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This is to certify that the

thesis entitled

Factors Influencing the Year-class Strength of
Reef-spawned Walleye in Western Lake Erie

presented by

Edward Francis Roseman

has been accepted towards fulﬁllment
of the requirements for

Master of Science Fish. & Wildl.

degree in

Mam

Major profesy r

 

 

 

Date July 22, 1997

 

0-7639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

 

 

LIBRARY

Michigan State
University

 

 

 

PLACE IN RETURN BOX
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DATE DUE DATE DUE DATE DUE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1/96 c/CIRCIDdoDm.p65~p.14

FACTORS INFLUENCING THE YEAR-CLASS STRENGTH OF REEF-SPAWNED
WALLEYE IN WESTERN LAKE ERIE

By

Edward Francis Roseman

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

MASTER OF SCIENCE

Department of Fisheries and Wildlife

1 997

ABSTRACT

FACTORS INFLUENCING THE YEAR-CLASS STRENGTH OF REEF-SPAWNED
WALLEYE IN WESTERN LAKE ERIE

By

Edward Francis Roseman

Variation in egg and larval survival have been suspected to be principal sources of
walleye Stizostedion vitreum recruitment variability in Lake Erie. I examined walleye
egg deposition and survival and larval vital rates in western Lake Erie in 1994 and 1995.
Densities of eggs and larvae were higher in 1994 than 1995. Growth of larval walleye
was greater in 1994. Larval densities were greater at western sites in 1994 and greater at
eastern and south-eastern sites in 1995. Slow water warming rates and frequent intense
winds contributed to the low density and survival of eggs on reefs in 1995 by prolonging
incubation periods and increasing the vulnerability of eggs to mortality factors. Optimal
year-class strength could result with precisely timed events providing high egg densities,
fast water warming rates and few wind storms in spring providing good egg survival and

high larval densities.

Dedicated to Ma, Dad, EOR,
and Dennis Hugick

iii

ACKNOWLEDGMENTS

This work was funded by the Michigan Department of Natural Resources, Ohio
Division of Wildlife, and Michigan State University. Funding was also provided by the
Saginaw Bay Walleye Club. Travel support to present results of this research at
professional meetings was provided by the MSU Department of Fisheries and Wildlife
Graduate Student Organization, MI Chapter of the American Fisheries Society, and the
North Central Division of the American Fisheries Society.

I thank my committee members, Dr. Daniel Hayes, Dr. Gary Mittelbach, and
Robert Haas for all of their constructive comments, guidance, and patience throughout the
duration of this research. I extend special thanks to my advisor, Dr. William Taylor, for
his support, guidance, trust, and patience over the past three years.

I thank the Lake Erie Biological Station of the US. National Biological Service
for supplying 1994 and 1995 water temperature data. My gratitude is also extended to
John Amberg, Dr. Carl Baker, Dr. Salvador Becerra-Munoz, Dr. Russell Brown, Mike
Bur, Rick Clark, Dave Davies, Brian Fedewa, Dr. Paola F ererri, Dave Fielder, Dr. John
Fomey, Eric Grundemann, Brian Ickes, Doug Jester, Jim Johnson, Myrle Keller, Mark
Kershner, James Ladonski, Stu Ludsin, Dr. Charles Madenjian, Scott Miller, Dr. Ed
Mills, Joseph Mion, Ken Muth, Ken Paxton, Pam Petrusso, Melinda Raths, Nancy

Roseman, Dr. Lars Rudstam, Dr. Edward Rutherford, Arthur Schaub, Mark Scheuerell,

Kristi Sitar, Shawn Sitar, Ted Sledge, Madeline Smith, Dr. Roy Stein, Mike Thomas,
Mark Turner, Jeff Tyson, and Dan Weisenreder for their assistance with various aspects
of this work. I am especially grateful to Robert Haas of the Mt. Clemens Fisheries Station
(MI DNR) and Roger Knight of the Sandusky Fisheries Station (Ohio Division of
Wildlife) for their unending patience and commitment beyond the call of duty.

I would like to thank my families in New York and Michigan for their love,
encouragement, and patience during my education. I am especially indebted to my son,
Edward Orville, from whom I constantly draw strength and inspiration. I sincerely hope
that someday he will understand why Dad spent so much time “in the Big Boat on the

Big Water.”

TABLE OF CONTENTS

LIST OF TABLES ............................................................................................................. ix
LIST OF FIGURES ........................................................................................................... xi
THESIS INTRODUCTION ................................................................................................. 1
Study Area ....................................................................................................................... 6
CHAPTER I: WALLEYE EGG DEPOSITION AND SURVIVAL .................................. 9
ABSTRACT. ........................................................................................................................... 9
INTRODUCTION ................................................................................................................... 10
STUDY AREA DESCRIPTION ................................................................................................. 1 1
METHODS ............................................................................................................................ 13
Egg Collection ................................................................................................................ 13
Egg Production ............................................................................................................... 15
Physical, Limnological, and Climatological Parameters ................................................ 16
Egg Predator Diet Examination ...................................................................................... 17
Larval Abundance ........................................................................................................... 17
Index of Year-Class Strength .......................................................................................... 18
Statistical Analysis ......................................................................................................... 18
RESULTS ............................................................................................................................. 20
Reef Substrates ............................................................................................................... 20
Walleye Egg Deposition ................................................................................................. 20
Walleye Egg Viability and Survival ............................................................................... 23
Egg Production ............................................................................................................... 27
Egg Predator Diet Examination ...................................................................................... 30
Age-O Walleye Abundance and Index of Year-Class Strength ...................................... 31
Physical, Limnologic, and Climatological Parameters .................................................. 32

vi

DISCUSSION ........................................................................................................................ 36
CHAPTER II: DISTRIBUTION, DIET, GROWTH, AND SURVIVAL OF AGE-O

WALLEYE IN WESTERN LAKE ERIE .......................................................................... 41
ABSTRACT .......................................................................................................................... 41
INTRODUCTION ................................................................................................................... 42
METHODS ............................................................................................................................ 44
Larval Distribution and Abundance ................................................................................ 44
Age-O Walleye Growth ................................................................................................... 47
Age-O Walleye Survival ................................................................................................. 47
Index of Year-Class Strength .......................................................................................... 48
Age-O Walleye Diets ....................................................................................................... 48
Zooplankton Sampling ................................................................................................... 49
Statistical Analysis ......................................................................................................... 50
RESULTS ............................................................................................................................. 50
Age-O Walleye Distribution and Abundance .................................................................. 50
Age-0 Walleye Diets ....................................................................................................... 6O
Zooplankton Community ................................................................................................ 66
Ichthyoplankton Prey Community .................................................................................. 7O
Age-O Walleye Prey Selectivity ...................................................................................... 74
Age-O Walleye Growth ................................................................................................... 76
Age-0 Walleye Mortality Rates ...................................................................................... 81
Index of Year-Class Strength .......................................................................................... 82
DISCUSSION ........................................................................................................................ 83
Age-0 Walleye Distribution and Abundance .................................................................. 83
Age-O Walleye Diets ....................................................................................................... 87
Age-O Walleye Growth ................................................................................................... 91
Age-0 Walleye Mortality Rates ...................................................................................... 92
THESIS SUMMARY ........................................................................................................ 95
Appendix 1. Walleye larval and egg sample Site coordinates and depths. ....................... 97
Appendix 2. Catch-at-age model predictions .................................................................... 99
Appendix 3. Length-dry weight relationships for species collected in western Lake Erie,
1994 and 1995. ................................................................................................................. 100
Appendix 4. List of genera and families included in functional prey groups. ............... 102

Appendix 5. Densities (#/ l ,000 m3) of larval ﬁshes collected in neuston nets at each site in
1994 and 1995. ................................................................................................................. 102

vii

Appendix 6. Area, volume estimates, and percent of walleye larvae collected from each
depth zone in western Lake Erie. ..................................................................................... 131

LIST OF REFERENCES ................................................................................................. 132

viii

LIST OF TABLES

Table 1. Approximate area < 7m depth and estimated egg production with 95%
conﬁdence limits in parentheses for reefs in western Lake Erie, 1994 and 1995. Reef
area estimates from Bolsenga and Herdendorf (1993). "' indicates reefs that were
sampled, all other egg production values are extrapolated ......................................... 29

Table 2. Average numbers of walleye eggs observed in ﬁsh stomachs collected from
Toussaint and Niagara reefs, 1995 ............................................................................. 30

Table 3. Number of wind events that caused signiﬁcant mixing of western Lake Erie
waters in 1994 and 1995. Wind direction and intensity criteria based on Busch et al.
(1975) .......................................................................................................................... 33

Table 4. Percent composition of age-O walleye diets collected in pelagic neuston samples
and bottom trawls from western Lake Erie in 1994. * indicates walleye collected in
bottom trawls; % MT = percent of empty stomachs observed; TL = walleye total
length; TPB = total dry-weight biomass of prey items in walleye guts excluding
empty stomachs; SC = small cladocerans; Cal = calanoid copepods; Cyc = cyclopoid
copepods; LC = large cladocerans; Ben = benthic invertebrates; Spin = Spiny-rayed
ﬁsh prey; Sof = soﬁ-rayed ﬁsh prey; UFR = unidentiﬁable ﬁsh remains ................... 62

Table 5. Percent composition of age-0 walleye diets collected in pelagic neuston samples
and bottom trawls from western Lake Erie in 1995. * indicates walleye collected in
bottom trawls; % MT = percent of empty stomachs observed; TL = walleye total
length; TPB = total dry-weight biomass of prey items in walleye guts; SC = small
cladocerans; Cal = calanoid copepods; Cyc = cyclopoid copepods; LC = large
cladocerans; Ben = benthic invertebrates; Spin = spiny-rayed ﬁsh prey; Sof = soﬁ-
rayed ﬁsh prey; UF R = unidentiﬁable ﬁsh remains .................................................... 63

Table 6. Frequency of occurrence (%) of prey items observed in age-0 walleye stomachs
collected in neuston nets and bottom trawls (*) in western Lake Erie, 1994. Number
examined = number of ﬁsh stomachs examined; % MT = percent of empty stomachs
encountered; TL (mm) = mean total length of ﬁsh examined; R-N = rotifers and
nauplii; SC = small cladocerans; Cal = calanoid copepods; Cyc = cyclopoid
copepods; LC = large cladocerans; Ben = benthic invertebrates ................................ 64

Table 7. Frequency of occurrence (%) of prey items observed in age-0 walleye stomachs
collected in neuston nets and bottom trawls (*) in western Lake Erie, 1995. Number
examined = number of ﬁsh stomachs examined; % MT = percent of empty stomachs
encountered; TL (mm) = mean total length of ﬁsh examined; R-N = rotifers and
nauplii; SC = small cladocerans; Cal = calanoid copepods; Cyc = cyclopoid
copepods; LC = large cladocerans; Ben = benthic invertebrates ................................ 65

LIST OF FIGURES

Figure l. Landings of walleye from United States and Ontario waters of Lake Erie, 1915-
1994. Data from Regier et a1. 1969; Hatch et a1. 1987; Walleye Task Group Report
1995 ............................................................................................................................... 2

Figure 2. Abundance of age-2 walleye in Lake Erie as determined by CAGEAN model
estimates, 1978-1995. Data from 1995 Lake Erie Walleye Task Group Report 1995 ..... 3

Figure 3. Map of western Lake Erie study area. The dashed line delineates the extent of
larval sampling and the ellipse encompasses the mid-lake reef complex ..................... 8

Figure 4. Map identifying egg sampling reefs; N = Niagara reef; T = Toussaint reef.
Inlays are bathymetric representations of Niagara and Toussaint reef; ﬁlled circles
represent egg sampling Sites ........................................................................................ 12

Figure 5. Map of western Lake Erie identifying larval sampling sites; ﬁlled circles
represent larval sampling sites .................................................................................... 19

Figure 6. Weighted mean numbers of walleye eggs collected per 2 - min tow on Toussaint
and Niagara reefs, 1994. No eggs were collected in samples taken on 31 March
1994; no egg samples were taken between 28 April and 17 May 1994 ..................... 22

Figure 7. Weighted mean numbers of walleye eggs collected per 2 - min tow on Toussaint
and Niagara reefs, 1995 ............................................................................................... 24

Figure 8. Mean numbers of walleye eggs (i 1 SE.) collected per 2 - min tow from
different depth strata on Toussaint and Niagara reefs, 1994. No eggs were collected in
samples taken on 31 March 1994; no egg samples were taken between 28 April and
17 May 1994 ................................................................................................................ 25

Figure 9. Mean numbers of walleye eggs (i 1 SE.) collected per 2 - min tow from
different depth strata on Toussaint and Niagara reefs, 1995 ....................................... 26

Figure 10. Walleye egg viability estimates for pooled samples from Toussaint and
Niagara reefs, 1994 and 1995 ...................................................................................... 28

xi

Figure 11. Densities of larval walleye (i l s.e.) collected at sites on and adjacent to reef
complex in western Lake Erie, 1994-95 ...................................................................... 34

Figure 12. Mean daily water temperatures recorded at Niagara Reef for Spring of 1994
and 1995 ...................................................................................................................... 35

Figure 13. Map of western Lake Erie identifying sampling sites; all circles represent
larval sampling sites; white ﬁlled circles represent zooplankton sampling Sites; B
indicates bottom trawl stations .................................................................................... 45

Figure 14. Decline in pelagic walleye abundance based on catches in neuston samplers
taken at 15 to 40 sites in western Lake Erie in the Spring of 1994 and 1995. Values
are mean density (#/1,000 m3) i s.e. using Ln (catch +1) transformed data .............. 52

Figure 15. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 29 April (top) and 2 May (bottom)
1994. Circles identify reef sites where egg sampling occurred ................................... 53

Figure 16. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 18 May (top) and 23 May (bottom)
1994. Circles identify reef sites where egg sampling occurred ................................... 54

Figure 17. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 30 May (top) and 6 June (bottom)
1994. Circles identify reef Sites where egg sampling occurred ................................... 55

Figure 18. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 9 June (top), 13 and 20 June (bottom)
1994. Circles identify reef Sites where egg sampling occurred ................................... 56

Figure 19. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 3 and 5 May (t0p), and 11 and 12
May (bottom) 1995. Circles identify reef Sites where egg sampling occurred ........... 57

Figure 20. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 18 May (top) and 26 May (bottom)
1995. Circles identify reef Sites where egg sampling occurred ................................... 58

Figure 21. Distribution and density (#/ l ,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 30 May (top) and 6 and 13 June
(bottom) 1995. Circles identify reef sites where egg sampling occurred .................... 59

Figure 22. Mean zooplankton dry-weight biomass in western Lake Erie estimated from
vertical tows at 3 to 7 Sites in spring of 1994 (top) and 1995 (bottom) ...................... 67

xii

Figure 23. Mean Size of crustacean zooplankton in the spring in western Lake Erie, 1994
and 1995 ...................................................................................................................... 68

Figure 24. Abundance of cyclopoid and calanoid copepods and large cladoceran
zooplankton in western Lake Erie in spring of 1994 (top) and 1995 (bottom) ........... 69

Figure 25. Density of Spiny and soﬁ-rayed ichthyoplankton (excluding walleye) in
western Lake Erie estimated from weekly catches in neuston nets in the spring of
1994 (top) and 1995 (bottom). Ordinate scale varies ................................................. 71

Figure 26. Dry-weight biomass (Ln g/ l ,000 m3) of ichthyoplankton in western Lake Erie
in the spring of 1994 and 1995 .................................................................................... 72

Figure 27. Relationship between walleye size and Size of prey observed in gut for 1994
and 1995 diets pooled. Zooplankton sizes are total lengths while ﬁsh prey sizes are
standard length ............................................................................................................ 73

Figure 28. Electivity values (Chesson’s or) for calanoid copepods (top), large cladoceran
(middle), and ﬁsh (bottom) prey items estimated for age-0 walleye diets in 1994 and
1995 ............................................................................................................................. 75

Figure 29. Electivity values (Chesson’s or) for nauplii and rotifers (top), small
cladocerans (middle), and cyclopoid copepods (bottom) prey items estimated for age-
0 walleye diets in 1994 and 1995 ................................................................................ 77

Figure 30. Top panel: Mean lengths ( :I: 1 s.e.) of age-0 walleye collected in neuston nets
and bottom trawls (after 9 June) in western Lake Erie in the spring of 1994 and 1995.
Bottom panel: Dry-weights (g) of age-0 walleye collected in neuston samplers and
bottom trawls (after 9 June) in western Lake Erie in the spring of 1994 and 1995....78

Figure 31. Top panel: Speciﬁc growth rates (g dry-weight) of pelagic age-0 walleye
collected in neuston samplers in western Lake Erie in the spring of 1994 and 1995.
Bottom panel: Relationship between log transformed total length (mm) and dry-
weight (g) of age-0 walleye collected from western Lake Erie in the spring of 1994
and 1995 ...................................................................................................................... 79

xiii

THESIS INTRODUCTION

Walleye (Stizostedion vitreum) have supported important Sport and commercial
ﬁsheries in Lake Erie for over 150 years (Regier et al. 1969). Commercial landings of
walleye increased steadily through the early part of the 20th century exceeding 6.8 million
kg in the mid 1950’s (Figure l). Catches declined dramatically in the late 1950’s when the
population diminished due to exploitation, pollution, and degraded spawning habitat. The
discovery of high levels of mercury in the tissue of walleye prompted closure of the ﬁshery
in 1970 allowing the population to rehabilitate. The ﬁshable stock increased ﬁ'om about
83,000 walleye in 1970 to over 14 million in 1976 (Hatch et al. 1987).

The Lake Erie walleye population is now managed under a quota system allocating
portions of the stock to the Ontario sport and commercial ﬁsheries and sport anglers in
Michigan, New York, Ohio, and Pennsylvania (Koonce et al. 1983). The harvestable
amount of the stock is determined using output from a catch-at-age model relying on
sequential projections of recruitment and reports of withdrawals from the stock (Deriso et
al. 198 8).

Lake Erie walleye populations exhibit wide ﬂuctuations in recruitment (Hatch et al.

1987). The abundance of age-2 ﬁsh varied as much as 60-fold since 1979 (Figure 2).

Landings
(Thousand Tonnes)

 

 

 

O I I I j
1915 1935 1955 1975 1995

 

 

Figure 1. Landings of walleye from United States and Ontario waters of Lake Erie, 1915-
1994. Data from Regier et al. 1969; Hatch et al. 1987; Walleye Task Group Report 1995.

120 ..

 

 

2:” 100 .
< ’m‘ 80 .
3 S
g g 60 u
g g 40 .
3 20
< "I
0 I I I
1975 1980 1985 1990 1995

Year

Figure 2. Abundance of age-2 walleye in Lake Erie as determined by CAGEAN model
estimates, 1978-1995. Data from 1995 Lake Erie Walleye Task Group Report 1995.

Although causes of Lake Erie walleye recruitment variation are speculative, interannual
variation in egg and larval survival is considered the principal source of recruitment
variability in many walleye populations (Carlander and Payne 1977; Koonce et al. 1977;
Ney 1978; Fomey 1980). Density-independent and density-dependent factors that affect
egg survival, and growth and survival of individual larval walleye may be the driving force
behind year class strength formation in western Lake Erie walleye populations.

Interannual variation in egg survival can contribute to recruitment variation in Lake
Erie walleye populations. Many naturally spawning walleye populations experience high
levels of mortality during the egg stage (Priegel 1970; Fomey 1976, 1980). Substantial egg
mortality is thought to be caused by dislodging from severe wind and wave action and
temperature reversals during spawning and incubation periods (Johnson 1961; Allbaugh
and Manz 1964; Hurley 1972; Busch et al. 1975; Koonce et al. 1977; Fomey 1980; Sems
1982). Predation by ﬁshes and invertebrates may also contribute to egg mortality
(Carlander et al. 1960; Wolfert et al. 1975). Optimal egg survival occurs when water
temperatures increase at a rate of 1 C/day (Smith and Koenst 1975). Incubation periods are
lengthened when water warms Slowly thereby increasing vulnerability to predation, disease,
and dislodging by wind generated currents (Hartman 1969).

Small changes in growth or mortality rates of larval ﬁshes can cause major changes
in recruitment (Houde 1987; Madenjian and Carpenter 1991; Madenjian et al. 1991; Jensen
1992; Pepin 1993). Houde (1987) conjects that coarse controls (i.e. nutrition,
climatological factors) in the larval stage may have greater impacts on recruitment potential

than ﬁner controls (i.e. cannibalism, parasitism) in subsequent stages.

Body size oﬁen dictates the survival probability of larval ﬁshes (Miller et al. 1988).
Swimming and foraging ability, size of food particles ingested, and susceptibility to
starvation and predation are all functions of body Size (Houde 1969; Mathias and Li 1982;
Sems 1982). Jensen (1992) determined that the earlier in the growing season age-0 walleye
achieve a large size the more likely they are to survive and relates faster growth to prey
community characteristics. The ability of larval walleye to compensate for small size by
increased growth may improve their chance of survival if survival is size selective (Jensen
1992). Additionally, high levels of initial mortality may generate compensatory responses
in growth rates of survivors resulting in increased survival to age-l (Mills and Fomey
1988)

Diet directly inﬂuences growth and survival of larval walleye (Houde 1967; Fomey
1980; Mathias and Li 1982). Experiments have revealed that a critical period for larval
mortality due to nutrition deﬁciency may occur when postlarvae switch from endogenous to
exogenous feeding. Larval walleye growth, survival, and amount of exogenous food
consumed is a function of ﬁsh density and positively related to water temperature and the
abundance of adequate sized prey (Li and Mathias 1982; Fox 1989; Moodie et al. 1989).

Noble (1972) discovered that larval walleye in Oneida Lake, New York became
concentrated in protected bays as a result of wind generated currents. Foraging success of
larval walleye in bays is determined by variations in prey densities common to large lakes
(Watson 1976; Patalas and Salki 1992). High prey densities can enhance growth rate and
increase larval survival (Houde 1987) whereas low prey densities can result in delayed

growth rate and increased mortality (Crowder et al. 1987).

Variability in year class strength of many ﬁsh species in large aquatic ecosystems
is primarily caused by variation in grth and survival during the early life stages.
Relatively small changes in growth and survival rates of these early life stages can
translate into large annual ﬂuctuations in subsequent year-class strength (Houde 1987).
My hypotheses is that a combination of abiotic and biotic factors occurring during the
incubation and pelagic larval stages is important in controlling the year-class strength of
walleye in western Lake Erie. The goal of this project was to measure important
parameters during the early life history stages to allow for the identiﬁcation of causal
mechanisms controlling year-class formation of walleye. My speciﬁc objectives were to:
1. Estimate walleye egg abundance and survival at selected depths and substrate types

on mid-lake Spawning reefs.

2. Estimate larval walleye abundance, distribution, and growth in areas adjacent to
mid-lake Spawning reefs.

3. Quantify diet of larval walleye and diet's inﬂuence on larval growth rate.

4. Monitor forage community composition and abundance.

5. Quantify abiotic factors (temperature, wind events, substrate morphology) during
walleye egg incubation and larval development period and relate to walleye

survival, growth, and recruitment success.

mm

The study area encompasses the area of western Lake Erie located between

latitudes N 41° 30’ to N 41 ° 43’ and longitudes W 82 ° 50’ to W 83 ° 14’.

The mid-lake reef complex iS located between latitudes N 41 ° 37’ to 41 ° 40’ and
longitudes W 82 ° 57’ to 83 ° 06’ (Figure 3). Detailed descriptions of egg and larval
sample locations are given in each chapter. Latitude and longitude coordinates for egg
and larval sampling sites are listed in Appendix 1.

Physical and chemical characteristics of western Lake Erie are well documented
(Herdemdorf and Braidech 1972; Boyce et al. 1987). The western basin has a mean
depth of 7.4 m and a total surface area of about 3,700 krnz. Mean water residence time is
about 2.4 months (Burns 1985). Generally, the western basin is isothermal throughout
the year due to mixing of its Shallow waters and seldom becomes anoxic. Bottom
substrates consist primarily of sand and clay, although dolomite limestone forms several
major reef complexes including Toussaint and Niagara reefs (Herdendorf and Braidech
1970)

Walleye are the dominant predator in the western basin supported by a prey base
of gizzard Shad (Dorosoma cepedianum), alewife (Alosa pseudoharengus), Shiners
(Notropis atherinoides and N. husonius), white perch (Morone americana), white bass
(Morone chrysops), and yellow perch (Percaﬂavescens). Other common ﬁsh Species
include carp (Cyprinus carpio), ﬁ'eshwater drum (Aplodinotus grunniens), rainbow smelt
(Osmerus mordax), channel catﬁsh (Ictalurus punctatus), and suckers (Catostomidae)

(Knight and Vondracek 1993).

       
   

: ...... ._ . .......... . Pelee I,

‘ 3
Reef '
'_, Bass 1.

' ﬂ Kelley’s I.

  

 

Figure 3. Map of western Lake Erie study area. The dashed line delineates the extent of
larval sampling and the ellipse encompasses the mid-lake reef complex.

Chapter 1
WALLEYE EGG DEPOSITION AND SURVIVAL ON REEFS
IN WESTERN LAKE ERIE

Abstract

Variation in egg survival has been suspected to be a principal source of walleye
Stizostedion vitreum recruitment variability in Lake Eric. I sampled walleye eggs and
larvae in western Lake Erie in 1994-95. Densities of eggs and larvae were higher in 1994
than 1995. Mean egg density peaked at over 8,000 per 2-min tow in 1994 and only 2,700
per 2-min tow in 1995. Egg survival for depths and reefs pooled averaged 37% in 1994
and 13% in 1995. I found white perch Morone americana to consume large numbers of
walleye eggs on reefs in 1995. Mean density of larvae from the date of ﬁrst hatch
through the end of May was 14 times higher in 1994 than 1995. Relatively slow water
warming rates and frequent intense winds contributed to the low density and survival of
eggs on reefs in 1995 by prolonging incubation periods and increasing the vulnerability

of eggs to predation and severe wind events.

10

Introduction

Lake Erie walleye Stizostedion vitreum populations exhibit wide ﬂuctuations in
recruitment (Hatch et al. 1987). Interannual variation in egg deposition and survival are
considered major sources of recruitment variability for many walleye populations
(Carlander and Payne 1977; Koonce et al. 1977; Ney 1978; F omey 1980) as many
naturally spawning walleye populations experience high levels of mortality during the
egg stage (Priegel 1970; Fomey 1976, 1980). Observed egg survival rates range from
0.00003 in Spirit Lake, Iowa (Jennings 1969) to 0.357 in Lake Winnibigoshish,
Minnesota (Johnson 1961). Substantial egg mortality is thought to be caused by
dislodging from severe wind and wave action during spawning and incubation periods
(Johnson 1961; Busch et al. 1975; Koonce et al. 1977; Fomey 1980; Sems 1982).
Walleye egg survival has also been directly related to ﬂuctuations in water temperature
during incubation periods (Johnson 1961; Allbaugh and Manz 1964; Hurley 1972; Sems
1982), with optimal egg survival occurring when water temperatures increase from 5° C
at a rate of 10 C/day (Smith and Koenst 1975). Incubation periods are lengthened when
water warms more slowly, thereby increasing vulnerability to severe wind events and
predation. Faster warming rates shorten incubation time and reduce the time eggs are
vulnerable to detrimental factors (Carlander et al. 1960; Hartman 1969; Wolfert et al.
1975)

Research investigating walleye egg deposition on western Lake Erie reefs

conducted from 1960 - 70 revealed that walleye spawning usually peaks during the third

11

week of April when water temperatures range from 5.4 to 83° C (Baker and Manz 1971).
Walleye spawning and egg density were higher at depths < 5 m where hard substrates
persist which walleye actively spawned over. No relationship was observed between egg
deposition, viability, and year class strength, but a direct relationship between walleye
year-class strength and water temperatures was observed (Busch et al. 197 5) with the
strength of the incoming year-class being inversely proportional to incubation time
(Baker and Manz 1971; Busch et al. 1975).

In this chapter I investigate walleye egg deposition and survival across a range of
depths on Toussaint and Niagara reefs in western Lake Erie in 1994 and 1995. I examine
the hypothesis that environmental factors inﬂuence walleye egg survival and that year

class strength is strongly related to egg abundance and survival.

Winn

Toussaint and Niagara reefs are the largest reefs among a large bedrock reef
complex located in the western basin of Lake Erie (Figure 4). This complex of reefs
encompasses over 70 km2 of surface area and extends to within 1.5 m of the surface.
The surfaces of the reefs have numerous crevices and cavities as well as a varied substrate
composition ranging from Silt to boulders and exposed bedrock. The relative Shallowness
of the reefs allows their surface to be scoured by ice movements as well as wind-
generated wave and current action. The lake bottom surrounding the reefs has low relief
at depths from 7 to 10 m and is covered with silt and mud (Hartley 1961; Herdendorf and

Braidech 1970; Bolsenga and Herdendorf 1993).

 

 

 

10km

 

 

 

Figure 4. Map identifying egg sampling reefs; N = Niagara reef; T = Toussaint reef.
Inlays are bathymetric representations of Niagara and Toussaint reef; ﬁlled circles
represent egg sampling sites.

13

Methods

13323111191191:

I sampled walleye eggs during 1994 and 1995 on Toussaint and Niagara reefs
beginning in late March and continuing through to mid-May when spawning ceased and
catches of walleye eggs were negligible. I used a 39-kg iron sled (0.25 m wide) attached
to a diaphragm pump at the surface by a ﬂexible hose 5 cm in diameter for egg
collections (Stauﬁ‘er 1981). At each Site, the sled was towed for 2 min at 0.5 m/S,
typically sampling 15 m2 in area. Egg sampling was stratiﬁed by depth to examine egg
deposition patterns; depths of < 3 m, 3-5 m, and 5-7 m were sampled (Figure 4). These
depth strata encompass the range of depths where walleye eggs were collected in a
previous study (Baker and Manz 1971). Three samples were taken at each sampling site
on each sampling day. I located sample sites by global positioning system coordinates
and marked them with an anchored buoy.

Eggs and benthic debris (Dreissenid mussels and shells, sand, benthic organisms)
were deposited from the pump apparatus into a 0.5 m3 basket lined with 0.5 mm square
mesh netting. The net liner containing the sample was then removed and placed in a
labeled plastic bag. Samples were refrigerated at 5° C until they could be sorted at the
laboratory 2.5 to 24 hours later. I found no indication that delays in processing of up to
24 hours inﬂuenced viability or survival estimates.

At the laboratory, samples were rinsed through a galvanized steel wire screen (6

mm bar mesh) to separate large debris from ﬁner particles and eggs. The small

l4

particulate matter was then examined for walleye eggs which were counted entirely or
subsampled. A single subsarnple was taken when there appeared to be more than 1,000
eggs in the total sample. Subsamples were typically 10% of the mass of the drained ﬁne
particulate matter. Identiﬁcation of eggs was based on egg diameter (mm), egg color, and
subsequent hatching of eggs. I found 3 Sizes of eggs on the reefs during this study; 3
mm, 2 mm, and 1.5 mm. Several eggs of each size category were placed in aquaria with
aerated lake water and incubated at 15° C. Hatched larvae were identiﬁed according to
Auer (1982). Collected eggs were examined with 10X magniﬁcation for viability and
measured (nearest 0.1 mm) before being preserved in Stockards solution (Galat 1972).
All eggs that were ruptured or Showed signs of opaqueness or fungal growth were
classiﬁed as dead eggs. All clear or eyed eggs were classiﬁed as viable eggs.

Walleye eggs were classiﬁed by developmental stage (Nelson 1968; McElman
and Balon 1979) using a phase-contrast microscope with variable magniﬁcation. Stage 1
eggs are pre-organogenesis stage (28 thermal units (TU); a thermal unit is each degree C
above a daily base temperature of 0° C; Allbaugh and Manz 1964) and stage 3 eggs are
late embryonic stage with developed eyes, pectoral ﬁn buds, and caudal mesenchyme
rays as well as chromatophores along the ventral line and yolk sac (>97 TU). Stage 2
eggs Show intermediate development. Hatching normally occurs when at least 115 TU’S
have accumulated (Nelson 1968; Hurley 1972; McElman and Balon 1979). Egg survival
(5) was estimated as

S = (#stage3ondayx)/(#stage1ondayO)

15

Day 3 was a function of the temperature dependent development rate. I pooled egg
survival data from all depths on each reef because wind and wave action displaced eggs

from Shallow Sites to deep Sites over the study period.

EggProrluction

I estimated total walleye egg production on each reef by summing the numbers of
stage 1 eggs collected from each depth stratum on Toussaint and Niagara reefs
individually over the course of the incubation period. Egg numbers were then
extrapolated using the amount of area each depth stratum contributes to each reef
(Bolsenga and Herdendorf 1993) to estimate the number of eggs deposited on each reef as
well as on the entire reef complex. I estimated the total number of stage 1 eggs deposited
by linear extrapolation between sampling dates and adjusting these numbers based on
temperature dependent development rates (Allbaugh and Manz 1964). I calculated the
mean number of stage 1 eggs using the Toussaint and Niagara reef data and then applied
these means to estimate egg production on other reefs in the complex. Because the egg
pump applies suction only 50% of the time due to the action of the diaphragm pump, 1
doubled my estimates of egg production to account for the reduced effort of the gear.

I estimated total potential fecundity for the entire Lake Erie walleye population
using age-speciﬁc fecundities reported by Muth and Ickes (1993) and stock size estimates
derived from the CAGEAN model (Lake Erie Walleye Task Group 1995). I assumed a

1:1 sex ratio and estimated the numbers of age-7, 8, 9, 10, and 11 ﬁsh by expanding the

l6

CAGEAN model estimates beyond the reported value given for age-7+ ﬁsh (Appendix

2).

El'lI'l'llL‘l'l'lE

Water temperatures (° C) on the reef complex were recorded with continuous
monitoring therrnographs (Ryan Instruments, Inc.). Bottom dissolved oxygen was
measured on the bottom at each sampling site using a calibrated YSI Model SOB
dissolved oxygen meter. Secchi disk readings (nearest 0.1 m) were taken at each egg
sampling Site as an index of water clarity. Wind direction, intensity, and duration at South
Bass Island, Ohio were recorded daily from the National Oceanographic and Atmospheric
Administration weather observation broadcasts. Additional wind speed and direction
data recorded at South Bass Island were obtained from the National Climatological Data
Center in Asheville, North Carolina. I used criteria described by Busch et al. (1975) to
determine the Signiﬁcance of wind events. Busch et al. examined a time series of water
temperature and wind direction and intensity data from western Lake Erie and concluded
that winds from N to NE exceeding 14.5 km/h, from the S to SW exceeding 17.5 km/h,
and from the W to NW exceeding 20.5 km/h mixed western basin waters enough to
reduce water temperatures by 0.5° C/day and be detrimental to incubating walleye eggs.

Substrate composition on the reefs was examined by SCUBA diving at each egg
sampling site. Divers measured substrate composition at three to ﬁve points at each egg
sampling site in 1994 and 1995. Substrate particle sizes are based on the modiﬁed

Wentworth scale (Cummins 1962).

l7

EEID'E"

Variable mesh gillnets were ﬁshed overnight on Toussaint reef during the peak
spawning period in 1994 and 1995 to collect potential walleye egg predators. Two 40 m
gillnets were ﬁshed simultaneously in 1994 and 3 were ﬁshed in 1995. The nets
consisted of a single 8 m x 2 m panel of each of the following stretch mesh Sizes: 2.2 cm,
4.4 cm, 5.5 cm, 6.6 cm, and 8.8 cm. Gillnets were ﬁshed on the bottom in 2.3 m to 4.2 m
of water on Toussaint reef. Upon capture, potential egg predators were measured to the
nearest 1 mm and stomachs were removed and preserved in 10% formalin. I counted all
eggs in stomachs anterior to pyloric caecum and in the anterior portion of the gut prior to
the ﬁrst ﬂexure for greater redhorse sucker Moxostoma valenciennesi. Identiﬁcation of
eggs in ﬁsh stomachs was based on egg size. I matched egg sizes observed in stomachs
with concurrent catches from egg pump samples. I also examined the gut contents of
ﬁshes captured incidentally in egg pump samples in 1995. These ﬁsh were preserved

whole in 10% formalin and dissected later.

LamalAhImdance

I used a 2.0 m2 framed ichthyoplankton net ﬁtted with 583 mm mesh netting to
sample pelagic larval ﬁshes. A ﬂow meter was positioned in the center of the mouth of
the net to record the volume of water sampled. The net was towed in the upper 2.0 m of
the water column at approximately 1.0 m/sec. for 5 min. I sampled ﬁom 15 to 40 sites

(Figure 5) per sample day and typically ﬁltered 600 m3 of water during each tow. Larval

l8

ﬁshes were preserved in 95% ethanol and identiﬁed following Auer (1982). Catches of
larval ﬁsh were Logc (x+1) transformed to produce normalized data with homogeneous
variance (O’Gorman 1984). I used mean larval density for the period from the ﬁrst batch

through 31 May as an index of larval abundance to compare between years.

Indexeerar-Llassﬁtrength
I use the catch of age-0 walleye in the Ohio Division of Wildlife’s assessment
bottom trawls in August (Ohio Division of Wildlife 1996) as an index of relative year-

class strength.

SUN].

I calculated weighted averages of the numbers of walleye eggs collected per 2 min
tow on each reef using the proportion of the reef surface area shallower than 7.0 m that
each depth strata contributes to the total area as weighting factors. Surface area
proportions were estimated from bathymetric maps of the reefs (Herdendorf and Braidech
1970). I used analysis of variance to test for differences in egg viability between depth
strata and reefs. I used analysis of variance in the form of a general linear model (SAS
1985) to detect differences in the numbers of eggs collected per 2 min tow between depth

strata and reefs. In all analyses I used an or - level of 0.05.

 

 

 

 

10km

 

Figure 5. Map of western Lake Erie identifying larval sampling sites (ﬁlled circles).

20

Results

ReefSubstrates

Substrate composition varied at each depth stratum on both reefs. In general, the
upper portions of the reefs (< 3 m) were composed of primarily large and small cobble (>
10 cm) and coarse gravel with little or no sand and silt. Sites with depths 3-5 m had
highly variable substrates ranging from 40% exposed bedrock to 50% silt. Silt depths at
the 3-5 m sites ranged from 0 to 20 cm. Gravels, cobbles, and boulders composed from 5
to 50% of the substrate at these sites. Sites 5 - 7 m deep were observed to have from 50 -
75% silt ranging from 2 to 40 cm deep with a conglomeration of gravels and small

cobbles underneath.

1M 11 E D . .
Reefs were ﬁrst sampled on 31 March 1994 but no walleye eggs were collected.
Walleye eggs ﬁrst appeared in samples from all depths at both reefs on 8 April 1994
when the water temperature was 4.2 ° C. In 1994 only walleye eggs were collected until
18 May when yellow perch Percaﬂavescens and Morone spp. eggs also appeared in the
samples. Equipment failure prevented any egg sampling between 28 April and 17 May
1994. In 1995, walleye eggs ﬁrst appeared in samples on 31 March when the water was
4.8 ° C. No samples were taken prior to this date in 1995. In 1995, lake Whiteﬁsh
Coregonus clupeaformis eggs were collected in the earliest samples and yellow perch,

Moron: spp. and sucker (Catostomidae) eggs were collected in late April and May. Lake

21

Whiteﬁsh eggs were the only large eggs (> 3.0 mm) identiﬁed. Walleye and sucker eggs
accounted for all the intermediate sized eggs (approximately 2.0 mm), but were easily
distinguished because sucker eggs have a much darker pigmentation than walleye eggs
which are clear to yellow. The smallest eggs (< 1.5 mm) were those of yellow perch and
Morone spp.

Walleye egg density peaked on 20 April 1994 on Toussaint reef, and on 10 April
1994 on Niagara reef when an average of over 11,300 and 5,500 eggs were collected per
2 min tow respectively (Figure 6). Viable eggs persisted in samples at all sites through 18
May 1994 when less than 100 walleye eggs were collected per 2 min tow.

Egg densities were roughly 50% lower on Toussaint and Niagara reefs in 1995.
Densities peaked on Toussaint reef on 24 April 1995 and on 21 April 1995 on Niagara
reef when only 3,300 and 1,900 eggs were collected per 2 min tow respectively (Figure
7). Viable walleye eggs were collected through 17 May 1995 when less than 50 walleye

eggs were collected per 2 min tow.

22

12000 .

 

10000- A --A- -- Toussaint

 

 

8000 - A: .‘A + Niagara

 

6000 i

No. Walleye Eggs
p.

4000 -

2000 -

.54 I.

31-Mar 10-Apr 20-Apr 30-Apr IO-May 20-May

 

 

 

 

Figure 6. Weighted mean numbers of walleye eggs collected per 2 - min tow on Toussaint
and Niagara reefs, 1994. No eggs were collected in samples taken on 31 March 1994; no
egg samples were taken between 28 April and 17 May 1994.

23

In 1994, egg density was generally higher at sites < S m deep than at sites 5 - 7 m
on both reefs (p < 0.05) (Figure 8) but in 1995, signiﬁcantly more eggs were collected
from sites < 5 m deep only on Toussaint reef (p<0.05). No Signiﬁcant difference in egg
densities between depths was observed on Niagara reef in 1995 (p = 0.17), however,
more eggs were collected ﬁ'om sites < 5 m deep on Niagara reef until 2 May when the
deeper sites were observed to contain more eggs (Figure 9). Signiﬁcantly more eggs
were collected per unit effort from Toussaint reef than Niagara reef in both 1994 and
1995 (mean = 3,907 and 1,734 per tow respectively for 1994 and 1,874 and 880 per tow

respectively for 1995; p < 0.05).

lllll E Il‘l'l' IS .1

Egg viability estimates were generally higher in 1994 than 1995 (Figure 10) with
the exception of three sample dates in mid-April 1995. Egg viability ranged from 41 to
74% between depths and reefs over the 1994 sampling period (mean = 56%) and did not
differ signiﬁcantly between depths or reefs (ANOVA; p = 0.51). In 1995, walleye egg
viability ranged from 6 to 76% across the sampling period and did not differ Signiﬁcantly
between depths or reefs (AN OVA; p = 0.29). Viability estimates generally increased in
early April 1995 reaching 70% by mid-April and declined to less than 40% in late April

and May.

24

 

 

 

 

 

 

12000-
1995 ' ”A ° Toussaint
100001
+ Niagara
3.3
m 8000-
d.)
>~.
2
"a 6000-
B:
o'
z 4000-
2000-
o

 

31-Mar 10-Apr 20-Apr 30—Apr lO-May 20-May

Figure 7. Weighted mean numbers of walleye eggs collected per 2 - min tow on Toussaint
and Niagara reefs, 1995.

25

 

 

 

 

No. Walleye Eggs

 

 

 

 

 

 

 

 

 

14000 .
Toussaint Reef
12000 .
[33m
10000 . '3'5'“
.>5m
8000 .
6000 .
4000 .
2000 .
0 U
a. a a a a. ‘- a
at <5 at s s 3 2
b O\ m h o In I;
— '-' N N .—
14000 .
Niagara Reef
12000 .
3’0 10000 .
OD
LL]
0 8000 .
>4
.2
g 6000 .
o'
2 0
00 1
0 U

 

 

 

7-Apr
1 3-Apr
20-Apr
1 7-May

Figure 8. Mean numbers of walleye eggs (i 1 SE.) collected per 2 - min tow from
different depth strata on Toussaint and Niagara reefs, 1994.

26

14000 .

Toussaint Reef

12000 .

10000 . (533‘ 1
.l3-5n1

8000 . |I5'7ml

6000 .

4000 . I-

I .. .:
2000 - II I I I
0 - - I I I ' 'i _

30 Mar 11 Apr 20 Apr 28 Apr 4 May 16 May

#No. Walleye Eggs

 

14000 -
12000 . Niagara Reef
10000 .
8000 .

6000 .

No. Walleye Eggs

4000

2000 .

01

30 Mar 11 Apr 20 Apr 28 Apr 4 May 16 May

 

Figure 9. Mean numbers of walleye eggs (:1: 1 SE.) collected per 2 - min tow from
different depth strata on Toussaint and Niagara reefs, 1995.

27

Estimates of walleye egg survival were higher in 1994 than 1995. My samples
allowed for a single estimate of egg survival from 10 April to 21 April 1994 (102 TU’S).
Egg survival for pooled depths was calculated at 43% for Toussaint reef and 30% for
Niagara reef and did not differ signiﬁcantly between reefs (p=0.48). I calculated 2
separate survival estimates for each reef in 1995. Walleye egg survival to stage 3 for the
period 7 April through 29 April 1995 (99 TU’S) was estimated at 14 % for Toussaint reef
and 7 % for Niagara reef. Survival for the period 15 April through 9 May (113 TU’s) was

estimated at 16 % and 15 % for Toussaint and Niagara reefs respectively.

Egglimduﬂien

Egg production on the entire reef complex was estimated at approximately 47.4
million stage-1 eggs in 1994 and 33.0 million stage-1 eggs in 1995. Toussaint reef was
observed to produce 36% of the 1994 total and 26% of the 1995 total, the highest of any
of the reefs in the complex (Table 1) and also had higher egg densities than Niagara reef
in both years of the study (Figures 6 and 7). These estimates are conservative as they do
not account for the efﬁciency of the egg collecting pump and assume homogenous egg
deposition rates across the reef complex for all substrate types. I estimated the total
potential fecundity (number of eggs) of the stock to be 2.7 trillion in 1994 and 2.2 trillion
in 1995. The potential total fecundity decreased despite an increase in the abundance of
the stock (Appendix 2). Changes in the age structure of the stock between the two years

account for the decease in fecundity. My estimates of egg deposition on the reef complex

80.

28

 

 

 

 

40..
30.
20.
10.

0

Viability (%)

 

60 . —I — 1995 II
50 ‘ N/
u

 

ZS-Mar

‘7

4-Apr 14-Apr 24-Apr 4-May 14-May

Figure 10. Walleye egg viability estimates for pooled samples from Toussaint and
Niagara reefs, 1994 and 1995.

29

account for less than 0.003 % of the total potential fecundity of the walleye stock in both

years.

Table 1. Approximate area < 7m depth and estimated egg production with 95%
conﬁdence limits in parentheses for reefs in western Lake Erie, 1994 and 1995. Reef area
estimates from Bolsenga and Herdendorf (1993). * indicates reefs that were sampled, all
other egg production values are extrapolated.

 

 

E E l . : .u. :
Reef Area (m2) 1994 1995
Cone 670 1.95 (1.50-2.40) 1.43 (1.15-1.71)
Crib 850 2.47 (1.90-3.04) 1.81 (1.46-2.16)
Locust 930 2.71 (2.09-3.33) 1.98 (1.59-2.37)
Little Pickerel 720 2.09 (1.61-2.57) 1.53 (1.23-1.83)
Niagara“ 2490 2.52 (1.94-3.10) 3.65 (2.94—4.36)
Round 880 2.56 (1.91-3.15) 1.87 (1.51-2.23)
Toussaint“ 1229 8.33 (641-1025) 4.27 (3.44-5.10)
Total 7769 22.63 (17.15-28.11) 16.54 (13.31-19.77)

 

30

EB! B'E"

No ﬁsh other than spawning walleye were collected in gillnets ﬁshed overnight on
20 and 26 April 1994. In 1995, a total of 49 ﬁsh were captured in 3 nights of gillnetting
from 12 April through 3 May and an additional 7 ﬁsh were collected with the egg pump
(Table 2). Few ﬁsh were captured in gill nets set on 12 April (11 = 4) but the catch
increased on subsequent nights, especially of white perch, the most common species

collected.

Table 2. Average numbers of walleye eggs observed in ﬁsh stomachs collected from

Toussaint and Niagara reefs, 1995.

 

Mean # Empty Average # Frequency of

 

Species # Fish TL (mm) Stomachs Walleye Eggs Occurrence (%)
Grtr. Redhorse 1 225 1 0 0
Johnny Darter 1 44 0 2 100
Logperch 3 68 1 10 66
Rock Bass 1 195 1 0 0
Sculpin 1 76 0 21 100
Trout Perch 13 107 6 4 38
White Perch 35 225 6 349 86
Yellow Perch 1 81 0 5 100

 

31

The stomachs of trout perch Percopsis omiscomaycus, yellow perch, log perch
Percina caprodes, johnny darter Etheostoma nigrum, white perch, and an unidentiﬁed
sculpin (Cottidae) contained walleye eggs. The stomachs of a Single rock bass
Ambloplites rupestris and greater redhorse sucker did not contain walleye eggs. Walleye

eggs appeared in 86% of white perch stomachs and each white perch stomach contained

an average of 349 walleye eggs (Table 2).

 

I collected the ﬁrst walleye ﬂy on 29 April 1994 and 3 May 1995. In 1994, the
catch peaked on 2 May when I captured 1328 fry in 33 tows for an average density of
95.2 fry / 1,000 m3 (Figure 11).

Equipment failure prevented any larval sampling between 2 May and 18 May 1994. In
1995, the peak catch occurred on 20 May when a total of 87 walleye fry were captured in
40 samples for an average density of 3.5 ﬁsh / 1,000 m3. Mean density of walleye ﬂy for
the period ﬁom ﬁrst hatch through the end of May was 14 times higher in 1994 than 1995
(28.4 and 2.0 ﬁ'y/ 1,000 m3 respectively). The catch of age-0 walleye in assessment
bottom trawl surveys in August also demonstrated that the 1994 year-class was stronger
than 1995; Ohio Division of Wildlife (1996) reported a catch rate of 18.2 age-0 walleye

per hour of trawling in August 1994 and only 1.9 ﬁsh per hour in 1995.

32

El'lI'l' 12].].12

Water temperatures warmed steadily in April and May 1994. Water temperatures
were slightly warmer in late March and early April 1995 but warming was slower than in
1994 (Figure 12). I calculated the average rate of warming per day from 1 April through
15 May which historically encompassed the walleye spawning and incubation periods in
western Lake Erie. The average rate of warming per day for this 45-day period was 0.19
° C/day in 1994 and 0.18 ° C/day in 1995. In contrast, the average rate of warming per
day from the date eggs were ﬁrst observed on the reefs to the date fry were ﬁrst observed
in samples was more rapid at 0.22 ° C/day in 1994 and lower in 1995 at 0.16 ° C/day.

Major wind events were more frequent in 1995 than 1994 (Table 3). Twenty one
days were observed to have winds qualifying as detrimental to incubating walleye eggs in
1995 whereas only 14 days were identiﬁed in 1994. Winds were primarily from the W-
NW in 1994 whereas E-NE winds predominated in 1995.

Secchi disk readings were generally greater on Toussaint Reef in 1994 than 1995
ranging from 0.3 m to 2.3 m in 1994 and 0.2 to 1.3 min 1995. On Niagara reef, secchi
disk readings ranged from 0.5 m to 1.2 m in 1994 and 0.3 to 1.9 m in 1995. Low secchi
readings in 1995 were a result of the continued mixing of the water due to the persistent
winds.

Bottom dissolved oxygen levels ranged from 3.8 mg/l to 6.2 mg/l on Toussaint
Reef and remained above 5.0 mg/l at all sites on Niagara Reef over the 1994 walleye egg

incubation period. In 1995, bottom dissolved oxygen levels were greater than 6.0 mg/l at

33

all sites on both reefs through 15 April. I observed a decline in bottom dissolved oxygen
levels at Sites > 3 m after 15 April when dissolved oxygen levels declined to a low of 1.3

mg/l at one site 5 - 7 m deep on Niagara reef on 17 May.

Table 3. Number of wind events that caused Signiﬁcant mixing of western Lake Erie
waters in 1994 and 1995. Wind direction and intensity criteria based on Busch et al.
(1975)

 

Wind Direction

 

and Intensity 1994 1995
N - NE 2 14.5 km/h 4 12
S - SW 2 17.5 km/h 0 6
W - NW 2 20.5 km/h 10 3

Total 14 21

 

34

 

8.00-
7.00. I 1994

6.00 . O 1995

5.00 '
4.00 '
3.00 '
2.00 '

W <5 III II-
.0010. i i #4 i. 0.?

 

 

 

 

Ln Catch+l (#/1,000 m3)

-100
-2.00 , I I

2 l-Apr S-May 1 9-May 2-Jun 16-Jun 30-Jun

 

Figure 11. Densities of larval walleye ( :1: 1 s.e.) collected at sites on and adjacent to reef
complex in western Lake Erie, 1994-95.

35

18 .
16 .
14 .
12 .
10 .
s .
6 .
4 .
2 .
20-Mar 30-Mar 9—Apr l9-Apr 29-Apr 9-May 19-May 29-May 8-Jun

 

 

 

 

 

Temperature (C)

 

 

Figure 12. Mean daily water temperatures recorded at Niagara Reef for spring of 1994
and 1995.

36

Discussion

A combination of frequent intense winds, lower water warming rate, and egg
predation appears to have been largely responsible for the reduced egg densities and
lower survival rates observed in 1995. Intense wind events cause mixing of lake waters
which retards water warming and creates currents that dislodge walleye eggs from
shallow reef substrates and deposit them in areas unsuitable for incubation (Eschmeyer
1950; Johnson 1961; Busch et al. 1975). I observed more intense wind events in 1995,
especially winds from the E - NE which have long fetches, contributing to the slow water
warming rate and displacing walleye eggs from reef habitats.

Many displaced eggs are likely deposited in deeper waters where silt substrates
and reduced bottom dissolved oxygen levels can suffocate the embryos. I observed lower
secchi readings in 1995 due to the continued mixing of lake waters caused by the more
frequent intense winds. Precipitation of suspended particles from the water column
contributes to low bottom dissolved oxygen readings (Zapotsky and Herdendorf 1980)
and can cover deposited walleye eggs. I observed bottom dissolved oxygen levels as low
as 1.3 mg/l at a Site 5-7 m deep on Niagara reef in 1995 and presume that oxygen levels
were also low at deeper Sites surrounding the reefs. McMahon et al. (1984) maintain that
dissolved oxygen levels above 6.0 mg/l are necessary for optimal walleye embryo
development and survival. Therefore, it is likely that the majority of walleye eggs

displaced to deep, Silt habitats experience high mortality.

37

The warming rate of western Lake Erie waters was greater in 1994 than 1995,
especially during the period ﬁom the ﬁrst observation of eggs on the reefs to the time fry
were ﬁrst observed. Other studies have concluded that spawning and incubation
temperatures are strongly related to hatching success (Busch et al. 1975). Rapid warming
reduces incubation time and consequently reduces vulnerability to low oxygen, Siltation,
disease, predation, and storm generated turbulence and currents that can occur on the
reefs.

Prolonged walleye egg incubation periods increase the potential for predation on
walleye eggs. Wolfert et al. (1975) observed that yellow perch were the most consistent
predators of walleye eggs on Kelley’s Island Shoal in a study conducted in 1969-71.
These authors concluded that the loss of walleye eggs to ﬁsh predation appeared to be
important only when the rate of water warming slowed or stopped and the walleye and
yellow perch reproductive periods overlapped. Our study shows the same temperature
effect on incubation periods, but with white perch as the most abundant ﬁsh on the reef
and the most important walleye egg predator.

Because I caught no potential egg predators in our gillnets in 1994, I feel that the
reproductive periods of walleye and potential egg predators probably did not overlap to
any point that could have signiﬁcantly impacted the incubating walleye eggs. I did
observe clearer water on Toussaint reef in 1994 than in 1995 which may have contributed
to low gillnet catches in 1994. Hanson and Rudstam (1995) conclude that increased
water clarity can lead to reduced catches and consequently diminish the effectiveness of

sampling programs. Additionally, the faster water warming rate allowed many of the

38

walleye eggs to hatch before substantial numbers of white perch occupied the reef. Our
gillnet catches in 1995 Show a gradual increase in the number of white perch inhabiting
Toussaint reef and that there was a Si gniﬁcant temporal overlap with the incubating
walleye eggs in late April and May. Examination of gut contents indicate that white
perch were the most important consumers of walleye eggs, though it is difﬁcult to assess
the impact that their predation may have on the reproductive success of walleye. I concur
with Wolfert et al. (1975) that an overlap in reproductive periods when waters warm
slowly gives potential predators more opportunity to consume the incubating walleye
eggs as seen in 1995. The longer the walleye eggs incubate, the more opportunity there is
for predation and the greater the potential for deleterious effects on walleye reproductive
success.

Changes in the abundance of adult ﬁsh in Lake Erie do not appear to explain the
differences in egg densities between 1994 and 1995 on Toussaint and Niagara reefs. The
Lake Erie walleye population (age 2 and older) was estimated at 40.2 million ﬁsh in 1994
and was projected to increase by 6% to 42.8 million ﬁsh in 1995 (Lake Erie Walleye
Task Group 1995). However, the age-structure of the population did change (Lake Erie
Walleye Task Group 1995) and accounts for a decrease in total potential fecundity of
17.7% from 1994 to 1995. Shuter and Koonce (1977) deduced that stock size explains
only a small part of the variation in recruitment of the western Lake Erie walleye
population.

My estimates of egg production on the reefs account for only about 0.003% of the

total potential fecundity of the Lake Erie population. My estimates are very likely biased

39

by several factors. First, I have no estimates of efﬁciency of the egg pump device on the
different substrates present on the reef. I would expect the gear to operate more
efﬁciently on smooth substrates (bedrock areas) than on more complex substrates like
gravel and boulder areas. This method still provides a reliable index of egg abundance
useful for year to year and site to Site comparisons. Secondly, I assumed that the mean
egg density observed on Toussaint and Niagara reefs represents the entire reef complex. I
immediately know that egg deposition is not homogenous across the reefs by looking at
the disparity between Toussaint and Niagara reefs. This may be a good question to
address in ﬁrture studies of walleye spawning in western Lake Erie. Lastly, I have no
estimates of the number and age structure of the spawners that reproduce on the reefs.

Energy surplus and allocation in female walleye may partially explain the lack of
consecutive strong year classes experienced in Lake Erie. Walleye growth rate was
higher in 1993 than in 1994, likely due to a preponderance of gizzard Shad in 1993 (Ohio
Division of Wildlife 1996), the preferred prey of walleye in western Lake Erie (Knight et
al. 1984). The abundant gizzard shad provided the energy surplus needed to produce
gametes and allowed the majority of females to Spawn in 1994 possibly accounting for
the higher egg densities observed in 1994. Henderson and Nepszy (1994) propose that
good year-classes of walleye are only possible if most spawning females accumulate a
surplus of energy the previous growing season and can direct this energy towards gamete
production. Replenishment of energy depleted by reproduction may not be accomplished
by all females thus limiting the number of ﬁsh capable of spawning the next year.

Additionally, some females may resorb their eggs in order to satisfy their own metabolic

40

needs if conditions are bad (i.e. harsh winter, cold spring, lack of prey) (Henderson and
Nepszy 1994). Presently, ﬁsheries managers and ecologists do not know how many
females actually Spawn on reefs in any given year nor do the managers and ecologists
fully understand the mechanisms that determine which females will spawn.

Additionally, females can allocate more or less energy to gametes depending on
conditions encountered during the growing season (Roff 1983). Gamete Size and energy
content can vary from year to year inﬂuencing the survival probability of different sized
eggs (Moodie et al. 1989; Brown and Taylor 1992). Larger eggs generally contain more
energy and produce larger larvae upon hatching providing a stronger survival probability
than small eggs (Miller et al. 1988; Moodie et al. 1989). Brown and Taylor (1992)
discovered that lake Whiteﬁsh eggs with higher caloric content produced larger larvae and
that the endogenous growth of larvae was highly dependent on egg lipid content. Moodie
et al. (1989) found that large walleye eggs contained more energy than small eggs and the
subsequent larvae from the large eggs hatched at a larger size, began exogenous feeding

sooner, and had greater survival than fry from small eggs.

Chapter 2
DISTRIBUTION, DIET, GROWTH, AND SURVIVAL OF
AGE-0 WALLEYE IN WESTERN LAKE ERIE.
Abstract
Walleye year-class strength in Lake Erie exhibits high interannual variability.
Interannual variability in growth and survival rates of walleye larvae and juveniles is
suspected to cause much of this variability. I examined the Spatial distribution, diet,
growth, and survival of pelagic larval and early demersal juvenile walleye in western
Lake Erie in 1994 and 1995. Pelagic walleye larvae were approximately 14 times more
abundant in 1994 than 1995 (28.4/1,000 m3 in 1994). Growth of larval walleye was
signiﬁcantly greater in 1994 than 1995 with a mean length at the end of June of 46.2 mm
and 25.6 mm TL, respectively. Instantaneous mortality rates of pelagic walleye were
estimated at 0.078/day in 1994 and 0.053/day in 1995 and did not differ signiﬁcantly.
Total mortality rates for pelagic larvae were approximately 75% in 1994 and 73% in
1995. Dispersal and distribution patterns of walleye larvae in both years were similar.
Calanoid copepods and large cladocerans dominated pelagic larval diets in both years.
Fish became the dominant prey in diets in early June of 1994 and late June 1995. Age-0
walleye were exclusively piscivorous by the end of June in both years. The relative

strength of the 1994 year-class was 14 times

41

42

greater than the 1995 cohort during the larval stage yet only 9 times stronger by the end
of August as indexed in bottom trawls indicating increased juvenile mortality during the

1994 summer or an inﬂux of ﬁsh from other regions of Lake Erie in 1995.

Introduction

Year class strength of many walleye populations is set by late fall (Kempinger and
Churchill 1972); however, the timing and controlling mechanisms of year class
establishment have not been satisfactorily identiﬁed for walleye populations in Lake Erie
(Lake Erie Walleye Task Group 1995). The greatest potential for year-class regulation in
many ﬁsh populations exists during the larval stage (Houde 1987). Variation in individual
larval growth and survival rates in response to density-independent and density-dependent
factors potentially inﬂuence recruitment success in many ﬁsh populations (Crecco and
Savoy 1985; Houde 1987; Rice et al. 1987; Jensen 1992). Jensen (1992) identiﬁed the
relationship between mortality and size as the most effective form of compensatory process
for larval walleye. Increases in larval size that result in a decrease in mortality may
substantially increase recruitment (Houde 1987; Jensen 1992; Pepin 1993). Examination of
the characteristics and variability of distribution, diet, and growth rate of the survivors will
elucidate factors inﬂuencing larval survival.

Walleye larvae are lirnnetic and consequently are subject to passive transport by
water currents (Houde and Fomey 197 0). Spatial distribution may inﬂuence survival of

these larvae, as suggested for many marine Species (Powles and Stender 1976; Thayer et al.

43

1983). Noble (1972) discovered that larval walleye in Oneida Lake, New York became
concentrated in protected bays as a result of wind generated currents. Foraging success of
larval walleye in bays is determined by variations in prey densities common to large lakes
(Watson 1976; Patalas and Salki 1992). High prey densities can enhance growth and
increase larval survival (Houde 1987) whereas low prey densities can result in reduced
growth rate and increased mortality (Crowder et al. 1987).

Body size often dictates the survival probability of larval ﬁshes (Miller et al. 1988).
Swimming and foraging ability, Size of food particles ingested, and susceptibility to
starvation and predation are all ﬁrnctions of body size (Houde 1969; Mathias and Li 1982;
Sems 1982). Jensen (1992) determined that the earlier in the growing season age-0 walleye
achieve a large Size the more likely they are to survive and relates faster growth to prey
community characteristics. The ability of larval walleye to compensate for small Size by
increased grth may improve their chance of survival if survival is Size selective (Jensen
1992). Additionally, high levels of mortality may generate compensatory responses in
growth rates of survivors resulting in increased survival (Mills and Fomey 1988).

Diet directly inﬂuences growth and survival of larval walleye (Houde 1967; Fomey
1980; Mathias and Li 1982). Experiments have revealed that a critical period for larval
mortality due to nutrition deﬁciency may occur when postlarvae switch from endogenous to
exogenous feeding. Larval walleye growth, survival, and amount of exogenous food
consumed is a function of ﬁsh density and positively related to water temperature and the

abundance of adequate sized prey (Li and Mathias 1982; Fox 1989; Moodie et al. 1989).

Cannibalism among larval walleye is considered a major cause of mortality in
walleye culture, occurring in ﬁsh as small as 9.0 mm (Cuff 1980; Li and Mathias 1982).
The heaviest losses to cannibalism of cultured walleye larvae occurred at the onset of
exogenous feeding and is considered a function of larval density and prey density (Li and
Mathias 1982). Cannibalism in natural walleye populations is thought to have the greatest
impact when members of older age-classes eat younger ﬁsh as a compensatory response to
reduced prey densities or excessive walleye density (Chevalier 1973). The signiﬁcance of
cohort cannibalism in natural larval walleye populations is unknown, but thought to be
minimal (Loadman et al. 1986).

In this chapter I will describe mechanisms goveming the growth and survival of
larval walleye in western Lake Erie in 1994 and 1995. Because individual size often
dictates the survival probability of larval ﬁshes (Miller et al. 1988), I have selected an
approach to investigate walleye early life history dynamics that focuses on size-dependent
mechanisms. In this chapter I document the dispersal and distribution of pelagic walleye

larvae and investigate the diet, growth, and survival of the 1994 and 1995 cohorts.

Methods

I 111' .1. 1!] l

I used a 2.0 m2 framed ichthyoplankton net ﬁtted with 583 mm mesh netting to
sample pelagic larval ﬁshes. A ﬂow meter was positioned in the center of the mouth of
the net to record the volume of water sampled. The net was towed in the upper 2.0 m of

the water column at approximately 1.0 rn/sec. for 5 min. I sampled from 15 to 40 sites

45

 

 

 
   
 

Michigan

  

Port Clinton/7

 

 

Figure 13. Map of western Lake Erie identifying sampling sites; all circles represent
larval sampling sites; white ﬁlled circles represent zooplankton sampling sites; B
indicates bottom trawl stations.

46

(Figure 13) per sample day and typically ﬁltered 600 m3 of water during each tow.

Larval ﬁshes were anesthetized with tricaine methanesulfonate to prevent egestion of
stomach contents and preserved in 95% ethanol. Identiﬁcations of larval ﬁsh follow Auer
(1982). I calculated the density of larvae at each sample site for each date. Numbers of
larvae caught during each trawl were adjusted to number of larvae per 1,000 m3 of water
ﬁltered. I used mean larval density for the period from the ﬁrst hatch through 31 May as
an index of larval abundance to compare between years.

I estimated the total number of walleye larvae in both years using estimates of the
volume of water in three distinct depth zones in my sample area. I used area and volume
values reported by Heniken (1977) and adjusted these values to account for differences in
study area Size and lake water level (Appendix 6). Lake water level information was
obtained ﬁ'om the National Climatological Data Center in Asheville, North Carolina. I
calculated an average walleye larvae concentration for each depth zone on the date of
peak larval abundance and multiplied this value by the volume estimate of the depth zone
to provide an abundance estimate. 1 used peak larval abundance because the majority of
these ﬁsh should have emerged from the reefs and the river larvae will not have inﬁltrated
the population to a great extent at this time.

I used a semi-balloon bottom trawl (3.4 m headrope; 4.3 m footrope; 12.7 mm cod
end; 6 mm stretch mesh cod liner) to collect demersal ﬁshes at 5 sites adjacent to the reef
complex (Figure 13). I towed the trawl for 10 min at about 1.5 m/sec at each site
beginning the ﬁrst week of June in 1994 and in mid-May in 1995. Bottom trawl samples

were taken weekly through June and once monthly in July, August, September, and

47

October in both years. Trawls typically sampled 3,900 m2 area. I selected bottom trawl
sites based on substrate and morphologic compatibility with the gear and catches of age-0
walleye. Bottom trawl samples were only used to investigate growth and diet of age-0

walleye.

Aztoﬂallexcﬂrmh

Fish total length (TL) was measured to the nearest millimeter and wet weight to
the nearest 0.001 g. I measured dry weight (0.0001 g) by drying larvae at 60°C until no
further weight loss was observed. I calculated length-dry weight regressions (Ricker
1975) for walleye and other larval ﬁshes in both years (Appendix 3). I calculated speciﬁc

growth rate (SGR) (Ricker 197 5) for pelagic walleye larvae.

W331

I estimated instantaneous mortality rates (Z) for larval walleye using the decline in
catch per unit effort as used by Noble (1972) and Henderson et al. (1984). Catches from
neuston samples were converted to number of larvae/1,000 m3 of water. I then
transformed these catch data to logc (x +1) to produce normalized data with homogeneous
variance (O’Gorman 1984) and plotted these against time. Mortality was estimated as the

slope of the descending limb of each catch curve (Ricker 1975).

48

Indenglearﬂasssnength
I used the catch of age-O walleye in the Ohio Division of Wildlife’s assessment

bottom trawls in August (Ohio Division of Wildlife 1996) as an index of relative year—
class strength.

Agcﬂallmﬂiets

Stomach contents of individual ﬁsh were removed by dissection under a
dissecting microscope. For larvae < 15mm TL when the digestive tract was
undifferentiated, prey items were identiﬁed and counted throughout the digestive tract.
For larvae > 15 mm TL, I counted all prey anterior to the pyloric caecum. All prey in the
stomach were identiﬁed according to the categories deﬁned in Appendix 4, counted, and
measured using 20 X magniﬁcation projected onto a computer-interfaced digitizing pad.
I applied length-dry weight regressions (R. Haas, MI DNR Mt. Clemens Fisheries
Station, unpublished data; Cornell University Biological Field Station, unpublished data)
to prey lengths to estimate the dry mass of prey items. When organisms were
unmeasurable due to breakage or digestion, I used average values for the same prey item
from ﬁsh examined from the same date.

Walleye diets were characterized by frequency of occurrence and percent
composition by biomass. I estimated dry weight biomass of ﬁsh remains in walleye
stomachs using Species-speciﬁc length-dry weight regressions derived ﬁom prey Species

captured concurrently with age-0 walleye (Appendix 3). Prey electivity was estimated

using the Manly-Chesson index ori calculated as:
m
ori=(ri/ni)/Zri/ni
i=1
where m is the number of prey sizes or species, ri is the proportion of prey i ingested,

and 111 is the proportion of prey i in the environment (Chesson 1983; Lechowicz 1982) .

49

For m prey species in a sample, an alpha value > l/m indicates positive selection of
species i. Electivity values were calculated using samples collected at sites 32, 33, and 34
because these sites produced consistent catches of walleye and are located near the mouth
of the Toussaint River in close proximity to each other . I used prey proportions
estimated from zooplankton and ichthyoplankton samples taken concurrent with walleye
samples to calculate electivity values for pelagic ﬁsh. For demersal age-0 walleye
collected in bottom trawls, I used prey ﬁsh proportions estimated from concurrent catches

in the bottom trawls.

ZooplanktonSampling

Zooplankton abundance and composition were determined from weekly vertical
hauls with a 0.5-m diameter plankton net equipped with 153-mm mesh netting at two to
seven sites in western Lake Erie (Figure 13). Samples were immediately preserved in
sugar-formalin (Haney and Hall 1973). One to 3 l-mL subsamples were withdrawn with
a Hensen—Stemple pipette from a known volume of sample. Additional subsamples were
counted until at least 150 individual zooplankters had been enumerated. All cladocerans
were identiﬁed to species while copepods were identiﬁed as Cyclopoida, Calanoida, or
nauplii (Pennak 1978; Balcer et al. 1984). Cladocera and copepods were measured for
total length using 20 X projection onto a digitizing pad interfaced with a microcomputer.
Numbers of organisms were transformed into biomass using taxon-speciﬁc length—dry

weight regressions (Cornell University Biological Field Station, unpubl. data). I

50

calculated average biomass and average numbers per liter for the pooled zooplankton

samples.

5"151'

I used a single factor analysis of variance (AN OVA) to assess the signiﬁcance of
the differences in zooplankton size between 1994 and 1995. I used analysis of covariance
(AN COVA) with a general linear model (SAS 1985) to assess differences in growth rates
for the log-transformed lengths and dry-weights of walleye larvae between 1994 and
1995. I also used analysis of covariance to assess the difference in survival rate as
estimated by the slopes of the descending limbs of the catch curves. 1 used a Loge (x+1)
transformation for the AN COVA tests to produce normalized data with homogeneous
variance (O’Gorman 1984). I used the sample correlation coefficient to assess
relationship between SGR and water temperature, zooplankton biomass, ichthyoplankton

biomass, ichthyoplankton density, walleye gut contents biomass, and walleye density.

Results

! 411M" 11' .1 . 1!] l
Walleye larvae ﬁrst appeared in neuston samples towed over the reef complex on

29 April 1994 (Figure 14 and 15). Walleye larvae were present over the reefs only during

hatching and dispersed to inshore sites southwest and southeast of the reefs in both years.

In 1994, walleye larvae became concentrated at inshore Sites southeast and southwest of

51

the reef complex (Figures 15-18). The most consistent catches in 1994 came from
inshore sites near Metzger Marsh and the mouths of the Toussaint and Portage rivers. In
areas where age-0 walleye were abundant, the catch was highest in water 2.7 - 6 m deep.
Few walleye larvae were collected from sites north of the reef complex (Figures 15-18).

Catches of larval walleye were much lower in 1995 than 1994 (Figure 14). The
most consistent catches of pelagic walleye larvae in 1995 were from sites southwest of
the reef complex (Figures 19-21) although some walleye larvae were collected from
inshore sites near the mouths of the Toussaint and Portage rivers, Similar to 1994. In
1995 we also observed a lack of pelagic walleye larvae at sites north of the reef complex
(Figures 19-21).

In 1994, the catch of pelagic walleye larvae peaked on 2 May when I captured
1328 ﬂy in 33 tows for an average density of 95.2 fry / 1,000 m3 (Figure 14). Equipment
failure prevented any larval sampling between 2 May and 18 May 1994. In 1995, the
peak catch occurred on 11 May when a total of 85 walleye fry were captured in 40
samples for an average density of 3.9 ﬁsh / 1,000 m3. Mean density of walleye fry for the
sample period was 14 times higher in 1994 than 1995 (28.4 and 2.0 fry / 1,000 m3
respectively). On the date of peak abundance, the larval population in my study area was

estimated at 70,277,000 ﬁsh (1 19 %) in 1994 and 2,616,000 ﬁsh (i 15%) in 1995.

52

 

8.00q
7.00' I 1994

6.00“ O 1995

5.00 ‘
4.00 '
3.00 '
2.00 '

100. <15 III II-
n]... f i Cite % a...

 

 

 

 

Ln Catch+1 (#/1,000 m3)

-1 .00
-2.00 I I l

21-Apr 5-May l9-May 2-Jun 16-Jun 30-Jun

 

Figure 14. Decline in pelagic walleye abundance based on catches in neuston samplers
taken at 15 to 40 Sites in western Lake Erie in the spring of 1994 and 1995. Values are
mean density (#/1,000 m3) i s.e. using Ln (catch +1) transformed data.

53

     
      
 

Toussaint R.

' 1015'
29 April 1994

Toussaint R.

10km

2 May1994

 

Figure 15. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 29 April (top) and 2 May (bottom) 1994.
Circles identify reef sites where egg sampling occurred.

54

  

Toussaint R.

 
    
 

10km

19 May1994

  

10km
23 May1994

 

 

 

Figure 16. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 18 May (top) and 23 May (bottom) 1994.
Circles identify reef sites where egg sampling occurred.

55

10km

30 May1994

 

6 Junel994

 

 

Figure 17. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 30 May (top) and 6 June (bottom) 1994.
Circles identify reef sites where egg sampling occurred.

S6

    

10km

9 Junel994

  

Portage R.

|10kmI

l3 & 20 Junel994

 

 

Figure 18. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 9 June (top), 13 and 20 June (bottom)
1994. Circles identify reef sites where egg sampling occurred.

57

 

 

11 & 12 May1995

 

 

Figure 19. Distribution and density (#/ 1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 3 and 5 May (top), and 11 and 12 May
(bottom) 1995. Circles identify reef sites where egg sampling occurred.

  

Toussaint R.

 
      

I10ka

18 May1995

  

26 May1995

 

 

Figure 20. Distribution and density (#/1,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 18 May (top) and 26 May (bottom) 1995.
Circles identify reef sites where eg sampling occurred.

59

    
 
      
 

Toussaint R.

10km

30 May1995

 

Toussaint R.

Portage R. ..

IIOka

6 &13 June 1995

 

 

Figure 21. Distribution and density (#/ l ,000 m3) of pelagic walleye larvae in western
Lake Erie based on catches in neuston samples 30 May (top) and 6 and 13 June (bottom)
1995. Circles identify reef sites where eg sampling occurred.

60

I collected the ﬁrst demersal walleye in bottom trawls towed off the mouth of the
Toussaint River and near Metzger Marsh on 6 June 1994 and 6 June 1995. No bottom
trawl samples were taken prior to 6 June 1994. My catches of age-0 walleye were
consistent throughout the summer and fall ( through 22 October) of 1994 but only one
age-0 walleye was collected in my bottom trawls after 20 June 1995 despite continued

monthly sampling through October.

WM

I examined the diets of 112 pelagic walleye larvae and 520 demersal age-0
walleye in 1994. In 1995 I examined the diets of 55 pelagic walleye larvae and 22
demersal age-0 walleye. Summaries of the percent composition (dry-weight biomass) of
the diet items observed in walleye guts in 1994 and 1995 are listed in Tables 4 and 5,
respectively. The mean total prey biomass per gut (dry-weight) for pelagic walleye
larvae did not exceed 0.08 mg/ gut in either year. In both years, calanoid copepods and
large cladocerans comprised the bulk of pelagic larval diets, typically accounting for over
60% of dry-weight biomass. Cyclopoid copepods usually ranked third in biomass while
ﬁsh, small cladocerans, rotifers, and nauplii always accounted for less than 20% (usually
less than 10%) of the stomach contents biomass of pelagic walleye larvae in both years.
In 1995 I observed the biomass of ﬁsh in pelagic larval diets to increase from a mean of
3.8% of gut contents biomass on 3 May to 19.3% on 30 May (Table 5) while the mean
biomass of ﬁsh in the diets of pelagic larvae in 1994 did not exceed 3.4% of gut contents

biomass (Table 4).

61

Percent frequency of occurrence for prey items observed in age-0 walleye diets in
1994 and 1995 are listed in Tables 6 and 7, respectively. Calanoid copepods were
observed in 60% to 80 % of the pelagic larval walleye stomachs examined in both years.
Large cladocerans were observed in 17% to 80% of the diets in both years. Cyclopoid
copepods typically occurred in less than 30% of the pelagic walleye guts examined while
small cladocerans, rotifers, and nauplii were typically observed in less than 20% of the
pelagic larval walleye guts examined. Fish were observed less frequently in pelagic
larval guts in 1994 occurring in only 6% of the ﬁsh examined on both 2 May and 18 May
and not at all on 29 May (Table 6). Fish appeared more frequently in pelagic larval diets
in 1995 ranging from 12-83% frequency of occurrence (Table 7).

The diets of demersal age-0 walleye typically contained more ﬁsh than the pelagic
diets, especially in 1994 when ﬁsh usually accounted for over 88% of the dry-weight
biomass observed in guts (Table 4). Large cladocerans and copepods comprised 68.4%
of the dry-weight biomass of demersal age-0 walleye on 6 June and 34.6% of the biomass
on 13 June in 1995. Fish accounted for nearly 100% of the diet of demersal age-0
walleye examined from 27 June through 22 October 1994 (Table 4) and on 20 June 1995
(Table 5). Benthic macro-invertebrates typically accounted for less than 5% of observed
dry-weight biomass in both years.

The frequency of occurrence for copepods and large cladocerans combined
dropped below 30% for demersal age-0 walleye in 1994 but remained high in 1995. In
1995 calanoid copepods were identiﬁed in 75% of walleye guts examined on 6 June and

27 % of the guts examined on 13 June while large cladocerans were identiﬁed in 75% of

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66

the diets on 6 June and 55% of the diets on 13 June. Fish were observed in 58% to 86%
of the demersal age-0 walleye diets examined in June 1994 (Table 6) and 64% to 75% of

the guts examined in 1995 (Table 7).

Zooplanktonﬁommunim

Zooplankton community dynamics for the spring of 1994 and 1995 are illustrated
in Figures 22, 23, and 24. Taxonomic descriptions of zooplankton groupings are listed in
Appendix 4. Calanoid copepods dominated the zooplankton community in April and
early May in both years. Although cyclopoid copepods were numerically most abundant
throughout May and June (Figure 24), the dry-weight biomass of both calanoid copepods
and large cladocerans was greater (Figure 22). In 1994, the abundance of copepods and
large cladocerans increased steadily through the month of May from an average of about
15 individuals per liter to over 50 individuals per liter by June (Figure 24). Zooplankton
biomass also increased steadily during this period, averaging about 50 ug/L in April and
peaking at over 450 ug/L in late June (Figure 22). Mean size of zooplankton in 1994
varied between 0.9 mm and 1.1 mm through the end of June (Figure 23).

Zooplankton biomass and abundance in May and early June of 1995 were
generally less than those observed in 1994. The abundance of copepods and large
cladocerans remained below 20 individuals per liter until late May in 1995 when a large

increase in the abundance of large cladocerans was observed (Figure 24). Zooplankton

67

500 - 1994

   
   

 

  

 

 

INauplii
400 . H Large Cladocerans
m I] Calanoid
3 300 ' ICyCIOpoid
E I Small Cladocerans
a 200 -
100 -
0 .
29-Mar 29-Apr 23-May 13—Jun 12-Jul
500 ' 1995
400 -
a 300 a
a
E
c
a 200 -
100 -
0 .

 

 

29-Mar 29-Apr 23—May 13-Jun 12-Jul

Figure 22. Mean zooplankton dry-weight biomass (pg/l) in western Lake Erie estimated
from vertical tows at 3 to 7 sites in spring of 1994 (top) and 1995 (bottom).

68

E L .. ’3‘ ,l‘l‘§
$0.6. {EWIH‘W §{

0.4 ..
| +199: I
. o - 1995

O I I I I I
22-Mar ll-Apr l-May 21-May lO-Jun 30-Jun

 

 

Figure 23. Mean size of crustacean zooplankton in the spring in western Lake Erie, 1994
and 1995.

Abundance (No/L)

Abundance (N o./L)

 

69

1994

—a— Calanoid C0pepods-l IQ
— e — Cyclopoid Copepods I
..*..Large Cladocerans J I \‘.\

 

 

 

 

 

1 l-Apr

30.
25..
20.
15.!
10.

5..

l-May lO-Jun 30-1111,

2 1 -May

1995

 

 

l l-Apr

 

  

 

l-May 21-May lO-Jun 30-Jun

Figure 24. Abundance of cyclopoid and calanoid copepods and large cladoceran
zooplankton in western Lake Erie in spring of 1994 (top) and 1995 (bottom).

70

biomass averaged about 50 ug/L until late May when the biomass increased dramatically
to nearly 300 ug/L in early June (Figure 22) coinciding with the increase in abundance of
large cladocerans (Figure 24). Mean size of zooplankton in 1995 varied between 0.5 and
0.9 mm through the end of June and was signiﬁcantly less than in 1994 (ANOVA; p <

0.001) when the mean size varied between 0.9 and 1.1 mm (Figure 23).

Ichthmplankmﬂrsxﬁommunitx

Ichthyoplankton community abundance for 1994 and 1995 are illustrated in
Figure 25 and the dynamics of ichthyoplankton biomass are shown in Figure 26. In 1994,
the average abundance of ichthyoplankton increased from about 25 ﬁsh/1,000 m3 in early
May 1994 to over 4,400 ﬁsh/1,000 m3 by late June. The abundance of both soﬁ- and
spiny-rayed ichthyoplankton species varied throughout the spring (Figure 25). Dry-
weight biomass of ichthyoplankton increased from about 0.04 g/1,000 m3 in late April
1994 and early May to over 120 g/ 1,000 m3 in late June 1994 (Figure 26).
Ichthyoplankton densities were consistently over 120 ﬁsh/1,000 m3 and biomass above
0.045 g/1,000 m3 during May and early June 1994, the period when age-0 walleye began
feeding on them.

Ichthyoplankton densities were generally much lower in 1995 than 1994. The
average abundance of ichthyoplankton in 1995 increased from about 20 fish/1,000 m3 in
late April and early May to over 140 ﬁsh/1,000 m3 at the end of June (Figure 25). Dry-
weight biomass of ichthyoplankton in 1995 increased from about 0.04 g/1,000 m3 in

early May to over 2.2 g/1,000 m3 in late June. Ichthyoplankton densities averaged less

71

3500
3000 - 1994
2500 .
2000 . + Spiny
1500. ..D..Soﬁ
1000 .

500 .

 

 

 

 

Abundance (No/1,000 m3)

 

 

 

7-Apr 21-Apr 5-May 19-May 2-Jun 16-Jun 30-Jun

160 .
140 - 1995
120 .
100 .
80 .
60 ..
40 'l
20 .
O 1 I F l
7-Apr 21-Apr 5-May 19-May 2-Jun l6-Jun 30—Jun

 

 

     

Abundance (No/1,000 tr?)

  

 

 

 

 

Figure 25. Density of spiny and soﬁ-rayed ichthyoplankton (excluding walleye) in
western Lake Erie estimated from weekly catches in neuston nets in the spring of 1994
(top) and 1995 (bottom). Ordinate scale varies.

72

 

+
3- +1995

 

 

Ln Biomass ( Dry-Wt.g/1,000 ni)

 

-7 ﬂ

7-Apr 21-Apr 5-May 19-May 2-Jun l6-Jun 30-Jun

 

Figure 26. Dry-weight biomass (Ln g/1,000 m3) of ichthyoplankton in western Lake Erie
in the spring of 1994 and 1995.

80.

73

 

 

 

 

D
70 _ ‘ Zooplankton
0 Fish

60 .
E 50 .
.g 40 .
m
5‘ 30 .
H
Du

 

 

 

 

0 20 40 60

I I I I I I I I

80 100 120 140 160 180 200 220
WalleyeTL(mm)

Figure 27. Relationship between walleye size and size of prey observed in gut for 1994
and 1995 diets pooled. Zooplankton sizes are total lengths while ﬁsh prey sizes are

standard length.

74

than 80 ﬁsh/1,000 m3 and biomass less than 0.06 g/1,000 m3 during May 1995 exceeding

100 ﬁsh/ 1,000 m3 and 0.25 g/1,000 m3 in early June.

! 413M“ E SI ..

Pelagic age-0 walleye ranging in size from 9 - 17 mm TL consumed a narrow
range of prey sizes compared to walleye larger than 17 mm in both years. The mean size
of prey items observed in guts at this size range was approximately 1 mm. Prey sizes
observed in diets of ﬁsh > 17 mm TL ranged from 1 to 12 mm for walleye 17 - 30 while
larger walleye diets contained ﬁsh prey items as large as 18 mm SL (Figure 27).

I calculated electivity values (Chesson’s a) for all prey categories except benthic
invertebrates. I grouped all ﬁsh prey into one functional group. Electivity values for
each prey category are detailed in Figures 28 and 29. Calanoid copepods occurred in age-
0 walleye diets in greater proportions than in the zooplankton community until late June
in both years. However, the oc-values were usually not much greater than 0.167, the value
of neutral selection (l/n) indicating that the walleye were eating calanoid copepods in
about the same proportions that the prey occurred in the environment (Figure 28).

Electivity index values suggest strong positive selection for large cladocerans in
both years, especially during May and early June when a-values often exceeded 0.5
(Figure 28) indicating that large cladocerans occurred in walleye diets in greater
proportions than in the zooplankton community. Electivity values for large cladocerans
declined in mid June of both years and was estimated at 0.0 on the last sampling date in

June when no large cladocerans were observed in diets (Table 4 and 5).

1.0 .
0.8 .
0.6 .
0.4 .
0.2 . .
0.0

 

 

75

[+1994 Calanoid

 

-_o— 1995 Copepods

    

 

l-May
1.0 .
0.8 .
0.6 .
0.4 .
0.2 .1

Electivity (x)

lS-May 29-May 12-Jun 26-Jun

—o— 199_5 Cladocerans

 

 

 

0.0
l-May

 

 

1

15-May 29-May 12-Jun 26-Jun

   
  
 
  

-O— 1995 F1811

——.—.~—=~.—J

L... 1994

 

 

 

 

15-May 29-May 12-J un 26-Jun

Figure 28. Electivity values (Chesson’s on) for calanoid copepods (top), large cladoceran
(middle), and ﬁsh (bottom) prey items estimated for age-0 walleye diets in 1994 and

1995.

76

Age-0 walleye increased their consumption of ﬁsh prey throughout May 1994 and
June 1995 (Table 4 and 5) and this increase is reﬂected in the increasing a-values for this
prey type (Figure 28). Electivity values for ﬁsh in 1994 remained below 0.167 (1/n)
throughout May and increased above neutral selection in early June when the walleye
were demersal. This suggests that age-0 walleye did not eat ﬁsh in greater proportions
than they were available in the pelagic environment but did select for ﬁsh during the
demersal stage in 1994. In 1995, a-values for ﬁsh were initially below 0.167 during the
ﬁrst two weeks of May but increased steadily through the remainder of May reaching 0.5
by early June and 1.0 by the last sample date on 27 June (Figure 28) when ﬁsh were
observed to be the only prey item in diets (Table 5). Electivity values for nauplii and
rotifers, small cladocerans, and cyclopoid copepods rarely exceeded 0.167 indicating that
these prey items occurred in walleye diets in equal or lower proportions than in the

zooplankton community (Figure 29).

AW

Grth rate of age-0 walleye from hatch through the end of June was
signiﬁcantly greater in 1994 than 1995. The regression of the log transformed total
lengths over day-of-year (DOY) in 1994 was Ln TL = 0.0353 (DOY)-2.5012 and for
1995 the regression equation was Ln TL = 0.0245 (DOY) - 1.1825. The slopes of these
regression lines are signiﬁcantly different indicating that walleye grew faster in 1994 than

1995 (AN COVA p<0.01). Newly hatched sac-fry walleye averaged between 6.0 and 7.2

77

 

 

 

 

 

 

 

 

1.0 .
1995 Rotifers
0.6 d Lf— ‘
0.4 .
0.2 .
0.0 : T : ——=u=fo=* if ,: o—p—
l-May lS-May 29-May 12-Jun 26-Jun
g 1.0 .
v 0.8 . + 1994 Small
b +1995 Cladocerans
,,_‘ 0.6 at - 7*
-§, 0.4.
O
2 0.2 . ;\ -
LU 0.0 m : ,c ,-
l-May lS-May 29-May 12-Jun 26-Jun
1.0 1 _
O 8 [+1997] Cyclopoid
#51935 Copepods
0.6 ,
0.4 .
0.2 .
0.0 .M—

 

1-May

lS-May 29-May 12-Jun

26-Jun

Figure 29. Electivity values (Chesson’s oz) for nauplii and rotifers (top), small
cladocerans (middle), and cyclopoid copepods (bottom) prey items estimated for age-0
walleye diets in 1994 and 1995.

78

 

 

 

 

4-0- .1994 .
I
a 30. 01995 . . E o
5 - a 5 °
.C: I a
820‘ 3§°° a
.3
z 1.0..
1—1
0.0

 

 

21-Apr S-May l9-May 2-Jun l6-Jun 30-Jun

 

 

 

 

 

0.00.
A 1994
‘39 '3-°°+ :1995 II E 6
g) I 9
g -6.00. I g 8
a. o
a -9.00. ¥ 3 g. g
._1
-1200 ,

 

23-Apr 7-May 21-May 4-Jun 18-Jun 2—Jul

Figure 30. Top panel: Mean lengths ( :t 1 s.e.) of age-0 walleye collected in neuston nets
and bottom trawls (after 9 June) in western Lake Erie in the spring of 1994 and 1995.
Bottom panel: Dry-weights (g) of age-0 walleye collected in neuston samplers and
bottom trawls (after 9 June) in western Lake Erie in the spring of 1994 and 1995.

 

79

 

 

 

 

0.35 ..
0.30 . I
0.25 . ..i§§4
{'3 0.20 - o 1995.
m 0.15 q i . -
0.10 . o 0 o
0.05 .
O I
0'00 I I I I I I
4-May ll-May l8-May 25-May l-Jun 8-Jun 15-Jun
0 .
’07) -3 ,p “O O
‘35 . 1994 page?"
-6 . 1995 W905”
12’ °_.
Q 8 0 .$.8 . O O
:3 '9 ' 3 o (13.0
0
-12 ﬁ r I i I
1.5 2 2.5 3 3.5 4
Ln Length (mm)

Figure 31. Top panel: Speciﬁc grth rates (g dry—weight) of pelagic age-0 walleye
collected in neuston samplers in western Lake Erie in the spring of 1994 and 1995.
Bottom panel: Relationship between log transformed total length (mm) and dry-weight
(g) of age-0 walleye collected ﬁ'om western Lake Erie in the spring of 1994 and 1995.

80

mm TL in both years but the 1994 cohort averaged 46.2 mm TL by the end of June where
the 1995 cohort was over 20 mm shorter at 25.6 mm TL (Figure 30).

Growth in terms of dry-weight was also signiﬁcantly greater in 1994 than 1995.
Sac-fry larvae weighed about 0.0002 g at hatch in both years and increased to an average
of 0.1305 g by the end of June 1994 but only 0.0321 g by the same time in 1995 (Figure
31). The regression equation estimating the growth of each cohort over time is
Ln DW = 0.1332 (DOY) - 25.7987 for 1994 and Ln DW = 0.0853 (DOY) - 19.8747 for
1995. The slopes of these regression equations are signiﬁcantly different (ANCOVA;
p<0.01) indicating that the growth rate in terms of dry-weight was greater in 1994 than in
1995.

I calculated speciﬁc growth rates (SGR) (Ricker 1975) for pelagic walleye larvae
only using the dry-weight data. I excluded sac-fry from the ﬁrst SGR in 1995 to avoid
bias of newly hatched ﬁsh entering the population and falsely depreciating the SGR
estimate. The highest SGR estimates were calculated for 1994 but these data show no
obvious trend with time (Figure 31). SGR estimates were generally lower in 1995 than
1994 (Figure 31).

I calculated the sample correlation coefficients (Snedecor and Cochran 1989)
between SGR and environmental variables of water temperature, zooplankton biomass,
ichthyoplankton biomass, biomass of walleye gut contents, and walleye density to discern
the closeness of the relationships between these variables. I used the environmental
variables and gut contents biomass observed on the last day of the growth stanza to

calculate the correlation coefficients. I pooled the data from both years to increase the

81

degrees of freedom. While I found no signiﬁcant correlation’s (r 2 0.602; 8 d.f.; a =
0.05) among the variables examined, I did ﬁnd less than signiﬁcant positive relationships
between SGR and zooplankton biomass (r = 0.51) and SGR and gut content biomass (r =
0.39). All other correlation’s were extremely close to zero.

The length—dry-weight relationship for age-0 walleye in 1994 and 1995 is plotted
in Figure 31. The regression of log transformed dry-weight against log transformed total
length between years had slopes which did not signiﬁcantly differ (AN COVA; p > 0.3).
The regression equation for the 1994 length-dry-weight data is Ln DW = 3.8182 (TL) -

16.649 and the regression equation for the 1995 data is Ln DW = 3.8833 (TL) - 16.629.

W

I estimated the mortality rate in 1994 using catch data from 19 May - 6 June
(Figure 14) for ﬁsh ranging in size from 9.9 mm on 19 May to 25 mm on 6 June (Figure
29). In 1995 I used catch data from 25 May - 13 June (Figure 14) when ﬁsh size ranged
from 9.9 mm on 25 May to 21 mm on 13 June (Figure 29). These time periods deﬁned
the descending limb of the catch curves for pelagic larvae. Instantaneous mortality rates
estimated for the period 19 May - 6 June 1994 and 25 May - 13 June 1995 were
0.078/day and 0.053/day respectively. The 95% conﬁdence limits for these estimates are
0.191 2 Z 2-0.035 for 1994 and 0.098 2 Z 20.009 for 1995. These instantaneous
estimates translate into total mortality rates of 75.4% and 73.4% for 1994 and 1995
respectively. Only the 1995 regression equation used to estimates Z is signiﬁcant (p =

0.017); the 1994 regression is not signiﬁcantly different from zero. Despite this result,

82

the AN COVA test indicated that the slopes of these regression equations do not differ

from each other (Type III sums of squares; p = 0.2371).

IndexoﬂeaaClassStrength

Catch rate in Ohio Division of Wildlife August bottom trawl assessments indicate
that the 1994 walleye year-class is larger than that developing in 1995. The catch rate in
August 1994 was 18.2 age-0 walleye per hour of trawling but only 1.9 age~0 walleye per

hour in August 1995 (Ohio Division of Wildlife 1996).

83

Discussion

! 411M" 12"1' ll] 1

My study is the ﬁrst comprehensive examination of the dispersal and abundance
of reef-spawned walleye larvae conducted in western Lake Erie. Fish (1932) provides
perhaps the earliest study of larval ﬁshes in Lake Erie, but did not include the western
basin in her sampling. She does report that walleye larvae were found primarily in “the
western part of the lake” from the middle of May until mid-June of 1928 and 1929. She
also reported that walleye were a very common ﬁsh in Lake Erie and notes that young
walleye may be seined in abundance in protected areas alongshore (Fish 1932).

More recent studies of the ichthyoplankton community in western Lake Erie
originate from studies conducted by the Center for Lake Erie Area Research. Heniken
(1977) reported that walleye larvae were most abundant (0. 1/ 1000 m3) in early May 1976
while Mizera et al. (1981) reported a peak density of 0.75 /1,000 m3 on 30 April 1977.
Heniken’s (1977) sampling design was quite comprehensive both spatially and
temporally. He sampled 25 to 60 sites at 10-day intervals in western Lake Erie including
Maumee and Sandusky Bays and areas within the Bass Islands archipelago from mid-
April through August in 1975 and 1976. Mizera et al. (1981) sampled only nearshore (<
5 m) sites along the MI and OH shores and in Maumee Bay.

My peak density estimates for 1994 and 1995 exceed all of the previously

mentioned values. These differences may be attributed to differences in spawning stock

84

size between the sampling periods. Stock size averaged only 4-9 million adults in 1975-
77 (Deriso et al. 1988) but exceeded 40 million in 1994 and 1995 (Lake Erie Walleye
Task Group 1995). Differences in sampling design and gear are also likely to inﬂuence
the comparability of these estimates. 1 used a larger sampler (2.0 m2 mouth) than
Heniken (1977) and Mizera et al.(l98l) who both employed a 0.75 m2 mouth opening.
The larger mouth opening allowed me to sample greater volumes of water than smaller
samplers which is a more effective means of collecting small pelagic walleye fry.

Based on abundance estimates from Ohio Division of Wildlife index bottom
trawls in August, the 1994 walleye year class is the third strongest year class since 1982
with a mean catch per effort of 19 ﬁsh/hour of trawling. The 1995 year class is the
second weakest year class since 1983 with a mean catch of only 1.9 ﬁsh/hour of trawling
(Ohio Division of Wildlife 1996). I used the sample correlation coefficient to determine
the strength and signiﬁcance of the relationship between larval peak abundance and
abundance estimates in August bottom trawls. I used peak larval abundance estimates
from Heniken (1977), Mizera et al. (1981) and this study and catch data from August
bottom trawls reported by Ohio Division of Wildlife (1996). I found a positive, though
insigniﬁcant at or = 0.05, correlation (r = 0.699) between peak larval abundance and
August catch per unit effort in bottom trawls. This relationship is signiﬁcant at or = 0.10
and could become signiﬁcant at or = 0.05 with only one more data point to increase the
degrees of freedom.

The positive relationship between peak larval abundance and August abundance

suggests that larval abundance does indeed forecast walleye year class strength in western

85

Lake Eric. I should also point out that the 1970’s bottom trawl values are from inshore
stations only and may not represent the entire year-class in these years. The Ohio
Division of Wildlife implemented a comprehensive sampling program in the mid 1980’s
increasing sampling effort and covering a broader range of habitats in western Lake Erie.
This sample design provides a more accurate estimate of walleye year-class strength as
well as the Lake Erie ﬁsh community in general (Ohio Division of Wildlife 1996).

I found age-0 walleye to become concentrated in the nearshore areas southwest
and southeast of the mid-lake reef complex in both years of this study. Because larval
walleye are principally lirnnetic (Faber 1967) they are subject to passive transport by
water currents in western Lake Erie (Houde 1969; Houde and Fomey 1970). The
generalized current patterns during the spring in the western basin explain the dispersal
patterns observed in 1994 and 1995. Herdendorf and Braidech (1970) illustrate
generalized surface current patterns in western Lake Erie in relation to predominant wind
forces experienced in the spring. The general ﬂow of water in western Lake Erie is from
west to east (Herdendorf and Braidech 1970) and winds over western Lake Erie in the
spring are predominately from the west/northwest or east/northeast (Table 3). These
combinations of forces direct current patterns over the midlake reef complex in similar
direction explaining how walleye larvae became distributed in the nearshore areas south
and southeast of the reefs. I would expect a different dispersal and distribution pattern
only if spring winds were strong (>20 km/hr) and from the south for the majority of the

period when walleye larvae emerge from the reefs. This would cause water currents to

86

ﬂow from south to north (Herdendorf and Braidech 1970) and move reef-spawned larvae
out towards the open waters of western Lake Erie north of the reef complex.

In 1994 I observed 56% of all pelagic age—0 walleye collected to come from sites
west of the reefs near Maumee Bay. Only 39% of the pelagic walleye collected in 1994
came from sites on and to the south-southeast of the reef complex. Because the majority
of my catch in 1994 came from sites far to the west of the reefs, this may suggest that a
large part of this relatively large walleye year-class originated in the Maumee River. In
contrast, the weak 1995 year-class may be composed primarily of reef ﬁsh as 64% of all
pelagic age-0 walleye collected in that year came from sites on the reef complex or south-
southeast of it where prevailing water currents would have transported them.

Heniken (1977) reported concentrations of larval walleye at nearshore sites near
Metzger Marsh and west of Catawba Island in 1976 (see Figure 13 for locations).
Similarly, Parsons (1972) found large numbers of demersal age-0 walleye at inshore sites
south and southwest of the reef complex during a bottom trawl survey conducted in July,
1959. His catches of age-0 walleye were highest at inshore sites 3-7 m deep from mid-
June through mid-August. Parsons also reported high densities of age-0 walleye in
bottom trawls taken along the Michigan shore from the mouth of the Detroit River south
to the Raisin River and at the mouth of Sandusky Bay (Parsons 1972).

More recent bottom trawl sampling conducted by the Ohio Division of Wildlife
Lake Erie Fisheries Unit from 1982 through 1995 indicate no substantial differences in
the catch rates of age-0 walleye between inshore (S 6 m) and offshore (> 6 m) sampling

stations in August and October (Ohio Division of Wildlife 1996). However, bottom trawl

87

catches of age-0 walleye were generally higher near Maumee Bay and in areas of low
water clarity (Lake Erie Fisheries Unit, Sandusky OH, unpublished data). It should be
noted, however, that the Lake Erie Fisheries Unit does not sample in the nearshore area
southeast and southwest of the reef complex from Port Clinton west to Bono (see Figure

13 for locations).

Agﬁﬂallcltﬂiﬁls

I observed calanoid copepods and large cladocerans to be the mainstay of pelagic
age—0 walleye diets in both years. Fish became increasingly prevalent in diets as larvae
grew and transformed to demersal juveniles. The increased occurrence of ﬁsh in age-0
walleye diets is also associated with increased abundance of ichthyoplankton in the
environment. Age-0 walleye became primarily piscivorous by early June in 1994 but
zooplankton remained an important part of the age-0 walleye diet until mid June in 1995.

Studies by Hohn (1966) and Paulus (1969) indicated that the ﬁrst food of walleye
larvae less than 9.0 mm TL in western Lake Erie in the 1960’s was diatoms. Both of
these authors indicated that zooplankton, primarily cyclopoid copepods, became
increasingly abundant in larval diets as growth exceeded 9.0 mm. While I found no
diatoms or phytoplankton of any kind in walleye diets, I did observe small cladocerans,
rotifers, and copepod nauplii in the diets of some small (<11.0 mm TL) walleye larvae
while calanoid copepods and large cladocerans dominated the diet above this size range.

I also found Leptodora kindtii, a large cladoceran, among the stomach contents of age-0

88

walleye in late May and June. Hurley (1986) observed Leptodora kindtii to be the
dominant component of age-0 walleye diets in the Bay of Quinte, Ontario.

Changes in the phytoplankton and zooplankton community associated with
changes in the trophic status of western Lake Erie are probably responsible for the
observed differences in larval walleye diets between the 1960’s results and this study.
Western Lake Erie was considered hyper-eutrophic in the 1960’s due to excessive
phosphorous loading and is more recently classiﬁed as mesotrophic (Makarewicz and
Bertram 1991). Hohn (1966) reported that diatoms accounted for nearly 100% of the
total phytoplankton during his study of larval walleye diets and that F ragilaria capucina,
an eutrophic indicator species was highly abundant. The abundance of this species of
diatom has decreased by over 90% since the 1960’s and the overall number of dominant
eutrophic diatoms has decreased dramatically in western Lake Erie (Makarewicz and
Bertram 1991).

The species composition and abundance of zooplankton also reﬂects the trophic
status of lakes. Eutrophic systems typically contain higher cyclopoid copepod and
cladoceran biomass than oligotrophic systems (Gannon and Stemberger 1978). Watson
(1976) found that cyclopoid copepods were the most abundant crustacean zooplankton
species in Lake Erie in 1970 whereas I observed more calanoid copepods in both years of
this study. Paulus (1969) found that Cyclops bicuspidatus was the dominant species in
the zooplankton community and reports no calanoid species at all during his investigation

in 1964 and 1965.

89

I found a variety of items in pelagic larval walleye diets but electivity index
values indicated selection for calanoid copepods and large cladocerans having a mean
body size of about 1 mm. Houde (1967) and Graham and Sprules (1992) found that ﬁrst-
feeding walleye larvae in Oneida Lake, NY actively selected copepods as prey and
Spykerman (1974) found similar results for walleye larvae in Clear Lake, IA. Mathias
and Li (1982) concluded that most postlarval walleye are primarily zooplanktivorous.
Walleye larvae are gape-limited predators and observations indicate a less than 5%
capture success rate when feeding on 1.2 mm Daphnia in a closed system (Mathias and Li
1982). Feeding success of walleye larvae depends on vision and their ability to pursue
and capture prey as well as prey size and escape mechanisms (Mathias and Li 1982;
Raisanen and Applegate 1983; Graham and Sprules 1992).

Rapid growth during the larval stage is critical for survival of age-0 ﬁsh (Miller et
al. 1988) so consumption of the most energetically proﬁtable prey type is essential.
Researchers seem to disagree on whether prey size or species is most important to young
ﬁsh in prey selection. Mathias and Li (1982) and Fox (1989) concur that the size of the
prey item is important in optimizing larval grth while Confer and Lake (1987) found
that ﬁsh grow at different rates when fed the same biomass of different prey species. My
results indicate that walleye larvae from western Lake Erie select taxonomic groups of
zooplankton prey but the size structure of the prey ingested does not differ greatly from
that observed in the zooplankton community.

Piscivory in walleye begins with cohort cannibalism (Li and Mathias 1982) and

cannibalism has been shown to cause high mortality in walleye culture operations

90

(N ickum 1978). The incidence of cannibalism is low among age-0 walleye in lakes
(Mathias and Li 1982). In support of this, I observed no evidence of cannibalism by age-
0 walleye in this study.

Many studies have surmised that size of prey ﬁsh relative to the size of walleye is
an important factor in regulating the success of a year—class, particularly when stocking
age-0 walleye into a system (Madenjian et al. 1991; Jensen 1992). Therefore, it also
makes sense that the sooner walleye larvae can grow to a size where piscivory is possible,
both grth and survival potential will be increased. I observed faster grth and an
earlier onset of piscivory in 1994 than 1995. Ichthyoplankton prey were also much more
abundant in May and early June of 1994 potentially increasing the encounter rate with
age-0 walleye.

Fish were uncommon in pelagic age-0 walleye diets in 1994 and 1995 but
increased in importance in June when the walleye cohorts became demersal. Age-0
walleye were almost exclusively piscivorous by the end of June, and except for the
occasional benthic invertebrate, remained piscivorous through fall of 1994. Soft rayed
prey occurred more frequently in age-0 walleye diets but I did observe changes in prey
use throughout the summer and fall of 1994. Hartman and Margraf (1992) found age-0
walleye in western Lake Erie to be exclusively piscivorous in late June of 1986, 1987,
and 1988 with Morone species comprising > 50% of their diet in all 3 years. In contrast,
Knight et al. (1984) found that age-0 walleye were primarily piscivorous after July in

1979, 1980 and 1981 and that soft rayed ﬁsh species dominated the diets in these years.

91

W

Age-0 walleye grew faster in 1994 than 1995, reaching 46 mm TL by the end of
June in 1994 and only 25 mm by the same time in 1995. Differences in water warming
rate and prey abundance between the two years readily explain these differences in
growth rate. Slower water warming rates during egg incubation resulted in later hatching
in 1995 (Roseman et al. 1996; also see Chapter 1). Water warming rates are positively
related to age-0 walleye growth in many systems, especially for pelagic larvae (F omey
1976; Sems 1982). Water temperature dictates physiological function rates in walleye by
limiting ﬁsh activity and digestive rates (Kitchell et al. 1977). Not only is water
temperature directly related to physiological rates in ﬁsh, but it also inﬂuences the timing
and production of prey biomass. Phytoplankton and zooplankton production rates are
positively related to water temperature (Mills and Fomey 1988). The timing of spawning
and the duration of incubation periods inﬂuence the production of ichthyoplankton in
western Lake Erie (Harnley et al. 1983) and thus the availability of prey for piscivores.
Slower water warming rates can delay spawning and embryonic development resulting in
low prey abundance.

Food limitation also affects the growth of young walleye. Age-0 walleye grth
has been positively related to the abundance of young yellow perch in many lakes
(Carlander and Payne 1977; Kempinger and Churchill 1972; Mills and Fomey 1988).
Fox (1989) discovered that walleye growth rate was inﬂuenced by chironornid density in

the benthos and, to a lesser degree, zooplankton biomass. Similarly, Kelso’s (1972)

92

experiments showed a positive relationship between ration and walleye growth rate.
Madenjian’s (1991) individual-based model of age-0 walleye growth found that ﬁsh in
Lake Erie encountered prey at a much higher rate than in Oneida Lake, NY explaining the
greater growth observed for Lake Erie ﬁsh.

Comparisons of the total lengths of age-0 walleye in late June that I observed with
previous observations from other studies indicate that ﬁsh grew slower in both 1994 and
1995 than in many previous years. I found walleye lengths averaging 40 and 28 mm TL
in late June of 1994 and 1995 respectively. Parsons (1972) reported a mean length of 63
mm in late June for the 1959 year class while Wolfert (1966) reported a mean length of
55 mm in late June 1962. Hatch et al. (1987) described factors causing the decline in
mean length of age-0 walleye in fall and Knight and Vondracek (1993) described changes
in prey ﬁsh populations in relation to walleye growth and predation in western Lake Erie.
Both studies attribute the decline in ﬁrst year growth of walleye to increased walleye

stock size and reductions in phosphorous loading.

WWW

My survival estimates are for three week periods during the larval period when
the ﬁsh are pelagic and vulnerable to my sampling gear. At present, these are the best
values I can estimate pending further study. My estimates are plagued with potential bias
from several sources. First, I currently have no estimates of size-selective avoidance and
therefore have not adjusted my catches accordingly. Noble (1972) adjusted his catches of

larval walleye collected in Miller samplers by employing an electric grid to incapacitate

93

and disorient ﬁsh and adjusted his catches accordingly. I attempted to sample at night to
create an adjustment factor for Lake Erie walleye collected in the neuston net, but my
night sampling produced no more walleye than the day sampling. If they had, I would
wonder if the increased catch was due to a lack of avoidance or vertical migration by the
ﬁsh.

Another factor potentially inﬂuencing my survival estimates is the immigration of
river-spawned walleye larvae into my population of reef spawned ﬁsh. This would tend to
artiﬁcially deﬂate my estimates of mortality. I sampled the Toussaint and Portage Rivers
in 1995 during the time I observed pelagic walleye in the lake and found no walleye
larvae. Upon investigation, these rivers proved to have no suitable spawning areas for
walleye. Researchers at Ohio State University are currently examining outrnigration
patterns of river-spawned walleye from the Maumee and Sandusky River. A comparison
of dispersal patterns between reef- and river-spawned larvae is planned and may elucidate
relative contributions of each spawning stock to the general Lake Erie population.

The relative strength of the year classes developed in 1994 and 1995 differed by a
factor of 14 during the pelagic larval period. This factor was reduced to 9.6 according to
relative abundance estimates from August bottom trawls. This could be due to greater
mortality occurring during the summer of 1994, an inﬂux of river-spawned ﬁsh in 1995,
or a combination of the two.

Studies in other systems and culture ponds show wide variability in mortality
rates and my mortality estimates ﬁt into the range of reported values found in the

literature. Instantaneous mortality rates ranged from 0.201 to 0.310 for stocked walleye

94

ﬂy in Oneida Lake, NY (Noble 1972; F omey 1975). Fox (1989) found instantaneous
mortality rates to range from 0.0055/day to 0.087/day for ﬁsh stocked in ponds as sac-fry
and recovered at 46 mm TL. Te Brugge and McQueen (1991) reported instantaneous
mortality rates ranging from 0.016/day to 0.028/day for walleye over a 50 day period (9.3
to 30 mm TL) in enclosures placed in Lake St. George, Ontario. Instantaneous mortality
rates ranged from 0.067/day to 0.26/day for stocked sac-fry to 20 days poststocking in

Rathbun Lake, IA (Mitzner 1992).

THESIS SUMMARY

Great disparity in year-class strength of reef spawned walleye in Lake Erie is
apparent in the egg stage. Egg density in 1994 was approximately twice that observed in
1995 and egg survival was 2.8 times better in 1994. The product of these factors provides
an initial year-class disparity factor of nearly 6. I observed pelagic walleye larvae to be
14 times more abundant in 1994 than 1995. Because white perch were present on the
reefs during late April and May 1995, the walleye hatch period, signiﬁcant numbers of
walleye larvae may have been removed by predation. The year-class disparity was
reduced to a factor of 9.6 by August as estimated by relative abundance in bottom trawls
indicating that either mortality was greater during the summer months in 1994 or more
river-spawned walleye entered the population in 1995.

The rate of water warming in the spring during both the egg and larval stages
appears to be the driving force behind survival of these life stages. Slower warming rates
prolong incubation increasing egg vulnerability to adverse conditions. The frequent
intense wind events during the incubation period are largely responsible for removing
walleye eggs from reefs while predation by ﬁshes is probably detrimental to a lesser

degree. Slower warming rates also delay prey production inhibiting walleye growth and

95

96

lengthening the duration of the larval stage and the walleye’s dependence on zooplankton

prey.

APPENDICES

Appendix 1. Walleye larval and egg sample site coordinates and depths (m).

97

 

Larval Sample Sites

Site #

\OOOQO‘Lh-kWNI-i

t—tu—ou—au—du—iI—nI—nu—bI—tI—I
chO‘M-AWN'HQ

19-1
20
20-1
21
22
23
24
25
25-I
26
27
28
29
29-1
30
3 1
32

Latitude

410 37.7'
410 39.8'
410 37.4'
410 39.8'
410 37.2'
410 40.3'
410 38.6'
41040.8'
410 38.2'
410 36.8'
410 39.5'
410 38.1'
410 39.6'
41040.8'
410 41.8'
410 42.5'
41040.1'
41042.5'
410 38.0'
410 37.6'
410 38.3’
41° 37.9'
41040.5'
41042.8'
410 41.2'
41043.1'
410 38.1'
410 38.2'
410 35.8'
410 33.9'
410 32.0'
410 32.9'
41° 32.7'
410 35.6‘
41042.0'
41° 35.0'

Lansimds:

830 01.4'
820 58.2'
820 59.8'
820 56.2'
830 01.7'
820 59.6'
830 01.3'
820 58.4'
820 57.7'
820 58.3'
820 53.8'
820 55.2'
830 03.0'
830 01.6'
820 55.2'
830 01 .2'
830 05.0'
830 03.8'
830 05.8'
830 05.8'
830 09.7'
830 09.7'
83° 09.7'
83° 09.7'
830 14.8'
830 14.8'
820 52.0'
820 51 .6'
820 54.7'
820 56.0'
820 55.5'
820 53.6'
820 53.0'
820 51.5'
82° 58.5'
83° 02.0'

EOOONOOOMGUJA

m—oowcxmqo-A

Appendix 1 continued.
$11111

32-I
33
34
34-1

35
Metzger Marsh
Egg Sample Sites

Toussaint Reef

NQMbWN—E

Niagara Reef

OOQO‘MAUJN—E

Latitude

41° 34.7’

41° 33.2'
41° 34.8'
41° 340'

Latitude
41 37.75
41 37.85
41 37.92
41 37.88
41 38.05
41 37.84
41 37.76

Latitude
41 39.90
41 39.85
41 39.95
41 40.05
41 40.00
41 39.95
41 39.80
41 39.85

98

Lungitude

83° 02.1’

82° 59.0'
82° 58.0’
82° 58.0'

Laneimds

83 01.15
83 01.07
83 00.80
83 00.68
83 01.05
83 01.31
83 00.93

Lansimde

82 58.45
82 58.55
82 58.45
82 58.41
82 58.80
82 59.00
82 59.00
82 58.75

Depth

wwwu‘qw

<3
3-5
<3

5-7
5-7

<3

3-5
3-5
3-5
3-5
5-7
5-7
3-5

99

 

 

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vmncd L 86%; 2‘3 do 33
named mam.mwm.m $3
339m ﬂ Tow< 0 ~ -ow< a0w< mow< Wow< came 30>

 

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do.“ 88 3323 1358 MO 83850 98 mommﬂoowm 33239: .8.“ 350.25% 98:55 .mcoaomwoa 3on 03-3-5me .N 5.52:?

100

Appendix 3. Length-dry weight relationships for species collected in western Lake Erie, 1994
and 1995. Relationship equation is simple linear regression of Ln transformed standard lengths

(SL) and dry weights (DW(g)) for species listed; N = sample size; CL = carapace length for

 

 

arnphipods.

Size Range Relationship
Species (mm SL) Ln DW=m(SL)+b N p-value R2
1994
Alewife 29.0 - 95.0 3.450 (SL)—14.365 55 < 0.001 0.98
Amphipoda 4.0 - 12.2 0.00052 (CL) - 0.00235 26 < 0.001 0.87
Clupeidae 8.5 - 25.5 6.193 (SL) - 23.532 60 < 0.001 0.97
Larvae
Cyrpinidae 7.0 - 18.1 3.063 (SL) - 14.227 116 < 0.001 0.76
Larvae
Emerald 21.0 - 43.0 2.649 (SL) - 11.749 26 < 0.001 0.95
Shiner
Freshwater 8.0 - 50.0 3.457 (SL) - 14.471 8 < 0.001 0.95
Drum
Gizzard 11.0 - 111.0 4.277 (SL) - 17.915 89 < 0.001 0.99
Shad
Johnny 49.0 - 60.0 4.582 (SL) - 18.902 5 0.001 0.97
Darter
Logperch 35.0 - 69.0 3.359 (SL) - 14.083 12 < 0.001 0.95
Morone sp. 6.0 - 80.0 3.765 (SL) - 15.146 418 <0.001 0.98
Larvae
Rainbow 16.0 - 53.0 3.085 (SL) - 13.6842 66 <0.001 0.76
Smelt
Spottail 30.0 - 93.0 3.411 (SL) - 14.170 62 < 0.001 0.97
Shiner
Troutperch 12.5 - 87.0 3.310 (SL) - 13.8511 106 <0.001 0.99
Yellow 11.0 - 80.0 3.295 (SL) - 13.829 269 <0.001 0.99

Perch

Appendix 3, continued.

101

 

 

Size Range Relationship
Species (mm SL) LN DW=m(SL)+b N p-value R2
1995
Catastomidae 5.0 - 6.5 3.035 (SL) - 14.359 6 0.103 0.53
Larvae
Channel 32.0 - 96 3.267 (SL) - 14.557 14 < 0.001 0.99
Catﬁsh
Clupiedae 6.0 - 46.5 4.875 (SL) - 19.773 111 < 0.001 0.96
Larvae
Cyprinidae 4.5 - 9.0 1.221 (SL) - 11.297 9 0.124 0.30
Larvae
Emerald 44.0 - 71.0 3.385 (SL) - 14.350 26 <0.001 0.95
Shiner
Freshwater 5.0 - 94.0 3.485 (SL) - 14.425 31 <0.001 0.99
Drum
Gizzard 54.0 - 104.0 0.033 (SL) - 2.963 32 < 0.001 0.98
Shad
Johnny 30.0 - 36.0 3.158 (SL) - 13.359 6 0.016 0.80
Darter
Morone sp. 6.5 - 72.0 3.950 (SL) - 15.677 112 < 0.001 0.95
Larvae
Rainbow 19.0 - 45.0 4.076 (SL) - 17.741 38 <0.001 0.88
Smelt
Spottail 19.0 - 99.0 3.390 (SL) - 14.057 103 <0.001 0.99
Shiner
Troutperch 8.0 - 77.0 3.552 (SL) - 14.729 63 < 0.001 0.99
White 35.0 - 73.0 3.509 (SL) - 14.241 63 < 0.001 0.97
Perch
Yellow 8.5 - 62.0 3.926 (SL) - 16.005 76 < 0.001 0.95

Perch

 

102

Appendix 4. List of genera and families included in functional prey groups.

 

EunctidnaLBrsaLCrrdup 3119—9195
Rotifers Rotatoria
Small Cladocerans Bosminidae, Chydoridae, Sida

crystallina, Ceriodaphnia sp.

Cyclopoid Copepods Acanthocyclops vernalis,
Eurytemora aﬂinis, Diacyclops
thomasi, Mesocyclops edax,
Tropocyclops prasinus mexicanus

Calanoid Copepods Epischura Iacustris, Leptodiaptomus
sicilis, Leptodiaptomus minutus,
Skistodiaptomus oregonensis

Large Cladocerans Daphnia galeata mendotae, Daphnia
retrocurva, Leptodora kindtii,
Diaphanosoma birgei

Benthic Prey Chironomidae, Hexagenia
Spiny Rayed Fish ApIodinotus grunniens, Morone spp.,
Percaﬂavescens, Percina caprodes,

Percopsis omiscomaycus

Soﬁ Rayed Fish Catastomidae, Clupeidae,
Cyprinidae, Osmeridae

 

103

Appendix 5. Densities (#/1,000 m3) of larval ﬁshes collected in neuston nets at each site in 1994
and 1995.

1994 Burbot (Lota Iota)

 

Site # 2 May
1 1.9
2 0.0
3 0.0
4 3.5
5 1.9
6 0.0
7 0.0
8 2.2
9 0.0
10 0.0
l l 0.0
12 0.0
13 0.0
14 0.0
15 0.0
17 0.0
18 0.0
19 0.0
20 5.5
21 0.0
22 0.0
23 0.0
24 0.0
25 0.0
26 0.0
27 0.0
28 0.0
29 0.0
30 0.0
31 0.0
32 2.3
33 0.0
34 0.0
MM 0.0

 

104

Appendix 5, continued.

 

1994 Catastomidae

Site # 19 May 23 May 30 May 6 Jun
1 0.0 0.0 2.0 0.0
2 0.0 0.0 0.0 0.0
7 0.0 0.0 0.0 0.0
8 0.0 0.0 5.5 0.0
9 0.0 0.0 0.0

10 0.0 0.0 0.0

1 l 0.0 0.0 0.0 1.7
12 0.0 0.0

13 0.0 0.0 0.0
14 0.0 0.0 0.0 0.0
15 0.0 0.0 0.0

17 0.0 0.0 0.0 0.0
18 0.0 0.0 0.0

19 0.0 2.5 0.0 0.0
191 0.0 0.0
20 0.0 0.0 0.0 0.0
21 0.0 0.0

22 0.0 0.0 0.0 0.0
23 3.1 0.0 0.0 0.0
24 0.0 0.0 0.0

25 0.0 0.0 0.0

251 0.0 0.0
26 0.0 0.0 0.0 0.0
27 0.0 0.0 0.0 0.0
28 0.0 0.0 0.0 0.0
29 0.0 0.0 0.0 0.0
291 0.0 0.0
30 0.0 0.0 0.0 1.6
301 0.0 0.0
31 0.0

32 0.0 0.0 0.0 0.0
321 0.0 0.0
33 0.0 0.0 0.0

34 0.0 0.0 2.0 1.7
341 0 0 0.0

MM 0.0 0.0 22.8 0.0

 

105

Appendix 5, continued.

1994 Centrarchidae

 

Site # 23 May
1 0.0
2 0.0
7 0.0
8 0.0
9 0.0
10 0.0
1 1 0.0
12 0.0
13 0.0
14 0.0
15 0.0
17 0.0
18 0.0
19 0.0
20 0.0
21 0.0
22 0.0
23 0.0
24 0.0
25 0.0
26 0.0
27 0.0
28 0.0
29 0.0
30 0.0
32 13.4
33 0.0
34 0.0

MM 0.0

 

Appendix 5, continued.

1994 Cluepidae

106

 

Site # 19 May 23 May 30 May 6 Jun 9 Jun 13 Jun 28 Jun

1 0.0 0.0 74.8 0.0 27.9 1.5 0.0

2 0.0 0.0 0.0 1.6 4.6 1.5 1.6

7 0.0 0.0 51.0 0.0 5.6 1.6

8 0.0 0.0 103.8 0.0 42.5 3.1

9 0.0 0.0 0.0

10 0.0 0.0 0.0 124.6 0.0 l 1 1.9
11 0.0 0.0 0.0 1.7

12 10.6 0.0

13 0.0 0.0 0.0

14 0.0 0.0 5.3 0.0

15 0.0 0.0 0.0

17 0.0 0.0 0.0 0.0

18 0.0 0.0 2.2

19 0.0 2.5 280.1 19.7 46.2 6.2 256.9
191 28.4 0.0

20 0.0 0.0 0.0 1.6 13.7

21 7.0 0.0 2536.9 1339.6

22 0.0 0.0 0.0 0.0 576.9

23 389.6 1 11.4 18.6 0.0 166.0

24 0.0 0.0 7.1 4.7

25 0.0 0.0 57.2 1.5

251 0.0 0.0 0.0 0.0
26 0.0 0.0 2.1 0.0 15.3

27 0.0 0.0 8.8 0.0

28 0.0 0.0 121.0 860.4 1584.8
29 0.0 0.0 6.9 0.0 23.0 1.6
291 16.5 0.0 0.0

30 0.0 0.0 2271.7 0.0

301 0.0 0.0 3.2

31 0.0

32 0.0 827.2 6.7 309.2 1697.2

321 0.0 1.8 67.1 462.0
33 0.0 4.9 2.0

34 0.0 0.0 8.1 5.1 183.7 34.8
341 2.0 0.0 75.0

MM 0.0 33.2 1351.9 117.3 6912.3 54.0

 

107

 

Appendix 5, continued.

1994 Cyprinidae

Site # 2 May 30 May 6 Jun 9 Jun 13 Jun 20 Jun 28 Jun
1 0.0 13.8 1.8 1.5 27.7 0.0 0.0

2 0.0 15.3 0.0 0.0 19.1 0.0 140.5
3 0.0

4 0.0

5 0.0

6 0.0

7 0.0 4.1 0.0 0.0 171.4 0.0

8 2.2 0.0 0.0 0.0 241.1 0.0

9 0.0 8.5

10 0.0 0.0 0.0 449.0 0.0 24.3

1 1 0.0 0.0 0.0 0.0

12 0.0

13 0.0 0.0

14 0.0 0.0 0.0

15 0.0 0.0

17 0.0 0.0 0.0

18 0.0 0.0

19 0.0 4.3 1.1 0.0 45.1 1530.2 115.1
191 30.6 0.0 0.0

20 0.0 2.5 0.0 71.4 0.0

21 0.0 0.0 1.6

22 0.0 0.0 0.0 81.4

23 0.0 4.6 0.0 1.6

24 0.0 0.0 4.7 0.0

25 0.0 0.0 429.5 1037.9

251 0.0 0.0 0.0 0.0 23.6
26 0.0 0.0 1.6 15.3 3.2

27 0.0 0.0 0.0 0.0

28 0.0 2.0 18.7 0.0 19391.7
29 0.0 20.8 0.0 21.5 8.3 365.6
291 0.0 0.0 16.5 0.0

30 0.0 29.2 12.6

301 0.0 1.5 1.6 0.0

31 0.0

32 0.0 0.0 1.8 392.4

321 0.0 3.6 191.6 34.7 0.0
33 0.0 2.0

34 0.0 8.1 0.0 0.0 1027.2
341 0.0 1.4 106.5 0.0

MM 37.3 8.3 0.0 20.0 205.8

 

108

 

Appendix 5, continued.

1994 Freshwater Drum

Site # 19 May 9 Jun 13 Jun 20 Jun 28 Jun
1 0.0 0.0 0.0 0.0 0.0
2 0.0 0.0 0.0 0.0 0.0
7 0.0 0.0 0.0 0.0

8 0.0 0.0 0.0 0.0

9 0.0

10 0.0 0.0 0.0 0.0 0.0
11 0.0

12 0.0

13 0.0

14 0.0

15 0.0

17 0.0

18 0.0

19 0.0 0.0 0.0 3.7 0.0
191 0.0

20 0.0 0.0 0.0

21 0.0 0.0 0.0

22 0.0 0.0

23 0.0 0.0

24 0.0 0.0 0.0

25 0.0 0.0 0.0

251 0.0 0.0 0.0
26 0.0 0.0 0.0

27 0.0 0.0

28 0.0 0.0 0.0
29 0.0 0.0 0.0 1.6
291 0.0 0.0

30 0.0

31 0.0

32 0.0 6.2

321 0.0 0.0 0.0
33 0.0

34 24.4 15.2 0.0
341 0.0 0.0

MM 0.0 0.0 0.0 0.0

 

109

 

Appendix 5, continued.
1994 Channel Catﬁsh
Site # 13 Jun
1 0.0
2 0.0
7 0.0
8 0.0
10 0.0
19 0.0
20 0.0
21 0.0
23 0.0
24 0.0
25 0.0
251 0.0
26 0.0
29 0.0
291 0.0
301 0.0
32 1.5
321 0.0
341 0.0

MM 0.0

 

110

 

Appendix 5, continued.

1994 Logperch

Site # 19 May 6 Jun 9 Jun 13 Jun
1 0.0 0.0 0.0 0.0
2 0.0 0.0 0.0 0.0
7 0.0 0.0 0.0 0.0
8 0.0 0.0 9.1 0.0
9 0.0

10 0.0 0.0 0.0
11 0.0 0.0

12 0.0

13 0.0 0.0

14 0.0 0.0

15 0.0

17 0.0 0.0

18 0.0

19 0.0 0.0 0.0 0.0
191 0.0

20 0.0 0.0 0.0
21 0.0 6.1 0.0
22 0.0 0.0 0.0

23 15.5 0.0 17.2
24 0.0 0.0
25 0.0 0.0
251 0.0 0.0
26 0.0 0.0 0.0
27 0.0 0.0

28 0.0 0.0

29 0.0 0.0 0.0
291 0.0 0.0
30 0.0 0.0

301 0.0 0.0
31 0.0

32 0.0 1.8 3.1
321 0.0 0.0
33 0.0

34 0.0 0.0 0.0

341 0.0 0.0

MM 3.1 0.0 0.0 4.0

 

111

Appendix 5, continued.

 

1994 Lake Whiteﬁsh.

Site # 4 Apr 29 Apr 2 May 19 May
1 62.0 13.0 0.0
2 7.8 0.0
3 7.1

4 0.0

5 36.5 24.1

6 0.0

7 0.0 0.0
8 4.3 0.0
9 1.9 0.0
10 1.8 0.0
11 0.0 0.0
12 0.0 0.0
13 6.9 0.0
14 5.3 0.0
15 0.0 0.0
17 12.5 0.0
18 9.4 0.0
19 1.7 12.4 0.0
20 23.9 0.0
21 9.6 0.0
22 0.0 0.0
23 55.5 0.0
24 13.3 0.0
25 3.1 0.0
26 0.0 8.3
27 14.0 0.0
28 11.8 2.4
29 0.0 0.0
30 70.0 0.0
31 3.2 0.0
32 154.3 36.2 0.0
33 41.5 7.4 0.0
34 8.1 2.3 0.0
MM 6.2

 

Appendix 5, continued.

 

1994 Morone spp.

Site # 19 May 23 May 30 May 6 Jun 9 Jun 13 Jun 20 Jun 28 Jun
1 0.0 5.8 78.7 28.6 6.2 4.6 0.0 1.7
2 0.0 175.9 13.1 13.1 1.5 1.5 0.0 0.0
7 0.0 0.0 142.7 1.8 2.8 3.2 0.0

8 0.0 0.0 0.0 0.0 1.5 12.3 0.0

9 0.0 8.3 2.1

10 0.0 14.7 6.8 6.2 13.8 0.0 0.0
1 l 0.0 0.0 0.0 0.0 0.0

12 0.0 0.0

13 0.0 0.0 0.0

14 0.0 0.0 0.0 0.0

15 0.0 6.3 0.0

17 0.0 0.0 0.0 6.1

18 0.0 0.0 0.0

19 36.6 5.0 157.3 28.5 6.2 4.7 5.6 12.6
191 238.3 0.0 0.0

20 6.7 0.0 427.4 6.5 0.0 0.0

21 7.0 14.6 457.5 42.4

22 29.4 0.0 4.1 0.0 109.0

23 408.2 0.0 315.5 9.5 0.0

24 114.3 0.0 7.1 1.6 0.0

25 0.0 0.0 45.8 16.6 0.0

251 0.0 0.0 0.0 0.0 0.0
26 0.0 0.0 2.1 0.0 0.0 0.0

27 0.0 6.2 4.4 0.0 0.0

28 2.4 4.2 62.5 297.6 0.0 88.0
29 2.6 45.7 85.5 0.0 3.1 165.7 0.0
291 0.0 0.0 0.0 0.0

30 18.1 0.0 43.8 0.0

301 0.0 0.0 4.8 0.0

31 0.0

32 5.0 3.4 250.3 126.9 2386.5

321 0.0 5.3 27.8 173.6 357.3
33 5.1 0.0 5.9

34 0.0 0.0 264.1 17.0 2209.2 0.0
341 21.7 0.0 225.1 1.8

MM 0.0 0.0 740.2 82.8 2950.8 431.8 3212.7

 

113

Appendix 5, continued.

1994 Northern Pike (Esox Iucious)

 

Site # 19 May
1 0.0
2 0.0
7 0.0
8 0.0
9 0.0
10 0.0
1 1 0.0
12 0.0
13 0.0
14 0.0
15 0.0
17 0.0
18 0.0
19 0.0
20 0.0
21 0.0
22 0.0
23 0.0
24 0.0
25 0.0
26 0.0
27 0.0
28 0.0
29 0.0
30 0.0
31 0.0
32 0.0
33 0.0
34 0.0

MM 3.1

 

114

Appendix 5, continued.

1994 Rainbow smelt (Osmeris mordax)

 

Site # 13 Jun 20 Jun
1 0.0 0.0
2 0.0 0.0
7 0.0 0.0
8 0.0 0.0
10 0.0 0.0
19 0.0 0.0
191 0.0
20 0.0 0.0
21 1.6

23 0.0

24 0.0 0.0
25 0.0 0.0
251 0.0 0.0
26 0.0 1.6
27 0.0
28 0.0
29 0.0 0.0
291 0.0 0.0
301 0.0 0.0
32 0.0

321 0.0 0.0
341 0.0 0.0

MM 0.0 3.8

 

115

Appendix 5, continued.

 

1994 Troutperch

Site # 28 Jun
1 0.0

2 0.0

10 0.0

19 0.0
251 0.0

28 0.0

29 6.5
321 0.0

34 0.0

 

Appendix 5, continued.

1994 Walleye

116

 

Site # 29 Apr 2 May 19 May 23 May 30 May 6 Jun 9 Jun 20 Jun
1 43.5 88.9 0.0 17.5 0.0 0.0 0.0 0.0
2 23.5 0.0 94.7 0.0 0.0 0.0 0.0
3 7.1

5 26.9 20.4

7 2.4 0.0 0.0 0.0 0.0 0.0
8 0.0 22.5 0.0 0.0 0.0 0.0
9 3.9 0.0 0.0 0.0

10 32.2 8.0 0.0 0.0 0.0 0.0
11 0.0 0.0 0.0 0.0

12 0.0 0.0

13 3.4 0.0 0.0 0.0

14 0.0 0.0 0.0 0.0

15 0.0 0.0 0.0

17 2.1 0.0 0.0 0.0 0.0

18 0.0 0.0 0.0

19 88.7 0.0 0.0 4.3 0.0 0.0 0.0
191 0.0 0.0

20 273.4 20.2 0.0 0.0 0.0

21 23.0 0.0 0.0 112.5 0.0
22 2.2 0.0 3.3 0.0 0.0 1.5

23 318.7 9.3 0.0 4.6 0.0 0.0
24 247.4 28.6 27.9 0.0 0.0
25 6.1 0.0 0.0 0.0 0.0
251 0.0 0.0
26 25.7 99.8 0.0 0.0 0.0 0.0
27 39.8 192.2 15.4 0.0 0.0

28 165.3 583.3 0.0 2.0 0.0

29 357.3 26.3 91.4 2.3 0.0 0.0
291 0.0 0.0 0.0
30 242.5 9.0 0.0 0.0 0.0

301 0.0 0.0 0.0
31 0.0 0.0

32 73.7 488.9 29.8 16.8 2.2 1.8 0.0
321 0.0 0.0 0.0 0.0
33 5.7 17.3 0.0 17.3 0.0

34 0.0 563.1 0.0 2.8 0.0 0.0 141.2

341 0.0 0.0 0.0
MM 93.7 438.8 0.0 2.1 143.5 37.5 4.0

 

117

Appendix 5, continued.
1994 Yellow perch.

Site # 2 May 19 May 23 May 30 May 6 Jun 9 Jun 13 Jun 20 Jun

 

l 0.0 l 1.7 23.4 0.0 0.0 0.0 0.0 0.0
2 0.0 769.2 121.8 0.0 0.0 0.0 0.0 0.0
3 0.0

4 0.0

5 0.0

6 0.0

7 0.0 74.1 0.0 0.0 0.0 0.0 0.0 0.0
8 0.0 742.4 22.5 0.0 0.0 0.0 0.0 0.0
9 0.0 164.6 37.4 0.0

10 0.0 140.5 32.4 2.3 50.7 0.0 0.0
1 1 0.0 17.4 0.0 0.0 0.0 0.0
12 0.0 105.7 0.0

13 0.0 0.0 0.0

14 0.0 656.1 0.0 0.0 0.0

15 0.0 9.4 0.0 0.0

17 0.0 2.5 0.0 0.0 0.0

18 0.0 61.3 2.9 0.0

19 0.0 256.4 0.0 2.2 0.0 21.5 0.0 0.0
191 2.2 0.0 0.0
20 5.5 431.0 0.0 0.0 0.0 0.0 0.0
21 0.0 42.1 0.0. 65.4 106.7

22 0.0 147.1 6.6 0.0 0.0 17.4

23 9.0 52.6 0.0 0.0 1.2 3.1

24 0.0 1 142.9 27.9 2.4 0.0 0.0
25 0.0 280.9 9.7 0.0 0.0 0.0
251 0.0 0.0 0.0
26 0.0 63.7 22.0 0.0 0.0 0.0 84.0
27 0.0 0.0 18.5 0.0 0.0 0.0
28 0.0 28.9 0.0 0.0 0.0 0.0
29 0.0 102.4 19.6 0.0 0.0 0.0 0.0
291 0.0 0.0 0.0 0.0
30 0.0 153.7 0.0 14.6 0.0

301 0.0 0.0 0.0 0.0
31 0.0 185.0

32 0.0 486.6 30.3 4.5 3.6 0.0

321 23.5 28.4 3.6 0.0 0.0
33 0.0 40.9 19.7 0.0

34 0.0 0.0 0.0 0.0 0.0 56.2

341 0 0 0.0 0.0 0 0

MM 93.7 49.8 0.0 35.2 0.0 106.0 0.0 34.3

 

Appendix 5, continued.

1995 Catastomidae

118

 

Site # 19 May 26 May 30 May 5 Jun 13 Jun 19 Jun
1 0.0 0.0 0.0 0.0 0.0 17.5
2 0.0 0.0 0.0

4 0.0

5 0.0 0.0 1.6

7 0.0 0.0 0.0 65.6
8 0.0

10 0.0 0.0 0.0

11 0.0 0.0 0.0

12 0.0 0.0

13 0.0 0.0

14 0.0 0.0 0.0

17 0.0 0.0 0.0 0.0

18 0.0 0.0 0.0

19 0.0 0.0 1.5 0.0
191 0.0 0.0 0.0 0.0 0.0
20 0.0 0.0 1.5
201 0.0 0.0 0.0 0.0 0.0
21 0.0 0.0

22 0.0

23 0.0 0.0

24 0.0

25 0.0

251 0.0 0.0 0.0 0.0

26 0.0 0.0 0.0

27 0.0 0.0 0.0

28 1.9 0.0 0.0 0.0

281 0.0
29 0.0 0.0 0.0 3.3
291 0.0 0.0 0.0 0.0

30 0.0 3.3
301 0.0 0.0 0.0 0.0
32 1.9 4.3 1.5

321 0.0 0.0 0.0 0.0
33 0.0 0.0 0.0

34 1.8 1.8 0.0

341 0.0 0.0 0.0 0.0 0.0 0.0
35 0.0 0.0 0.0 1.9 7.8 0.0
MM 4.0 0.0 0.0 1.6 0.0

 

119

 

Appendix 5, continued.
1995 Centrarchidae
Site # 13 Jun
1 0.0

2 0.0

17 0.0

19 0.0
191 0.0

20 0.0
201 0.0

23 0.0
291 0.0

30 1.5
341 0.0

35 0.0

MM 0.0

 

120

 

Appendix 5, continued.

1995 Clupeidae.

Site # 12 May 19 May 26 May 30 May 5 Jun 13 Jun 19 Jun 26 Jun
1 0.0 0.0 16.4 4.6 3.5 5.9 1.6
2 0.0 0.0 0.0 0.0

3 0.0 0.0

4 0.0 0.0

5 0.0 0.0 0.0 0.0

6 0.0

7 0.0 0.0 0.0 0.0 55.5
8 0.0 0.0

9 0.0

10 0.0 0.0 219.5 0.0

11 0.0 0.0 0.0 0.0

12 0.0 0.0 0.0

13 0.0 3.8 1.9

14 0.0 0.0 0.0 0.0

15 0.0

17 0.0 0.0 40.0 0.0 1.6

18 0.0 0.0 0.0 0.0

19 0.0 0.0 13.4 15.2 1.5 1.6
191 0.0 0.0 184.0 6.1 197.5 496.8 9.2 28.6
20 0.0 3.1 307.7 6.1
201 0.0 0.0 40.6 0.0 0.0 0.0 260.7 25.5
21 0.0 0.0 22.2 4.0

22 0.0 0.0 0.0

23 21.7 0.0 0.0 1.4

24 1.8 8.3

25 0.0 0.0

251 0.0 0.0 20.9 0.0 0.0

26 0.0 0.0 104.4 13.6

27 0.0 0.0 81.8 0.0

28 0.0 0.0 15.8 0.0 5.4

281 3.1
29 0.0 1.9 3.6 154.0

291 0.0 14.6 0.0 9.0 126.0 6.7
30 0.0 0.0

301 0.0 13.9 9.0 0.0 4.7
31 0.0

311 0.0

32 0.0 26.6 176.4 1.5 49.9 31 1.8 70.0
321 0.0 31.6 349.1 194.5 36.8
33 0.0 0.0 1344.8 1.6

34 0.0 0.0 104.4 0.0 15.9

341 0.0 18.3 21.7 34.6 96.6 0.0
35 0.0 14.8 355.5 7.5 12.5 0.0

MM 0.0 0.0 4.5 1.6 9.8 7.8

 

121

Appendix 5, continued.

 

1995 Cyprinidae.

Site # 19 May 26 May 30 May 5 Jun 13 Jun 19 Jun
1 0.0 0.0 0.0 0.0 7.3 46.2
2 0.0 0.0 1.5

3 0.0

4 0.0

5 0.0 0.0 0.0

7 0.0 0.0 0.0

8 0.0

10 0.0 8.7 0.0

11 0.0 0.0 0.0

12 0.0 0.0

13 0.0 0.0

14 0.0 0.0 0.0

17 0.0 0.0 0.0 0.0

18 0.0 0.0 0.0

19 0.0 13.4 0.0 0.0 3.2
191 0.0 0.0 0.0 0.0 0.0 7.7
20 0.0 0.0 1.5 24.3
201 0.0 0.0 0.0 0.0 3.1 46.3
21 0.0 3.7 0.0

22 0.0 0.0

23 0.0 0.0 1.4

24 0.0

25 0.0 4.7

251 0.0 0.0 0.0 0.0

26 0.0 0.0 0.0

27 0.0 0.0 0.0

28 0.0 3.5 0.0 0.0

281 56.2
29 1.9 1.8 3.0

291 0.0 22.9 0.0 0.0 0.0 1.7
30 0.0

301 9.9 0.0 1.5 7.9
32 1.9 6.4 1.5 41.1
321 0.0 4.0 0.0 12.7
33 0.0 0.0 1.6

34 0.0 3.7 1.8

341 0.0 1.8 0.0 0.0 0.0 106.7
35 2.0 1.9 0.0 1.9 0.0 1.6

MM 0.0 0.0 0.0 1.6 4.7

 

122

 

Appendix 5, continued.

1995 Deepwater Sculpin.

Site # 30 Apr 12 May
1 1.8 0.0
2 0.0 0.0
3 0.0
4 0.0 0.0
5 0.0 0.0
6 0.0
7 0.0
8 0.0
9 0.0
10 0.0
11 0.0
12 0.0 0.0
13 0.0 0.0
14 0.0 0.0
15 0.0
17 0.0 0.0
18 0.0
19 0.0
191 0.0
201 0.0
21 0.0
22 0.0
23 0.0
25 1.8
251 0.0
26 0.0
27 0.0
28 0.0
29 0.0
30 0.0
301 0.0
31 0.0
311 0.0
32 0.0
321 0.0
33 0.0
34 0.0

 

123

Appendix 5, continued.

1995 Freshwater Drum.

 

Site # 26 May 13 Jun 19 Jun
1 0.0 1.5 0.0
2 0.0 0.0 0.0
5 0.0

7 0.0

8 0.0

10 0.0

11 0.0

13 0.0

14 0.0

17 0.0 0.0

18 0.0

19 0.0 0.0 1.6
191 0.0 0.0 0.0
20 0.0 0.0
201 0.0 0.0 0.0
21 0.0

23 0.0 0.0
251 0.0

26 0.0

27 0.0

28 0.0

281 0.0
29 0.0

291 0.0 0.0 0.0
301 0.0 0.0 1.6
31

32 0.0

321 0.0 0.0
33 0.0

34 3.7

341 0.0 0.0 0.0
35 3.7 0.0 0.0

 

124

 

Appendix 5, continued.

1995 Lake Whiteﬁsh.

Site # 28 Mar 5 Apr 10 Apr 18 Apr 21 Apr 24 Apr 28 Apr 30 Apr 3 May
1 5.2 9.1 7.1 7.1 11.4 21.6 1.8 12.8
2 6.7 6.5 15.8 37.2 13.8
3 0.0
4 7.1 3.5
5 12.9 0.0
6 12.4 3.5
7 45.3 0.0
8 7.4 19.8 6.9
10 3.5 25.3 23.7

11 0.0
12 3.7 1.9
13 16.5 1.7
14 0.0 16.4 10.2
17 58.2 12.9 47.2
18 17.6
19 22.6 25.5 29.7
191 8.9 3.5 9.2 0.0
20

201 17.2

21

22 12.8
23 27.2 26.0
24 7.3
25 1.8
26 0.0
27

28 0.0 8.9
29 3.6
30

31 0.0
32

321 143.7 53.0 0.0

33 10.4 32.1 0.0
34 10.9 7.2 1.8
341 3.6 0.0

MM 93.4 35.8

 

125

Appendix 5, continued.
1995 Lake Whiteﬁsh, continued.

Site # 9 May 12 May 19 May 26 May

 

l 1.9 3.6 0.0 0.0
2 0.0 0.0 0.0
3 0.0 11.4

4 2.0 2.0

5 4.7 0.0 0.0
6 2.4 0.0

7 0.0 3.5 1.8
8 0.0 4.2 0.0
9 0.0

10 28.6

1 1 l 1.4 0.0 0.0
12 5.5 0.0

13 0.0 0.0 0.0
14 0.0 0.0 0.0
15 0.0

17 0.0 3.7 0.0
18 2.5 0.0 0.0
19 1.9 13.1 0.0 1.9
191 0.0 0.0 0.0 3.7
20 0.0

201 0.0 0.0 1.9
21 21.7 0.0 0.0
22 0.0 1.9

23 18.1 2.0

24 3.6

25 12.5 2.3

251 0.0 0.0 0.0
26 1.8 0.0 0.0
27 7.0 0.0 0.0
28 0.0 3.7 0.0
29 0.0 0.0 0.0
291 0.0 0.0
30 5.4 0.0

301 0.0 0.0
31 0.0

311 0.0

32 0.0 1.9 0.0
321 0.0 0.0 0.0
33 1.8 0.0 0.0
34 1.7 0.0 0.0
341 0.0 0.0
35 0.0 0.0

MM 2.5 0.0

 

126

 

Appendix 5, continued.

1995 Morone spp.

Site # 12 May 19 May 26 May 30 May 5 Jun 13 Jun 19 Jun
1 0.0 3.7 25.5 0.0 3.5 11.7 1.6
2 0.0 0.0 0.0 0.0

3 0.0 0.0

4 0.0 0.0

5 0.0 0.0 0.0 0.0

6 0.0

7 0.0 1.8 5.5 0.0 5.0
8 0.0 0.0

9 0.0

10 0.0 0.0 0.0 0.0

11 0.0 0.0 0.0 0.0

12 0.0 0.0 0.0

13 0.0 1.9 3.8

14 0.0 0.0 15.4 0.0

15 0.0

17 0.0 0.0 40.0 0.0 3.1

18 0.0 2.3 77.1 0.0

19 0.0 1.8 11.5 3.0 21.6 1.6
191 0.0 0.0 38.6 1.5 0.0 0.0 36.9
20 0.0 0.0 1.5 10.6
201 0.0 0.0 29.0 0.0 0.0 7.8 260.7
21 1.8 0.0 7.4 0.0

22 0.0 0.0 0.0

23 10.9 0.0 0.0 1.4

24 0.0

25 0.0 0.0

251 0.0 0.0 81.8 0.0 0.0

26 0.0 4.5 6.0 0.0

27 0.0 18.3 8.4 0.0

28 0.0 1.9 0.0 0.0 0.0

281 7.8
29 0.0 21.3 5.4 11.6

291 34.6 0.0 0.0 0.0 2.3 0.0
30 0.0 0.0

301 0.0 2.0 0.0 1.5 6.2
31 0.0

32 5.7 26.6 85.0 1.5 54.5

321 0.0 154.2 82.7 0.0 11.3
33 0.0 4.3 186.7 0.0

34 0.0 0.0 5.5 0.0

341 0.0 9.1 1.5 0.0 4.9 17.3
35 2.0 14.8 1.6 0.0 0.0 0.0

MM 0.0 0.0 1.5 0.0 0.0 6.2

 

127

 

Appendix 5, continued.
1995 Troutperch.

Site # 26 May
1 1.8
2 0.0
5 0.0
7 0.0
8 0.0
10 0.0
11 0.0
13 0.0
14 0.0
17 0.0
18 0.0
19 0.0
191 0.0
201 0.0
21 0.0
251 0.0
26 0.0
27 2.1
28 0.0
29 0.0
291 0.0
30 0.0
301 2.0
32 0.0
321 0.0
33 0.0
34 0.0
341 0.0

35 0.0

 

128

 

Appendix 5, continued.

1995 Log Perch

Site # 12 May 19 May 26 May 30 May 5 Jun 19 Jun
1 0.0 0.0 0.0 0.0 0.0 0.0
2 0.0 0.0 0.0

3 0.0 0.0

4 0.0 0.0

5 0.0 0.0 0.0 0.0

6 0.0

7 0.0 0.0 0.0 0.0 0.0
8 0.0 0.0

9 0.0

10 0.0 0.0 0.0 0.0

11 0.0 0.0 0.0 0.0

12 0.0 0.0 0.0

13 0.0 0.0 0.0 0.0

14 0.0 0.0 0.0

15 0.0

17 0.0 0.0 0.0 0.0

18 0.0 0.0 0.0 0.0

19 0.0 0.0 0.0 1.5 0.0
191 0.0 0.0 0.0 0.0 0.0 0.0
20 0.0 0.0 0.0
201 0.0 0.0 0.0 0.0 0.0 0.0
21 12.6 0.0 0.0 0.0

22 0.0 0.0 0.0

23 0.0 0.0 0.0

24 0.0

25 0.0 0.0

251 0.0 0.0 0.0 0.0 0.0

26 0.0 0.0 0.0 0.0

27 0.0 0.0 0.0 0.0

28 0.0 0.0 0.0 0.0 0.0

281 0.0
29 0.0 0.0 1.8 5.8

291 0.0 0.0 0.0 0.0 0.0
30 0.0 0.0

301 0.0 0.0 0.0 0.0
31 0.0

311 0.0

32 0.0 1.9 2.1 1.5

321 0.0 0.0 0.0 4.6 4.2
33 0.0 0.0 0.0 0.0

34 0.0 0.0 0.0 0.0

341 0.0 0.0 0.0 0.0
35 0.0 1.9 0.0 0.0 0.0
MM 0 0 0.0 0.0 0.0

 

129

 

Appendix 5, continued.

1995 Walleye.

Site # 3 May 9 May 12 May 19 May 26 May 30 May 5 Jun 13 Jun
1 11.0 5 .7 8.9 0.0 0.0 0.0 0.0 0.0
2 0.0 2.2 3.8 0.0 0.0 0.0
3 0.0 0.0 0.0

4 0.0 0.0 0.0

5 0.0 23.5 0.0 0.0 0.0

6 0.0 0.0 0.0

7 1.7 0.0 3.5 0.0 0.0

8 0.0 0.0 0.0 0.0

9 0.0

10 0.0 0.0 0.0 0.0

1 1 0.0 0.0 0.0 0.0 0.0

12 0.0 0.0 0.0 0.0

13 0.0 4.0 5.8 0.0

14 0.0 0.0 4.3 0.0 0.0

15 0.0

17 0.0 0.0 5.5 0.0 0.0 0.0
18 0.0 0.0 0.0 0.0 0.0

19 0.0 23.1 11.5 0.0 1.9 1.5 1.5
191 0.0 0.0 0.0 12.9 0.0 0.0 0.0
20 1.7 15.6 0.0 0.0 0.0
201 3.8 0.0 1 1.6 0.0 0.0 0.0
21 5.4 0.0 1.8 0.0

22 0.0 0.0 0.0 0.0

23 0.0 7.2 0.0 0.0 0.0
24 0.0 1.7

25 0.0 1.7 0.0

251 0.0 0.0 0.0 0.0 0.0

26 0.0 0.0 0.0 3.0 0.0

27 5.2 0.0 0.0 0.0

28 0.0 1.8 0.0 0.0 0.0 0.0

29 0.0 5.2 0.0 0.0 2.9

291 0.0 0.0 0.0 0.0 0.0
30 0.0 0.0

301 0.0 0.0 0.0 0.0
31 0.0 0.0

311 0.0

32 18.9 9.4 6.4 9.0

321 5.9 0.0 0.0 0.0

33 0.0 3.6 0.0 10.9

34 0.0 3.5 0.0 1.8 0.0

341 8.7 0.0 23.8 0.0 0.0 0.0
35 2.0 0.0 1.6 0.0 0.0

MM 25.5 32.7 8.0 1.5 0.0 0.0

 

130

 

Appendix 5, continued.

1995 Yellow Perch.

Site # 9 May 12 May 19 May 26 May 30 May 5 Jun 13 Jun
1 0.0 0.0 0.0 1.8 0.0 0.0 0.0
2 0.0 0.0 0.0 6.1 0.0
3 0.0 0.0

4 0.0 0.0

5 0.0 0.0 6.0 0.0

6 0.0 0.0

7 0.0 0.0 3.7 0.0

8 0.0 0.0 0.0

9 0.0

10 0.0 0.0 0.0 0.0

11 0.0 0.0 0.0 0.0

12 0.0 0.0 0.0

13 0.0 0.0 3.8

14 0.0 0.0 5.8 0.0

15 0.0

17 0.0 0.0 4.0 0.0 0.0
18 0.0 0.0 2.0 0.0

19 3.8 0.0 0.0 11.5 1.5 3.1
191 0.0 3.9 0.0 5.5 0.0 0.0 0.0
20 0.0 0.0 3.1
201 3 .8 0.0 1.9 0.0 0.0 0.0
21 0.0 0.0 1.8 0.0

22 5.4 0.0 0.0

23 0.0 0.0 0.0 0.0
24 0.0

25 0.0 0.0

251 0.0 0.0 0.0 0.0 0.0

26 0.0 0.0 3.0 0.0

27 0.0 0.0 4.2 0.0

28 0.0 0.0 0.0 0.0 0.0

29 3.5 0.0 5.4 8.7

291 0.0 0.0 0.0 0.0 0.0
30 0.0 0.0

301 0.0 0.0 1.6 0.0
31 0.0

311 0.0

32 0.0 3.8 6.4 18.1

321 0.0 1.9 24.2 0.0

33 0.0 0.0 7.2 0.0

34 3.5 3.7 0.0 0.0

341 0.0 0.0 0.0 0.0 3.3
35 0.0 1.9 3.3 0.0 0.0

MM 0.0 0.0 4.5 0.0 0.0

 

131

Appendix 6. Area, volume estimates, and percent of walleye larvae collected from each
depth zone in western Lake Erie.

 

 

_%_Qf_C_atch__

Depth Range (m) Area (kmz) Volume (m3) 1994 1995
0-4 103.12 2.66X108 58 60
4 - 8 235.88 13.93 x 108 29 35

8 - 12 52.57 4.73 x 108 13 5

 

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