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Potential competition among young-of-year fish in western Lake Erie

Trauben, Bruce Kenneth, Ph.D. The Ohio State University, 1991

UMI 300 N. Zeeb Rd. Ann Arbor, MI 48106

POTENTIAL COMPETITION AMONG YOUNG-OF-YEAR FISH

IN WESTERN LAKE ERIE

DISSERTATION

Presented in Partial Fulfillment of the Requirement for

the Degree Doctor of Philosophy in the Graduate

School of the Ohio State University

Bruce Kenneth Trauben, B.S., M.S.

The Ohio State University

1991

Dissertation Committee Approved by

David A. Culver

Sheldon I. Lustick

11 ACKNOWLEDGMENTS

I want to thank my adviser, Dr. David A. Culver, for his

assistance throughout this project. This project would not have been

possible were it not for his efforts in recognizing the need for the

study, and in obtaining the resources necessary to pursue it. Dr.

Culver’s guidance and patience were indispensible in every phase of the

study. I would also like to thank the other members of the Dissertation

Committee: Drs. Sheldon Lustick and Bruce Vondracek for their

encouragement and constructive criticism during the preparation of this dissertation. Dr. F. Joseph Margraf was also instrumental in getting this project off the ground, and I want to express my gratitude for his efforts.

This project would not have come to completion were it not for the efforts of many assistants. I want to express my gratitude to Lisa

Bohman Egbert, Brad Egbert, Robert Fletcher, Lisa Meadows, Tom Rice,

Dana Shepard, Roseanne Smrtnik Hetterscheidt, Theresa Villanueva,

Sylvia Wong, and Tracey Zemel for their assistance in the laboratory and in the field. These assistants cheerfully endured the unpleasant task of identifying fish stomach contents, and coding and entering data. I would also like to thank Drs. David Gar ton, Robert S. Hayward,

Sheldon I. Lustick, F. Joseph Margraf, and Gary G. Mittelbach for their assistance with methodology and data analysis. The young-of-year fish

iii samples, year-class data, and chemico-physical data were obtained with the assistance of the Ohio Department of Natural Resources Division of

Wildlife, who allowed me to accompany them on young-of-year survey cruises. This project would not have been possible were it not for the assistance of personnel at the Ohio Department of Natural Resources.

Personnel of the Co-operative Fisheries Research Unit at The Ohio State

University, also graciously assisted with the sampling for this project.

This work is a result of research sponsored in part by the Ohio

Sea Grant College Program, Project No. R/LR-1 under grant NA8/AA-D00079 of the National Sea Grant College Program, National Oceanic and

Atmospheric Administration in the U.S. Department of Commerce, and from the State of Ohio. Computer services were provided by the

Instructional and Research Computer Center (IRCC) of The Ohio State

University. VITA

August 25, 1954 ...... B o m - Akron, Ohio

1977...... B.S., Kent State University, Kent, Ohio

1982...... M.S., The University of Akron, Akron, Ohio

1981-1988 ...... Graduate Research/Teaching Associate, Department of Zoology, The Ohio State University, Columbus, Ohio

1985-1986 ...... Research Intern, Battelle Memorial Institute, Columbus, Ohio

1989...... Information Specialist, Geo/Resource Consultants, Inc., Washington, D.C.

1989-Present...... Legal Assistant, Bryan, Cave, McPheeters, and McRoberts, Washington, D.C.

PUBLICATIONS

Trauben, B. K., and J. H. Olive. 1983. Benthic macroinvertebrate assessment of water quality in the Cuyahoga River, Ohio - an update. Ohio Journal of Science 83(4): 209-212.

FIELDS OF STUDY

Major Field: Environmental Biology

Studies in: Limnology and Aquatic Ecology

v TABLE OF CONTENTS

ACKNOWLEDGMENTS...... iii

VITA ...... v

LIST OF TABLES ...... vii

LIST OF FIGURES...... xii

CHAPTER PAGE

I. INTRODUCTION...... 1

II. RESOURCE SHARING AMONG YOUNG-OF-YEAR FISH IN WESTERN LAKE ERIE...... 5

Introduction...... 5 Methods...... 7 Results...... 18 Nearshore Versus Offshore Diets and Dietary Overlaps, 1983...... 18

1983 Versus 1984 Diets and Dietary Overlaps at Middle Sister ...... 37 D i s c u s s i o n ...... 93

III. RESOURCE AVAILABILITY PC® YOUNG-OF-YEAR FISH IN WESTERN LAKE ERIE: A BIOENERGETICS APPROACH...... 103

Introduction ...... 103 Methods...... 106 Energy Losses ...... 106 Consumption...... 115 Results...... 120 D i s c u s s i o n ...... 124

IV. SUMMARY AND CONCLUSIONS...... 133

LIST OF REFERENCES ...... 144

APPENDIX Sample Sizes, Fish Sizes, and Stomach Contents Data for Chapter II...... 152 vi LIST OF TABLES

TABLE PAGE

1. Bottom trawl samples used in this study...... 13

2. Fish species included in this studv...... 14

3. Fish species pairs for which diet overlap was greater than, or equal to, sixty percent (60%) on more than one occasion during the s t u d y ...... 35

4. Switching to benthic prey by freshwater drum as a function of mean overlap ...... 95

5. Switching to benthic prey by yellow perch as a function of mean overlap ...... 96

6 . Estimated proportional overlap when another resource dimension, prey size, is considered ...... 98

7. Fish diets in the western basin of Lake Erie in 1958 and 1983...... 99

8 . Diet overlap among young-of-year fish in 1958 and 1983 in western Lake Erie...... 102

9. Summary of sample sizes, fish sizes, and temper ature used in respiration experiments for each fish species ...... 113

10. Gastric evacuation rates (r) and standard errors (SE) for freshwater drum, white bass, white perch, and yellow perch taken near Middle Sister Island in western Lake E r i e ...... 119

11. The effect of fish species on the relationship between the rate of oxygen consumption (mg O 2 consumed/day) and the independent variables, wet weight (loge wet weight in grams), swimming speed (body lengths/s), and temperature (°C) ...... 121

vii Energy available for growth of the average-sized young-of-year fish in the western basin of Lake Erie during summer of 1983 and 1984......

Growth rates of age-0 freshwater drum, white bass, white perch, and yellow perch caught near Middle Sister Island in the western basin of Lake Erie during the Summer, 1983 and 1984, expressed as a percent increase in biomass per day......

Geometric means of numbers caught per trawling hour and percent change between seasons of young- of-year freshwater drum, white bass, white perch, and yellow perch during Summer and Fall, 1983 and 1984, in the western basin of Lake Erie......

Summary of Student’s t-tests for significant differences in fish dry weight (g), using log*- transformed data, between 1983 and 1984 at the offshore site, Middle Sister ......

Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl at the offshore site near Middle Sister Island, western Lake Erie on July 13-14, 1983 ......

viii 20. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, emerald shiner, gizzard shad and rainbow smelt examined. The fish were collected by bottom trawl at the offshore site near Middle Sister Island, western Lake Erie on September 8-9, 1983 . . . 163

21. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among spottail shiner, trout-perch, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl at the offshore site near Middle Sister Island, western Lake Erie on July 13-14, 1983...... 166

22. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl at the nearshore site in western Lake Erie near Bono on July 11, 1983. . . .169

23. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl at the nearshore site in western Lake Erie near Bono on July 28, 1983. . . . 171

24. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl at the nearshore site in western lake Erie near Bono on August 8 , 1983 . . . 174

25. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl, nearshore, in western Lake Erie near Bono on August 24, 1983 ...... 177

26. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, emerald shiner, gizzard shad, rainbow smelt, and spottail shiner examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on July 24-25, 1984...... 180

ix 27. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among trout-perch, walleye, white bass, white perch, and yellow perch examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on July 24-25, 1984...... 184

28. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, emerald shiner, gizzard shad, and rainbow smelt examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on August 6 , 1984 ...... 187

29. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among trout-perch, walleye, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on August 6 , 1984 ...... 190

30. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, gizzard shad, rainbow smelt and spottail shiner examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on August 21, 1984 ...... 193

31. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among trout-perch, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on August 21, 1984...... 196

32. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, emerald shiner, gizzard shad,: and rainbow smelt examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on September 5-6, 1984...... 199

x 33. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among trout-perch, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on September 5-6, 1984 . . . 203

xi LIST OF FIGURES

FIGURE PAGE

1. Numbers of young-of-year fish caught per hour trawling in the western basin of Lake Erie during summer surveys performed in 1980 through 1984 by the Ohio Department of Natural Resources ...... 9

2. Map of Lake Erie showing the general location of the sampling sites in the western b a s i n ...... 11

3. Prey biomass (percent) consumed by young-of-year fish nearshore (Bono) in western Lake Erie on July 11, 1983...... 20

4. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish offshore (Middle Sister) in western Lake Erie on July 13-14, 1983 ...... 22

5. Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in westemJLake Erie on July 28, 1983...... 24

6 . Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in western Lake Erie on August 8, 1983...... 26

7. Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in western Lake Erie on August 24, 1983...... 28

8 . Prey biomass (percent) consumed by young-of-year fish nearshore (Bono) in western Lake Erie on July 28, 1983...... 30

9. Prey biomass (percent) consumed by young-of-year fish nearshore (Bono) in western Lake Erie on August 8, 1983 ...... 32

10. Prey biomass (percent) consumed by young-of-year fish nearshore (Bono) in western Lake Erie on August 24, 1983...... 34

xii Taxonomic overlap index values for diets of pairs of fish species caught nearshore (Bono) in western Lake Erie during July and August, 1983 ...... 39

Taxonomic overlap index values for diets of pairs of fish species caught offshore (Middle Sister) in western Lake Erie during July and August 1983. . . . 42

Prey size distributions for the diets of young- of-year fish from nearshore (Bono) in western Lake Erie on July 11, 1983 ...... 45

Prey size distributions for the diets of young- of-year fish from offshore (Middle Sister) in western Lake Erie on July 13 and July 14, 1983 . . . 47

Prey size distributions for the diets of young- of-year fish from nearshore (Bono) in western Lake Erie on July 28, 1983 ...... 49

Prey size distributions for the diets of young- of-year fish from offshore (Middle Sister) in western Lake Erie on July 28, 1983 ...... 51

Prey size distributions for the diets of young- of-year fish from nearshore (Bono) in western Lake Erie on August 8 , 1983...... 53

Prey size distributions for the diets of young- of-year fish from offshore (Middle Sister) in western Lake Erie on August 8 , 1983...... 55

Prey size distributions for the diets of young- of-year fish from nearshore (Bono) in western Lake Erie on August 24, 1983 ...... 57

Prey size distribution for the diets of young- of-year fish from offshore (Middle Sister) in western Lake Erie on August 24, 1983 ...... 59

Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish at the Middle Sister site in western Lake Erie on July 24-25, 1984 . t ...... 62

Prey biomass (percent) consumed by young-of-year fish at the Middle Sister site in western Lake Erie on August 6 , 1984 ...... 65

xiii 23. Prey biomass (percent) consumed by young-of-year fish at the Middle Sister site in western Lake Erie on August 21, 1984...... 68

24. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish at the Middle Sister site in western Lake Erie on September 8-9, 1983...... 70

25. Prey biomass (percent) and prey preference (in percent biomass) of by young-of-year fish at the Middle Sister site in western Lake Erie on September 5-6, 1984...... 73

26. Taxonomic overlap index values for diets of pairs of fish species caught at the Middle Sister site in western Lake Erie during 1984...... 76

27. Taxonomic overlap index values for diets of pairs of fish species caught at the Middle Sister site in western Lake Erie on September 8-9, 1983 ...... 79

28. Prey size distributions for the diets of young- of-year fish caught at the Middle Sister site in western Lake Erie on July 24-25, 1984...... 81

29. Prey size distributions for the diets of young- of-year fish caught at the Middle Sister site in western Lake Erie on August 6 , 1984...... 84

30. Prey size distributions for the diets of young- of-year fish caught at the Middle Sister site in western Lake Erie on August 21, 1984 ...... 87

31. Prey size distributions for the diets of young- of-year fish caught at the Middle Sister site in western Lake Erie on September 8-9, 1983 ...... 89

32. Prey size distributions for the diets of young- of-year fish caught at the Middle Sister site in western Lake Erie on September 5-6, 1984 ...... 92

33. Schematic drawing of the respiration chamber designed for this study...... 109

34. Median and quartiles of relative stomach dry weight for yellow perch (Perea flavescens) versus time of day on July 13-14, 1983 at Middle Sister in western Lake E r i e ...... 117 xiv 35. Temperature and dissolved oxygen profiles of the study site near Middle Sister Island, in the western basin of Lake Erie, during the Sumners of 1983 and 1984...... 142

xv CHAPTER I

INTRODUCTION

Fishery biologists and ecologists have, for many years, studied the causes of variation in year-class strength in Lake Erie. Because of the economic importance of percids (especially yellow perch, Perea flavescens, and walleye, Stizostedion vitreum vitreum) in western Lake

Erie, much research has been directed toward determining the effects of environmental factors upon their year-class strength (Koonce et al.

1977, Busch et al. 1975, Hartman 1972, Jobes 1952). More recent studies have examined the effects of biotic factors such as prey availability (Hayward and Margraf 1987), potential competition (Parrish

1988, Schaeffer and Margraf 1986), and predation (Knight et al. 1984) upon percid populations in Lake Erie. While sane of these studies have focused on interactions between two species, none has examined whether conpetition for food among the entire young-of-year fish coninunity may be a factor in determining year-class strength for any Lake Erie fish species.

Evidence from studies performed in Oneida Lake, New York suggests that, at least for yellow perch, fish growth and survival sire linked to zooplankton abundance. Mills et al. (1989), Noble (1975) and Mills and Forney (1981) have found significant correlations between growth of young (age 0) yellow perch and the density of Daphnia sp. During the years when Daphnia abundance was low due to intense predation, yellow perch were forced to switch to a diet of benthic invertebrates and, consequently, suffered a reduction in growth rate. The growth rates of juvenile yellow perch, during these years of low Daphnia abundance, averaged lower than in years when Daphnia remained abundant into Autvnnn

(Mills and Forney 1981). A relationship between yellow perch growth rates and year-class strength was not clear in Oneida Lake (Noble 1975,

Forney 1971). However, a later study was able to show that faster growing cohorts of yellow perch in Oneida Lake experienced less mortality by walleye predation (Nielsen 1980).

Working with young-of-year yellow perch in western Lake Erie, Wu and Culver (in press) also found a shift in diet composition to benthic organisms when zooplankton abundance was low, but no reduction in fish growth rates was detected. Reduced yellow perch young-of-year growth rates and year-class strength were observed in Lake Michigan when large zooplankton became unavailable and benthic invertebrates were used as an alternative food source (Crowder et al. 1987). These studies suggest that, in some lakes, survivorship of young-of-year yellow perch is dependent upon the availability of zooplankton.

When zooplankton abundance is low, whether competition among young-of-year fish is a factor affecting year-class strength of yellow perch, or any other species in western Lake Erie, remains unclear. It is known, however, that many common fish species in Lake Erie depend 3

upon zooplankton for food, often during the early stages of their lives

(Muth and Busch 1989, Norden 1968, Price 1963, Ewers 1933), and that

zooplankton abundances and biomass vary seasonally in Lake Erie

(Reutter and Eeutter 1975, Hubschman 1960, Jahoda 1949). Thus, there

are periods of seasonally low zooplankton biomass when competition for

food among young-of-year fish may be an important factor affecting

their growth and survival in western Lake Erie.

Therefore, the objective of this research was to contribute to

the goal of determining the degree to which fish year-class strength is

affected by the availability of zooplankton forage in western Lake

Erie. Towards this goal, this study was undertaken to specifically

determine: 1) the degree to which the young-of-year of the dominant

fish species in western Lake Erie consume the same taxa and size

classes of prey; 2 ) whether the young-of-year of each fish species in

the community are consuming sufficient quantities of food to meet their

daily energy requirements, i.e. whether food resources are limiting;

and 3) the relative competitive abilities of the young-of-year of those

fish species that are likely competitors for food in western Lake Erie.

This research also provides a record of the diets of young-of- year fish in western Lake Erie just prior to the recent invasions by

the cladoceran, Bythotrephes cederstroemi (Bur et al. 1986), and the zebra mussel, Dreissena polymorpha. The previously most recent study of Muth and Busch (1989) provided data from 1975 and 1976 on the food of the young-of-year of four of the eleven major fish species (alewife, gizzard shad, white bass, and freshwater drum), however, they were collected at only one site (nearshore) in the western basin of Lake

Erie. A comprehensive study of the diets of young-of-year fish in western Lake Erie was last performed in 1958 by Price (1963) who included ten fish species from nearshore and offshore areas of the lake. Therefore, the results of this research include the most recent data on the food of eleven fish species that were collected at a nearshore and an offshore site, and may be more useful to detect the effects upon young-of-year diets and survival caused by the recent invasions of Bythotrephes and Dreissena polymorpha. CHAPTER I I

RESOURCE SHARING AMONG YOUNG-OF-YEAR FISH IN WESTERN LAKE ERIE

Introduction

The first step toward determining whether competition for food

affects survival of young-of-year fish is to identify which fish

species are sharing food resources. In this chapter, I identify which

fish species have common food resources as young-of-year at two

stations, one nearshore and one offshore, in western Lake Erie during

July through early September, in 1983 and 1984. In subsequent chapters, these results will be used, in conjunction with estimates of fish daily energy needs and daily rations, to determine whether any

fish species is likely to be adversely affecting another through exploitative competition.

The last study that comprehensively examined the diets of young- of-year fish in western Lake Erie was performed in 1958 (Price 1963).

Since that time, and prior to this study, Lake Erie has been invaded by white perch (Morone americana) and by Eurytemora affinis, a euryhaline calanoid copepod (Busch et al. 1977, Engel 1962). Because white perch and Eurytemora affinis have become well established in western Lake

Erie, changes in young-of-year diets since 1958 may be expected. 6

During this same time period there have been some dramatic

abiotic events as well. Total phosphorus loading rose from about

18,000 metric tons (t) per year in 1958 to about 30,000 t per year in

1970 (Sly 1976), and then declined to a low of about 10,000 t per year

in 1983 (International Joint Commission (IJC) 1987). While p h o s p h o r u s

loading increased to a maximum and then decreased, the concentration of

nitrite .and nitrate steadily increased during the years 1970 to 1983

(IJC 1987). Although cultural eutrophication is still occurring in

Lake Erie, its rate appears to be slowing down as evidenced by a slowly

declining concentration of chlorophyll a (an indicator of phytoplankton

biomass (Wetzel 1983)) during the years 1970 through 1986 (IJC 1987).

All of these events may have directly, or indirectly, affected the

relative abundance of young-of-year fish in western Lake Erie and their

diets, since Price’s study in 1958 (Price 1963).

Therefore, the data on fish consumption that are available from

Price’s study in 1958 (Price 1963) could not be relied upon to describe

the diets of young-of-year fish in western Lake Erie at the time this

research was initiated. Price’s data, however, can serve as an historical record against which the results of this study can be compared.

Changes in the nearshore environment due to eutrophication, and extension of these changes to offshore areas over the past sixty years in western Lake Erie are well reported in the literature (Beeton and

Edmondson 1972, Beeton 1965, Carr and Hiltunen 1965). This increasing homogeneity of the western Lake Erie basin suggests that fish diets may 7

also be similar between nearshore and offshore areas of western Lake

Erie, especially among benthivores. Therefore, I hypothesized that

there is no difference in prey composition and diet overlaps among

young-of-year fish nearshore and offshore. Additionally, because the

effects of eutrophication have persisted in western Lake Erie (Hayward

and Margraf 1987), I hypothesized that there is no difference in the

composition of young-of-year fish diets at a particular site from year

to year. However, since young-of-year fish abundance data of the Ohio

Department of Natural Resources (Fig. 1) show that the number of young-

of-year fish increased significantly between 1983 and 1984 (p < 0.05,

paired t-test on log*-transformed data), an increase in predation

pressure upon zooplankton may be a factor affecting zooplankton

availability in 1984.

Methods

All young-of-year (YOY) fish were collected by 10 minute bottom

trawls (12.7 mm mesh, stretched) made from the Ohio Division of

Wildlife’s research vessel, Explorer II. In 1983, fish were sampled

from two stations, one nearshore, near Bono, Ohio (the "Bono" site),

and one offshore, near Middle Sister Island ("Middle Sister") (Fig. 2).

The nearshore area (Bono) sampled was approximately 200 m from the

shoreline, approximately 8 m deep, and had a soft bottom. The offshore area (Middle Sister) sampled was about 25 km north of Bono, and 16 km

from the nearest mainland shoreline. Middle Sister also had a soft, or muck, bottom and was about 13 m in depth. In 1984, fish were sampled Figure i. Numbers of young-of-year fish caught per hour trawling in the western basin of Lake Erie during summer surveys performed in 1980 through 1984 by the Ohio Department of Natural Resources. WA = walleye, YP = yellow perch, WB = white bass, FD = Freshwater drum, SS = spottail shiner, GS = gizzard shad, AL = alewife, and WP = white perch. Data are from Ohio Department of Natural Resources (1985).

8 Figure 1. Figure No. Caught/Hour Trawling 10000 10000 0 0 0 0 1 10000 0 0 0 0 1 10000 10000 1000 1000 1000 1000 1000 100 100 100 100 100 10 10 10 10 10 1 1 1 1 i

A P B D S S L WP AL GS SS FD WB YP WA ih Species Fish — 1 . - I ■ . ' ■ — 1 1 1 1981 1980 98' 98' 98!2 98 — * — % 3 Figure 2. Map of Lake Erie showing the general location of the sampling sites in the western basin. The dashed lines approximately divide Lake Erie into its three basins: western, central, and eastern. The solid line depicts the international boundary between Canada and the United States. Modified from Hayward (1988).

10 LAKE ERIE

DETROIT ERIE

SAMPLING SITES

1 MIDDLE SISTER TOLEDO CLEVELAND 2 BONO

N . A 0 80 kilometers

Figure 2. 12 at Middle Sister only. This sampling scheme allows comparisons of fish diets to be made between nearshore and offshore, in 1983, and between years at Middle Sister. During both years at Middle Sister, diel sampling was performed by a series of eight 10-minute bottom trawls approximately three hours apart. Fish were collected on a total of nine dates, on four of which diel sampling was performed; the remainder were single samples taken during the daytime (Table 1). Immediately after each trawl, YOY fish were placed in bags and quick-frozen on dry ice. The fish were sorted by species in the laboratory using species characteristics described by Trautman (1981). Eleven fish taxa were relatively common, and were included in this study (Table 2).

In the laboratory, ten fish of each species, when available from each collection, were randomly selected for stomach analyses. Fish total and standard lengths were measured (mm) before their stomachs were removed. Stomach contents were identified, measured (to the nearest 0.02 mm), and enumerated. Dry weights (mg) of fish remains and stomach contents were obtained by drying to constant weight at 80PC.

(The number of fish stomachs examined, and the ranges of fish standard lengths and dry weights are tabulated for all fish species by site and collection date in the Appendix.)

The proportion of the total prey biomass represented by each prey taxon was used as a measure of the relative importance of each taxon to each fish species’ diet. Hie relative importance of each prey taxon was based on prey biomass rather than number, because numerical methods overemphasize the importance of small prey when consumed in large 13

Table 1. Bottom trawl samples used in this study. D = diel sampling performed, T = single trawl.

Day Site Date Number Type

1983

Middle July 13-14 194-195 D Sister July 28 209 T

August 8 220 T

August 24 236 T

September 8-9 251-252 D

Bono July 11 192 T

July 28 209 T

August 8 220 T

August 24 236 T

1984

Middle July 24-25 206-207 D Sister August 6 219 T

August 21 234 T

September 5-6 249-250 D 14

Table 2. Fish species included in this study.

Common Name Scientific Name Abbreviations

Alewife Alosa pseudoharengus (Wilson) ALWF, AL

Gizzard shad Dorosoma cepedianum (Lesueur) GSHD, GS

Emerald shiner Notropis atherinoides atherinoides Rafinesque ESHNi ES

Spottail shiner Notropis hudsonius (Clinton) SSHN, SS

Rainbow smelt Osmerus mordax (Mitchill) RSMT, RS

Trout-perch Fercopsis omiscontaycus (Walbaum) TRTP, TP

White perch Morone americana (Gmelin) WPCH, WP

White bass Morone chrysops (Rafinesque) WBAS, WB

Yellow perch Perea flavescens (Mitchill) YPCH, YP

Walleye Stizostedion vitreum vitreum (Mitchill) WALL, WA

Freshwater drum Aplodinotus grunniens Rafinesque DRUM, FD 15

numbers (Hyslop 1980).

To determine the relative biomass of each prey taxon to the total

diet of each fish species, estimates of prey dry weight were obtained,

when available, from published regressions of prey weight on length

(Culver et al. 1985, Rosen 1981, Dumont et al. 1975), or from published

individual mean prey weights (Hawkins and Evans 1979). For chironomid

larvae, the relationship,

W = 3.308L 2,306 ( 1)

where W is weight (tig), L is length (mm), was used (Mittelbach, pers.

commun.). For oligochaete worms, estimates of prey weight were

obtained from the regression:

W = 3.57L1-254 .D1,io6 (2) where W is weight (fig), L is length (ram), and D is width. This

relationship for oligochaete worms was developed by cutting cultured

Tubifex worms into pieces of varying length and width, drying to constant weight at 80 °C, and weighing on an electronic balance to the nearest 0.1 Mg. For Eurytemora affinis, the mean individual weight,

6.1 Mg, was obtained by drying (80 °C) and weighing 34 groups comprised of two to ten individuals (obtained from zooplankton samples preserved in formalin) of nearly equal length. For relatively rare prey taxa, when no published regressions or mean individual weights were available, the regression equation, or mean individual weight, that was available for a prey taxon of similar size and morphology was used. 16

The biomass of each prey type, i, that was consumed by an

individual of each fish species, x (Wz,i) was calculated by multiplying

the number of each prey type i observed in a fish stomach by the mean

estimated weight of that prey type. The total biomass represented by

prey type i, in the diet of fish species x on a given day (or 24 hour

period on those dates when diel sampling was performed on consecutive

days; see Table 2) was obtained by summing (pooling) W x,i over all N

individuals of fish species x that were examined for stomach contents.

Thus, the proportional contribution of biomass of each prey taxon, i,

to the diet of fish species x on a given day (P*, i) was calculated with

the equation:

N £ Wx.i PX i I - n = 1 (3)

" » I N E E 1=1 n = 1 where N is the total number of fish species x in the sample, and I is the total number of prey taxa consumed by fish species x. (The data thus obtained for all fish species on each collection date are summarized in the Appendix along with the percentage of stomachs in which a prey taxa occurred.)

Diet overlap was calculated for each fish species paired with every other species collected at each station on the same sampling date, from pooled stomach contents data. The fraction of each fish species’ diet that was shared when paired with each of the other 17

species was calculated with Schoener’s (Schoener 1970) index:

Dp = 1 - 1/2 £ |P*.i - Pjr.,1, (4) i where Dp is the fraction of diet shared (overlap), and P*,i and Py,i are the proportions of prey, i, consumed by fish species x and y, respectively (see equation (3)). Overlap values can range from 0 (no overlap) to 1 (complete overlap), and a value greater than 0.60 is considered to be biologically significant (Wallace 1981). In this study, due to rounding, I considered overlap values greater than or equal to 0.6 (nominally, 60%) to be biologically significant.

To estimate fish preferences for various zooplankton taxa, zooplankton were qualitatively sampled by vertical net tows (120 |im mesh) during diel sampling. Prey selectivity was estimated with the

Linear Index (Strauss 1979):

L = ri - pi, (5) where ri and pi are the relative abundances (expressed as proportions of biomass) of prey item i in the gut and habitat, respectively.

Preference values can range from -1.0, indicating avoidance, to +1.0, for highly preferred prey, or from -100% to +100% when L is multiplied by 100. Preference values were calculated only for prey taxa that are known to have been encountered by a particular fish species, i.e., prey taxa that were found in at least one gut of a particular fish species in the sample. 18

Results

Nearshore Versus Offshore Diets and Dietary Overlaps. 1983

In early July, crustacean zooplankton comprised the majority of

the prey biomass of the young-of-year of all fish species collected at both sites (Fig. 3 and 4), except for the single yellow perch and white

perch specimens at Bono which had consumed a larval fish. While copepods, especially Eurytemora affinis. Acanthocyclops vemalis, and

Mesocyclops edax, were important diet items for some fish species at both sites, cladocerans (mostly Daphnia retrocurva) were obviously more prevalent in nearshore fish diets (Fig. 3 and 4). Daphnia retrocurva was apparently available offshore at Middle Sister on July 13-14, 1983, but was avoided, as evidenced by the negative preference values for D. retrocurva for three of the seven species (Fig. 4).

While crustacean zooplankton continued to comprise the majority of prey biomass for most fish species offshore through August (Fig. 5,

6, and 7), benthic prey became increasingly important to the young-of- year diets of several fish species neairshore (Fig. 8, 9, and 10). In particular, chironomid larvae often comprised a large proportion of the diet biomass of freshwater drum, trout-perch, yellow perch, and white perch nearshore (Fig. 8, 9, and 10), relative to offshore samples

(Fig. 5, 6, and 7).

Diet overlap for the species pairs which were found at both sites was consistently high at both sites only for two: white bass paired with white perch, and white perch paired with yellow perch (Table 3). Figure 3. Prey biomass (percent) consumed by young-of-year fish near-shore (Bono) in western Lake Erie on July 11, 1983. In parentheses is the number of fish included in the sample of diet items. D = Diaphanosoma. Dr = Daphnia retrocurva. Dg = Daphnia galeata mendotae. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. Av = Acanthocyclops vernalis, Dt = Diacyclops thomasi. Me = Mesocyclops edax. and F = fish.

19 Figure 3. Figure Biomass (%) 100 100 *CC 100 25 SC- 75' 100 25 50 75 25 50 75 90 75 75 0< 0 V A ano set (3) smelt Rainbow rj-ec ( Trcjt-perch D D E E A D M F Me Dr Av Ea Ec Dg Dr 0 White bass ( bass White nt prh os) perch Wnite Yellow perch ( perch Yellow n n n uy 1 1983 11, July ■ ■ - ■ , ■ ■ —.- ry Taxa Prey Bono H 12 n_Q ) 11 .re .re r— 12 =L J=

—, —, 1 ,— ,— ,— .— ) ) n 1 .1 I n r—

Figure 4. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish offshore (Middle Sister) in western Lake Erie on July 13-14, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti, D = Diaphanosoma. Dr = Daphnia retrocurva. B1 = Bosmina longirostris. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. Ls = Leptodiaptomus sicilis. Av = Acanthocyclops vernalis. Dt = Diacyclops thomasi. and Me = Mesocyclops edax.

21 Biomass (%) . 100 0 -1 - . - -ICO -75 -75 5 -2 -50 -50 - 50 -5 -25 75 -7 - 5 -2 100- 0 10 -75 -75 -50 -25 00 1 100- 100 100 50 75 75 75 50 50 75 75 - - ' - - ' . ' k D B E E L A D Me Dt Av Ls Ea Ec Bl Dr D Lk Trout-perch Trout-perch Figure 4. Yellow perch(71) White perch (57) perch White White bass( 17) bass( White (* 0 ) uy 14, 1983 , 4 -1 3 1 July ide Sister Middle Prey Taxa Prey 100 0 -1 100 0 -1 -100 75 -7 50 -5 25 -2 75 -7 50 -5 5 -2 75 -7 0 -5 25 -2 100 100 100 25 50 75 50 75 25 50 75 - rswtrdu () G (1) drum Freshwater Gizzard shad shad Gizzard Rainbow smelt (20) smelt Rainbow Preference Percent Composition Composition Percent intc prey Limnetic □ Linear index Linear ( 9 ) Figure 5. Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in western Lake Erie on July 28, 1983. In parentheses is the number of fish included the sample of diet items. Lk = Leptodora kindti. D = Diaphanosoma. Sc = Sida crystalline. Dr = Daphnia retrocurva. El = Epischura lacustris. Ea = Eurytemora affinis. L = Leptodiaptomus. Av = Acanthocyclops vernalis. Dt = Diacyclops thomasi. F = fish.

23 Figure 5. Figure Biomass (%) •CO 100 00 1 100 0 5 25 75 50 75 25 0 5 75 50 75 25 0 O' 0- 0 - - ' - - n n n k S D E E L v t F Dt Av L Eo El Dr Sc DLk elw ec (3) perch Yellow rswtrdu (7) drum Freshwater White bass (17) bass White ht prh (9) perch White a uy 8 1983 28, July ide Sister Middle Prey Taxa n

Figfure 6. Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in western Lake Erie on August 8, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. D = Diaphanosoma. Dr = Daphnia retrocurva. Dg = Daphnia galeata mendotae. Ec = Eubosmina coregoni. El = Epischura lacustris. Ea = Eurytemora affinis. Av = Acanthocyclops vernalis. Me = Mesocyclops edax. F = fish, 0 = Oligochaeta, C = Chironomidae.

25 Middle Sister August 8, 1983 White bass (4) Walleye 0 ) 100 100

25 25

White perch (4) Rainbow smelt (1) 100 100

50 50

Freshwater drum (2) 100 100

75 75

5 0 '

Yellow perch (6) Trout—perch (5) 100 100

75 -• 75

Lk D Dr Dg Ec El Av Me Lk D Sc Dr Ec Ea Av F 0 C Prey Taxa

Percent Composition D Umnetic prey H I Benthic prey

Figure 6. Figure 7. Prey biomass (percent) consumed by young-of-year fish offshore (Middle Sister) in western Lake Erie on August 24, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Lentodora kindti. D = Diaphanosoma. Dr = D a p h n i a retrocurva. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. Av = Acanthocvclops vemalis. Me = Mesocyclops edax. F = fish, be = benthic crustacea, and C = Chironomidae.

27 Biomass {%) 100 too '00 100 25 50 75 50 75 25 50 25 75 25 75 50 0- 0 0 0 - - ' Figure 7. o D. _o k D E E A M F e C be F Me Av Ec Ec Dr D Lk ru—ec (10) Trout—perch Freshwater drum drum Freshwater (10) perch Yellow White fl n JL J 0- JJ Derch Derch 02) JL n 11) C ) 1 (1 uut 4 1983 24. August ide Sister Middle Prey Taxa Prey 100 100 100 25 50 50 75 25 75 25 50 75 0 0 k D E E A W F e C be F We Av Ea Ec Dr D Lk ano sn Rainbow Gizzar mrid hnr() F (1) Emercild shiner P n Percent Composition Composition Percent n BMW orev prey I Benthic Limnetic I sa 1 t (1) shad d et 6 G (6)neit Figure 8. Prey biomass (percent) consumed by young-of-year fish near-shore (Bono) in western Lake Erie on July 28, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. D = Diaphanosoma. Dr = Daphnia retrocurva. Dg = Daphnia galeata mendotae. LI = Leptodiaptomus siciloides. Av = Acanthocyclops vernalis, Me = Mesocvclops edax, F fish, be = benthic Crustacea, C = Chironomidae (larvae and pupae).

29 Biomass (%) n o 5- >• 5" 5" 0" 5' 0- 0 5- O' Figure 8. Figure Lk Trout- Gizzar Yellow Fresh D Dr Dg Dg Dr D prh (15) -perch ae du (2 A (12) drum water . d shad shad d ec (2 B (12) perch „ n n n n , , LI _ n _ _ , .n. v e b C be F Me Av n „ n . l . n 7 c (7) -0 ... IB uy 8 1983 28, July ry Taxa Prey D

Bono 100 100 SO 25 75 25 50 75 25 75 50 O' 0 0

k D g I v e b C be F Me LI Av DrDg D Lk Walleye (1) Walleye ht perch White fl n ht bass White n P ercen t C om position position om C t ercen P n n eti prey Benthic ■ ■ prey Limnetic O 0 F .0)

8 E (8) 30 G Figure 9. Prey biomass (percent) consumed by young-of-year fish near-shore (Bono) in western Lake Erie on August 8, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. D = Diaphanosoma. Dr = Daphnia retrocurva. Ec = Eubosmina coregoni, LI = Leptodiaptomus siciloides. Av = Acanthocyclops vernalis. Me = Mesocvclops edax. N = Nematoda, A = Acarina, be = benthic crustacea, and C = Chironomidae. 32 CO Limnetic prey CO Limnetic ■ i prey Benthic Percent Composition Freshwater drum (6)White bass (3) Freshwater drum (6)White Trout-perch (3) Lk Lk Ec0U Or MeNAv A be C

75 25 50 25 100 100 Bono B A C Prey Taxa August 8, 1983 White White perch fiO) Yellow perchYellow (9} Gizzard shad (5) Lk Lk D Dr Ec LI Av Me N A be C Figure 9. 25 so too 100 100 100 («g) ssDuuoia Figure 10. Prey biomass (percent) consumed by young-of-year fish nearshore (Bono) in western Lake Erie on August 24, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. Dr = Daphnia retrocurva. Ec = Eubosmina coregoni. LI = Leptodiaptomus sioiloides. Av = Acanthocyclops vernalis. Me = Mesocyclops edax, be = benthic Crustacea, C = Chironomidae.

33 Biomass (%) 100 100 100 25 50 75' 25' 100 50' 75 25' 50- 75- 25' 50' O' 75 O' O' 0 Figure 10. Figure ' - ' ' Trout-perch (8) Trout-perch Yellow perch (6; perch Yellow k r c I v e e C be Me Av LI Ec Dr Lk White perch '(5) perch White Freshwater drum (6) drum Freshwater uut , 3 1 8 9 4, 2 August P e rc e n t C om position position om C t n e rc e P eti prey Benthie I ■ prey Limnetic D C PreyTaxa Bono 100 100 100 25- 50- 75 100 25 SO 75 25 50 75 25 50 75 OJ 0 0 0

II k r c I v e e C be Me Av LI Ec Dr Lk shad Gizzard a n White bass (5) bass White ano s l (4-) elt sm Rainbow mrl shinerf2) Emerald IL (5) n n H 34 Table 3. Fish species pairs for which die! overlap was greater than, or equal to, sixty percent (6022) on «ore than one occasion during the study. Species abbreuiations may be found in Table 2. "GE* means diet overlap was greater than or equal to 60X, and *lt* means less than 6072. R dash <~> indicates that at least one member of the pair was either not caught, or had only empty stomachs. The % column indicates the fraction of dates when overlap exceeded 60X for that species pair.

Species Bono Middle Sister Pairs 1983 1983 1984 X 7/11 7/28 8/8 8/24 7/13-14 7/28 8/8 8/24 9/8-9 7/24-2S 8/6 8/21 9/5-6 UBRS-UPCH it EE GE GE GE GE GE - GE 6E GE It It 75 UPCH-YPCH GE GE 6E GE GE It GE GE It GE It It GE 69 HLUF-GSHD ------GE 6E GE It It 60 fiLUF-VIBflS ------It GEGE It GE 60 flLUP-UPCH ------6E GE GE It It 60 RLUF-ESHN------6E It It - GE 50 DRUH-TRTP - It GE GE It - It GE It GE GE It It 45

ESHN-UBflS ---GE - - - . - It It It - GE 40 6SHD-UPCH - It It It It - GE It 6E 6E GE It It 36 SSHO-YPCH - GE It It It - GE It It GE GE It It 36 ORUM-YPCH - GE It GE It It It GE It It It GE It 33 ESHN-GSHO - -- It --- GE 6E It It - It 33 GSHD-UB8S - It It It It - GE - It GE GE It It 30 ORUM-UPCH - It It GE It It It It It GE It It GE 25 Table 3. (continued),

Specie* Bono Middle Slmtor Pair* 1983 1983 1984 X 7/11 7/28 8/8 8/24 7/13-14 7/28 8/8 8/24 9/8-9 7/24—25 8/6 8/21 9/5-6 TRTP-UPCH 11 It It GE GE - It It It It It It GE 25 TRTP-YPCH It It It GEGE - It It GE It It It It 25 RSMT-UBRS It -- It GE - It -GE It It It It 22 RSMT—UPCH It - - It GE - It It 6E It It It It 20 ORUM-uens - It It GE It It It - It It It It GE 18 TRTP-UBflS GE It It It GE - It - It It It It It 18 UBflS-YPCH It It It It GE It It - It 6E It It It 17

LO o> 37

Diet overlap was apparently greater offshore, since sixty-three percent

(63%) of the diet overlap values for all of the species pairs compared between sites (cf. Fig. 11 and Fig. 12) were greater at Middle Sister than at Bono. These differences in diet overlap values between sites were statistically significant (p < 0.001, two-tailed Wilcoxon paired- sample test). However, the differences in diet overlaps between sites varied throughout the sampling season since an analysis of diet overlaps by collection date shows that they were only significantly different (p < 0.05) between sites during early July and early August,

1983.

Prey sizes in July (for example, cf. Fig. 13 and 14) were greater nearshore, at Bono because greater proportions of larger zooplankton such as Daphnia sp. and fish larvae were consumed nearshore (for example, cf. Fig. 3 and 4). By August, most fish species were consuming larger prey (mostly Daphnia sp. and Leptodora kindti. see

Figs. 6 and 7) in greater proportions at Middle Sister (cf. Fig. 17 and

18, and Fig. 19 and 20). Prey eaten at Middle Sister (Figs. 13-20) were generally significantly larger (p < 0.05, G-statistic, Sokal and

Rohlf 1969) for fish species caught at both sites on the same date.

1983 Versus 1984 Diets and Dietary Overlaps, at Middle Sister

There were several differences in fish diet composition between years. In late July, 1984, while copepods such as Acanthocyclops vemalis continued to comprise a large share of the biomass of fish diets, Daphnia galeata mendotae became the most commonly consumed Figure 11. Taxonomic overlap index values for diets of pairs of fish species caught nearshore (Bono) in western Lake Erie during July and August, 1983. The fish species to the left of an ampersand is paired with those listed to the right, groups of pairs are separated by a semi-colon. Fish species names and abbreviations are listed in Table 2.

38 Overlap Index Values Bono July 11, 1983 1.0-r 0.9 j WPCH& YPCH 0.8 j- 0.7 { 0.6 j TRTP & WBAS 0 .5 | TRTP & WPCH; TRTP & YPCH 0.4 +| RSMT & TRTP 0.34-| 0.2 + RSMT & WBAS. 0.1 + 0 .0 -

July 28, 1983 1.0 f 0.9 | 0.8 { 0.7 J WBAS & WPCH; YPCH & DRUM, GSHD 0.6 | DRUM & GSHD; WPCH & YPCH 0 .5 1 DRUM &TRTP. WPCH 0.41 GSHD & TRTP, WPCH; TRTP & YPCH 0.3 + TRTP & WPCH; WBAS & DRUM. YPCH I 0.2+ WBAS & GSHD. TRTP 0.1 I 0.0 -I- WALL & DRUM. GSHD, TRTP. WBAS, WPCH, YPCH

Figure 11. Figure 11 (continued) Overlap Index Values Bono August 8, 1 983 1.0- 0.9- 0.8-- DRUM 3c TRTP 0.7 - WBAS 3c WPCH 0.6- - WPCH 3c YPCH 0.5- - YPCH 3c DRUM, TRTP 0.4- 0.3- - GSHD k WPCH, WBAS 0.2- - GSHD 3c WBAS; WPCH 0.1 -- GSHD 3: DRUM, TRTP. 0.0-

August 24, 1 983 1 .0 t 0.9- 0.8 } DRUM 3c WPCH 0 .7 -j- YPCH & TRTP, WPCH 0.6 " DRUM 3c TRTP, WBAS, YPCH; ESHN 3c RSMT. WBAS; WPCH 3c TRTP, WBAS 0.5 - ESHN 3c WPCH; RSMT 3c WBAS 0.4+ DRUM 3c ESHN; WBAS & TRTP, YPCH 0.3 -- ESHN 3c TRTP, YPCH; GSHD 3c WBAS 0.2 4- GSHD 3c ESHN, RSMT; RSMT 3c YPCH 0.1 + GSHD k TRTP, WPCH, YPCH; RSMT 3c DRUM, TRTP, WPCH 0 . 0 DRUM 3c GSHD Figure 12. Taxonomic overlap index values for diets of pairs of fish species caught offshore (Middle Sister) in western Lake Erie during July and August 1983. The fish species to the left of an ampersand is paired with those listed to the right, groups of pairs are separated by a semi-colon. Fish species names and abbreviations are listed in Table 2.

41 Overlap Index Values

Middle Sister July 13-14, 1983 1 .0 t 0.9 t WBAS & WPCH 0.8-}- YPCH & WBAS, WPCH 0.7 j- RSMT & WBAS, WPCH; TRTP & WBAS, WPCH, YPCH 0.6 - 0.5-- RSMT & TRTP. YPCH 0 .4 " 0.3 + GSHD & RSMT, TRTP. WBAS, WPCH, YPCH 0.2 - 0 .1 " 0.0 -I- DRUM & GSHD, RSMT, TRTP. WBAS, WPCH, YPCH

July 28, 1983

I.Ot 0 .9 - 0.8-- WBAS & WPCH 0 .7 - 0.6 - 0.5 | DRUM & WBAS. WPCH 0 .4 " 0.3- 0. 2 -

0.1 -• 0 .0 -J- YPCH & DRUM, WBAS, WPCH

Figure 12. Figure 12 (continued)

Overlap Index Values

Middle Sister August 8, 1 983 1 .0 T 0.9- 0.8 -f GSHD tc YPCH; WBAS tc WPCH 0.7 -f GSHD tc WPCH; WPCH & YPCH 0.6 -■ GSHD & WBAS 0.5 - WBAS tc TRTP. YPCH 0 . 4 - - DRUM tc WBAS, WPCH; TRTP tc GSHD, WPCH 0.3 + DRUM tc TRTP; TRTP tc YPCH 0.2+ DRUM & GSHD, YPCH 0.1 | GSHD tc RSMT n n i -< RSMT & DRUM- TRTP> WALL- WBAS» WPCH- YPCH u , u ^ WALL tc DRUM, GSHD, TRTP, WBAS, WPCH, YPCH

August 24, 1 983 1.0 j 0.9 - 0.8 } WPCH & YPCH 0.7- 0.6 I DRUM & TRTP, YPCH; ESHN tc GSHD 0.5 -- DRUM tc ESHN, WPCH; ESHN tc WPCH. YPCH 0.4-- TRTP & RSMT. YPCH 0.3-- TRTP & ESHN, WPCH 0.2 -- DRUM tc GSHD. RSMT; GSHD tc TRTP. WPCH. YPCH 0.1 -- RSMT tc WPCH, YPCH 0.0-I- RSMT tc ESHN, GSHD Figure 13. Prey size distributions for the diets of young-of-year fish from nearshore (Bono) in western Lake Erie on July 11, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm).

44 45

Bono July 11, 1983

Yellow perch 12( ) 100

0 CL. White perch (15) 100-

75-

US Q J] White bass (12) S'*? 100

V) 75 V) O 50- E o 25- CD 0 a Trout-perch ( 1 1) 100

75 50- n 25

0- Rainbow smelt (3) 100

75-

SO-

0 0.8 1.6 2.4 3.2 4.0 4.8 7.6 < Prey Size (mm)

Figure 13. Figure 14. Prey size distributions for the diets of young-of-year fish from offshore (Middle Sister) in western Lake Erie on July 13 and July 14, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm).

46 Figure Figure Biomass (%) " 5 0-- o-. 5-- O'. - 0 n.n. n . n t )• J. ■ )■ . % r-i. s■■ )■ 5- - O'. Yell °i - 5 p., Troi Whi Wh . 16 . 32 . 4.8 4.0 3.2 2.4 1.6 0.8 14 tprh(0 D (40) jt-perch wprh(1 C (71) perch ow e t e ss a b te . — .. — .r-i .— ... ,— ...... m m. .m. perch perch (17) (17) 5) B (57) ...... n . . . . . n uy 14, 1983 , 4 -1 3 1 July ry ie (mm) Prey Size Middle Sister Sister Middle * 100 100 100 25. 50. 75- 25 50 75 25 50 7* 0 0 C 06 . 24 . 40 4.8. 4.0 3.2 2.4 1.6 0.6 0 ' Freshwater drum (1) drum Freshwater (9) shad Gizzard Rainbow smelt smelt Rainbow J] ( 20 ) 47 Figure 15. Prey size distributions for the diets of young-of-year fish from nearshore (Bono) in western Lake Erie on July 28, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for chironomidae where prey size is based on width (ran).

48 Biomass {%) too 100 100 100 25 so in 5 • 75 251- 50' 75: 25- 25 50 75 50 75 0 0 08 . 24 . 40 . 5.6 *.B 4.0 3.2 2.4 1.6 0.8 0 ELD Trout-perch (15) Trout-perch J] Gizzard shad shad Gizzard Cl perch Yellow 2) rswtr drum Freshwater Figure 15. Figure a O) 1) A (12) XL ry ie mm) m (m Size Prey uy 8 1983 28, July Bono Bono 1C0 100 100 50 75 25 50 75 25 50 75 0 0 0 WalleyeCi) White perch perch White White bass (8) bass White 0.& 5 2 V5 H O a A . 40 4^8 ‘V6<’ 4.0 3.2 (9) n 49 Figure 16. Prey size distributions for the diets of young-of-year fish from offshore (Middle Sister) in western Lake Erie on July 28, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size classes are based on prey length (mm).

50 Middle Sister July 28, 1983 White perch (9)

a n White bass (17) B

0 a n Freshwater drum (7) C 100

0 j u J j i i i i n L_ Yellow perch (3) D 10 0 '

75-

50-

25-

0- )—i |ll|^ 1 1 1 1 1 1 h-H— f ( 0.9 1.6 2.4 3.2 4.0 4.8 7.6 < Prey Size (mm)

16. Figure 17. Prey size distributions for the diets of young-of-year fish from nearshore (Bono) in western Lake Erie on August 8, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Nematoda and Chironomidae where prey size is based on width (mm).

52 Biomoss (%) 100- 100 100 100 25- 50- 75- 25 50 25 75' 75 25 50 50 75 0- O' 0 0 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0

Figure 17. Figure elw ec 9 c (9) perch Yellow izr sa 5 D (5) shad Gizzard ht prh(0 B (10) perch White White bass (3) bass White H R ry ie (mm) Prey Size uut8 18,August 983 Bono 100 100 25 50 75 25 50 75 0 0 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0

n.l In rswtrdu 6 E (6) drum Freshwater ru-ec 3 F (3) 'rout-perch 53 Figure 18. Prey size distributions for the diets of young-of-year fish from offshore (Middle Sister) in western Lake Erie on August 8/ 1983. Prey size distributions are expressed as the "percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Oligochaeta and Chironomidae where prey size is based on width (mm).

54 Biomass (%) 100 100 100 100 25 50 75 25 50 75 50 25 25 50 75 75 O' 0 0 0 Yellow perch (6) perch Yellow White perch (4-) perch White Gizzard shad (2) shad Gizzard White bass (4-) bass White . 16 . 32 . 48 5.6 4.8 4.0 3.2 2.4 1.6 0.8 □ iue 18. Figure l J=L H ry ie mm) m (m Size Prey uut , 1983 8, August ide Sister Middle 100 100 100 100 25 50 75 25 50 75 25 50 75 25 50 75 0 0 0 0 a, a rswtr drum(2) Freshwater ) Walleye0 ano set0) 0 smelt Rainbow . 16 . 32 . 48 7.6 < 4.8 4.0 3.2 2.4 1-6 0.8 rout—perch(5) n 55 Figure 19. Prey size distributions for the diets of young-of-year fish from nearshore (Bono) in western Lake Erie on August 24, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Chironomidae where size class is based on width (mm).

56 Biomass (%) 100 100 too too? 75 so ?5 Trout-perch (8) Trout-perch Yellow perch (6) perch Yellow iue 19. Figure Freshwater drum (6) White bass (5) bass White (6) drum Freshwater . 60 0.8 0 6.0 4.8 ry ie (mm) Size Prey uut 4 1983 24, August D C B A □ Bono 100 100 100 100 50 Gizzard shad (5) shad Gizzard ,r~). Rainbow smelt (4) smelt Rainbow Emerald shiner (2) shiner Emerald .57 Figure 20. Prey size distribution for the diets of young-of-year fish from offshore (Middle Sister) in western Lake Erie on August 24, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (nan), except for Chironomidae where prey size is based on width (mm).

58 Biomass (%) too 100 IOC too 50 75 25 50 75 25 50■ 75 25 25■ 50• 75 ■ 0 0 • 06 1.6 0.6 2.4 2.2 0 Figure 20. Figure Trout-perchOO) Yeliow perch perch (10) Yeliow White perch (12) perch White rswtrduO) C drumO1) Freshwater n n n ,} . ' a.2 4,.} n, * P uut 4 1983 24, August ry ie (mm) Prey Size idl Sister Mi'ddle U • ICO too 100 50 25 75 25 50 75 25 50 75 0 0 OS . 24 . 40 5.6 4 8 4.0 3.2 2.4 1.6 O.S 0 XL izr shaaO) Gizzard Rainbow smelt (6) smelt Rainbow mrl shiner(l) Emerald 59 60

cladoceran by weight (cf. Fig. 5 and 21). Daphnia galeata mendotae was

preferred in 1984 over retrocurva which was present, .but avoided, as

evidenced by its negative preference values (Fig. 21). In contrast to

1983, Daphnia galeata mendotae continued to be consumed in greater

proportions than Ih retrocurva. in early August 1984 by several fish

species, except gizzard shad which mostly consumed vemalis (Fig.

22).

Among the benthivores, freshwater drum began to consume benthic

prey, especially chironomid larvae, earlier in 1984 than in 1983 (cf.

Fig. 6 and 21). Benthic prey comprised a larger proportion of young-

of-year fish diets (except rainbow smelt) in late August, 1984, when

the diets of those species caught at this time in both years are

compared (cf. Fig. 10 and 23). While the percent contribution of

benthic prey to fish diets increased in September, 1984 for several

fish species, including trout-perch, white perch, gizzard shad,

freshwater drum, and white bass, it decreased for yellow perch when

compared to September, 1983 (cf. Fig. 24 and 25).

With few exceptions, fish diets in early September 1984 included

lower proportions of the relatively large zooplankter, Leptodora

kindti. than in 1983. This prey item was positively selected in 1983 by five fish species (Fig. 24), but in September 1984 not one fish

species was consuming kindti in a proportion equal to, or greater than, its proportion in the environment (i.e., there were no positive preference index values) (Fig. 25). Also note that in the September,

1984 collection, Sida crystallina. also a relatively large zooplankter, Figure 21. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish at the Middle Sister site in western Lake Erie on July 24-25, 1984. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. Dr = Daphnia retrocurva. Dg = Daphnia galeata mendotae, B1 = Bosmina longirostris, Ec = Eubosmina coregoni, Ea = Eurytemora affinis. L = Leptodiaptomus. La = Leptodiaptomus ashlandi. Ls = Leptodiaptomus sicilis. Av = Acanthocyclops vemalis. F = fish, 0 = Oligochaeta, be = benthic Crustacea, and C = Chironomidae. Open bars = limnetic prey, shaded bars = benthic prey, and black bars = preference.

61 62 D E F 1 n i „ HI III n i ™ ■1 _ „ r „ ■ ■ . r Lk Dr Dg Ea Av F n White bass (54) White perch (58) Yellow perch (48) _ : : n i 0 0 0 25 75 50 25 75 50 25 100 100 -25 -50 -75 -25 -75 -50 -25 -50 -75 -100 -1 0 0 -100 Prey Prey Taxa i i i Limnetic prey (TO Benthic prey Middle Sister m Percent Composition Preference I I ■■ Linear index July 24-25, 1984 ------n « n « m shiner(2) C ■ ■ __ s h a n d i (2 6 ) B 1 l | m e (13) A _ Alewif ■ ■ ■ ■» ■» Gizzard S p o ttai Lk Dr Dg Ec L La Ls Av — » • ---1----1----1---- 0 0 75 so 25 75 50 25 100 -25 -50 -50 -75 -25 -75 -IOC -1 0 0 Figure 21. (og) SSDUUOI.a Biomass (%) Figure 21 (continued) Figure -100- -100 -75- -25- -50- 75 5 -7 -50 -25 1DO- 100 25' 50- 75 • 25 SO 75 O' 0

Tr - ch( H ) 3 (2 h rc e t-p u ro T • k r g a v C e b 0 Av Ea Dg Dr Lk - _l 1 - 1 - 111 l _ n - n ehwae du (8 G (38) drum ater w resh F 1 0 . 1 — 1 • . -100) I " 5 -7 0 -5 " 5 2 - > 0 I • 25 50" 00 5 n 75" C. «—0_ J—LUi OJH— 0-_— — —« Cl. 0 Eead hnr4 K { K shiner(4) Emerald " k r g 1 Ec 01 Dg Dr Lk u y2-5 1984 July24-25, Middle Sister ry Taxa Prey — TOO -100 -75! -75! —50i -25- 50 -5 75 -7 25 -2 100 100 25- 50- I ' 25 50 75 0 J Rainbow sm elt (43) elt sm Rainbow Walleye (7) (7) Walleye k g a Av Ea Dg Lk

i --- 1 1 1 I 1 J 63 Figure 22. Prey biomass (percent) consumed by young-of-year fish at the Middle Sister site in western Lake Erie on August 6, 1984. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. Sc = Sida crystallina. Dr = Daphnia retrocurva. Dg = Daphnia galeata mendotae. B1 = Bosmina longirostris. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. La = Leptodiaptomus ashlandi. Av = Acanthocyclops vernalis. Dt = Diacyclops thomasi. Me = Mesocyclops edax, be = benthic Crustacea, 0 = Oligochaeta, and C = Chironomidae.

64 Biomass {%) 100 100 100 100 25 50 25 50 50 25 TC 75 75 25 50 75 • ■ t O Oq Or M n n Gizzard Alewife(5) White bass (6) bass White White perch (6)White perch Figure 22.Figure III II n n n , n l c a c v t e C e b Me Dt Av Lc Ea Ec Bl shed (6) shed n n il n -1 1 uut . 1984 6. August „ 5 ide Sister Middle ry Taxa Prey H M u rv , 5 « ICO ICC 50 25 50 k r g l c g Lc Eg Ec Bl Dg Dr Lk elw perch(5) Yellow Rainbow smell (8) smell Rainbow Emerold shiner (2) shiner Emerold JL Ct Ccr-.srslt/cn c C t tn 'C e r ( S 3 B e o* n r n t~ c■__] £r®y p r » y JL n n fiv Ct Ct t.'e e C be 65 66 Figure 22 (continued)

Middle Sister August 6, 1984 WalleyeO) 100

0 Trout—perch (4) 100

cn 75 co o E 50 o in 25 0- n Freshwater drum(4) J 1 0 0 '

75 50- 25-

o- n Lk S c Dg Ea Av Me F b e 0 Prey Taxa Figure 23. Prey biomass (percent) consumed by young-of-year fish at the Middle Sister site in western Lake Erie on August 21, 1984. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. Dr = Daphnia retrocurva. Bl = Bosmina longirostriB. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. Av, = Acanthocyclops vernalis. Me = Mesocyclops edax. F = fish, O = Oligochaeta, A = Acarina, be = benthic crustacea, and C = Chironomidae. Open bars = limnetic prey, shaded bars = benthic prey.

67 Biomass (%) 100 100 100 0 0 1 100 25+ 75 5 75” 75- 50 - Figure 23.Figure Trout-perch (6) Trout-perch White perch perch White(10) Yellow perch (9) Rainbow smelt (6) smelt Rainbow (9) perch Yellow Freshwater drum(3) Freshwater Spottail shiner (1) shiner Spottail Lk Ea Av e b C be 0 Me uut 1 1984 21, August ide Sister Middle ry Taxa Prey E D C A B 100 100 100 100 25 50 50 75 50 White bass (11 bass White k r l c o v A F Av Eo Ec Bl Dr Lk Gizzard shad (5) shad Gizzard AlewifeO) 68 Figure 24. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish at the Middle Sister site in western Lake Erie on September 8-9, 1983. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. Sc = Sida crystallina. Dr = Daphnia retrocurva. Ec = Eubosmina coregoni. Ea = Eurytemora affinis. Av = Acanthocyclops vemalis. Me = Mesocyclops edax. 0 = Oligochaeta, W = nematode and oligochaete worms, bo = benthic Crustacea, and C = Chironomidae.

69 B i o m a s s (%) 100 0 -1 -100- -100 -100- -75+ -25- -50- -75- -SO- -25' -75' -25- -75- -50' -50- -25- 100- 100 00 10 00 10 25- 50 75 ■ 25' SO- 75- 50- 25- 75- 25- SO' 75- 0- 0- 0- 0-

- '

White White k E E A M 0 b C be 0 Me Av Ea Ec c S Lk m ni n m l Alewife (9) Alewife Figure Figure G izzard sh a d (3) d a sh izzard G Em erald sh in er (17) er in sh erald Em perch perch 24 (44-) . September Middle ry Taxa Prey - -100 100 0 -1 -75- -50- -25 -75 -50 -25 -75 -50 -25 100 100 100 100 8- 50 25 75 25 50 75 25 50 75 Si 0 0 0 ' 9, 3 8 9 ,1 -9 ster eh tr rm 9) G (91) drum ater reshw F Lk D Sc Dr Dr Sc D Lk (4) s s a b White Rainbow sm elt (35) elt sm Rainbow Preference Preference P ercent Composition Composition ercent P I J j ■ I Linear index Linear I ■ prey Bentnic prey B B Limnetic □ E g e e C be 0 Me •jo EL a 70 71 Figure 24 (continued)

Middle Sister September 8—9, 1983

100 • Yellow perch (58) H 75 50 25 0 fl „ - m — H fl fl -25 -50 -75 -1 0 0 100 ■ Trout-perch(90) 1 *-— ■. 7 5 & 50 tn 25 n n « B8 ..fl. I 8 o ■ £ -25 0 -50 S -75 -1 0 0 100 ■ Spottail shiner (76) J 75 50 25 0 ' . . h * 1 -25 -50 -75 -!Q0 Lk Sc Ea Av Me w be C Prey Taxa Figure 25. Prey biomass (percent) and prey preference (in percent biomass) of young-of-year fish at the Middle Sister site in western Lake Erie on September 5-6, 1984. In parentheses is the number of fish included in the sample of diet items. Lk = Leptodora kindti. D = Diaphanosoma, Sc = Sida crystallina. Dr = Daphnia retrocurva. Bl = Bosmina longirostris. Ec = Eubosmina coregoni. El = Epischura lacustris. Ea = Eurytemora affinis. Av = Acanthocyclops vernalis. Me = Mesocyclops edax. 0 = Oligochaeta, A = Acarina, be = benthic Crustacea, and C = Chironomidae. Open bars = limnetic prey, shaded bars = benthic prey, and black bars = preference.

72 Biomass (%) Figure 25.Figure k D B E aA M e C be Av MeEa0 Ec Bl Dr D Lk F resh w ater drum (32) drum ater w resh F White b a ss (16) ss a b White Alewife (11) Alewife rl shi (4 A‘ r(14) e in h s erald m E ni n« ni ni_n« - -TSf -Mf -15 100 ioof Rainbow sm elt (2 9 ) ) 9 (2 elt sm Rainbow ioof sol 25 • *- etme —. 1984 5—6. September T k c r l Ea El Dr Sc Lk Middle Sister ry Taxa Prey 100 0 -1 100 0 -1 100 0 -1 k l cE vM e0 A e C be A AvMa Ea Ec Me 0 Bl Lk »*»_ hb it G izzard sh a d (23) d a sh izzard G elw rh( ) 2 (2 erch p Yellow White perch (29) perch White outper 29) 9 (2 h rc e t-p u ro T i w mffl—

l r r OL . a ..a 73 74

had all but disappeared as a diet item (Fig. 25), while, at this time

in 1983, this zooplankter comprised over 50% of the prey biomass of

freshwater drum, and was an important diet item of several other fish

species (Fig. 24).

While diet overlap between white bass and white perch exceeded

60% in every collection in which both species were caught at Middle

Sister in 1983, overlap values for this species pair were greater than

60% in only two of the four collections in 1984 (Table 3). Although

the incidence of significant diet overlap (i.e., > 60%) was lower in

1984 than in 1983 at Middle Sister (Table 3), there was no significant

difference (p > 0.05, two-tailed Wilcoxon paired-sample test) in diet

overlaps between years.

Different fish species shared food resources to a significant

degree (> 0.60) in 1984. For example, alewife were rarely caught in

1983, but in 1984, they shared food resources with several other fish

species, sometimes by as much as 90%, especially in late July and early

August (Fig. 26).

During the latter weeks of the summer in 1984 young-of-year fish

were preying upon smaller prey than during the same time period in 1983

(cf. Fig. 20 and 30, and Fig. 31 and 32). In 1984, greater proportions

of small prey such as copepods and bosminids (Eubosmina coregoni and

Bosmina longirostris), and smaller proportions of large prey such as

Leptodora kindti. were consumed (cf. Fig. 24 and 25). Although there was no discemable trend during the early summer months (cf. Fig. 16 and 18 to Fig. 28 and 29, respectively), prey size distributions were Figure 26. Taxonomic overlap index values for diets of pairs of fish species caught at the Middle Sister site in western Lake Erie during 1984. The fish species to the left of an ampersand is paired with those listed to the right, groups of pairs are separated by a semi colon. Fish species names and abbreviations are listed in Table 2.

t 76

Overlap Index Values

Middle Sister July 24-25, 1984 1.0 j 0 . 9 - ALWF & GSHD; WBAS & WPCH

0 . 8 -- ALWF & WBAS; GSHD 3c SSHN; RSMT 3c WALL; YPCH & WBAS, WPCH

0 .7 -j- ALWF 3c SSHN, WPCH, YPCH; GSHD 3c WBAS

0 . 6 I DRUM 3c TRTP, WPCH; GSHD 3c WPCH, YPCH; SSHN lc WBAS

0 . 5 ■ ■ DRUM lc ALWF, WBAS, YPCH; SSHN 8c WPCH, YPCH

0 . 4 - DRUM lc GSHD

0 . 3 + DRUM 8c SSHN; TRTP 8c WBAS, WPCH, YPCH . ESHN lc ALWF, DRUM, SSHN, TRTP, WBAS, WPCH, YPCH 0 . 2 -- - < RSMT lc ALWF, DRUM, GSHD, SSHN, TRTP, WBAS, WPCH, YPCH „ „ TRTP 8c ALWF, GSHD. SSHN 0.1 f ESHN 6c GSHD, RSMT 0 . 0 -I- WALL lc ALWF, DRUM, ESHN, GSHD, SSHN, TRTP, WBAS, WPCH, YPCH

August 6, 1 984

1.0-

0 . 9

0 . 8 + DRUM lc TRTP; WBAS lc WPCH

0 . 7

0 . 6 + ALWF lc GSHD, RSMT, WBAS. WPCH; GSHD 8c WBAS. WPCH, YPCH

0 . 5 -- RSMT lc ESHN, GSHD, WBAS. WPCH. YPCH; YPCH & ALWF WBAS, WPCH

0 . 4 + DRUM lc WPCH

0 . 3 - DRUM lc WBAS; TRTP lc WPCH

0 . 2 + ALWF lc DRUM, ESHN; DRUM lc GSHD. RSMT, YPCH; TRTP & WBAS 0.1 ESHN lc GSHD, YPCH; TRTP lc ALWF, GSHD, YPCH ESHN 3c DRUM. TRTP, WALL, WBAS, WPCH; RSMT 3c TRTP 0 . 0 ^ ‘ WALL 3c ALWF, DRUM, GSHD, RSMT, TRTP, WBAS, WPCH, YPCH

Figure 26. Figure 26 (continued)

Overlap Index Values Middle Sister August 21,1 984 1.0 0.9 0.8 - - DRUM k YPCH 0.7 -- SSHN k DRUM, YPCH 0.6 0.5 -- RSMT k WPCH 0.4 -■ GSHD k WPCH 0.3 -- TRTP & DRUM, WPCH, YPCH; WPCH k YPCH 0.2 - ■ ALWF 8c RSMT, WPCH; DRUM 8c WPCH; GSHD & YPCH , GSHD k ALWF, DRUM, RSMT, TRTP; RSMT k TRTP, YPCH 0.1 " “ 'SSHN k TRTP, WPCH .. _/ALWF k DRUM, SSHN, TRTP, WBAS. YPCH; RSMT k DRUM. SSHN, WBAS 0.0 SSHN k GSHD; WBAS k DRUM, GSHD, SSHN, TRTP. WPCH. YPCH

September 5-6, 1984 1.0 0.9 0.8 -- ALWF k ESHN 0.7 -- TRTP k WPCH; WBAS k ALWF, DRUM 0.6 -- ESHN k WBAS; WPCH k DRUM, YPCH 0.5 -- DRUM & TRTP. YPCH; GSHD k WPCH, YPCH; WBAS k WPCH 0.4 DRUM k ALWF, GSHD; RSMT & YPCH; TRTP & WBAS 0.3 DRUM k ESHN; GSHD & TRTP, WBAS; YPCH k TRTP, WBAS , ALWF k GSHD, RSMT, WPCH, YPCH; GSHD k ESHN, RSMT 0.2 RSMT & DRUM, WBAS, WPCH 0.1 ESHN k RSMT, WPCH, YPCH; TRTP k ALWF, RSMT 0.0 ESHN k TRTP Figure 27. Taxonomic overlap index values for diets of pairs of fish species caught at the Middle Sister site in western Lake Erie on September 8-9, 1983. The fish species to the left of an ampersand is paired with those listed to the right, groups of pairs are separated by a semi-colon. Fish species names and abbreviations are listed in Table 2.

78 79

Overlap Index Values Middle Sister

September 8-9, 1983

1 .O t ESHN & GSHD 0 .9 - 0.8 - • ALWF & ESHN, GSHD; RSMT & WBAS 0.7 f TRTP & YPCH; WPCH & ALWF, WBAS 0.6 - SSHN & TRTP; WPCH & ESHN, GSHD, RSMT 0.5 - WBAS & ALWF, DRUM; YPCH & SSHN, WPCH n A ALWF & SSHN, TRTP, YPCH; DRUM & RSMT, SSHN, TRTP, WPCH, YPCH u ‘* ' ' ' RSMT tc YPCH; WBAS & ESHN, GSHD, SSHN, YPCH; WPCH & SSHN, TRTP 0 3 - - - / ALWF

Figure 27. Figure 28. Prey size distributions for the diets of young-of-year fish caught at the Middle Sister site in western Lake Erie on July 24-25, 1984. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Oligochaeta and Chironomidae where prey size is based on width (nan).

80 81 n n. 0.8 0.8 1.6 2.4 3.2 4.0 4.8 < 7.6 White White bass(54) White perchWhite (58) Yellow Yellow perch(48) 0 0 0- 75 50 50' 25 25 75 75- 50- 25- 100 100' 100 Middle Sister Prey Size (mm) July 24-25, 1984 d Figure 28. Figure D Gizzard Gizzard shad(26) Alewife(13) Spottail shiner(2> JZU

. 0 0 0.8 1.6 2.4 3.2 4.0 4.8 5.6 O' 0- 0 50- 75' 75 50 25- 25 75- 25- s o - . 100- 100' 100- ssDuuoig Biomass (%) 100 too 100 25' 50 75 25' 50 75 25 75 50 0- ' . O' O' iue28(continued) 8 2 Figure

08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0

Emerald shiner (4) shiner Emerald rswtr rm(8 G (38) drum Freshwater 'rout—perch (23) n n I a L £ uy 25, 1984 , 5 -2 4 2 July ry ie (mm) Size Prey ide Sister Middle 100 100 25 50 75 25 50 75 0 0 Walleye (7) ano smeit(43) Rainbow . 16 . 22 . 48 7.6< 4.8 4.0 2.2 2.4 1.6 0.8 ,n,n, -4r- 82 Figure 29. Prey size distributions for the diets of young-of-year fish caught at the Middle Sister site in western Lake Erie on August 6, 1984. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Oligochaeta and Chironomidae where prey size is based on width (mm).

83 Biomass (%) 100- 100 100' 100 25- 50- 75- 25 50- 75 25' SO' 75' 25 50' 75- 0- o- 0- O’ ' H H Figure 29.Figure Gizzard shad (6) shad Gizzard Alewife (5) White perch (6) perch White White bass (6) bass White . 16 . 32 . 48 5.6 4.8 4.0 3.2 2.4 1.6 0.8 a a n XL ry ie (mm) Size Prey uut , 1984 6, August ide Sister Middle 100 100 100 25' 50- 75 25 50 75 25 50 75 0- 0 0 Yellow perch (5) perch Yellow mrl shiner(2) Emerald ano smelt(8) Rainbow . 16 2 1.6 0.8 A . 40 . 5.6 4.8 4.0 3.2 84 Figure 29 Figure (continued)

Biomass 100- 100 100 25- SO- 75- 25' 50 75 25 75 50 0- 0 08 . 2.4 1.6 0.8 0 Freshwater drum (4)drum Freshwater Trout—perch(4). Walleye(l) ry ie (mm) Size Prey a uut , 1984 6, August ide Sister Middle 3.2 . 48 7.6 < 4.8 4.0 Figure 30. Prey size distributions for the diets of young-of-year fish caught at the Middle Sister site in western Lake Erie on August 21i 1984. Prey size distributions are expressed as the percent biomass consumed within each prey size class. Prey size is based on length (ran), except for Chironomidae where prey size is based on width (ran).

86 Biomass (%) 100 100 100 25- 50' 100 75 25 100 50 75 25 50 75 25 SO 75 25 0 50 75 0 0 0 0 Figure 30. Figure 08 . 24 . 40 . 7.6 4.8< 4.0 3.2 2.4 1.6 0.8 0 .a n outper 6) (6 h rc e t-p u ro T ht per (10) h rc e p White elw ch(9) h rc e p Yellow ehwae du () B (3) drum ater w resh F oti shi l) ( r e in h s pottail S u II II ry ie mm) m (m Size Prey uut , 1984 1, 2 August ide Sister Middle 100 100 100 25 100 50 75 25 SO 75 25 50 75 25 50 75 0 0 0 0 08 . 24 . 40 . 7.6 < 4.8 4.0 3.2 2.4 1.6 0.8 0 Q White b a s s (11) s s a b White Rainbow sm elt (6) elt sm Rainbow AlewifeO) zad had(5) d a sh izzard G EL n 87 Figure 31. Prey size distributions for the diets of young-of-year fish caught at the Middle Sister site in western Lake Erie on September 8-9, 1983. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Nematoda, Oligochaeta, and Chironomidae where prey size is based on width (mm).

88 Biomass (%) r- .n.n.n 3 5" D- - 5 O'1 0 0 _ S' ID ■ '5' X) • )• 5" White 5 5" • 5 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0 ^ Jill Alewife(9) Gizzard shad (3) shad Gizzard mrl shinerO Emerald Figure 31.Figure ...... ( ) 4 (4 h c r e p etme 8-9, 1983 , 9 - 8 September ) A 7) ry ie (mm) Size Prey ide Sister Middle D c B 100 100 100 25 50 75 25 50 75 25 50 75 0 0 0 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0 l W Freshwater drum(9l) drum(9l) Freshwater White bass (4-) bass White Rainbow smelt (35) smelt Rainbow n XI £ g 89 Figure 31Figure (continued)

Biomass (%) 100 100 100 so 25 etme 8-9, 1983 , 9 - 8 September Trout-perch(90) Spottail shiner (76) shiner Spottail (58) perch Yellow ry ie mm) m (m Size Prey Middle Sister

Figure 32. Prey size distributions for the diets of young-of' -year fish caught at the Middle Sister site in western Lake Erie on September 5-6, 1984. Prey size distributions are expressed as the percent of prey biomass consumed within each prey size class. Prey size is based on length (mm), except for Oligochaeta and Chironomidae where prey size is based on width (mm).

91 Biomass (%) Figure 32. Figure 100 too 100 50 100 25 75 25 50 75 50 25 75 25' so 75 0 0 o 0 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0 la Freshwaterdrum(32) White bass (16) Alewife'(H) Emerald a shiner shiner n (14) etme 1984 , 6 - 5 September rySz (mm) Size Prey ide Sister Middle 100 100 100 100 25 30 100 73 25 50 In 75 25 50 75 25 SO 75 25 SO 75 0 0 0 0 0 08 . 24 . 40 . 5.6 4.8 4.0 3.2 2.4 1.6 0.8 0 Q Q a la Yellow perch(22) Gizzard shad (23) a no ml 2) I Rainbow smelt (29) White perch (29) Trout-perch(29) H 92 93 significantly different (p < 0.05, G-statistic, Sokal and Rohlf 1969) between years for every fish species on each collection date, except for rainbow smelt in early August (cf. Fig. 18 and 29).

Discussion

There were obvious differences in diet composition between the nearshore and offshore sites in 1983, and between years, 1983 and 1984, at the offshore site (Middle Sister). Most notably, young-of-year fish included greater proportions of benthic prey in their diets nearshore than offshore in 1983 (cf. Figs. .5-10), and in 1984 compared to 1983 at the offshore site (e.g., compare Fig. 24 and Fig. 25). Other researchers have observed yellow perch shift to benthic prey when zooplankton availability declined (Wu and Culver in press, Crowder et al. 1987, Mills and Forney 1981). Zooplankton data are not available for the nearshore site, however, for the offshore site there was no significant difference (p > 0.20, n(iss3)=4, no«84)=5, Mann-Whitney la test) between years in zooplankton biomass (mg zooplankton/sample) on the dates on which diel fish sampling was performed (see Table 1).

Makarewicz (1988) observed a substantial decrease in zooplankton abundance in all basins from 1983 to 1984, but he does not state whether this was statistically significant. Therefore, the inclusion of greater proportions of benthic invertebrate prey in 1984 compared to

1983 at Middle Sister cannot be confidently ascribed to a reduction in zooplankton availability.

When fish species change their diets to include larger 94

proportions of benthic prey, they often will then achieve a greater

dietary separation from other species that do not switch. For example,

when freshwater drum switched from a predominantly planktonic diet on

July 28, 1983 to a benthic invertebrate diet at Bono on August 8, 1983,

the mean diet overlap with the young-of-year community simultaneously

decreased by eighteen percent (18%) (Table 4). This trend occurred at

Middle Sister also, but only weakly in 1983 (Table 4). Mean diet

overlap with the young-of-year community decreased by fourteen percent

(14%) when yellow perch increased the proportion of benthic prey in its

diet at Bono in early August, 1983 (Table 5). However, this trend was not evident at Middle Sister in 1983, and only weakly so, at Middle

Sister, in 1984 (Table 5).

Thus, some fish species may switch to benthic prey in response to the presence of other fish species that are feeding on the same food resources - triggered, perhaps, by interference competition. It is also possible that juvenile fish avoid pelagic zooplankton prey in response to the presence of predators (Turner and Mittelbach 1990).

However, exploitative competition for rare zooplankton prey cannot be ruled out by these results because data on zooplankton availability at

Bono were not available.

When considering whether diet overlap may affect prey selection by young-of-year fish in western Lake Erie, it must be kept in mind that resource partitioning occurs along dimensions in addition to prey type. Further resource partitioning, along a prey size gradient, for example, should increase the number of fish species which can co-exist 95

Table 4. Switching to benthic prey by freshwater drun as a function of mean overlap. Mean percent overlap + SD and the percentage of benthic prey in fish diets are shown for selected dates. Differences among mean diet overlaps are not significant (p > 0.05) (student’s t-test, two-tailed, performed on arcsin- transformed data). n for mean overlap is the number of overlap values; n for percent benthic prey is the number of fish in the sample with food.

______Bono______Middle Sister_____ Date Mean Percent Mean Percent (mo/day/yr) Overlap Benthic Prey Overlap Benthic Prey

7/28/83 52+15 16 33+29 3 (n=5)

8/8/83 34+31 85 25+15 57 (n=5) (n=6) (n=6) (n=2)

7/24-25/83 _ 42+16 42 (n=9) (n=38)

8/6/84 _ 29+24 2

8/21/84 __ 26+32 75 (n=8) (n=3) 96

Table 5. Switching to benthic prey by yellow perch as a function of mean overlap. Mean percent overlap + SD and the percentage of benthic prey in fish diets data are shown for selected dates. Differences among mean diet overlaps are not significant (p > 0.05) (student’s t-test, two-tailed, performed on arcsin transformed data). n for mean overlap equals the number of overlap values; n for percent benthic prey equals the number of fish in the sample with food.

______Bono______Middle Sister_____ Date Mean Percent Mean Percent (mo/day/yr) Overlap Benthic Prey Overlap Benthic Prey

7/28/83 54+18 5 0+0 0 (n=5)

8/8/83 40+20 35 42+31 0 (n=5) (n=9)

8/24/83 43+24 55 43+26 0 (n=7) (n=6)

9/8-9/83 _ 41+14 45 (n=9) (n=58)

8/6/84 _ 38+21 0 (n=8)

8/21/84 _ 30+30 70 (n=8) (n=9)

9/5-6/84 — _ 36+17 25 (n=8) (n=22) by decreasing the shared proportion of each species’ niche hypervolune

(Whitakker 1972). For example, for white perch-white bass and white perch-yellow perch species pairs, mean diet overlap is significantly

reduced (p < 0.05, Student’s t-test, arcsin-transformed data) when overlap across prey size classes is factored into the calculation of

total diet overlap, D» (Table 6). Dt was obtained by multiplying Dp by

D s, where Dp is diet overlap based on prey type from equation (4) and

Da is diet overlap based on prey size obtained by substituting prey size class i for prey taxon i in equation (4). Separation along other resource gradients would further reduce niche overlap, increasing the opportunities for co-existence in western Lake Erie.

To compere the diets of young-of-year fish observed in this study to those observed by Price (1963) in 1958, the 1983 data from the nearshore and offshore sites were pooled because Price's data were also pooled from fish obtained at nearshore and offshore sites. Also, because Price (1963) presented his data for each fish species by size class rather than age class, I assumed that the fish in his study that were in size classes falling within the range of young-of-year fish total lengths observed in this study for each species were also young- of-year . Thus, data from Price (1963) for only those size classes that were co-extensive in length with the fish in this study were included in the comparison.

Between 1958 and 1983, amphipods and insects declined in their proportional contribution to small fish diets (Table 7). Most fish species compensated for these reductions by increasing the proportion Table 6. Estimated proportional overlap when another resource dimension, prey size, is considered. For ease of comparison, the proportion of diet overlap based only on prey type is provided in parentheses in the next row. The mean overlap, ♦ 50, for each species pair over all collection dates is presented in the column to the right. See Table 2 for fish species abbreviations.

Spacia* B o n o Hlddl a S i s U r Pair* 1983 1983 1984 X 5/11 7/28 8/8 8/54 7/l3-i6 5/28 8/8 8/24 6/8-9 7/24-25 6/6 6/21 9/5-6 UPCH-UBRS 0.2 O.S 0 . 5 0.4 0 . 9 0.7 0.6 - 0 . 3 0 . 7 0.6 0 . 0 0 . 3 0 . 4 8 ♦ 0 . 2 5 (0.5) <0.7) <0.7) <0.6) <0.9) <0.8) <0.6) - <0.7) <0.9) <0.8)<0.0)

lO 00 Tab 1* 7. Fish diets in tha uastcrn basin oF Lak* Erie in 1958 and 1983. Percent pray caapo*i t ion For* 1958 was calculated fro* pooled annual pray uoluaas provided by Price (1963), For Fish size classes containing the aaxlaua Fish total length observed in 1983, and saaller. Data For 1983 were calculated Froe pooled prey bioeass (see Methods, supra) For all 1983 collections. In parentheses under the year is the number oF stomachs In the samp le. For yellow perch, number in parentheses is the percent composition when two Incidences oF larval Fish consumption are omitted, t = trace and p — present.

Yellow Trout Gizzard Spottai1 Smelt Drum Uhite Bass • Perch Perch Shad Shiner <<100mm> <<100mm> (<76mm) <<100mm) <<152mm> (<76mm) 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983 number samp1ed 655 69 242 136 609 70 158 187 1346 182 198 322 319 76

Rlgae P t 63.1 P 0.3 Nematoda t t t 16 Ol igochaeta 3.1 0.7 0.1 0.5 4.8 2.5 5 1.2 2 (1.1) Hirudinea 0.7 t 5.0 1.2 Rearina 1.4 4 C 1 adoce-ra S6.0 40.2 11.0 16.3 38.0 44.4 52.9 18.3 7.4 23.1 20.2 95.1 18.5 38 (38.4) □stracoda 0.3 1.7 4.6 0.1 0.7 1.4 8.7 3.1 (1.5) Copepoda 43.4 59.4 4.5 55.3 9.5 54.9 20.0 19.4 2.4 29.7 7.5 4.3 1.5 2 (40.8) Rmphipoda 0.1 20.4 0.3 0.6 1.2 0.1 9.3 0.5 0.2 0.9 (0.2) Table 7. (continued),

Yellow Trout Gizzard Spottai1 Smelt Drum Uhite Bass Perch Perch Shad Shiner (<76mm) (ClOOmm) (<100mm) ( (<152mm) <76mm) 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983 1958 1983

Isopoda 0.2 <0.4) Gastropoda t

Pelecypoda 0.1 t 0.5 17.6 Diptera 0.2 51.7 20.7 11.5 25.0 8.0 54.9 34.7 0.2 41.8 33 <16.8) lnsecta 2.7 • 0.3 0.7 0.1 8.3 0.2 17.1 (non-dipterous) (0.2) Fish 39.6 52.4 (0.0) 100 101

of crustacean zooplankton (i.e., cladoceran and copepods) in their diet

(Table 7). Hayward and Margraf (1987) observed a decrease in consunption of amphipods and non-dipterous insects by yellow perch (>

75 ran) in western Lake Erie between 1958 and 1983 which they attributed to the effects of cultural eutrophication. Larger yellow perch tended to replace these prey by increasing their consumption of mollusks, oligochaetes, Chironomidae (Diptera), and zooplankton (Hayward and

Margraf 1987). Small yellow perch (< 75 nm) sampled in this study were not as affected by the decline in the availability of these prey since

1958, because zooplankton comprised the majority (> 70%) of their diets in 1958, as in 1983 (omitting the two individuals that consulted a larval fish) (Table 7). Thus, among the fish species compared, young- of-year yellow perch, rainbow smelt, and, perhaps, gizzard shad, were least affected by the decline in amphipods and insects, because they are primarily zooplanktivorous during their early life history (Table

7).

However, since more fish species were consuming relatively large proportions of zooplankton prey in 1983 than in 1958, diet overlaps in

1983 may be expected to be greater than in 1958. To test this hypothesis, I used the data in Table 7 and equation (4) to calculate diet overlaps for 1958 and 1983 (Table 8). Diet overlaps were found to be significantly greater in 1983 when compared to 1958 (p < 0.001, paired Student's t-test on arcsin-transformed overlap values). Thus, as populations of prey species, such as amphipods and insects, diminished due to the cultural eutrophication of western Lake Erie, the likelihood of competition among young-of-year fish increased. 102

Table 8. Diet overlap among young-of-year fish in 1958 and 1983 in western Lake Erie. Data for 1958 are from Price (1963). For yellow perch in 1983, percent composition without larval fish were used (see Table 7). Fish species abbreviations are summarized in Table 2.

Species

RS GS SS FDTP WB YP

pecies 1958 CM 00 00 1 1 1 • RS • .20 .16 .10 .74

GS -- .21 .17 .12 .28 .28

SS -- .59 .61 .33 .47

FD -- .79 .28 .43

TP -- .22 .37

WB -- .60

YP --

1983 • -O RS -- .45 .40 to .53 .95 .79

GS -- .42 .21 .30 .49 .44

SS -- .41 .60 .40 .58

FD -- .71 .71 .76

TP -- .53 .72

WB ___ .79 CHAPTER III

RESOURCE AVAILABILITY FOR YOUNG-OF-YEAR FISH

IN WESTERN LAKE ERIE: A BIOENERGETICS APPROACH

Introduction

Estimates of niche overlap among young-of-year fiBh (Chapter II), alone, are insufficient to determine whether any fish species may be competing for food resources - it is also necessary to know whether food resources are limiting (Gause 1934). The bioenergetics approach, which applies the First Law of Thermodynamics (Phillipson 1975), has been successfully used to gain insight into fish growth and resource availability (for a review, see Soofiani and Hawkins 1985). The general equation:

G = C - (R + F + U), (6) where G is the energy stored in tissues (growth), C is the energy consumed, R is the energy used in metabolic processes, and F and U are the amounts of energy lost through feces and excretory products

(urine), respectively (Elliott 1979, 1976a, Ursin 1979, Webb 1978), can be used to assemble an energy budget. Estimates of any two of the main components (i.e., considering energy lost to the environment,

103 104

R + F + U, as one component) can be used to obtain an estimate of the

third.

The effects of competition among fish species can be more easily

measured by changes in growth rates in controlled enclosure experiments

(Hanson and Leggett 1985). However, such manipulations are not

feasible in a large lake environment. Additionally, growth rates are

not a good measure of resource availability among wild populations because estimates of growth rates of the young-of-year of natural fish

populations are affected by inmigration, emigration, size selective

sampling, and by size selective mortality through predation or other causes (Bagenal and Tesch 1978). Also, fish growth rates are highly plastic and can respond to abiotic factors, such as temperature, that are unrelated to the availability of food resources (Weatherley 1990).

A better indicator of resource availability for natural fish populations is the energy available for growth, although difficult to obtain because of the difficulties associated with estimating the respiration rates of active fish in the wild (Soofiani and Hawkins

1985). This study attempts to overcome some of these difficulties by applying estimates of respiration rates of swimning young-of-year fish, obtained in the laboratory, to young-of-year fish in the western basin of Lake Erie. Because the energy required to pursue prey and to escape predators is indeterminable, I calculated the amount of energy necessary for a juvenile fish to maintain itself within a specific area of the lake. Thus, the energy surplus (or net energy), obtained by deducting the energy necessary for in situ maintenance from the energy 105

consumed, is the amount of energy available for survival activities,

such as pursuing prey and escaping from predators, and growth.

The bioenergetics approach was used by Kitchell et al. (1977) to

model an energy budget for yellow perch in western Lake Erie, including

young-of-year. However, they assumed an activity factor of 1.0, so the

energetic costs of swimming were not included in their bioenergetics

model (Kitchell et al. 1977). Mills and Forney (1981) used the

bioenergetics approach to estimate the energy available for growth of

young-of-year yellow perch in Oneida Lake, New York. Their estimates

of metabolism did incorporate foraging and food utilization, but because swimming activity was not controlled they could only

characterize their estimates of metabolism as somewhere between standard and active (Mills and Forney 1981). To assemble an energy budget for young-of-year white bass in Lake Mendota, Wisconsin, Wissing

(1974) measured the respiration rates of groups of feeding fish, but also did not control swimming speed.

Therefore, in this study, I designed and used a flow-through respirometer to model the energetic costs of swimming for young-of-year of freshwater drum (Aplodinotus grunniens), white bass (Morone chrysops), white perch (Morone americana), and yellow perch (Perea flavescens) from western Lake Erie. These fish species were used because data obtained from stomach contents suggest that these species frequently exhibit relatively high diet overlap (Table 3, Chapter II), and may be competing if food resources are limiting.

Because fish species may differ in energy resource requirements 106

for maintenance and in consumption rates, I used the model obtained from the respiration experiments to estimate the in situ energy

requirements of average-sized young-of-year freshwater drum, white bass, white perch, and yellow perch in the western basin. These estimates of in situ maintenance requirements were compared against energy intake (consumption) to determine whether these fish species were able to satisfy those requirements. The magnitude of the surplus energy consumed provides an estimate of the relative competitive abilities of the young-of-year of these fish species.

Methods

Energy Losses

Energy lost through metabolism, R, in equation (6), above, can be further broken down into its components:

R = Rb + Ra + Rd, (7) where Rb is the energy of metabolism for unfed and resting fish, R a is the energy required for swimming and other activity, and Rd is the energy required for digestion (Elliott 1976a). To obtain an estimate of Rb + Ra (hereinafter, Rb+a), respiration rates of unfed fish swimming at different speeds were obtained, and Rd was estimated as a fixed percentage of consumption (Kitchell et al. 1977).

Fish respiration rates were measured in a continuous flow, closed loop respirometer that was designed after the system of Brett (1964).

The apparatus included a chamber (approximately 230 ml), constructed of 107

glass, that had a stoppered access port through which fish could be

introduced to, and removed from, the chamber, a port for an oxygen probe, and a port for a temperature probe (Fig. 33). To reduce turbulent flow, two screens were placed at the front of the chamber. A screen was also placed at the rear of the chamber to prevent fish from being swept out. If necessary, a mild electric charge, using two D batteries as a power source, could be placed between a brass ring and the rear screen (Fig. 33) to encourage the fish to swim upstream. To prevent fish from seeking refuge from the flow, a floor was placed across the bottom and an extended stopper was used to completely occupy the access port (Fig. 33).

Flow through the system was generated by a submersible centrifugal pump that was controlled with a rheostat. The circulating water in the respirometer was supplied from an aerated reservoir

(carboy) of well water. The temperature of the water in the respirometer was maintained at Lake Erie surface (0-1 m) temperature by passing it through a copper coil immersed in the fish holding tank filled with continuously circulating Lake Erie water. There was no significant difference (p > 0.05, paired Student’s t-test, two tailed) between the lake surface temperature and the temperature of the respirometer water for the duration of the study. The total volume of the respirometer was approximately 420 ml, or 465 ml, depending upon the configuration of apparatus, i.e. length of tubing, copper coil, etc., used on a particular day.

Dissolved oxygen in the respirometer was monitored with a Yellow Figure 33. Schematic drawing of the respiration chamber designed for this study (see text).

108 3.2 cm 1.1 cm M H Oxygen Probe Port Access Port

Diffusion Screens \ o Brass Ring • Screen (Chargeable)

Thermistor Port 4.4 cm

Figure 33. 110

Springs Instruments (YSI) probe model #5331 that was connected to a YSI model #53 meter. Die meter was connected to a Bausch and Lomb

Ctani Scribe™ plotter. The meter, and plotter base lines were calibrated by measuring the concentration of dissolved oxygen with the modified (azide) Winkler titration method (Wetzel and Likens 1979).

Young-of-year freshwater drum, white bass, white perch, yellow perch were obtained from Lake Erie by seining nearshore, or by bottom trawls (performed off the Ohio State University’s research vessel,

Biolab, by students and researchers at the Franz Theodore Stone

Laboratory, Put-in-Bay, Ohio). The fish were kept in a tank that was continuously supplied with fresh Lake Erie water, and were maintained on a photoperiod of approximately 16 hours light, 8 hours dark. The fish held in captivity were fed zooplankton once a day. However, before each respiration experiment, fish were isolated and starved for at least 24 hours because ingested food is known to affect oxygen consumption (Jobling 1981, Glass 1968). To prevent fish from feeding and to help acclimate the fish to the confines of the respirometer, several individuals were isolated, within the holding tank, in a 500 ml beaker. The beaker was covered with large mesh (0.5 mm) netting to exclude zooplankton, and an air stone was inserted into the beaker to prevent oxygen depletion. In spite of this precaution, a few fish stomachs or intestines were found to contain food at the completion of a series of trials, and were excluded from the analyses.

Before and after an experiment (i.e., a series of trials) with a particular fish, the oxygen demand of the respirometer was measured. Ill

Hie mean rate of oxygen consumption of the respirometer without fish was used as a control for the intervening series of trials with fish.

At the start of a trial, either for a control or with a fish, the respirometer was flushed with aerated water until the oxygen meter indicated a return to the initial oxygen concentration. To facilitate acclimation, the chamber was painted dark green and illuninated by a 60

Watt incandescent bulb positioned approximately one meter above the chamber to simulate sunlight. Observations of fish behavior were noted, and trials where the fish appeared agitated were excluded from the analysis. A trial was initiated by closing off the outflow and inflow to the loop, and adjusting the rheostat to the appropriate flow rate. Two flow rates, 1 cm/s and 2 cm/s, were used, alternately. At the end of the trial, the pump was shut off, a water sample was taken to determine the concentration of ammonia-nitrogen, and the inlet and outlet were sequentially opened to flush the respirometer. At no time was the dissolved oxygen concentration allowed to decrease below 5.0 mg/L and it rarely went below 6.0 mg/L. The temperature of the respirometer water was measured with a thermistor (calibrated with a mercury thermometer). When a series of trials was completed for a particular fish, it was anesthetized with MS-222, towel dried, measured, weighed (wet), examined for food, and then dried to constant weight at 80*C.

The continuous plot of the change in oxygen concentration over time was sampled at the start of each trial (to) and every three minutes thereafter. After converting oxygen concentration to the 112

amount of oxygen consumed by multiplying by the volttne of the respir

ometer, the rate of oxygen consumption (mg Oj/min) was obtained by

least squares regression. Trials with fish lasted from 9 to 26

minutes, so no fewer than 4 points were used to calculate a regression.

The slopes of the regression thus obtained for trials with fish were

adjusted for the oxygen taken up by the respirometer by subtracting the

mean slope of the regressions for the controls. The mean rates of

oxygen consumption for each of the two flow rates used in each

experiment were analyzed with the General Linear Models Procedure (GLM)

of SAS, using swimming speed (body lengths/s), temperature (°C), and

fish weight (g) as the independent variables. Oxygen consumption rates

were converted to caloric equivalents using the factor, 3.24 cal/mg O 2,

recommended by Elliott and Davison (1975) for ammoniotelic carnivorous

fish.

To obtain several oxygen consumption curves for small fish at each flow rate within a sufficiently short period of time so as to avoid fatiguing the fish, several fish (< 1.5 g) of nearly equal length were simultaneously placed in the respirometer. This was necessary for six of the eight experiments with yellow perch and one of the eight experiments with white perch. For such experiments, the total fish biomass (g) and swimming speed (body lengths/s) based upon the mean total length of the fish in the chamber, were used as independent variables, as discussed above. A summary of the sample sizes, fish sizes, and temperatures used in the respiration experiments for each fish species is presented in Table 9. 113

Table 9. Sunnary of sample sizes, fish sizes, and temperatures used in respiration experiments for each fish species.

Range of Range of No. ■ Range of Fish Total Tempera Fish No. Experi No. Biomass(gm) Length ture Species Fish ments Trials wet dry (cm) (°C)

Fresh water drum 2 2 9 1.9-2.6 0.35-0.49 6.2-7.3 24.1-25.1

White bass 3 3 14 1.9-3.1 0.43-0.68 6.0-6.9 25.0-26.5

White perch 9 8 33 1.3-3.5 0.27-0.85 5.1-6.9 24.0-26.2

Yellow perch 20 8 37 2.0-4.8 0.43-1.01 5.1-6.9 25.9-27.5

Totalb 34 21 95 1.3-4.8 0.27-1.01 5.1-7.3 24.0-27.5 a One experiment is a series of trials at two flow rates, 1 cm/s and 2 cm/s, with a given fish, or group of fish (see text). b Where a number is given the sum of the column is shown, and where a range is given, the range for all fish subjects is provided. 114

At the end of each trial a water sample was taken to measure the

concentration of ammonia-nitrogen using the colorimetric method of

Parsons et al. (1984). Control runs without fish were also analyzed.

The rate of ammonia-nitrogen generated (mg NHa-N/min), or excretion

rate, was calculated by multiplying the NH3-N concentration by the

volume of the respirometer and dividing by the duration of the trial.

The rates thus obtained were analyzed with the GLM, using the same

independent variables as in the analysis for oxygen consumption.

Excretion rates were converted to caloric equivalents using 5.94 cal/mg

NH 3-N, the factor recommended by Elliott and Davison (1975).

Energy lost by egestion (F) was estimated as a percentage of

consumption. According to Bartell et al. (1986), using a proportion of

the energy ingested to estimate egestion adds little error to energy

budget calculations. In this study, egestion was estimated as 16X of

consumption (i.e., 0.16C) (Kitchell et al. 1977).

The energy lost during digestion of food, Rd, including specific

dynamic action (Elliott 1976a), was similarly modeled as a proportion

of consumption, although it represents a potential source of error

(Beamish and Trippel 1990, Bartell et al. 1986). Ideally, the increase

in oxygen consumption due to digestion and internal movement of food would have been directly estimated, but this was not feasible with the

flow-through respirometer used. Therefore, Rd, was estimated as

0.17(C-F) which is within the range of proportions reported for estimating specific dynamic action (Beamish and Trippel 1990, Hewett and Johnson 1987), a major component of Rd (Webb 1978). 115

Consumption

Fish consumption rates were estimated from diel samples (obtained

at three hour intervals by otter trawls performed off the Ohio Division

of Wildlife’s research vessel, Explorer II on four occasions near

Middle Sister Island in western Lake Erie (Fig. 2, Table 1)) using the

method of Elliott and Persson (1978):

Ct = (St - So - e-rt) rt , (8) 1 - e-ft

where Ct is the amount of food consigned in t hours, So and St are the

relative stomach contents at the beginning and end of the interval

between trawls, respectively, and r is the rate of gastric evacuation.

The sian of Ct over a twenty-four hour period yields the amount of food

consumed per day (Co). Median values of relative stomach contents were

used for So and St after Cochran and Adelman (1982).

The gastric evacuation rates, r (expressed as h -1> or 100(r)

equals %h_1), were estimated from the slopes of the curves fitted to

loge-transformed relative stomach contents data (Cochran and Adelman

1982) obtained from wild fish. For example, for yellow perch on July

13-14, 1983 (Fig. 34), I assumed that feeding ceased after attaining a maximum at 2300 h so that the subsequent rate of decrease in relative stomach contents, until 0830, represents only evacuation; the slope of this portion of the curve equals r. This method is similar to the method used by Kolok and Rondorf (1987) to estimate gastric evacuation rates for juvenile chinook salmon in the Columbia River. Gastric Figure 34. Median and quartiles of relative stomach dry weight for yellow perch (Perea flavescens) versus time of day on July 13-14, 1983 at Middle Sister in western Lake Erie. See Table 10 for the slope (evacuation rate, r) and standard error (SE) for the portion of the curve between 2300 and 0800.

116 Figure 34. Figure

mg Food/gm Fish Dry Weight 20 25 30 15 10 70 00 2300 2000 1700 200 Time 0 800 500 YELLOW PERCH YELLOW July 13/14, 1983 13/14, July 10 1400 1100 118 evacuation rates that were statistically different from zero (p < 0.05) ranged from 8.4%/h to 28.2%/h, i.e. from 11.9 h to 3.5 h, respectively.

To determine whether any of these evacuation rates could be combined, a

Student-Newman-Keuls multiple range test was used to perform the multiple comparisons among slopes (Zar 1974). These results Eire summarized in Table 10. The evacuation rates for freshwater drum and white bass that are enclosed within a box in Table 10 are significantly different (p < 0.05) from the value for white perch in the other box, but boxed rates axe not significantly different from any of the unenclosed rates. Therefore, to simplify calculations with equation

(8), the mean evacuation rate, 0.18h-1 (which is the mean of all evacuation rates, with, and without, r for white perch in September

1984) was used for all fish species except white perch on September 5-

6, 1984. For white perch on that date, r w?as set to 0.20h_1 (which is the mean evacuation rate excluding r for freshwater drum and white bass in September 1984).

Consumption rates were converted to caloric equivalents by multiplying the total relative biomass consumed per day (Ca) by the proportion of the diet (Pi) represented by each prey taxon, i (see

Chapter II), to obtain an estimate of the total relative biomass of each prey taxon consumed per day (PiCa). After multiplying PiCa b y the appropriate caloric density (cal/g dry weight) taken from the literature (Cummins and Wuycheck 1971, Wissing and Hasler 1971,

Slobodkin and Richman 1961), and summing, the calories consumed per gram of fish per day (cal/g/day) wfas obtained. These rates of 119

Table 10. Gastric evacuation rates (r) and standard errors (SE) for freshwater drum, white bass, white perch, and yellow perch taken near Middle Sister Island in western Lake Erie. Each of the values in the separate boxes are significantly different (p < 0.05) from each other (see text).

Fish 7/13-14/83 9/8-9/83 7/24-25/84 9/5-6/84 Species r SE r SE r SE r SE

Freshwater - - 0.239 0.042 n.s. 8 Ij 0.103 0.0371 drum I 9 9 1 (0.08 4 0.07 89White bass - - - - 0.102 0.047 (0.084 0.0789White

White perch 0.226b 0.042 0.282 0.065 n.s. 9 0.25 0.0281 0.187 0.063

Yellow perch 0.137 0.039 0.170 0.036 0.217 0.076 0.174 0.023 a n.s. = r not significantly different from zero (p>0.05). b White perch had two feeding peaks on this day, yielding two evacuation rates. 120

consumption (in cal/g/d) were converted to calories/day for the

"average" freshwater drum, white bass, white perch, and yellow perch by

multiplying by the appropriate median fish dry weight.

Results

To determine whether the relationship between oxygen consumption

and the independent variables, including fish wet weight (W),

temperature (T), and swimming speed (S), is a function of the fish

species tested, a test for heterogeneity of slopes using an analysis of

covariance was performed (Table 11). The interaction effects show

that there is no significant difference in the relationship between the

rate of oxygen consumption and swimming speed and between the rate of

oxygen consumption and temperature for the four fish species tested

(Table 11). However, there is a significant difference in the

relationship between the rate of oxygen consumption and fish wet weight

for the fish species tested (Table 11). Ibis difference in slopes among fish species for the relationship between oxygen consumption and wet weight is due to the higher range in fish biomass for yellow perch

(Table 9) that resulted from testing more than one fish at a time.

Indeed, when only coextensive data for all four fish species are included in an analysis of covariance, the species interaction, for the relationship between oxygen consumption and wet weight, ceases to be significant (p >>0.05, n=32, 3 degrees of freedom). Thus, the data were lumped for all species, since there were no significant differ- 121

Table 11. Hie effect of fish species on the relationship between the rate of oxygen consumption (mg O 2 consumed/day) and the independent variables 1 wet weight (log. wet weight in grains), swindling speed (body lengths/s), and temperature (*C). An asterisk (*) indicates statistical significance with p < 0.05.

Interaction n DF MSE SSF P

Wet Weight/Species 42 3 0.078 1.008 4.31 0.01*

Swimming Speed/Species 42 3 0.119 0.08 0.22 0.89

Temperature/Species 42 3 0.074 0.513 2.31 0.10

ences in oxygen consumption slopes among species when coextensive datawere included, and since there were also no significant differences in the intercepts (p > 0.05) among fish species, even when the full range of yellow perch data were included in the analysis. Stepwise regression yielded the best model (rz = 0.694):

Rb*. = (0.022)W0.824 (l,256)T (4.547)*, (9)

where Rb*. is the respiration rate of an unfed swimming fish (mg

02/day), W is fish wet weight (g), T is temperature (*C), and S is swimming speed (body lengths/s). The model accounted for 69.4% of the variation in Rb*a, with 50.2% attributable to wet weight, 15.3% attributable to temperature, and 3.9% is attributable to swimming speed, and all independent variables were significant (p < 0.05).

Only fish wet weight (g) was found to significantly (p < 0.001) contribute to the variation in excretion rates (mg N H 3-N/day) by an analysis of covariance. The relationship between excretion rate, U (mg 122 NHs-N/day), and gram wet weight (W):

U = (0.16)W*-<>’, (10)

weis obtained by least squares regression. The model explains 65.0% of

the variation in U (r2 = 0.65, p < 0.001).

Median wet weights of fish taken near Middle Sister Island during

diel sampling (see Chapter II) were used in equations (9) and (10) to

estimate in situ maintenance energy requirements for the typical young-

of-year freshwater drum, white bass, white perch, and yellow perch in western Lake Erie. Fish swimming speeds in Lake Erie were based on the vector-averaged currents of 1.0 cm/s in July and 1.25 cm/s in September

from Saylor and Miller (1983) for a site near Middle Sister Island.

These current velocities were divided by fish total length to obtain S, swimming speed, in body lengths/s, for equation (9). Because bottom

trawls were performed to collect the young-of-year fish to estimate consumption, the temperatures used in equation (9), are the mean

temperatures for the bottom five meters of the water column on each date.

Net energy available for growth and survival activities (En) was estimated by subtracting energy losses (F + U + Ra + Rb + a) from energy intake (C) for freshwater drum, white bass, white perch, and yellow perch for the dates for which consumption estimates were available

(Table 12). Note, in Table 12, that among these fish species, white perch consistently had the largest amount of net energy (En) available for growth and survival activities. These differences among fish 123

Table 12. Energy available for growth of the average-sized young-of-year fish in the western basin of Lake Erie during summer of 1983 and 1984. Fish species abbreviations as in Table 2.

(F) (U) Med- Energy Energy (Rd) (R.«.) ian Mean (C) Lost Lost Specific Active (En ) • Weight- Date wet Total Energy in in Dynamic Met- Net specific (mean Fish wt. Length Consumed Feces Urine Action abolism Energy E n T,*C) Sp. n (g) (cm) (cal/d) (cal/d) (cal/d) (cal/d) (cal/d) (cal/d) (cal/g/d)

July WPCH 64 0.16 2.7 17.4 2.8 0.03 2.5 4.3 7.8 48.8 13-14 1983 YPCH 77 0.24 3.2 17.9 2.9 0.07 2.6 5.6 6.7 27.9 (22.2)

Sept. DRUM 96 4.58 8.0 279.1 44.7 16.40 39.9 67.1 111.0 24.2 8-9 1983 WPCH 44 1.67 5.8 234.4 37.5 2.50 33.5 32.0 128.9 77.2 (23.5) YPCH 61 2.66 6.5 121.8 19.5 5.90 17.4 45.3 33.7 12.7

July DRUM 43 0.47 3.6 10.8 1.7 0.23 1.5 9.6 -2.2 -4.7 24-25 1984 WBAS 59 0.28 3.2 16.3 2.6 0.09 2.3 6.6 4.7 16.8 (22.4) WPCH 60 0.31 3.3 23.3 3.7 0.11 3.3 7.1 9.1 29.4 YPCH 56 0.78 4.4 31.0 5.0 0.60 4.4 13.5 7.5 9.6

Sept. DRUM 60 2.99 7.3 83.9 13.4 7.40 12.0 27.3 23.8 8.0 5-6 1984 WBAS 25 1.78 6.0 91.3 14.6 2.80 13.0 18.8 42.1 23.7 (21.0) WPCH 59 2.38 6.2 242.2 38.8 4.80 34.6 23.7 140.3 58.9

YPCH 47 2.08 6.2 56.8 9.1 3.7 8.1 21.2 14.7 7.1 124

species in E n , ultimately depend upon three factors: (1) the amount of energy consumed (C), (2) fish weight (W), and (3) fish total length

(which determines S).

If food resources are limiting growth of these young-of-year fish species, then fish growth rates would depend upon the net energy (Eh) available for growth (and other activity). To test this relationship,

I hypothesized that instantaneous fish growth rates would be positively correlated with En. Instantaneous fish growth rates were estimated for the two week period immediately after the July diels, and for the two week period immediately before the September diels, in 1983 and 1984, using the exponential model of growth:

G = log. W2 - log. Wi , (11) t* - ti where Wi and W 2 are the mean weights of the fish at times ti and t 2, respectively (Weatherly 1972) (Table 13). Fish growth rates were not correlated with net energy, En (0.10 < p < 0.20, Spearman Rank

Correlation), nor with energy intake, C (0.05 < p < 0.10).

Discussion

Seme of the variables for energy losses, such as F and U in equation (6), were estimated with parameters from the middle to low end of their reported range (Elliott 1976b, Dabrowski et al. 1986).

However, a study of the sources of error in bioenergetics models has shown that little error is introduced by representing energy losses in 125

feces (F) and. urine (U) as fixed proportions of consumption (Bartell et

al. 1986). In this study, F was estimated as a fixed proportion of

consumption (C), and U was estimated with a model developed for starved

fish that expressed U as a function of fish wet weight in grams (see

equation (10). The proportion of the ingested energy that is lost in

feces and urine (F + U) is known to vary with temperature and ration

size (Elliott 1976b). Also, DabrowBki et al. (1986) have shown that,

for juvenile coregonids, the rate of ammonia excretion may be a

function of swimming speed, and the quality of the diet. They observed

ammonia excretion to increase as the proportion of protein in the diet

increased (Dabrowski et al. 1986). Thus, by assigning a fixed proportion of C as an estimate of F, and by modeling U only as a

function of W, these components of the bioenergetics model were probably under-estimated.

The proportion of the calories consumed per day (C) that U represents, in Table 12, ranged from 0.2 to 8.8%, and averaged 2.9% of

C. Elliott (1976b) found that a mean value of 8% with a range of 4 to

12% of the ingested energy adequately estimates the excretory losses of brown trout (Salmo trutta). The model used here (equation (10)) yielded proportions of the ingested energy that are closer to the range

(3 to 5%) recommended by Winberg (1956, cited in Elliott 1976b), and are not unreasonable.

The estimate for metabolic energy necessary to digest food (Ra), of which specific dynamic action, or the "apparent heat increment," comprises the largest component (Beamish and Trippel 1990, Webb 1978), 126 was also conservatively estimated as a fixed proportion of the net e n e r g y intake (C - F ) . Beamish and Trippel (1990) have shown that the proportion of energy intake that is required for the apparent heat increment increases as the proportion of protein in the diet increases.

In their survey of the literature, Beamish and Trippel (1990) cite 3 to 41% as the widest range reported for the apparent heat increment, when expressed as a percentage of digestible, or net, energy intake. The average minimum (+ SD) and maximum of the ranges that they reported are 11% (+6) to 28% (+9). Since the dry weight of zooplankton may be comprised of as much as 63% protein and 8.7% lipid

(Filatov 1972), it would be expected that planktivorous fish exhibit an apparent heat increment that tends toward the higher end of the range reported by Beamish and Trippel (1990). Assuming this to be true, because zooplankton often comprise the majority of the diets of young- of-year freshwater drum, white bass, white perch, and yellow perch (see

Chapter II), the proportion of the digestible energy intake used in the bioenergetics model, here, for Rd may be from 2 to 20% too low. This is the range of differences between the average maximum percentage (+ 1

SD, i.e., 28% + 9) for heat increment reported by Beamish and Trippel

(1990) and the percentage used in this study (17%). If the higher percentage of the digestible energy intake (37%) were used to estimate the apparent heat increment (Rd)» the net energy available for growth and survival activity (Eh in Table 12), would be reduced by about 50%, on average.

To determine whether the model derived to estimate active 127 metabolism (Rb+a), equation (9), yields reasonable estimates, I compared its output to that obtained from equation (6) of Stewart et al. (1983) that was developed for lake trout (Salvelinus namaycush) that weigh 1 g to 2000 g, at 3.5 to 15 *C:

Rd = (0.010)W-°**®5 (1.061)T (0.0232)", (12) where Ru is metabolism in terms of gram equivalents (g/g/d), W is wet weight (g), T is temperature (*C), and U is swimning speed (can/s).

Equation (12) is the closest in form to equation (9) that I found in the literature, however, some manipulations of equation (9) are necessary to compare then. To make this comparison, I duplicated the manipulations performed by Stewart et al. (1983) to express equation

(12) in gram equivalents. Thus, I divided the intercept in equation

(9), 0.022, by 1000 to convert to g 02/d, subtracted 1.0 from the slope, 0.824, to convert to g 02/g/day, and then converted to gram equivalents (g/g/d) by multiplying by the factor, 13560/6280, to correct the intercept for the relative energy density of oxygen and fish. Equation (9) for Rb+a thus becomes:

Rb + a = (4.75 x 10"®)W~0.176 (1.256)T (4.547)». (13)

The weight, temperature, and fish total length for white perch on July

13-14, 1983 and for freshwater drum on September 8-9, 1983, were used as input into both models, and encompass the range of fish weights used to estimate metabolic losses (Table 12). For the median white perch weight on July 13-14, 1983, equation (13) yielded an estimate of 0.018 128

g/g/d compared to 0.065 g/g/d obtained with equation (12) from Stewart

et al. (1983). For freshwater drum on September 8-9, 1983, the

estimates were slightly closer: 0.009 g/g/d (equation (13)) compared to

0.026 g/g/d (equation (12)). These equations yield results that are

remarkably close (only a 2.8 to 3.6 fold difference), considering that they were developed for vastly different ranges of fish sizes (1-2000 g

for equation (12) compared to 1.3-4.8 g for equation (13), see Table

11) and temperatures (3.5-15 *C compared to 24.0-27.5 *C, Table 11).

These comparisons engender confidence in the estimates of metabolism of unfed swimming juvenile fish obtained in this study (Table 12).

The estimated amount of calories ingested, C, may have been under-estimated if the gastric evacuation rate used in equation (8),

0.18h_1, or 5.6 hours, is slower than the actual rate. If the relationship between gastric evacuation rate and the total length of age-0 yellow perch (15 mm to 34 ran, at 18*C to 22°C) that was established by Mills and Forney (1981), or by Mills et al. (1984), were used to predict evacuation rates, they would range from 0.71 (1.4 hours) for a 27 ran fish to 0.45 (2.2 hours) for a 44 ran fish. Their rates are about 2.5 to 4 times as fast as the rate used in this study for fish within this size range. For an example of how a fester gastric evacuation rate may affect the estimates of En, the fastest evacuation rate, 0.72h-1 (= 4 x 0.18h_1), was used to recalculate energy consumption and En for white perch on July 13-14, 1983. The energy consumed, C, increased by a factor of about 4.2, to 72.4 cal/d, and the net energy available for growth increased by almost six times, 129

to 46.1 cal/d (cf. Table 12). A four-fold increase in r caused a

greater increase in C because the method of Elliott and Persson (1978)

that was used to estimate C, is based on an exponential gastric

evacuation rate. The effect on En was even greater because active

metabolism (Rb+a) and energy lost through urine (U) do not vary with

consumption in the model developed in this study.

The gastric evacuation rates of Mills and Forney (1981) are among

the fastest reported in the literature for juvenile fish. Noble (1973)

reported gastric evacuation rates that ranged from 1.5 to 6.5 hours for

30 to 40 inn yellow perch (22aC), with the faster rates occurring when

the initial meal was followed by additional food. Kolok and Rondorf

(1987) reported a gastric evacuation rate of about 6.6 hours for juvenile chinook salmon (115 - 121 mm fork length, 14°C) from the

Columbia River. Thus, the rates used in this study, 5.6 and 5.0 hours, fall within the range of reported evacuation rates.

The calculated net energy, En, was positive for all four fish species on each date except on July 24-25, 1984 for freshwater drum.

This suggests that food resources were not sufficiently available for freshwater drum to meet its energy requirements on this date.

Freshwater drum may have not been able to meet its energy requirements on this date because they were feeding primarily upon relatively small

Crustacea (cf. Figs. 21 and 28). Since freshwater drum were near the bottom of the water column, as evidenced by the inclusion of benthic prey in their diet (Fig. 21), it may have been able to avoid water currents which often diminish with depth, especially wind generated 130

currents (Hutchinson 1975). If freshwater drum were engaged in less

activity than modeled by avoiding water currents, Rt>+* may have been

over-estimated so that En was under-estimated. However, the very low

growth rate observed for freshwater drum at this time, 0.9% per day

(Table 13), supports the conclusion that food resources were limiting

at this time.

In July, 1984, net energy (En) for white perch and yellow perch

did not vary much from estimates for July, 1983 (Table 12). However,

in September, En decreased in 1984 by 78.6% and 56.4% for freshwater

drum and yellow perch, respectively, but increased by about 9% over En

in September, 1983 for white perch (Table 12). Thus, for some fish

species, food resources were apparently less available in 1984 than in

1983. This is supported by evidence that the mean density of

zooplankton (number of organisms/m3) decreased substantially (44.6%),

lake wide, from 1983 to 1984 (Makarewicz 1987), although my data show

that there was no significant difference between years in zooplankton

biomass (mg zooplankton/sample) at the offshore site on the dates on

which diel fish sampling was performed (see Chapter II). In September,

1984, the majority of the diet biomass of freshwater drum and yellow

perch was comprised of zooplankton, but white perch preyed mostly upon benthic crustaceans (Fig. 25). Thus, in September, 1984 freshwater drun and yellow perch may have been better off, energetically, if they had fed more upon benthic invertebrates, as did white perch, than upon zooplankton.

This study has shown that bioenergetics modeling can be used to 131

Table 13. Growth rates (G) of age-0 freshwater drum, white bass, white perch, and yellow perch caught near Middle Sister Island in the western basin of Lake Erie during the sunnier, 1983 and 1984, expressed as a percent increase in biomass per day. G was calculated with equation (11), see text.

Fish Growing No. Initial Final Species Period of Mean dry Mean dry G x 100 Days Biomass Biomass (mo/day/yr) (g) (g) (%/d)

Freshwater 7/14-7/28/83 14 0.040 0.011 - 9.22 drum 8/24-9/09/83 16 0.497 0.915 3.81

7/25-8/06/84 12 0.078 0.087 0.91

8/21-9/06/84 16 0.381 0.647 3.31

White 7/14-7/28/83 14 0.038 0.158 10.18 bass 8/08-9/09/83 32 0.155 0.490 3.60

7/25-8/06/84 12 0.060 0.065 0.67

8/21-9/06/84 16 0.627 0.422 - 2.47

White 7/14-7/28/83 14 0.043 0.114 6.96 perch 8/24-9/09/83 16 0.291 0.503 3.42

7/25-8/06/84 12 0.068 0.098 3.05

8/21-9/06/84 16 0.229 0.606 6.08

Yellow 7/14-7/28/83 14 0.055 0.073 2.02 perch 8/24-9/09/83 16 0.403 0.563 2.09

7/25-8/06/84 12 0.159 0.257 4.00

8/21-9/06/84 16 0.557 0.447 - 1.38 132

determine whether food resources are sufficient to meet a fish’s in

situ maintenance energy requirements. Ideally, the bioenergetics model

used would have included a component for apparent heat increment, or

specific dynamic action (SDA), that was based upon the increase in

oxygen consumption of feeding juvenile fish. Unfortunately, this was

not feasible with the closed-loop, flow-through respirometer that was

designed for this study. Should such a system be developed for

juvenile fish, it would also enable researchers to make better

estimates of the energy lost in urine, which is known to vary with

ration and swimming speed, depending upon food quality (Dabrowski et

al. 1986, Elliott 1976b).

The results of this study did not show a correlation between

instantaneous growth rates and energy intake (C), nor with net energy

(En). This result is not surprising because fish energetics were

estimated over a twenty-four hour period, while growth rate estimates

were based on data collected over several weeks. During the weeks between sampling for growth, many events, such as emigration, -

immigration, and mortality, which may affect estimates of fish growth

rates (Bagenal and Tesch 1978) could occur. Thus any relationship between fish growth rates and bioenergetics may have been masked by these intervening events. Enclosure experiments, like those performed by Hanson and Leggett 1985 would overcome seme of these problems, but they have not been found to be feasible in Lake Erie (Parrish 1988). CHAPTER IV

SUMMARY AND (XtNCLUSIONS

In this chapter, I sunmarize the evidence assembled in Chapters

II and III, including diet overlaps, maintenance energy requirements,

and fish growth among others, that indicate that young-of-year fish may

compete for food resources in western Lake Erie. I then address which

fish species’ recruitment may be affected by competition, if it is

occurring.

In Chapter II, I showed that diet overlap between white perch

(Morone americana) and white bass (M. chrysops), and between white

perch and yellow perch is greater than or equal to 60% on most sampling

dates (Table 3). In fact, white perch had diet overlaps greater than

or equal to 60% with at least one of these fish species on every

sampling date except one (August 21, 1984). However, white bass and

yellow perch only occasionally shared food resources in such high proportions (Table 3). Freshwater drum (Aplodinotus grunniens) shared

food resources with either white bass, white perch, or yellow perch, on

50% of the sampling dates on which it was caught (Table 3). These results show that the diets of some young-of-year fish species in western Lake Erie significantly overlap.

However, there may be no limit to these fish species’ similarity

133 134 in diet, if food resources are not in limited supply (Abrams 1983,

Gause 1934). Therefore, an energy budget was constructed for the median-sized individual, in Chapter III, to determine whether these young-of-year fish species were able to consume sufficient quantities of food, in 1983 and 1984, to meet their minimum energy requirements, i.e., to satisfy their in situ maintenance energy requirements.

Additionally, the difference between the amount of energy consumed and the amount of energy required for maintenance is a relative measure of each fish species’ competitive ability- i.e., the species that acquires the greater surplus quantities of energy will be able to grow faster while engaging in other necessary activities such as pursuing prey, and escaping from predators.

Among the four fish species studied, freshwater drum, white bass, white perch, and yellow perch, only freshwater drum, on one occasion, did not consume a sufficient quantity of food to meet its maintenance energy requirements (see negative entry in column En, Table 12).

White perch had the greatest amount of surplus, or net, energy (Eh) on each of the four dates for which an energy budget was assembled (Table

12), thus, we might expect the best recruitment for this species. In

September of 1983 and 1984, the surplus energy available for yellow perch was the lowest among the other species, and only equaled about 10 to 26% of the net energy available (12 to 17% of the normalized Eh) to white perch (Table 12). Thus, the bioenergetics approach revealed that, for freshwater drum, food resources were limiting on at least one occasion. However, because growth rates were not found to be 135

significantly correlated with net energy, E n , it could not be shown

that food resources were generally limiting for growth. This lack of a

significant correlation persisted even when white perch data were

excluded from the analysis.

I also hypothesized that, if food resources are limiting, then,

one may expect to find a negative correlation between diet overlap and

net energy (En). Least squares regression of net energy versus the sun

of the diet overlaps for freshwater drum, white bass, white perch, and

yellow perch on a particular date (see Chapter II) produced a line with

a negative slope, but the correlation coefficient was not statistically

significant (r2 = 0.04, n = 13, p > 0.50). Since there is some

evidence that fewer food resources were available in 1984 than in 1983

(Makarewicz 1987), I performed the analysis, again, with only 1984

data. Although improved, the correlation coefficient was, again, not

statistically significant (r2 = 0.30, n = 8, 0.10 < p < 0.20).

Normalizing En and diet overlap (D) by dividing by median fish wet

weight, and by arcsin transformation, respectively, did not improve the

relationship. Thus, the bioenergetics approach, as applied in this

study, may be better suited to exploring relative fish competitive abilities (Abrams 1983), rather than resource availability.

Given that the energy intake of young-of-year white perch was consistently more than sufficient to meet its minimum in situ energy requirements and yielded the largest energy surpluses, white perch appears to be the most capable competitor under the conditions studied.

Although yellow perch and white bass were both found in this study 136

(Chapter II) to frequently have high diet overlaps with white perch,

the data from the bioenergetics study (Chapter III) suggest that young-

of-year yellow perch are more likely to be negatively affected by

competition with young-of-year white perch when food resources become

scarce. Thus, one may hypothesize there should be a negative

correlation between white perch biomass and yellow perch biomass in

western Lake Erie, especially since annual young-of-year surveys

conducted by the Ohio Department of Natural Resources (1985) show that

white perch numbers increased exponentially during the early 1980's

(Fig. 1).

Using stepwise multiple regression correlation of recruitment

variables (biomass) of age-0 yellow perch on community variables

(biomass of the other fish species in the community) for the different

basins of Lake Erie during the years 1965 to 1987, Henderson and

Nepszy (1990) found a positive, but not significant (p > 0.05),

correlation between yellow perch and white perch, in the western basin,

and a negative (nonsignificant) correlation in the eastern and central basins (combined). Henderson and Nepszy (1990) also found that

interspecific correlations of biomass over time (temporal correlations)

increased with the degree that fish species share the same habitat

(spatial correlations). This suggests that larger numbers (or biomass) of certain fish species are attracted to those habitats that are capable of supporting a greater biomass of fish, i.e., where resources sure not limiting. Given the relatively high diet overlap between yellow perch and white perch (Chapter II), one would expect them to be 137

concentrated in the same habitats where their shared food resources are

abundant. Thus, a lack of a negative correlation between yellow perch

biomass and white perch biomass in the western basin, is insufficient

evidence to rule out the possibility of competition in those habitats

(areas of the lake) where food resources are limiting.

The number of young-of-year fish caught per hour of trawling in

the western basin of lake Erie in 1984 was significantly greater (p <

0.05) than in 1983, due to almost a ten-fold increase in white perch

and white bass (Fig. 1). This significant increase in young-of-year

fish numbers in 1984 may have caused the substantial decrease in

zooplankton abundance from 1983 to 1984 (Makarewicz 1987). By

affecting food resources, the increase in young-of-year abundance may

have caused the observed decreases in net energy (En) from 1983 to 1984

for yellow perch, freshwater drum, and white bass (see column En, Table

12, Chapter III). However, fish growth rates (Table 13) in 1984 were

not significantly different (p > 0.20, paired-sample Student's t-test)

from growth rates in 1983. Thus, the evidence that young-of-year fish

in western Lake Erie were competing for scarce food resources during

1984 is inconclusive.

Competition among young-of-year fish was more likely to have affected year-class strength in 1984 than in 1983. The geometric means of catch per hour trawling between sumner and fall may be compared as an index of young-of-year fish mortality (Table 14), although

immigration and emigration would also affect catch (note that more young-of-year freshwater drum in both years, and yellow perch in 1983 138

Table 14. Geometric means of numbers caught per trawling hour and percent change between seasons of young-of-year freshwater drum white bees, white perch, and*yellow perch during Summer and Fall, 1983 and 1984, in the western basin of Lake Erie. Data from Ohio Department of Natural Resources (1990) and Mark Turner (Ohio Department of Natural Resources, Sandusky, Ohio pers. comnun.).

1983 1984

Fish Species Sumner Fall % Sumner Fall %

Freshwater drum 2 443+221 19 43 +126

White bass 136 0 -100 965 8 - 99

White perch 217 182 - 16 2230 2017 - 10

Yellow perch 9 16 + 78 679 246 - 64

were caught in fall). The greatest change between years occurred for yellow perch, which decrease by 64% from sumner to fall in 1984, but increased in 1983. Consistent changes between sumner and fall in

1983 and 1984 were seen for white bass, white perch and freshwater drum. While white bass substantially decreased (100 and 99%) from sumner to fall in both years, white perch decreased by less than 20% in both years (Table 14). Although the number of yellow perch was greater in 1984 than in 1983, the relatively large percent decrease in 139 yellow perch numbers in 1984 suggests that competition was more likely to have affected yellow perch 1984 recruitment.

Additionally! a comparison of fish dry weights near the end of the growing season (September) in western Lake Erie, on about the same day of the year in 1983 and 1984, showed freshwater drum, and yellow perch were significantly smaller in 1984 (Table 15). Fish size at the end of the growing season may affect winter survival when food is limiting. Johnson and Evans (1990) found that white perch winter mortality may be influenced by fish body size, winter duration, temperature and food availability. When food was withheld, mortality increased for small fish (Johnson and Evans 1990). Summer mean water temperatures (Fig. 35) were significantly (p < 0.01, Student’s t-test) lower in 1984, by 2*C, than in 1983, and may partially explain why some fish accumulated less b i o m a s s by early September 1984 than in 1983

(Table 15). However, data presented by McCormick (1976) show that yellow perch growth rates differed by only 0.1% between 24 and 22 *C, when fed ad libitum. Assuming that other factors, such as predation

(Nielsen 1980), that may affect young-of-year survival were constant between years, these results also suggest that competition was more likely to have affected year-class strength in 1984 than in 1983.

Future research should explore the effects of predation on young- of-year fish interactions. Predators may allow co-existence of competing species by preventing the better competitor from monopolizing limiting resources (Paine 1966). Since white perch have significantly increased in numbers since Knight et al. (1984) studied predation by Table 15. Stannary of Student’s t-teats for significant differences in fish dry weight tag), using log»-transformed data, between 1983 and 1984 at the offshore site, Middle Sister.

Date of Collection Fish (1983) July 28 August 8 August 24 Sept. 8 Species (1984) July 24 August 6 August 21 Sept. 5

1984 » Alewife --- a --- (9, 14)c (<0.05)"

1984 ns* ns 1983 Freshwater (10, 46) (2, 4) (53, 3) (631, 60) drum (<0.001) 00.50) 00.20) (<0.001)

1983 --- One raid • (44, 41) shiner KO.Ol)

ns 1984 1984 Gizzard --- (2, 11) (2, 10) (3, 23) shad 00.50) (<0.002) (<0.001)

1984 ns 1984 1983 Rainbow (7, 59) (3, 10) (7, 10) (43, 45) smelt (<0.05) 00.05) (<0.005) (<0.05) 1983 ns 1983 Trout- --- (7, 4) (54, 8) (322, 65) perch KO.Ol) 00.05) (<0.002)

ns 1983 ns White (22, 60) (13, 10) --- (4\ 25) bass 00.05) (<0.02) 00.50)

ns ns ns 1984 White <13, 62) (13, 10) (12, 10) (123, 59) perch 00.10) 00.05) 00.50) (<0.02) 1984 ns 1984 1983 Yellow (3, 56) (6, 5) (10, 10) (193, 47) perch (<0.01) 00.20) (<0.02) (<0.001)

» Dash indicates none, or an insufficient ntanber, was collected. » The year indicates when the fish were significantly larger, c Sample size (m, nt), where ni=sample size for 1983, and nt=1984. 4 Significance level, p, for two-tailed tests. * No significant difference indicated. Figure 35. Temperature (upper panel) and dissolved oxygen (lower panel) profiles of the study site near Middle Sister Island, in the western basin of Lake Erie, during the Sumners of 1983 and 1984. Data were provided by Robert S. Hayward (pers. commun.) and the Ohio Department of Natural Resources (pers. commun.).

141 Depth (m) Depth (m) 14 -1 -12 -10 -10 14 -1 -12 -12 -10 -8 4 - -6 _o -6 -8 -2 4 - 0 0 . 30 . 50 . 70 . 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 0 1 2 3 4 5 6 27 26 25 24 23 22 21 20

Figure 35. Figure CLOSED 1983 = / 8/6 9/5 P N 1984 OPEN = isle Oye ( g/l) (m Oxygen Dissolved eprtr (°C) Temperature r e t s i S e l d d i M

■ ■ 8/8 CLOSED 1983 = T A P N 1984 OPEN = O V □ O * mco o V D O V

142 143 walleyes and yellow perch in western Lake Erie, the impact of predation on the young-of-year of this competitively superior species is not known.

Additionally, future research should focus on the spatial variations in fish distributions, feeding habits, and bioenergetics.

The results of this study show that fish feed on different prey near shore compared to offshore (Chapter II), which may result in spatial variations in fish bioenergetics (Boisclair and Leggett 1989). Also, correlation analyses have shown that certain groups of fish species are likely to be found together, occupying the same habitat (Henderson and

Nepszy 1990). Thus, as those habitats, and young-of-year food resources, continue to be affected by cultural eutrophication (Hayward and Margraf 1987), and possibly by invading exotic species, such as the zebra mussel, changes in the interactions among the young-of-year may occur. This research has shown that yellow perch, freshwater drum and white bass are among those fish species that are most likely to be negatively affected by competition with white perch, if a reduction in food resources occurs in western Lake Erie. LIST OF REFERENCES

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SAMPLE SIZES, FISH SIZES, AND STOMACH CONTENTS

DATA PC® CHAPTER II

152 Table 16. Percent, composition (P) of prey by dry weight per individual fish examined and percent occurrence CF) of prey among fish examined. The fish were collected by bottom trawl at the offshore site near Middle Sister Island, western LaUe Erie on J u l y 13-14, 1983.

Fish Species3

DRUM GSHD RSMT T R T P UBflS UPCHYPCH n, n with foodb 3, 1 9, 9 47, 20 55, 40 20, 17 62, 57 75, 71 Standard 1ength, fflin. — max. (mm) 19-22 25- 30 23-39 18-36 18-32 15-32 18-32 Dry uei ght, min. — max. (mg) 31-46 28- 77 19-66 12-120 11-89 11-113 15-113 prey weight (ug/fish) 2.9 242.6 10.8 76.3 221.8 429.7 323.9

Prey taxa P F P F P F P F P F P F P F filgae -- c 36

C 1adocera Leotodora U i ndt i 2 22 6 2 6 20 6 35 7 55 3 35 Diaohanosoma so. < ie 22 6 8 1 20 tf 2 t 3 Sida crustallina 1 11 < 1 4 < 1 3

Daohni a relrocurva 67 lOO 9 17 4 29 1 io 2 27 1 28 Table 16 (continued),

Fish Species Prey Taxa DRUM GSHD RSMT TRTP UBRS UPCH YPCH ______PF PF PF PF PF PF PF D. oa1eata mendoiae 111 3 2 2 9 < 1 5 < 1 S B o s m i na longirostr is 2 4 15 49 1 10 2 42 5 52 Eubosm i na coreooni 1 2 5 15 t 5 < 1 17 Leudigia sp. <1 11 11uocruptus sp. <1 2 E u c o p e p o d a C a l a n o i d a Epischura lacustris <1 2 Eurutemora affinis < 1 11 54 2 9 19 24 44 70 43 85 30 72 Leptod i aptomus sp9 1 2 < 1 5 t 5 t 4 L. m i n u l u s t 2 L. sici1 is 2 2 L. siciloides 425< 12 lyclopoida f l c a n t h o c u c 1o p s u e r n a I i s 2 4 7 8 15 1 5 4 0 2 2 4 3 6 0 4 4 8 4 5 9 7 2 D i acuc1ops thomas i 4 56 1 2 2 9 < 1 20 1 2 9 1 2 5 Mesocuclops edax 100 3 3 1 2 2 2 4 2 2 5 < 1 3 < 1 3 r i b e D s r e t t e l r u o F a a r e t p i D Table.- (continued), 16

id a n e h i a iC m d o n o r o- Rotifer-a. d d e n s a o p e m a o g c l e R d f y o l h F g for- i h D H h S t G s i t w n l e l h t = s N n i o f c f h o c a e m o v t i s s u l c x E a x a T y e r P < = O.SOJi. d n a 1 . 0 n e e w t e b e g n a r = “ 1 *< " --- = . d e i f i t n a u q t o n = ” n 2. e l b a T in d e n i f e d e d o c F P F P D H S G M U R D . F P F P. F P H C P Y H C P U S R B U P T R T T M S R i sh Spec c e iF p i S s e h s 9 h " = less than a h t s s e l = " "t f --

2 4

. s i r b e D f o F r o f P T R T 9 ? = N . s i r b e D so. f s o u m F o t r p o f a i d H o C t P p Y e L 9 ? d = e N i f i t n e d i n U

108. . O a

2 1 U. F P 156

Table 17. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom trawl at the offshore site near Middle Sister Island, western Lake Erie on July 28, 1983. Footnotes as in Table 16.

FiBh Species*

DRUM RSMT WALL WBAS WPCH YPCH n, n with food*3 10, 7 7, 0 1, o 17, 17 9,, 9 3, 3 Standard length min. - max. (mm) 9- 21 26- 30 63 18- 56 20-- 47 19- 37 Dry weight min. - max. (mg) 7- 30 19- 3 559 14-477 18-435 20-138 prey weight (ug/fish) 33.5 0 0 1532.3 872.0 4423.3

Prey taxa P F P F P F P FPF P F

Cladocera Lentodora kindti 17 20 18 82 13 56 56

Dianhanosoma s d . < 1* 35 4 89 t» 33 Sida crystallina 40 40 1 35 <1 44

Danhnia retrocurva 12 71 7 67 t 33

D. fialeata mendotae < 1 18 2 22 Eubosmina coreaoni < 1 35 < 1 22 t 33 Eucopepoda Calanoida Eoischura lacustris 6 10 1 53 1 56 t 33 Eurvtemora affinis 5 65 13 100 3 33

LentodiantomuB sn.( < 1 18 3 56 t 33

L. ashlandi < 1 24 1 44

L. siciloides < 1 24 < 1 33 t 33 157

Table 17. (continued),

Fish Species

Prey Taxa DRUM RSMT WALL WBAS WPCH YPCH

P F P F P F P F P F P F

Cyclopoida AcanthocvcloDB vemalis 27 40 51 82 49 89 1 67 Diacvclore thomasi 7 30 6 71 3 100 MesocvcloDG edax 3 53 2 44 Amphipoda 3 6 Diptera Chironooidae 3 10 t 6 1 11

Osteichthyes 96 33 Debris — e 30 Table 18. Percent composition (P) of prey by dry weight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish uere collected by bottom trauil at the offshore site near Middle Sister Island, uestern LaUe Erie on Rugust 8, 1983. Footnotes as in Table X6 *

Fish Species3

DRUM GSHDRSMTTRTP UIRLL UBfiS UPCHYPCH n, n with foodb 2, 2 2, 2 3, 1 5, 5 2, 1 4, 4 4, 4 6, 6 Standard length, min. - max. (mm) 2 9 - 3 0 31 3 3 - 3 5 35-39 68-80 23-43 27-44 43-50 Dry weight, min. ~ max. (my) 85-114 62-96 3 6 - 4 5 137-189 871-872 4 5 - 4 5 4 95-582 258-368 prey weight, < u g / f i s h ) 23.8 108.7 3.9 50.2 12801.2 992.7 1882.6 718.8

P r e y t a x a P F P F P F P F P F P F P F P F

01igochaeta 6 4 0 tf 3 3 C.1a d o c e r a Leptodora Uindti 12 5 0 19 40 21 100 12 100 4 83

Diaohanosoma s d . 6 1 0 0 41 3 3 3 2 0 1 1 0 0 3 5 0 < l8 3 3 Sida crystal 1ina 2 5 0 2 9 2 0 < 1 5 0 Oaohni a retrocurva 12 50 70 100 13 40 37 100 51 100 78 100 D. qaleata mendotae 2 2 0 1 5 0 2 5 0 Table 18.,

F i sh S p e c i es Prey Taxa □RUM GSHDRSMT T R T P UfiLL UBRS UPCH YPCH P F P F P F P F P F P F P F P F

Bosmina lonairostris < 1 25 1 83 Eubosmina coreaoni 59 33 < 1 50 < 1 50 4 83 Leudiaia so. 2 40 Eucopepoda C a l a n o i d a Epischura lacustris 2 50 2 75 o in O T ■•J O Eurulemora aFfinis ** < 1 50 75 1 2 1 67 Lentodiapiomus so. t 25 I 17 C y c 1 cipo i da Rcanthacuc1ops v e r n a l is 30 50 7 100 11 <10 35 100 28 lOO lO 67 Diacuclops thomasi 1 50 1 1U0 < 1 33 Mesocuc 1 ops edax 3 50 1 50 1 50 D i p t e r a Chi ronumi dae S7 100 5 20 Usteichlhyes 100 50 D e b r i s ---c 25 --- 25 159 Table 19. Percent composition (P) of prey by dry ueight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish were collected by bottom traul at the offshore site near Middle Sister Island, western LaUe Erie on August 24, 1983. Footnotes as in Table 16 •

Fish Specie#

DRUM ESHN GSHD RSMT TRTP UPCH YPCH n, n with fooc 11, 11 2, 1 1, 1 7, 6 10, 10 12, 12 10, 10 Standard length, min. — max. (mm) 39-64 65-67 31-47 28-33 25-46 22-52 43-51 Dry ueight, min. — max (mg) 245-1149 554-745 19-430 17-45 43-290 42-810 2 5 5 - 4 8 5 prey ueight,

P r e y t a x a P F P F P F P F P F P F P F

1urbe11ar i a < ie 20 Nematoda tf 9 < 1 3 0 □1igochaeta t 4 5 1 7 0 --- 1 0 R o t i f e r a t 8 C l a d o c e r a Leotodora Uindti 38 73 40 50 5 lOO 13 30 61 lOO 7 5 9 0 Diaphanosoma so. < 1 9 8 l O O 1 2 0 4 9 2 1 4 0 Table 19(conlinued),

F ish S p e c i es Prey Taxa DRUM ESHN GSHD RSMT TRTP UPCH YPCH PF PF PF PF P F_____ P F P F Sida crustaI 1ina i 25 1 10 Daphn i a retrocurua 10 82 55 50 82 100 4 14 18 100 8 92 9 70 B o s m i na lonoirostris <19 t 8 < 1 10 Eubosmi na coretaon i 2 50 t 33 1 luocrtiptus sp. 4 27 12 30 I 10 Eucopepoda C a 1a n o i da Episehura 1acusiris 1 10 Eurutemora afFinis 18 82 96 86 39 90 4 92 9 90 Leptodi apiomus sp.g < 1 10 L . s i c i 1 is t. 17 C yc 1opoi da flcanthocuc1ops uerna I i s 23 82 10 40 1 92 2 30 Diacuclops thomasi I 33 Hespcuc1ops edax 7 45 3 20 < 1 58 3 30 D i p l e n a Chironomidae 2 40 Table 19 (continued),

Fish Species P r e y T a x a DRUMESHN GSHD RSMT TRTP UPCHYPCH P F P F P F P F P F P F P F □steichthyes 2 2 8 D e b r i s -- C 91 --- 4 0 162 Table 2 0. Percent conposi tion (P) of prey by dry u e i g h t per individual fisfi examined and percent, occurrence (F) of prey among aleuife, Freshuater drum, emerald shiner, gizzard shad and rainbow smelt, examined. Fish were collected at the offshore site near Middle Sister Island, western LaUe Erie on September 8-9, 1983. Prey listed uere identified from these and the fish species listed in Table 21- Footnotes as in Table 16 .

Fish Specie#

ftLUF DRUMESHNGSHDRSMT n, n uith foodb 9, 9 92, 91 17, 17 3, 3 38, 3 5 Standard length, min. — max. (mm) 40-90 48-75 35-62 3 2 - 6 3 2 7 - 4 2 Dry uei gh t , min. - max. (mg) 98-1884 329-1964 148-540 86-1348 2 1 . 4 - 1 1 7 prey ueight

P r e y t a x a P F P F P F P F P F

Turbe11ari a < f* 3 N e m a t o d a tf 4 R o t i fer a t 1 □1igochaeta 5 8 7 --- c 10 < 1 8 R e a r i na 3 2 163 Table 20(continued),

Fish Species Prey Taxa flLUF DRUM ESHN GSHD RSMT ______PF PF PF PF PF C l a d o c e r a Leptodora Uindli 78 100 9 55 99 82 96 100 20 24 D i aphanosoina sp. < 1 78 < 1 13 1 5 Latpna set i Fera Sida crusta 1 1 ina 6 56 58 36 2 33 31 29 Daphn i a retrocurua 1 44 1 4 3 13 D. galeata mendotae I 11 Bosm ina 1onqi rostr i s < 1 44 < 1 29 < 1 33 Eubosmi na coreooni 2 78 <1 6 <1 33 Chudorus sp- t 1 1 luocrLiptus sp. 2 11 Ostracoda 3 12 E u c o p e p o d a nauplius larua C a l a n o i d a Epischura 1acustri s I 1 Eurqtemora affinis 5 78 2 36 < 1 33 44 53 164 Tab1e 20 ,

Fish Species Prey T axa RLUIF DRUM ESHN GSHD RSMT P F P F P F P F P F Leotodiaptomus sici1 is I 11 Cyclopoi da Rcanthocucloos uernalis < 1 6 ? 234 <1 33 <1 3 Diacuclops thomasi < 1 4 4 1 3 H e s o c u c 1o p s e d a x 3 89 562 1 33 H a r p a c i i co i da Canthacampius robertcoUeri t 2 R m p h i po d a l s o p o d a D i p t e r a C h i ro n o m i da e 3 11 12 2 2 Tr ichoptera D e b r i 5 -- 3 0 --- 6 7 --- 13 165 Table 21 - Percent composition (P) of prey by dry ueight per individual fish examined and percent occurrence

F i sh S p e c i e#

SSHNTRTP UBflS U P C H YPCH n, n with foodb 80, 76 91, 90 4, 4 45, 44 59, 58 Standard length, min. — max. (mm) 28-59 35-67 41-66 30-58 39-57 Dry weight, min. — max. (mg) 2 3 - 9 3 5 115-1276 226-1213 80-1172 163-810 prey ueight ( u g / f i s h ) 2 9 . 9 257. 1 2368.7 1804.3 2 2 8 . 8

T u r b e 11ar i a 2 16

N e m a t o d a 16 18 10 14 R o t i fe r a Oliyochaeta 2 3 0 12 81 3 6 1 9 51 H e a r i na 4 1 C 1a d o c e r a Leptodora Uindt i 28 20 18 46 35 100 56 91 22 64 Table 21 (continued).

F i sh S p e c i es Prey Taxa SSHN TRTP UBRS UPCH YPCH ______PF PF PF PF PF Diaphanosoma sp. I ? 1 75 < le 38 t 5 Latona setifera <1 1 Si da crustal I ina 8 5 8 43 34 75 15 67 5 14 Daphn i a retrocurua t 7 <1 75 <1 27 t 3 D. oaleata mendotae Bosmina longirostris < 1 4 1 2 t 13 t 3 Eubosmina coreoon i < 1 22 t 2 C h u d o r u s sp. t 1 I luocruptus sp. 2 4 13 48 2 22 3 17 Ostracoda 41 613 <14 25 E u c o p e p o d a nauplius larva t 1 C a 1a no i da Epischura lacustris Eurutemora aff inis < 1 1 5 58 29 75 20 84 14 41 Leptodiaptomus siciI is CycIopoi da 167 Table 21 (continued),

Fish Species P r e y T a x a SSHN TRTP UIBflS U P C H Y P C H P FP F PFPFPF flcanthocuclops vernal is 1 3 < 1 io 1 5 0 1 5 8 1 19 Diacuclops thomasi 1 3 < 1 7 5 t 9 < 1 7 Mesocwc1ops edax 1 3 3 46 < 1 2 5 2 5 8 3 34 H a r p a c t i co i da Canlhocamplus robertcoUeri < 1 4 t 1 < 1 2 0 < 1 7 R m p h i p o d a 3 1 5 2 I s o p o d a 7 2 D i p l e r a C h i ro n on i da e 3 3 8 2 9 2 5 < 1 25 < 1 11 18 10 T r i di o p t e r a < 1 2 D e b r i s -- c 6 8 -- 2 0 -- 18 -- 24 168 Table 22- Percent composition fish uere collected by bottom traul at the nearshore site in uestero LaUe Erie near Bono on July 11, 1983. Footnotes as in Table 16 .

F i sh S p e c i e^

RSMTTRTP UBfiS U P C H YPCH n, n uilh fooct3 10, 3 11, 11 12, 12 15, 15 14, 12 Standard length, min. — max. (mm) 2 4 - 3 2 2 4 - 3 1 2 0 - 2 6 1 8 - 2 9 2 3 - 4 1 D r y u e i yh l , min. — max. 16-30 43- 73 1 9 - 6 0 1 0- 91 3 3 - 1 6 3 prey ueight < u g / f i s h ) 3 . 3 1 4 7 . 0 5 6 1 . 9 5 7 6 . 1 5 3 7 . 6

P r e y t a x a P F P F P F P F P F

C 1a d o c e r a Leptodora lindti 1 8 1 13 1 7 Diaoh'inosoma sp. 5 0 lO < l e 17 1 4 0 Sida crustallina < 1 9 tf 7 Daphnia relrocurua 32 10 44 lOO 16 83 2 0 8 7 15 71 D. oaleata mendotae 5 3 6 2 3 3 6 6 7 3 5 0 Bosmina Ionairnstris 1 9 169 Table 22

F i sh S p e c i es P r e y T ax a RSMTTRTP UBfiS UPCHYPCH P F P FPFP F P F Eubosmina coreaoni 2 9 t 8 Leudiaia sp. 1 5 5 Eucopepada C a 1a n o i da

Eurutemora aFFinis 18 1 0 2 2 7 1 4 2 1 5 3 1 2 9 Leptodiaptomus so.a < 1 7 < 1 7 L . a s h 1a n d i t 8 < 1 13 t 7 L. siciloides 1 3 3 1 2 7 1 3 6 C y c 1opoi da flcanthocuc 1 ops u e m a 1 i s 21 7 3 3 8 l O O 8 8 0 8 7 9 Diacuclons thomasi 2 2 7 8 9 2 3 6 0 3 71 Mesocuc1ops edax 2 0 7 3 3 2 9 2 13 8 0 14 7 9 D i p t e r a Ch i ronomi dae 1 9 Ostei chthyes 467 5 3 7 D e b r i s --- o 8 --- 7 170 Table 23. Percent composition (P) of prey by dry ueight per individual fish examined and percent occurrence (F) of prey among fish examined. The fish uere collected by bottom traul at the nearshore site in uestern Lake Erie near Bono on July 28, 1983. Footnotes as in Table 16 .

F i sh S p e c i es a

DRUM GSHD TRTP UfiLL UBfiS UPCH YPCH

^ n, n uith food*3 13, 12 7, 7 IS, 15 1. 1 8, 8 9, 9 12, 12 Standard length, 1 min. — max. (mm) 18-31 2-1-33 24-39 5 2 2 1 - 4 0 2 3 - 4 4 3 0 - 3 7 D r y u e i gh t , min. - max. (mg) 19-96 2 7 - 9 4 45-189 297 30-282 45-394 87-164 prey ueight < u g / f i s h ) 1 1 2 . 8 1 6 8 . 8 327.6 4026.4 547.5 1969.9 6 4 7 . 6

Prey taxa P F P F P F P F P F P F P F

B l g a e --- C N e m a t o d a 1 8 □1igochaeta t* 8 1 4 7 C 1a d o c e r a Leotodora ki ndt i 9 31 1 14 1 13 1 l OO 6 7 5 8 8 9 < l e 8 Dianhanosoma so. 2 5 7 I 7 < 1 5 0 < 1 5 6 Sida crustal1ina < 1 13 171 lable 23 (coritinuedl,

F i sh S p e c i es P r e y T a x a DRUM GSHD TRTPUHLL UBFISUPCH YPCH

D a p h n i a r e l r o c u r u a 56 7 8 1 0 0 2 4 9 3 11 75 32 lOO 64 lOO D. aa 1cata m e n d o t a e 15 2 7 12 63 17 lOO 8 8 3 B o s m i n a 1 an a i i-os tr i s t 2 2 Eubosmi na c o r e g o n i 4 3 < 1 13 <1 25 <1 33 L e u d iQ i a sp. 1 7 3

I luocr~upt.us sp. 1 13

O s t r a c o d a 8 13 E u c o p e p o d a C a l a n o i d a a f F i n i s < 1 13 1 11 2 17 Leplodiaptomus so.a 1 3 3 L. a s h 1 andi < 1 3 3 1 4 2 L. sici1 is < 1 7 1 5 6 1 4 2 L. siciloides 2 8 2 43 120 66 100 3 7 l O O 9 7 5

1 P| jc> i C y c d a 172 Table 23 (continued),

F i sh S p e c i es P r e y T a x a DRUMGSHD TRTP UfiLL UBfiS UPCH YPCH PF PF PF P F P F PF PF flcanthocuc1 ops werna1i s 13 38 2 4 3 2 4 0 2 6 3 1 8 9 5 l O O Oiacuclaps tliomasi 1 2 0 t 2 2 < 1 17 Hesocuclops edax 2 15 12 1 0 0 9 7 3 3 75 2 8 9 2 4 2 D i p i e r a C h i r-onom i da e 15 15 4 9 6 7 6 17 Oste i chthyes 99 lOO D e b r i s -- 31 -- 13 --- 13 173 Table 24 • Per-cent, composition (P) of prey by dry ueight per individual fish examined and percent occurrence

Fish Species^

DRUM 6 S H D TRTP UBfiS UPCH YPCH in n, n uith foodb 6, 6 in 4, 3 3, 3 10. 10 9, 9 Standard length, min. — max. (mm) 35- 53 28-41 34-46 32-46 28-42 38-50 Dry ueight, min. — max. (mg) 147- 555 42-191 124-300 113-142 60-348 172-405 prey ueight ( u g / f i s h ) 461 . 1 593. 1 368.0 793.8 1245.6 951.4

Prey taxa P F P F P F P F P F P F filgae __ C 17 -- 20 N e m a t o d a 4 33 R o t i f e r a --- 20 Oligochaeta tf 50 --- 33 t 50 t 22 ficarina 7 17 r 1a d o c e r a Leolodora Uindti 3 50 23 80 3 50 1 5 l O O 19 90 2 56 T a b 1e 24 *cont i nued),

F > sh S p e c i es Prey Taxa DRUM GSHD TRTP UBflS UPCH YPCH ______P F_____ P F P F_____ P F P F P F

Diaphanosoma sp. < ie 17 13 1 0 0 3 1 0 0 1 8 0 Daphnia retrocurua 1 5 0 2 8 1 0 0 1 2 5 2 6 7 4 1 0 0 3 7 8 D. aaleata mendotae < 1 2 0 < 1 2 0 < 1 11 Bpsmina lonoirostris < 1 2 2 Eubosmina coreqon i 31 1 0 0 < 1 6 7 < 1 5 0 t 11

L e u d i q i a s o . < 1 5 0 I s t r a c o d a 4 17 2 0 5 0 2 2 2 iucopepoda C a l a n o i d a Eoischura tacustris t 10

L e o t o d i a o t o m u s s p . q t 10 L. aehlandi < 1 2 0 L. sici1 is t io L. siciloi des 1 33 2 4 0 1 2 5 8 0 l O O 5 4 1 0 0 2 9 l O O C yc Iop o i da flcanthocuclops vernal is 5 1 0 0 1 4 0 1 2 5 1 3 3 7 8 0 1 3 1 0 0 Diacyclops Ihomasi < 1 2 0 t 11 Hesocuc1 ops edax 6 6 7 2 8 0 6 5 0 < 1 3 3 8 5 0 17 8 9 Table 24 (continued),

Fish Species P r e y T a x a DRUM GSHD TRTP UBfiS UPCHYPCH P F P F P F P F P F P F O i p t e r a Chi ro n o m i da e 7 0 6 7 68 50 6 30 33 56 Trichoptera 1 11

Debris --- 2 5 -- 11 176 Table 25- Percent composition (P) of prey by dry weight, per individual fish examined and percent, occurrence (F) of prey among Fish examined. The fish were collected by bottom trawl, nearshore, in western Lake Erie near Qono on Rugust 24, 1983. Footnotes as in Table 16 *

Fish Speciesa

DRUM ESHN GSHD RSMT TRTP UBfiS UPCHYPCH n, n with f ood k ?, 6 4, 2 5, 5 lO, 4 8, 8 5, 5 5, 5 6, 6 Standard length, min. - max. (mm) 48-65 19-25 3 0 - 5 8 24-35 40-65 21-29 45-55 47-52 Dry ueight, min. - max. (mg) 453-1285 13-25 5 6 - 7 8 2 1 5 - 4 8 2 0 3 - 9 1 6 2 4 - 7 7 338-925 388-540 prey ueight ( u g / f i s h ) 2121.2 11.7 566.2 4.2 3 9 9 . 3 236.4 9474.6 593.6

P r e y t a x a P F P F P F P F P F P F P F P F

HI ga e -- c 2 0 R o t i fe r a --- 2 0 01igochaeta t f 4 3 --- 2 0 --- 2 0 1 8 8 --- 14 t 6 7 C 1a d o c e r a Leptodora Ui ndt i 5 9 2 5 2 0 4 0 6 5 10 2 3 8 2 0 71 4 6 3 5 3 3 N O Diaohanosoma so. A Latona set i fera < 1 14 1 13 T a b 1e 25

F i sh S p e c i es Pneij Taxa DRUM ESHN GSHD RSMT TRTP UBfiS UPCH YPCH ______PF PF PF PF PF PF PF PF Daphn i a reirocurua t 14 6 2 6 0 < 1 2 9 I 13 < 1 3 3 Eubosm i na coreqoni 13 8 0 < 1 1 3 < 1 14 < 1 5 0 < 1 17 Leudi a i a s o . 1 6 3 < 1 2 5 < 1 17 I luocmotus sp. < 1 13 Ostr-acoda 6 4 3 9 2 5 1 13 6 17 Eucopepoda ■ C a l a n o i d a Eurutemara aFFinis < 1 13 t 13 Leptodi aptamus s i c i I is < 1 2 0 L. siciloides t 14 t 2 0 2 5 io < 1 1 3 19 5 7 < 1 2 5 1 17 Cyclopoida f i c a n t h o c u c 1o p s u e r n a i i s 6 7 86 41 25 280 30 l O O 5 0 71 5 9 6 3 2 5 8 3 Mesocyr. 1 ops edax 1 2 8 6 2 4 0 10 10 3 0 8 8 IO 5 7 3 5 0 12 8 3 Harpacti co i da Canihocamptus robertcoUeri t 13 D i p t e r a C h i rononi i da e 14 5 ? 2 6 3 8 3 2 13 5 0 3 3 178 Table 25 (continued),

Fish Species Prey Taxa DRUM ESHN GSHD RSMT TRTP UBfiS UPCH YPCH li. U. Q. L l P F P F P F CL CL P F P F

D e b r i s --- 7 1 -- 2 0 --- 1 3 --- 2 0 --- 5 0 179 Table 26* Percent composition

of prey by dry weight per individual fish examined and percent occurrence (F> of prey among alewife, freshwater drum, emerald shiner, gizzard shad, rainbow smelt, and spottai1 shiner examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on July 24- 25, 1984. The prey Iisted were identified from these and the fish Iisted in Table 27. Footnotes as in Table 16.

Fish Speciesa

flLUF D R U M ESHN GSHD RSMT SSHN n, n uith food^ 15, 13 43, 3 8 4, 4 27, 26 57, 43 2, 2 Standard length, min. - max (mm) 19-44 1 6 - 3 7 27-29 20-41 26-45 2 3 Dry uei ght , min. - max. (mg) 1 3 - 1 9 9 11-119 34-50 9-176 11-107 21-23 p r a y cie i gh t ( ug /f i sh) 1050.5 103.9 131.0 457.3 150.9 1 1 9 . 5

P r e y t a x a P F P F P F P F P F P F

R o t i fe r a tf 13 1 2 5 t 7 □1igochaeta 4 2 4 t 2 C l a d o c e r a Leptodora Uindti 5 60 12 26 6 25 2 41 5 23 Diaohanosoma sp. t 13 1 5 t 4 < f 4 T abIe 26 (conti nued),

F i sh S p e c i es P r e y T a x a BLUF DRUMESHNGSHORSMTSSHN p F PFPF Laiona set i fera < 1 Sida crustal1ina < 1 2 Hoi opedium gi bberum t 7 t 2

Cer i odaphni a sp. t 20 t 2

Paphni a retrocurua 2 6 0 4 21 2 2 5 2 5 9 2 19

D - oaIeata mendotae 5 4 8 7 15 21 7 7 5 6 7 9 3 6 3 0 5 8 5 0 D. p u l e x < 1 3 3 < 1 7 t 2 P. schodleri < 1 7

B os m i na 1ongi rostri s 1 6 0 < 1 12 8 5 0 < 1 2 6 < 1 18 2 5 0 Eubosmina coreqoni 3 6 7 t 2 7 6 5 0 2 2 6 2 2 6 7 5 0 Chudorus sp. t 7 Lendi qi a sp. t 2

1 Uiocruptus sp. < 1 ? Q s t r a c o d a E u c o p e p o d a nauplius larua 20 11 C a I a n o ida 181 Table 26 (continued),

Fish Species Prey Taxa flLUF DRUM ESHN GSHORSMT SSHN P F P F P F P F PFP F EDischura lacuslris t 7 Eurutenora aFFinis < 1 4 0 3 17 < 1 19 2 14 3 5 0

Leptodiaptomus sp.q 1 7 3 < 1 7 < 1 9 7 5 0 L. a s h 1andi 2 6 0 3 7 1 9 9 5 0 L. m i n u l u s : 1 2 7 t 4 L. sici1 is 2 6 0 3 11 1 7 5 5 0

L. sici1 aides 1 4 7 < 1 2 1 —y% 1 14 Sic i st o d i ap l o n u s oreoonensi s t 13 < 1 2 Cyclopoida Rcanthocuc1ops Verna1i s 2 4 8 7 2 2 6 0 16 70 4 18 9 l O O Diacuclops thomasi 2 8 0 1 4 8 1 18 Eucuclops soeralus Hacrocuclops albidus « 1 13 Mesocuclops edax 1 4 7 1 io 1 15 < 1 2 D i p i e r a C h i ro n o m i da e 3 8 12 Qste i chthyes 75 4 182 Table 26(conli nued) ,

Fish Species

P r e y Taxa flLUF DRUM ESHN GSHD RSMT SSHN P F P F P F P F P F P F D e b r i s ---c 16 183 Table 27. Percent composition (P) of prey by dry ueight per individual fish examined and percent occurrence (F) of prey among trout—perch, walleye, white bass, white perch, and yellow perch examined. The fish were collected by bottom trawl, offshore, in western Lalce Erie near Middle Sister Island on July 2 4 — 25, 1984. The prey listed were identified from these and the fish listed in Table 26, Footnotes as in Table 16 .

Fish Species3

TRTP UftLL U B R S U P C H Y P C H

n , n w i th food ^ 25, 2 3 7. 7 57, 54 58, 58 50, 48

1 Standard length, min. — max. (mm) 2 5 - 3 6 4 3 - 6 7 17-45 18-48 2 2 - 4 3

Dry we i gh t , min — max. (mg) 35-131 222-820 11-358 18-209 26-281

prey we i ght (ug/fish) 200. 7 4 0 1 7 . 6 532 . 7 845. 7 1009.1

P r e y t a x a P F P F P F P F P F

R o t i f e r a

01igochaeta 1 28 tf 2 t 5 t 10

C l a d o c e r a Leotodora Lindti 32 40 lO 74 lO 78 4 52

D i aohanosoma s p . t 2 t lO

Latona set ifera t 2 t 2 184 Table 27 (conlintied) ,

Fish Spec i es P r e y T a x a T R T P UflLL DBAS UPCHYPCH p F PF P F Sida cruslal1ina < le H o 1oped i ua ai bberum t 2 t 2 Ceriodaphni a sp. I 5 t 10 Daphn i a retrocurua 4 6 0 3 61 4 6 2 5 7 0 D. oaleata mendoiae 8 4 0 14 45 79 37 83 34 76 D. p u l e x < 1 4 < 1 5 t 2 < 1 22 D. schodIeri < 1 14 t 2 < 1 3 t 2

Bosmina lonpirostris < 1 20 t 9 t 2 2 < 1 4 0 Eubosmina coreqoni t 11 < 1 28 3 64 Chudorus sp.

LeudiQia sp. 5 6 4

1luocruotus sp. < 1 8

C lstracoda 2 4 E u c o p e p o d a naup1i us 1arua C a l a n o i d a Epischura lacustr is < 1 185 T ab 1 e 27< co n i i nu e d ) ,

Fish Species Prey Taxa TRTP UflLL UBflS UPCH YPCH P F P F P F PF P F Eurutemora affinis lO 5 2 < 1 14 3 4 3 1 6 5 2 Leptodiaotomus sc.Q t 9 t 1 2 L . a s h 1 andi < 1 2 5 < 1 3 3 t 14 L - m i nu t us t 2 L. sici1 is < 1 5 < 1 19 t 4 L. siciloides < 1 19 < 1 l O t 2 S U i st o d i an t o n u s oreaonensi s CycIopo i da flcanthocyc1ops vernal is 6 3 2 3 2 7 9 4 0 9 8 32 9 0 Diacuclops thomasi 1 2 0 3 4 9 3 71 3 8 0 Eucucloos speratus t 4 MacrocucIops albidus Mesocuclops edax 1 16 2 4 4 1 41 J 3 2 D i p t e r a Chi rc n o m i da e 3 0 16 1 3 1 4 □s iei chthyes 1 0 0 l O O 3 2 D e b r i s --- c 11 -- 2 -- 7 186 Table 28. Percent, composition (P) of prey by dry ueight per individual fish examined and percent occurrence CF) of prey among aleuife, freshwater drum, emerald shiner, gizzard shad and rainbow smelt examined. The fish were collected by bottom trawl, offshore, in western Lake Erie near Middle Sister Island on August 6, 1984. The prey listed were identified from these and the fish listed in Table 291 Footnotes as in Table 16.

F i sh S p e c i es a

flLUF DRUM E S H N G S H D RSMT n, n with food^ 5, 5 4, 4 2, 2 6, 6 10, 8 Standard length, min. — max. (nun) 18-35 24-35 28-3? 24-44 26-35 Dry wei ght, min. — max.

Prey taxa P F P F P F P F P F

Rot i fera < le 50 □1igochaela 2 5 0 Cladocera Leotodora kindti 3 8 0 7 6 7 5 1 17 DiaDhanosoma so. < 1 2 0 < 1 2 5 1 1? Sida crustal1ina 3 2 5 187 Table 28 < cont i i iued ) ,

Fish Species P r e y T a x a flLUF D R U M E S H N G S H D R S M T p F P FP F

Daphni a reirocurva 1 20 2 3 8 3

D- galeata mendotae 6 100 5 0 2 5 0 2 0 1 0 0 11 lO

Bosmi na 1onqi rostr i s 5 100 3 5 100 1 5 0 37 6 0

Eubosm i na coreqon i 13 10 0 6 3 l O O 4 3 3 13 3 0 Eurucercus lamellalus 6 1 7

L e u d i q ia sp. 1luocruptus sp.

O s t r a c o d a 20 E u c o p e p o d a nauplius larua 20 17 C a l a n o i d a

Episehura lacustris <■ 1 20 EuruEemora affinis 2 3 0 2 5 Leplodiaptoaus sp.g • 2 8 0 L. a s h 1a n d i 17 8 0 < 1 17 L . m i n u i u s t 20

L. s i c i l i s < 1 20 188 Table 28(canti nued>,

F i sh S p e c i es P r e y T a x a flLUF DRUM ESHN GSHD RSMT P F P F P F P F P F L . s i c i1o ides 1 6 0 C y c I o p o i da

Rcanthocuic 1 o d s uerna 1 is 41 8 0 14 5 0 4 2 l O O 3 3 2 0 Diacucloos ihomasi 4 8 0 1 5 0 6 lO

H a c r o c u c 1o d s a 1b idus

H e s o c u c I q d s e d a x 2 8 0 2 5 0 U i p t e r a Chironomi dae Ostei chthyes

D e b r i s -- c 5 0 --- 5 0 189 Table 29, Percent, composition

of prey by dry weight per individual fish examined and percent occurrence

F i sh S p e c ie

T R T P UflLL UBflS UPCHYPCH n, n with food^ 4, 4 1. 1 6, 6 6, 6 5. 5 Standard length, min. — max. (an) 2 9 - 3 6 7 0 2 0 - 2 9 1 6 - 3 7 2 0 - 4 6 Dry ueight, min. — max. (mg> 6 9 - 1 4 2 1040 24-73 13-238 1 8 - 3 9 6 prey ueight t u g / f i s h ) 116.4 1616.7 7 7 0 . 7 1 5 4 0 . 0 1 2 2 1 . 5

P r e y t a x a P F P F P F P F P F

R o t i fe r a U1igochaeta 2 5 0 C 1a d o c e r a Lentodora hindti 73 7 5 lO l O O 21 1 0 0 3 6 0 Di aphanosoma sp. < le 17 < 1 5 0 tf 2 0 Table 29 (continued),

Fish Species Prey Taxa TRTP UflLL UBRS UPCH YPCH ______P F_____ P F_____ P F_____ P F_____ P F Daphnia retrocurva 1 2 5 1 5 0 2 6 7 8 1 0 0 D. oaleata mendotae 2 2 5 11 8 3 9 1 0 0 4 8 l O O Bosmina lonairostris < 1 5 0 < 1 6 7 2 1 0 0 Eubosmina coreqoni 2 6 7 2 6 7 5 8 0 Eurucercus lamellatus

L e u d i q i a s o • 4 1 0 0 t 17 < 1 6 0 Iluocruptus sp. 1 2 5 O s t r a c o d a F u c o p e p o d a naupt ius larva C a l a n o i d a Epischura Iacustri s Eurutemora affinis 12 5 0 1 3 3 2 lOO Leptodiaptomus sp.a t 17 1 6 7 L. a s h 1andi 1 6 7 2 8 3 1_ m i n u t u s t 17 L . s i c i l i s t 17 t 33 191 Table 29 (continued),

Fish Species Prey Taxa TRTP UfiLL UBflS UPCH YPCH P F P F P F PFPF L. sicila ides < 1 2 0 C y c l o p o i d a flcanthocuclops uernalis 6? 100 51 100 2 8 1 0 0

D i ac u c 1d d s t h o m a s i 2 6 7 2 l O O 1 8 0

H a c r o c u c 1 ods a 1 b i ckis < 1 17 Hesocgc1ops edax 6 2 5 6 8 3 1 100 1 6 0 D i p t e r a C h i ron om i da e 5 17 Oste i chthyes lOO lOO D e b r i s 192 Table 30.. Percent, composition (P) of prey by dry ueight per individual fish examined and percent occurrence (F) of prey among alewife, freshwater drum, gizzard shad, rainbou smelt and spottai1 shiner examined. The fish uere collected by bottom traul, offshore, in western LaUe Erie near Middle Sister Island on August 21, 1984. The prey listed uere identified from these and the fish listed in Table 31. Footnotes as in Table 16 •

F i sh S p e c i es a

flLUF D R U M GSHD RSMT SSHN

b n, n with food 2, 1 3, 3 5, 5 10, 6 1. 1 Standard length, min. — max. (mm) 2 4 - 2 5 4 4 - 5 0 70-82 30-46 35 Dry ueight, min. — max (mg) 2 3 - 6 2 2 291-498 1216-2604 28-128 138 Prey ueight < u g / f i s h ) 3934.5 140.5 1044.3 24.8 4 6 7 8 . 9

P r e y t a x a P F P F P F P F P F

N e m a t o d a

R o t i fe r a tf 5 0 < P 1 0 0 D1igochaeta 2 6 7 L 1 0 0 flcar i na 11 6 0 C 1a d o c e r a Leotodora kindti 9 8 5 0 7 l O O 15 2 0 Table 30 (coniinued),

Fish Species Prey Taxa flLUF DRUM GSHD RSMT SSHN ______PF PF PF PF PF Diaphanosoma sp. t SO Latona set i fera Daphn ia retrocurua < 1 50 < 1 40 6 30 < 1 lOO Bosmi na lonoirosiris t 50 < 1 33 15 100 Eubosmi na coreqoni t 50 38 100 t 100 fllcna sp. Leudioia sp. < 1 33 < 1 60 t 100 I 1uocruptus sp. < 1 20 Ostracoda 2 20 E u c o p e p o d a nauplius larva t 20 C a l a n o i d a Epischura lacustris < 1 50 Eurutemora afF inis < 1 50 3 67 7 100 79 40 < 1 100 Leptodiaptomus sp. g t 20 C y c 1o p o i da fleanthocucIops vernal is 1 50 2 33 17 100 < 1 100 Diacuclops thomas i t 50 Table 30 (continued),

Fish Species P r e y T a x a flLUF DRUM GSHD RSMT SSHN P F P F P F P F P F

H a c r o c u c 1o d s a I b i du s

H e s o c u c 1O D S e d a x 2 1 6 ? 1 6 0 H a r p a c t i co ida Canthocamptus roberlcokeri t 2 0 D i pt e r a C hi ronoin i da e 71 3 3 9 9 l O O Ostei chthyes D e b r i s -- c 1 0 0 --- l O O 195 Table 31, Percent, composilion (P) of prey by dry weight, per individual fish examined and percent occurrence (F) of prey among trout-perch, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl, offshore, in western LaUe Erie near Middle Sister Island on Rugust 21, 1984. The prey listed were identified from these and the fish listed in Table 30, Footnotes as in Table 16.

F i sh S p e c i e#

TRTP UBOSUPCHYPCH n, n with fooc^ 6, 6 11, 11 10, lO 9, 9 Standard length, min. - max. (mm) 3 4 - 4 4 39-61 28-49 46-60 Dry ueight, min. - max. (mg) 120-286 2 4 9 - 1 0 6 6 69-694 350-846 prey ueight ( u g / f i s h ) 3 6 8 . 1 1344? 1539.1 734.7

P r e y t a x a P F P F P F P F

N e m a t o d a tf 11 R o t i fera □1igochaeta 2 8 3 t 3 0 t 2 2 O c a r i n a Cladocei'a Leotadara Icindti < le 6 4 1 8 7 0 1 3 3 Table 31 (continued),

F i sh S p e c i es a Pr-ey 1 axa TRTP UBflS UPCH YPCH ______P F______P F______P F______P F Diaphanosoma sp. Laiona set ifera < 1 2 0 1 2 2 Daohnia retrocurua t 36 < 150 1 33 Bosmina lonair-ostr-is < 1 17 < 1 7 0 t 11 Eubosmina coreaoni < 1 17 1 6 0 < 1 44 fllona so. t 11

L e u d i q i a s o . 3 1 00 1 9 0 < 1 44 Iluocruotus sp. 3 8 3 2 7 0 1 6 7 □ s t r a c o d a 5 4 6 7 3 6 0 E u c o p e p o d a nauplius larva C a 1a n o i da Epischura lacustris Eurutemora affinis 14 l O O t 9 3 2 l O O 12 7 8 Leptodiaptomus so.a C y c 1o p o i da Bcantliocuc 1 ops vernal is 3 5 0 t 18 3 2 100 9 8 9 Oiacuclops thomasi t 9 < 1 6 0 1 3 3 Table 31 (continued),

Fish Spec i esa Preu Taxa TRTP (JBftS UPCH YPCH P F P F P F P F

H a c r o c u c 1o d s a 1b id u s < 1 11 Mesocuclops edax 9 SO t 9 2 8 0 4 8 9 Harpacti co i da Canthocamptus robertcoUeri < 1 6 0 D i p t e r a Chironomidae 11 17 7 4 0 7 0 11 Osteichthyes 9 9 5 5 D e b r i s -- ^ 6 7 -- 3 0 --- 7 8 198 Table 32. Percent, composition (P) of prey by dry ueight per individual Pish examined and percent occurrence (F) of prey among aleuife, freshwater drum, emerald shiner, gizzard shad, and rainbow smelt examined. The fish were collected by bottom trawl, offshore, in western LaUe Erie near Middle Sister Island on September 5-6, 1984. The prey listed uere identified from these and the fish listed in Table 33, Footnotes as in Table 16.

Fish Species3

FlLUF D R U M ESHN GSHDRSMT n, n with food^* 11, 11 33, 32 16, 14 23, 23 36, 2 9 Standard length, min. — max. (mm) 64-80 40-70 40-49 79-113 26-43 Dry w e i gh t , min. — max. (mg) 9 8 6 - 2 0 7 9 227-1308 134-390 1576-6939 16-110 prey ueight ( u g / f i s h ) 2166.6 234.9 125. 1 9 8 4 : 3 2 6 . 2

Prey taxa P F P F P F P F P F

Turbellaria N e m a t o d a tf 17 R o t i fer a t 3 6 t 3 8 < le lOO □1igochaeta 3 6 0 t 13 H i r u d i n e a < 1 3 t 6 199 Table 32 (continued),

F i sh S p e c i es Prey Taxa flLUF DRUMESHN GSHD RSMT

O c a r i n a <1 9 13 4 3 C l a d o c e r a Leptodora U i ndt i 7 6 l O O 33 79 86 81 6 91 11 22 D i aphanosoma sp. 1 -15 1 2 7 < 1 3 5 2 8 Sida crustal1ina 2 3 Daphn i a retrocurua 4 2 7 < 1 < 1 < 1 3 9 6 22 D. p a 1e a t a m e n d o t a e 1 9

Bosoi i na 1 on q irostris ‘ 1 55 t 12 7 7 S 15 100 < 1 6 Eubosmina coreqoni 9 64 t 3 7 6 3 13 8 3 2 17 fllona sp. i 13 Chudorus sp. < 1 2 7

L e u d i q ia sp. < 1 9 < 1 3 5

1luocruptns sp. 6 4 5 1 7 0 O s t r a c o d a 3 36 2 2 2 4 9 3 9 E u c o p e p o d a nauplius larva t 3 5 C a l a n o i d a Ep i sc h u r a 1acustr i s < 1 200 Table 32 (continued),

F i sh S p e c i es Prey Taxa flLUF DRUM ESHN GSHD RSMT

Eurutemora affinis < 1 18 3 3 3 9 7 2 5 6 LeptodiapLomus sp.g L. a s h 1 andi L. m i n u t u s t 18 L. sici1 is t 18 L. sici ioides 1 18 Cyclopoida flcanthocuc1ops vernal is 3 3 6 lO 5 8 14 7 8 1 3 D i acu c 1ops thomas i < 1 18 < 1 2 6 < 1 3 E u c u c 1o p s s p e r a t u s Hacrocuc1ops albidus 1 3 t 4

M e s o c u c 1o p s e d a x 2? 8 5 2 < 1 17 1 H ar pa c ti ca i da Canthocaaptus robertcoUeri < 1 < 1 3 0 flmph i po d a 201 Table 32 (continued),

F i sh S p e c i es P r e y T a x a flLUF DRUM ESHN GSHD RSMT P F P F P F P F P F D i p t e r a Chi ronami dae 12 3 0 21 17

Debr- i s -- c 41 -- 7 0 202 Table 33* Percent, composition (P) of prey by dry ueight per individual fish examined and percent occurrence (F) of prey among trout-perch, white bass, white perch and yellow perch examined. The fish were collected by bottom trawl, offshore, in western LaUe Erie near Middle Sister Island on September 5-6, 1984. The prey listed were identified from these and the fish listed in Table 32* Footnotes as in Table 16 .

F i sh S p e c i es®

TRTP UBflS UPCH YPCH n , n with food^ 31, 2 9 20, 16 29, 2 9 22, 2 2 Standard length, min. — max. (mm) 3 6 - 5 1 4 1 - 5 2 3 6 - 5 9 4 4 - 5 5 Dry ueight, min. — max. (mg) 173-483 266-601 149-1192 287-659 prey weight < u g / f i s h ) 611.9 481.2 3636.9 7 2 8 . 7

P r e y t a x a P F P F P F P F

Turbellar ia t f 3 t 5 t 3 t 5 N e m a t o d a t 10 t 5 t 3 8 t 18 R o t i fe r a t 5 t 7 t 5 01igochaeta 3 81 t 5 < le 6 6 < 1 41 H i r u d i n e a 1 6 t 5 t 3 t 5 203 Table 33 (continued),

Fish Spec i esa P r e y T a x a TRTP UBflS UPCH YPCH

R e a r i na C 1a d o c e r a Leptodora Ui ndt i 1 2 9 5 4 6 0 12 9 7 10 91 Diaphanosoma sp. t 3 3 4 0 < 1 5 2 S i da crustal1ina < 1 3 t 7 < 1 14 Daphn i a retrocurua t 3 2 4 0 t 2 8 D. oaleata mendoiae t 3 t 5 B osm i na 1onqi rostri s t 19 <1 20 < 1 7 6 < 1 5 0

Eubosmina coreqoni t 6 t 10 < 1 6 9 < 1 18 flI on a sp. Chudorns sp. Leudioi a sp. < X 6 5 < 1 5 < 1 9 0 < 1 5 5 1luocrnptus sp. 3 0 9-4 5 3 3 1 0 0 4 9 5 □ s t r a c o d a 3 9 5 5 17 5 12 9 7 3 2 3 E u c o p e p o d a nauplius larva C a l a n o i d a Epischtira laeustris < 1 10 204 Table 33 (continued),

F i sh S p e c i es Prey Taxa TRTP UBflS UPCH VPCH ______P F______P F P F______P F Eurutemora aFf inis 5 81 6 20 8 97 24 82 Leptodiaptomus sp.g t 7 L. a s h 1 and i L. minutus <1 5 L . sici1 is L ■ sici1oi de s < 1 5 C y c 1o p o i da Ocanthocuc1ops vernal is 3 68 3 25 17 100 39 95 D i acuc1ops thomasi t 3 <1 15 < 1 59 < 1 18 Eucuc1ops speratus t 5 Hacrocuc1ops a1b i dus < 1 3 < 1 5 t21 1 27 Mesocuc1 ops edax 3 65 4 25 3 93 1 45 H a r p a c t i co i da Canfchocamptus robertcokeri < 1 23 < 1 5 1 86 < 1 27 flmph i poda 1 3 D i p t e r a Ch i ronom i dae 14 32 1 5 lO 66 15 32 205 Table 33 (continued),

Fish Species P r e y T a x a TRTP UBRS UPCH YPCH P F P F P F P F D e b r i s — C 3 2 --- 1 5 --- 6 6 --- 2 3 206