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dissertation entitled

CHANGES IN GROWTH, CONDITION, FECUNDITY, AND
EGG LIPID CONTENT OF LAKE WHITEFISH IN THE UPPER
GREAT LAKES BETWEEN 1986-87 AND 2003-05

presented by

Jud Fisher Kratzer

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CHANGES IN GROWTH, CONDITION, FECUNDITY, AND
EGG LIPID CONTENT OF LAKE WHITEFISH IN THE UPPER
GREAT LAKES BETWEEN 1986-87 AND 2003-05
By

Jud Fisher Kratzer

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

2006

ABSTRACT
CHANGES IN GROWTH, CONDITION, FECUNDITY, AND
EGG LIPID CONTENT OF LAKE WHITEFISH IN THE UPPER
GREAT LAKES BETWEEN 1986-87 AND 2003-05
By
Jud Fisher Kratzer

Lake whitefish (Coregonus clupeaformis) support the single largest and most
valuable commercial fishery in the Laurentian Great Lakes. In recent years, fishery
managers have reported declining growth and condition of lake whitefish in the upper
Great Lakes. Proposed causes of the observed declines in individual growth rates include
changes in: l) lake Whitefish density, 2) food quality and abundance, 3) population
genetics, and 4) climatic conditions. I evaluated the relationships between each of these
factors and lake Whitefish growth in selected regions of the upper Great Lakes (i.e., Lakes
Michigan, Huron, and Superior). I found that lake Whitefish growth declines began with
the development of a very strong 1991 year class due to favorable climatic conditions,
leading to density dependent growth dynamics, which were exacerbated by a dramatic
decline in the high-energy, benthic prey item (Diporeia spp.) toward the latter part of the
1990’s.

Additionally, I described the changes in lake Whitefish growth, condition,
fecundity, egg lipid content, and total ovary lipid content in selected regions of the upper
Great Lakes in 1986-87 and 2003-05, two time periods with different lake Whitefish and
diporeia densities. Lake whitefish grew more slowly in 2003-05 than in 1986-87 at all
sites. The condition of these fish was also generally lower during 2003-05. Under

conditions of high lake Whitefish density and low diporeia density, female lake Whitefish

generally produced fewer eggs. Individual egg lipid content, however, increased at all
sites from 1986-87 to 2003-05, regardless of changes in lake whitefish or diporeia
densities. I found that total ovary lipid content and lake whitefish abundance were
inversely related, while there was no significant relationship between total ovary lipid
content and diporeia density.

Growth, condition, and egg production of lake Whitefish is lower now than it was
20 years ago at most of the sites studied. This study provides evidence that growth of
lake Whitefish in these regions of the upper Great Lakes is influenced by the abundance
of young lake Whitefish that are not yet recruited to the fishery and that condition and
total ovary lipid content are more strongly affected by lake Whitefish abundance than by
diporeia density. Despite recent changes to the Great Lakes foodweb that have occurred
as a result of dreissenid mussel invasion, managers may be able to use harvest regulations
that result in reduced lake Whitefish densities to increase lake Whitefish condition, which
should result in a plumper, more marketable fish, and to increase total ovary lipid
content, which should benefit reproductive dynamics. Fisheries managers likely have
less control over lake Whitefish growth because growth rate appears to be more
influenced by the abundance of pre-recruits, which can not be readily manipulated by

managers, as their abundance is largely determined by density independent factors.

ACKNOWLEDGMENTS

This research was funded by the Michigan Agriculture Experiment Station. I
thank the MSU Graduate School, and Dean Karen Komplarens in particular, for awarding
me a University Distinguished Fellowship.

I thank my advisor, Dr. William Taylor, for his outstanding mentoring. As the
chair of the Fisheries and Wildlife Department and an important figure with so many
responsibilities, he is a very busy man, but he always made time for me when I needed it.
Without his guidance, the quality of this dissertation would have suffered tremendously.
He also provided me with many good memories of fishing trips on the Old Grin.

I thank Dr. Daniel Hayes, Dr. Michael Jones, Dr. Doran Mason, and Dr. Richard
Merritt for serving on my committee and for there many helpful comments and
suggestions that helped to improve this dissertation.

I thank Matt Altenritter, Kim Berry, Pete Datema, and Krista Ecklin for their
assistance in the lab.

I thank Nathan Nye for his assistance during the field season. I will always
remember our duck hunting excursions and the time that the horses tried to eat the truck.
I also thank Greg and Karen Wright (Chippewa/Ottawa Resource Authority) for
providing me a place to stay during the field season.

I thank Mark Turner (Ohio Department of Natural Resources) for providing the
data for the 1986-87 time period, without which chapters three and four would have been
impossible. I also thank Mark Ebener (Chippewa/Ottawa Resource Authority) for

helping me to obtain samples of fish from the commercial fishery and for providing data.

Tom Goniea (Michigan Department of Natural Resources), Steve Lozano (Great Lakes
Environmental Research Lab), Tom Nalepa (Great Lakes Environmental Research Lab),
Erik Olsen (Grand Traverse Band of Ottawa and Chippewa Indians), and Aaron Woldt
(US Fish and Wildlife Service) also provided data and samples, and I thank them for it.

I also thank the members of the Taylor/Hayes lab for their support, help, and
friendship over the past few years.

Most importantly, I thank God for the successful completion of this dissertation.
The only reason I am alive today is because of His amazing grace, and He has blessed me
so abundantly during the past nearly four years of my life at Michigan State University.

None of this dissertation would be possible without Him.

TABLE OF CONTENTS

LIST OF TABLES ................................................................................. viii
LIST OF FIGURES .................................................................................. x
CHAPTER I
INTRODUCTION TO THE DISSERTATION: LAKE WHITEFISH PRODUCTION
DYNAMICS IN THE UPPER GREAT LAKES ................................................ 1
References .................................................................................. 12
CHAPTER 2
FACTORS AFFECTING GROWTH OF LAKE WHITEFISH IN THE UPPER
LAURENTIAN GREAT LAKES ................................................................. 17
Abstract ...................................................................................... 18
Introduction ................................................................................. l 9
Methods and Materials ..................................................................... 23
Study Sites ......................................................................... 23
Data Sources ....................................................................... 23
Evaluation of Factors Affecting Lake Whitefish Growth .................... 26
Results and Discussion .................................................................... 28
Climate Variables and Lake Whitefish Abundance ........................... 28
Food Energy Availability ......................................................... 32
Population Genetics ............................................................... 34
Summary ........................................................................... 34
Acknowledgements ........................................................................ 36
References .................................................................................. 37
CHAPTER 3

CHANGES IN GROWTH, CONDITION, AND LIVER WEIGHTS OF LAKE
WHITEFISH (COREGON US CL UPEAFORMIS) IN THE UPPER LAURENTIAN

GREAT LAKES BETWEEN 1986-87 AND 2003-05 ......................................... 41
Introduction ................................................................................. 4 1
Methods ...................................................................................... 45

Study Sites .......................................................................... 45
Sampling ........................................................................... 45
Results ....................................................................................... 47
Growth .............................................................................. 47
Condition ........................................................................... 49
Environmental Changes ......................................................... 54
Discussion ................................................................................... 54
Conclusion ......................................................................... 58
References .................................................................................. 59

vi

CHAPTER 4
CHANGES IN FECUNDITY AND EGG LIPID CONTENT OF LAKE WHITEFISH
(COREGONUS CLUPEAFORMIS) IN THE UPPER LAURENTIAN GREAT LAKES

BETWEEN 1986-87 AND 2003-05 .............................................................. 62
Abstract ...................................................................................... 64
Introduction ................................................................................. 65
Materials and Methods ..................................................................... 69

Fecundit}I ........................................................................... 70

Egg and Ovary Lipid Content .................................................... 70
Results ....................................................................................... 71
Discussion ................................................................................... 73
Conclusion .................................................................................. 79
Acknowledgements ......................................................................... 80
References ................................................................................... 81

CHAPTER 5

SUMMARY AND MANAGEMENT IMPLICATIONS ...................................... 84
References ................................................................................... 86

vii

LIST OF TABLES

Table 2.1. Average instantaneous fishing mortality (F) from 1976 to 2003, mean fishable
biomass of lake Whitefish from 1990-1999 (EBENER et al. 2005), and diporeia density at
depths less than 60 m for the Lakes Huron and Michigan sites and diporeia density for the
eastern quarter of Lake Superior (T. NALEPA & S. LOZANO, Great Lakes
Environmental Research Lab, NOAA, unpublished data ...................................... 25

Table 2.2. Results of linear regression of growth index on biomass and changes in growth
index between the 1991 and 1998 year classes .................................................. 29

Table 2.3. Ice, wind, and mean May air temperature (°C) conditions during years of low,
moderate, and high recruitment of lake Whitefish as estimated by BROWN et al. (1993).
The long-term average May air temperature was 9.7 °C ....................................... 31

Table 3.1. Estimated lake Whitefish abundances and diporeia densities at the study sites.
Lake Whitefish data were provided by M. Ebener (Chippewa Ottawa Resource Authority,
unpublished data, 2005) and T. Goniea (Michigan Department of Natural Resources,
unpublished data, 2004). Diporeia data were provided by T. Nalepa ( NOAA, Great
Lakes Environmental Research Lab, unpublished data, 2004) and Scharold et al.

(2004) .................................................................................................. 46

Table 3.2. Average age (in years) at which female lake Whitefish reached the minimum
legal length (432 mm) at each site during the two time periods .............................. 48

Table 3.3. Von Bertalanffy growth parameters (K and Lao), their standard errors, and the
number of fish used to back-calculate length at age ............................................ 50

Table 3.4. Direction of change in lake Whitefish and diporeia densities and length-at-age
of fish older than age-7, total weight-at-length, and liver weight-at-length of lake
whitefish between 1986-87 and 2003-05. (Tl indicates changes were not consistent for all
lengths) ................................................................................................ 56

Table 4.1. Egg lipid content (mg per egg) of lake Whitefish collected during the two time
periods with p-values from t-tests ........................................................... 74

Table 4.2. Predicted (ANCOVA) ovary lipid content of a 550 mm fish in 1986-87 and
2003—05 and p-value of time effect in ANCOVA ................................................ 75

Table 4.3. Estimated lake Whitefish abundances and diporeia densities at the study sites.
Lake Whitefish data were provided by M. Ebener (Chippewa Ottawa Resource Authority,
unpublished data, 2005 ) and T. Goniea (Michigan Department of Natural Resources,
unpublished data, 2004). Diporeia data were provided by T. Nalepa ( NOAA, Great
Lakes Environmental Research Lab, unpublished data, 2004) and Scharold et al.

(2004) ................................................................................................. 76

viii

Table 4.4. Direction of change in lake Whitefish and diporeia densities and fecundity, egg
lipid content, and total ovary lipid content of lake Whitefish between 1986-87 and 2003-
05 ....................................................................................................... 78

ix

LIST OF FIGURES

Figure 1.1 Commercial yield of lake whitefish from all Great Lakes combined, 1879-
1999 (data from Baldwin et al. 2000) .............................................................. 2

Figure 2.1. Approximate locations of study sites within the Laurentian Great Lakes: 1)
northwestern Lake Huron, 2) northern Lake Michigan, 3) northeastem Lake Michigan,
and 4) eastern Lake Superior ....................................................................... 24

Figure 2.2. Plots of growth index (sum of the mean weights-at-age for the three youngest
recruited ages) against mean biomass in time. Dates correspond to the first, last, and 1991
year classes ........................................................................................... 29

Figure 2.3. Historical fishing mortalities, averaged for all recruited ages, at each of the
four sites .............................................................................................. 35

Figure 3.1. Map of the Great Lakes with study sites. AL=Alpena, BD=Big Bay de Noc,
BP=Bayport, CB=Cheboygan, GT=Grand Traverse Bay, NB=Naubinway,
WB=Whitefish Bay ................................................................................. 42

Figure 3.2. Von Bertalanffy growth curves for lake Whitefish during the two time
periods ................................................................................................ 51

Figure 3.3. Mean total weight-at-length during the two time periods with p-values for the
time effect in ANCOVA ............................................................................ 52

Figure 3.4. Liver weight-at-length of lake Whitefish during the two time periods with p-
values for the time effect in ANCOVA .......................................................... 53

Figure 4.1. Annual yield of lake Whitefish from selected waters of northwestern Lake
Huron, northern and eastern Lake Michigan, and southeastern Lake Superior 1976 to
2003, all gear types combined ..................................................................... 66

Figure 4.2. Map of the Great Lakes with study sites. AL=Alpena, BD=Big Bay de Noc,
BP=Bay Port, CB=Cheboygan, GT=Grand Traverse Bay, NB=Naubinway,
WB=Whitefish Bay ................................................................................. 67

Figure 4.3. Mean fecundity at length of lake Whitefish collected from the study sites
during 1986—87 and 2003-05 with p-values for time effect in ANCOVA ................... 72

CHAPTER ONE
Introduction to the Dissertation:
Lake Whitefish Production Dynamics in the Upper Great Lakes

Lake Whitefish (Coregonus clupeaformis) are native to northern North America,
with the southernmost portion of their range being the Laurentian Great Lakes (Hubbs
and Lagler 2004). Adult lake whitefish are generally benthivores, eating mollusks,
crustaceans, and insects, but they have been reported to occasionally eat plankton and
small fish (Walden 1964, Ihssen et al. 1981, Pothoven 2005). Lake Whitefish are deep
water fish, preferring to live in 15-50 m of water during much of their life history
(Walden 1964). They migrate to the shallows of lakes or connecting rivers in late October
and November to spawn by broadcasting eggs and milt over gravel or cobble substrate in
less than five meters of water (Hart 1930). As such, they are important integrators of
offshore and nearshore energy dynamics in the Great Lakes.

Lake Whitefish are also important economically in the Great Lakes region.
Currently, this species supports the single largest and most valuable commercial fishery
in the Laurentian Great Lakes, accounting for approximately 40% of total weight and
value of fish harvested from the Great Lakes (Daniels 2003). Lake Whitefish are
harvested using large mesh trap nets and gill nets and must be at least 432 mm in length
(typically age-2 to 4) to be legally harvested in most regions of the upper Great Lakes
(Bence and Ebener 2002). Nearly 11,000 metric tons of lake whitefish were harvested
from all Great Lakes combined in 1879, and yields declined to all time lows in the 19608

and 19703 (Figure 1.1). This decline in lake Whitefish abundance has been attributed to

 

12000

10000- 0 ii

Metric tons

 

2000‘

 

 

 

 

O U U I r I

1875 1895 1915 1935 1955 1975 1995
Year

Figure 1.1 Commercial yield of lake Whitefish from all Great Lakes combined, 1879-
1999 (data from Baldwin et al. 2000).

overfishing, predation on adults by the invasive sea lamprey (Petromyzon marinus),
predation on larvae and competition with larvae by the invasive alewife (A 103a
pseudoharengus) and rainbow smelt (Osmerus mordax), and degradation of water quality
and habitat (Nalepa et al. 2005). Lake Whitefish abundance has since rebounded as a
result of sea lamprey control, better management of the commercial fishery, phosphorus
abatement, and the introduction and recovery of large bodied piscivores, which
suppressed alewife and rainbow smelt numbers and deflected sea lamprey predation away
from lake Whitefish (Cook et al. 2005, Mohr and Ebener 2005, Schneeberger et al. 2005).
Yield of lake Whitefish from Lake Michigan generally increased starting in the 19603,
reaching a peak of nearly 4,000 metric tons in the mid-19903, a yield that was the highest
recorded in over 100 years (Schneeberger et al. 2005). Similarly, in the main basin of
Lake Huron, catch-per-unit-effort of lake Whitefish increased steadily starting in the
19703, peaking in the mid to late 1990’s (Mohr and Ebener 2005).

Although the commercial harvest of lake Whitefish from the Great Lakes
continues to be large, there have been concerns regarding recent declines in growth and
condition of lake Whitefish in parts of the upper Great Lakes. During the 19903, there
were widespread reports from commercial fishermen on Lake Michigan that lake
Whitefish girth was declining, and they were returning legal-length fish to the water
because they were not heavy enough to be marketable (Schneeberger et al. 2005).
Madenjian et al. (2002) reported that lake whitefish growth declined during the 19903 and
that condition factor dropped rapidly from 1995 to 1998 in Lake Michigan. Pothoven et
al. (2001) showed that growth and condition of lake Whitefish in southern Lake Michigan

were lower during 1992-1999 than during 1985-1991. In Lake Huron’s main basin,

growth and condition of lake Whitefish have declined over the past 10 to 15 years (Mohr
and Ebener 2005). Several possible causes of these declines in grth and condition
have been suggested, including changes in lake Whitefish population abundance, climate
change, changes in the composition and quality of the food-web, changes in population
genetics, and parasitism or disease (Law 2000, Conover and Munch 2002, Nalepa et al.
2005).

The density of lake Whitefish has been found to affect their grth and condition
through intraspecific competition for food. More fish in an area means less food
available for each individual fish, which can cause decreased growth and condition (Van
Den Avyle and Hayward 1999). Healey (1980) and Mills et al. (1995) experimentally
subjected lake whitefish populations to different levels of exploitation, and demonstrated
that growth increased as population densities decreased. Bidgood (1973) and Henderson
et al. (1983) also reported density dependent growth of lake whitefish. Density
dependence has been cited as at least part of the reason that lake Whitefish growth and
condition have declined in Lakes Michigan and Huron (Schneeberger et al. 2005, Mohr
and Ebener 2005).

Climate change has also been implicated as a possible cause of decreasing lake
Whitefish growth and condition because climate influences year class strength, which in
turn affects growth and condition though density dependent mechanisms. Year class
strength of lake Whitefish is strongly dependent on weather conditions during spawning,
egg incubation, and larval stages. Freeberg (1985) noted that year class strength was
much higher when ice formed over spawning beds before the first winter storms

(generally by late December) and hypothesized that strong wind generated currents that

destroyed developing eggs in suboptimal habitats on the spawning grounds. Ice generally
begins to melt by mid- to late March in the upper Great Lakes (Asse12003). In years that
experience rapid warming in the spring, investigators reported the development of
relatively large year classes; a function of increasing available food for newly hatched
larval lake Whitefish, which was hypothesized to increase the growth and survival at this
life history stage (Brown et al. 1993).

Recently, research scientists have also hypothesized that a possible cause of
decreased growth and condition of lake Whitefish is the changing Great Lakes food-web,
in particular recent declines in Diporeia spp. Diporeia are crustaceans belonging to the
order Amphipoda (Nalepa et al. 2000). Maximum diporeia densities occur between 30
and 70 m of depth, where they live on and in the bottom sediments of deep, cold lakes
and feed on diatoms and organic particles that sink to the lake bottom (Dermott and
Kerec 1997, Nalepa et a1. 1998, Lozano et al. 1999, Dermott 2001, Dittman and Owens
2001, Lozano et al. 2001, Nalepa et al. 2001a, Nalepa et al. 2001b, Pothoven et al. 2001).
By eating organic matter that settles from the pelagic regions of lakes and by serving as
prey for fish, diporeia has historically represented a major link between pelagic primary
production, the benthos, and upper trophic levels (Madenjian et al. 2002, Scharold et al.
2004). Benthic biomass production in the upper Great Lakes has historically been
dominated by diporeia (Cook and Johnson 1974), which have been reported to be a
significant component of the lake Whitefish diet in this region (Pothoven et al. 2001,
Pothoven 2005).

Diporeia abundance has declined in all Great Lakes except Lake Superior over the

past decade, and a likely explanation is food limitation brought on by competition with

the invasive dreissenid mussels (Nalepa et al. 2005). Zebra and quagga mussels
(Dreissena polymorpha and D. bugensis) are natives of the Ponto-Caspian region and
were introduced into the Great Lakes via the ballast water of commercial shipping vessels
(Vanderploeg et a1. 2002). Dreissenid mussels filter algae from the water column, and it
has been hypothesized that as algal consumption by dreissenid mussels increases, the
quantity of settled algae available for diporeia consumption decreases, leading to
decreased diporeia production (Lozano et al. 2001, Dermott 2001, Vanderploeg et a1.
2002, Nalepa et al. 2005). During the 19903 diporeia have declined while dreissenids
have increased in Lake Erie (Dermott and Kerec 1997), Lake Ontario (Lozano et al.
1999, Dermott 2001, Dittman and Owens 2001 , Lozano et al. 2001), Lake Michigan
(Nalepa et al. 1998, Nalepa et al. 2001a, Pothoven et al. 2001), and Lake Huron (Nalepa
et al. 2001b). Many parts of the Great Lakes are now totally devoid of diporeia, which
historically occurred at densities of over 10,000/m2 in some areas (N alepa et al. 2005, T.
Nalepa, Great Lakes Environmental Research Lab, unpublished data).

Declines in the biomass of the relatively energy rich diporeia (4,429 J/g wet mass)
and increases in the biomass of the relatively energy poor dreissenid mussels (1,047-
2,478 J/g wet mass of sofi tissue) have been hypothesized to have lowered the quality of
the lake whitefish diet (Schneider 1992). Changes in lake Whitefish diet have been
demonstrated near Muskegon, Michigan (Lake Michigan), where diporeia nearly
disappeared between 1998 and 2000, and the proportion, by weight, of lake Whitefish diet
comprised by diporeia fell from 70% to 25% (Pothoven et al. 2001). With fewer diporeia
available, lake Whitefish shified their diet to include dreissenid mussels and other lower

energy prey (e.g., chironomids, zooplankton), resulting in decreased individual somatic

growth of these fish. Pothoven (2005) discovered a similar trend in small (<430 mm)
lake whitefish during the late 1990’s in southeastern Lake Michigan, where diporeia went
from 57% to 1% (dry weight) of their diet. In shallow (< 60 m) waters of Lake Ontario,
lake Whitefish diet shifted to include more dreissenids, sphaeriids, and Mysis relicta
following the loss of diporeia (Owens et a1. 2005). In Lake Huron and Lake Ontario,
fishing effort for lake Whitefish has shifted further offshore (Hoyle 2005, Mohr and
Ebener 2005). For example, in one region of southern Lake Huron, average fishing depth
increased from 30 m in 1992 to 61 min 1999, where diporeia still exist, although in
reduced numbers (Mohr and Ebener 2005). The shifting of fishing effort to deeper
waters suggests that the fish have shifted to deeper waters, possibly in response to loss of
diporeia in nearshore areas due to the establishment of dreissenids in those areas (Hoyle
2005, Mohr and Ebener 2005).

Delines in diporeia have been associated with declines in growth and condition of
lake whitefish in regions of the Great Lakes. For instance, decreases in growth and
condition of lake Whitefish were at least partially attributed to declines in diporeia
abundance in Lake Ontario and Lake Michigan (Pothoven et al. 2001, Hoyle 2005,
Schneeberger et al. 2005). Researchers noted a 53% decrease in lipid content of lake
Whitefish in Lake Michigan between 1983-1993 and 1996-1999, which they attributed to
decreases in diporeia abundance (Wright and Ebener 2006). Growth and condition of
lake Whitefish, however, have remained high in Lake Erie, despite the total disappearance
of diporeia, presumably because these fish are able to feed heavily on an abundant and

diverse benthic invertebrate community (Cook et al. 2005).

Potential changes in the genetic make-up of lake Whitefish pOpulations have also
been implicated in the changes noted in the individual growth of lake Whitefish over the
past decade. During the 1990’s, the harvest of lake whitefish was at all time highs in
many parts of the Great Lakes (Nalepa et al. 2005). It has been documented in other fish
species that intense fishing efforts through many generations of fish can exert powerful
selective forces that can have lasting effects on the genetics of fish populations, resulting
in slower individual growth rates (Law 2000, Conover and Munch 2002). The proposed
mechanism for this phenomenon is that faster growing fish are harvested more heavily
because they reach the minimum length of the fishery more quickly than slower growing
members of their cohort, thus reducing the probability that the faster growing fish will
reproduce before being harvested. This ultimately leaves predominately slower growing
fish to spawn and produce offspring that on the average exhibit slower growth than
before the fishery exerted heavy mortality pressures on the population. Such a
phenomenon was demonstrated by Conover and Munch (2002), who experimentally
harvested large, fast growing fish from a population ofMem'dia menidia, which
eventually led to lower yields and slower growth of individuals because the “fishery”
severely reduced the faster growing genotypes. The commercial lake Whitefish fishery
that has existed on the Great Lakes since the early 18003 (Brown et a1. 1999) would tend
to remove faster growing individuals from the population and could potentially result in
slower growing fish being more likely to pass their genes on to succeeding generations.
As such, if the fishery has been causing a change in lake Whitefish genetics, the expected

outcome would be a reduction of growth rate through time.

Decreases in growth and condition of lake Whitefish could also affect other
aspects of their population dynamics, such as the number of eggs produced or the amount
of energy incorporated in each egg, both of which are important to development of year
class strength in lake Whitefish (Brown and Taylor 1992). Fecundity is clearly related to
fish grth because larger fish have the capacity to produce more eggs (Bell et al. 1977,
Jude et al. 1987, Smale 1988). Fish with higher quality (more energy dense) diets
produce higher quality (more energy dense) eggs (Leray et al. 1985, Hardy et al. 1990,
Corraze et al. 1993). Eggs with larger lipid stores provide more energy to developing
larval fish, which allows for faster somatic grth and a longer time before larval fish
must begin consuming prey (Brown and Taylor 1992). A key point in the early life
history of fish occurs during the critical period, when larval fish switch from endogenous
to exogenous food (Cushing 1990). In lake Whitefish, this critical period generally occurs
approximately 20 days after they hatch in mid-March to mid-April (Freeberg et a1. 1990).
During the egg and early larval stages, the developing fish depends on endogenous
energy, which is stored as yolk by the mother. Once this endogenous food supply is
expended, larval fish must switch to eating exogenous food, such as zooplankton (Taylor
and Freeberg 1984). Thus, sufficient exogenous food of the right size and nutritional
value is critical for larval survival (Brown and Taylor 1992). Weather conditions often
determine year class strength in lake Whitefish because warm spring conditions allow for
high abundances of zooplankton, which are needed when the larval fish expend their
endogenous energy stores (Brown et al. 1993). Larvae from larger, more yolk-filled,
eggs have a survival advantage because they are able to survive longer before they need

to switch to exogenous food, and more food is available to them because of their larger

size, which enables them to consume a wider size range of food and a faster swimming
speed to find their prey and to avoid predators (Miller et al. 1988, Brown and Taylor
1992). Decreases in lake Whitefish reproductive success, as measured by year class
strength, were associated with the disappearance of diporeia in Lake Ontario, presumably
because changes in the food-web reduced the quality of the lake Whitefish diet, resulting
in reduced nutritional status and egg quality (Hoyle 2005).

The overall goal of this research was to describe the changes in growth, condition,
fecundity, and egg and ovary lipid content from 1986-87 to 2003-05 in seven regions of
the upper Great Lakes and to relate these changes to changes in lake Whitefish
abundance, diporeia abundance, population genetics, and climatic conditions. My
dissertation consists of 5 chapters, including this introduction and a summary. In chapter
two, I evaluate the possible causes for the noted changes in lake Whitefish grth
dynamics in the upper Great Lakes. My objectives for this chapter were to assess the
effects of lake Whitefish abundance, diporeia abundance, population genetics, and
climatic conditions on lake Whitefish individual growth in four regions of the upper Great
Lakes which differed in lake Whitefish abundance, food energy availability, and fishing
mortality over time. In chapter three, I specifically describe the changes in lake whitefish
growth and condition between 1986-87 and 2003-05 in my study areas. The objectives of
this chapter were to evaluate the changes in length-at-age, body weight-at-length, and
liver weight-at-length in seven regions of the upper Great Lakes that exhibited different
combinations of changes in lake Whitefish and diporeia densities, in order to ascertain the
relative importance of the influence of lake Whitefish and diporeia abundances on growth

and condition of lake Whitefish. In chapter four, I describe changes in the reproduction

10

dynamics of lake Whitefish in seven regions of the upper Great Lakes between 1986-87
and 2003-05. Specifically, 1 evaluated the changes in fecundity, egg lipid content, and
total ovary lipid content of lake Whitefish in my study areas, where lake Whitefish and
diporeia densities have changed during the past 20 years. In chapter five, I summarize
the key findings of my research and make suggestions for enhanced management of this

fishery in the future.

11

REFERENCES

Assel, R. 2003. NCAA Atlas: An Electronic Atlas of Great Lakes Ice Cover
Winters: 1973 — 2002. http://www.glerl.noaa.gov/data/ice/atlas/.

Baldwin, N. A., Saalfeld, R. W., Dochoda, M. R., Buettner, H. J., and Eshenroder, R. L.
2000. Commercial Fish Production in the Great Lakes 1867—2000.
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Bell, G., Handford, P., and Dietz, C. 1977. Dynamics of an exploited population of lake
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13

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14

northwestern Ontario. Arch. Hydrobiol. Spec. Iss. Adv. Limnol. 46:361-368.

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15

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growth and reproduction of lake Whitefish in northern Lake Michigan. Arc. fiir
Hydrobiologie.

16

CHAPTER TWO

This chapter is currently in press in Archive of Hydrobiology Special Issues in Advanced
Limnology and is copyrighted therein. The formatting follows the guidelines for the
Archive of Hydrobiology, but I did renumber the tables and figures.

Kratzer, J. F., Taylor, W. W., Ferreri, C. P. & Ebener, M. P. (in press, 2006). Factors
affecting growth of lake Whitefish in the upper Laurentian Great Lakes. In Jankun,
M., Brzuzan, P., Hliwa, P., and Luczynski, M. (Eds.) Biology and Management of
Coregonid Fishes. Archive of Hydrobiology Special Issues in Advanced
Limnology.

l7

Jud F. KRATZER', William W. TAYLOR', C. Paola FERRERIZ, Mark P. EBENER3

'Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI,
USA
2School of Forest Resources, Pennsylvania State University, University Park, PA, USA

3 Chippewa Ottawa Resource Authority, Sault Ste. Marie, MI, USA

Factors Affecting Growth of Lake Whitefish in the Upper Laurentian Great Lakes
Abstract

Lake Whitefish support the single largest and most valuable commercial fishery in the
Laurentian Great Lakes. Recently, fishery managers have reported declining growth and
productivity of lake Whitefish in the upper Great Lakes. Several causes for the declines
noted in individual growth rates have been proposed. These include changes in: 1) lake
whitefish density, 2) food quality and abundance, 3) population genetics, and 4) climatic
conditions. We evaluated the relationships between each of these factors and lake
whitefish growth in selected regions of the upper Great Lakes. Specifically, we
examined the timing of the changes in the environment with lake Whitefish growth to
determine causal relationships. Lake Whitefish growth declines began with the
development of a very strong 1991 year class due to favorable climatic conditions,
leading to density dependent growth dynamics, which were exacerbated by a significant
decline in the high-energy, benthic prey item (Diporeia spp.) toward the latter part of the
1990’s. It appears that declines in Diporeia density, which are related to the introduction
of two invasive species (Dreissena spp.) have resulted in a lower carrying capacity for
lake Whitefish in the upper Great Lakes. As such, managers need to implement
conservative harvest strategies that protect the viability of these stocks under lower
productivity conditions.

1Department of Fisheries and Wildlife, Michigan State University, 12 Natural Resources
Building, East Lansing, MI 48824, USA

2School of Forest Resources, Pennsylvania State University, 207 Ferguson Building,
University Park, PA 16802, USA

3Chippewa Ottawa Resource Authority, 179 W. Three Mile Rd., Sault Ste. Marie, MI
49783, USA

18

Introduction

Lake whitefish (Coregonus clupeaformis) are native to northern North America,
with the southernmost portion of their range being the Laurentian Great Lakes (HUBBS &
LAGLER 2004). Adult lake Whitefish are generally benthivores, eating mollusks,
crustaceans, and insects, but they have been reported to occasionally eat plankton and
small fish (WALDEN 1964, IHSSEN et a1. 1981, POTHOVEN 2005). These deepwater fish
prefer to live in depths of 15 to 50 m during much of their life history (WALDEN 1964).
Lake Whitefish are broadcast spawners, migrating to the shallows of lakes or connecting
rivers in late October and November to spawn over gravel or cobble substrate in less than
five meters of water (HART 1930). These life history traits make lake Whitefish important
integrators of offshore and nearshore energy dynamics in the Great Lakes. Year class
strength of lake whitefish is strongly dependent on weather conditions during spawning,
egg incubation, and larval stages. F REEBERG (1985) noted that year class strength was
much higher when ice formed over spawning beds by late December, before the first
winter storms, and hypothesized that strong wind generated currents and destroyed
developing eggs in marginal habitats on the spawning grounds. Ice generally begins to
melt by mid to late March in the upper Great Lakes (ASSEL 2003). In years that
experience rapid warming in the spring, investigators have reported the development of
relatively large year classes; a function of increasing available food for newly hatched
larval lake Whitefish, which was hypothesized to increase the grth and survival at this
life history stage (BROWN et al. 1993).

Lake Whitefish support the single largest and most valuable commercial fishery in

the Laurentian Great Lakes. In 2002, lake Whitefish accounted for approximately 40% of

19

total weight and total value of fish harvested from all the Great Lakes (DANIELS 2003).
Recently, concerns have arisen regarding declining growth and productivity of lake
Whitefish in regions of the upper Great Lakes. For example, during the 1990’s, declining
growth of lake whitefish was observed in northern Lake Michigan (MADENJIAN et al.
2002), southern Lake Michigan (POTHOVEN et al. 2001), and Lake Huron (MOHR &
EBENER 2005). Several possible causes of recent declines in lake Whitefish growth have
been proposed, including 1) density dependent grth due to relatively high lake
Whitefish abundance; 2) declines in the food base due to reduced nutrient loadings and
impact of invasive species on the food web, particularly the loss of the high-energy and
important food resource Diporeia spp., a benthic amphipod; 3) a change in the population
genetics of lake Whitefish due to fisheries harvest regimes; 4) the presence of
parasitism/disease; and finally 5) the impact of changes in climatic conditions (N ALEPA et
a1. 2005, LAW 2000, CONOVER & MUNCH 2002). Lake Whitefish growth rates are known
to be elastic, given differing population densities and environmental conditions. Studies
by BIDGOOD (1973), HEALEY (1980), and MILLS et al. (1998) demonstrated that lake
Whitefish growth is related to the amount of food available per fish and that density
dependent changes in growth can occur because of changes in lake Whitefish abundance
or forage availability.

Over the last decade, lake whitefish abundance has been relatively high compared
to historic abundances in Lakes Michigan, Huron, and Superior (NALEPA et al. 2005).
The food base in Lakes Michigan and Huron has changed dramatically over the last
decade, and primary production has decreased over the past 30 years due to reduced

nutrient loadings from the surrounding watersheds (MADENJIAN et al. 2002, DOBIESZ et

20

al. 2005). As such, the amount of food energy available to lake whitefish has declined in
Lakes Michigan and Huron while abundance of these fish has increased. The food-web
changes noted in the upper Great Lakes, especially the declines in the benthic amphipod
diporeia, are believed to have caused significantly lower food quantity and quality for
lake Whitefish in these regions (POTHOVEN et a1. 2001). The decline of diporeia, a
historically important, high-energy prey item for lake Whitefish, has been associated with
the establishment of the invasive zebra and quagga mussels (Dreissena polymorpha and
Dreissena bugensis). Dreissenid mussels are natives of the Ponto-Caspian region and
were introduced into the Great Lakes via the ballast water of commercial shipping vessels
(VANDERPLOEG et a1. 2002). The exact mechanism by which dreissenid mussels inhibit
diporeia abundance is unknown, but a likely explanation is competition for algae
(LOZANO et al. 2001, DERMOTT 2001, VANDERPLOEG et al. 2002, NALEPA et al. 2005).
Dreissenid mussels filter algae from the water column, and diporeia eat algae that fall to
the lake-bottom. It has been hypothesized that as algal consumption by dreissenid
mussels increases, the quantity of settled algae available for diporeia consumption
decreases, leading to decreased diporeia production. Declines in diporeia biomass
(energy rich - 4,429 J/g wet mass) and increases in zebra mussel biomass (energy poor —
1,047-2,478 J/g wet mass of soft tissue) have been proposed to result in a lower quality of
prey available to lake whitefish (SCHNEIDER 1992), as these fish now consume less
energy-rich items than before the decline of diporeia. As an example, POTHOVEN et al.
(2001) found that diporeia in Lake Michigan near Muskegon, Michigan nearly
disappeared between 1998 and 2000, resulting in a decrease in the proportion of diporeia,

by weight, in lake Whitefish diet from 70% to 25%. Thus, with fewer diporeia available

21

in this region, lake Whitefish were forced to shift their diet to include dreissenid mussels
and other lower energy prey, which made less energy available for growth.

In addition to the effects of changing environmental factors, the potential changes
in the genetic make-up of lake Whitefish populations have also been implicated in the
changes noted in the individual grth of lake whitefish over the past decade. During the
1990’s, the harvest of lake Whitefish was at all time highs in many parts of the Great
Lakes (NALEPA et al. 2005). It has been documented in other fish species that intense
fishing efforts over a sustained period of time can exert powerful selective forces that can
have lasting effects on the genetics of fish populations, resulting in slower individual
growth rates (LAW 2000, CONOVER & MUNCH 2002). The proposed mechanism for this
phenomenon is that faster growing fish are harvested more heavily because they reach the
minimum length requirement more quickly than slower growing members of their cohort,
thus reducing the probability that the faster growing fish will reproduce before being
harvested. This ultimately leaves predominately slower growing fish to spawn and
produce offspring that on the average exhibit slower growth than before the fishery
exerted heavy mortality pressures on the population. Such a phenomenon was
demonstrated by CONOVER & MUNCH (2002), who experimentally harvested large, fast
growing fish from a population of Mem'dia menidia, which eventually led to lower yields
and slower growth of individuals because the “fishery” weeded out faster growing
genotypes.

The goal of this study was to evaluate the causes for changing lake Whitefish
individual growth rates in four regions of the upper Great Lakes which differed in lake

Whitefish abundance trends, food energy availability, and fishing mortality.

22

Materials and Methods

Study Sites

We selected four sites in the upper Great Lakes in which to evaluate lake
Whitefish growth (Figure 2.1). Lake Whitefish are found throughout the upper Great
Lakes, and stocks are roughly delineated by spawning sites and defined as Whitefish
management units (BENCE & EBENER 2002). The four sites used in this study correspond
to Whitefish management units: northwestern Lake Huron (WFH-Ol), northern Lake
Michigan (WFM-03), northeastern Lake Michigan (WFM-05), and eastern Lake Superior
(WFS-07). Lake Whitefish in these sites are recognized as distinct stocks for fishery
management purposes (EBENER et al. 2005). These sites have historically been
productive fishing grounds for lake Whitefish and differ in lake Whitefish abundance,
food energy availability, and fishing mortality trends over the past 30 years (Table 2.1).
We selected these four sites because they were geographically located near each other,
thus experiencing similar climatic variables, while the Whitefish populations within these

sites are reproductively isolated from one another (BENCE & EBENER 2002).

Data Sources

Information on lake whitefish growth, biomass, and fishing mortality came from
data derived from the annual Chippewa/Ottawa Resource Authority (CORA) assessments
of the commercial fishery and the statistical catch-at-age (SCAA) models that are used to
manage the lake Whitefish fisheries in these waters (QUINN & DERISO 1999, EBENER et al.
2005). In particular, SCAA provided us with the abundance and weight-at-age data

needed to calculate biomass-at-age statistics for the fishery.

23

   
 

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northwestern Lake Huron, 2) northern Lake Michigan, 3) northeastern Lake Michigan. and
4) eastern Lake Superior.

24

 

 

 

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25

The index of growth we used in this study was the sum of the mean weights-at-
age for ages three, four, and five for each cohort. Age-three was the first age we used for
the Lakes Michigan and Huron sites, as lake Whitefish recruit to the fishery at an average
age of three years in these regions, while in Lake Superior, they recruit to the fishery at
age-four, on average (BENCE & EBENER 2002). To be legally harvested by commercial
fishermen in the upper Great Lakes, lake Whitefish must be longer than 430 mm TL
(POTHOVEN 2005). As the fishery at each of these three sites is predominantly composed
of three age classes, we used ages three, four, and five in Lakes Michigan and Huron and
ages four, five, and six in Lake Superior to assess grth and density at each site. These
age classes composed at least 75% of the total abundance of recruited fish during the time
period evaluated, although fish older than age-ten were infrequently harvested.

Data on diporeia abundance and primary production (phosphorus loadings) for
Lakes Michigan, Huron, and Superior came from T. NALEPA and S. LOZANO (Great
Lakes Environmental Research Lab, NOAA, unpublished data), MADENJIAN et al. (2002),
BRONTE et al. (2003), and DOBIESZ et al. (2005).

Evaluation of factors affecting lake Whitefish growth

We evaluated potential causes of the decreased growth of lake Whitefish by
comparing the observed changes in growth to outcomes predicted by the hypothesized
causes. We assessed the hypothesis that lake Whitefish abundance changes were
responsible for the growth declines in these regions by performing linear regression of
each cohort’s growth index on the mean total biomass of lake Whitefish in the fishery. It

was expected that if lake Whitefish abundance was causing reduced growth at any given

26

location and time, growth would be relatively high when biomass was low for that
location and time, while growth would be relatively low when biomass was high.

We evaluated the possibility that food energy availability was responsible for
changes in grth dynamics of lake whitefish by assessing several hypotheses. First, we
evaluated the impact of the declining diporeia resource on lake Whitefish grth by
comparing the timing and location of lake Whitefish growth declines to the timing and
location of declining diporeia abundance. Evidence in support of the hypothesis that
diporeia abundance determined lake Whitefish grth dynamics would be simultaneous
declines of diporeia abundance and lake whitefish growth. We also evaluated the effects
of declining primary productivity on lake Whitefish grth rate. Evidence in support of
the primary production hypothesis would be decreasing lake whitefish growth during
declines in phosphorus loadings into the upper Great Lakes (MADENJIAN et al. 2002,
DOBIESZ et al. 2005).

We evaluated the hypothesis that changes in lake Whitefish population genetics
led to slower growing fish by determining if grth declines in these fish were most
evident at sites where fishing mortality was highest and least evident where fishing
mortality was lowest. This pattern would be consistent with what would be predicted for
lake Whitefish growth based on this hypothesis because the four study sites represent four
largely non-interbreeding stocks of lake Whitefish (BENCE & EBENER 2002).

We evaluated the impact of climate-related variables on lake Whitefish growth
dynamics by analyzing the timing of declining lake Whitefish growth. While the four
sites occur in three different Great Lakes, they are spatially close enough together that

they should be exposed to similar air temperatures and wind speeds, both of which have

27

 

 

 

 

 

been shown to affect year class strength (BROWN et al. 1993), which in turn affects
growth via intraspecific competition for food (BIDGOOD 1973, HEALBY 1980). Evidence
in support of the hypothesis that climatic conditions are the key drivers in lake Whitefish
growth would be a decline in lake Whitefish grth at all four sites at the same time, as
only weather variables, which are density independent, would be expected to have the
same impact at all sites, at the same time. We also used data on ice cover, wind speed,
and air temperature (ASSEL 2003, NCAA 2005) to evaluate this hypothesis because we
expected strong year classes when ice cover, wind speeds, and spring temperatures were

favorable for maximum egg survival (BROWN et a1 1993).

Results and Discussion

Climate variables and lake Whitefish abundance

At all four sites, lake Whitefish grth was found to decline starting with the 1991
year class and remained low thereafter (Figure 2.2). Of the hypotheses listed in this
study, only the influence of climate variables was expected to cause the same pattern in
growth at all four sites, at the same time. As such, we believe that climate variables are
the key factors driving the decreased growth observed in these fish during this time
period. Interestingly, there was no significant relationship between abundance of fish in
the fishery and individual growth rates at any of the sites (Table 2.2). Of the four sites,
the highest percentage of variation in growth rate that could be explained by abundance
was only 19% (northern Lake Michigan).

The mechanism by which climate variables affected the growth of lake whitefish

in the upper Great Lakes is likely through the development of year class strength and its

28

 

.9”?
cure:
I.

d-srogow

Cohort Weight (kg)

o'mom
I

0.5 ‘

Northwestern Lake Baron

1973

1991

1998

 

 

 

P
O
O

1 2
Mean Biomass (trillion kg)

3

 

4.0
3.3.5 «
373.0 .
$2.5 1
g 2.0 «
:15 a
g 1.0 .
o 0.5 -

0.0

 

1991

m
1978

1998

Northeastern Lake Michigan

 

 

0.0

V V T

0.5 1.0 1.5
Mean Biomass (trillion kg)

2.0

 

4.0
Ass-
3’30 «
32.5 .
$2.0 .
21.5-
0
451.0 «

U 0.5 1
0.0

 

Northern Lake Mlcligan
1983 1991

 

 

0

4.0 -
33.5 -
133.0 «
5.2.5 .
m I
g 2.0
111.5 '
21.0 .
O
o 0.5

0.0

 

2 4
Mean Biomass (million kg)

 

{1991
1972

199

Eastern Lake Superior

 

 

0.0

T V

0.5 1.0 1.5
Mean Biomass (million kg)

2.0

Figure 2.2. Plots of growth index (sum of the mean weights-at-age for the three youngest
recruited ages) against mean biomass in time. Dates correspond to the first, last, and
1991 year classes.

Table 2.2. Results of linear regression of growth index on biomass and changes in growth
index between the 1991 and 1998 year classes.

 

 

 

 

Regression Growth Index
Site R2 Slope P 1991 1998* % change_
NW Lake Huron 0.008 -0.09 0.67 2.0 0.9 -53%
N Lake Michigan 0.193 -0.34 0.09 2.5 1.2 -50%
NE Lake Michigan 0.000 -0.01 0.94 3.0 2.5 -18%
E Lake Superior 0.028 -0.15 0.42 3.2 2.7 -16°/o

 

' WFS-07 data only goes to the 1997 year class, so it was substituted for 1998.

29

relationship to density dependent growth. The 1991 year class was one of the strongest
year classes in the past 20 years across Lakes Michigan, Huron, and Superior (M.
EBENER, unpublished). In lake Whitefish, strong year classes are generally a function of
favorable climatic conditions in the winter and early spring, which impact egg survival
and larval growth and survival, respectively. F REEBERG (1985) found that larval survival
of lake Whitefish was higher when ice formed before the first winter storms occurred over
the spawning area because the ice reduced wind-generated currents and allowed eggs to
successfully incubate and hatch in sub-optimal rearing habitats. Spring warming before
hatching is important, as rapid warming contributes to favorable planktonic food
resources for larval lake Whitefish, which sustain good growth and survival during the
critical period (LJUNGREN 2002), thus making for the establishment of a large year class
(BROWN et al. 1993). Weather data from the National Oceanic and Atmospheric
Administration (N OAA) indicated that the timing of early winter ice formation and wind
conditions were not especially favorable for a strong 1991 year class, but that May
temperatures were warmer than average during 1991 (Table 2.3, ASSEL 2003, NCAA
2005). Warm air temperatures in May suggest that spring water temperatures may have
risen relatively rapidly, which would favor the development of a strong year class due to
very positive larval growth and survival dynamics (BROWN & TAYLOR 1992). The
development of this strong year class in 1991 resulted in a high density of young lake
whitefish, which in turn negatively impacted individual grth rates of this, and
successive, cohorts. The fact that growth rates of lake whitefish were generally not

affected by biomass of adult lake Whitefish but were affected by climatic conditions

30

Table 2.3. Ice, wind, and mean May air temperature (°C) conditions during years of low,
moderate, and high recruitment of lake Whitefish as estimated by BROWN et al. (1993).

The long-term average May air temperature was 9.7 °C.

 

 

Year Ice“ Windb Temperature
Low Recruitment
1976 9-Jan 12 8.7
1982 7-Jan 10 13.4
Moderate Recruitment
1973 5-Jan 8 7.9
1983 15-Jan 10 7.4
High Recruitment
1977 22-Dec 13 12.9
1991 9-Jan 18 13.2

 

° Date when 40% ice cover first occurred
b Number of days of two-day average wind speed above 10 knots prior to the formation of 40%

ice cover.

31

1‘.“

 

 

 

suggests that growth rates were determined by year class strength, before the fish were
recruited to the fishery.

It is difficult to predict the effects that global warming could have on year class
strength and individual grth rates of lake whitefish because warmer temperatures
would cause later ice formation, which would tend to decrease egg survival in marginal
habitats, thereby potentially reducing year class strength. However, the warmer climatic
conditions would also result in better larval food resources in the spring, which would
tend to increase the growth and survival of larval lake Whitefish, thereby potentially
increasing year class strength. The relative importance of ice cover/wind speed and
spring warming rates in determining year class strength of lake Whitefish may be site-
dependent. BROWN et al. (1993), in a study that compared an index of lake Whitefish
recruitment to weather conditions over a 24-year time period, found that the influence of
ice cover and wind speed on lake Whitefish recruitment was stronger than the influence of
spring warming rates in Big Bay de Noc, Lake Michigan, but that the opposite was true
near Naubinway, Lake Michigan. As such, it is unclear at this time what the overall
effect of global warming would be on lake Whitefish population abundance and growth
dynamics in the upper Great Lakes.

Food energy availability

The original decline in lake Whitefish growth in the 1990’s could not be attributed
to declining diporeia densities because the timing of declining growth of these fish did
not coincide with the timing of declining diporeia. At all four sites, the growth index for
lake Whitefish started to decline with the 1991 year class, when diporeia were still

relatively abundant in the upper Great Lakes (Table 2.1). As such, our study does not

32

.‘j’i

 

 

 

 

support the hypothesis proposed by other researchers (POTHOVEN et al. 2001, HOYLE
2005, NALEPA et al. 2005) that declining diporeia abundances were responsible for
declines in lake Whitefish growth observed during the mid to late 1990’s in the Great
Lakes. However, it is possible that the changes in food base of the Great Lakes may be
responsible for the continued relatively slow growth and reduced lipid content of lake
Whitefish throughout the past decade (WRIGHT & EBENER 2006, this issue). This decline
in diporeia in the latter half of the 1990’s likely exacerbated the already poor growing
conditions in these areas due to high competition for food among an abundant lake
Whitefish population. Such a scenario would lead to intense density dependent growth
suppression, something that we observed in all regions evaluated. The fact that growth
remained low at all four sites even in later year classes, some of which were below
average in density, may be evidence that low diporeia densities, while not responsible for
the initial collapse of lake Whitefish growth rates, are inhibiting their recovery.

Our analysis does not support the hypothesis that declines in primary production
have affected lake Whitefish growth. MADENJIAN et al. (2002) showed that phosphorus
loadings to Lake Michigan generally declined from the 1970’s to 1995, and most of this
decline occurred early in this time span, while DOBIESZ et al. (2005) showed that
phosphorus loadings to the main basin of Lake Huron decreased during the 1970’s and
have remained low ever since. In contrast, growth of lake Whitefish in the Lakes
Michigan and Huron sites did not decline through the time period coinciding with the
reduction in phosphorus levels, but rather decreased abruptly starting with the 1991 year

class (Figure 2.2). Additionally, lake Whitefish growth declined at the same time in Lake

33

Superior as it did in Lakes Michigan and Huron, even though phosphorus loadings have
been relatively low and stable there over the past century (BRONTE et al. 2003).
Population genetics

In our study, there was no evidence in support of the hypothesis that the slower
growth rates of lake Whitefish in the regions studied were related to changes in the
genetics of these populations. During the period of study, fishing mortality rates were
similar for the northwestern Lake Huron, northern Lake Michigan, and eastern Lake
Superior sites, but were lower in northeastern Lake Michigan (Figure 2.3), the latter area
having been closed to commercial harvest of lake Whitefish from the 1950’s to the late
1970’s (EBENER 2002). Thus, if growth dynamics were solely determined by the genetics
of these fish, the northeastern Lake Michigan fish would be expected to exhibit no or a
lesser decline in growth than the other three sites. Instead, we found that lake Whitefish
in Lake Superior exhibited the smallest decline in their growth over the time studied, yet
had the highest fishing mortality (Table 2.2).

One additional hypothesis for the declining growth of lake Whitefish in the upper
Great Lakes is that disease or parasites were impacting the bioenergetics of these
populations (PICKERING 1993). While this hypothesis cannot be totally eliminated by the
data we analyzed, neither parasitism nor disease appear to be the main cause of declining
growth index, as excessive symptoms of parasite or disease infection were not reported
by the commercial fisheries or assessment biologists during this time.
Summary

Given the spatial and temporal patterns in lake Whitefish growth in the areas of

the upper Great Lakes studied, it appears that climatic variables and density dependent

34

‘1}1‘

 

 

 

 

 

 

—0- NW Lake Huron
—a— N Lake Mich.
—x -NE Lake Mich.

0.5a /" AIR“ L‘K—u— ELakeSup.

‘L' (M.,...Xx

 

’

o
h
n

 

00

PJ
./'
\

‘ .

 

Instantaneous Fishing Mort lity

9.0.0.0
.A

 

O
a
a
a
q
d

1981 1986 1991 1996 2001

'65
N
0')

Year

Figure 2.3. Historical fishing mortalities, averaged for all recruited ages, at each of
the four sites.

35

growth dynamics were responsible for the decline in lake Whitefish growth. This decline
began with the development of a very strong 1991 year class and was exacerbated by a
significant decline in the high energy prey item, diporeia, toward the latter part of the
1990’s, which appears to have prevented the recovery of lake Whitefish growth rates in
spite of reduced lake Whitefish abundance (POTHOVEN et al. 2001, HOYLE 2005, NALEPA
et al. 2005). As such, it appears that the carrying capacity for lake Whitefish in the upper
Great Lakes has been diminished due to a changing food web caused by invasive species,
and managers must implement conservative harvest strategies that protect the viability of
these stocks under lower productivity conditions.
Acknowledgements

Funding was provided by the Michigan Agriculture Experiment Station and
Michigan State University Graduate School. We would like to thank Jim Bence (MSU),
Tom Nalepa (NOAA-GLERL), and Steve Lozano (NOAA-GLERL) for providing data

and technical assistance.

36

References

ASSEL, R. (2003): NOAA Atlas: An Electronic Atlas of Great Lakes Ice Cover
Winters: 1973 — 2002. http://www.gler1.noaa.gov/data/ice/at1as/.

BENCE, J. & EBENER, M. (2002): Summary status of lake trout and lake Whitefish
populations in the 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan in 2000, with recommended yield and effort levels for 2001. - Technical
Fisheries Committee, 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan.

BIDGOOD, B. (1973): Divergent growth in two lake Whitefish (Coregonus clupeaformis)
populations. — J. Fish. Res. Board Can. 30: 1683-1696.

BRONTE, C., EBENER, M., SCHREINER, D., DEVAULT, D., PETZOLD, M., JENSEN, D.,
RICHARDS, C., & LOZANO, S. (2003): Fish community changes in Lake
Superior, 1970-2000. — Can. J. Fish. Aquat. Sci. 60: 1552-1574.

BROWN, R. & TAYLOR, W. (1992): Effects of egg composition and prey density
on the larval grth and survival of lake Whitefish (Coregonus clupeaformis
Mitchill). — J. Fish. Biol. 40: 381-394.

BROWN, R., TAYLOR, W., & ASSEL, R. (1993): Factors affecting the recruitment
of lake whitefish in two areas of northern Lake Michigan. — J. Great Lakes Res.
19(2): 418-428.

CONOVER, D., & MUNCH, S. (2002): Sustaining fisheries yields over evolutionary
time scales. - Science 297(5578): 94-96.

DANIELS, J. (2003): Marketing Great Lakes Whitefish. - Upwellings 26(3): 4-7.

DERMOTT, R. (2001): Sudden disappearance of the amphipod Diporeia from eastern Lake
Ontario, 1993-1995. - J. Great Lakes Res. 27(4): 423-433.

DOBIESZ, N., MCLEISH, D., ESHENRODER, R., BENCE, J ., MOHR, L., EBENER, M.,
NALEPA, T., WOLDT, A., JOHNSON, J., ARGYLE, R. & MAKAREWICZ, J. (2005):
Ecology of the Lake Huron fish community, 1970-1999. — Can. J. Fish. Aquat.
Sci. 62(6): 1432-1451.

EBENER, M. (2002): WFM-OS (Grand Traverse Bay stock). — In: BENCE, J. & EBENER,
M. (Eds.): Summary Status of Lake Trout and Lake Whitefish Populations in the
1836 Treaty-Ceded Waters of Lakes Superior, Huron, and Michigan in 2000, with
Recommended Yield and Effort Levels for 2001. —- pp. 103-106 Technical
Fisheries Committee, 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan.

37

 

EBENER, M., BENCE, J., NEWMAN, K., & SCHNEEBERGER, P. (2005): Application
of statistical catch-at-age models to assess lake Whitefish stocks in the 1836
treaty-ceded waters of the upper Great Lakes. - In: MOHR, L. & NALEPA, T.
(Eds.): Proceedings of a Workshop on the Dynamics of Lake Whitefish
(Coregonus clupeaformis) and the Amphipod Diporeia spp. in the Great Lakes. —
pp. 271-308 Great Lakes Fishery Commission Technical Report 66.

FREEBERG, M. (1985): Early life history factors influencing lake Whitefish (Coregonus
clupeaformis) year-class strength in Grand Traverse Bay, Lake Michigan. - Thesis
for the degree of M. S., Michigan State University.

HART, J. (1930): Spawning and early life history of Whitefish (Coregonus clupeaformis)
in the Bay of Quinte, Ontario. — Contr. Can. Biol. Fish. 40: 165-214.

HEALEY, M. (1980): Growth and recruitment in experimentally exploited lake Whitefish
(Coregonus clupeaformis) populations. - Can. J. Fish. Aquat. Sci. 37: 255-267.

HOYLE, J. (2005): Status of lake whitefish (Coregonus clupeaformis) in Lake Ontario
and the response to the disappearance of Diporeia spp. - In: MOHR, L. &
NALEPA, T. (Eds.): Proceedings of a Workshop on the Dynamics of Lake
Whitefish (Coregonus clupeaformis) and the Amphipod Diporeia spp. in the
Great Lakes. — pp. 47-66 Great Lakes Fishery Commission Technical Report 66.

HUBBS, C., & LAGLER, K. (2004): Fishes of the Great Lakes Region. University of
Michigan Press, Ann Arbor, MI, USA.

IHSSEN, P., EVANS, D., CHRISTIE, W., RECKAHN, J., & DESJARDINE, R. (1981): Life
history, morphology, and electrophoretic characteristics of five allopatric
stocks of lake Whitefish (Coregonus clupeaformis) in the Great Lakes region.
- Can. J. Fish. Aquat. Sci. 38: 1790-1807.

LAW, R. (2000): Fishing, selection, and phenotypic evolution. - ICES J. Mar. Sci. 57(3):
659-668.

LJUNGREN, L. (2002): Growth response of pike perch larvae in relation to body size and
zooplankton abundance. — J. Fish Biol. 60(2): 405-414.

LOZANO, S., SCHAROLD, J. & NALEPA, T. (2001): Recent declines in benthic
macroinvertebrate densities in Lake Ontario. - Can. J. Fish. Aquat. Sci. 58(3):
518-529.

MADENJIAN, C., FAHNENSTEIL, G., JOHENGEN, T., NALEPA, T.,VANDERPLOEG, 11.,
FLEISCHER, G., SCHNEEBERGER, P., BENJAMIN, D., SMITH, E., BENCE, J.,
RUTHERFORD, E., LAvrs, D., ROBERTSON, D., JUDE, D. & EBENER, M. (2002):
Dynamics of the Lake Michigan food web, 1970-2000. - Can. J. Fish. Aquat. Sci.
59: 736-753.

38

MILLS, K., MCCULLOCH, B., CHALANCHUK, S., ALLAN, D. & STAINTON, M. (1998):
Growth, size, structure, and annual survival of lake Whitefish (Coregonus
clupeaformis) during the eutrophication and oligotrophication of lake 226, the
experimental lakes area, Canada. - Archives of Hydrobiology Special Issues in
Advanced Limnology 50: 151-160.

MOHR, L. & EBENER, M. (2005): Status of lake Whitefish (Coregonus clupeaformis) in
Lake Huron. - In: MOHR, L. & NALEPA, T. (Eds.): Proceedings of a Workshop on
the Dynamics of Lake Whitefish (Coregonus clupeaformis) and the Amphipod
Diporeia spp. in the Great Lakes. - pp. 105-125 Great Lakes Fishery Commission
Technical Report 66.

NALEPA, T., MOHR, L., HENDERSON, B., MADENJIAN, C. & SCHNEEBERGER, P. (2005):
Lake Whitefish and Diporeia spp. in the Great Lakes: an overview. - In: MOHR,
L. & NALEPA, T. (Eds.): Proceedings of a Workshop on the Dynamics of Lake
Whitefish (Coregonus clupeaformis) and the Amphipod Diporeia spp. in the
Great Lakes. - pp. 3-20 Great Lakes Fishery Commission Technical Report 66.

NOAA. (2005): National Climatic Data Center Serial Publications, Sault Ste. Marie, MI.
httpzl/www7.ncdc.noaa.gov/Seria1Publications/LCDPubs?action=directgetpublica
tions&wban= l 4847.

PICKERING, A. (1993): Growth and stress in fish production. Aquaculture 111: 51-63.

POTHOVEN, S. (2005): Changes in lake Whitefish diet in Lake Michigan, 1998-2001. - In:
MOHR, L. & NALEPA, T. (Eds.): Proceedings of a Workshop on the Dynamics
of Lake Whitefish (Coregonus clupeaformis) and the Amphipod Diporeia spp. in
the Great Lakes. - pp. 127-140 - Great Lakes Fishery Commission Technical
Report 66.

POTHOVEN, S., NALEPA, T., SCHNEEBERGER, P. & BRANDT, S. (2001): Changes in diet
and body condition of lake whitefish in southern Lake Michigan associated with
changes in benthos. — N. Am. J. Fish. Manag. 21: 876-883.

SCHNEIDER, D. (1992): A bioenergetics model of zebra mussel, Dreissena polymorpha,
growth in the Great Lakes. - Can. J. Fish. Aquat. Sci. 49: 1406-1416.

QUINN, T. & DERISO, R. (1999): Quantitative Fish Dynamics. Oxford University
Press, New York, USA.

VANDERPLOEG, H., NALEPA, T., JUDE, D., MILLS, E., HOLECK, K., LlEBIG, J.,
GRIGOROVICH, I. & OJAVEER, H. (2002): Dispersal and emerging ecological
impacts of Ponto-Caspian species in the Laurentian Great Lakes. - Can. J. Fish.
Aquat. Sci. 59(7): 1209-1228.

39

WALDEN, H. (1964): Familiar Freshwater Fishes of America. Harper and Row,
NewYork, USA.

WRIGHT, G. & EBENER, M. (2006, this issue): Potential effects of dietary lipid reduction

on growth and reproduction of lake Whitefish in northern Lake Michigan. - Archiv
fur Hydrobiologie.

4O

{i

 

CHAPTER THREE
Changes in growth, condition, and liver weights of lake
Whitefish (Coregonus clupeaformis) in the upper Laurentian

Great Lakes between 1986-87 and 2003-05

INTRODUCTION

Lake whitefish (Coregonus clupeaformis) are harvested from the Laurentian
Great Lakes with large mesh trap nets and gill nets (Bence and Ebener 2002). These fish
support the single largest and most valuable commercial fishery in the these waters,
accounting for approximately 40% of total weight and value of fish harvested from the
Great Lakes in 2002 (Daniels 2003).

In recent years, concern has been expressed about declining growth and condition
of lake Whitefish in many regions of the upper Great Lakes (Figure 3.1, Madenjian et al.
2002, Pothoven et al. 2001, Mohr and Ebener 2005). Growth of lake Whitefish has been
shown to be directly related to the amount of food available per fish, and density
dependent changes in growth occur because of changes in lake Whitefish abundance or
forage availability (Bidgood 1973, Healey 1980, Mills et al. 1998). As such, two of the
more commonly suggested causes of declines in lake Whitefish grth in the Great Lakes
have been increases in lake Whitefish density and decreases in the density of the
amphipod, Diporeia spp., an energy-rich and historically important part of the lake
whitefish diet (Nalepa et al. 2005).

Lake Whitefish abundance is currently high relative to 20 years ago in many parts

of the upper Great Lakes. Annual yield of lake Whitefish, a surrogate measure of

41

Lake SSuIDeI‘K’r Kilometers
02‘:—

0 100 200
Canada

WB

 
   
   

Lake Huron

U.S.A.

Lam 6‘0

Figure 3.1. Map of the Great Lakes with study sites. AL=Alpena, BD=Big Bay de Noc.
BP=Bay Port, CB=Cheboygan, GT=Grand Traverse Bay, NB=Naubinway, WB=Whiteflsh
Bay

42

I;

 

abundance, increased from a low of less than 1.5 million kg in 1977 to a high of over four
million kg in 1998 in waters of northwestern Lake Huron, northern and eastern Lake
Michigan, and southeastern Lake Superior (Figure 3.1). In contrast, lake Whitefish
abundance during the 1950’s and 1960’s was less than half of current numbers due to the
effects of invasive species, overexploitation, and habitat degradation (Nalepa et al. 2005).

While lake Whitefish abundance increased in the upper Great Lakes, forage
availability also changed. From 1980 to 1993, primary production decreased in nearshore
waters of Lake Michigan because of stricter water quality standards, which resulted in
reduced nutrient input into the Great Lakes, thus contributing to the decreased abundance
of benthic invertebrates, including diporeia (Madenjian et al. 2002). Additionally, food-
web changes due to invasive species, especially dreissenid mussels (Dreissena
polymorpha and Dreissena bugensis), have been correlated with declines in diporeia,
resulting in lower food quantity and quality for lake Whitefish (Pothoven et al. 2001).
Furthermore, declines in the abundance of diporeia have been associated with reduced
growth and condition of lake Whitefish in Lake Michigan (Pothoven et al. 2001) and
Lake Ontario (Hoyle 2005).

The exact mechanism by which dreissenid mussels inhibit diporeia abundance is
unknown, but a likely explanation is via competition for algae (Nalepa et al. 1998,
Nalepa et al. 2000, Dermott 2001, Lozano et al. 2001, Nalepa et al. 2001, Vanderploeg et
al. 2002). Dreissenid mussels filter algae from the water column, and diporeia eat algae
that settle to the lake-bottom. It has been hypothesized that as algal consumption by
dreissenid mussels increases, the quantity of algae available for diporeia consumption

decreases, thereby reducing diporeia production. Thus, declines in the biomass of the

43

relatively energy rich diporeia (4,429 J/g wet mass) and increases in the biomass of the
relatively energy poor dreissenid mussels (1,047-2,478 J/g wet mass of soft tissue) have
lowered the quality of prey available to lake Whitefish (Schneider 1992). This change in
lake Whitefish diet has been demonstrated near Muskegon, Michigan (Lake Michigan),
where diporeia nearly disappeared between 1998 and 2000, with the result being that the
proportion, by weight, of lake whitefish diet comprised by diporeia declined from 70% to
25% (Pothoven et al. 2001). With fewer diporeia available, lake Whitefish shifted their
diet to include dreissenid mussels and other lower energy prey (e.g., chironomids,
zooplankton), resulting in an observed decrease in somatic growth. Pothoven (2005)
discovered a similar trend in small (<430 mm) lake Whitefish during the late 1990’s in
southeastern Lake Michigan, where diporeia went from 57% to 1% (dry weight) of their
diet.

The combined effects of increased lake Whitefish abundance and decreased high
energy prey sources would be expected to contribute to reduced grth and condition.
The goal of this study was to determine the combined influence of changes in lake
Whitefish and diporeia densities on lake whitefish growth and condition. The Specific
objectives were to evaluate the changes in length-at-age, body weight-at-length, and liver
weight-at-length in seven regions of the upper Great Lakes that have exhibited different
combinations of changes in lake Whitefish and diporeia densities and to determine the
relative importance of lake Whitefish and diporeia densities in determining the grth

and condition of female lake Whitefish.

44

METHODS
Study sites
Growth and condition were assessed at seven locations in the upper Great Lakes

(Figure 3.1). These locations correspond to seven lake Whitefish management units in the
three upper Great Lakes: Alpena (WFH-OS), Bay Port (WFH-07), Big Bay de Noc
(WFM-Ol), Cheboygan (WFH-Ol), Grand Traverse Bay (WFM-05), Naubinway (WFM-
03), and Whitefish Bay (WFS-07) (Bence and Ebener 2002). These sites were chosen
because they have experienced different directions and magnitudes of changes in lake
Whitefish abundance and diporeia density since the 1980’s (Table 3.1) and because lake
whitefish growth and condition had been assessed in these management units in 1986 and

1987, a time prior to the establishment of dreissenid mussels in these regions.

Sampling

Lake Whitefish females were collected from the commercial fishery during the
spawning season (late October and early November) in 1986, 1987, 2003, 2004, and
2005. Most fish were purchased from the local fish processing facilities where
commercial operators sell their catch, while some fish from the Big Bay de Noc,
Cheboygan, and Naubinway sites were provided by other fisheries researchers who were
using trap nets to collect lake whitefish for a mark-recapture study. Workers at fish
processing facilities process each fisherman’s catch separately and know the timing and
location of each fisherman’s catch. Target sample sizes were 40 to 50 randomly selected,

mature females from each location.

45

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553 .5. .8 5:39: 925 San 522.53 95.. .525 3:5 05 5 555: £23.: :5 5850::5 55.2.3 95. 5.25.8. fin 25...

46

The fish were transported, on ice, back to Michigan State University campus,
where total length (mm) and wet weight (g) were recorded and reproductive condition
was recorded as either ripe or running. Running fish, those that very easily lost eggs
when squeezed, were not used in condition analysis because not all eggs were present in
the fish at time of capture. Fish were sampled and processed on the same day that they
were harvested.

I compared grth and condition of lake whitefish at each site during two time
periods, 1986-87 and 2003-05. I back-calculated length-at-age using scale annuli, fit von
Bertalanffy curves with to set to zero, and plotted grth curves (Quinn and Deriso
1999). Condition was described with weight-at-length, with plumper fish having better
condition (Anderson and Neumann 1996), and with liver weight (Strange 1996, Dutil and
Lambert 2000). The liver stores energy reserves, thus a smaller liver suggests that a fish
has lower energy reserves (Dutil and Lambert 2000), which could be as a result of low
amounts of food energy available per fish. I compared both measures of condition using
ANCOVA, with total body or liver wet weight as the dependent variable, time as the
categorical variable, and total length as the covariate. If there was no time by length
interaction for a given site, the interaction term was dropped and ANCOVA was run

again to test for the time effect.

RESULTS
Growth
The average age at which female lake Whitefish reached the minimum legal length

(432 mm) increased from 1986-87 to 2003-05 at all sites (Table 3.2), suggesting slower

47

Table 3.2. Average age (in years) at which female lake whitefish reached the minimum
legal length (432 mm) at each site during the two time periods.

 

 

Site 1 986-87 2003—05
Alpena 3.6 5.9
Naubinway 3.1 5.5
Bayport 2.9 5.0
Big Bay de Noc 4.5 5.3
Cheboygan 4.0 5.6
Grand Traverse Bay 4.6 5.1
Whitefish Bay 3.7 4.8

 

48

grth rates during the current time period. The average increase was 1.6 years, with the
largest increase observed at Naubinway, where average age at the minimum legal length
increased from 3.1 to 5.5 years of age. This change in grth rate was further evidenced
by evaluating the von Bertalanffy parameter, K, which was significantly lower (t-test, p <
0.05) during 2003-05 than during 1986-87 at all sites (Table 3.3). The values of K
observed at each site decreased from a range of 0.25-0.65 in 1986-87 to 0.15-0.21 in
2003-05. While growth rates were lower in 2003-05 than in 1986-87 at all sites, L... was
significantly higher (t-test, p< 0.05) at all sites during 2003-05. Additionally, length-at-
age of fish older than age-7 during 2003-05 was observably higher than that of similarly
aged fish during 1986-87 at Cheboygan, Grand Traverse Bay, and Whitefish Bay (Figure

3.2).

Condition

Condition, as described by total body wet weight-at-length, was significantly
different between the two time periods at all sites except Grand Traverse Bay (Figure
3.3). Mean weight-at-length was consistently lower in 2003-05 than in 1986-87 at
Alpena, Bayport, Cheboygan, and Naubinway. Mean weight-at-length was higher for
most lengths in 2003-05 than in 1986-87 at Whitefish Bay. Mean liver weight-at-length
was significantly lower during 2003-05 at Bayport but significantly higher in 2003-05 at
Cheboygan, Naubinway, and Whitefish Bay (Figure 3.4). At Grand Traverse Bay, liver

weight-at-length was higher in 2003-05 than in 1986-87 for fish smaller than 550 mm.

49

Table 3.3. Von Bertalanffy growth parameters (K and L...). their standard errors, and the number
of fish used to back-calculate length at age.

 

 

 

1986-87 2003-05
Site K SE L... SE n K SE L- SE n
Alpena 0.36 0.02 594 9 73 0.16 0.02 707 35 50
Naubinway 0.25 0.01 632 12 121 0.21 0.02 651 24 99
Bayport 0.42 0.02 614 7 93 0.18 0.02 724 31 45

Big Bay De Noc 0.65 0.04 496 7 77 0.18 0.01 690 24 50
Cheboygan 0.33 0.02 554 10 61 0.18 0.01 702 29 72
Grand Traverse Bay 0.34 0.02 574 7 100 0.15 0.01 758 23 101
Whitefish Bay 0.32 0.02 623 10 35 0.17 0.01 762 18 96

50

 

 

 

. Naubinway

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  

 

 

 

 

’5‘ 100« I .
E o . . . - .
5
u:
C
3 700
600. Cheboygan ‘
500‘ -
4001 I q
300‘ I .
200- I -
100- I -
0 I I U 1 I I I V U I
o 2 4 6 8 10
Age (years)
700
500 . Whitefish Bay
500‘ —
400. 1986 87
300-
200'-
100- I
0 . . - ' . — '2003-05
0 2 4 6 8 10
Age (years)

 

Figure 3.2. Von Bertalanffy growth curves for lake Whitefish during the two time periods.

51

 

 

Weight (kg)

 

 

 

 

 

 

 

 

 

4
Alpena Naubinway
3 u
2 . ,
' a
1 . .. r
p = 0.001 p < 0.001
0 . . . .
Big Bay de Mac
0
p = 0.004

 

 

 

 

 

 

 

 

 

Cheboygan

Grand Traverse Bay

 

 

 

 

 

 

 

 

 

 

p=0.003 ’ p=o.17

o . . . .

4 400 500 600 700

Whitefish Bay ,. " “"9“ (mm)

3‘ .v u’

,. —1986-87

1 1 a
p < 0.001

0 . . - - - 2003-05

400 600 700

500
Length (mm)

 

Figure 3.3. Mean total weight-at-Iength during the two time periods with p-values for the
time effect in ANCOVA.

52

 

 

Liver Weight (g)

 

50

 

4o-
30-
20-

10-

 

Alpena

 

2%: 0.051

 

Naubinway

 

 

50

 

 

40-
30q
20-
10-

 

 

 

 

Big Bay de Noc

 

 

50

 

40¢
30-
20-‘

10'

 

 

 

     

.f

p < 0.001

 

 

50

 

40-
30-
20-
10-I

0

p = 0.006

 

 

400

500

600

Length (mm)

 

700

500 600
Length (mm)

700

— 1986-87

- - '2003-05

 

Figure 3.4. Iver weight-at-length of lab whitefish during the two time periods with p-values
for the time effect in ANCOVA.

53

 

qr

 

 

 

 

Environmental changes

Between the two time periods for which lake Whitefish growth and condition were
evaluated, lake whitefish and diporeia densities changed in varying ways at the sites
sampled (Table 3.1). Lake Whitefish density increased at Alpena, Big Bay de Noc,
Bayport, and Naubinway, while it decreased at Cheboygan, Grand Traverse Bay, and
Whitefish Bay. It was unclear what changes if any occurred in diporeia density at Big
Bay de Noc due to insufficient data. However, diporeia density decreased at all other
sites in Lakes Michigan and Huron, where dreissenid mussels had become established
between 1987 and 2003. Whitefish Bay, where dreissenid mussels had not become
established, did not exhibit a decrease in diporeia abundance between the two time

periods.

DISCUSSION

Growth rate (K) was lower at all sites in 2003-05 than in 1986-87, and lake
whitefish reached the minimum legal length of 432 mm at older ages in 2003-05 than in
1986-87 at all sites. The fact that grth rate decreased to similar values ranging from
0.15-0.21 at all sites suggests that a density independent factor, such as climate, has acted
on all sites. Kratzer et al. (2006) observed a decrease in the grth rate of lake whitefish
at four sites in the upper Great Lakes (northwestern Lake Huron, northern and
northeastern Lake Michigan, and eastern Lake Superior) and theorized that climatic

conditions that were favorable for survival of eggs and larvae of lake Whitefish allowed

54

for the production of strong year classes, which in turn reduced growth rates through
intraspecific competition for food (Brown and Taylor 1992, Brown et a1. 1993).

While growth rate was likely affected by density of pre-recruit lake Whitefish, the
length of fish older than age-7 and condition may be more sensitive to density of lake
Whitefish that are recruited to the fishery. Length-at-age of fish older than age-7
increased from 1986-87 to 2003-05 at the three sites where lake whitefish density
decreased between those two time periods, and decreased at the four sites at which lake
whitefish density increased between the two time periods (Table 3.4). Whitefish Bay was
the only site at which diporeia densities did not decrease, but lake Whitefish densities
decreased through time (Table 3.4). The increase in condition of longer fish observed at
Whitefish Bay is evidence that changes in lake Whitefish density alone, regardless of
changes in diporeia density, can affect condition of lake Whitefish. Estimates of lake
whitefish abundance used in this study included only those fish that were recruited to the
fishery. The relationship we observed between lake Whitefish abundance and the length-
at-age of older fish and condition suggests that intraspecific competition among lake
Whitefish that are recruited to the fishery can reduce the lengths of older fish and the
condition of fish that are recruited to the fishery. These findings agree with those of
Bidgood (1973) and Healey (1980), who observed that lake whitefish grth was higher
for highly exploited lake whitefish populations, which had lower densities of fish that
were recruited to the fishery.

Additionally, there was evidence that diporeia density alone can affect condition
of lake whitefish. At Grand Traverse Bay, there was no change in condition of lake

whitefish between the two time periods, despite the decrease in lake Whitefish and

55

Table 3.4. Direction of change in lake whitefish and diporeia densities and Iength-at-age
of fish older than age-7. total weight-at-length, and liver weight-at-length of lake whitefish
between 1986-87 and 2003-05. (11 indicates changes were not consistent for all lengths)

 

Length Weight Liver Weight

 

Site Lake Whitefish Diporeia awe-8+ at Length at Length

Alpena 1 1 1 1 no change
Naubinway 1 1 1 1 1
Bayport T l l l 1

Big Bay de Noc 1 NA 1 11 no change
Cheboygan l l t l 1
Grand Traverse Bay 1 1 1 no change 11
Whitefish Bay 1 no change I 11 I

 

56

diporeia densities. An increase in growth and condition would be expected as the lake
Whitefish population declined, but there was no change in condition between 1986—87 and
2003-05. As such, it is likely that the disappearance of diporeia that occurred between
1986-87 to 2003-05 prevented lake whitefish from increasing their condition even though
intraspecific competition decreased. Reduced growth and condition of lake Whitefish
associated with declines in diporeia densities have been reported for Lakes Michigan,
Huron, and Ontario (Pothoven et al. 2001, Nalepa et al. 2005). Although we observed
evidence for a relationship between diporeia density and lake whitefish condition, we did
not observe a relationship between diporeia density and lake whitefish growth.

Grand Traverse Bay provides additional evidence that lake Whitefish density is
more important than diporeia density in determining overall grth dynamics and
condition of lake Whitefish. Lake Whitefish density decreased by 56% and diporeia
density decreased by 100% between the two time periods, resulting in no change in lake
Whitefish condition. If these changes in lake Whitefish and diporiea densities actually
counterbalanced one another, the fact that the smaller percent change was observed in
lake whitefish density suggests that lake Whitefish condition was more sensitive to lake
whitefish density than to diporeia density.

Liver weight was not a good indicator of fish condition in this study. Liver
weight-at-length and body weight-at-length were significantly correlated for all sites and
times combined (p < 0.001), but changes in liver weight-at-length were not related to
changes in lake Whitefish condition as described by weight-at-length (Table 3.4).
Additionally, changes in liver weight-at-length were not related to changes in lake

Whitefish or diporeia densities in any consistent way (Table 3.4). Dutil and Lambert

57

tqi

 

 

 

 

(2000) and Lambert et al. (2000) were able to use livers weights to describe condition of
Atlantic cod (Gadus morhua) that were starved for food. It is possible that fish must be
very close to starvation before liver size starts to noticeably decrease. Thus, although
growth and condition of lake Whitefish in the upper Great Lakes have been affected by
lake Whitefish and diporeia densities, they do not show any physiological evidence of

suffering severe starvation at this time.

Conclusion

Growth and condition of lake Whitefish have changed over the past twenty years
in the upper Great Lakes. These changes have been affected by changes in the densities
of lake Whitefish and diporeia. Growth rates were lower in 2003-05 than in 1986-87 at
all sites. We found lake whitefish grth and condition to be more sensitive to changes
in lake Whitefish density than to changes in diporeia density. Despite recent changes to
the Great Lakes foodweb that have occurred as a result of dreissenid mussel invasion,
managers may be able to affect lake whitefish condition through harvest regulations that
result in reduced lake whitefish densities. Managers likely have less control over lake
Whitefish growth because grth rate is likely affected by the abundance of pre-recruits,
which can not be readily manipulated by managers. While length-at-age of lake
whitefish older than age-7 may be related to the abundance of lake whitefish that are
recruited to the fishery, fish older than age-7 make up a small proportion of the harvest

(typically 25% or less), and high fishing mortalities would fiirther reduce this proportion.

58

REFERENCES

Anderson, R. 0., and Neumann, R. M. 1996. Length, weight, and associated structural
indices. In Fisheries Techniques Second Edition, ed. B.R. Murphy and D.W.
Willis, pp. 447-482. Bethesda, MD: American Fisheries Society.

Bence, J ., and Ebener, M. 2002. Summary status of lake trout and lake whitefish
populations in the 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan in 2000, with recommended yield and effort levels for 2001. - Technical
Fisheries Committee, 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan. Great Lakes Fishery Commission, Ann Arbor, MI.

Bidgood, BR 1973. Divergent growth in two lake whitefish (Coregonus clupeaformis)
populations. J. Fish. Res. Board Can. 30:1683-1696.

Brown, R.W., and Taylor, W.W. 1992. Effects of egg composition and prey density on
the larval grth and survival of lake Whitefish (Coregonus clupeaformis
Mitchill). J. Fish Biol. 40:381-394.

Brown, R.W., Taylor, W.W., and Assel, R. 1993. Factors affecting the recruitment
of lake Whitefish in two areas of northern Lake Michigan. J. Great
Lakes Res. 19:418-428.

Daniels, J. 2003. Marketing Great Lakes Whitefish. Upwellings 26:4-7.

Dermott, R. 2001. Sudden disappearance of the amphipod Diporeia from eastern Lake
Ontario, 1993-1995. .1. Great Lakes Res. 27:423-433.

Dutil, J .-D., and Lambert, Y. 2000. Natural mortality from poor condition in Atlantic cod
(Gadus morhua). Canadian Journal of Fisheries and Aquatic Sciences 57(4):826-
837.

Healey, MC. 1980. Growth and recruitment in experimentally exploited lake Whitefish
(Coregonus clupeaformis) populations. Can. J. Fish. Aquat. Sci. 37:255-267.

Hoyle, J. A. 2005. Status of lake Whitefish (Coregonus clupeaformis) in Lake Ontario
and the Response to the Disappearance of Diporeia spp. In Proceedings of a
workshop on the dynamics of lake Whitefish (Coregonus clupeaformis) and the
amphipod Diporeia spp. in the Great Lakes, eds. L. Mohr and T. Nalepa, pp. 47-
66. Ann Arbor, MI: Great Lakes
Fishery Commission Technical Report 66.

Kratzer, J. F ., Taylor, W. W., F erreri, C. P. & Ebener, M. P. in press, 2006. Factors
affecting growth of lake Whitefish in the upper Laurentian Great Lakes. In Jankun,
M., Brzuzan, P., Hliwa, P., and Luczynski, M. (Eds) Biology and Management of
Coregonid Fishes. Archive of Hydrobiology Special Issues in Advanced

59

Limnology.

Lambert, Y., Dutil, J .-D., and Ouellet, P. 2000. Nutritional condition and reproductive
success in wild fish populations. Reproductive Physiology of Fish, pp. 77-84.

Lozano, S.J., Scharold, J .V., and Nalepa, TR 2001. Recent declines in benthic
macroinvertebrate densities in Lake Ontario. Can. J. Fish. Aquat. Sci. 58:518-529.

Madenjian, C.P., Fahnensteil, G.L., Johengen, T.H., Nalepa, T.F., Vanderploeg, H.A.,
Fleischer, G.W., Schneeberger, P.J., Benjamin, D.M., Smith, E.M., Bence, J .R.,
Rutherford, E.S., Lavis, D.S., Robertson, D.M., Jude, D.J., and Ebener, M. P.
2002. Dynamics of the Lake Michigan food web, 1970-2000. Can. J. Fish. Aquat.
Sci. 59:736-753.

Mills, K.H., McCulloch, B.R., Chalanchuk, S.M., Allan, D.J., and Stainton, M. P. 1998.
Growth, size, structure, and annual survival of lake Whitefish (Coregonus
clupeaformis) during the eutrophication and oligotrophication of lake 226, the
experimental lakes area, Canada. Archives of Hydrobiology Special Issues in
Adv. Limnol. 50:151-160.

Mohr, L., and Ebener, M. 2005. Status of lake whitefish (Coregonus clupeaformis) in
Lake Huron. In Proceedings of a workshop on the dynamics of lake Whitefish
(Coregonus clupeaformis) and the amphipod Diporeia spp. in the Great Lakes,
eds. L. Mohr and T. Nalepa, pp. 105-125. Ann Arbor, MI: Great Lakes
Fishery Commission Technical Report 66.

Nalepa, T.F., Fanslow, BL, and Messick, M. 2001. A further examination of the
decline in the benthic amphipod Diporeia in southern Lake Michigan. Abstracts
from the 44th Conference on Great Lakes Research, June 10-14, 2001. Great
Lakes Science: Making it Relevant, p. 100.

Nalepa, T. F., Hartson, D. J., Buchanan, J ., Cavaletto, J. F., Lang, G. A., and Lozano, S.
J. 2000. Spatial variation in density, mean size and physiological condition of the
holarctic amphipod Diporeia spp. in Lake Michigan. Freshwater Biol. 43(1):107-
119.

Nalepa, T. F., Hartson, D. J., Fanslow, D. L., Lang, G. A., and Lozano, S. J. 1998.
Declines in benthic macroinvertebrate populations in southern Lake Michigan,
1980-1993. Can. J. Fish. Aquat. Sci. 55(11): 2402-2413.

Nalepa, T., Mohr, L., Henderson, 8., Madenjian, C., and Schneeberger, P. 2005.
Lake Whitefish and Diporeia spp. in the Great Lakes: an overview. In
Proceedings of a workshop on the dynamics of lake Whitefish (Coregonus
clupeaformis) and the amphipod Diporeia spp. in the Great Lakes, eds. L. Mohr
and T. Nalepa, pp. 3-20. Ann Arbor, MI: Great Lakes Fishery Commission
Technical Report 66.

60

Pothoven, S. 2005. Changes in lake Whitefish diet in Lake Michigan, 1998-2001.
In Proceedings of a workshop on the dynamics of lake Whitefish (Coregonus
clupeaformis) and the amphipod Diporeia spp. in the Great Lakes, eds. L. Mohr
and T. Nalepa, pp. 127-140. Ann Arbor, MI: Great Lakes Fishery Commission
Technical Report 66.

Pothoven, S.A., Nalepa, T.F., Schneeberger, P.J., and Brandt, SB. 2001. Changes in
diet and body condition of lake whitefish in southern Lake Michigan associated
with changes in benthos. N. Am. J. Fish. Manag. 21:876-883.

Quinn, T., and Deriso, R. 1999. Quantitative Fish Dynamics. New York: Oxford
University Press.

Scharold, J .V., Lozano, S.J., and Corry, TD. 2004. Status of the amphipod Diporeia
spp. in Lake Superior, 1994-2000. J. Great Lakes Res. 30(Suppl.l):360-368.

Schneider, D.W. 1992. A bioenergetics model of zebra mussel, Dreissena polymorpha,
growth in the Great Lakes. Can. J. Fish. Aquat. Sci. 49: 1406-1416.

Strange, R]. 1996. Field examination of fishes. In Fisheries Techniques Second
Edition, ed. B.R. Murphy and D.W. Willis, pp. 433-446. Bethesda, MD:
American Fisheries Society.

Vanderploeg, H.A., Nalepa, T.F., Jude, D.J., Mills, E.L., Holeck, K.T., Liebig, J .R.,
Grigorovich, I.A., and Ojaveer, H. 2002. Dispersal and emerging ecological
impacts of Ponto-Caspian species in the Laurentian Great Lakes. Can. J. Fish.
Aquat. Sci. 59:1209-1228.

61

CHAPTER FOUR

At the time of submission of this dissertation, this chapter was in review for publication
in the Journal of Great Lakes Research. The formatting follows the guidelines for the
Journal of Great Lakes Research, but I did renumber the tables and figures for this
dissertation.

62

Changes in Fecundity and Egg Lipid Content of Lake Whitefish
(Coregonus clupeaformis) in the Upper Laurentian Great

Lakes between 1986-87 and 2003-05

Jud F. Kratzer“, William W. Taylor', and Mark Turner2

lDepartment of Fisheries and Wildlife, Michigan State University,

13 Natural Resources Building, East Lansing, MI 48824 U. S. A.

2Department of Natural Resources, Division of Wildlife,

Lake Erie Fisheries Unit, Sandusky, OH 44870 U. S. A.

*Corresponding author: Jud Kratzer, Michigan State University, 12 Natural Resources
Building, East Lansing, MI 48824 USA, Phone 1-(517)-353-6697, Fax 1-(517)-432-1699,
email: kratzerl @msu.edu

William Taylor, Michigan State University, 14 Natural Resources Building, East
Lansing, MI 48824 USA, Phone l-(517)-353-3048, Fax 1-(517)-432-1699, email:
taylorw@msu.edu

Mark Turner, Department of Natural Resources, Division of Wildlife, Lake Erie Fisheries

Unit, Sandusky, OH 44870 USA, email: Mark.Turner@dnr.state.oh.us

Running title: Fecundity and egg lipids in lake Whitefish

63

ABSTRACT. Lake Whitefish (Coregonus clupeaformis Mitchill), an important
commercial species in the Laurentian Great Lakes, have experienced decreased growth
and condition in parts of the upper Great Lakes over the past 20 years. Increases in lake
Whitefish density and decreases in the density of Diporeia spp., an energy rich and
historically important part of the lake Whitefish diet, have been implicated in the recent
declines in lake Whitefish growth and condition. The goal of this study was to describe
lake Whitefish fecundity, egg lipid content, and total ovary lipid content in selected
regions of Lakes Huron, Michigan, and Superior in 1986-87 and 2003-05, two time
periods with different lake Whitefish and diporeia densities. Under conditions of high
lake Whitefish density and low diporeia density, female lake Whitefish in the upper
Laurentian Great Lakes generally produced fewer eggs. Egg lipid content, however,
increased at all sites from 1986-87 to 2003-05, regardless of changes in lake Whitefish or
diporeia densities. Total ovary lipid content and lake Whitefish abundance were inversely
related, while there was no significant relationship between total ovary lipid content and
diporeia density. Lake Whitefish abundance had a stronger influence on the amount of
energy that lake Whitefish invested in egg production than did diporeia density, thus
managers may be able to influence the reproductive dynamics of lake Whitefish in the

upper Great Lakes through harvest regulations that affect population density.

INDEX WORDS: Coregonus clupeaformis, Diporeia, fecundity, egg lipid, ovary

64

0";

 

 

 

 

INTRODUCTION

Lake Whitefish (Coregonus clupeaformis Mitchill) are native to northern North
America, with the southernmost portion of their range being the Laurentian Great Lakes
(Hubbs and Lagler 2004). These fish are generally deepwater benthivores, preferring to
live in depths of 15 to 50 m during much of their life history (Walden 1964, Ihssen et al.
1981, Pothoven 2005), migrating to the shallows in late October and November to spawn
over gravel or cobble substrate in less than 5 m of water (Hart 1930, Taylor and Freeberg
1984). Today, lake Whitefish support the single largest and most valuable commercial
fishery in the Laurentian Great Lakes, accounting for approximately 40% of total weight
and value of fish harvested from these waters in 2002 (Daniels 2003). Annual yield of
lake Whitefish over the past 30 years has increased from a low of less than 1.5 million kg
in 1977 to a high of over four million kg in 1998 in waters of northwestern Lake Huron,
northern and eastern Lake Michigan, and southeastern Lake Superior (Fig. 4.1).

Recently, concerns have arisen regarding declining growth and condition of lake
Whitefish in many regions of the upper Great Lakes (Fig. 4.2). During the 1990’s,
declining growth rates of lake Whitefish were observed in northern Lake Michigan
(Madenjian et al. 2002), southern Lake Michigan (Pothoven et al. 2001), and Lake
Huron’s main basin (Mohr and Ebener 2005). Previous studies by Bidgood (1973),
Healey (1980), and Mills et al. (1998) demonstrated that lake Whitefish growth is directly
related to the amount of food available per fish, and that density dependent changes in
growth occur because of changes in lake Whitefish abundance or forage availability. The
two most commonly suggested causes of the recent declines in lake Whitefish growth and

condition observed in the upper Great Lakes have been increases in lake Whitefish

6S

 

 

 

 

A 5.0

U!

x

C .

.9 4.0

E 3.0-

E

.93 2.0

>.

g 1.0

C

C

< 0.0 l I I I I I
1976 1981 1986 1991 1996 2001

Year

Figure 4.1. Annual yield of lake Whitefish from selected waters of northwestern Lake Huron,
northern and eastern Lake Michigan, and southeastern Lake Superior 1976 to 2003, all
gear types combined.

66

 

Lake Superior Kilometers

m:—

0 100 200

Canada

WB

tN Lake Huron

U.S.A.

 

Figure 4.2. Map of the Great Lakes with study sites. AL=Alpena, BD=Big Bay de Noc,
BP=Bay Port, CB=Cheboygan, GT=Grand Traverse Bay, NB=Naubinway, WB=Whitefish
Bay

67

 

density and decreases in the density of Diporeia spp., an energy-rich and historically
important component of the lake Whitefish diet (N alepa et al. 2005). Diporeia are
thought to be suppressed through competition for food with the invasive dreissenid
mussels, which were first discovered in the Great Lakes ecosystem in 1988 (Vanderploeg
et al. 2002).

Decreases in growth and condition of lake Whitefish could affect their population
dynamics and future production via changes in the number of eggs produced or the
amount of energy incorporated in each egg, both of which are important to the
development of year class strength (Brown and Taylor 1992). Fecundity is directly
related to fish growth, as larger fish produce more eggs (Bell et al. 1977, Jude et al. 1987,
Smale 1988). Fish with higher quality diets, which allow for higher grth rates and
condition, produce a larger number of eggs that are generally of higher quality (Leray et
al. 1985, Hardy et al. 1990, Corraze et al. 1993). These eggs have larger lipid stores,
which provide more energy to developing larval fish than lower quality eggs, and thus
allow for faster somatic growth and a longer time interval before larval fish must begin
consuming prey exogenously (Brown and Taylor 1992). A key point in the early life
history of lake Whitefish occurs during the critical period when larval fish switch from
endogenous to exogenous food (Cushing 1990). During the egg and early larval stages,
the developing fish depends on endogenous energy, which is stored as yolk by the
mother. Once this endogenous food supply is expended, the larval fish must switch to
eating exogenous food, such as zooplankton (Taylor and Freeberg 1984), thus sufficient
exogenous food of the right size and nutritional value is critical for larval survival

(Brown and Taylor 1992). Larvae from larger, more yolk-filled eggs have a survival

68

 

advantage because they are able to survive longer before they need to switch to
exogenous food in early spring, when food conditions are often unpredictable due to
weather conditions (Taylor and Freeberg 1984). Additionally, more food types are
available to these larvae because of their larger size (Miller et a1. 1988, Brown and
Taylor 1992).

The goal of this study was to describe the reproduction dynamics of lake
Whitefish through an assessment of their fecundity, egg lipid content, and total ovary lipid
content in seven areas of the upper Great Lakes (Fig. 4.2) in 1986-87 and 2003-05; two
time periods with differing densities of these fish and their primary food source, diporeia.
The locations from which lake Whitefish were sampled corresponded to seven Whitefish
management units that have been defined by the managers of these fisheries: Alpena
(WFH-OS), Bay Port (WFH-O7), Big Bay de Noc (WFM-Ol), Cheboygan (WFH-Ol),
Grand Traverse Bay (WFM-OS), Naubinway (WFM-03), and Whitefish Bay (WFS-O7)

(Bence and Ebener 2002).

MATERIALS AND METHODS
Female lake Whitefish were collected from the commercial fishery during the
spawning season in late October and early November in 1986, 1987, 2003, 2004, and
2005. In general, 40 to 50 randomly selected dead female lake whitefish were purchased
from the local fish processing facilities where commercial operators sell their catch.
Workers at these facilities process each fisherman’s catch separately and know the timing

and location of each fisherman’s catch.

69

 

Lake whitefish collected from the commercial fishery were transported, on ice,
back to Michigan State University campus, where total length (mm), wet weight (g), and
reproductive condition were recorded. Fish were sampled and processed on the same day
that they were harvested. Ovaries were removed and frozen in air-tight freezer bags for
later determination of fecundity and egg lipid content. Running fish, those that very
easily lost eggs when squeezed, were not used in fecundity calculations because not all
eggs were present in the fish at time of capture, but eggs from these fish were used in
lipid content analysis.

F ecundity

In the laboratory, fecundity of each fish was determined. The ovaries were first
thawed and weighed, providing the mass composite of each fish’s eggs (wet weight, g).
Then, three sub-samples of 100 eggs were counted, and wet weight (g) of each sub-
sample was determined. Fecundity was calculated for each fish (total number of eggs per
female) based on total ovary wet weight and average wet weight per 100 eggs (Crim and
Glebe 1990). These lOO-egg samples were dried at 70-80°C for 24 hours and weighed to
determine dry weight of eggs. As fecundity increases with fish size (Strange 1996),
analysis of covariance (ANCOVA) was used to compare fecundities during the two time
periods with log(fecundity) as the dependent variable, time period (1986-87 or 2003-05)
as the categorical variable, and log(length) as the covariate.

Egg and Ovary Lipid Content

Egg lipid content was measured using a Foss Tecator Soxtec HT6 solvent

extraction system (AOAC International 2000). For each fish, three 0.7 g sub-samples of

dried eggs, which had been finely ground, were placed in individual cellulose thimbles

7O

 

for lipid analysis. Petroleum ether was used to dissolve the lipids from the sub-samples
and deposit them in pre-weighed aluminum cups. Afier the ether was evaporated, the
weight of lipids in the sample was calculated by subtracting the original weight of the cup
from the final weight. We calculated the mg of lipid per egg based on the mean dry
weight per egg and mean percent lipid in the dried egg samples. Lipid content of eggs
during the two time periods was compared with a two sample t-test because we found no
significant correlation between fish size and egg lipid content.

Finally, to assess the total amount of energy that fish invested in egg production,
the number of eggs in each female was multiplied by the amount of lipid per egg to
calculate the total amount of lipid in the ovaries of each fish. The two time periods were
compared using ANCOVA with log(g of lipid in the ovary) as the dependent variable,
time period as the categorical variable, and log(length) as the covariate.

RESULTS

For all sites and dates combined, lake Whitefish fecundity ranged from a
minimum of 1,689 eggs in a 631 mm female from Whitefish Bay in 1986-87, to a
maximum of 107,548 eggs in a 640 mm female from Grand Traverse Bay in 1986-87.
Mean fecundity was lowest (15,265) at Cheboygan in 1986-87 and highest (39,699) at
Bay Port during the same time period. The only site where fecundity increased
significantly from 1986-87 to 2003-05 was Whitefish Bay (Fig. 4.3), where the average
fecundity of a 550 mm fish (based on ANCOVA) increased by 5.7%. Fecundity
significantly decreased between the two time periods at Alpena, Bay Port, Big Bay de

Noc, and Grand Traverse Bay (Fig. 4.3), where average fecundity of a 550 mm fish

71

 

 

 

 

 

Alpena

Naubinway

p = 0.462

 

 

I U

 

 

 

Big Bay de Noe

 

 

 

 

 

 

 

 

 

 

 

 

 

 

m
U)
‘3, 0
s8 '
°- Cheboygan
‘- 6 a: d
4 . .
2 q -I - I - - >-
p=o.1o1 ' P=°-019
0 1 I I I
8 400 500 600 700
WhitefiSh say I Length (mm)
6 w ’
4« , r —1986-87
2 d ‘ f t 4..
.. 4.:
p = 0.015
O . .
400 500 600 700 - - 2003-05

Length (mm)

 

 

 

Figure 4.3. Mean fecundity at length of lake Whitefish collected from the study sites during
1986-87 and 2003-05 with p-values for time effect in ANCOVA.

72

decreased by 3.0%, 2.2%, 2.0%, 1.1%, respectively. There was no significant difference
between time periods at Naubinway and Cheboygan.

For all sites and dates combined, milligrams of lipid per egg ranged from a
minimum of 0.251 mg in a 436 mm female from Naubinway in 1986-87 to a maximum
of 0.988 in a 733 mm female from Whitefish Bay in 2003-05. Mean mg lipid per egg
was highest at Whitefish Bay in 2003-05 (0.655) and lowest at Naubinway in 1986-87
(0.458, Table 4.1). The amount of lipid per egg was significantly higher for all
populations during 2003-05 than in 1986-87 (p < 0.005).

The total amount of lipid in the ovaries was significantly lower in 2003-05 than in
1986-87 at Alpena and Naubinway, while it was significantly higher in 2003-05 at
Cheboygan, Grand Traverse Bay, and Whitefish Bay. No significant difference between
time periods was observed in the lake Whitefish sampled at Bay Port or Big Bay de Noc
(Table 4.2).

DISCUSSION

Between the two time periods for which we evaluated lake Whitefish fecundity
and egg lipid content, there were different combinations of changes in lake whitefish and
diporeia densities at the different sites (Table 4.3). Lake Whitefish density increased at
Alpena, Big Bay de Noc, Bay Port, and Naubinway, and it decreased at Cheboygan,
Grand Traverse Bay, and Whitefish Bay. Dreissenid mussels have become well
established in all of the Great Lakes except Lake Superior between the two time periods
(Vanderploeg et a1. 2002, Scharold et al. 2004), and diporeia densities declined between
the two time periods at all sites except for Whitefish Bay. As such, lake whitefish in

parts of the upper Great Lakes have experienced decreased food energy available per fish

73

TABLE 4. 1. Egg lipid content (mg per egg) of lake Whitefish collected during the two

time periods with p-values from t-tests.

 

 

 

 

1986-87 2003-05

Site Mean St. dev. n Mean St. dev. n p
Alpena 0.464 0.052 73 0.569 0.129 86 <0.001
Naubinway 0.458 0.092 121 0.564 0.107 144 <0.001
Bay Port 0.504 0.068 93 0.569 0.162 65 0.003
Big Bay de Noc 0.507 0.069 77 0.606 0.098 88 <0.001
Cheboygan 0.517 0.059 51 0.549 0.118 74 <0.001
Grand Traverse Bay 0.484 0.087 129 0.527 0.093 135 <0.001
Whitefish Bay 0.581 0.067 25 0.655 0.102 137 <0.001

 

74

TABLE 4.2. Predicted (ANCOVA) ovary lipid content of a 550 mm fish in 1986-87

and 2003-05 and p-value of time effect in ANCOVA.

 

 

 

Ovary Lipid Content (9)

Site 1986-87 2003-05 Percent Change p
Alpena 15.4 13.3 -14% 0.036
Naubinway 16.1 12.2 -24% <0.001
Bay Port 15.3 14.5 -5% 0.510
Big Bay de Noc 16.8 16.1 -4% 0.436
Cheboygan 7.9 12.2 54% 0.002
Grand Traverse Bay 16.4 17.9 9% <0.001
Whitefish Bay 9.4 18.0 91% <0.001

 

75

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76

as a result of decreased diporeia density and increased lake Whitefish density, and these
changes could be expected to affect lake Whitefish reproduction dynamics.

Smith and Fretwell (1974) found that fish tend to produce fewer, high quality
eggs rather than a constant number of lower quality eggs when food energy is limited
because this life history strategy maximizes their fitness, or likelihood of passing genetic
material onto successive generations. Lake whitefish sampled in this study behaved
similarly with respect to fecundity by generally producing fewer eggs during periods of
high lake whitefish densities and low diporeia densities (Table 4.4). Similarly, Healey
(1978) observed increased fecundity of lake Whitefish afier exploitation by the fishery
reduced population density.

The observed increase in egg lipid content during the current time period,
regardless of changes in lake Whitefish and diporeia densities, was not expected, and it is
possible that increases in egg lipid content could compensate for decreases in fecundity,
resulting in no net loss of recruitment. Brown and Taylor (1992) showed that egg lipid
content is positively correlated with larval length at hatch and endogenous growth rate,
and higher lipid stores allow larval fish to live longer before having to consume external
sources of energy. Based on their data, we calculated that the higher lipid content of eggs
during 2003-05 should result in significantly larger larvae at the time when they switch
from endogenous to exogenous food. While the calculated increase in size of larval lake
Whitefish from 1986-87 to 2003-05 was statistically significant, it is unclear whether this
difference is biologically significant, as the greatest increase in expected length at any
site was only 0.16 mm or 1.3% (Naubinway). Additionally, it is unlikely that this change

in lipid content has had any observable affect on lake Whitefish recruitment because their

77

 

TABLE 4.4. Direction of change in lake Whitefish and diporeia densities and
fecundity, egg lipid content, and total ovary lipid content of lake Whitefish
between 1986-87 and 2003-05.

 

 

Grand Traverse Bay

1 l T

Whitefish Bay no change 1‘

Site Lake Whitefish Diporeia Fecundity Egg Lipid Ovary Lipid
T l i T l
Naubinway T i not sig. T l
Bay Port T l l T not sig.
Big Bay de Noc T no data l T not sig.
Cheboygan l i not sig. T T
l T
l T

 

78

year class strength is largely determined by density independent factors, particularly
weather (Taylor and F reeberg 1984, Brown et al. 1993).

Lake Whitefish abundance appears to have influenced the total amount of lipid in
the ovaries of lake Whitefish in the upper Great Lakes. The three sites that experienced
decreased lake Whitefish abundance from 1986—87 to 2003-05 (Cheboygan, Grand
Traverse Bay, and Whitefish Bay) had increased total lipid content of the ovaries (Table
4.4). At sites where lake Whitefish abundance increased, ovary lipid content decreased
(Alpena and Naubinway) or did not change significantly (Big Bay de Noe and Bay Port).
Changes in diporeia density were not consistently related to total ovary lipid content, as
ovary lipid content increased, decreased, and remained the same at sites where diporeia
density decreased (Table 4.4). Especially noteworthy in this case, is Grand Traverse Bay,
where total ovary lipid content increased significantly, despite the total disappearance of
diporeia.

Conclusion

Reproduction dynamics of lake Whitefish changed between 1986-87 and 2003-05
in parts of the upper Great Lakes. Female lake Whitefish produced fewer eggs in 2003-05
than in 1986-87 at four sites, and fecundity only increased at one site. Fish at all sites
produced eggs with higher lipid content in 2003—05 than they did in 1986-87. It is
unclear whether increases in egg lipid content have been high enough to cause an
increase in age-O survival sufficient to compensate for the reduced fecundity that has
occurred in parts of the upper Great lakes, although current abundances of lake Whitefish
remain high, implying high age-0 survival (Brown et al. 1993, Nalepa et al. 2005).

Density of lake Whitefish had a stronger influence on the amount of energy that lake

79

Whitefish invested in egg production than did diporeia density because ovary lipid content
and lake Whitefish abundance were inversely related, and this relationship was not
affected by changes in diporeia density. Thus, managers may be able to influence the
reproductive dynamics of lake Whitefish in the upper Great Lakes through harvest
regulations.
ACKNOWLEDGMENTS

This study was funded by the Michigan Sea Grant College Program, Michigan
Agriculture Experiment Station, and Michigan State University. We would like to thank
Tom Nalepa and Steve Lozano, (Great Lakes Environmental Research Lab, National
Oceanic and Atmospheric Administration), Mark Ebener (Chippewa/Ottawa Resource
Authority), and Tom Goniea (Michigan Department of Natural Resources) for providing
data and Erik Olsen (Grand Traverse Band of Ottawa and Chippewa Indians) for

assistance in obtaining samples.

80

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Bell, G., Handford, P., and Dietz, C. 1977. Dynamics of an exploited population of lake
Whitefish (Coregonus clupeaformis). J. Fish. Res. Board Can. 341942-953.

Bence, J ., and Ebener, M. 2002. Summary status of lake trout and lake Whitefish
populations in the 1836 Treaty-Ceded Waters of Lakes Superior, Huron, and
Michigan in 2000, with recommended yield and effort levels for 2001. - Technical
Fisheries Committee, 1836 Treaty-Coded Waters of Lakes Superior, Huron, and
Michigan. Great Lakes Fishery Commission, Ann Arbor, MI.

Bidgood, BE. 1973. Divergent growth in two lake Whitefish (Coregonus clupeaformis)
populations. J. Fish. Res. Board Can. 30:1683-1696.

 

Brown, R.W., and Taylor, W.W. 1992. Effects of egg composition and prey density on
the larval growth and survival of lake Whitefish (Coregonus clupeaformis
Mitchill). J. Fish Biol. 401381-394.

Brown, R.W., Taylor, W.W., and Assel, R. 1993. Factors affecting the recruitment
of lake Whitefish in two areas of northern Lake Michigan. J. Great
Lakes Res. 19:418-428.

Corraze, G., Larroquet, L., Maisse, G., Blane, D., and Kanshik, S. 1993. Effect of
temperature and of dietary lipid source on female broodstock performance and
fatty acid composition of the eggs of rainbow trout. In Fish Nutrition in Practice,
eds. S.J. Kaushik and P. Luquet, pp. 61-66. Paris, France: Institut National de la
Recherche Agronomique.

Crim, L.W., and Glebe, B.D. 1990. Reproduction. 1n Methods for Fish Biology, eds. C.B.
Schreck and PB. Moyle, pp. 529-553. Bethesda, MD: American Fisheries
Society.

Cushing, DH. 1990. Plankton production and year-class strength in fish populations:
an update of the match/mismatch hypothesis. Adv. Mar. Biol. 26:249-293.

Daniels, J. 2003. Marketing Great Lakes Whitefish. Upwellings 26:4-7.

Hardy, R.W., Matsumoto, T., Fairgrieve, W.T., and Stickney, RR. 1990. The effects of
dietary lipid source on muscle and egg fatty acid composition and reproductive
performance of coho salmon (Oncorhynchus kisutch). In The current status of
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Hart, J. 1930. Spawning and early life history of Whitefish (Coregonus clupeaformis)
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Healey, MC. 1978. F ecundity changes in exploited populations of lake Whitefish
(Coregonus clupeaformis) and lake trout (Salvelinus namaycush). J. Fish. Res.
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Healey, MC. 1980. Growth and recruitment in experimentally exploited lake Whitefish
(Coregonus clupeaformis) populations. Can. J. Fish. Aquat. Sci. 37:255-267.

Hubbs, C., and Lagler, K. 2004. Fishes of the Great Lakes Region. Ann Arbor, MI:
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Ihssen, P., Evans, D., Christie, W., Reckahn, J., and DesJardine, R. 1981. Life
history, morphology, and electrophoretic characteristics of five allopatric
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Jude, D.J., Mansfield, P.J., Schneeberger, P.J., and Wojcik, J.A. 1987. Compensatory
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Madenjian, C.P., Fahnensteil, G.L., Johengen, T.H., Nalepa, T.F., Vanderploeg, H.A.,
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Mills, K.H., McCulloch, B.R., Chalanchuk, S.M., Allan, D.J., and Stainton, M. P. 1998.
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eds. L. Mohr and T. Nalepa, pp. 105-125. Ann Arbor, MI: Great Lakes
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Nalepa, T., Mohr, L., Henderson, 8., Madenjian, C., and Schneeberger, P. 2005.
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In Proceedings of a workshop on the dynamics of lake Whitefish (Coregonus
clupeaformis) and the amphipod Diporeia spp. in the Great Lakes, eds. L. Mohr
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Pothoven, S.A., Nalepa, T.F., Schneeberger, P.J., and Brandt, SB. 2001. Changes in
diet and body condition of lake Whitefish in southern Lake Michigan associated
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83

CHAPTER FIVE
Summary and Management Implications

Lake Whitefish of the upper Great Lakes have experienced changes in growth,
condition, fecundity, egg lipid content, and total ovary lipid content between 1986-87 and
2003-05. The overall density of lake Whitefish appears to be the dominant causal agent
of changes noted in lake Whitefish production dynamics over the past two decades, as
demonstrated by the declines in lake Whitefish growth that began with the unusually
strong 1991 year class. This was further substantiated by my findings that lake Whitefish
abundance influenced their condition and the amount of energy they invested into egg
production. Unlike other investigators (i.e., Pothoven et al. 2001, Hoyle 2005,
Schneeberger et al. 2005), this study provides only limited evidence that declines in
diporeia have affected lake Whitefish production dynamics. Although changes in growth,
condition, fecundity, and egg and ovary lipid content were not consistently related to
changes in diporeia density, the fact that growth rates remain low even in areas where
lake Whitefish density has declined suggests that declines in diporeia may have lowered
the carrying capacity of lake Whitefish in the Great Lakes by decreasing the amount of
food energy available to them.

Because the density of lake Whitefish directly affects their condition, it also
affects the marketability of the commercial harvest. If abundance is too high, the fillets
produced by harvested fish tend to be smaller, leading to reduced profits and
dissatisfaction with the fishery. Managers can reduce the abundance of lake Whitefish
through harvest regulations that would result in an increase in the condition and

marketability of these fish. Managers have less control over lake Whitefish growth, as

84

 

growth rate appears to be more influenced by the abundance of pre-recruits, which is

largely determined by density independent factors (i.e., weather conditions).

 

85

REFERENCES

Hoyle, J. 2005. Status of lake Whitefish (Coregonus clupeaformis) in Lake Ontario and
the response to the disappearance of Diporeia spp. In Proceedings of a workshop
on the dynamics of lake Whitefish (Coregonus clupeaformis) and the amphipod
Diporeia spp. in the Great Lakes, eds. L. Mohr and T. Nalepa, pp. 47-66. Ann
Arbor, Michigan: Great Lakes Fishery Commission Technical Report 66.

Pothoven, S. A., Nalepa, T. F., Schneeberger, P. J., and Brandt, S. B. 2001. Changes in
diet and body condition of lake Whitefish in southern Lake Michigan associated
with changes in benthos. N. Am. J. Fish. Manag. 21:876-883.

Schneeberger, P., Ebener, M., Toneys, M. and Peeters, P. 2005. Status of lake Whitefish
(Coregonus clupeaformis) in Lake Michigan. In Proceedings of a workshop on
the dynamics of lake Whitefish (Coregonus clupeaformis) and the amphipod
Diporeia spp. in the Great Lakes, eds. L. Mohr and T. Nalepa, pp. 67-86. Ann
Arbor, Michigan: Great Lakes Fishery Commission Technical Report 66.

 

 

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