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This is to certify that the

dissertation entitled

Physical and Biological Processes Influencing
Walleye Early Life History in Western
Lake Erie

presented by

Edward Francis Roseman

has been accepted towards fulﬁllment
of the requirements for

PhoDo degreein FiSh. & Wildlo

' /\
Major professor ﬂ

 

 

Date May 10, 2000

 

MSU 1': an Affirmative Action/Equal Opportunity Institution 0-12771

 

PLACE IN RETURN BOX to remove this checkout from your record.
TO AVOID FINES return on or before date due.
MAY BE RECALLED with earlier due date if requested.

 

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1100 mm.“

 

PHYSICAL AND BIOLOGICAL PROCESSES INFLUENCING WALLEYE EARLY

LIFE HISTORY IN WESTERN LAKE ERIE

By

Edward Francis Roseman

AN ABSTRACT OF A DISSERTATION

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

DOCTOR OF PHILOSOPHY

Department of Fisheries and Wildlife

2000

ABSTRACT

PHYSICAL AND BIOLOGICAL PROCESSES INFLUENCING WALLEYE EARLY
LIFE HISTORY IN WESTERN LAKE ERIE
By

Edward Francis Roseman

Walleye (Stizostedion vitreum) are the dominant piscivore in western Lake Erie
and provide valuable sport and commercial ﬁsheries in Canada and the United States.
Historical records of their abundance reﬂect unstable levels of recruitment primarily due
to highly variable year-class formation. To investigate the mechanisms underlying
variable year-class strength formation of reef-spawned walleye in western Lake Erie, I
sampled walleye eggs on mid-lake reefs (Cone, Crib, Locust Pt., Niagara, Round and
Toussaint) and larvae on and adjacent to the reefs from 1994 through 1999. Reefs varied
in depth and size and egg sampling was stratiﬁed by depth. Larval sampling sites
extended from Maumee Bay to the Bass Islands complex and were stratiﬁed by depth and
distance from Shore. The initiation of Spawning was generally consistent, beginning in
the ﬁrst week of April, although Spawning began noticeably earlier in mid-March 1998.
Egg abundance varied among reefs and between years. Shallow sites on reefs had higher
egg relative abundance early in the incubation period but this trend reversed later in April
and early May as eggs were removed from exposed shallow areas on reefs by currents
and predators. Egg viability was generally lowest early in egg incubation periods and
showed an increasing trend as incubation progressed. Abundance of egg predators

increased after peak egg abundance occurred. Egg survival was generally highest in

years when lake waters warmed quickly and few wind events occurred during incubation
periods. Egg survival was also higher for cohorts of eggs spawned later in the spawning
season due to quicker incubation rates. Analysis of recruitment indices from 1960 - 1997
indicate that a water warming of at least 0.2 °C/day during egg incubation periods is
necessary for good year-classes to form.

Abundance, growth, and survival of larval walleye varied between years and was
positively related to egg abundance and survival, water temperature, and prey abundance.
Larvae became concentrated in shallow nearshore areas of western Lake Erie. These
areas were warmer, darker, and had higher abundance of zooplankton and
ichthyoplankton prey than offshore areas. Abundance of demersal age-0 walleye in
October index bottom trawl surveys was highest in 1996 (30.8/h trawling), a year with
moderately high egg abundance (7,230/tow), good egg survival (21%), moderately high
larval abundance (8.1/1 ,000 m3), good larval growth (0.34 mm/day), and exceptional
larval survival (72%). The weakest year class was formed in 1995 when the October
bottom trawl index was only 0.2/hour of trawling. This year had low egg abundance
(3,610/tow), low egg survival (0.105), low larval abundance (3.5/1,000 m3), slow larval
growth (0.31 mm/day), and low larval survival (36.5%). This research emphasizes the
importance of physical processes like wind and water warming rate in tempering the
environmental setting that biological processes take place. Further, this study exposed

speciﬁc nearshore areas in western Lake Erie important as nursery zones for walleye.

ACKNOWLEDGEMENTS

This dissertation is a result of work sponsored by the Michigan Sea Grant College
Program, project number R/GLF 43, from the Ofﬁce of Sea Grant, National Oceanic and
Atmospheric Administration (N OAA), US. Department of Commerce, and funds from
the state of Michigan and Michigan State University. The US. government is authorized
to produce and distribute reprints for governmental purposes notwithstanding any
copyright notation appearing hereon. Fellowship and scholarship support was provided
by the College of Agriculture and Natural Resources in the form of a dissertation
completion fellowship, Department of Fisheries and Wildlife, the SeaSpace Foundation,
and Saginaw Bay Walleye Club.

I thank the members of my committee, Dr. Dick Groop, Mr. Robert Haas, Dr.
Daniel Hayes, and Dr. Gary Mittelbach for their suggestions and critical review of this
manuscript. I extend my most sincere gratitude to Dr. William Taylor for his guidance,
support, patience, and ﬁiendship during my graduate career at Michigan State.

I gratefully thank the following people for their assistance with ﬁeld collections
and laboratory work: Stacy Emdt, Brian Frost, Eric Grundemann, Bill Hill, John
Holloway, Matt Kozlowski, Jeff Leighton, Kurt Newman, Corey Sipher, Greg Struck,
Dave Thomas, Brad Thompson, Dan Weisenreder, and Bill Wellencamp. I thank all of
my lab mates for their friendship and insightful comments on my work. I appreciate the
tireless efforts of Andy, Bud and the rest of the crew at Mobile RV and Marine in Oak

Harbor, OH for keeping the Osmerid ﬂoating and capable of returning to home port.

iv

I extend a special thank you to Jackie Hill for her friendship, love, and for making
me feel like part of her family. I also give special thanks to Tim and Deb Thompson for
their friendship and for allowing me refuge in their home. I also thank Sheri Franklin
from Lubbock, TX for her support and friendship over the years. Thanks to my Alaska
tn'p buddies; Kurt, Lois, and Kris. Thanks to my family in upstate New York for visiting
and sending goodies to keep me motivated.

Special thanks to Keith and Julie Traver for all they have done for me and my
family since moving to Michigan in 1993. I will enjoy our friendship for ever. Thanks
for all the hunting, ﬁshing, and relaxation opportunities you have provided and my
eternal thanks for T-Bone.

I thank my son, Edward Orville, for his help with sample collecting and
processing and for his patience and understanding while I did all the “boring stuff ’
necessary to complete this project. You were my inspiration when everything else

seemed worthless.

Table of Contents

LIST OF TABLES ...................................................................................................................................... viii
LIST OF FIGURES ........................................................................................................................................ x
DISSERTATION INTRODUCTION ............................................................................................................. 1
STUDY AREA ............................................................................................................................................... 9
WALLEYE LIFE HISTORY ........................................................................................................................... l 1
CHAPTER 1

PHYSICAL AND BIOLOGICAL PROCESSES INFLUENCING WALLEYE

EARLY LIFE HISTORY STAGES IN WESTERN LAKE ERIE ................................................. 13
ABSTRACT ............................................................................................................................................. 13
INTRODUCTION .................................................................................................................................... 15
METHODS ............................................................................................................................................... 18

Egg Collection ...................................................................................................................................... 18
Larval Sampling ................................................................................................................................... 22
Larval Growth ...................................................................................................................................... 24
Age-0 Walleye Survival ....................................................................................................................... 24
Zooplankton Sampling ......................................................................................................................... 25
Water Temperature ............................................................................................................................... 25
Water Clarity ........................................................................................................................................ 26
Wind Severity ....................................................................................................................................... 27
RESULTS ................................................................................................................................................. 28
Water Temperature and Warming Rate ............................................................................................... 28
Water Clarity ........................................................................................................................................ 29
Walleye Egg Abundance and Distribution ........................................................................................... 29
Egg Viability and Survival ................................................................................................................... 45
Wind and Storm Events ........................................................................................................................ 54
Larval Walleye Abundance and Distribution ....................................................................................... 56
Zooplankton Abundance ...................................................................................................................... 61

vi

lchthyoplankton Prey Abundance ........................................................................................................ 65

Growth of Age-0 Walleye .................................................................................................................... 69
Larval Walleye Survival ....................................................................................................................... 76
Fall Age-0 Walleye Abundance Index ................................................................................................. 77
DISCUSSION ........................................................................................................................................... 80
CONCLUSION ........................................................................................................................................ 90
CHAPTER 2
PREDATION ON WALLEYE EGGS BY FISH ON REEFS IN WESTERN
LAKE ERIE ................................................................................................................................... 91
ABSTRACT ............................................................................................................................................. 91
INTRODUCTION .................................................................................................................................... 92
METHODS ............................................................................................................................................... 93
RESULTS ................................................................................................................................................. 94
DISCUSSION ......................................................................................................................................... 106

DISSERTATION SYNTHESIS

LINKING EVENTS DURING WALLEYE EARLY LIFE HISTORY TO

YEAR-CLASS DEVELOPMENT ............................................................................................... 110
MANAGEMENT IMPLICATIONS ...................................................................................................... 117
APPENDICES ............................................................................................................................................ 121
REFERENCES ............................................................................................................................................ 126

vii

List of Tables

Table 1. Surface area of reefs (kmz) in western Lake Erie sampled for walleye
eggs (area shallower than 5 m is shown in parentheses). ........................................... 22

Table 2. Water warming rates (°C/day) during typical egg incubation(April 1 —
May 15), zooplanktivorous larval (May 1 -— June 10), and piscivorous juvenile
(June 10 — June 30) periods 1994 through 1999. ....................................................... 28

Table 3. Walleye egg survival estimates for reefs in western Lake Erie, 1996 -
1998. ........................................................................................................................... 53

Table 4. Number of days when wind events occurred over the western Lake Erie
reef complex with velocities 25 — 50 km/hr and >50 km/hr during walleye egg
incubation periods, 1994 - 1999. ............................................................................... 55

Table 5. Speciﬁc growth rates of age-0 walleye during periods of zooplanktivory,
piscivory, and for entire period May - June in western Lake Erie from 1994 —
1999. ........................................................................................................................... 69

Table 6. Daily instantaneous mortality rates (Z), 95% conﬁdence limits, total
mortality rates (A), and p-values for regressions used to calculate

instantaneous mortality rates for pelagic larval walleye collected in western
Lake Erie, 1994 — 19998. ........................................................................................... 77

Table 7. Water warming rate during walleye egg incubation periods, number of
days between April 1 and May 15 with winds 25-50 km/h originating from
between 260° and 110°, number of days between April 1 and May 15 with
winds exceeding 50 km/h originating from between 260° and 110°, mean
walleye egg relative abundance on reefs, mean walleye egg survival (%),
index of larval walleye abundance (#/1,000 m3), pelagic larval walleye
survival (%), speciﬁc growth rate (mm/d) of age-O walleye from May
through June, and October bottom trawl index values for demersal age-0
walleye in western Lake Erie, 1994 — 1998. * - 2 of the 14 wind days in 1998
exceeded 50 km/h. ...................................................................................................... 81

Table 8. Dates, times and locations where gillnets were ﬁshed in western Lake
Erie in 1994 through 1999. Effort was constant across all sample periods ............... 97

Table 9. Date, location, species, and number (in parentheses) of ﬁsh collected
incidentally during egg sampling on reefs in western Lake Erie. 1995 — 1999. ........ 98

viii

Table 10. Catch per net-hour (CPUE), total number of ﬁsh collected, mean
length (TL) of ﬁsh collected, number of empty stomachs, average number of
walleye eggs per stomach, and frequency of occurrence of walleye eggs in
stomachs for ﬁsh collected from reefs in western Lake Erie in the spring of
1995. n/a in CPUE column indicates ﬁsh not collected in gillnets. ....................... 101

Table 11. Catch per net-hour (CPUE), total number of ﬁsh collected, mean length
(TL) of ﬁsh collected, number of empty stomachs, average number of walleye
eggs per stomach, and frequency of occurrence of walleye eggs in stomachs
for ﬁsh collected from reefs in western Lake Erie in the spring of 1996. n/a
in CPUE column indicates ﬁsh not collected in gillnets. ......................................... 102

Table 12. Catch per net-hour (CPUE), total number of ﬁsh collected, mean length
(TL) of ﬁsh collected, number of empty stomachs, average number of walleye
eggs per stomach, and frequency of occurrence of walleye eggs in stomachs
for ﬁsh collected from reefs in western Lake Erie in the spring of 1997. n/a
in CPUE column indicates ﬁsh not collected in gillnets. ......................................... 103

Table 13. Catch per net-hour (CPUE), total number of ﬁsh collected, mean length
(TL) of ﬁsh collected, number of empty stomachs, average number of walleye
eggs per stomach, and frequency of occurrence of walleye eggs in stomachs
for ﬁsh collected from reefs in western Lake Erie in the spring of 1998. n/a
in CPUE column indicates ﬁsh not collected in gillnets. ......................................... 104

Table 14. Catch per net-hour (CPUE), total number of ﬁsh collected, mean length
(TL) of ﬁsh collected, number of empty stomachs, average number of walleye
eggs per stomach, and frequency of occurrence of walleye eggs in stomachs
for ﬁsh collected from reefs in western Lake Erie in the spring of 1999. n/a
in CPUE column indicates ﬁsh not collected in gillnets. ......................................... 105

ix

List of Figures

Figure 1. (Top) Landings of walleye from United States and Ontario waters of
Lake Erie, 1915-1994. (Bottom) Number of age-2 walleye entering the Lake
Erie walleye stock as determined by CAGEAN model estimates for the 1977-
1998 year-classes. Data are from the 1999 Lake Erie Walleye Task Group
Report. .......................................................................................................................... 4

Figure 2. Western Lake Erie study area. Numbers indicate reef locations: 1 -
Cone reef, 2 - Crib reef, 3 - Locust Pt. reef, 4 - Niagara reef, 5 - Round reef, 6
- Toussaint reef. Filled circles (0) indicate larval sampling sites. Stars
indicate larval sampling sites that are also bottom trawl sites. Reef sites 2, 3,
4, and 5 are also larval sampling sites. ....................................................................... 10

Figure 3. Water temperature on Toussaint reef, 1994-1999. ............................................ 31

Figure 4. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1994. ................................................................................................... 32

Figure 5. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1995. ................................................................................................... 33

Figure 6. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1996. ................................................................................................... 34

Figure 7. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1997. ................................................................................................... 35

Figure 8. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1998. ................................................................................................... 36

Figure 9. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake
Erie in spring, 1999. ................................................................................................... 37

Figure 10. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1994 and 1995. ............................................................................ 4O

Figure 11. Walleye egg relative abundance (i 1 standard deviation) on reefs in

western Lake Erie, 1996. ............................................................................................ 41
Figure 12. Walleye egg relative abundance (i 1 standard deviation) on reefs in

western Lake Erie, 1997. ............................................................................................ 42
Figure 13. Walleye egg relative abundance (2t 1 standard deviation) on reefs in

western Lake Erie, 1998. ............................................................................................ 43
Figure 14. Walleye egg relative abundance (i 1 standard deviation) on reefs in

western Lake Erie, 1999. ............................................................................................ 44
Figure 15. Proportion of walleye eggs collected from shallow sites (< 5m) on

reefs in western Lake Erie, 1994 and 1995. ............................................................... 46
Figure 16. Proportion of eggs collected from shallow sites (< 5m) on reefs in

western Lake Erie, 1996 and 1997. ............................................................................ 47
Figure 17. Proportion of eggs collected from shallow sites (< 5m) on reefs in

western Lake Erie, 1998 and 1999. ............................................................................ 48
Figure 18. Walleye egg viability on reefs in western Lake Erie, 1994 and 1995. .......... 50
Figure 19. Walleye egg viability on reefs in western Lake Erie, 1996 and 1997. ............ 51
Figure 20. Walleye egg viability on reefs in western Lake Erie, 1998 and 1999. ........... 52

Figure 21. Log-transformed (Ln Catch +1 #/ 1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1994 and 1995. ............................. 58

Figure 22. Log-transformed (Ln Catch +1 #/1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1996 and 1997. ............................. 59

Figure 23. Log-transformed (Ln Catch +1 #/1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1998 and 1999. ............................. 60

Figure 24. Abundance of zooplankton at nearshore sites in western Lake Erie
during the period from May 1 — June 10, 1994 — 1999. ............................................. 62

Figure 25. Deviations from mean annual values for zooplankton at sampling sites
in western Lake Erie in spring, 1996, and 1997. ........................................................ 63

Figure 26. Deviations from mean annual values for zooplankton at sampling sites
in western Lake Erie in spring, 1998, and 1999. ........................................................ 64

xi

Figure 27. Abundance of ichthyoplankton prey at nearshore sites in western Lake
Erie during the period 10 June — 30 June, 1994 — 1999. ............................................ 66

Figure 28. Deviations from mean annual values for non-walleye ichthyoplankton
prey species at sampling sites in western Lake Erie in spring, 1994, 1995, and
1996. ........................................................................................................................... 67

Figure 29. Deviations from mean annual values for non-walleye ichthyoplankton
prey species at sampling sites in western Lake Erie in spring, 1997, 1998, and
1999. ........................................................................................................................... 68

Figure 30. Log-transformed (Ln) total lengths (mm) of age-0 walleye collected in
western Lake Erie, 1994 and 1995. ............................................................................ 70

Figure 31. Log-transformed (Ln) total lengths (mm) of age-0 walleye collected in
western Lake Erie, 1996 and 1997. ............................................................................ 71

Figure 32. Log-transformed (Ln) total lengths (mm) of age-O walleye collected in
western Lake Erie, 1996 and 1997. .......................................................................... 712

Figure 33. Relationship between speciﬁc growth rate of pelagic walleye larvae
and zooplankton abundance (top panel) and pelagic walleye larvae and water
warming rate (bottom panel). ..................................................................................... 74

Figure 34. Relationship between speciﬁc growth rate of pelagic walleye larvae
and zooplankton abundance (top panel) and pelagic walleye larvae and water
warming rate (bottom panel). ..................................................................................... 75

Figure 35. Catch of age-O walleye in Ohio Division of Wildlife October bottom
trawl surveys, 1992 - 1999 (Top). Relationship between spring water
warming rate and abundance of age-0 walleye collected in Ohio Division of
Wildlife bottom trawls. Data from Busch et a1. 1975, Roseman 1997, Ohio
Division of Wildlife 2000. ......................................................................................... 79

Figure 36. Catch-per-unit-effort (CPUE) of potential egg predators (excluding
walleye) in gillnets ﬁshed on reefs in western Lake Erie 1995 — 1999 .................... 100

xii

Dissertation Introduction

Walleye (Stizostedion vitreum) have supported important sport and commercial
ﬁsheries in Lake Erie for over 150 years (Regier et a1. 1969, Knight 1997). 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 1). Catches declined dramatically in the late
1950’s when the population diminished due to exploitation, pollution, eutrophication, and
degraded spawning habitat. The discovery of high levels of mercury in the tissue of walleye
prompted closure of the ﬁshery in 1970, offering the exploited population a reprieve from
harvest. Following the 1972 adoption of the Great Lakes Water Quality Agreement,
basin-wide management strategies focused on reducing organic inputs to the lake in
efforts to improve ﬁsh habitat and rehabilitate populations (Burns 1985, Makarewicz and
Bertram 1991). The ﬁshable stock increased from about 83,000 walleye in 1970 to over 14
million in 1976 (Hatch et a1. 1987) and landings increased accordingly (Figure 1). Adult
population abundance peaked in 1988 when population estimates exceeded 99 million ﬁsh
age-2 and older. The current population is estimated to exceed 60 million ﬁsh (Ohio
Division of Wildlife 2000).

Because walleye are the dominant predator in Lake Erie and support important
sport and commercial ﬁsheries, ﬂuctuations in their population size and structure can
have direct implications for the entire Lake Erie ecosystem. For example, Knight and
Vondracek (1993) found that increases in the abundance of walleye in the late 1970's and

1980’s played a major role in the decline in abundance of soft-rayed species such as

emerald shiner (Notropis atherinoides), spottail shiner (N. hudsonius) and alewife (Alosa
pseudoharengus). They concluded that management goals focusing primarily on walleye
affected not only the targeted species but the entire ﬁsh community of western Lake Erie.
Further, Nicholls (1999) hypothesized that the changes in the ﬁsh community
documented by Knight and Vondracek were partially responsible for reductions in total
phosphorous in western Lake Erie prior to the invasion of Dreissenidae. Nicholls
suggested that the increase in piscivorous walleye reduced planktivore biomass thereby
increasing phytoplankton grazing by zooplankton allowing increased levels of
phosphorous to be transferred into the foodweb.

After the ﬁshery recuperated, abundant walleye populations attracted interest of
anglers throughout the midwestem United States and led to the development of a
substantial sportﬁshing industry in the states bordering the lake as well as a rejuvenated
commercial gillnet ﬁshery in Canada. Consequently, ﬂuctuations in the walleye
population have resulted in direct economic consequences to businesses and families
relying on these ﬁsheries (Knight 1997, Lichtkoppler 1997). The Lake Erie walleye
population is currently managed under a quota system allocating portions of the stock to
Ontario sport and commercial ﬁsheries and sport anglers in Michigan, New York, Ohio, and
Pennsylvania (Koonce et a1. 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. 1988).

Despite its large adult population size, the Lake Erie walleye population exhibits
wide ﬂuctuations in recruitment. The abundance of age-2 ﬁsh entering the stock has varied

as much as 60-fold since 1977 (Figure 1). Although causes of Lake Erie walleye

recruitment variation are speculative, interannual variation in egg and larval survival are
considered the principal source of recruitment variability for walleye populations in other
lakes (Carlander and Payne 1977; Koonce et al. 1977; Ney 1978; Fomey 1980). For most
ﬁsh species in large systems, 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.

Density-independent physical processes and density-dependent biological factors
that affect egg survival, and the growth and survival of individual larval walleye may be the
driving force behind walleye year-class strength formation in western Lake Erie.
Preliminary studies performed in 1994 and 1995 indicated that physical processes (water
warming rate and wind events that created strong water currents) and biological processes
(prey density, growth) played important roles in structuring year-class strength during early
life history stages (Roseman et al. 1996, Roseman 1997). My dissertation research
examines more closely the interactions and inﬂuence of physical and biological processes
occurring in western Lake Eric on age-0 walleye demographics. Speciﬁcally, my research
examines the linkages between life stages and habitats as well as the degree of spatial and
temporal overlap between age-0 walleye and habitat conditions conducive to good walleye

development, growth, and survival.

3.
7.
6-
5.
4.
3.
2.
1.
0 . . . . . a

1900 1920 1940 1960 1980 2000

Landings (Tonnes)

 

 

 

 

Year

140 .
120 d
100 a
80 -
60 -
40 -
20 -

O I I r I

1975 1980 1985 1990 1995 2000

Number Age-2 (Millions)

 

 

 

Year-Class

Figure 1. (Top) Landings of walleye from United States and Ontario waters of
Lake Erie, 1915-1994. (Bottom) Number of age-2 walleye entering the Lake Erie
walleye stock as determined by CAGEAN model estimates for the 1977-1998
year-classes. Data are from the 1999 Lake Erie Walleye Task Group Report.

Many naturally spawning walleye populations experience high levels of mortality
during the egg stage (Priegel 1970; F omey 1976, 1980). Processes such as water warming
rate have prolonged indirect effects on development rate and survival of ﬁsh embryos by
determining the duration of incubation periods. Optimal egg survival occurred in
laboratory experiments when water temperature increased at a rate of 1°C/day from a
starting temperature of 5 °C (Smith and Koenst 1975). Incubation periods are prolonged
when water warms more slowly, thereby increasing vulnerability of eggs to predation,
disease, and removal by wind generated currents (Wolfert et al. 1975, Koonce et al. 1977;
Roseman et al. 1996). Other processes such as catastrophic storms can produce
immediate devastation of complete cohorts of ﬁsh (Martin et al. 1992; Letoumeur et al.
1993). 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; Roseman et al. 1996).

Predation by ﬁshes and invertebrates may also contribute to egg mortality
(Carlander et al. 1960; Wolfert et al. 1975; Roseman et al. 1996). In western Lake Erie
tributaries, exotic white perch (Morone americana) were found to consume large
quantities of walleye and white bass (Morone chrysops) eggs in 1981-83 (Schaefer and
Margraf 1987) while Wolfert et al. (1975) found yellow perch (Percaﬂavescens) to be
the most important predator of walleye eggs on Kelly’s Island Shoal in western Lake Erie
from 1969-71. The recent invasion of Lake Erie by round gobies (Neogobius

melanostomus, Jude et al. 1992) creates increased concern about ﬁsh recruitment

variability as this species is suspected to be a major predator on ﬁsh eggs on Lake Erie
reefs (DeSorcie and Edsall 1995).

Pelagic walleye larvae are poor swimmers (Houde 1969) and consequently are
subject to transport by water currents. These currents serve as the mechanism by which
larvae move from spawning areas to nursery areas both in rivers and on reefs (Houde and
F omey 1970, Mion et al. 1998, Roseman 1997). Walleye spawned on reefs in western
Lake Erie rely on current patterns in the spring to transport the larvae to the warmer and
more productive nearshore nursery habitats (Roseman 1997). lchthyoplankton samples
collected in 1994 and 1995 showed high densities of walleye larvae and other
ichthyoplankton in nearshore areas of western Lake Erie suggesting that current patterns
during this time of year act to transport pelagic larvae to these areas (Mion 1996,
Roseman et al. 1996, Roseman 1997). These nearshore areas warm quickly in the spring
and are known to have higher densities of prey than offshore areas providing habitat
conditions favorable to larval walleye growth and survival (Roseman 1997).

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 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. He 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-1 (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 post-larvae 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 appropriate 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 slower
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 growth 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 year-class strength (Houde 1987). Both
episodic events (weather-related events) and subtle variability (temperature dependent
development) in early life history vital rates can signiﬁcantly effect the year-class
development of ﬁshes. Episodic events are usually catastrophic in nature, removing large
numbers of individuals from the population (Houde 1989). Such events may relieve

survivors of density-dependent regulatory mechanisms (i.e. competition) and shorten the

duration of vulnerable early life history stages, allowing good growth and survival of the
remaining cohort. Conversely, decelerated development and larval growth rates
precipitated by unfavorable temperatures or low prey availability can lead to substantially
longer early life history stage duration over which high mortality rates can operate
resulting in fewer recruits (Houde 1987).

My hypotheses is that a combination of abiotic physical processes and biotic
factors occurring during the egg 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 of
walleye in western Lake Erie to allow for the identiﬁcation of causal mechanisms
controlling year-class formation. I also strive to identify areas in western Lake Erie that
are important for age-0 walleye recruitment (i.e. spawning and nursery areas) to assist
ﬁshery managers in the rehabilitation and conservation of the Lake Erie walleye ﬁshery.
My speciﬁc objectives were to:

1. Determine spatial and temporal patterns in spawning, larval hatching,

abundance, growth, and survival of reef-spawned walleye in western Lake Erie.

2. Evaluate the timing of larval dispersal from reefs and their subsequent
distributions in relation to the distribution of zooplankton and ichthyoplankton

prey resources.

3. Evaluate interactions between selected lacustrine processes (water temperature
and currents), abundance of prey resources, and growth and survival of walleye

larvae.

4. Assess the importance of various lake habitats to walleye growth, survival and

recruitment.

Study Area

My 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 2). 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 the Appendix.

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 km2. 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 (Herdendorf and Braidech 1972).

83° 30’ 78°50’

420 501—— M

4102147 —L 41°21’

83° 30’ 78°50’

   

 

 

 

 

 

Figure 2. Western Lake Erie study area. Numbers indicate reef locations: 1 -
Cone reef, 2 - Crib reef, 3 - Locust Pt. reef, 4 - Niagara reef, 5 - Round reef, 6 -
Toussaint reef. Filled circles (0) indicate larval sampling sites. Stars indicate
larval sampling sites that are also bottom trawl sites. Reef sites 2, 3, 4, and 5 are
also larval sampling sites.

10

Walleye are the dominant predator in the western basin supported by a prey base
of gizzard shad (Dorosoma cepedianum), alewife , shiners, white perch, white bass, and
yellow perch. Other common ﬁsh species include carp (C yprinus carpio), freshwater
drum (Aplodinotus grunniens), rainbow smelt (Osmerus mordax), channel catﬁsh
(Ictalurus punctatus), and suckers (Catostomidae) (Trautrnan 1957, Knight and
Vondracek 1993).

Several invasive exotic species of ﬁsh and invertebrates have also become
established in western Lake Erie in the past decade. Many of these species have the
potential to alter ﬁsh community and trophic dynamics (Mills et al. 1993). For example
exotic dreissenid mussels are well established in western Lake Erie (Mills et al. 1999) and
are altering nutrient dynamics by shifting energy from pelagic to benthic pathways.
These mussels also alter substrate morphology which may have important ramiﬁcations
to walleye egg incubation on reefs. Round goby abundance has increased dramatically in
western Lake Erie since 1996, and, as mentioned earlier, these ﬁsh may be important

predators on ﬁsh eggs (DeSorcie and Edsall 1995).

Mleve Life History

In western Lake Erie, walleye spawn on mid-lake reefs in the western basin as well
as in tributaries such as the Maumee, Sandusky, and Detroit rivers. Spawning typically
begins shortly after ice-out and peaks around the middle of April (Baker and Manz 1971,
Roseman et al. 1996). Walleye broadcast their eggs over hard substrates and provide no
direct parental protection. Eggs typically hatch in 7 to 15 days depending on water

temperature (Hurley 1972, Nepszy et al. 1991 , Roseman et al. 1996). Small interstitial

ll

spaces in the substrate provide the benthic eggs some protection from predation and
displacement but eggs remain vulnerable to physical processes such as water warming
rate, wind induced wave and current action, and sedimentation that can inﬂuence the
duration of incubation, egg abundance, and survival (Roseman et al. 1996).

In Lake Erie, walleye larvae emerge from the substrate immediately upon
hatching and rely on lake currents for transport to nursery areas (N epszy et al. 1991). The
yolk-sac is usually absorbed within 3 to 5 days when the larvae are about 9.5 mm total
length (TL). The duration of the pelagic larval stage is temperature dependent and
typically lasts from 3 to 4 weeks until the young ﬁsh become demersal at about 30 mm
TL (McElman and Balon 1979). Due to their small size, limited mobility, and delicate
nature, larval walleye are susceptible to a variety of direct and indirect inﬂuences from
physical processes like water temperature and wind generated currents. These processes
can inﬂuence the timing and magnitude of larval development, distribution, growth, and
survival.

My research examines the interactions between physical and biological processes
occurring in western Lake Erie and their role in structuring walleye early life history vital
rates and year-class development. I present data I collected from 1994 — 1999 that
reveals patterns in egg distribution and survival and larval abundance, distribution,
growth, and survival and I relate trends in these data to concurrent physical and biological
processes that occurred in western Lake Erie. I conclude my dissertation with a
discussion and synthesis of my research that includes some implications for the

management of the Lake Erie walleye population and its habitat.

12

Chapter 1

PHYSICAL AND BIOLOGICAL PROCESSES INFLUENCING WALLEYE EARLY
LIFE HISTORY STAGES IN WESTERN LAKE ERIE

Abstract

Walleye are the dominant piscivore in western Lake Erie and also provide
valuable sport and commercial ﬁsheries. Historical records in their abundance reﬂect
highly variable recruitment with much of the ﬂuctuations in abundance due to interannual
differences in year-class formation. To investigate the mechanisms underlying variable
year-class strength formation of reef-spawned walleye in western Lake Erie, I sampled
walleye eggs on mid-lake reefs (Cone, Crib, Locust Pt., Niagara, Round and Toussaint)
and larvae on and adjacent to the reefs in western Lake Erie from 1994 through 1999.
Reefs varied in depth and size and egg sampling was stratiﬁed by depth. Larval sampling
sites extended from Maumee Bay to the Bass Islands complex and were stratiﬁed by
depth and distance from shore. Walleye spawning generally began during the ﬁrst week
of April, although spawning began noticeably earlier in mid-March 1998. Egg abundance
varied among reefs and between years. Shallow reefs generally had higher egg relative
abundance than deep reefs. Shallow sites on reefs had higher egg relative abundance
early in the incubation period but this trend reversed later in April and early May as eggs

were removed from shallow areas on reefs. Egg viability was generally lowest early in

13

egg incubation periods showing an increasing trend as incubation progressed. Egg
survival was generally highest in years when lake waters warmed quickly and few wind
events occurred during incubation periods. Egg survival was also higher for cohorts of
eggs spawned later in the spawning season due to quicker incubation rates. Analysis of
recruitment indices from 1960 - 1997 indicate that a water warming of at least 0.2 °C/day
during egg incubation periods is necessary for good year-classes to form.

Abundance, growth, and survival of larval walleye varied between years and was
positively related to egg abundance and survival, water temperature, and prey abundance.
Larvae became concentrated in shallow nearshore areas of western Lake Erie. These
areas were warmer, darker, and had higher zooplankton and ichthyoplankton prey
abundance than offshore areas. Demersal age-0 walleye abundance in October index
bottom trawl surveys was highest in 1996 (30.8/h trawling), a year with moderately high
egg abundance (7,230/tow), good egg survival (21%), moderately high larval abundance
(8.1/1 ,000 m3), good larval growth (0.34 mm/day), and exceptional larval survival (72%).
The weakest year class was formed in 1995 when the October bottom trawl index was
only 0.2/hour of trawling. This year also had low egg abundance (3,610/tow), low egg
survival (0.105), low larval abundance (3.5/ 1,000 m3), slow larval growth (0.31 mm/day),
and low larval survival (36.5%). This research emphasizes the importance of physical
processes like wind and water warming rate in tempering the environmental setting that
biological processes take place. Further, this study exposed speciﬁc nearshore areas in

western Lake Erie important as nursery zones for walleye.

l4

Introduction

Lake Erie supports the world’s largest naturally reproducing population of
walleye providing valuable sport and commercial ﬁsheries in the United States and
Canada. Like most natural populations, Lake Erie walleye have exhibited signiﬁcant
variation in year-class strength over the past 20 years. The abundance of age-2 ﬁsh
entering the stock has ﬂuctuated nearly 60 fold since 1977 (Figure 1) and the causes of
this recruitment variability have been unclear (Henderson and Nepszy 1994, Madenjian
et al. 1996). Recent ﬁeld research in western Lake Erie, however, reveals the importance
of density-independent physical processes in walleye year-class formation with the
strongest year-classes occurring in years with fast water warming rates and few storm
events during egg incubation and larval dispersal periods (Mion et al. 1998, Roseman et
al. 1996). These studies concluded that variability in environmental conditions inﬂuenced
the timing of life history events and caused differential survival rates during the egg and
larval stages which translated into variability in year-class strength and recruitment to the
adult stock.

Physical processes and other abiotic factors can have powerﬁrl, although usually
indirect effects on ﬁsh population and community dynamics by tempering the
environmental conditions in which many important biological processes operate (Dunson
and Travis 1991). For example, water temperature has been shown to be one of the most

inﬂuential physical factors in walleye egg development and survival (Allbaugh and Manz

15

1964, Hurley 1972). In western Lake Erie, Busch et al. (1975) and Roseman et al. (1999)
found a positive relationship between water warming rate and walleye year class strength.
Egg incubation periods are lengthened when waters warm more slowly, thereby
increasing the amount of time eggs are exposed to predation, disease, and severe wind
events (Wolfert et al. 1975, Roseman et al. 1996). Further, water temperature mediates
larval walleye activity including metabolism, feeding rate, growth rate, and survival
(Hokanson and Koenst 1986, Santucci and Wahl 1993, Mion et al. 1998, Roseman 1997).

Water clarity is another important physical characteristic of walleye habitat.
Walleye possess a special layer in the eye, the T apetum lucidum, which reﬂects light
within the eye and allows the ﬁsh to feed and perform other activities in low light
conditions (e. g., turbid waters, crepuscular periods). The Tapetum lucidum makes
walleye sensitive to bright light intensities and the ﬁsh actively seek darker conditions
(i.e., secchi < 2 m) to avoid the brightness (Scott and Crossman 1973). Laboratory
studies have further revealed that growth and survival rates of larval walleye are higher in
turbid waters than in clear waters (Bristow et al. 1996, Rieger and Summerfelt 1997).

A ﬁnal physical process of great importance to reef-spawning ﬁsh in western
Lake Erie is storm-related wind and wave action. Because of the east-west orientation of
the lake, the western basin is susceptible to the effects of storm generated waves and
currents, especially those originating from easterly direction which have long fetches and
carry high wave energy (Gedney and Lick 1972). Several studies have documented the
storm-induced mortality and disappearance of cohorts of ﬁsh in marine and estuarine
systems as the result of single catastrophic events (Peterrnan and Bradford 1987; Walker

et al. 1991; Moring 1996). The effects of similar storm events on freshwater ﬁsh

16

communities, especially in large lakes, is not as well documented though still considered
important to ﬁsh population dynamics (Shuter and Post 1990). Storm events on large
lakes like Lake Erie can create strong wind—driven currents and strong wave action
(Gedney and Lick 1972; Hamblin 1979) and some studies have inferred that such
processes cause mortality during the early life history stages of ﬁsh thereby reducing
year-class strength and limiting recruitment (Busch et al. 1975, Houde 1989).

Because walleye are broadcast spawners, their eggs are vulnerable to mortality
caused by dislodging from severe wind and wave action during spawning and incubation
periods (Johnson 1961; Sems 1982). Prolonged strong wind events create wave and
current conditions that can transport ﬁsh large distances (Martin et al. 1992) as well as
cause damage to delicate larvae (Cordone and Kelley 1961, Mion et al. 1998). Further,
heavy wave action is known to stir up sediments causing increased turbidity associated
with sediment transport (Gedney and Lick 1972). Increased turbidity reduces the
phototrophic zone thereby reducing primary productivity (Wetzel 1975) which can
translate to reductions in ﬁsh growth (Carpenter and Kitchell 1993). These processes can
have signiﬁcant negative effects on walleye year-class development by reducing egg and
larval abundance and survival.

While many physical processes are difﬁcult to predict (i.e. weather), we can gain
insight into the response of ﬁsh populations to such factors by understanding how
physical processes inﬂuence ﬁsh and their habitat. Some factors such as water warming
rate have gradual effects on development rate and survival of ﬁsh embryos (Koonce et al.
1977), whereas other factors such as severe and catastrophic storms can produce

immediate devastation of complete cohorts of ﬁsh (Martin et al. 1992; Letourneur et al.

17

1993). Therefore, it is important to identify and understand the various physical
processes that structure ﬁsh populations and determine how physical processes inﬂuence
the biological processes involved in ﬁsh population dynamics. In this chapter, I use data
I collected from 1994 through 1999 to evaluate the relationship between physical
processes and the distribution, abundance, and survival of reef-spawned walleye eggs and
larvae in western Lake Erie. Speciﬁcally, I will 1) assess the relationship between water
temperature and walleye egg development, larval distribution, and larval growth; 2)
assess the relationship between water clarity and larval walleye distribution; 3)
demonstrate the effects of severe wind events on reef-spawned walleye egg abundance

and survival.

Methods

Egg Collection

I combined data on egg abundance and survival collected on Toussaint and
Niagara reefs in 1994 and 1995 (Roseman 1997) with new information collected from
1996 - 1999. From 1996-1999 I sampled eggs on Cone, Crib, Locust Pt., Niagara,
Round, and Toussaint reefs which are located among a bedrock reef complex in the
western basin of Lake Erie (Figure 2). Area and depth of the study reefs varied. Total
reef surface area ranged from 0.67 km2 to 2.49 km2 but surface area above the 5 m
contour, where the majority of walleye spawning occurs (Baker and Manz I971;
Roseman et al. 1996), ranged from 0.0 km2 to 1.5 km2 (Table 1; Bolsenga and Herdendorf
1993). 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 which provide

18

incubation sites for walleye eggs (Herdendorf and Braidech 1972; Roseman et al. 1996).
The shallowness of the reefs allows the reef surface to be scoured by ice movements as
well as by wind-generated waves and currents. 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 1972; Bolsenga and Herdendorf 1993).

Walleye egg sampling on reefs typically began in mid to late March shortly aﬁer
ice-out and continued through to mid-May when spawning ceased and catches of walleye
eggs were negligible. Egg sampling was stratiﬁed by depth to examine egg deposition
density; depths of 0-5 m, and 5-7 m were sampled. These depth strata encompass the
range of depths where walleye eggs were collected in previous studies (Baker & Manz
1971 , Roseman et al. 1996, Roseman 1997). Three samples were taken at each depth on
each sampling day. I located sample sites by global positioning system coordinates and
marked them with an anchored buoy. I used a 39-kg iron sled (Stauffer 1981) attached to
a diaphragm pump at the surface by a ﬂexible hose 5 cm in diameter for egg collections.
For each sample, the sled was towed for 2 min at 0.5 m/s.

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 acclimated and refrigerated at 5 0C until they could be
sorted at the laboratory which typically took from 2.5 to 24 h. I found no indication that
delays in processing of up to 24 h inﬂuenced egg viability or survival estimates.

At the laboratory, samples were weighed then rinsed through a galvanized steel

wire screen (6 mm bar mesh) to separate large debris from ﬁner particles and eggs. The

19

small particulate matter was then examined for walleye eggs which were counted entirely
or subsampled. A single subsample 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 acclimated 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
(8) was estimated as

s = (# stage 3 on day x ) / (# stage 1 on day 0)

20

Day x 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.

To compare relative egg density between reefs, I calculated weighted averages of
numbers of walleye eggs collected per 2 min tow on each reef. I used the proportion of
the reef surface area contributing to both depth strata as weighting factors for each reef.
Surface area proportions were estimated from bathymetric maps of the reefs (Herdendorf
and Braidech 1972). To examine the effects of a severe storm event that occurred during
the egg incubation period in 1998, I used analysis of variance in the form of a general
linear model to assess the signiﬁcance of differences in egg relative density between
sampling dates, between reefs, and between depths before and after the storm occurred.
Percent loss of eggs was used as the dependent variable and depth and reef were the

interacting class variables. I used a signiﬁcance level of 0.05 for all statistical tests.

21

Table 1. Surface area of reefs (kmz) in western Lake Erie sampled for walleye eggs (area
shallower than 5 m is shown in parentheses).

 

 

Reef Area (kmz)

Cone 0.67 (0.00)
Crib 0.85 (0.65)
Locust Pt. 0.93 (0.80)
Niagara 2.49 (1.50)
Round 0.88 (0.79)
Toussaint 1.23 (1.02)

 

Larval Sampling

I combined data collected in 1994 and 1995 on the abundance, growth,
distribution, and survival of larval walleye in western Lake Erie (Roseman 1997) with
new information gathered in 1996 — 1999. From 1996 — 1999, larval walleye were
sampled at 30-36 sites on and adjacent to the reefs (Figure 2). Larval sampling typically
began in mid-April before eggs hatched on reefs. Pelagic larvae were sampled once per
week ending in late June when most age-0 walleye had become demersal. 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. Larval ﬁshes were euthanized with a lethal dose of

tricaine methanesulfonate and preserved in 95% ethanol. Identiﬁcations of larval ﬁsh

22

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. Mean larval density for the period from the ﬁrst hatch through May
31was used as an index of larval abundance to compare between years. I examined the
distribution of larvae for years 1994-99 using a geographic information system (GIS). To
create a graphical representation of trends in the distribution of larval ﬁsh for each year, I
used the GIS to plot the deviations from the overall annual mean density estimate for
each sampling site for each year as discrete point samples. I used the natural break
function in ArcView to group data into distinct categories. This method minimizes the
sum of the variance within each data class (Environmental Systems Research Institute
1999). Estimates of daily walleye densities for 1994 and 1995 are in Roseman (1997). I
used the sample correlation coefﬁcient (Snedecor and Cochran 1989) to assess the
relationship between lake depth at sample sites and walleye density at that site. I used the
geometric mean catch of age-0 walleye collected in bottom trawls in October as an index
of walleye year-class strength (Ohio Division of Wildlife 2000).

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 age-0 walleye at 9 sites adjacent to
the reef complex (Figure 2). Trawls were towed for 10 min at about 1.5 m/sec at each
site beginning the last week of May. Bottom trawl samples were taken weekly from late
May through June in all years of the study. Trawls typically sampled a 3,900 m2 area.
Bottom trawl sites were selected based on substrate compatibility with the gear and
consistent catch results of age-0 walleye. Fish collected in bottom trawl samples were

only used to evaluate growth rates of age-0 walleye.

23

Larval Grth

Fish total length (TL) was measured to the nearest millimeter. I pooled pelagic
and demersal captured ﬁsh for my analysis. To compare growth rates of age-0 walleye
between years and between periods within years, I calculated the speciﬁc growth rates
(Ricker 1975) of larval walleye during the zooplanktivorous and piscivorous periods.
The period of zooplanktivory typically occurs from May 1 — June 10 and the period when
age-0 walleye are primarily piscivorous occurs after June 10 (Roseman 1997). I assessed
the relationship between speciﬁc growth rates and prey abundance and water warming

rates using sample correlation coefﬁcients and regression analysis (Snedecor and Cochran

1989).

Age-0 Walleye Survival

I estimated daily 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 log, (x +1) to produce normalized data with
homogeneous variance (O’Gorrnan 1984) and plotted these against time. Mortality was
estimated as the slope of the descending limb of each catch curve (Ricker 1975). I
converted the daily instantaneous rates (Z) to total mortality estimates (A) for the time
periods covered by the regression equations as follows:

A = 1 - e‘"

where e is the constant (2.71828...) and t is the number of days included in the regression.

24

Zooplankton Sampling

Zooplankton abundance and composition were determined from weekly vertical
hauls with a 0.5-m diameter plankton net equipped with 153-mm mesh netting.
Zooplankton data collected in 1994 and 1995 are reported in Roseman (1997). From
1996-1999, zooplankton samples were collected at each larval ﬁsh sampling site
concurrent with ﬁsh sampling (Figure 2). Samples were immediately preserved in sugar-
formalin (Haney and Hall 1973). One to three 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. I calculated
average numbers per liter for the pooled zooplankton sample using taxa known to be
consumed by young walleye. Based on previous diet studies, I knew that walleye
consumed mainly copepopds and large cladocerans (Roseman 1997). To create a
graphical representation of trends in the distribution of zooplankton for each year (1996-
99), I used the GIS to plot the deviations from the overall annual mean density estimate
for each sampling site. I used the natural break function in ArcView to group data into
distinct categories (Environmental Systems Research Institute 1999). Because
zooplankton are known to occur in patches of high and low abundance (Patalas and Salki

1992), I treated the zooplankton data as discrete point samples.

Water Temperature
To compare with egg development on reefs, water temperatures (C) on Toussaint

reef were recorded with continuous monitoring therrnographs (Ryan Instruments, Inc.). I

25

calculated the rate of water warming on the reefs for the period lApril through 15 May
because this time period typically covers the walleye egg incubation period on the reefs
(Roseman et al. 1996). I also recorded water temperature 2 m below the water surface at
each larval sampling site using a YSI digital temperature meter. To examine the effects
of water temperature on walleye growth rate, I calculated average water warming rates
during the period when pelagic larval walleye are primarily zooplanktivorous (May 1-
June 10) and primarily piscivorous (June 10 - June 30; Roseman 1997). To create a
graphical representation of geographic patterns in water temperature across my study
area, I used a GIS to plot the deviations from the overall annual mean water temperature
for each sampling site as discrete point samples. I used the natural break function in
ArcView to group data into distinct categories (Environmental Systems Research
Institute 1999). I used the sample correlation coefﬁcient (Snedecor and Cochran 1989)

to assess the relationship between depth and water temperature.

Water Clarig

Secchi disk readings (nearest 0.1 m) were taken at each egg and larval sampling
site as a measure of water clarity. To create a graphical representation of patterns in
water clarity across my study area, I used GIS to plot the deviations from the overall
annual mean secchi disk reading for each sampling site as discrete point samples. I used
the natural break function in ArcView to group data into distinct categories
(Environmental Systems Research Institute 1999). I used the sample correlation
coefficient (Snedecor and Cochran 1989) to assess the relationship between depth and

water clarity.

26

W'md Severity

Wind velocity and direction data recorded at South Bass Island in western Lake
Erie were obtained from the National Climatic Data Center web site (National Climatic
Data Center 2000). South Bass Island is the nearest weather station and is located
approximately 20 km east of the reef complex. I determined the number of days between
April 1 and May 15 when wind events having velocities between 25 - 50 km/h and > 50
km/h occurred. This time period typically covers the walleye egg incubation period on
reefs in western Lake Erie (Baker and Manz 1971; Roseman et al. 1996; Roseman 1997).
Busch et al. (1975) determined that winds exceeding 25 km/h were sufﬁcient to remove
incubating eggs from reefs. 11 separated wind events exceeding 50 km/h from the ﬁrst
category because storm events of this magnitude were rare during my study period
(N CDC 2000) and I observed that they had a different impact on incubating eggs than
storms of a lesser magnitude. Additionally, I considered only winds originating from
directions with fetches > 10 km (260° — 110°) because wave energy increases with fetch
(Gedney and Lick 1972) and I observed that southerly offshore winds with shorter fetches
produced smaller wave amplitudes and had minimal effects on the abundance of

incubating eggs on reefs.

27

Results

Water Temperature and Warming Rate

Mean daily water temperature on reefs in western Lake Erie are presented in
Figure 3. The calculated water warming rates during the egg incubation,
zooplanktivorous larval, and piscivorous age-0 periods for each year are listed in Table 2.
Waters warmed fastest during the egg incubation period in 1998 at a rate of 0.24 °C/day
and slowest in 1995 at a rate of only 0.16 °C/day (Figure 3, Table 2). Lake waters
warmed fastest during the zooplanktivorous larval period in 1995 at a rate of 0.25 °C/day
and slowest in 1999 at a rate of only 0.12 °C/day (Figure 3, Table 2). Waters warmed
fastest during the piscivorous age-0 period in 1997 at a rate of 0.39 °C/day and slowest in

1994 at a rate of only 0.11 °C/day (Figure 3, Table 2).

Table 2. Water warming rates (°C/day) during typical egg incubation (April 1 - May 15),
zooplanktivorous larval (May 1 — June 10), and piscivorous juvenile (June 10 — June 30)
periods 1994 through 1999.

 

 

 

 

Lear Incubaiion Period Zooplanktivorous Period Piscivorous Period
1994 0.22 0.24 0.11
1995 0.16 0.25 0.23
1996 0.22 0.22 0.35
1997 0.19 0.18 0.39
1998 0.24 0.19 0.35
1999 0.18 0.12 0.20

 

28

Water temperatures were generally warmer at inshore sites than at offshore sites
in all years. Figures 4 - 9 display the deviation from the daily average water temperature
at my larval sampling sites for 1994 through 1999. Water temperatures consistently
exceeded the daily mean water temperature at shallow nearshore sites. I found a
signiﬁcant but weak negative relationship between depth and water temperature across all

years of my study (sample correlation coefﬁcient r = -0.192, p < 0.001 , n = 1,156).

Water Clarity

Secchi disk readings varied widely between sampling sites and sampling dates but
were generally lower (darker water) at nearshore sites than at offshore sites in all years
(Figures 4 - 9). I found a weak signiﬁcant positive relationship between depth and secchi

disk depth (sample correlation coefﬁcient r = 0.109, p < 0.001, n = 1,156).

Walleye Egg Abundance and Distribution

Walleye egg relative abundance (mean number of eggs collected per two-minute
tow) for years 1994 through 1999 are presented in Figures 10 — 14. In 1994 and 1995 I
sampled only Niagara and Toussaint reefs. From 1996-1999 I sampled the six reefs listed
in the methods; Cone, Crib, Locust Pt., Niagara, Round, and Toussaint. No eggs were
found in samples collected on April 1, 1994. Walleye eggs ﬁrst appeared in samples
from both reefs on April 7. Egg abundance peaked on the reefs on April 21 when and
average of over 11,300 walleye eggs were collected in a single 2-minute tow. Sampling
frequency on Niagara reef was not sufﬁcient to determine the timing of peak egg density

but an average of over 2,300 eggs/tow was collected in a single tow on April 10. Viable

29

eggs persisted in samples at all sites through May 18, 1994 when less than 100 walleye

eggs were collected per 2 min tow (Figure 10).

30

30-

 

+ 1994

 

 

 

 

 

 

 

20-

A

U

o

v

0

h

a O I I I I f j
E 20-Mar 9-Apr 29-Apr 19-May 8-Jun 28-Jun 18-Jul
Q

Q:

E 30 .

G)

H

,_ 25 .

G)

H

g

 

 

 

15-

10-

 

 

 

O T I I I r I

20—Mar 9-Apr 29-Apr 1 9-May 8-Jun 28-Jun 1 8-Jul

Figure 3. Water temperature on Toussaint reef, 1994-1999.

31

   
 
  
 

- -0.3 to -0.2
o -0.2 to -0.1
o -0.1 to 0.1 1994 Water
0 0.1 to 0.2 Temperature

C 0.2 to 0.6

 
  
  
 

. -0.9 to -0.5
o -0.5 to -0.2

O -0.2 to 0.0 1994
O 0.0 to 0.4 Secchi

O 0.4 to 0.7

 
  
 
  

. -70.2 to -37.1
o -37.1 to -20.2

o -20.2 to 0.1 1994
O 0.1 to 45.6 Walleye

O 45.6 to 98.8 DGHSiW

Figure 4. Deviations from mean annual values for water temperature, secchi
disk reading, and pelagic larval walleye density at sampling sites in western

Lake Erie in spring, 1994.

32

    
 
  
 

0 -0.3
e -0.3 to -0.1

9 '0-1 *0 “-0 1995 Water
0 0.0 to 0.1 Temperature

0 0.1 to 0.4

   
 
 
  

- -0.8 to -0.4
o -0.4 to -0.1

O -0.1 to 0.3 1995
O 0.3 to 0.7 Secchi

O 0.7 to 1.3

    
 
  
 

. -4.1 to -2.6
e -2.6 to -1.0

O -l.0 to 11.3 1995
O 1.3 to 4.0 Walleye

O 4.0 to 10.0 Density

Figure 5. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake Erie

in spring, 1995.

33

   
 
  
 

. -0.8 to -0.6
e -0.6 to -0.3

0 '0-3 *0 0-0 1996 Water
0 0.0 to 0.6 Temperature

0 0.6 to 1.0

 
  
  
 
   
 
 
  

- -0.7 to -0.4
e -0.4 to -0.2

O -0.2 to 0.1 1995
O 0.1 to 0.5 Secchi

O 0.5 to 0.9

° -6.6
O -6.6 to -2.1

O -2.1 to 2.8 1996
O 2.8 to 7.4 Walleye

O 7.4 to 33.9 Density

Figure 6. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake Erie

in spring, 1996.

34

   
 
  
 

. -l.0 to -0.9
o -0.9 to -0.4
9 -0.4 to 0-1 1997 Water
0 0.1 to 0.6 Temperature

    
 
  
 

O 0.6 to 1.3
0 o o
o O O
. . £1
'0 ° 0‘7
. -0.4 to -0.3 .
. -0.3 to -0.1

o -0.1 to 0.3 1997
O 0.3 to 0.5 Secchi

O 0.5 to 0.7

  
 
 
  

. -l6.2 to -8.8
e -8.8 to -4.4
e -4.4 to -1.7 1997
Q -l.7 to 6.0 Walleye

O 6.0 to 33.6 Density

Figure 7. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake Erie

in spring, 1997.

35

  
 
 
  

' -l.2 to -0.8
9 -0.8 to -0.5

9 -0.5 to 0.0 1998 Water
0 0.0 to 0.6 Temperature

O 0.6 to 1.5

  
 
  
 

' -0.6 to -0.5

- -0.5 to -0.3
0 -0.3 to 0.1 1998

O 0.1 to 0.5 3909”
O 0.5 to 0.8

  
 
 
  

' -12.7 to -8.7
9 -8.7 to -l.9

0-1.9 to 12.6 1993
O 12.6 to 38.3 Walleye

O 38.3 to 75.9 Density

Figure 8. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake Erie
in spring, 1998.

36

   
 
 
  

- -2.1 to -1.5
. -1.5 to -0.5
9 -0.5 to 0.3 1999 Water
0 0.3 to 0.9 Temperature

O 0.9 to 1.6

  

-0.6 to -0.4
-0.4 to -0.2
-0.2 to 0

0 to 0.2

0.2 to 0.6

  
  

  
 

. 1999
e 0to6 Walleye
o 6to9 Dens'ty

Figure 9. Deviations from mean annual values for water temperature, secchi disk
reading, and pelagic larval walleye density at sampling sites in western Lake Erie

in spring, 1999.

37

Egg densities were roughly 50% lower on Toussaint and Niagara reefs in 1995
than in 1994. Eggs were present in low numbers on Toussaint reef on April 1 but didn’t
appear in samples from Niagara reef until after April 1. Densities peaked on Toussaint
reef on April 24 and on April 21 on Niagara reef when 3,300 and 1,900 eggs were
collected per 2 min tow from each reef respectively. Viable walleye eggs were collected
through May 17, 1995 when less than 50 walleye eggs were collected per 2 min tow from
both reefs (Figure 10).

In 1996, no walleye eggs were found in samples collected from reefs on March
31. Walleye eggs ﬁrst appeared in samples collected from all reefs on April 8. Egg
relative abundance peaked on Cone, Crib, Locust Pt., Niagara and Round reefs on April
21 when I collected an average of 3,336, 2,015, 3,338, 2,387, and 2,454 eggs per 2-
minute tow from each reef respectively. Egg abundance peaked on Toussaint reef on
April 17 when I collected an average of 7,308 eggs per 2-minute tow. Toussaint reef was
observed to have the highest egg relative abundance in 1996. Viable walleye eggs
persisted in samples through May 13 when eggs numbers in samples became negligible
(Figure 11).

Eggs ﬁrst appeared in samples collected from Niagara and Toussaint reefs on
March 30, 1997 and on April 1 from Cone, Crib, Locust Pt., and Round reefs. Egg
abundance peaked on April 14 on Locust Pt. Reef when I collected an average of 1,280
eggs per 2-minute tow. Egg abundance peaked on Cone, Crib, Niagara, and Toussaint
reefs on April 19 when I collected and average of 1,688, 415, 563, and 1,077 eggs from

the four reefs, respectively. Egg abundance peaked on Round reef on April 23 when an

38

average of 2,852 eggs were collected. Viable walleye eggs persisted in samples collected
from all reefs through May 11 (Figure 12).

In 1998 I collected the ﬁrst walleye eggs on March 23 from Locust Pt. and
Toussaint reefs, about a week earlier than the other 5 years of my study. Eggs were
present on all reefs on March 29. Egg relative abundance peaked on Toussaint reef on
April 3 when I collected an average of 2,747 eggs per 2-minute tow. Egg relative
abundance peaked on Crib, Locust Pt., Niagara, and Round reefs on April 6 when I
collected an average of 540, 1,063, 1,340, and 562 egg per 2-minute tow. Egg abundance
peaked on Cone reef on April 15 when I collected 1,164 eggs per 2-minute tow. Viable
walleye eggs were collected from all reefs through April 28 while eggs were found on
only Locust Pt. and Niagara reefs on May 3 (Figure 13).

Eggs were sampled only three times during 1999 due to equipment failure. Eggs
ﬁrst appeared in samples collected on March 31. Egg abundance averaged 932, 1,928,
674, 1,281 3,437, and 581 on Cone, Crib, Locust Pt., Niagara, Round and Toussaint reefs
respectively on April 8. Eggs were still present in low numbers on all reefs on May 5

(Figure 14).

39

14000 - 1994

12000 - -

 

- El- Niagara

10000 « -O—Toussaint

 

 

 

8000 -
6000 -
4000 -

2000 - [II

I
I

 

0. .a

U U I

27-Mar 6-Apr 16—Apr 26-Apr 6—May 16-May 26-May

5000 1
1 995

 

4000 - - D- Niagara

+Toussaint

 

 

 

Number Walleye Eggs

3000 ‘1

2000 -

I
l
I
l I |
’

1000- ., ‘. é - ..
1% I. H U . i’

o ' l" t I I
22-Mar 1-Apr 11-Apr 21-Apr 1-May 11-May 21-May

 

 

f 1

Figure 10. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1994 and 1995. Abscissa scales vary.

40

10000 1

 

 

 

 

 

 

 

 

 

 

 

 

1996
8000 . +Cone
-l-Crib
- O- L tPt.
6000-l ocus
:1:
$ 000
4 .
LIJ
“>1
2 2000 1
'6‘
E o-
B 26-Mar 5-Apr 15-Apr 25-Apr 5-May 15-May 25-May
§ 10000 -
Z .
- El- Niagara
8000 ' —O—Round
+Toussaint
6000 .
4000 - l
r I
2000 - / . i . .
/ ‘§ 1: . '
’m I, ~
0 .1 ' I r - _s

 

26-Mar 5-Apr 15-Apr 25-Apr 5-May 15-May 25-May

Figure 11. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1996.

41

3500 -

3000 -

2500 -

2000 -

1500 -

 

3500 -
3000 1

2500 -l

Number Walleye Eggs

2000 -

1500 -

1000 -

500 -

 

1997 + Cone
+ Crib
- 0- Locust Pt.

 

 

 

    

1
r-I’Ai

    

 

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

1

l

 

- El- Niagara
+Round I
+Toussaint /

 

 

 

 

O

 

 

I

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

Figure 12. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1997.

42

3500 -

 

 

 

 

 

 

 

 

1998 +Cone
3000 4 _._ Crib
2500 . - 0- Locust Pt.
2000 -
1500 ..
1000 -
816
OD 500 q
LL]
0) 0 - .
if 16-Mar 26-Mar 5-Apr 15-Apr 25-Apr 5-May 15-May
§
ii") 3500 -
,0 - EI- Niagara
S 3000 " —O-Round
T .
Z 2500 ‘ + oussalnt

 

 

 

 

2000 -

1500 -

1000 -

500 -

 

o .
16-Mar 26—Mar 5-Apr 15-Apr 25—Apr 5-May 15-May

Figure 13. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1998.

43

Number Walleye Eggs

5000 -

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1999
4000 - -°-Cone
+Crib
- O- .

3000 ‘ Locust Pt
2000 -
1000 -

o .

27-Mar 3-Apr 10-Apr 17-Apr 24—Apr 1-May 8-May
5000 -
4000 . - El- Niagara

+Round
—0—Toussaint
3000 - / \
/ \
\
/ \ \
2000 - l/ \ \
1000 - l ’i ’ ‘ ‘ - \ \
l I ’ - ..... \
I ’ . T - ., \
1x ‘ - - \
0 ' I I I I :a-LI
27-Mar 3-Apr 10-Apr 17-Apr 24-Apr 1-May 8-May

Figure 14. Walleye egg relative abundance (i 1 standard deviation) on reefs in
western Lake Erie, 1999.

44

In general, I found more eggs at shallow sites on reefs than deep sites early in the
spawning season of each year. This trend reversed later in the egg incubation period as

eggs were removed from shallow sites and displaced to deeper sites on the reefs (Figures

15- 17).

Egg Viability and Survival

Walleye egg viability did not differ substantially between reefs or depths. In 1994
walleye egg viability remained relatively steady at values ranging between 50 and 60%
(Figure 18). In 1995 viability was low on both reefs early in the egg incubation period,
increased to over 60% by mid-April, then decreased to about 20 — 30% by late April and
May when I noticed large numbers of fungused eggs in the samples (Figure 18). Egg
viability increased from values around 20% on all reefs in early April, 1996, 1997, 1998,
and 1999 to about 60% by early May in each of those years (Figures 19 and 20).

I estimated egg survival for distinct cohorts of eggs on each reef in each year of
the study except 1999. As I reported in my thesis (Roseman 1997), egg survival
estimates were higher in 1994 than 1995. My samples allowed for a single egg survival
estimate from ApriI 10 to April 21, 1994. Egg survival for pooled depths was 0.430 for
Toussaint reef and 0.300 for Niagara reef . I calculated 2 separate estimates for each reef
in 1995. Walleye egg survival to stage 3 for the period April 7 to April 29, 1995 was
estimated at 0.140 for Toussaint reef and 0.070 for Niagara reef. Estimates for the period
April 15 — May 9, 1995 were 0.160 and 0.150 for Toussaint and Niagara reefs

respectively.

45

 

 

 

 

 

 

 

 

 

 

 

. 1994
. E1
0'8 E DNiagara
oToussaint
0.6 -
e
0.4 - e
I:

0.2 -
3
o 0 I I I f I
=
.2 6-Apr 16-Apr 26-Apr 6-May 16-May 26-May
:11
8 1.
"-1
I: [:1
8.. o 7 1995
e 0-81 I: '3 DNiagara
9-4 eToussaint

0.6 - o

9 e
0.4 - B E I
D
o

0.2 -

0 I I I I T j

22-Mar 1-Apr 11-Apr 21-Apr 1-May 11-May 21-May

Figure 15. Proportion of walleye eggs collected from shallow sites (< 5m) on
reefs in western Lake Erie, 1994 and 1995.

46

 

 

 

 

 

 

 

 

 

 

 

 

1996
a I ' ICrib
0.8 -
o g D 1:1 oLocust Pt.
0 . . DNiagara
0.5 . I I <>Round
0 0 eToussaint
0 ° '3 a "I
0.4- I 0 u
I D o
C]
0.2 -
B
2 O I I I I I
p—r
g 26-Mar 5-Apr 15-Apr 25-Apr 5-May 15-May 25-May
(0
c:
O 1.
0E .
8.. E! H 1:] 1997
o 0.8 - 0 o o
H e .
D-l 9 O
0.6- ‘ ' 6 .
I D I o 9 .
lCrib 0 o I 9 a
0.4, oLocust Pt. 0 I 0 ﬂ
DNiagara
oRound
0‘2 ' e Toussaint
O I I I I T j
21-Mar 31-Mar 10-Apr 20-Apr 30-Apr 10-May 20-May

Figure 16. Proportion of eggs collected from shallow sites (< 5m) on reefs in
western Lake Erie, 1996 and 1997.

47

 

 

 

 

 

 

 

 

 

 

1 1
a . 1998
9 a ' .
0.8 . D I CHI.)
0 Locust Pt.
1 ° :1 Niagara
0'6 . , 0 Round
. 9 e Toussaint
0.4 - a 3 I :
I o :
I
0.2 '1 i D B
3
o 121
:3 O ‘——l I I I r I ﬂ
g 16-Mar 26-Mar 5-Apr 15—Apr 25—Apr 5-May 15-May
:1
O
”—1
E 1 - I
9.. [3 1999
8 9
GI! 08 - I Crib
o o Locust Pt.
0 El Niagara
0'6 ' I 0 Round
’ e Toussaint
0.4 ‘ .
e
o
0.2 1 H
0 r I j I I

 

 

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

Figure 17. Proportion of eggs collected from shallow sites (< 5m) on reefs in
western Lake Erie, 1998 and 1999.

48

In 1996 I calculated 2 walleye egg survival rates for each of the six reefs sampled.
Survival ranged between 0.097 — 0.181 between the six reefs and averaged 0.138 for the
period April 17 — April 28, 1996. Survival was signiﬁcantly higher (paired t-test, 5 d.f., p
= 0.012) for the period April 24 — May 3, 1996. Estimates ranged between 0.199 and
0.390 and averaged 0.276 (Table 3).

In 1997 I calculated 2 walleye egg survival rates for each of the six reefs sampled.
Survival ranged between 0.094 — 0.143 between the six reefs and averaged 0.129 for the
period April 9 — April 23, 1997. Survival was signiﬁcantly higher (paired t-test, 5 d.f., p
< 0.001) for the period April 19 — April 29, 1997. Estimates ranged between 0.299 and
0.481 and averaged 0.389 (Table 3).

I calculated 3 walleye egg survival values in 1998. Survival ranged between
0.001 — 0.010 on Crib, Locust Pt., Niagara, Round, and Toussaint reef and was
substantially higher on Cone reef at 0.185 for the period March 26 — April 10, 1998.
Survival averaged 0.019 across all reefs for the ﬁrst period estimated. Survival was
signiﬁcantly higher on all reefs for the period April 15 — April 28, 1998 ranging from
0.190 — 0.285 and averaging 0.216 (paired t-test, 5 d.f., p < 0.001). Survival was also
signiﬁcantly higher for the period April 23 — May 3 than the earliest period (paired t-test,
5 d.f., p < 0.001) but did not differ signiﬁcantly from the second survival estimate (p =
0.320). Walleye egg survival averaged 0.395 and ranged between 0.295 and 0.508 for the

period April 23 — May 3, 1998 (Table 3).

49

 

 

 

 

 

 

 

 

 

 

 

1994
0'8 . ’ EINiagara
eToussaint
0.6 4 1:1 I
[:1 e . 9 e

0.4 - 9

0.2 -
b 0 '—'. ﬁ I I I I ﬁ
57‘: 27-Mar 6-Apr 16-Apr 26-Apr 6-May 16-May 26—May
.0
c6
.... 1 .
>> 1995
83

0.8 -
m nNiagara

eToussaint D 9
0.61 * * '3‘
l. O .
E] e
0.4- n B 0
[:1
e D B
0.2 - . E
0 I I I I I l

 

22-Mar 1-Apr 1 1-Apr 21 -Apr 1-May 11-May 21-May

Figure 18. Walleye egg viability on reefs in western Lake Erie, 1994 and 1995.

50

1 996

0 Cone

I Crib

o Locust Pt.
0-5 ‘ D Niagara I
9 Round

04 . e Toussaint

 

0.8 -

O

 

 

GOO-O

 

D .0
CO.

DUO

0.2 -

El.)

.GO
-.
I130

 

 

09H l I F I T l
26-Mar 5-Apr 15-Apr 25-Apr 5-May 15—May 25—May

1997

0.8 . 0 Cone

I Crib

o Locust Pt.
1:] Niagara
0 Round
0.4 - o Toussaint

Egg Viability

 

0.6 -

DO
OI). [O

 

 

 

00-21”
0 OE.
00 SI.
.0

0.2 -

00-
0.013

 

 

9g ;
o-l——I. . . . . w

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

Figure 19. Walleye egg viability on reefs in western Lake Erie, 1996 and 1997.

51

 

 

 

 

 

 

 

 

 

 

 

 

1998
0.8 - 9 Cone
I Crib
0.6 .. o Locust Pt. .
[:1 Niagara a
0 Round 0 . o O
0'4 ' o Toussaint D :
U l .
0.2 - g 8 g . 3 O
8 a Q
B
b 0 '—. I I I I I I
E 16-Mar 26-Mar 5-Apr 15-Apr 25-Apr 5-May 15-May
'8
OI-i
> 1
DD 1
on 1999
L11 0 Cone
0-8 ‘ - Crib
o Locust Pt.
05 . El Niagara
0 Round 0 U
o Toussaint n
0.4 - I o
o D
o
0.2 - 'I
a
0 l I I 1 I
21-Mar 31 -Mar 10-Apr 20-Apr 30-Apr 10-May

Figure 20. Walleye egg viability on reefs in western Lake Erie, 1998 and 1999.

52

Table 3. Walleye egg survival estimates for discrete time intervals for reefs in western
Lake Erie, 1996 - 1998.

 

1 996

Cone

Crib

Locust Pt.

Niagara
Round

Toussaint

1997

Cone

Crib

Locust Pt.

Niagara
Round

Toussaint

1998

Cone

Crib

Locust Pt.

Niagara
Round

Toussaint

April 17 —- April 28

April 24 - May 3

 

0.149
0.197
0.199
0.101
0.181
0.158

April 9 — April 23

0.199
0.277
0.277
0.299
0.203
0.296

April 19 — April 29

 

0.131
0.126
0.143
0.139
0.142
0.094

March 26 - April 10

April 15 - April 28

0.299
0.387
0.377
0.391
0.399
0.481

April 23 - May 3

 

0.185
0.001
0.010
0.009
0.003
0.008

0.197
0.193
0.285
0.235
0.194
0.190

0.299
0.295
0.405
0.391
0.475
0.508

 

53

WM Storm Events

The numbers of days having wind events with velocity and direction sufﬁcient to
remove incubating walleye eggs from reefs are listed in Table 4. I observed two different
types of effects of wind on egg abundance and survival. First, during the incubation
period in 1995, a total of 21 storm events having severe winds (25-50 km/h) occurred
which gradually reduced total egg numbers on reefs by about 50% (Figure 10) and
substantially increasing egg mortality. These frequent storm events also likely
contributed to the slower water warming rate observed on the reefs during the egg
incubation period in 1995 (Figure 3, Table 2). I considered the effects of the frequent
storms in 1995 on egg abundance and survival to be cumulative, where multiple episodes
each contributed to the total loss of eggs from the reefs.

In 1998 I had the unique opportunity to observe the effects of a single gale-force
storm event on the relative density, distribution, and survival of walleye eggs on reefs in
western Lake Erie. The storm occurred between April 8 and the morning of April 10,
well after spawning had begun that year (Figure 12). This storm brought gale force winds
in excess of 80 km/h from the east-northeast and persisted for over 36 h (Table 4; NCDC
2000). Resulting waves (some > 4 m in height) scoured western basin reefs. I found
about 80% fewer eggs in samples collected on April 10 than on April 6 and this
difference was signiﬁcant (ANOVA, p < 0.001). All reefs except Cone experienced a
signiﬁcant decrease in egg relative density between April 6 and April 10. Shallow sites
(< 5 m) on reefs lost signiﬁcantly more eggs (87%) than deep sites (50%) (AN OVA, p <
0.0001; Figure 17). Cone reef is a deep reef having no area with depth less than 6 m

during my investigation in 1998. I observed a difference in egg relative density of only

54

8% between April 6 and April 10 on Cone reef and this difference was not statistically
signiﬁcant (p = 0.08).

On average, over 80% of the eggs were collected from shallow sites on the reefs
before the storm while only 19% of the eggs were collected from shallow sites after the
storm (Figure 17). Egg survival for the period that includes the storm (March 26 — April
10) was quite low ranging from 0.001 — 0.010 on reefs with shallow sampling sites but
noticeably higher on Cone reef at 0.185 (Table 3). Walleye continued to spawn on the
reefs after the storm, as evidenced by increasing egg relative abundance (Figure 13). Egg
survival was much higher on the reefs during mid-April ranging from 0.190 — 0.508

(Table 3).

Table 4. Number of days when wind events occurred over the western Lake Erie reef
complex with velocities 25 — 50 km/hr and >50 km/hr during walleye egg incubation
periods, 1994 — 1999.

 

 

25 — 50 l_(m/hr. > 50 km/hr.
1994 15 0
1995 21 0
1996 15 0
1997 17 0
1998 12 2
1999 17 0

 

55

Larval Walleye Abundance and Distribution

I collected the ﬁrst pelagic larval walleye on April 28, 1994. The catch peaked on
May 1, 1994 when densities averaged 92.5 ﬁsh/1,000 m3 of water. The larval walleye
abundance index was 20.7/1,000 m3 in 1994, the highest 1 observed during the six years
of my study. Pelagic walleye larvae were last collected on June 20, 1994 (Figure 21).
Walleye larvae were consistently most abundant at shallow inshore sites west and
southeast of the reefs through April, May and early June, 1994 (Figure 4).

In 1995, I collected the ﬁrst pelagic walleye larvae on May 3. The catch of
walleye larvae peaked on May 9, 1995 when catches averaged 5.2 ﬁsh/1,000 m3 of water
sampled (Figure 21). The larval walleye abundance index was 3.5/1,000 m3 in 1995, the
lowest observed during my study. Walleye larvae persisted in samples through June 14,
1995. Similar to the distribution of larvae I observed in 1994, the majority of pelagic
walleye larvae were collected from shallow inshore sites west and southeast of the reefs
(Figure 5).

I collected the ﬁrst walleye larvae on April 24 in 1996. The catch of walleye
larvae peaked on May 26 with an average density of 42.3 ﬁsh/1,000 m3 of water sampled.
The larval walleye abundance index estimate was 8.1/1,000 m3 in 1996. Walleye larvae
persisted in samples through June 17, 1996 but catches were low (Figure 22). I collected
more pelagic walleye larvae from shallow nearshore sites west of the reefs than elsewhere
in 1996 (Figure 6).

I collected the ﬁrst walleye larvae on April 28 in 1997. The catch of walleye
larvae peaked on May 10 with an average density of 30.9 ﬁsh/1,000 m3 of water sampled.

The larval walleye abundance index was 13.1/1,000 m3 in 1997. Walleye larvae persisted

56

in samples through June 20, 1997 but catches were low (Figure 22). I collected the
majority of pelagic walleye larvae from nearshore sites west and south of the reefs in
1997 (Figure 7).

I collected the ﬁrst walleye larvae on April 14 in 1998. The catch of walleye
larvae peaked on April 20 with an average density of 27.3 ﬁsh/1,000 m3 of water
sampled. The larval abundance index estimate was 16.8/1,000 m3 in 1998. Walleye
larvae persisted in samples through June 3, 1998 (Figure 23). The impact of the loss of
walleye eggs from the reefs due to the April 8-10 storm was evident in the distribution
and abundance of walleye larvae collected in western Lake Erie in 1998. Larval walleye
abundance was consistently low (< 0.01/1,000 m3) at sampling sites adjacent to reefs
during late April and May 1998. Catches of walleye larvae were high at sites near
Maumee Bay throughout April and May (densities oﬁen > 30/1,000 m3) while catches on
and near the reefs remained low (Figure 8). In fact, over 90% of all walleye larvae
collected in my samples came from six sites closest to Maumee Bay suggesting that a
large portion of the walleye larvae I collected in western Lake Erie in 1998 were of
Maumee River origin.

In 1999 I collected the ﬁrst pelagic walleye larvae on May 3. Densities of pelagic
larvae peaked on May 28 with a mean density of 4.32 ﬁsh/1,000 m3 of water sampled.
The larval walleye abundance index was 3.8/1 ,000 m3 in 1999. Pelagic walleye larvae
persisted in samples through June 7, 1999 (Figure 23). The majority of pelagic walleye

were collected from sites west of the reefs in 1999 (Figure 9).

57

3'5 ' 1994

3.0 d

2.5 ul

 

2.0 -

1.5-

1.0-

0.5 -

 

0.0 I I I V
20-Apr 5-May 20-May 4-Jun 19-Jun

 

3.5 -
1995

3.0 -

2.5 -

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

2.0 -

1.5-

1.0-

0.5 -

 

 

0.0
26-Apr 1 1-May 26-May 10-Jun 25-Jun

 

Figure 21. Log-transformed (Ln Catch +1 #/1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1994 and 1995.

58

3.5 -
3-0 ‘ 1996
2.5 -
2.0 -
1.5 .
1.0 -

0.5 -

 

0.0 - r . , j
15-Apr 30-Apr 15-May 30-May 14-Jun 29-Jun

 

3.5 -

3.0 - 1997

2.5 4

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

2.0 «-

1.5-

1.0«

0.5 -

 

0.0 ‘ T I I I I
1 5-Apr 30-Apr 1 5-May 30-May 14-Jun 29-Jun

 

Figure 22. Log-transformed (Ln Catch +1 #/1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1996 and 1997.

59

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

3.5 -

3.0 -

2.5 «l

2.0 -

1.5-

1.0-

0.5 -

 

0.0

31-Mar

3.5 -

3.0 -

2.5 -

2.0 -

1.5-

1.0-

0.5 -

1998

 

r I I I

1 5-Apr 30-Apr 1 5-May 30-May 14-Jun

1999

 

 

 

0.0

25-Apr

I r I I

10-May 25-May 9-Jun 24-Jun

Figure 23. Log-transformed (Ln Catch +1 #/1,000 m) densities of pelagic walleye
larvae collected from sites in western Lake Erie, 1998 and 1999.

60

N
«a
A)

-2.

Ulric.-
liter 1
1'0 111:
rprlr

IO 01

Zooplankton Abundance

Zooplankton density was approximately 10 per liter in early May 1994 and
increased to over 60 per liter by June 15, 1994. Zooplankton numbers were about 10 per
liter in early May of 1995, 1996, and 1998 and increased at a similar rate in all three years
to just over 40 individuals per liter by June 15. Zooplankton were most abundant in the
spring of 1999 with an initial density of about 10 individuals per liter but a large increase
to over 130 per liter by June 15. Zooplankton were least abundant in 1997, not exceeding
20 organisms per liter during May and early June (Figure 24). Zooplankton were
generally more abundant at inshore sites in 1996 and 1999 but this trend was not as

evident in 1997 and 1998 (Figures 25 and 26).

61

140 -

p L,
+ 1994 ;
120 -

- O- 1995 l

100‘ g —;—1996 l

80-

0

 

 

 

 

 

 

 

 

A
"<
=13:
V
O)
0
g
“g 21-Apr 1-May 11-May 21-May 31-May 10-Jun 20-Jun
,0
<2
:1 140-
O
+1997 1‘ A
120- /
- o- 1998 /
3100‘ —A—1999 /
o ,
o /
N 804
604
3...,
40- '
r'r ..--~
20. (If;
.0’
O I I I I I
21-Apr 1-May 11-May 21-May 31-May 10-Jun 20-Jun

Figure 24. Abundance of zooplankton at nearshore sites in western Lake Erie

during the period from May 1 — June 10, 1994 — 1999.

62

   
 
 
 

. -14to-9
o -9to-5
O -5 to3 1996
O 3t015

O 15 t037

 

. 3to7

Figure 25. Deviations from mean annual values for zooplankton at sampling sites
in western Lake Erie in spring, 1996, and 1997.

63

   
 
  
 
     
 
 

. -ll to-9
o -9t0-3
O -3 mo 1998
O 0to7

. 7tol4

. -37
o -37 to ~14

0 ~14 to -4 1999
O -4 to 17

O 17to49

Figure 26. Deviations from mean annual values for zooplankton at sampling sites
in western Lake Erie in spring, 1998, and 1999.

64

lchthyoplankton Prev Abundance

Density of larval ﬁsh was over 1,500/1,000 m3 in early June 1994, then decreased
to under 500/ 1,000 m3 by the third week of the month before increasing again to over
2,500/1,000 m3 at the end of June. Density of larval ﬁsh prey was lowest in 1995 with
only 11/1,000 m3 in early June and showed an increase throughout the month to almost
SOD/1,000 m3 by the end of June. In 1996, larval ﬁsh prey density was about 50/1,000 m3
and increased steadily throughout the month to 987/1,000 m3 by the end of June. Larval
ﬁsh prey density was about 50/1,000 m3 in early June 1997 and increased steadily to
987/1,000 m3 by the end of June. Larval ﬁsh density was highest throughout June of
1998, beginning at over 1,200/1,000 m3 in early June and increasing to almost 2,000/m3
by the end of the month. Larval ﬁsh density increased from about 60/1,000 m3 in early
June, 1999 to over 1,100/1,000 m3 at the end of the month (Figure 27). Similar to the
distributions of walleye larvae and zooplankton, densities of ichthyoplankton were

generally higher at shallow nearshore sites (Figures 28 and 29).

65

3000 -

 

 

 

r:.— ”1—994 1
2500- l - o- 1995 l

1 —A—1996
2000. *' ‘*
1500-
1000- / A
500‘ — , a.

.... .‘."-’:’- . . - Q “““
0-—‘='=."‘ :— . . . -

5—Jun 10-Jun 15-Jun 20-Jun 25-Jun 30-Jun

3000 -

 

+1997
2500 - - '0' 1998
—A—1999

 

 

 

2000 -

1500 q

lchthyoplankton Abundance (#/ 1,000 m3)

1000 -

500 -

 

 

o .M , , . ,, __M__,_~___ ___,

5-Jun 10—Jun 15-Jun 20-Jun 25-Jun 30-Jun

Figure 27. Abundance of ichthyoplankton prey at nearshore sites in western Lake
Erie during the period 10 June - 30 June, 1994 — 1999.

66

  
  

. -371 to -227
o -227 to -29
O -29 to 278 1994

o 278 to 786
O 786 to 1916

  
 
 
 
  
 
 
 

. -65 to -42

. -42 to -19
o -19to34 1995
C 34to 116
O 116t0258
0 o O
0* 1. o
o . gr.

. -57 to -45
o -45t0-23
o -23 to 5 1996

0 Sta 48
O 48t0110

Figure 28. Deviations from mean annual values for non-walleye ichthyoplankton
prey species at sampling sites in western Lake Erie in spring, 1994, 1995, and

1996.

67

  
  
  
    
  

. -77 to -56

o -56t0-34

o -34 to 26 1997

C 26to81

O 81to313

0
. O
o 0 .

. . 9
- ' ° ' 0*"
o

- -313 to -241
o -241 to -151

o -151to-48 1993
C -48 to 145
O 145 to 704
0 o o
. o C
O o o g

  
 
  

. -73 to -55
o -55 to -14
O -14 to 19 1999

C 19 to 90
O 90 to 148

Figure 29. Deviations from mean annual values for non-walleye ichthyoplankton
prey species at sampling sites in western Lake Erie in spring, 1997, 1998, and

1999.

68

Growth of Age_-0 Walleve

Newly hatched sac-fry walleye averaged between 6.0 and 7.2 mm TL in all years
of the study. Age-0 walleye grew to a length of 46 mm TL by the end of June 1994, 25
mm TL by the end of June 1995, over 30 mm TL by the end of June 1996, over 34 mm
TL by the end of June 1997, greater than 35 mm TL by the middle of June 1998, and over
44 mm TL by the end of June 1999 (Figures 30, 31, and 32). Speciﬁc growth rates of
zooplanktivorous walleye were greatest in 1994 and 1999 with rates of 0.53 and 0.45
mm/day respectively. Speciﬁc growth rate was lowest during the zooplanktivorous larval
period in 1996 at a rate of only 0.19 mm/day (Table 5). Speciﬁc grth rates during the
piscivorous age-0 period were highest in 1998 and 1999 with rates of 1.39 and 1.32
mm/day respectively. Speciﬁc growth rate was lowest during the piscivorous period in

1995 with a rate of only 0.29 mm/day (Table 5).

Table 5. Speciﬁc growth rates of age-0 walleye during periods of zooplanktivory,
piscivory, and for entire period May - June in western Lake Erie from 1994 — 1999.

 

 

 

Year Zooplantivorous Period Piscivorous Period May - June
1994 0.53 1.18 0.70
1995 0.32 0.29 0.31
1996 0.19 0.82 0.34
1997 0.31 1.00 0.53
1998 0.36 1.39 0.49
1999 0.45 1.32 0.73

 

69

Ln Total Length (mm)

4.0 q
3.5 -
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -

 

0.0

1994

 

26-Apr

4.0 .
3.5 -
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -

 

0.0

I I I I I I I

6-May 16—May 26-May 5-Jun 15-Jun 25—Jun 5-Jul

1995

 

26-Apr

r I I I I I I

6-May 16-May 26-May 5-Jun 15-Jun 25-Jun 5-Jul

Figure 30. Log-transformed (Ln) total lengths (mm) of age-0 walleye collected in
western Lake Erie, 1994 and 1995.

70

 

Ln Total Length (mm)

4.0 a
3.5 -
3.0 d
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -
0.0

1 996 i

 

 

20-Apr

4.0 -
3.5 -
3.01
2.5 1
2.0 -
1.5 1
1.0 -
0.5 -

I I I I I I I

30-Apr 10-May 20-May 30-May 9-Jun 19-Jun 29—Jun

1997 I}
,i
iiiiiii

 

 

0.0

25-Apr

I I f I I I I

5-May 15-May 25-May 4-Jun 14-Jun 24-Jun 4-Jul

Figure 31. Log-transformed (Ln) total lengths (mm) of age-0 walleye collected in
western Lake Erie, 1996 and 1997.

71

Ln Total Length (mm)

4.0 -
3.5 -
3.0 -
2.5 .
2.0 -
1.5 -
1.0 -
0.5 -

 

0.0

1998 i
i

 

5—Apr

4.0 1
3.5 -
3.0 -
2.5 -
2.0 -
1.5 -
1.0 -
0.5 -

 

0.0

I I I I I I I

15-Apr 25-Apr 5-May 15-May 25-May 4-Jun 14-Jun

1999

 

30-Apr

I I I r I 1

10-May 20-May 30-May 9-Jun 19-Jun 29-Jun

Figure 32. Log-transformed (Ln) total lengths (mm) of age-0 walleye collected in
western Lake Erie, 1998 and 1999.

72

Speciﬁc growth rates of pelagic larval walleye during the period May 1 through
June 10, when the ﬁsh were zooplanktivorous, were positively associated with
zooplankton densities during the same time period in each year (sample correlation
coefﬁcient r = 0.66, p = 0.16, n = 6; Figure 33). A regression equation using an
exponential function ﬁt to these data showed that zooplankton density explained about
26% of the variability in speciﬁc growth of zooplanktivorous walleye larvae from 1994 —
1999 ( the linear regression equation explained 43%). Conversely, the relationship
between speciﬁc growth rate of larval zooplanktivorous walleye and water warming rate
during the same time period was less pronounced (sample correlation coefﬁcient r =
0.155, p = 0.769, n = 6; Figure 33). I found similar results when I examined the
relationship between speciﬁc growth rate of age-0 walleye after June 10 when the ﬁsh are
primarily piscivorous. Speciﬁc growth rate was positively associated with abundance of
ichthyoplankton prey (sample correlation coefﬁcient r = 0.694, p = 0.126, n = 6; Figure
34) and the logistic regression ﬁt to these data showed that ichthyoplankton prey density
accounted for over 67% of the variability in speciﬁc growth rate during this time period
during the six years of my study. Similar to the relationship between speciﬁc growth rate
of zooplanktivorous walleye and water warming rate, the grth of piscivorous walleye
demonstrated no discemable association with water warming rate (sample correlation

coefﬁcient r = -0.152, p = 0.720, n = 6; Figure 34).

73

0.6 -

y = 0.0959Ln(x) + 0.061 0
R2 = 0.2598 .

0.5 -

 

 

0.0 I I f I I
0 10 20 30 40 50

Zooplankton Density (#Il)

 

0.6 7

0.5 4

Speciﬁc Growth Rate (mm)

0.4 l
0.3 - 0 ‘
0.2 - o

0.1-

 

 

O I I I I I I

0 0.05 0.1 0.15 0.2 0.25 0.3

Water Warming Rate

Figure 33. Relationship between speciﬁc growth rate of zooplanktivorous pelagic
walleye larvae and zooplankton abundance (top panel) and pelagic walleye larvae
and water warming rate (bottom panel) for the period May 1 - June 10, 1994-99.

74

Speciﬁc Growth Rate (mm)

1.6 a
1.4 -
1.2 -
1.0 -
0.8 -
0.6 -
0.4 -
0.2 4

 

0.0

 

y = 0.3916Ln(x) - 1.4675
R2 = 0.6722

 

1.6-
1.4-
1.2-

0.8 -
0.6 -
0.4 -
0.2 -

 

I I I I

500 1000 1500 2000
lchthyoplankton Density (#I1,000 m3)

 

I I I I ‘I

0.1 0.2 0.3 0.4 0.5

Water Warming Rate

Figure 34. Relationship between speciﬁc growth rate of piscivorous pelagic
walleye larvae and ichthyoplankton abundance (top panel) and pelagic walleye
larvae and water warming rate (bottom panel) for the period June 10 — June 30,

1994 - 99.

75

Larval Walleye Survival

I estimated the daily instantaneous mortality rate in 1994 using catch data from
May 19 - June 6 (Figure 21) for ﬁsh ranging in size from 9.9 mm on May 19 to 25 mm
on June 6 (Figure 30). In 1995 I used catch data from May 25 — June 13 (Figure 21)
when ﬁsh size ranged from 9.9 mm on May 25 to 21 mm on June 13 (Figure 30). In 1996
I used catch data from May 26 - June 10 (Figure 22) when ﬁsh ranged in size from 11.1
mm on May 26 to 17.8 mm on June 10 (Figure 31). I estimated the mortality rate in 1997
using catch data from May 17 — June 20 (Figure 22) when pelagic walleye larvae ranged
in size from 8.9 mm on May 17 to 22.1 mm on June 20 (Figure 31). In 1998 I estimated
the mortality rate using catch data from May 4 - June 3 (Figure 23) when pelagic walleye
larvae ranged in size from 8.4 mm on April 30 to 24.7 mm on June 10 (Figure 32). In
1999 I estimated the mortality rate using catch data from June 3 — 7 (Figure 23) when
pelagic walleye larvae were 21.5 and 23.5 mm TL, respectively (Figure 32). These time
periods deﬁned the descending limb of the catch curves for pelagic walleye larvae.

The instantaneous mortality rates, their 95% conﬁdence limits, and translations
into total mortality rates are listed in Table 6. The regression lines used to estimate the
mortality rates for 1995, 1998, and 1999 were signiﬁcantly different from zero. The
instantaneous mortality estimate for 1996 was the lowest at 0.022/day while the rate
estimated for 1994 was the highest at 0.078/day. Total mortality was lowest in 1996 with

an estimate of 28.1% and highest in 1998 at 83.8% (Table 6).

76

Table 6. Daily instantaneous mortality rates (Z), 95% conﬁdence limits, total mortality
rates (A), and p-values for regressions used to calculate instantaneous mortality rates for
pelagic larval walleye collected in western Lake Erie, 1994 — 19998.

 

_Z_ 95% Conﬁdence Limit M) -value
1994 0.078 0.191 2 Z 2 -0.035 75.4 0.094
1995 0.053 0.098 2 Z 2 0.009 63.5 0.017
1996 0.022 0.075 2 Z 2 -0.031 28.1 0.069
1997 0.030 0.114 2 Z 2 -0.054 63.9 0.241
1998 0.065 0.125 2. Z 2 0.005 83.8 0.039
1999 0.118 0.145 2 Z 2 0.013 37.6 0.021

 

 

Fall Age-0 Walleye Abundance Index

Demersal age-0 walleye abundance in Ohio Division of Wildlife October bottom
trawl surveys ranged from a low of 0.2/hr of trawling in 1995 to a high of 30.8/hr of
trawling in 1996. The low value in 1995 indicates that this was the weakest walleye year-
class to form during the six years of my study while the high value in 1996 indicates that
this was the strongest year-class formed. Index values in 1994, 1997, 1998, and 1999
were 8.3, 8.2, 7.8, and 8.6 ﬁsh/hr of trawling respectively (Figure 35, Table 7).

To assess the relationship between water warming rate during the walleye egg
incubation period and the fall year-class strength index, I plotted the index of fall walleye

abundance against spring water warming rate for years from 1960 to 1997. Historic data

77

were obtained from the Ohio Division of Wildlife and Busch et al. (1975). The index of
fall walleye abundance never exceeded 5 ﬁsh per hour of trawling when waters warmed
at rates less than 0.2 degrees C/day but greatly exceeded that number at higher warming
rates (Figure 35) indicating that 0.2 degrees C/day may be a critical minimum threshold

warming rate for walleye egg survival in western Lake Erie.

78

Catch (#lhr)

Fall Walleye Abundance

35-
30.
25-
20~
15..
10-

5‘ I

 

0 r
1991 1992

401
35-
30.
25-
20-
15-
10-

5.

 

1993 1994 1995 1996 1997 1998

5-.....4

I ’ I I I I I
1999 2000

Year

 

0 0.05

 

0.1 0.15 0.2 0.25 0.3 0.35 0.4

Water Warming Rate ("C/day)

Figure 35. Catch of age-0 walleye in Ohio Division of Wildlife October bottom
trawl surveys, 1992 — 1999 (Top). Relationship between spring water warming
rate and abundance of age-0 walleye collected in Ohio Division of Wildlife
bottom trawls. Data from Busch et al. 1975, Roseman 1997, Ohio Division of
Wildlife 2000.

79

Discussion

Based on the catch of demersal age-0 walleye in Ohio Division of Wildlife
October bottom trawl surveys, my research was able to document the events that
occurred during the early life history stages of reef-spawned walleye that led to the
formation of a broad range of year-class strengths. In 1995 I observed processes
contributing to the development of one of the weakest year-classes in the past 15 years. In
contrast, I documented the events that led to the formation of one of the strongest walleye
year-classes in 1996. While fall indices of year-class strength were quite similar for years
1994, 1997, 1998, and 1999, the events that occmred during the ontogeny of these year-
classes were dramatically different. Using data presented above and summarized in Table
7, I will compare and contrast the events that led to the formation of these six year-
classes.

The 1995 walleye year-class is one of the weakest year-classes formed in the past
2 decades (Lake Erie Walleye Task Group 1999). The walleye egg incubation period in
1995 was one of the least favorable for egg survival that I observed. Water warming rate
in 1995 was the lowest in all 6 years of my study and strong wind events were frequent
during the egg incubation period. Because slow water warming rates increase egg
incubation time (Smith and Koenst 1975), eggs experienced prolonged exposure to the
effects of wind and wave action that displaced eggs from favorable incubation areas on
reefs. The prolonged incubation period also increased the risk of predation and disease
(Johnson 1961, Hurley 1972). I observed that egg viability decreased on reefs through
April and early May in 1995 when I noticed a large amount of fimgus on the eggs. Mean

egg survival estimates in 1995 were lowest of any of the six years of my study. Egg

80

 

.88 626:3 .6 spies 6.50 a
.83 .130 5880M 88m 2

 

0.x mud ado w.m rrrrrrrrrr 5 36 mag
ms mvd N4; ”2 SNd mac *3 vmd woe
Nd mmd mom ~.m_ mmmd omvw : Ed hoe
wdm :6 Q: mm :md Ommﬁ mg mmd cog
Nd _md mom Wm 3:: 39m _N Ed 32
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81

viability generally increased during incubation periods in other years of my study.

Congruent with low egg densities and survival on reefs, pelagic larval walleye
were also rare in samples in 1995 with a larval walleye density index value of only
3.5/1,000 m3. Average growth rate of age-0 walleye through June was the lowest of all
six years of my study. Even though water temperatures warmed quickly in late April and
May when walleye feed primarily on zooplankton, the abundance of zooplankton
remained below 20/ liter through May, limiting walleye growth during this period. Water
temperature rose slowly during June in 1995 and the abundance of edible
ichthyoplankton prey was also very low. Survival of pelagic larvae was 36.5% and,
coupled with low larval abundance, led to the lowest fall abundance index observed
during my study of 0.2 ﬁsh/ h of trawling. Numerous laboratory and ﬁeld studies have
demonstrated that growth of larval walleye is limited by low water temperatures and low
prey abundance (Kelso 1972, Spykerman 1974, Li and Mathias 1982, Serns 1982, Fox
1989, Johnston 1999) and can lead to low survival rates, consistent with my conclusions
for factors controlling walleye year-class formation in western Lake Erie in 1995 .

In contrast to the extremely weak year-class formed in 1995, the 1996 year-class
was exceptionally strong, with a fall abundance index of 30.8 ﬁsh/h of trawling. I
observed relatively high egg abundance on reefs and good egg survival in 1996. Waters
warmed quickly in 1996 at 0.22 °C/day and the frequency of wind events was low (15)
providing favorable conditions for egg incubation, resulting in high egg survival rate
(0.211) and moderate abundance of pelagic larvae (8.1/1,000 m3). The factor that

contributed most to the high fall abundance of age-0 walleye in 1996 was the

82

exceptionally high larval survival rate of 71.9%. While mean zooplankton abundance
was low in May and early June, with mean densities similar to those observed in 1995,
zooplankton abundance was higher at inshore sites where larval walleye were
concentrated. The abundance of edible ichthyoplankton was also higher in 1996 and
waters warmed quickly during June contributing to good growth rates and the high
survival of pelagic larvae.

While October bottom trawl index values were similar in 1994, 1997, 1998, and
1999 at about 8 age-0 walleye/h of trawling, the combination and magnitude of factors
contributing to year-class formation varied between years. I observed the highest egg
abundance in 1994 accompanied by fast water warming during incubation and few strong
wind events leading to high egg survival and the highest larval walleye densities observed
during my study. Zooplankton were very abundant and waters warmed quickly during
the zooplanktivorous feeding period. Zooplanktivorous walleye larvae responded to the
good conditions exhibiting high speciﬁc growth during this time period. lchthyoplankton
prey abundance was high in June but water warming rate during the piscivorous period
in June was slow in 1996. Piscivorous walleye still exhibited good growth rates. Despite
the high abundance and good growth of larval walleye, survival was only 24.6% leading
to the moderate fall abundance index value of 8.3 ﬁsh/h of trawling (Table 7).

In 1997, water warming rate during the egg incubation period was somewhat low
at 0.19 °C/day, the frequency of wind events was low and egg abundance and survival
were moderate. Abundance of pelagic larval walleye was moderate at 13.1/1,000 m3 but

zooplankton abundance was low, averaging less than 10/1 throughout May and early June.

83

Water warming rate during the zooplanktivorous period was also somewhat low at 0.18
°C/day and zooplankton numbers were also low. Speciﬁc growth rate during the
zooplanktivorous period was moderate at only 0.31 mm/day. Water warming rate was
quite high during the piscivorous period in June and edible ichthyoplankton prey were
plentiful. Consequently, walleye speciﬁc growth rate was higher in June at 1.00 mm/day.
Survival of pelagic walleye larvae was moderate in 1997 at 36.1% leading to a moderate
catch rate of demersal walleye during the fall bottom trawl survey of 8.2/h of trawling
(Table 7).

Walleye began spawning on reefs in mid-March of 1998, about a week earlier
than in other years of my study, and egg numbers were quite high when the catastrophic
storm hit on April 8. While water warming rate was high during the egg incubation
period in 1998 (0.24 °C/day) and the total number of days with strong wind events was
low (14). However, the egg incubation period experienced the effects of 2 days worth of
gale-force winds. On average, over 80% of the eggs spawned prior to the storm event
were removed by the strong wind-generated wave and current action created by the
storm. Consequently, mean egg abundance on reefs was quite low in 1998 and egg
survival was moderate. Larval abundance was moderately high at 16.8/1,000 m3, despite
the loss of eggs from reefs. Zooplankton abundance was above average during May and
early June and water warming rate was moderate at 0.19 °C/day. These factors translated
into a moderate speciﬁc growth rate for zooplanktivorous pelagic walleye of 0.36
mm/day. Edible ichthyoplankton abundance was exceptionally high in June and water

warming rate was high at 0.35 C/day during the piscivorous period in June.

84

Corresponding to these favorable growth conditions, speciﬁc growth rate of piscivorous
walleye was the highest observed during my study at 1.39 mm/day. Larval survival was
14.2%, the lowest observed in this study, producing a fall abundance index estimate of
7.8/h of trawling (Table 7).

Water warming during the egg incubation period of 1999 was somewhat low at
only 0.18 C/day and 17 strong wind events occurred. Egg abundance on reefs in 1999
appeared to be comparable with those of 1996 and 1997, although data from the peak
abundance period are missing. Egg survival was probably low in 1999 based on the low
water warming rate during egg incubation and subsequent low abundance of pelagic
larvae. Water warming rate was slow during May and early June but zooplankton
abundance was quite high. Speciﬁc growth rate of zooplanktivorous larvae was high at
0.45 mm/day. Edible ichthyoplankton were plentiful in 1999 and water warming rate was
moderate at 0.20 C/day. Speciﬁc growth rate of piscivorous walleye was quite high at
1.32 mm/day. The relatively favorable conditions experienced during the piscivorous
larval period allowed fast growth rates which were transmitted to high larval survival
(62.4%). Despite low larval abundance, the high survival of the larvae was reﬂected in
the moderate fall year-class strength index of 8.6/h of trawling (Table 7).

In summary, the best walleye year-classes are formed in years with fast water
warming rates throughout egg incubation and pelagic larval periods, storm events are rare
during the egg incubation period, and prey abundance is high in May and June. These
favorable conditions promote high egg abundance and survival on reefs and fast growth
rates and high survival rates of larvae. Because having this combination of factors occur

all in the same year is rare, the ability of a walleye cohort to compensate for poor survival

85

at an early life history stage by increasing survival later in life is important in order to
produce strong year-classes. My data provide some evidence that age-0 walleye
demonstrate such compensatory responses. For example, egg abundance and survival on
reefs was probably low in 1999 and produced a low number of larvae in the western
basin. The cohort was able to compensate for low egg survival and low larval abundance
by taking advantage of favorable conditions and responding with high growth and
survival rates during zooplanktivorous and piscivorous feeding stages resulting in a
moderate fall year-class strength (Table 7).

While evidence of compensatory responses in walleye growth and survival are
common for older ﬁsh, few studies have documented such responses for age-0 walleye.
Through a population modeling exercise, Jensen (1993) concluded that compensation
during the larval life stage was not necessary for regulation of populations size. Other
studies have focused on size selective mortality of walleye, speciﬁcally cannibalism
during the winter period (Chevalier 1973, Fomey 1976, 1980, Madenjian et al. 1991,
Madenjian et al. 1996). These studies concluded that if ﬁrst year growth was slow, then
age—0 walleye were exposed to predation by older walleye for longer periods. However,
cannibalism is rare among walleye in Lake Erie (Knight et al. 1984, Francis and
Vondracek 1990, Hartman and Margraf 1992, Madenjian et al. 1996) and recruitment of
age-2 ﬁsh to the stock was unrelated to ﬁrst year growth (Madenjian et al. 1996).

I observed important patterns in physical and biological processes that occurred
repeatedly during the six years of my study. First, I found that egg abundance was
greatest on shallow points of reefs early in walleye spawning and egg incubation periods

but gradually decreased as eggs were washed to deeper sites on the reefs. This pattern

86

indicates that walleye actively spawn on the shallowest sites on the reefs and rely on
water currents to transport the eggs to favorable incubations sites. Previous work on
Lake Erie reefs found the shallow areas of reefs to be smoother with less complexity (less
porous, low variety of particle sizes) than deeper sites (Herdendorf and Braidech 1970,
Roseman 1997). Wave energy models developed by physical limnologists indicate that
shear stress, the amount of energy necessary to move bottom particles, decreases with
depth (Miller et a1. 1977). Eggs remaining on shallow exposed sections of reefs would be
more vulnerable to removal by wave and current action caused by storm events than those
incubating at deeper sites. My data show this to be true as egg abundance at deep sites
(like Cone reef) did not decline as sharply during the April 8-10, 1998 storm.

I also found a deﬁnite pattern in egg viability and survival. The proportion of
viable eggs in samples was generally higher later in the egg incubation period, with 1995
being the exception, as I explained above. Also, egg survival estimates were generally
higher for periods later in the egg incubation period. These results suggest that egg
mortality rates are higher early in the incubation period which is supported by laboratory
studies conducted by other scientists. Latif et al. (1999) and Heidinger et al. (1997)
observed the majority of egg mortality to occur during the ﬁrst 100 hours after
fertilization. Latif et al. (1997) considered the ﬁrst 100 hours as a critical period for egg
development and added that any environmental stress on eggs during this period would
increase mortality. As I mentioned earlier, Allbaugh and Manz (1964) observed that egg
viability increased as incubation periods progressed because dead walleye eggs became

buoyant and were washed from incubation sites.

87

The third important pattern I observed was the accumulation of walleye larvae at
shallow nearshore areas along the coast of the western basin. These areas proved to be
more conducive to good growth and survival of age-0 walleye by having increased water
temperature, darker waters, and higher prey densities than offshore sites. Growth rate and
development of walleye sac-fry is temperature dependent as temperature determines the
rate of yolk absorption while growth of post sac-fry is a function of food consumption
and metabolism, both of which are temperature regulated (McElman and Balon 1979,
Johnston and Mathias 1994). As described earlier, much evidence exists to demonstrate
the relationship between warmer water temperatures and larval walleye growth and
survival (Trometer and Busch 1999, Rieger and Summerfelt 1999) and this advantage
was evident in my data. Also, walleye are known to perform better in darker waters,
showing increased growth and survival in laboratory experiments (Bristow et al. 1996,
Regier and Summerfelt 1997), also evident in my data. Finally, the literature abounds
with evidence deﬁning the positive relationship between prey abundance and walleye
growth and survival (Carlander and Payne 1977, Kelso 1972, Kempinger and Churchill
1972, Mills and F omey 1988, Fox 1989) that is also supported by my observations
(Figures 33 and 34). Ultimately, my research underscores the importance of these coastal
areas for age-0 walleye growth and survival and emphasizes the need to understand
coastal processes and their signiﬁcance to walleye ecology.

One repeatable process that I did not measure but was still evidently critical to
walleye year-class strength formation is the role of lake currents in dispersing ﬁsh from
reefs and transporting them to the shallow coastal nursery areas. Because I observed age-

0 walleye to become concentrated in the same locations year after year during my

88

research (Figures 3 — 9), lake currents must function in similar manners during at least
portions of every spring when walleye larvae are dispersing from egg incubation areas.
These currents provide the physical linkage between egg incubation areas and the
warmer, more productive coastal zone nursery areas. The lack of information on water
current patterns and their role in larval walleye dispersal and distribution represents a

void in our knowledge about walleye ecology in western Lake Erie.

89

Conclusion

My results emphasize the important role of physical processes in structuring the
year-class strength of walleye in western Lake Erie. My results are unique in that few
studies have shown the direct cause and effect relationships between physical processes
and ﬁsh population dynamics in freshwater systems. My results revealed that both
episodic events (weather-related events) and subtle variability (temperature dependent
development) in early life history vital rates can signiﬁcantly effect the year-class
development of walleye in western Lake Erie. While we can modify the physical habitat
in which ﬁsh populations exist, we do not have the capabilities to manage or manipulate
most physical processes. For example, we can construct artiﬁcial reefs with deep crevices
to shelter eggs from strong wave and current action, but we cannot alter the actual wave
and current action to any appreciable degree that would beneﬁt egg survival. Instead, we
must rely on developing a sound understanding of the linkages between physical
processes and the ecological processes that regulate ﬁsh production and recruitment. By
doing so, we will be able to better predict the response of ﬁsh populations to variability in

their habitat and respond with appropriate management strategies.

90

 

Chapter 2

PREDATION ON WALLEYE EGGS BY FISH
ON REEFS IN WESTERN LAKE ERIE

Abstract

Predation on ﬁsh eggs can negatively impact the recruitment of some ﬁshes. To
assess the potential impact of egg predation on walleye year-class development, I
examined the diets of ﬁshes from gillnet and egg pump collections on reefs in western
Lake Erie during walleye egg incubation periods from 1994 — 1999. I collected no
potential egg predators in samples taken in 1994 but from 1995 — 1999 I caught up to 11
different species of ﬁsh on reefs in addition to spawning walleye. Catch per effort of
potential egg predators in gillnets generally increased as egg incubation periods
progressed. Catch per unit effort of white perch was highest in all years except 1998
when catches of trout perch and yellow perch were higher. On average, white perch
stomachs contained more eggs than other egg predators in all years except 1998 when
yellow perch were observed to eat more eggs. I also found low numbers of walleye eggs
in the stomachs of logperch, trout perch, sculpin, spottail shiner, rock bass, and round
goby. My results indicate that prolonged incubation periods may increase the potential

for egg loss due to predation.

91

 

Introduction

Dense patches of ﬁsh eggs produced by mass spawning offer exceptional feeding
opportunities to predators (Wolfert et al. 1975, Frank and Leggett 1984, Schaefer and
Margraf 1987). At a more general level, prey aggregations are widely known to attract
large numbers of predators, and aggregated prey can suffer high mortality under these
circumstances (Kerfoot and Sih 1984). While egg predation has been observed by avian ,u
predators (Botton 1984) and invertebrates (caddis larvae, Fox 1978; planarians, Newburg
1974; amphipods, DeBlois and Leggett 1991; crayﬁsh, Horns and Magnuson 1981), ﬁsh
are considered the most important predators of ﬁsh eggs in many aquatic communities.

Mortality estimates ranging from 1.6 to 70% of the annual egg production have been
reported in studies examining benthic egg predation by ﬁsh (Bailey and Houde 1989).

In Lake Erie, walleye deposit their eggs on reefs and in rifﬂe areas of tributaries in
early spring and provide no parental care (Ney 1978). This leaves dense aggregations of
eggs vulnerable to a host of potential mortality factors including removal by water
currents, siltation, and predation. Wolfert et al. (1975) found yellow perch to be the most
important predator of walleye eggs on Kelly’s Island Shoal in western Lake Erie in 1969-

71. During a study in western Lake Erie tributaries from 1981-83, exotic white perch
were found to consume large quantities of walleye and white bass eggs (Schaefer and
Margraf 1987). These studies concluded that prolonged egg incubation periods increase

the vulnerability of eggs to predation and increase the impact that predation might have

on year-class development. Further, the recent invasion of Lake Erie reefs by round

92

gobies (Neogobius melanostomus, Jude et al. 1992) has created increased concern about
walleye recruitment variability as these invasive ﬁsh may become major predators on ﬁsh
eggs.

Predation of incubating walleye eggs on reefs in western Lake Erie could have a
serious detrimental effect on walleye year-class strength when incubation periods are
prolonged and egg predators become abundant on reefs. Further, the observed high
density of round gobies on reefs in the summer of 1998 and 1999 (> 20/m2) (personal
communication, Dr. Ken Baker, Heidelberg College, Tifﬁn, OH) raises questions about
the impact that these ﬁsh will have on the abundance and survival of reef-spawned
walleye eggs. In this chapter I document the extent of predation by ﬁsh on incubating
walleye eggs on reefs in western Lake Erie. My speciﬁc objectives are to determine the
timing of appearance and relative abundance of potential egg predators and the extent that

they feed on walleye eggs.

Methods

Variable mesh gillnets were ﬁshed overnight on reefs during peak spawning
periods in April and early May 1994 - 1999 to collect potential walleye egg predators.
Two 40 m gillnets were ﬁshed simultaneously. 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 to 4.2 m of water on either Toussaint or
Locust Pt. reef. Table 8 lists sampling sites and dates for each year. I selected Toussaint
and Locust Pt. reefs as sampling sites for egg predators because I observed high walleye

egg densities on these reefs and for logistical considerations.

93

Upon capture, potential egg predators were anesthetized in tricaine
methanesulfonate, 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 common sucker (Catastomus
commersonii), quillback sucker (Carpiodes cyprinus), and 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 (Table 9). These ﬁsh were preserved whole in 10% formalin and dissected later.
I calculated the average number of eggs per stomach and percent frequency of occurrence
of eggs in stomachs for each egg predator (Bowen 1996). I also calculated the catch-per-
unit-effort (CPUE) for all species collected in gillnets by dividing the total catch of each
species by the total number of hours gillnets were ﬁshed for each sampling date and for

the entire sampling period.

Results
No ﬁsh other than spawning walleye were collected in gillnets ﬁshed overnight on
April 20 and 26, 1994. In 1995 I collected a total of 49 ﬁsh in 3 nights of gillnetting
totaling 30 hours of effort (Table 8). I collected an additional 7 ﬁsh with the egg pump
(Table 9). Following walleye (1.20/hour), white perch had the highest CPUE (1.12/hour)
while spottail shiner had the lowest (0.11/hour; Table 10). Few ﬁsh were captured in
gillnets set on 13 April 1995 (n = l 1) but CPUE increased on subsequent nights (Figure

36), especially of white perch, the most common species collected. The stomachs of trout

94

 

perch Percopsis omiscomaycus, yellow perch, logperch Percina caprodes, johnny darter
Etheostoma nigrum, white perch, and an unidentiﬁed sculpin (Cottidae) contained
walleye eggs in 1995. The stomachs of walleye, rock bass Ambloplites rupestris and
greater redhorse sucker did not contain walleye eggs. Walleye eggs appeared in 86% of
white perch stomachs with an average of 349 walleye eggs per stomach (Table 10).

In 1996 I collected 58 ﬁsh in 3 nights of gillnetting totaling 35 hours of ﬁshing
effort (Table 8). I collected one logperch with the egg pump (Table 9). CPUE of all
potential egg predators increased throughout the sampling period from a low of 0.75 on
April 13 to over 1.46 on May 3 (Figure 36). CPUE was highest for white perch (Table
11). I found walleye eggs in the stomachs of log perch, spottail shiner, trout perch, white
perch, and yellow perch in 1996. White perch were observed to consume the largest
numbers of walleye eggs averaging 372 eggs/stomach and walleye eggs were in 90% of
stomachs examined. Walleye eggs also appeared in stomachs of logperch, spottail shiner,
troutperch, and yellow perch in 1996 (Table 11).

In 1997 I collected 210 ﬁsh in 3 nights of gillnetting with a combined effort of 38
hours. I collected a single logperch with the egg pump (Table 9). Catch per unit effort
was highest for white perch and troutperch at 2.10 and 2.03/hour respectively (Table 12).
CPUE of all potential egg predators increased from a low of 1.16 on April 19 to 8.92 on
May 2 (Figure 36). Walleye eggs appeared in stomachs of logperch, silver chub
(Hybopsis storeriana) spottail shiner, troutperch, white perch, and yellow perch in 1997.
White perch were again observed to consume the most walleye eggs at an average of 131
per stomach. Frequency of occurrence of walleye eggs in white perch stomachs was 43%

while 50% of yellow perch stomachs had eggs. Stomachs of alewife (Alosa

95

 

pseudoharengus), brown bullhead(1ctalurus nebulosus), common sucker, smallmouth
bass (Micropterus dolomieu), walleye, and white bass did not contain walleye eggs
(Table 12).

I collected 142 ﬁsh in gillnets in 1998. I also collected 4 logperch with the egg
pump in 1998 (Table 9). Troutperch appeared most frequently in collections with a catch
per unit effort of 1.39/hour. Yellow perch were the next most common followed by white
perch (Table 13). Catches of potential egg predators increased throughout April. CPUE
increased from 0.50 to 6.75 between April 6 and April 23 (Figure 36). Round gobies
appeared in my samples for the ﬁrst time in 1998, I collected 21 in gillnets and 14 with
the egg pump. Eggs were found in the stomachs of logperch, rock bass, round goby,
spottail shiner, trout perch, white perch, and yellow perch. Eggs appeared in higher
numbers in the stomach of yellow perch (3 85/stomach) than any other ﬁsh. Stomach of
white perch averaged 208 eggs while round gobies averaged only 2 (Table 13). Stomachs
of common sucker, freshwater drum (Aplodinotus grunniens), and walleye did not

contain eggs (Table 13).

96

 

Table 8. Dates, times and locations where gillnets were ﬁshed in western Lake Erie in
1994 through 1999. Effort was constant across all sample periods (2 - 40 m variable

mesh gillnets).

 

Date

April 13, 1994

April 17, 1994

April 18, 1994
Total effort (hrs)

April 13, 1995

April 17, 1995

April 24, 1995
Total effort (hrs)

April 13, 1996
April 21, 1996
May 3, 1996

Total effort (hrs)

April 19, 1997

April 26, 1997

May, 2, 1997
Total effort (hrs)

April 6, 1998
April 15, 1998
April 18, 1998
April 23, 1998
Total effort (hrs)

April 7, 1999

April 11, 1999

April 30, 1999
Total effort (hrs)

Location
Toussaint
Toussaint
Toussaint

Toussaint
Toussaint
Toussaint

Toussaint
Locust Pt.
Locust Pt.

Toussaint
Toussaint
Toussaint

Locust Pt.
Locust Pt.
Locust Pt.
Locust Pt.

Locust Pt.
Locust Pt.
Locust Pt.

Time Fished

1800 - 0700
1800 — 0700
1100 - 1500

30

2000 - 0700
1900 - 0700
1900 - 0700

35

1900 - 0700
1900 - 0700
1900 - 0800

37

1900 - 0800
1900 - 0700
1900 - 0800

38

1900 - 0700
1900 - 0700
1900 - 0800
1900 - 0700

49

1900 — 0700
1900 - 0700
1900 - 0700

36

 

97

Table 9. Date, location, species, and number (in parentheses) of ﬁsh collected
incidentally during egg sampling on reefs in western Lake Erie. 1995 — 1999.

 

.D_at§
April 13, 1995
April 17, 1995
April 24, 1995
April 13, 1996
April 19, 1997
April 10, 1998

April 15, 1998

April 18, 1998

April 23, 1998

April 28, 1998

March 31, 1999
April 8, 1999

May 5, 1999

Lem
Niagara Reef
Toussaint Reef
Niagara Reef

Cone Reef
Toussaint Reef
Crib Reef
Locust Pt. Reef
Niagara Reef
Crib Reef
Niagara Reef
Round Reef
Toussaint Reef
Crib Reef
Niagara Reef
Toussaint Reef
Cone Reef
Crib Reef
Toussaint Reef
Niagara Reef
Toussaint Reef
Locust Pt. Reef
Cone Reef
Crib Reef
Locust Pt. Reef
Niagara Reef
Locust Pt. Reef
Niagara Reef
Round Reef
Toussaint Reef
Cone Reef
Crib Reef
Locust Pt. Reef
Niagara Reef
Round Reef
Toussaint Reef

Species (number)

Logperch (2)
Sculpin (1)

Johnny Darter (1)

Logperch (1)

Logperch (1)

Logperch (1)
Round Goby (2)
Round Goby (3)

Logperch (1)

Logperch (1)

Logperch (2)
Round Goby (3)
Round Goby (3)
Round Goby (2)
Round Goby (1)
Round Goby (2)
Round Goby (1)
Round Goby (1)
Round Goby (1)
Round Goby (1)
Round Goby (1)
Round Goby (1)
Round Goby (6)
Round Goby (9)
Round Goby (5)
Round Goby (5)
Round Goby (7)
Round Goby (2)

Round Goby (10)

Round Goby (8)
Round Goby (3)
Round Goby (5)
Round Goby (7)
Round Goby (2)
Round Goby (1)
Round Goby (1)

 

98

 

I collected a total of 157 ﬁsh in gillnets ﬁshed for a total of 36 hours on reefs in
1999. I collected more round gobies in 1999 than in 1998, especially with the egg pump.
I collected 9 round gobies in gillnets (Table 14) and an additional 72 with the pump
(Table 9). White perch were the most frequently encountered species with a catch per
unit effort of 3.25/hour (Table 14). The increasing trend in CPUE over time was again
evident in 1999. CPUE for all ﬁsh combined increased from 1.25 on April 7 to 9.42 on
April 30 (Figure 36). Eggs were prevalent among the stomach contents of white perch
and yellow perch with an average of 397 and 387 eggs per stomach respectively. Round
gobies consumed eggs in relatively low numbers averaging less than 2 per ﬁsh. Eggs
were also found in the stomachs of quillback sucker, spottail shiner, troutperch, and white
sucker (Table 14).

Fish on reefs also consumed prey items other than walleye eggs. White perch and
yellow perch were observed to have amphipods, zooplankton, and ﬁsh in their stomachs.
Walleye diets were composed mainly of ﬁsh although some stomachs contained
amphipods. Troutperch, logperch, and spottail shiners all consumed amphipods. Round

goby diets consisted primarily of small dreissenid mussels (<5 mm) and amphipods.

99

 

 

 

 

 

 

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.1995 O D
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100

 

 

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105

Discussion

I collected no egg predators in gillnets in 1994 suggesting that egg predation was
not a major source of egg mortality in that year. In the following years, I documented
that several species of ﬁsh inhabited reefs during walleye egg incubation periods and did
indeed consume eggs. While species composition and relative abundance of ﬁsh was
different between years, I found it difficult to identify a deleterious effect that egg
predation might have had on egg abundance or survival. In most years, egg predators did
not become abundant on reefs until late in the egg incubation period, after eggs had
started to hatch and after the effects of wind and water currents had taken place.
Therefore, it is difﬁcult to notice any appreciable decline in egg abundance or survival
due speciﬁcally to predation by examining trends in egg abundance.

Based on CPUE, the relative abundance of egg predators was noticeably different
between years. CPUE was highest in late April and early May of 1997, 1998, and 1999
suggesting the potential for egg predation was also higher in those years. However, egg
abundance, egg survival, and larval abundance were moderately high in 1997 (Table 7)
showing no discemable impact from predation. In 1998, the effects of the storm in early
April outweighed any other source of egg mortality in that year. In 1999, I did not have
sufﬁcient egg sampling data to determine trends in egg abundance and survival, but larval
abundance was very low suggesting low egg abundance and/or increased egg mortality
during that spring (Table 7). Relative abundance and CPUE of egg predators was higher
in 1999 than any other year allowing me to conclude that egg predation likely was a

larger source of egg mortality in 1999 than in other years.

106

Survival rates of viable walleye eggs ranged from about 10% to 50% during
incubation periods across the six years of this study. Egg survival is generally much
higher for species that exhibit parental guarding of eggs through hatching. Bain and
Helfrich (1983) observed over 65% of bluegill (Lepomis macrochirus) eggs to emerge
from nests guarded by adult bluegill but only 14% of eggs hatched in unguarded nests. In
contrast, eggs that are spawned in fall and totally abandoned by their parents can suffer
high mortality from predation. Burbot (Lota Iota) and deepwater sculpin
(Myoxocephalus thompsom') are known to eat large numbers of lake trout (Salvelinus
namaycush) and Whiteﬁsh (Coregonus clupeaformis) eggs in lakes Michigan and
Superior (Bailey 1972, Wojcik et al. 1986). In some European lakes, ruffe
(Gymnocephalus cernuus) feed extensively on coregonine eggs and may suppress
coregonine populations. Ruffe consumed 80 - 90% of vendace (Coregonus albula) eggs
in Lake Syamozera, Russia and egg predation by ruffe is also considered a major factor in
the decline of European Whiteﬁsh (Coregonus lavaretus) in the same lake (Pokrovskii
1961 cited in DeSorcie and Edsall 1995). The egg survival rates I estimated for walleye
on western Lake Erie reefs appear intermediate of those reported in these other studies;
higher than species that afford no parental care yet lower than species providing total
parental care. I hypothesize that, because walleye remain on the reefs during much of the
egg incubation period, many predators are deterred from the reefs by the presence of a
congregation of large piscivores. My CPUE estimates indicate that abundance of ﬁsh
other than walleye begins to increase only after peak walleye spawning has occurred and

walleye abundance decreases on reefs.

107

 

White perch appeared to be the most important consumers of walleye eggs on
reefs during this study. White perch were also considered important predators of ﬁsh
eggs in other systems. Schaefer and Margraf (1987) found ﬁsh eggs (including walleye
eggs) in white perch stomachs collected from the Sandusky River, OH in the spring of
1982 and 83. White perch are also thought to be important predators of striped bass
Morone saxatilis eggs and larvae in Chesapeake Bay (Setzler et al. 1980; Monteleone and
Houde 1992). Yellow perch are also considered important predators on ﬁsh eggs in some
systems. Similar to my results, Wolfert et al. (1975) found yellow perch to consume
substantial numbers of walleye eggs on Kelly’s Island Shoal in western Lake Erie in the
late 19603. Yellow perch were observed to consume lake trout eggs from spawning
shoals in large quantities in Keuka Lake, NY, hindering efforts to establish self-
sustaining lake trout stocks in the lake (Fitzsimons 1990).

Round gobies appeared in my egg predator collection in 1998 and became quite
abundant in 1999, especially as incidental catch in egg pump samples. Ohio Division of
Wildlife scientists also observed large numbers of age-0 round gobies in bottom trawls in
1998 (ODW 2000). The size of the round gobies I collected from reefs in 1998 and 1999
is below that reported by other researchers. Several large (>150 mm TL) round gobies
were observed during SCUBA surveys on reefs in July and August of 1998 and 1999
(personal communication, Dr. Ken Baker, Heidelberg College, Tifﬁn, OH). Round
gobies were observed to exceed 200 mm TL in the St. Clair and Detroit rivers (Jude et al.
1995). The ﬁsh I collected in egg pump samples and gillnets were considerably smaller,
averaging only 51 mm in 1998 (Table 12) and 69 mm in 1999 (Table 13) and were

probably not representative of the round gobies population on reefs in those years.

108

 

 

Round gobies did not consume eggs in any appreciable numbers. Mean number
of walleye eggs in round goby stomachs was about 2 in both years when I collected round
gobies on reefs (Tables 12 and 13). The low numbers of eggs consumed by round gobies
may be a function of their size. Chotkowski and Marsden (1999) found that round gobies
smaller than 50 mm TL did not consume lake trout eggs in laboratory studies. They also
found that mottled sculpin consumed more lake trout eggs than round gobies of similar
sizes. Even though walleye eggs are about half the diameter of lake trout eggs (2 mm vs.
5 mm; Auer 1982), round gobies still did not consume them in appreciable numbers on
western Lake Erie reefs. Still, the potential for round gobies to become important
predators on walleye eggs remains.

I observed that egg predator relative abundance and CPUE increased during April
and May in all years of the study (Figure 36). Wolfert et al (1975) also observed a
successive increase in the abundance of ﬁsh on Kelly’s Island Shoal after peak walleye
egg abundance occurred in 1969-71. This trend of increasing predator abundance is
important, especially in years when waters warm slowly, prolonging incubation periods.
The longer the incubation period, the more opportunity there is for predation and the

greater the potential for deleterious effects on walleye reproductive success.

109

Dissertation Synthesis

LINKING EVENTS DURING WALLEYE EARLY LIFE HISTORY TO
YEAR-CLASS DEVELOPMENT

Physical processes structure the environmental setting in which many
biological processes take place. In the previous chapter I identiﬁed speciﬁc factors
and mechanisms that inﬂuence the vital rates of egg and larval stages of walleye
providing insight to the ecological functions mediated by physical processes. I was
able to relate physical processes (such as storm events and water warming rate) and
physical habitat characteristics (depth, clarity) to the distribution, abundance, growth,
and survival of walleye early life history stages. My ﬁeld research has provided the
opportunity to examine walleye year—class strength development across a broad range
of environmental extremes in terms of physical and biological habitat characteristics
which led to large interannual differences in walleye year-class strength. My data
reveal important repeatable patterns that occur during walleye early life history
ontogeny that play important roles in structuring walleye year-class strength. In this
dissertation synthesis, 1 will describe these repeatable patterns and discuss the
linkages between physical and biological processes that inﬂuence walleye early life
history vital rates in western Lake Erie and how these events structure walleye year-
class strength.

Lake Erie supports the world’s largest naturally reproducing population of

walleye. Spawning stock size ﬂuctuated between 46.8 (1994) and 70.8 (1998) million

110

 

ﬁsh during the course of my study. The l7-year long-term average stock size is about
65.6 million ﬁsh (Lake Erie Walleye Task Group 1999). Early studies on Lake Erie
walleye found a weak relationship between walleye stock size and year-class strength
but concluded that spring water warming rate was positively correlated to recruitment
(Busch et al. 1975). More recent population modeling work revealed a stronger
stock-recruitment relationship by including prey abundance in fall prior to spawning
(especially age-0 gizzard shad abundance) and spring water warming rate into the
stock recruitment model (Madenjian et al. 1996). Madenjian et al. (1996) were able
to explain 92% of the variation in recruitment of age-2 walleye between 1981 and
1993 with their model. Their results support the hypothesis proposed by Henderson
and Nepszy (1994) that mature females needed adequate lipid reserves during the
winter to spawn the following spring. While these studies were able to relate spawner
characteristics and condition to recruitment on a lake-wide basis, they provide little
insight about the dynamics of year-class formation of speciﬁc spawning stocks in the
lake.

The Lake Erie walleye population is composed of many discrete spawning
stocks (Stepien 1995), some of which spawn in different rivers and reefs in the east,
central, and western basins of the lake (Regier et al. 1969, Hatch et al. 1987). Due to
the large geographic expanse of Lake Erie, different spawning areas can be exposed to
different environmental conditions within a given year which affect year-class
development of the different stocks. While exact proportions are unknown, there is
consensus among researchers and ﬁsheries managers that the majority of walleye

spawning occurs in the western basin of the lake, either in tributary rivers or on

111

midlake reefs (Hatch et al. 1987, Knight 1998). Research conducted by scientists at
Ohio State University and Ohio DNR in the Maumee and Sandusky rivers concurrent
with the ﬁrst 2 years of my study revealed a signiﬁcant negative relationship between
river discharge and indices of fall walleye year-class strength in western Lake Erie
(Mion et al. 19998). Years with high levels of precipitation resulted in high river
discharge and low larval walleye abundance and survival rates. Further, Mion et al.
found a strong positive relationship between peak larval walleye abundance in rivers
and indices of walleye year-class strength in fall with the highest values occurring in
1994 and the lowest in 1995, similar to what I observed for reef-spawned ﬁsh in those
same years.

Walleye typically spawn earlier in the Maumee and Sandusky rivers than on
reefs in western Lake Erie. The peak larval walleye out-migration period in the rivers
occurs between mid-April and early May (Mion et al. 1998) usually coinciding with
the peak spawning and egg incubation period on reefs. Therefore, because walleye
life history stages most vulnerable to physical processes associated with storms
overlap in time (larvae in rivers, eggs on reefs), spring storms occurring over the
western basin can limit survival in both river and reef habitats simultaneously. The
same spring storms that produce high winds creating strong wave and current action
on the reefs also typically deposit precipitation in the surrounding watershed
increasing discharge in tributaries.

This was indeed the case in 1995, when storms were prevalent and
precipitation was high in April and early May (> 13 cm; NCDC 2000), larval

abundance was low in rivers (Mion et al. 1998), larval abundance was low throughout

112

 

 

the western basin, and the fall index of walleye year-class strength was low. In
contrast, the April 1998 storm occurred at a time in the month when spawning activity
on reefs was high but before hatching and out-migration of larvae in rivers likely had
peaked. Therefore, the April 1998 storm likely had no effect on larval survival in the
Maumee River. I observed a moderately high mean larval abundance in the western
basin in 1998 and the fall index of year-class strength was also above average despite
the loss of eggs from the reefs due to the April storm. Based on my observations of
larval abundance and distribution in western Lake Erie, I postulate that years like
1998 that experienced poor recruitment from one source (reefs) may be buffered by
good recruitment from the other source (tributaries) and 1998 appears to be one of
those types of years. In support of this argument, catches of walleye larvae were
consistently higher at sites near Maumee Bay in 1998; over 90% of all walleye larvae
collected in 1998 were captured at 6 sites adjacent to Maumee Bay. My hypothesis
relies on the assumption that reef spawned larvae were not transported via lake
currents to these sites near Maumee Bay. Unfortunately, information on water
currents with resolution adequate to estimate larval drift patterns in spring is not
presently available.

Eggs on reefs are vulnerable to storms. In years like 1995, when many storm
events occurred, there was a cumulative effect of egg loss from the reefs reducing egg
abundance and survival. In 1998, however, the reefs experienced few storm events
but the timing and magnitude of the storms was critical. Walleye began spawning on
reefs earlier than usual in 1998 due to early ice-out and warm temperatures during

March. I collected the ﬁrst eggs on March 23, 1998 and by the ﬁrst week of April

113

 

 

egg numbers were comparable to those observed in mid-April in previous years.
Because a large portion of the total spawning stock had already spawned on the reefs
by this time, the catastrophic storm event that occurred between April 8 and 10
removed a large portion of reef-spawned eggs limiting the production of walleye from
reef habitats in 1998.

Early in the spawning season I observed the highest numbers of eggs on
shallow sites on reefs. As incubation progressed, egg numbers declined at shallow
sites and were generally more abundant at deep sites. For example, in 1998 over 80%
of the eggs were collected from shallow sites on the reefs before the storm while only
19% of the eggs were collected from shallow sites after the storm. The substrate at
the shallow summits of reefs is typically smoother with less complexion than deeper
sites, especially for the shallowest of reefs (Herdendorf and Braidech 1972) allowing
eggs to be removed by currents more easily than from deep sites. Wave energy
models developed by physical limnologists indicate that shear stress, the amount of
energy necessary to move bottom particles, decreases with depth (Miller et al. 1977).
Thus, we would expect egg removal to be inversely related to depth.

Years with a high frequency of spring storms also typically have low water
warming rates. My results support those of Allbaugh and Manz (1964) and Busch et
al. (1975) who observed slower water warming rates in years when spring storms
were prevalent. In my study, the highest frequency of spring storms occurred in 1995
and this year also had the lowest water warming rate. Conversely, spring storms were
infrequent in 1994 and 1998, years when waters warmed quickly. The index of fall

walleye abundance never exceeded 5 ﬁsh per hour of trawling when waters warmed at

114

 

 

a rate less than 0.2 °C/day but greatly exceeded that number at higher warming rates
indicating that 0.2 °C/day may be a critical minimum threshold warming rate for
walleye egg survival in western Lake Erie. As I explained in greater detail in the
previous chapter, faster water warming rates promote egg and larval survival by
decreasing the period of time these life history stages are vulnerable to mortality
caused by storms, disease, and predation.

Slow water warming rates during egg incubation and pelagic larval periods
prolong the duration that these life history stages are exposed to predation. While
predation can have substantial effects on the year-class development of some ﬁshes
GBailey and Houde 1989), it is difficult to determine the magnitude of predation on
walleye eggs and larvae in western Lake Erie. While my study and that of previous
researchers on western Lake Erie reefs documented that ﬁsh consumed walleye eggs
(Wolfert et al. 1975), these studies were unable to determine the magnitude of egg
predation as a source of mortality due to a lack of information concerning the
abundance of egg predators. Both studies were able to identify what ﬁshes were
present on the reefs during walleye egg incubation periods and how many eggs these
ﬁshes consumed. Both studies documented an increase in predator abundance over
the course of the egg incubation period. These studies concluded that the longer the
eggs incubated on the reefs, the greater the potential for predation. Fast water
warming rates reduce incubation periods and shorten the time that eggs are vulnerable

to mortality agents such as predation.

115

 

 

Water temperature also has signiﬁcant consequences for walleye during the
pelagic larval period. Studies have shown that walleye larvae have higher gas bladder
inﬂation rates, higher prey consumption and assimilation rates, faster swimming
speeds, faster growth rates, and higher survival rates in warmer waters than in cold
waters (Clapp et al. 1997, Regier and Summerfelt 1999, Trometer and Busch 1999).
My results show that walleye larvae become concentrated in shallow nearshore areas
of western Lake Erie after hatching in each year of my study. These nearshore areas
have different limnological characteristics than offshore areas. My data indicate that
nearshore waters are generally warmer and darker (more turbid) than offshore waters
and thereby provide better nursery habitat for developing age-0 walleye. Because
growth of ﬁsh is temperature-dependant, warmer nearshore areas are conducive to
faster growth rates for larval walleye than cooler offshore waters. Unfortunately, I
collected few walleye larvae at offshore sites and catches were inconsistent providing
me with no means to estimate growth rates for ﬁsh at offshore areas of my study area.
My data from nearshore sites does provide a comparison of growth rates between
years and shows that walleye grow faster in years with warmer waters. Faster growth
of age-0 walleye moves ﬁsh through the size-speciﬁc predatory gauntlet faster,
thereby reducing the potential for predation and other mortality agents that can occur
during vulnerable early life history stages.

Productivity of prey resources is also generally higher in warmer waters than
cooler waters (Wetzel 1975) providing ﬁsh with an additional growth advantage by
inhabiting areas with warmer waters. My data indicate that zooplankton usually had

higher densities were generally higher at nearshore sites during late April and May

116

 

 

when walleye are zooplanktivorous (Roseman 1997). lchthyoplankton prey were also
generally more abundant in nearshore areas in June when age-0 walleye switch from
eating zooplankton to ﬁsh (Roseman 1997). Coinciding with the switch in diet from
zooplankton to ﬁsh, I observed age-0 walleye to become demersal between 25 and 30
mm TL, typically occurring by mid-June in each year of my study. Once walleye
become demersal, the young ﬁsh disperse throughout the western basin and follow
schools of baitﬁsh into deeper waters of the central and eastern basin of the lake in the
fall (Regier et al. 1969, Knight and Vondracek 1993). Walleye generally return to
natal spawning sites in the western basin as mature adults at age-3 (Muth and Ickes
1993)

Nearshore waters were also generally more turbid than offshore waters in all
years of my study. As I discussed in greater detail in Chapter 1, larval and juvenile
walleye are known to perform better in darker waters. Laboratory studies have shown
that larval walleye had faster swimming speeds, faster growth, improved gas bladder
inﬂation, and higher survival rates in darker waters (Bristow et al. 1996, Regier and
Summerfelt 1997). In western Lake Erie, nearshore waters are darker due to the
mixing action of lake waters against the shoreline and the input of suspended

sediments from tributaries (Burns 1985).

Management Implications

Water levels in western Lake Erie show natural ﬂuctuations during spring due
to seiche activity associated with storms (Gedney and Lick 1972, Burns 1985).

Further, a declining trend in lake water levels has been observed over the past three

117

 

 

years (Army Corps of Engineers 2000). Lower water levels increase the amount of
reef surface area exposed to high-energy wave and current action. My research
indicates that wave and current action can displace eggs from favorable incubation
areas decreasing egg abundance and increasing mortality. While natural ﬂuctuations
in lake water levels will occur due to variable precipitation and evaporation rates in
the Great Lakes basin, resource managers need to consider the implications of low
water levels in regard to ﬁsh habitat before initiating plans that would further reduce
water levels in Lake Erie (large scale withdrawals, dams, canals).

Additionally, my research on egg distribution on reefs provides important
information useful in creating new spawning shoals. Walleye eggs were observed in
high abundance on the tops of reefs suggesting that the majority of spawning takes
place over the shallowest points on the reefs, typically < 5 m. Eggs were subsequently
washed off the tops off the reefs and deposited at deeper sites on reefs or in
surrounding areas, depending on the severity of the wave and current energy that
removed them. Artiﬁcial reef construction should consider this fact and possibly
construct reefs with wide peripheral margins of porous substrate (such as cobble) at
deeper depths surrounding the summit to catch eggs that wash off the peak of the
reefs. Further, reefs should be positioned to avoid strong wind and wave activity
associated with storms that could remove eggs from incubation sites. Lastly, the reef
should be located in an areas where lake currents will transport emerging larvae to
favorable nursery areas.

My research identiﬁed that nearshore coastal areas in western Lake Erie are

important as nursery habitat for ﬁsh and emphasizes the need to restore and protect

118

 

 

 

these areas. Speciﬁcally, areas such as Potters Pond (larval sampling site 4, Appendix
1) and Metzger Marsh in 1994 (see Roseman 1997) that are/were embayments from
the main portion of the basin proved to be exceptionally important nursery areas for
larval ﬁsh. I consistently observed the highest densities of larval ﬁsh at these areas
and sites adjacent to them. Metzger Marsh was dyked off from the main lake basin
between fall of 1994 and the spring of 1995. I continued to sample outside of the
dyke and still collected large numbers of larvae, but the quantity of the habitat was
greatly reduced and the natural coastal processes (currents, sediment movements,
thermal regime; Bowden 1983) were modiﬁed. Much of the shoreline in western
Lake Erie has been reinforced with hard materials to prevent erosion and act as ﬂood
control. This armoring of the shoreline removes the natural land/water interface and
interferes with lacustrine processes responsible for structuring the limnological
characteristics of nearshore waters important as nursery habitat for walleye and other
ﬁshes. Coastal zone planners should consider the biological value of these coastal
areas and their associated natural processes. Efforts should be devoted to
reconstructing natural hydrologic patterns to facilitate the continued restoration of
Lake Erie and its ﬁsheries.

History has shown that management decisions for one species can have
reverberating effects throughout aquatic ecosystems, as we have seen with the
walleye population and ﬁsh community in Lake Erie (Knight and Vondracek 1993,
Koonce et al. 1999, Nicholls 1999). The continued rehabilitation and future
sustainability of our ﬁshery resources depends on the application of new information,

such as I have presented in this dissertation, towards a holistic ecosystem

119

 

 

management approach (Ferreri et al. 1999). My work has provided a detailed account
of factors contributing to the development of six walleye year-classes, emphasizing
the role of physical processes in mediating walleye early life history vital rates that
added to the instability of the population. While I do not propose that physical
processes are more important than biological processes in determining the vital rates
of walleye eggs and larvae or structuring year-class strength, I do contend that
physical processes create the environment in which biological processes occur.
Further, I agree with Walters and Collie (1988) that research efforts should not focus
solely on examining physical processes but rather should involve multidisciplinary
approaches that examine the ecological linkages through which environmental
variability inﬂuences the vital rates of ﬁsh populations, as I have attempted to do

here.

120

 

 

 

 

APPENDICES

121

 

Appendix 1. Coordinates (decimal degrees) of western Lake Erie reef sampling sites

for 1996 — 1999.

Reef
Cone
Crib
Locust
Niagara
Round
Toussaint

83.046333
83.008833
83.065467
82.975050
82.987383
83.016667

122

Longitude Latitude

41.666817
41.646400
41.645867
41.664533
41.618550
41.631667

Appendix 2. Coordinates (decimal degree) for larval sampling sites in western Lake

Erie, 1996 - 1999.

She

wwwNNNNNNNNNN—t-A—s—t—t-A-s—s-s-A
N-socoooucnoi:wNAocomxrmm:wN—so‘°°°“°’m1*“N4

Long

83.40000
83.35000
83.33333
83.30000
83.30000
83.30000
83.22500
83.22500
83.22500
83.22500
83.12500
83.12500
83.12500
83.12500
83.06333
83.05000
83.01667
83.00833
83.04167
83.04167
83.04167
82.93500
82.93500
82.93500
82.91667
82.91500
82.93500
82.88333
82.84667

82.8583
82.86667
82.88333

123

Lat

41.72500
41.70000
41.73333
41.68000
41.70000
41.72167
41.64167
41.65167
41.68000
41.72167
41.53333
41.55000
41.66667
41.72167
41.59167
41.60000
41.63167
41.64667
41.64667
41.70000
41.73333
41.52000
41.54167
41.60833
41.65000
41.59333
41.73333
41.70000
41.63833

41.603
41.53833
41.53833

 

 

 

Appendix 3. Use of a geographic information system in identifying patterns during
walleye early life history stages in western Lake Erie.

Geographic information systems (GIS) are quickly becoming a popular tool to
analyze ﬁsheries data. The most common ﬁsheries-related uses of GIS include
mapping and modeling ﬁsh distributions and aquatic habitats and evaluating the
effects of watershed land use on aquatic communities and habitat (Stanbury and Starr
1999, Fisher and Toepfer 1998). The use of GIS in my analysis, while initially a
large undertaking to organize and format the data for the software, yielded a faster
and more easily interpretable product than the visual analysis methods I employed in
my thesis (Roseman 1997). GIS is a useful tool to examine ﬁsh population
demographics in relation to habitat features that affect their life histories. I found it
easier to summarize my large dataset and view trends in attributes across the large
spatial expanse of my sampling area as well as across temporal scales within and
between years.

While I treated all of the data in my GIS as discrete point samples in my
analysis, statistical kriging routines do exist that allow the interpolation of point data
into continuous contoured surfaces (Little et al. 1997). Most kriging routines assume
that there is a continuous rate of change in attribute values between points and some
software platforms allow the user to input their own statistical algorithm. These
methods construct statistically optimal predictions for data at unobserved locations
using a relatively small spatially explicit sample with low resolution (Oliver and
Webster 1990, Little et al. 1997). Data that I collected on water temperature and

water clarity most likely conform to this assumption because they usually change at a

124

gradual rate from one sampling site to the next. Biological data such as ﬁsh and
zooplankton densities do not typically conform to these assumptions. Fish and
zooplankton typically have patchy distributions with discrete areas of high and low
density (this study, Patalas and Salki 1992). These types of distributions would have
abrupt changes in their values between sampling points which would violate the
assumption of a smooth or continuous rate of change between sites.

An interesting ﬁeld study would be to sample ichthyoplankton and
zooplankton at small spatial intervals throughout a grid to assess the degree of change
in their density through space. The spatial interval between sampling points would
determine the resolution of the data (10 m, 100 m, 1,000 111, etc.). Such ﬁne-scale
distribution information would be useful in developing a kriging algorithm based on
known rates of change between points. Implementing this type of sampling design in
areas with consistent densities should not be necessary, such as the offshore regions
of my study area where walleye densities were consistently low. A more useful
application of this design would be to begin the sampling in a nearshore zone where
we know densities are high and extend the sampling grid towards offshore points.

Spatial modeling and data management using GIS will become increasingly
important as ﬁsheries management principles move from single-species scenarios to
ecosystem and watershed paradigms. GIS is rapidly becoming a standard method in
solving ﬁsheries management problems. The ﬁsheries management agencies
responsible for managing the Lake Erie ﬁsh community are presently incorporating
the ArcView system as one of their analysis tools. The GIS I developed using my

larval ﬁsh and habitat data will serve as a uniform data model for the development of

125

the Lake Erie ﬁsh community GIS. This GIS will include all historic ﬁsheries
assessment and habitat data concerning the Lake Erie ﬁsh community (Personal
communication, R. Knight, Ohio DNR, Sandusky Fisheries Unit, Sandusky, OH) and
be useful in developing management plans that facilitate the rehabilitation and
sustainability of Lake Erie ﬁshery resources. Additionally, my data will be in a format
that will make it possible for other researchers to directly incorporate into their work
for comparative analysis and further ﬁeld sampling, highlighting the value of GIS in
providing a level of coordination and continuity important for cooperative

multidisciplinary research.

126

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127

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