding rate estimated from 24-hr studies,
Little Bear and Douglas Lakes, 1985-1986.
Feeding rates are expressed as wet weight of
food eaten per day as a percentage of the wet
body weight of the fish.

Lfimflelkarlake

lxme SUIBCh TamxuaUnszwmxathmmrahe Eaxungzzme

 

 

fulhxss 6%» Pmmsunrfiehi Hansen 51001
1985
Jun 19 0.165 0.191 0.489 0.758 1.907
J01 11 0.309 0.299 0.456 2.221 3.383
J01 31 0.137 0.369 0.484 1.218 1.597
Aug 21 0.158 0.308 0.565 1.168 2.145
Oct 27 0.112 0.071 0.478 0.190 1.282
1986
May 22 0.779 0.112 0.367 2.099 2.193
J0n 25 0.314 0.260 0.451 1.960 3.225
J01 30 0.114 0.456 0.203 1.246 0.551
Sep 3 0.155 0.260 0.681 0.965 1.814
Duxflaslake
Irma Shaman TamxnatmmaEmmnmmddnzzme Eaaflnglmme
fhthss (PC) Ihmsaxthfld. Peaxmn 51001
1985
J0n 26 0.216 0.197 0.216 1.021 1.121
J01 17 0.145 0.299 0.425 1.045 1.484
Aug 8 0.133 0.413 0.230 1.315 0.733
Aug 27 - 0.295 0.229 - -
1986
may 14 0.180 0.098 0.135 0.423 0.584
J0n 18 0.165 0.197 0.231 0.779 0.915
J01 23 0.128 0.339 0.409 1.046 1.261
Aug 27 0.073 0.226 0.209 0.394 0.364

80

rate of decrease in. mean stomach fullness during non-
feeding periods. Estimates obtained using equation (4)
are generally lower than those obtained from the
instantaneous rate of decrease in stomach content weight
(Table 28). Feeding rate estimates were made using both of
the above estimates of evacuation rate. Due to the lower
estimates of R obtained from equation (4), feeding rate
estimates were also lower. The feeding rate estimates
obtained using either method were low, ranging from 0.423
wet weight of food per day as a percentage of the fish's
wet body weight in Douglas Lake on May 14, 1986, to 3.383%
in Little Bear on July 11, 1985.
Adult White Suckers

The feeding rate of adult white suckers could not be
estimated due to the lack of samples during some time
periods during each of the 24-hr sampling dates.
Overlap

Diet overlap between adult yellow perch (95—140 mm)
and adult white suckers was very low on all sampling dates
(Table 29).
Growth

The growth of yellow perch was determined by scale
analysis and by changes in mean length of fish caught
during the 24-hr studies. Scale analysis indicates that
growth was very slow, with a mean total length of only 117

mm at the fourth annulus in Little Bear Lake, and 125 mm

81

Table 29. Schoener's diet overlap indices between adult
yellow perch (95-140 mm TL) and adult white
suckers (>95 mm TL) caught during 24-hr studies
in Little Bear Lake and Douglas Lake, 1985-1986.

LITTLE BEAR LAKE

 

Date Overlap
1985

Jun 19 0.008
Jul 11 0.032
Jul 31 0.014
Aug 21 0.012
Oct 27 0.013
1986

May 22 0.014
Jun 25 0.011
Jul 30 0.053
Sep 3 0.014

DOUGLAS LAKE

 

DATE OVERLAP
1985

Jun 26 0.009
Jul 17 0.016
Aug 7 0.036
Aug 27 0.019
1986

May 14 0.222
Jun 18 0.016
Jul 23 0.021
Aug 27 0.017

82

 

Table 30. Length (mm) at age of yellow perch and white
sucker as determined by scales or fin ray
sections.

thamfiham:Age
Lake 0 I II III IV V Source
‘0fllowlkmdh
little Bear age 4 46 63 98 117 - -
little Bear age 3 63 97 112 - - -
little Bear age 2 67 107 - - - -
Douglas age 4 63 93 114 125 - -
Douglas age 3 74 106 122 - - -
Douglas age 2 86 120 - - - -
South Twin, MI 87 86 118 129 169 - Esdmeyer (1937)
Lake Erie - 144 168 187 217 - Eschmeyer
Wawasee, IN 86 129 167 198 220 - Esclmeyer
Nebish, WI 124 157 173 209 245 - Fsdmeyer
Weber, WI - 130 158 174 191 - Eschmeyer
Silver, WI - 109 120 145 173 - Eschmeyer
Lake Erie 94 170 216 241 264 279 Jobes (1952)
Saginaw Bay 76 135 203 241 272 305 Jobes
Green Bay 71 117 160 201 229 259 Jobes
Lake of the Woods 99 137 175 206 234 267 Jcbes
Red Lakes (male) 74 132 172 201 221 234 Heyerdahl and
Red Lakes (female) 74 132 178 218 241 254 Smith (1971)
Mamphremagog (high) 75 115 170 200 - - Persson (1983)
Rhmphremagog (low) 60 105 155 190 - - Persson
Opinioon 60 96 119 136 - - Persson
West German lakes 80 122 148 189 - — Persson
32 FinniSh.ponds 56 95 124 143 - - Persson
Vitalampa, Sweden 60 104 127 143 - - Persson
Abborrtjarn.l, Swe. - 78 98 111 - - Persson
Ivosjon, Sweden 80 115 160 195 - - Persson
Sovdeborgssjon. 75 97 109 117 - - Persson
Big Bear (high) 105 135 165 - 220 - Sdhneider and
Big Bear (low) 96 126 144 - 165 - Crowe (1980)
Whflhasudem'
little Bear 91 149 189 211 - -
Douglas 87 211 298 - - -
Iumsden 75 105 150 175 200 220 Beamish (1974)
Croche (male) - 129 191 235 257 281 Verdon and
Creche (female) - 139 197 244 271 294 Magnin (1977)

83

in Douglas Lake (Table 30). Due to potential difficulties
in accurately aging stunted perch, growth was also assessed
by estimating mean length and weight of the dominant size
class of perch caught in gill nets. These data also
indicate that growth was very slow (Table 31). Annual
increments by fish in the dominant size class were small in
Douglas Lake, 5 mm/year for males and 7 mm/year for
females. Annual increments were somewhat larger in Little
Bear, 9 mm/year for males and 14-21 mm/year for females. A
range is given for the growth of females since the mean
length of perch caught decreased from 133 mm on May 22,
1986 to 126 mm on June 25, 1986.

The mean length at age of suckers in Douglas Lake was
larger than in Little Bear' Lake (Table 30). Fix: ray
sectioning was not used as most of the suckers sampled were
young enough that scale samples ‘were considered ‘to be
accurate indicators of age and length at age (Beamish
1974).

Prev Reeourcee
Zooplankton

Significant differences in the abundances of
individual zooplankton genera on the different depth
contours were sometimes found with ANOVA analysis using a
significance level of 0.05. Interpretation of these results
is difficult as these differences were not always

consistent between lakes or between years. In addition,

84

Table 31. Mean length (mm) and weight (g) of adult yellow
perch caught during 24-hr studies. Standard
errors are in parentheses. Sample sizes are
denoted by N.

Lumielkerleke
Immune 100s

this N lengfla wemmu: II Inmth wehmu:
1985

Jun 19 176 111.6 (0.4) 13.49 (0.13) 28 107.2 (0.9) 12.28 (0.30)
Jul 11 130 115.0 (0.9) 15.56 (0.51) 36 109.8 (1.9) 13.47 (0.96)
Jul 31 86 121.1 (1.3) 16.60 (0.81) 31 110.3 (1.9) 12.63 (0.41)
Aug 21 63 122.3 (1.5) 17.09 (0.90) 57 113.4 (0.9) 13.63 (0.31)
Oct 27 33 125.5 (1.9) 17.93 (0.89) 60 117.6 (1.0) 15.30 (0.43)
'1986

.May 22 56 132.6 (2.9) 24.42 (2.28) 76 116.5 (0.9) 14.06 (0.53)
J0n.25 155 125.7 (1.1) 19.98 (0.61) 160 117.6 (0.6) 16.19 (0.22)
Jul 30 57 124.2 (2.6) 19.48 (1.65) 63 118.1 (1.3) 16.52 (0.48)
Sep 3 92 130.2 (2.0) 21.03 (1.10) 82 119.0 (1.2) 16.02 (0.55)
Damflasleke
Reade rude

this N lemma: wenmu: N lemma: wenmu:
1985

J0n 26 133 119.8 (0.5) 15.04 (0.18) 64 114.5 (0.7) 13.45 (0.20)
J01 17 181 122.0 (0.5) 16.47 (0.20) 122 116.3 (0.7) 14.49 (0.17)
Aug 8 94 123.5 (0.7) 16.88 (0.25) 61 116.1 (0.7) 14.38 (0.22)
Aug 27 53 123.7 (1.0) 16.63 (0.37) 35 118.8 (0.8) 14.65 (0.31)
1986

.May 14 65 126.4 (1.1) 15.86 (0.62) 100 119.7 (0.5) 13.18 (0.14)
Jun 18 100 126.3 (0.8) 16.23 (0.41) 116 120.4 (0.5) 14.26 (0.14)
J01 23 89 124.7 (0.8) 16.62 (0.29) 70 119.0 (0.6) 14.67 (0.20)
Aug 28 54 125.1 (1.1) 16.49 (0.39) 50 121.8 (0.7) 15.15 (0.25)

85

significant date x depth interactions were found,
suggesting that these differences were not persistent
throughout the year within each lake. In order to
emphasize seasonal aspects, and between lake differences in
the zooplankton communities of these lakes, estimates of
the population density of zooplankton for the each lake
were calculated using a weighted mean (for weighting
factors see methods under adult fish distribution).

The zooplankton communities of Little Bear and Douglas
Lakes both showed blooms of rotifers during the spring and
early summer months (Tables 32 - 35). During 1985,
Keratella and Kellicottia were the predominant rotifers in
Little Bear Lake (Table 32). During 1986, the abundance of
Keratella and Kellicottia were lower than in 1985, and
Polvarthra was the predominant rotifer (Table 34). In
Douglas Lake, Kellicottie was by far the most abundant
rotifer during 1985, but during 1986 densities of
Kellicottia, Keratella, and. Polyarthra. were all similar
(Tables 33 and 35).

Bosmina was the most numerous cladoceran during the
spring both years, and was succeeded in both lakes by
Daphnia in mid to late June (Tables 32 - 35). Cerioda hnia,
Diaphanosoma, or Chydorus were occasionally the most
abundant cladoceran but no patterns were discerned in their

appearance as the predominant taxon (Tables 32 - 35).

86

r
all
tZe
0......
he
r+.
e r
Dana
00.
n B
non
100.6
.kbkl
nat
a+0t
1 I.
DLSL
01
Oman
2071
.n
f s
ouur
ouu
r+uo
aunt
.mnun
a0
0110
may
r
nle
aat
ece
m4lm
t .
.0018
08
.tuvd
h n .
nem.05
{lo 8
0.179
Wf41

Table 32.

mm

Mayl3 May29 J0n10 J1m30 JullS J0129 110913 M27

 

130.
0.0.0.

14.nU.
0.nm0.

2.10.
0.0.0.

47.0.
11.20.00“

651
2.1..0.

990”
730

930

530
o

D

1

2.7 0.9 0.1 0.4 0.1 0.1 0.1

1.7

87

4.

I

Weighted mean number of zooplankton per liter

from vertical plankton hauls taken on the 2

Table 33.

mile
0.0 0.0 0.3 0.1 0.3 0.1 0.3

1.2

Mayl3 May29 Junlo Jun30 J0115 30129 M13 M27

and 8-meter contours in Douglas Lake, 1985.

nauplii

 

Other

88

Table 34. Weighted mean number of zooplankton per liter
from vertical plankton hauls taken on the 2, 4,
and 8-meter contours in Little Bear Lake, 1986.

 

 

Date
May 22 JDn 25 J01 30 Sep 3
Rotifers
Keratellg 28.8 13.9 3.5 5.1
Ellloottia 52.6 11.6 0.7 5.3
291% 137.0 8.8 0.0 0.0
Genera
Mia 4.3 2.2 1.3 3.3
Bosmina 48.3 1.3 5.0 3.9
ggkemhua 23 L1 L9 21
Diephgngegme 0.4 2.1 9.7 0.7
011091313 0.0 0.0 0.0 0.1
flgggggg 02 ml 00 ml
305$“
Diegtgmge 24.2 1.9 2.9 1.3
Irgpggyelgpe 9.8 3.4 9.8 2.6
Diegyelgpe 12.8 0.3 1.8 1.7
nauplii 20.4 8.3 8.8 7.0
other

89

Table 35. Weighted mean number of zooplankton per liter
from vertical plankton hauls taken on the 2, 4,
and 8-meter contours in Douglas Lake, 1986.

 

mte
may 14 June 18 J01 23 Aug 27
minus
figmlla 11.3 2.1 0.9 0.0
Ellioottia 16.7 0.4 0.1 0.0
Bflmgflua 104 17 L3 04
Change
00003 05 53 7a 42
Bosmige 42.4 22.8 3.7 1.1
gem 0.0 0.3 0.1 0.8
Diaphangegme 0.0 1.2 4.6 1.2
Chygorge 0.9 1.1 2.2 0.3
1000000 00 08 00 mo
apqnh
mm 45.9 38.4 25.1 22.8
Iggpggyglgpe 19.1 4.0 4.4 2.9
Diggyglgpe 1.7 2.1 2.8 2.1
nauplii 60.5 5.2 24.9 10.0
Other

90

In both lakes, the three most abundant copepod taxa
were Dia tomus, Tropocvclops, and Diacyclops. In Little
Bear Lake, copepods were approximately equal in density to
cladocerans both years. In Doulgas Lake, copeopods were
more abundant than cladocerans, especially from mid-June to
the end of August during 1985.
Benthos

Like zooplankton, densities of benthic invertebrates
were variable between depth contours, dates, and lakes. In
order to generalize seasonal and between lake differences,
weighted mean population densities were calculated.

Chironomid larvae, Chaoborus, and mayfly naiads
(Caenis) were the three most abundant taxa of the benthos
sampled (Tables 36 - 37). Chironomid larvae were usually
the most abundant of these taxa, but Chaoborus larvae
sometimes predominanted, particularly in Douglas Lake,
and in Little Bear Lake during June. The density of
chironomid larvae was generally higher in Little Bear than
in Douglas Lake during 1985, but during 1986 there was
little difference between the two lakes. Chaoborus
densities were similar between the two lakes both years,
but densities were generally higher during 1986 in both
lakes.

A variety of other invertebrate taxa were caught, but
their densities rarely made up a significant (>1o%)

proportion of the total from any given depth or date.

91

Mean number of items per square foot (929 square
cm) in Ekman dredge samples taken from Little

Bear Lake and Douglas Lake,

Table 36.

1985.

Ififikaamdma

(nadxxma
Olflmximmta
mipoda

30.11800
50.50.0nm0

6.9w60.0.1nw
90.10.09m0.

6334..nU.0.nU.
ngulnmnmo.

9327.50.0.

314..4..5nm0.
1 2

4nd..80.350.
90.2nU.60.0.

11

Chinmxmddlamae
Chmdxxuslknwae
Chmflxmuslmmae
Camus
Ikmaeyfia

Oflma:

Chinmxmddlhuwae

 

Dmmflaslzme

26.0.2nu.

M10.3nu.

27038
M3000

6nwnU.4..
0.nan.nU.

JUl 8

18000
moooo

8
20363
YOOOI

(nadaxxa
Olhmximmma
Hmhzmarhul

9430000
9040000

6107400
7162200
1

0.4..24“2nwnu.

8nm—h4u3nwnu.
.l. 1

885~I.14..nU.

0.nm~I.0.9nU.nU.
1 1

1670663
1010900

3

metonnslanmm
Chmixmuslamae

Camus
Ikmacafia

Chtnxnmnilarwua
Chbnxxmddlamae
Gamm'

 

1986.

92
Mean number of items per square foot (929 square

cm) in Ekman dredge samples taken from Little

Bear Lake and Douglas Lake,

Claixxma
Olkxnhmfia
Imphnxda
Hydnnzmina

Table 37.

9nU.6.0.0.20.
lnmnhnwmnwnm

8277604
1170100
2

5073005
2011000
1 1

7010008
8170000
2 4

Chinmxmddlmmae
Chmixmusikuwae
Chmflxmuslamae
Camus
rmmaexfia

Ofluu'

(lfirummudjknwae

 

(nigaflmmma
Imphhxfla
(mdnmxmddluuwae

Camixmma
Hmhzwanba.

0.0.0.nwnw0.0.
8&80.nu.0.0.

30.3an4..8

20.20.30.1—
1 1..

AAAJSZA

10.nw0.4..1nU.
2 7

1630.880.

dummmnmnwo.
3

Chmixuuslknwae
Chaflxmuslggzm
caafis

Chtnxxmddlmmae
Ikmacafla

 

93
Benthic microcrustaceans such as chydorid cladocerans,
harpacticoid copepods, and cyclopoid copepods were not
noted in dredge samples, possibly due to their size

relative to the mesh size of the sieve used.

Discussion

The goal of this study was to describe and compare the
life-history of coexisting yellow perch and white suckers
in order to identify potential axes of competition between
these species. The response of yellow perch to sucker
removal has primarily been studied with an empirical
approach (Schneider and Crowe 1980, Johnson 1977) and it
has not been successful in determining the mechanisms
responsible for improvements observed. I believe that
information on the realized niches of these species in
sympatry, and the axes of competition is necessary to
provide a basis for inferring mechanisms involved in the
response of perch abundance or growth to sucker removal.
The results of this study provide data on several aspects
of the realized niches of yellow perch and white suckers in
Little Bear and Douglas Lakes. From these results, I have
drawn inferences on potential axes of competition between
these species. These inferences are a priori predictions
of the expected outcome of competition experiments, and in
my opinion, can not be used to directly prove or disprove
competition.

One of the prerequisites for the identification of
axes of competition is to identify ‘when resources are
limiting to an organism. One indication of resource
limitation, especially in organisms with indeterminate

94

95
growth such as fish, is slow somatic growth.

Initial growth of YOY yellow perch in Little Bear and
Douglas Lakes was similar to that in other north temperate
lakes. Mean length at the end of June ranged from 29 to 31
mm, whereas length at this time of year averaged 27 mm in
Red Lakes, Minnesota, (Ney and Smith 1975) and 38 mm in
Lake Winnebago, Wisconsin (Weber and Les 1982). After this
point in time, growth during their first summer was slower
than in other lakes reported in the literature (Table 30).
After the first year of life, growth of yellow perch in
Little Bear and Douglas Lakes was comparable to the slowest
growing population reported in the literature (Table 30).

Although slow growth was evident by the end of the
first year of life, the deceleration of growth in little
Bear and Douglas Lakes became more distinct during the
second year. These data indicate that growth of perch was
severely limited when perch reached a size of about_95-l40
mm. This pattern of relatively good initial growth
followed by a rapid slowdown of growth after the first year
has been observed in other populations of stunted yellow
perch (Eschmeyer 1937: Schneider 1972) and the European
perch (Alm 1946, Persson 1983), suggesting a common cause
of stunting in perch.

Diet Ontogeny, Resource Limitation and Growth
In lakes where perch growth is relatively good, such

as the Laurentian. Great Lakes, they typically show' an

96
ontogeny of diet from zooplankton to benthos to fish or
crayfish (Schneider 1972). A diet shift from zooplankton
to benthos typically occurs during the first year of life
when YOY perch are about 30-35 mm in length (Forney 1971:
Weber and Les 1982; Guma'a 1978). Perch usually feed on
benthos from this size until they reach a size of about
150-200 mm when their diet shifts to fish or crayfish
(Elrod et al. 1981; Clady 1974; Ken Dodge, Michigan
Department of Natural Resources, personal communication) .
However, this pattern of diet shifts was not followed by
perch in Little Bear Lake and Douglas Lake. Young-of-the-
year perch did shift from a zooplankton to a benthos diet
at about 30-35 mm, but perch 95-140 mm in length returned
to a diet of crustacean zooplankton and Chaoborus. The
observed electivities of perch 95-140 mm in length for
crustacean zooplankton appear to be at least partly due to
the average size of the various prey taxons. Da hnia,
Holopedium and Leptodorg include most of the larger bodied
taxa of cladocerans present in both lakes. Diaphanosoma
showed a strong negative electivity for reasons not due to
size, as it is similar in length to Daphnia. Copepods were
generally small-bodied, and combined with a lower capture
efficiency by fish (Drenner et a1. 1978) were strongly
selected against in the diet of perch in this size class.
The electivities of Cerioda hnia, Bosmina, and Chydorus are

difficult to interpret due to the wide range of values

97
observed for these ‘generam The electivities of these
genera were generally close to zero, but occasionally took
on relatively high or low values.

Adult perch 140-170 mm in length also deviated from
the "typical" ontogeny of diet, feeding on zooplankton more
heavily than in other systems. Perch greater than 170 mm
in length returned to the typical diet sequence, feeding
primarily on crayfish and fish.

The atypical ontogeny of diet of perch in Little Bear
and Douglas Lakes indicates that benthos availability to
perch. was severely limited” ‘Under the assumptions of
optimal foraging (Schoener 1971) the predominance of
zooplankton over benthos in the diet of perch 95 to 140 mm
indicates that feeding on zooplankton was energetically
more profitable than feeding primarily on benthos. Feeding
rates of perch in this size class, using estimates of
evacuation ,rate derived from diel patterns of stomach
fullness, averaged close to 2% wet weight of food per wet
weight of fish per day, a value ‘which is close to
maintenance ration (Schneider 1973). Estimates of feeding
rate using Persson's (1979) relationship between
temperature and evacuation rate generally were below
maintainance ration, and for this reason are judged to be
less accurate than estimates made using field estimates of
evacuation rate and feeding rate. Since feeding rates

presumably would have been lower' if“ perch. had fed on

98
benthos instead of zooplankton, they probably could not
have maintained themselves on a diet of benthos under the
conditions present in Little Bear and Douglas Lakes.

A bottleneck in growth due to low abundance of benthos
has often been cited as the reason for stunted populations
of perch in other lakes (Schneider 1972; Persson 1986; Alm
1946) and appears to be the case in Little Bear and Douglas
Lakes. There are at least three hypotheses that may account
for the low abundance of benthos in Little Bear and Douglas
Lakes. First, intraspecific competition between perch may
decrease the availability of benthos to the perch
population in general. Second, interspecific competition
between perch and suckers may achieve the same result.
Third, the limnological characteristics of the lakes may be
unsuitable for the production of benthos sufficient to
support the growth of a large number of non-stunted perch.
These factors are probably all important to some degree,

but each will be discussed separately.

Intraspecific Competition

Intraspecific competition for benthos between age
classes of the European perch has been demonstrated by
Persson (1983), indicating that perch can effectively
decrease the availability of benthos to other members of
their population. This does not appear to be the case in

Douglas or Little Bear Lake as benthos made up a small

99

proportion of the diet of. perch in all size classes except
young-of-the-year. Such low predation pressure would
probably not greatly impact the population of benthos
unless productivity of the benthic community was also low.
Interspecific Competition with White suckers

The diet of white suckers was almost exclusively
benthic invertebrates, making predation by this species a
potential controlling factor of the abundance of benthos.
These results are similar to those obtained by Koehler
(1978). Two other studies, however, have listed
cladocerans as the predominant item in the diet of white
suckers (Barton 1980, Ialancette 1977). The effects of
sucker predation have been little studied, and I am not
aware of any studies showing conclusive evidence that white
suckers are able to control the abundance of benthic
invertebrates. Comparing the abundance of benthos in
Little Bear and Douglas Lakes, there does not appear to be
any pattern of differences between the two lakes. Sucker
catch rates, however, were 6 to 10 times higher in Douglas
than in Little Bear Lake. The lack of difference in
benthos abundance combined with the large difference in
sucker densities suggests that sucker predation did not
control the abundance of benthos in these lakes. This is
not conclusive evidence, however, as there may have been
other differences between the lakes that compensated for

differences in predation pressure by suckers.

100

Limnological Characteristics

The nutrient levels and substrate characteristics of a
body of water have been shown to have a large effect on the
composition and abundance of the benthic community (Hall et
al. 1970). In this study nutrient concentrations and
substrate characteristics were not measured and their
effects on the benthos can not be evaluated, but their
potential importance should not be ignored.
Pote tial for Com etit o be wee erch uc e s

The diets of perch and suckers overlapped very little
at all life stages over all time periods sampled. There
are, however, two conflicting interpretations of these
data. First, the low overlap may be taken as an indication
that the two species did not compete to any significant
degree due to the disparity in their feeding habits. An
alternate viewpoint is that suckers were efficient enough
at feeding on benthic invertebrates to deplete these
resources .to the point where they had competitively
excluded. perch from feeding on ‘benthos. .As indicated
earlier, current data suggest that sucker predation was not
the primary factor limiting the abundance of benthos. If
it is true that suckers are not limiting the abundance and
availability of benthos, it follows that suckers and perch
are not competing in Little Bear and Douglas Lakes. 0n the
other hand, if suckers decreased the availability of

benthos to perch, it is possible that the two species were

101
competing. The potential axes of competition are difficult
to determine, as the low diet overlaps measured do not
provide an indication of which of the suckers' prey items
could be important to perch growth. Literature data
indicate that chironomid larvae and mayfly larvae are
common items in the diet of perch between 30 and 150 mm
and could be an important food item of perch in Little Bear
and Douglas Lakes if they were more abundant (Clady 1974:
Guma'a 1978; Weber and Les 1982; Elrod et al. 1981). Based
on this information, these items appear to be the primary
candidates as axes of food competition. This possibility
can not be verified without manipulating the density of
suckers in one of the study lakes, however.
Spatial Distribution and Activity
The spatial distribution and activity pattern of

perch and suckers were originally included in this study to
clarify potential spatial or temporal food resource
partitioning between the two species. Since their diets
overlap so‘ little, these data can not be used for this
purpose. Spatial distribution and habitat selection are,
however, important characteristics of the realized niche of
these species.

Recent studies have successfully predicted the
distribution and habitat selection of fish, especially
centrachids, using measures of prey abundance and

distribution, and the predation risk present in different

102

habitats (Mittelbach 1981, Werner et al. 1983). These
models are based on the concept of optimal foraging and
have been extended to include predation risk. Basically
these models state that fish should forage in the habitat
that maximizes the ratio of energy intake rate to mortality
rate or risk (Werner et al. 1983).

From the observation that adult perch in Little Bear
Lake and Douglas Lake were concentrated on the 8-meter
contour, it can be inferred that foraging profitability was
higher in this area of the lake, or that predation risk was
lower on this depth contour relative to shallower sites.
Results of tests comparing stomach fullness indicate that
there were no consistent differences in foraging rate
between the three contours at any time of day. This
observation is consistent with results on prey
distribution, which indicate that there were no strong
differences in the abundance of prey items between the
three depth contours. We are thus left with the hypothesis
that predation risk was greater at the shallow sites in
both lakes. Unfortunately, this hypothesis can not be
tested with the data available. A small number of adult
tiger muskie, northern pike, and largemouth and smallmouth
bass were examined for their diets, and it was found that
all four species (or hybrid) consumed adult perch. The
overall predation risk posed by these species across the

depth contours could not be estimated, however, as the

103
number caught was too small to estimate either the feeding
rate or the spatial distribution of these piscivores.

Adult suckers in Douglas Lake showed a slightly
greater catch rate on the 8-meter contour compared to the 2
and 4-meter contours, but were not as strongly associated
with the deep water as the perch were. Due to the small
sample size of adult suckers, differences in gut fullness
between contours were not tested for. 0f their main prey
items, chydorid cladocerans were not sampled with either
the Wisconsin net, nor the Ekman dredge, and thus the
influence of the distribution of their prey could not be
evaluated. Adult suckers were found only in the stomachs
of tiger muskies in Little Bear Lake, and were not found in
the diet of any of the aforementioned piscivores in Douglas
Lake. Their low vulnerability to the predators present in
Douglas Lake suggests that predation risk should play a
minor role in shaping the distribution of adult suckers in
that lake.

The high proportion of perch caught at the
deepest sites (8-meter contour) is comparable to results
obtained by Maloney (1969), Hasler and Bardach (1949), and
Sandreinridh and Hubert (1984). Other studies have found
perch to be concentrated in shallower water closer to shore
(Carlander and Cleary 1949; Emery 1973; Hall and Werner
1977). The reasons for these differences in spatial

distribution are unknown. Unfortunately the diet of

104
perch and predation risk were not included in a sufficient
number of the above studies to assess their influence on

the spatial distribution of perch in those systems.

SUMMARY

Perch in Little Bear Lake and Douglas Lake can be
described as slow growing or stunted, with slow growth
being evident before the end of the first year of life. The
growth of adult perch encountered a bottleneck at a size of
about 95-140 mm, when perch in lakes where growth is good
typically feed on benthic invertebrates. The primary food
of adult perch in little Bear and Douglas lakes, however,
was crustacean and insect zooplankton, dominated
numerically by crustacean zooplankton. The few adults
greater than 170 mm TL that were captured returned to the
"typical" diet ontogeny, feeding primarily’ of fish. and
crayfish. The break from ‘the typical diet ontogeny
indicates that benthic invertebrates were the resource that

most limited the growth of perch in the study lakes.
The growth of adult white suckers did not appear to
be exceptionally slow, and relative to the perch was very
rapid. The diet of adult white suckers was composed mostly

of benthic invertebrates, particularly chironomid larvae

O

and chydorid cladocerans.

White suckers fed on benthic food items that were
potentially limiting to the‘ growth of perch, but the
disparity in sucker density between Little Bear Lake and
Douglas Lake indicated that sucker predation was not the
major factor controlling the abundanCe of benthos in these

lakes. Diet overlap between these species was low during

105

106
all time periods sampled for all life-stages sampled. If
competition was taking place between the two species, the
only possible mechanism was that suckers depleted the
benthic resources to the point where they had competitively
excluded perch from utilizing those resources. In order
to evaluate this possibility, it would be necessary to
manipulate the density of suckers and observe the response

of perch and their food resources to this treatment.

LIST OF REFERENCES

Alm, Gunnar. 1946. Reasons for the occurrence of stunted
fish populations with special regards to the perch.
Swedish State Institute of Freshwater Research Report
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107

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110

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112

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Ecology 64:1540-1548.

APPENDIX A. Diet composition of young-of-the year yellow perch.

J01 2
0.0 0.0

JUn 25

114
Juan. mmln
0.2 0.0 0.0

mm4

0.0

 

Diet composition of young-of-the-year yellow
ww2l

perch.
of-the-year perch caught with ichthyoplankton

trawls in Little Bear Lake, 1985.

minus

Table 38. Mean number of items in the stomachs of young-

APPENDIX A.

30.7.0.0.0.0.0.3
L650.0.0.0.0.0.

80.0.0.0.0.0.0.0.
L0.0.0.0.0.0.0.0.

0.0.0.0.0.00.0.0.

mnmmmommo.

0.0.0.0.0.0.0.0.0.
10.0.0.0.0.0.0.0.

10.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.

0.0.0.0.0.0.0.0.nw
0.0.0.0.0.0.0.0.0.

0.0 0.0 0.0 0.0 0.0

0.0

lhquhan

Cwflqnhk
Nauplii

onmnmu

land:

Gannfla

0.0.30.
0.0.0.0.

0020
0000

0.0.0.0.
0.0.0.0.

2.0.0.0.
0.0.0.0.

W W.

0.0
0.0

0.0 0.0 0.0
0.0 0.0 0.0 0.0

0.0

0.0
0.0

(Barman

JLLS

APPENDIX A. Diet composition of young-of-the-year yellow
perch.

Table 39. Mean number of items in the stomachs of young-
of-the-year perch caught with ichthyoplankton
trawls in Douglas Lake, 1985.

May 21 Jun 4 Jun 11 Jun 18 Jun 25 Jul

 

Rotifers 0.0

0
O
0

I
0
0
I

I

Cladooera
lemma;
Quimnmmflh
Bosmina
Latona
Dgnmmnmrhs
imemnbmuis
Chydorids
Macrothricids
Leptodora

000000000

0 O O O O O 0
000000000
000000000
0 I O C O O C C 0
000000000
I I I I I I I I I
000000000
”00000000

Copepoda
Cyclopoids 0.
Calanoids 0.

Harpacticoids 0.

o.
0

Nauplii

Oetracoda

0 0000
0 0000
I I I I
0 0000
0 000”
I I l I

Insecta
Chironomids
Ephemeropterans
b

0 0 0000

Gastropoda

0
0
0
Other dipterans 0
0
other 0

0 0 0000

116

APPENDIX A. Diet composition of young-of-the-year yellow
perch.

Table 40. Mean number of items in the stomachs of young-

of-the-year perch caught with ichthyoplankton
trawls in Little Bear Lake, 1986.

May12 myzo May27 am: June

 

Roti fers

0 0 0.0 0 0 0.0 0.0
Cladooera
m; 0.0 0.0 0.0 0.2 2.6
Modem 0.0 0.0 0.0 0.0 0.0
m 0.0 0.0 0.0 1.6 0.0
Latona 0.0 0.0 0.0 0.0 0.0
W 0.0 0.0 0.0 0.0 0.0
gm 0.0 0.0 0.0 0.0 0.0
Chydorids 0.0 0.0 0.0 0.0 0.0
Macrothricids 0.0 0.0 0.0 0.0 0.0
Iszmxkanl 0.0 0.0 0.0 0.2 0.0
CMflanb (L2 m6 ox) mo om
alamids 0.0 2.6 1.4 1.6 0.2
Harpacticoids 0.0 0.0 0.0 0.0 0.0
umpnl L6 04) (L0 mo on
OS!!!“ 0.0 0.0 0.0 0.0 0.0
Inna:
Chironauids 0.0 0.0 0.0 0.0 0.0
Wm 0.0 0.0 0.0 0.0 0.0
m 0.0 0.0 0.0 0.0 0.0
Other dipteram 0.0 0.0 0.0 0.0 0.0
Gastrtpoda 0.0 0.0 0.0 . 0.0 0.0
Other 0.0 0.0 0.0 0.0 0.0

117

young-of-the-year yellow

Diet composition of

perch.

APPENDIX A.

young-
ght with ichthyoplankton

trawls in Douglas Lake, 1986.

Table 41. Mean number of items in the stomachs of
of-the-year perch cau

mwzw :ey27 aux: (mus

mwlz

 

0.0 0.0 4.0

0.0

0.0

mxuem

m

C

n~0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.

0.0.00.0.0.0.0.0.
0.0.0.0.0.0.0.0.nm

0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.

0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.0.0.0.

000000000
0 e e e e e e o e
000000000

.11
l

anflukmh

m
m
a

My

2.2.0.0
0.0.0.3

26..
0100

30.0.0
0.10.1.

«Mafia
10.0.2.

0.0
0.0

0.
0.

lhqmiknkb

Nmpui

Cwflanh
Gdanfib

0.0

0.0

0.0

0.0

0.0

0.0.0.0.
0.0.0.0.

00.0.0
0000

0.0.0.0.
0.0.0.0.

ommm
0000

0000
0000

0.0 0.0 0.0 0.0

0.0

(hfimmdh

0.2

0.0

0.0

0.0

0.0

118

young-of-the-year yellow

Diet composition of

perch.

APPENDIX A.

young-
8 in

ght with seine haul

of-the-year perch cau

Table 42. Mean number of items in the stomachs of
Douglas Lake, 1985.

 

0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0

0.0

kmfimm

0.0.0.0.0.0.0.0.0.
0.0.0.0u0.0.0.0.0.
oomsmommo
000000300
mmmmmmamm
000000000
0.0.0.30.0.00.0.
0.0.0.0.0.0.00.0.

0.0.0.00.0.0.0.0.
0.0.0.1“0.0.n0.0.

0.0.0.00.0.2.0.0.
0.0.0.10.0.30.0.

0.0.0.J0.0.00.0.
0.0.0.0.0.0.0.0.0.

‘0..J.J0.0.0.0.0.
0.0.0.30.0.7.0.0.

‘00:00..‘.0.0.
200000000

0.0.0.0.
0.0.0.0.

0500
0000
JJ0.0.
0.0.0.0.

0.00.0.
0.10.0.

0.0.0.0.
0.0.0.0.

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0

(bnmafla

0.2 0.2 0.0 0.3 1.0 7.8 5.0 1.0

0.0

Autumn

0.0 0.0 0.0

0.0

0.0 0.0

0.0 0.0

0.2

munuuhn
Imwdm

0.0.0.0.
1.0.0.1

5000
0000
1

0.0.0.0.
2.0.0.0.

0.0.0.0.
2.0.0.0.

0.0.0.3
0.0.0.0.

x...
2000
00.0.0.
10.0.0.

00.0.0.
0.0.0.0.

0000
1000

(inmrrrnddb
khan

OUnrdanmu

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0

0.0 0.4 0.0 0.0 0.5 0.0 0.0 8.0

0.0

119
me me mo mo mo mo mm on

0.0

 

Diet composition of young-of—the-year yellow

perch.
of-the-year perch caught with seine hauls in

Little Bear Lake, 1985.

Rotifers

Table 43. Mean number of items in the stomachs of young-
c1

APPENDIX A.

0.0.60.0.0.J0.0.
0.0.2.0.10.30.0.

000°00‘0.0

0.0.2.0.80.60.0.
0.0.10.10.0.0.0.

0.0.80.80.0.0.0.
0.0.u0.1.0.“.0.0.

o.o.0.0.0.0.2.0.0.
0.0.0.0.0.nm&0.0.

o.0.30.0.0.0.0.°.
o.0.0.0.0.0.2.0.0.

2280.0.0.4.0.0.
0.0.0.0.0.0.7.0.0.

0.60.0.0.0.60.0.
mummmmmmo.

60000000.0.

m_£@!

Iééfi;

W

Chydorids

Macrothric ids
ra

coma.
Ceri

0.0
0.0
0.0
0.0
0.0

0.0
0.0
0.0
0.0
0.0

0.0
0.0
1.8
0.0
0.0

0.0
0.2
0.2
0.0
0.0

0.0
0.0
0.8
0.0
0.0

0.0
0.0
0.0
0.0
0.0

0.0
0.0
0.0
0.0
0.0

0.0
0.0
0.0
0.0
0.0

0.0
0.0
0.0
0.0
0.0

(Yelcpoids
llarpact icoids
Nauplii

Galanoids

Gastrqaoda
other

Mphipoda
Hydracarina

Ostracoda

Oopepoda

0.0 0.0 0.0 0.0

29
0.0

120
22
on

1986.
7 15
OJ mo

JUn JUn Jul Jul Jun JUI
23 30
0.2 0.0

 

Diet composition of young-of-the-year yellow

perch.
of-the-year perch caught with seine hauls in

Douglas Lake,

Table 44. Mean number of items in the stomachs of young-
Rotifers

APPENDIX A.

0.0.0.0.0.0.60.0.
0.0.0.2.0.0.7.0.0.

0.0.0.0.0.0.0.0.0.
0.0.0.“...0.0.50.0.

J0.0.0.o.0.80.0.
0.0.0.0.0.0.60.0.

2.0.0.60.0.80.0.
0.0.0.2.0.30.0.0.

0.0.“‘0.0.0.0.
0.0.0.0.0.0.2.0.0.

20.880.0.60.0.
0.0.0.60.0.7.0.0.

0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.30.0.

J0.2.0.0.0.60.0.
0.0.‘.0.0.0.L0.0.

50.0.0.0.0.80.0.
10.0.0.0.0.0.0.0.

.qa.A.O.Unvn.0.d
6.0.10.nm0.0.0.nw

1 .MJ
1am mm

Scaphlober_§
Chydorids

Macrothriciw

‘00.0
0000

0.0.0.0.
”0.0.0.

30.0.0.
7.0.0.0.

0.0.0.0.
00.0.0.

60.0.0.
QH0.0.0.

6000
5000
‘000
1000
0.0.0.0.
0.1.0.0.

0.9w0.0.
0.0.0.0.

‘200
0200

cyclopoids
calanoids
Narpacticoids
Nauplii

0.2
0.8
0.0

0.0
1.0
0.0

0.0
0.2
0.0

0.2
0.4
0.0

0.0
1.‘
0.0

0.0
6.2
0.0

0.0
0.0
0.0

0.2
0.0
0.0

0.0
0.0
0.0

0.0
0.0
0.0

Ostracoda
Hydracarina
Insecta

Amphdpoda

60.0.0.
0.0.0.0.

0000
0000

2000
O...
0000

Chironcmdds
other'di

Gastropoda
other

0.0
1.2

0.0 0.0 0.0 0.0 1.2 0.0 0.0
0.0 0.0 0.0 0.2 0.0 0.0 0.2 1.0

0.0

0.0
0.0

APPENDIX 8. Diet carposition of qug-of-the-year white sucker.

121

Diet composition of young-of-the-year yellow

perch.

APPENDIX A.

of-the-year perch caught with seine hauls in

Table 45. Mean number of items in the stomachs of young-
Little Bear Lake, 1986.

9
2

mm

0
3

3
2

 

0.0 0.0 0.0 0.2 5.0 5.6 0.0 2.8 0.0

0.0

muhn

C1

0.0.0.30.0.80.0.
0.0.0.L0.0.4.0.0.

0.0.0.00.0.0.0.0.

0.0.0.00.0.0.0.0.

‘wad-J0.0.0.0.0.0.
1~I.0.0.0.0.0.0.0.

0.0.60.0000.0.

0.0.60.0000.0.

2.0.4.80.0.00.0.
0.0.30.0.0.4.0.0.

002000000.

oommmmmmo

604.0.0.0.0.00.

m7n0.0.0.0.00.

.mommmmmm
000000000
64060.0600.
101600000

4.0.0.2.0.0.30.0.
0.0.0.0.0.0.0.0.0.

0.0 0.2 0.0 0.2 0.0 0.2 0.0 0.0 0.2

0.0

Os

0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.4

0.2

MHMnh

0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0

0.0

WMmuma

4.0.0.0.
10.0.0.

00.0.0
0000
0.0.0.0.
0.0.0.0.

0.0.0.0.
0.0.0.0.

mmmm
1000
30mm
0000
doom
0000
4mmm
0000
30.0.4.
10.0.0.

600.0
0000

“a.

a
omudmmmm

Gmhmm

0.0 0.0 0.0 0.0 0.04 0.0 0.0 0.0 0.0

0.0

as

0.0 16.0 14.4 0.2 0.6 116.31 0.2 0.0

0.0

0.0

lfimfihrmgéngggg

WMr

122

APPENDIX B. Diet composition of young-of-the-year white
sucker.

Table 46. Mean number of items in the stomachs of young-
of-the-year white suckers caught with

ichthyoplankton trawls in Douglas Lake,
1985-1986.

.mnn aunzs mm May 27

 

1985 1985 1986 1986
Rotifers 0.0 0.0 0.0 1.0
auburn
0.0 0.0 0.0 0.0
eggsmmmu mp 04) mo 04)
________ 0.0 0.0 0.0 1.3
gm 0.0 0.0 0.0 0.0
g 0.0 0.0 0.0 0.0
59% 0.0 0.0 0.0 0.0
Chydorids 1.0 5.0 0.0 2.5
kerothricids 0.0 0.0 0.0 0.0
upuaxa 04> (L0 mo om
cyclopoids 0 O 1.0 0.0 0.2
Calamids O 0 0.0 0.0 0.0
Harpactiooids 0 0 0.0 0.0 0.0
nauplii 0 0 0.0 0.0 0.0
Ostracoda 0 0 0.0 0.0 0.0
Immdn
mimuuids 0 O 0.0 0.0 0.0
W O 0 0.0 0.0 0.0
gm 0 O 0.0 0.0 0.0
Other'dipteranl 0.0 0.0 0.0 0.0
Gastropoda 0 0 0.0 0.0 0.0
Other 0 O 0.0 0.0 0.0

123

APPENDIX B. Diet composition of young-of—the-year white
sucker.

Table 47. Mean number of items in the stomachs of young-
of-the-year white suckers caught with

ichthyoplankton trawls in Little Bear Lake,
1985-1986.

Jun 4 Jul 2 May 27 Jun 2 Jun 9
1985 1985 1986 1986 1986

 

g
5
9
o
9
c
U
a
o
o
9
o

Cladooera
m 0.0 0.0 0.0 0.0 0.0
grim 0.0 0.0 0.0 0.0 0.0
m 0.0 0.5 1.0 0.0 8.5
Lam 0.0 0.0 0.0 0.0 0.0
mggmgflfig (L0 mo an up om
mmg 1.0 1.5 0.0 0.0 0.0
Chydorids 0.0 0.0 1.0 0.0 8.5
Macrothricids 0.0 0.0 0.0 0.0 0.0
leptodora 0.0 0.0 0.0 0.0 0.0
cwflanb 04) mo OJ) mo 04)
Calamids 0.0 0.0 0.8 0.0 0.0
Harpacticoids 0.0 0.0 0.8 0.0 0.0
Nauplii 0.0 0.0 0.0 0.0 0.0
Ostramda 0 0 0.0 0.0 0.0 0.0
Imecta
(himids 0.0 2.5 0.5 0.0 0.0
Wm 0.0 0.0 0.0 0.0 0.0
m 0.0 0.0 0.0 0.0 0.0
other dipteram 0.0 0 0 0.0 0.0 0.0
Gastmopoda 0.0 0.0 0.0 0.0 0.0
Other 0.0 0.5 0.0 0.0 0.0

124

APPENDIX B. Diet composition of young-of-the-year white
sucker.

Table 48. Mean number of items in the stomachs of young-

of-the-year white suckers caught with seine hauls
in Douglas Lake, 1985-1986.

 

Jul 3 Jul 9 Jul 16 Jun 23 Jul 7
1985 1985 1985 1986 1986
Rotifers O 4 0.0 0.0 0.0 0.0
Cladooera
mg 0.0 0.0 0.0 0.0 0.7
_Cgiggaflmia 0.0 0.0 0.0 0.0 0.0
-_.____ 4.8 0.3 0.0 0.3 0.0
Pugh 04) up mo on mo
Mix 0.0 0.0 0.0 0.0 0.0
gym 0.4 0.0 0.0 0.0 0.0
Chydorids 86.2 53.8 42.0 15.5 35.7
Mcrothricids 0.0 0.0 0.0 0.0 0.0
Leptodora 0.0 0.0 0.0 0.0 0.0
cwnanh mo mo mo OJ L3
(2133101133 0.0 0.0 0.0 0.0 0.0
Harpactiooids 5.4 25.8 0.0 0.0 0.0
umpnl 04) am mo a» mo
Ostracoda 0.0 0.0 0.0 0.0 5.3
kahuna. ox) om mo om mo
Bydracarma 0.6 0.3 0.0 0.0 0.0
Insecta
Chironunicb 1.0 0.3 0.0 1.8 0.7
menarcpterans 0.0 0.0 0.0 0.3 0.0
anoggg 0.0 0.0 0.0 0.0 0.0
other dipterans 0.0 0.4 0.0 0.0 0.0
Gastrqaoda 0.0 0.0 0.0 0.0 0.0
Other 0.0 0.0 0.0 16.0 14.4

125

young-of-the-year white

Diet composition of

sucker.

APPENDIX B.

young-

ght with seine hauls

of-the-year white sucker cau

Table 49. Mean number of items in the stomachs of
in Little Bear Lake, 1985.

 

0.0

0.0 0.0 0.0 0.0

0.0

Rmdflus

000000500.

00......

000000n00
2

mammmmmmm
000000%00
000000400.
mammmmnmo
1
gmmmmmamm
000000-W00
3
400000400
mammmmimm

500000.50.0.
000000n00

9.0

0.0 11.8 49.8

0.0

0.0

1.5

0.0 0.0 0.0 0.0

0.0

thmuh

0.0

0.0 0.0 0.0 0.8

0.3

ha

Imnda

0.0

0.0 0.0 0.0 0.0

0.0

Gmhmgfla

ouer

0.0

0.0 0.0 0.0 0.0

0.0

126

young-of-the-year white

Diet composition of

sucker.

APPENDIX B.

young-

ght with seine hauls

of-the-year white sucker cau

Table 50. Mean number of items in the stomachs of
in Little Bear Lake, 1986.

9
2

2

5

0
3

2

 

0.0

0.0 0.0 0.5 0.0 0.7 0.2 1.0 2.8

0.0

Rotifers

Cl

0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.m0.0.

0.0.0.0.0.0.7.0.0.
0.0.0.0.0.0.m0.0.

0.0.2.0.0.0.2.0.0.
0.0.0.0.0.0.4.0.0.

0.0.0.0.0.0.0.n~0.
0.0.4.0.0.0.anw0.
2
0.0.0.0.0.0.30.0.
0.0.0.0.0.0.60.0.
1
0.0.0.0.0.0.00.0.
0.0.0.0.0.0.7.0.0.
n
0.0.0.0.0.0.50.0.
0.0.0.0.0.0.60.0.

0.0.0.nw0.0.0.0.0.
0.0.0.0.0.0.50.0.
1
000000300
mmmmmmumm

0.0.0.0.0.0.0.0.0.
0.0.0.0.0.0.80.0.

moo.
2000
1.

7000

1.0

0.0 71.0 372.0 50.8 76.3 92.6 256.6 67.0

3.0

Gunman
Anhknh

0.0 0.0 1.5 0.0 0.0 0.0 0.0 1.3 0.0

0.2

0.3 0.0 0.5 0.4 0.0 0.0 0.0 0.0 0.0

0.0

mumnnhn

 

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0

(hflmmuh
0Uer

0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.8 0.0

0.0