THE FEEDING DYNAMICS OF OUT-MIGRATED AGE-0 CHINOOK SALMON
(ONCORHYNCHUS TSHAWYTSCHA) IN LAKE ONTARIO
A Thesis
Presented to the Faculty of the Graduate School
of Cornell University
in Partial Fulfillment of the Requirements for the Degree of
Master of Science
by
Nicholas Dino Principe
May 2005
© 2005 Nicholas Dino Principe
ABSTRACT
The purpose of this study was to examine gastric evacuation, feeding
chronology, daily ration, growth, diet, and prey selectivity of recently out-migrated
young-of-the-year (YOY) chinook salmon (Oncorhynchus tshawytscha) in Lake
Ontario.
To determine gastric evacuation rates, chinook salmon ranging from 40-80 mm
in total length, were fed to satiation and maintained at 10, 13, 16, or 19oC in the
laboratory for 24 hours. Five fish were sampled randomly every four hours from each
temperature treatment and the complete digestive tract (CDT) contents were removed.
The CDT contents and the remainder of each fish were subsequently dried and
weighed. Results show that evacuation rate (R) was dependent on temperature, with
estimates of R ranging from 0.214·h-1 to 0.352·h-1, at 10oC and 19oC, respectively.
Field sampling for daily ration estimates was conducted on five dates from
May 21 – June 25, 2001. Sub-yearling chinook salmon were captured using a seine
near the mouth of the Salmon River, beginning 30-60 minutes after sunrise and
continuing at approximately 4-hour intervals for 24 hours. Estimates of mean daily
ration ( D ) were derived using the Eggers (1977) model. Results showed that gut
fullness varied significantly (p < 0.05) with both date and time of day, but there was
no indication of synchronous diel variability in gut fullness between dates.
Because D did not vary as a function of date (p > 0.05), an overall D (28.3 g dry
wt·100 g dry wt-1·d-1) was calculated using the grand mean for all five sampling dates.
Daily ring counts of sagittal otoliths revealed that in 2001, YOY chinook
hatched between February 21 and April 2, and exhibited a mean growth rate of
0.65 mm·day-1. The early spring hatch dates indicated that the captured chinook
salmon were naturally produced, as 2001 hatchery chinook hatched in November.
For diet analyses, out-migrated YOY chinook salmon, along with potential
prey items, were sampled biweekly, at dusk, at two near-shore sites (i.e., Sandy Creek
and the Salmon River) in Lake Ontario from April – July of 2000. In 2001, weekly
diet and prey sampling was conducted from April – July at the Salmon River site only.
On five dates from mid-May to late-June 2001, prey and fish samples were collected
throughout the day to assess diel shifts in prey availability and selection.
Mid-water and surface prey sampling was conducted using a 1000 µm neuston
net pulled across the surface and parallel to the shoreline in water about one meter
deep. Out-migrated, age-0 chinook salmon were captured using a seine concurrent
with prey samples in both 2000 and 2001. Results showed that YOY chinook salmon
in Lake Ontario were primarily diurnal feeders as indicated by both a decrease in gut
content wet weight and the lack of identifiable prey in stomach samples examined
after midnight. Sub-yearling chinook sampled at dusk at both sites in 2000 and 2001
fed heavily on aquatic taxa, with mature chironomids constituting the bulk of the diet.
Similarly, chinook salmon sampled during the day at the Salmon River site in 2001
consumed at least 71% aquatic taxa.
Moreover, there was little evidence of a diel diet shift. Although amphipods,
homopterans, and developing chironomidae often dominated the prey samples,
daytime diet data collected at the Salmon River site in 2001 revealed that mature
chironomidae remained the most frequently consumed prey. Strauss’s (1979) index of
prey selection (L) revealed that in general, YOY chinook actively selected (L = 0.30.5) for chironomidae, while negatively selecting for non-chironomids.
This study shows that naturally produced chinook salmon are thriving in the
near-shore areas of Lake Ontario and consequently have an excellent chance to recruit
to the lake’s Pacific salmon fishery.
BIOGRAPHICAL SKETCH
Nicholas Principe graduated Summa Cum Laude from North Carolina State
University (NCSU) in December 1998 at the age of 31. There he received a B.S in
Fish and Wildlife Science and minored in Environmental Science. He completed an
independent study of largemouth bass (Micropterus salmoides) mark-recapture
success in 1998 with his undergraduate advisor and former Cornell doctoral student,
Dr. Richard Noble. In addition, while at NCSU, he worked closely with Dr. Randy
Jackson on young-of-the-year largemouth bass recruitment variability in reservoir
systems using otolith daily aging.
In February 2000, Nick began his M.S. studies in the Natural Resources
Department at Cornell University as a New York Sea Grant (NYSG) Scholar working
on a large collaborative study of Lake Ontario salmonines. There he was co-advised
by Dr. Clifford Kraft and Dr. Edward Mills, Director of the Cornell Biological Field
Station (CBFS). In addition, Dr. Randy Jackson, a senior research associate at CBFS,
was chosen to serve as an ad hoc member of Nick’s thesis committee. After
completing two successful field seasons of data collection on the feeding dynamics of
age-0 chinook salmon (Oncorhynchus tshawytscha) in Lake Ontario, Nick applied for
and received the prestigious Thesis Completion Award from NYSG. He also won an
award for the best student paper at the New York Chapter of the American Fisheries
Society Annual Symposium in Canandaigua, NY in January 2002.
From July 2002 – August 2004, Nick worked full-time as a biometrician at the
Stroud Water Research Center in Avondale, PA. There he was responsible for the
data management and statistical analyses of various ecologically related studies, such
as the monitoring of water quality through macroinvertebrate indicator species in
several watersheds surrounding New York City.
iii
Nick successfully defended his thesis on January 13, 2005 and will graduate
from Cornell University with a M.S. in Fisheries and Aquatic Science in May 2005.
He is currently teaching in the Biology Department at Ursinus College in Collegeville,
PA.
iv
ACKNOWLEDGMENTS
Funding for this research project was provided by New York Sea Grant.
Without them, this effort would not have been possible.
With such a large collaborative effort, such as the one that I undertook during
my graduate work at Cornell University, it becomes difficult to recall the countless
number of people that were involved directly or indirectly in the project. However,
there are several people that I would like to personally thank and if I left anyone out,
please accept my apologies and be assured that I am eternally grateful to all that were
involved.
First, I would like to thank the members of my thesis committee, including my
thesis advisors, Drs. Clifford Kraft and Edward Mills, and my former Wolfpack
brethren, Dr. Randy Jackson, for their continued intellectual, professional, and
personal guidance throughout the duration of my graduate studies.
I would also like to acknowledge the efforts of those that assisted me in the
field or in the laboratory including the two other Sea Grant Scholars working on the
“Salmonid Project,” Micah Dean and Nate Smith, our super field technician, Mike
Putnam, and my two outstanding summer interns, Mark Leao (2000) and Angie
Patterson (2001).
I also owe a debt of gratitude to Dr. Patrick Sullivan, whose team leadership
was unwavering and whose willingness to share his unrivaled bio-statistical prowess
with not just me, but everyone else on the Salmonid team, was greatly appreciated.
Also, thank you to Robert Elliott, of the National Marine Fisheries Service in
Green Bay, Wisconsin, for being kind enough to share his experience of capturing
young chinook salmon in the Great Lakes. For without his help, we would have been
v
hard-pressed to collect enough fish samples to make this project such a resounding
success.
Of course, I must also thank Charlie Dow, of the Stroud Water Research
Center, who generously provided me with the time, motivation, and statistical
assistance while I trudged my way through the many drafts of this thesis.
Last but certainly not least, I owe the most sincere thanks to my wife Gabrielle
for her love, patience, fortitude, emotional support, and complete munificence not only
throughout my graduate education, but also throughout my life. To my children
Isabella and Dominic…daddy loves you.
vi
TABLE OF CONTENTS
Biographical sketch…………………………………………………………………...iii
Acknowledgments…………………………………………………………………..…v
List of figures………………………………………………………………………….ix
List of tables…………………………………………………………………………..xi
Chapter One - Introduction
Background…………………………………………………………………….1
Goals and objectives…………………………………………………………...5
Chapter Two - Daily ration and growth of out-migrated, naturally produced, age-0
chinook salmon (Oncorhynchus tshawytscha) in Lake Ontario
Introduction…………………………………………………………………….7
Methods…………….…………………………………………………………10
Study site.……………………………………………………………..10
Gastric evacuation…...…………………………………………….….12
Fish capture and transfer……………………………………...12
Acclimation.…………………………………………………..14
Experimental protocol………………………………………...14
Calculation of evacuation rate………………………………...15
Daily ration………………………………………………………..….16
Growth………………...……………………………………………...17
Results…………….…………………………………………………………..18
Gastric evacuation…...…………………………………………….….18
Evacuation rate model………………………………………...19
Daily variation in CDT.……….……………………………...19
Daily ration……………………………….…………………………..22
vii
Growth……………………………….……………………………….23
Discussion……….…………………………………………………………....24
Chapter Three – Diet and prey selection of out-migrated age-0 chinook salmon
(Oncorhynchus tshawytscha) in Lake Ontario
Introduction…………………………………………………………………...29
Methods…………….…………………………………………………………31
Study site.……………………………………………………………..31
Prey collection, 2000...…………………………………………….….32
Fish collection, 2000...…………………………………………….….33
Prey collection, 2001...…………………………………………….….34
Fish collection, 2001...…………………………………………….….35
Prey selectivity...…………………………………………….………..37
Results…………….…………………………………………………………..38
Nocturnal feeding, 2000………………………………………………38
Prey, 2000…………………………………………………………….39
Diet, 2000……………………………………………………………..42
Prey, dusk 2001……………………………………………………….46
Prey, daytime 2001………………………………………………..….47
Diet, dusk 2001……………………………………………………….50
Diet, daytime 2001………………………………………………..…..52
Prey selectivity, dusk 2000-2001………………………………....…..54
Prey selectivity, diel 2001………………………………....………….55
Discussion………………………………....………………………………….56
Bibliography……………………………....………………………………………….60
viii
LIST OF FIGURES
Figure 1.1
Lake-wide stocking levels of chinook salmon in
Lake Ontario (1967-2002)……………………………………………..2
Figure 2.1
The Salmon River study site near Pulaski, NY
where sub-yearling chinook salmon were
collected for evacuation rate and daily ration
estimation in 2001…………………………………………………….11
Figure 2.2
Schematic of raceway, stock tank, and
supplemental water supply for controlled
laboratory trials to estimate evacuation rate
of age-0 chinook salmon in 2001……………………………………..13
Figure 2.3
Mean gut fullness of out-migrated age-0
chinook salmon captured near the mouth of the
Salmon River in Lake Ontario in 2001……………………………….21
Figure 2.4
Mean daily ration of age-0 chinook salmon
captured in near-shore habitat near the mouth of
the Salmon River in Lake Ontario in 2001…………………………...22
Figure 2.5
Hatch-date frequencies for age-0 chinook
salmon captured near the mouth of the Salmon
River in Lake Ontario from May – June 2001….….………………....24
Figure 3.1
Chinook salmon seining stations located along
the southern coast of Lake Ontario. The Sandy
Creek site, west of Rochester, NY was sampled
in 2000, while the Salmon River site, located
near Pulaski, NY was sampled in both 2000 and
2001…………………………………………………………………...32
Figure 3.2
Mean wet weights of stomach contents and
percentage of empty stomachs of out-migrated
age-0 chinook salmon captured after dusk on
May 16, 2000 near the mouth of the Salmon
River in Lake Ontario, NY……………………………………………38
ix
Figure 3.3
Relative abundance (%) of amphipods,
chironomid adults, chironomid larval/pupae,
other aquatic prey, and terrestrial organisms in
both the field and the stomachs of age-0
chinook salmon sampled at dusk near Sandy
Creek in Lake Ontario during May – June 2000….………………….45
Figure 3.4
Relative abundance (%) of amphipods,
chironomid adults, chironomid larval/pupae,
other aquatic prey, and terrestrial organisms in
both the field and the stomachs of age-0
chinook salmon sampled at dusk near the
Salmon River in Lake Ontario during
May – June 2000.……………………………………………………..46
Figure 3.5
Relative abundance (%) of amphipods,
chironomid adults, chironomid larval/pupae,
other aquatic prey, and terrestrial organisms in
both the field and the stomachs of age-0
chinook salmon sampled at dusk near the
Salmon River in Lake Ontario during
May – July 2001…………………..…………………………………..52
Figure 3.6
Pattern of selectivity of chironomidae by age-0
chinook salmon captured at dusk near Sandy
Creek in 2000 and the Salmon River in
2000 and 2001………………………………………………………...55
Figure 3.7
Diel pattern of selectivity of chironomidae by
age-0 chinook salmon captured near the Salmon
River in 2001…………………………….……………………………56
x
LIST OF TABLES
Table 2.1
Design and number of incidental mortalities of
age-0 chinook salmon immediately prior to
laboratory experiments of evacuation rate.…………………………...14
Table 2.2
Comparison of observed and predicted gastric
evacuation rates for age-0 chinook salmon fed
adult chironomidae at four water temperatures…...…………………..19
Table 2.3
Summary of sampling conditions used to
estimate daily ration for out-migrated age-0
chinook salmon collected near the mouth of
the Salmon River in Lake Ontario in late May
through June 2001.………………………….………………………...20
Table 2.4
Comparison of evacuation rate and daily ration
among various salmonine species as
estimated by several previous studies………………………………...25
Table 3.1
Number and size of out-migrated age-0
chinook salmon collected from Lake
Ontario for stomach examination in 2000………………………….…34
Table 3.2
Number and size of out-migrated age-0
chinook salmon collected near the mouth of
the Salmon River, Lake Ontario at dawn,
midday, and dusk in 2001……….…….……………………………...36
Table 3.3
Relative abundance (%) of prey items
sampled at dusk using a 1000 µm neuston net
near Sandy Creek in Lake Ontario in 2000……………………….….40
Table 3.4
Relative abundance (%) of prey items
sampled at dusk using a 1000 µm neuston net
near the Salmon River in Lake Ontario in
2000………………….……………………………………………….41
Table 3.5
Relative abundance (%) of prey items
consumed at dusk by out-migrated age-0
chinook salmon near Sandy Creek in Lake
Ontario in 2000………………….……………………………………43
xi
Table 3.6
Relative abundance (%) of prey items
consumed at dusk by out-migrated age-0
chinook salmon near the Salmon River in
Lake Ontario in 2000……….………………..…………………….…44
Table 3.7
Relative abundance (%) of prey items
sampled at dusk using a 1000 µm neuston net
near the Salmon River in Lake Ontario in
2001………………..……….………………..…………………….…47
Table 3.8
Relative abundance (%) of prey items
sampled at dawn and midday (time, 1400)
using a 1000 µm neuston net near the Salmon
River in Lake Ontario in 2001…..…………..…………………….…48
Table 3.9
Relative abundance (%) of prey items
consumed at dusk by out-migrated age-0
chinook salmon near the Salmon River in
Lake Ontario in 2001……….………………..…………………….…50
Table 3.10
Relative abundance (%) of prey items
consumed at dawn and midday (time, 1400)
by out-migrated age-0 chinook salmon near
the Salmon River in Lake Ontario in 2001…..…………………….…53
xii
CHAPTER ONE
INTRODUCTION
Background
The chinook salmon (Oncorhynchus tshawytscha), also known as the king
salmon, is the largest of all the Pacific salmonids, typically attaining weights of 13 to
18 kg and lengths of nearly 100 cm (Smith 1985). Chinook salmon are anadromous,
as well as semelparous, and they spawn either in the spring, summer, or fall in their
native ranges, with most offspring out-migrating from their natal streams into ocean
waters within the first year of life (Scott and Crossman 1973). Chinook salmon grow
quickly and individuals usually reach sexual maturity within the first two to four years
(Scott and Crossman 1973).
In North America, the chinook’s native range extends from southern
California, north to Point Hope, Alaska and in Asia, chinook range from Hokkaido,
Japan north to the Anadyr River (McPhail and Lindsey 1970; Major et al. 1978).
Through intensive stocking programs, chinook salmon range extensions have also
been established in other parts of the world. For example, introduced chinook salmon
have been returning to the South Island in New Zealand to spawn since the early
1900s (Unwin 1986) and landlocked, as well as limited anadromous returns have been
reported in southern Chile (Lindbergh 1982). Moreover, thriving populations of
chinook salmon have been established in the Laurentian Great Lakes since about 1968,
after many failed stocking attempts dating back to 1873 (Smith 1968; Christie 1974).
In Lake Ontario, as with the other four Great Lakes, chinook salmon were
originally stocked for the purpose of establishing a put-grow-and-take fishery, with
little expectation of natural reproduction in a landlocked, freshwater environment
(Parsons 1973). As the popularity of the new sport fishery began to increase rapidly
throughout the 1970s, the number of chinook stocked annually lake-wide into Lake
1
2
Ontario also increased from about 100,000 in the late 1960s to a peak of about
4,500,000 in 1984 (Parsons 1973; Jones et al. 1993; Figure 1.1).
Number stocked (1000s)
5000
4000
3000
2000
1000
0
1967
1972
1977
1982
1987
1992
1997
2002
Year
Figure 1.1. Lake-wide stocking levels of chinook salmon in Lake Ontario. New York
data from Eckert (1998). Canadian data courtesy of Tom Stewart, Assessment
Supervisor Ministry of Natural Resources, Lake Ontario Management Unit, Glenora
Fisheries Station, RR #4, Picton, Ontario K0K 2T0. Stocking levels in 2000-2002,
courtesy of Dan Bishop, New York State Department of Environmental Conservation,
1285 Fisher Avenue, Cortland, NY 13045-1090.
However, beginning in the early 1980s, evidence of reduced alewife (Alosa
pseudoharengus) abundance, the chinook’s preferred prey, in Lakes Michigan and
Ontario produced new concerns about increased stocking levels and the long-term
sustainability of Pacific salmon populations (Kitchell and Crowder 1986; Stewart and
Ibarra 1991; Rand et al. 1994a). Consequently, many researchers began to examine
the survival, growth, and bioenergetics of pelagic Pacific salmon in Lakes Michigan
3
and Ontario. For example, Stewart and Ibarra (1991) presented evidence that the Lake
Michigan salmonine community was stressed, based upon finding a decrease in
salmonine growth and survival, a shift in diet to less preferred prey items, and an
increase in bacterial kidney disease. Similarly, in Lake Ontario during the 1980s,
Rand et al. (1994a) reported that because of declining prey numbers and condition,
chinook salmon would have to greatly increase consumption rates to sustain high
growth rates that had been consistently achieved. In response to these concerns,
annual stocking rates of chinook salmon (i.e., 1,600,000 lake-wide in 2000) were
reduced in Lake Ontario from their mid-1980s peak (Eckert 1998; Schaner et al.
2000).
As researchers studied the bioenergetics of chinook salmon and measured
mortality rates based on spawning returns of stocked fish in the Great Lakes (e.g.,
Stewart and Ibarra 1991), several researchers began to report significant natural
reproduction of chinook salmon occurring in some Great Lakes tributaries. For
example, Johnson and Ringler (1981) documented that substantial natural
reproduction of chinook salmon was occurring in the Salmon River, a large tributary
of Lake Ontario located near Pulaski, New York. Similar observations of naturally
reproducing chinook salmon were reported from three other Great Lakes, including
Lake Michigan in the early 1970s (Rybicki 1973; Taube 1974), Lake Superior in the
early 1980s (Kwain and Thomas 1984), and Lake Huron in the 1980s (Powell and
Miller 1990).
Despite the presence of naturally produced chinook salmon in the Great Lakes
and their potential contribution to the fishery, little information is available regarding
the early life history of naturally produced chinook salmon in the Great Lakes.
Furthermore, the diet and bioenergetics of out-migrated, naturally produced young-ofthe-year (YOY) chinook salmon in the Great Lakes have not been closely evaluated.
4
Most studies of the feeding dynamics of YOY chinook salmon have focused on
riverine and estuarine habitats, particularly in the Pacific Northwest (Peterson et al.
1982; Rondorf et al. 1990; Muir and Coley 1996;) and in New Zealand (Sagar and
Glova 1987, 1988). In the Great Lakes, research has centered primarily on the growth
and bioenergetics (Goyke and Brandt 1993; Rand et al. 1994a; Mason et al. 1995;
Rand and Stewart 1998), predator-prey interactions (Stewart et al. 1981; Jones et al.
1993), and diets (Brandt 1986; Jude et al. 1987; Diana 1990) of post-smolt (> 4 g)
chinook salmon occupying the pelagic zones of these large lakes.
A small number of studies have examined the early life history of chinook
salmon in the Great Lakes. For example, from the early 1980s to the early 1990s,
Michigan researchers examined the contribution and distribution of naturally produced
chinook salmon in Lake Michigan tributaries (Carl 1982; 1984; Seelbach 1985; Zafft
1992; Heese 1994). Also, Elliott (1994) reported on the diet of both stocked and
naturally produced YOY chinook salmon in the near-shore waters (< 3 m) of Lake
Michigan and Johnson (1981; 1983), in Lake Ontario, examined the diets of recently
out-migrated hatchery chinook and the diets of naturally produced chinook residing in
tributaries.
During the course of their research, Elliott (1994) and Johnson (1983)
determined that recently out-migrated chinook salmon remained in the near-shore
waters of Lake Michigan and Lake Ontario, respectively, for up to several weeks
before moving offshore as smolts. However, little is known about the relative health
and potential survival of these naturally produced fish occupying shallow water
refugia in the Great Lakes. Understanding the feeding ecology and bioenergetics of
naturally produced chinook salmon in the Great Lakes can provide additional insights
into the ability of Lake Ontario to sustain chinook salmon populations.
5
In addition, since the stocking of Pacific salmon began in Lake Ontario over 30
years ago, significant ecosystem changes have occurred that could ultimately affect
the success of the Pacific salmon sport fishery. For example, after decades of
unabated phosphorus loading from urban sources (from about 1940 – 1970), nutrient
management strategies implemented through the 1972 Great Lakes Water Quality
Agreement resulted in substantial declines in phosphorus loading during the 1980s
(Hartig et al. 1991; Schelske, 1991). These phosphorus declines coupled with the
filtering activity of recently invading mussels (i.e., Dreissena polymorpha and
Dreissena bugensis) will likely result in a decrease in primary productivity, thus
reducing growth and biomass of planktivorous alewife (Hartig et al. 1991; Mills et al.
1993). These lower food web alterations could ultimately result in a reduction of
growth and production of Pacific salmon in Lake Ontario (O’Gorman et al. 1997).
Therefore, it is imperative that fisheries managers are cognizant of the contribution of
naturally produced chinook salmon to the overall predator biomass in Lake Ontario
before making decisions about annual stocking levels.
This research was initiated to provide information regarding the feeding
dynamics of naturally produced YOY chinook salmon in the Great Lakes. Moreover,
the knowledge gained from this study contributes to a better overall understanding of
the juvenile ecology of Pacific salmonines in lentic systems and will hopefully lead to
more educated decisions regarding future management goals and stocking programs of
Pacific salmonines in the Great Lakes.
Goals and Objectives
The goal of this study was to examine the feeding dynamics of recently outmigrated, naturally produced YOY chinook salmon in Lake Ontario, using a
combination of field observations and controlled laboratory experiments. The
objectives of this study were to examine: 1) the feeding chronology, daily ration,
6
gastric evacuation, and growth of YOY chinook salmon in Lake Ontario (Chapter 2)
and; 2) the diet, prey selectivity, and feeding patterns of recently out-migrated YOY
chinook salmon in Lake Ontario (Chapter 3).
For this study, I examined YOY chinook salmon in the New York waters of
Lake Ontario during the spring and summer of 2000 and 2001. In 2000, two study
areas were established along the Lake Ontario shoreline that were each sampled
biweekly: 1) near the mouth of the Salmon River, near Pulaski, New York; and 2) near
the mouth of Sandy Creek, about 50 km west of Rochester, New York. In 2001, only
the Salmon River area was studied and samples were collected on a weekly basis. I
distinguished between hatchery and naturally produced YOY chinook salmon in Lake
Ontario using comparative otolith daily aging.
CHAPTER TWO
DAILY RATION AND GROWTH OF OUT-MIGRATED, NATURALLY
PRODUCED, AGE-0 CHINOOK SALMON (ONCORHYNCHUS TSHAWYTSCHA)
IN LAKE ONTARIO
Introduction
Chinook salmon (Oncorhynchus tshawytscha) exhibit the fastest growth rate
and the greatest forage demand of all the Pacific salmonines stocked in the Laurentian
Great Lakes (Stewart et al. 1981). In Lake Ontario, Rand et al. (1994a) found that
adult chinook salmon fed almost exclusively on large alewife (Alosa pseudoharengus;
>120 mm) and consumed about 2.2 – 3.2 percent of their wet weight per day.
However, a decline in the abundance of large alewife in Lakes Michigan and Ontario
during the 1980s and early 1990s, coinciding with a rise in Pacific salmon stocking
rates, raised concerns about the long-term sustainability of Pacific salmon populations
in the Great Lakes (Kitchell and Crowder 1986; Stewart and Ibarra 1991; Rand et al.
1994a). These concerns, coupled with the chinook’s popularity as a sport fish, led to
many studies of the bioenergetics of stocked Pacific salmon in the Great Lakes (e.g.,
Stewart et al. 1981; O’Gorman et al. 1987; Rand et al. 1994a; 1994b; Rand and
Stewart 1998; 1998b). However, these studies have focused primarily on post-smolt
chinook, coho (O. kisutch), and steelhead (O. mykiss) occupying the pelagic regions of
the Great Lakes.
Previous studies of the energy intake of small young-of-the-year (YOY)
chinook salmon (< 4 g) have focused on riverine environments in the Pacific
Northwest (e.g., Kolok and Rondorf 1987) and in New Zealand (e.g., Sagar and Glova
1988). Similarly, bioenergetic evaluations of other YOY Pacific salmon found in the
Great Lakes, (i.e., coho and steelhead), have been conducted exclusively in lotic
7
8
systems, as both species reside at least one year in their natal streams before outmigration (Seelbach 1985; 1993). Previous studies have shown that YOY Pacific
salmon in lotic habitats are opportunistic feeders, relying heavily on terrestrial and
aquatic insects located at the air-water interface (Johnson 1981; Rondorf 1987; Sagar
and Glova 1988). Although the energy intake of YOY Pacific salmonines in lotic
systems has been described, it is unknown whether results from these studies are
comparable to the scoured littoral regions of the Great Lakes, where the air-water
interface is subjected to frequent high winds and intense wave action (Wetzel 2001).
A common method used by fisheries scientists to quantify daily energy intake
is to estimate mean daily ration (i.e., average food intake per day). Estimation of the
daily ration of fish has been used by researchers to examine questions related to
competition (e.g., Parrish and Margraf 1990), differential growth and survival (e.g.,
McGurk 1984; Walsh et al. 1988; Boisclair and Leggett 1989), predation pressure on
prey communities (e.g., Boisclair and Leggett 1985; Ruggerone 1989; Buckel and
Conover 1997), and habitat suitability (e.g., Swenson 1977; Hayward and Margraf
1987; Angradi and Griffith 1990). Daily ration can be evaluated from in situ
experiments (e.g., Kolok and Rondorf 1987; Sagar and Glova 1988), laboratory
feeding trials (e.g., Elliott 1975; Wahl and Stein 1991), or from a combination of both
methods (e.g., Mills and Forney 1981; Amundsen and Klemetsen 1988).
Eggers (1977) defined mean daily ration as the product of the mean gut
fullness for the day ( F ), the gastric evacuation rate prevailing for that day (R), and the
number of hours in a day (24). The gut fullness index ( Ft ) for each individual fish is
the ratio of the weight of gut contents and fish weight. Thus, the mean gut fullness for
the day is the average gut fullness measured over a certain number of evenly spaced
intervals, usually three or four hours, for an entire 24-hour period (Boisclair and
Leggett 1988). In many cases, there is a tendency for gut fullness data within each
9
interval to be skewed positively; therefore, either the median or transformed data from
each interval is sometimes used to calculate daily ration rather than the arithmetic
mean (Amundsen and Klemetsen 1988; Parrish and Margraf 1990b; Hayward 1991).
Moreover, to minimize the risk of missing a feeding period and to reduce the biases
associated with this error, gut fullness is often calculated using the weight of the
complete digestive tract (CDT = stomach + intestine) contents (Boisclair and Leggett
1989; Boisclair and Marchand 1993).
For those fish that exhibit an exponential rate of decline in mean gut fullness
over time, the gastric evacuation rate (i.e., rate at which a food item passes through the
body) is calculated as the slope of the relationship between the natural logarithm of
food content and time for fish evacuating food during a field or laboratory
experimental trial (Eggers 1977; Persson 1979; Boisclair and Leggett 1988). Studies
have shown that the gastric evacuation rate differs for every species and can depend
on many variables including water temperature, prey type, fish size, stomach volume,
and stress (Noble 1973; Mills et al. 1984; Boisclair and Leggett 1988). In order to
control for some of these variables, many researchers have used laboratory feeding
trials to determine gastric evacuation rate rather than in situ methods (e.g., Boisclair
and Leggett 1985, 1988, 1989; Trudel and Boisclair 1993; Johnston and Mathias
1996).
Three primary objectives were addressed in this study. They were: 1) to
determine gastric evacuation rates for YOY chinook salmon at multiple temperatures
in the laboratory, then use those results to develop a predictive model of gastric
evacuation rates for YOY chinook salmon captured in the field at various
temperatures; 2) to estimate the mean daily ration of out-migrated, naturally produced,
YOY chinook salmon captured in Lake Ontario using a combination of the Eggers
(1977) model and the gastric evacuation model; and 3) to measure short-term growth
10
rates and assess hatchery versus natural origin of out-migrated YOY chinook salmon
using a combination of otolith daily aging and length at capture data.
Methods
Study Site
Daily ration was estimated (May – June 2001) for recently out-migrated,
naturally produced, YOY chinook salmon occupying near-shore waters south of the
mouth of the Salmon River (near Pulaski, New York), near its confluence with Lake
Ontario. The Salmon River, which is home to New York State’s largest salmon
hatchery, is known for substantial natural reproduction of Pacific salmon (Johnson and
Ringler 1981). Coarse sand substrate dominated the study area, with little or no
available natural or artificial refuge from predation and a maximum depth of
approximately one meter. Evacuation rates for YOY chinook salmon were estimated
by means of controlled laboratory experiments conducted at the Cornell Biological
Field Station (CBFS) in Bridgeport, New York. Out-migrating chinook salmon used
for the evacuation rate component of the study were collected on June 5, 2001 via
shoreline seining along the Salmon River, just upstream from the Lighthouse Marina
(Figure 2.1).
11
Lighthouse
Figure 2.1. The Salmon River study site near Pulaski, NY. Chinook salmon captured
at Site 1 were used in evacuation experiments and at Site 2 for daily ration estimation.
12
Gastric Evacuation
Fish capture and transfer
Young-of-the-year chinook salmon, ranging from about 35 – 70 mm in total
length (TL), were collected from the Salmon River using a 1.2 x 36 m delta knotless
bag seine. The seine had 0.95 cm mesh in the first 10.7 m of each wing and 0.32 cm
mesh in the remainder of the seine. Field water temperature at the time of capture was
approximately 14oC. All captured fish were placed immediately into several large
plastic bags containing chilled lake water and pure oxygen. The fish were then
transported to the CBFS, where approximately 40 individuals were placed in each of
four isolated holding bays contained within two separate temperature-controlled MinO-Cool raceways (Figure 2.2). The raceways were 208 x 55 x 53 cm and each held
approximately 600 L of water. Each holding bay was 63 x 55 x 53 cm and was
covered and divided from the remainder of the raceway with a 1-mm mesh screen.
Initial laboratory water temperature was 13oC. Surplus chinook salmon were placed in
a separate 1500 L holding tank at 13oC and were used to replace incidental mortalities
from any of the four experimental bays. In addition, a separate 1500 L tank containing
de-chlorinated water was used to maintain consistent water levels in the two raceways
during the study period.
Bay 1
Drain
Bay 3
H
C
H
C
H
Bay 2
F
Bay 4
F
C
Stock Tank
H = Heater
F = Filter
C = Chiller
Figure 2.2. Schematic of raceway, stock tank, and supplemental water supply for controlled
laboratory trials to estimate evacuation rate of YOY chinook salmon, early May through June 2001.
Raceway 1
Valves
Raceway 2
-
Supplemental
Water Supply
F
13
14
Acclimation
Water temperatures in both raceways were maintained at 13oC for the first
week and were then adjusted by 1oC per day until the respective experimental
temperature (i.e., 10, 13, 16, or 19oC) was attained. These experimental temperatures
were selected because they approximated the range of water temperatures
observed near the mouth of the Salmon River in Lake Ontario from May – June 2000
(i.e., 9 – 21oC). All fish were acclimated at their respective experimental temperature
for approximately one week prior to the feeding trials. During the acclimation period,
all chinook salmon kept in the laboratory were fed once daily to satiation with
Ziegler No. 3 hatchery crumble acquired from the Salmon River Hatchery. Overall
incidental mortality for the duration of the study was less than 10%, of which
approximately 65% occurred within two days of capture and transfer (Table 2.1).
Table 2.1. Design and number of incidental mortalities of YOY chinook salmon
immediately prior to laboratory experiments of evacuation rate. Incidental mortalities
were immediately replaced with fish from the supplemental stock tank.
Bay
Temperature
(oC)
Number of
fish in trial
Size class
mm (TL)
1
2
3
4
Total
10
13
16
19
—
38
38
38
38
152
45–62
40–60
47–67
57–80
40–80
Number of incidental
mortalities first
48 hours
3
4
1
3
11
Total number
of mortalities
5
4
3
5
17
Experimental Protocol
Immediately prior to the beginning of each evacuation rate trial, experimental
chinook salmon were starved for 48 hours. After the starvation period, three fish were
sampled at random from each bay, measured to the nearest mm (TL), and dissected to
ensure that the CDT was empty. Then, from about 0600 – 0630, the remaining fish
15
from each bay were fed to satiation with frozen adult chironomids (mean body
length = 2.9 mm; se = 0.09) that had been collected from Oneida Lake, NY prior to the
experiments. This prey type and corresponding size range was selected for these
experiments because of the abundance of similar prey in the diet of out-migrated,
YOY chinook salmon in Lake Ontario (Chapter 3). Immediately after feeding, all
uneaten prey items were removed from each bay using a siphon and a dip net. About
30 minutes after feeding, five fish were sampled at random from each bay, measured
to the nearest mm (TL), and dissected to remove the CDT contents. The CDT
contents and the remainder of the fish were then placed in separate aluminum
weighing dishes and dried to constant weight at 60oC for 72 hours (Bowen 1996). The
sampling procedure was repeated for each temperature at four-hour intervals for a 24hour period. All dried material was weighed to the nearest 0.0001 g. Controlled
variables were prey type, prey size, and fish length, while the manipulated variable
was water temperature.
Calculation of Evacuation Rate
The gut fullness (Ft) of each fish sampled at time t was determined using a
variation of Boisclair and Leggett’s (1988) gut fullness index in equation 1:
G
(1) Ft  t  100
Pt
where Gt is the dry weight (grams) of the CDT contents and Pt is the dry weight of the
fish (grams).
Several authors (Bajkov 1935; Elliott 1972, 1975; Persson 1979, 1982; Boisclair
and Leggett 1988) have demonstrated that in fish with a distinct stomach, gut fullness
decreases exponentially when fish are deprived of additional food:
(2) F(t 1)  Ft e RT
16
which, in its logarithmic form is:
(3) ln F(t 1)  ln Ft  RT
where Ft and F(t 1) are the mean gut fullness at the beginning and end of time interval T
(4 h), respectively. The evacuation rate, R, is estimated as the slope of the correlation
between ln Ft and time (Persson 1979; Boisclair and Leggett 1988).
Daily Ration
Field sampling for daily ration estimates was conducted on five dates,
spanning a six-week period from late spring to early summer in 2001. Recently outmigrated, naturally produced, YOY chinook salmon were captured using a 1.2 x 36 m
delta knotless bag seine, with a 0.95 cm mesh in the first 10.7 m of each wing and a
0.32 cm mesh in the remainder of the seine. Seining began 30 – 60 minutes after
sunrise and was then conducted at approximately 4-hour intervals for no more than a
total of 20 hours for each sampling date. Water temperature was noted at the
beginning of each interval for all sampling dates. For each of the five sampling dates,
a minimum of six YOY chinook salmon were randomly selected from each interval
for daily ration estimation. When necessary, a maximum of two consecutive seine
hauls were conducted at any one interval to reach the minimum sample size. Upon
capture, the fish were anesthetized using MS-222, then immediately preserved in 90%
ethanol. Within 36 hours of capture, CDT contents and fish were placed in separate
aluminum weighing dishes and dried to constant weight at 60oC for 72 hours. The gut
fullness (Ft) of each fish sampled at time t was determined using equation 1.
Estimates of mean daily ration were derived using the Eggers (1977) model:
(4) D  F  R  24
where F is the mean gut fullness of all fish collected during the sampling date, R is the
evacuation rate, and 24 is the number of hours per day. Sample interval gut fullness
data were normalized using an arcsine-square root transformation (Hayward 1991).
17
The standard error (SE) associated with the daily ration estimates was
calculated using the following equation for multiplying two independent variances
(Zar 1999):
(5) SE ( DT )  var( F  R)  24 2
where DT is the mean daily ration estimate at temperature (T), F is the mean gut
fullness for the day, R is the evacuation rate prevailing for the day, 24 is the number of
hours per day. The variance (var) of the product of F and R is defined by the equation
(Zar 1999):
(6) var( F  R)   2 var( F )   2 var( R)
where  is the estimate of evacuation rate at temperature (T), and  is the mean gut
fullness per day.
Growth
In order to differentiate between naturally and hatchery-produced YOY
chinook salmon, an additional 15 YOY fish were sampled at random from each date
(i.e., 75 total) for otolith analysis. Individual hatch dates were estimated for each fish
by counting daily growth rings on the sagittal otoliths using a compound microscope
at 40x magnification. Otoliths were attached to microscope slides, sulcus side up,
using heated Crystal-bond® plastic adhesive and then gently wet-sanded until flat
(approximately 2-3 minutes) using fine grit sandpaper (Neilson and Geen 1986). A
total of four counts, performed by a single reader, were made for each fish’s otolith
and the mean of the four counts (i.e., number of post-hatch days) was recorded. Mean
growth rate (mm·day-1) from emergence until capture was calculated by dividing the
mean length at capture (mm TL) by the number of post-hatch days.
18
Results
Gastric Evacuation
Although every attempt was made to control for fish length between the four
experimental temperatures, incidental fish growth which occurred between the first
temperature tested (10oC) and the last temperature tested (19oC), resulted in a
significant difference in fish lengths among the four temperature groups (F3,24 = 92.50;
p < 0.0001). Follow-up group contrasts using a Tukey’s studentized range test
showed that fish lengths did not differ between 10oC and 13oC (M = 50.8 mm and 51.5
mm TL, respectively). However, the mean fish length of 56.2 mm TL for the 16oC
group and 67.7 mm TL for the 19oC group were significantly different from all other
groups (p < 0.05). Thus, the colinearity between fish length and temperature (i.e., as
temperature increased, fish length also increased) resulted in a situation where length
could not be considered an additional independent variable (Zar 1999). Therefore, any
effect of length on evacuation rate could not be determined for this experiment. In
addition, the size range of chinook across all four experimental temperatures (40-80
mm TL; Table 2.1) was well within range of previous studies that showed a constant
evacuation rate relative to fish length for large YOY fish (e.g., Mills et al. 1984).
Gastric evacuation rate (R) was dependent on temperature, with estimates of R
ranging from a low of 0.214, to a peak of 0.352·h-1, at 10oC and 19oC, respectively
(Table 2.2).
19
Table 2.2. Comparison of observed (Robs) and predicted (Rpred) gastric evacuation
rates and corresponding standard error (sRpred) for YOY chinook salmon fed adult
chironomidae at four water temperatures in the laboratory. All values of Robs were
significant (p < 0.0001).
Bay Temperature (oC)
1
10
2
13
3
16
4
19
Robs
0.214
0.266
0.276
0.352
Rpred
0.193
0.252
0.310
0.368
sRpred
0.011
0.014
0.017
0.021
Moreover, there was a significant overall relationship between evacuation rates across
all four temperatures (multiple comparison test for slopes; GLM method; F3,20 = 3.08;
p = 0.05). Since there was no significant difference in y-intercepts among the four
temperatures (multiple comparison test for y-intercepts; GLM method; p = 0.45), the
y–intercepts were assumed to be equal in the evacuation rate model. Predicted
estimates of gastric evacuation rates based on the resulting linear model of evacuation
time were comparable to the observed evacuation rates for YOY chinook salmon in
the laboratory experiments.
Evacuation Rate Model
The general linear model used to predict evacuation rate was found, using
multiple linear regression, to be:
(7) ln F  1.7052  (0.0193  T )  t
where (0.0193  T) is the slope of the relationship between the natural log of gut
fullness (ln F ) and time (t). Moreover, the model was significant (F1,26 = 315.05;
p < 0.0001) and accounted for 92% of the variance in R.
Daily Variation in CDT
Mean water temperature ranged from 12 – 19oC and mean fish length
increased from 47.6 to 63.0 mm TL over the sampling period (Table 2.3).
20
Table 2.3. Summary of sampling conditions used to estimate daily ration for outmigrated YOY chinook salmon collected near the mouth of the Salmon River in Lake
Ontario in late May through June 2001.
Date
Number of
fish
May 21
June 6
June 12
June 18
June 25
Total
36
60
60
60
50
266
Size class
mm (TL)
Mean water
temperature (oC)
36–63
43–65
44–85
50–75
53– 75
36–85
12
15
17
19
18
16
Number of intervals
with chinook : total
number of intervals
4:6*
6:6
6:6
6:6
5:6**
27:30
* intervals 3, 4, and 6 had six, zero, and zero chinook, respectively
** interval 6 had zero chinook
Back-transformed mean gut fullness values ranged from 2.95 g dry·100 g dry-1
on June 25 to 4.78 g dry·100 g dry-1 on June 6. Gut fullness varied significantly with
both date (F4,239 = 37.56; p < 0.0001) and time of day (F5,239 = 10.20; p < 0.0001),
while non-synchronous diel variability in gut fullness between dates was indicated by
the significance of the interaction term (F17,239 = 9.26; p < 0.0001; Figure 2.3).
21
8
6
4
May 21
2
0
8
Mean gut fullness index (g dry · 100 g dry-1)
6
4
June 6
2
0
8
6
4
June 12
2
0
8
6
4
June 18
2
0
88
66
June 25
44
22
00
0
1
0600
2
1000
3
1400
4
1800
2200
5
0200
6
5
6
7
0600
Time of day
1
2
3
4
7
Sampling interval
Figure 2.3. Mean gut fullness of out-migrated, YOY chinook salmon captured near
the mouth of the Salmon River in Lake Ontario, late May through June 2001. Error
bars represent 95% confidence intervals.
22
Individual contrasts using a Tukey’s studentized range test showed that there was no
significant difference in mean gut fullness between May 21 and June 6 or between
June 12 and June 18 (p > 0.05), however all other contrasts among dates were
significant (p < 0.05). In addition, gut fullness varied with time of day on May 21
(F1,34 = 15.92; p < 0.001), June 6 (F1,58 = 7.16; p < 0.01), and June 18 (F1,58 = 20.90;
p < 0.0001), while June 12 and June 25 showed no significant diel trend (p > 0.05).
Daily Ration
Mean daily ration (g dry wt·100 g dry wt-1·d-1) ranged from 24.62 (± 2.79) on
.
June 25 to 33.27 (± 3.70) on June 6 (Figure 2.4).
38
Mean daily ration
(g dry wt·100 g dry wt -1·d-1)
36
34
32
30
28
26
24
22
20
21-May
28-May
4-Jun
11-Jun
18-Jun
25-Jun
Date
Figure 2.4. Mean daily ration of age-0 chinook salmon captured in near-shore habitat
near the mouth of the Salmon River in Lake Ontario, late May through June 2001.
Error bars represent 95% confidence intervals.
23
Scheffe’s (1953) multiple contrasts revealed that the peak in mean daily ration on June
6 was significantly different from the lowest daily ration estimate, which occurred on
June 25 (p < 0.05). However, paired contrasts between May 21, June 12 and June 25
showed that mean daily ration did not vary significantly between dates (p > 0.05).
Because of the lack of a time trend across the sampling period (ANOVA; p > 0.05), I
estimated an overall mean daily ration (28.3 ± 3.18 g dry wt·100 g dry wt-1·d-1) for the
six-week study period by calculating a grand mean for all five sampling dates.
Growth
Evaluation of sagittal otoliths revealed that the estimated hatch dates of YOY
chinook salmon in Lake Ontario in 2001 ranged from February 21 – April 2, 2001,
with the majority of fish emerging between February 28 and March 20 (Figure 2.5).
Because the hatching period of the 2001 stocked chinook salmon originating from the
Salmon River Hatchery was in November 2000 (NYDEC Salmon River Hatchery,
pers. comm.; April 2002), it was concluded that chinook captured for daily ration
estimation in 2001 were naturally produced.
24
25
n = 75
Frequency
20
15
10
5
0
2/21-2/27
2/28-3/6
3/7-3/13
3/14-3/20 3/21-3/27
3/28-4/3
Hatch date
Figure 2.5. Hatch-date frequencies for age-0 chinook salmon captured near the mouth
of the Salmon River in Lake Ontario from May – June 2001.
Age-0 chinook salmon sampled in the near-shore waters of Lake Ontario had a mean
growth rate of 0.65 (± 0.018) mm·day-1. Moreover, there was not a significant
relationship between mean growth rate and date of capture (p > 0.05), indicating that
chinook hatching in late March grew at the same rate as fish hatching earlier.
Discussion
Although our predicted evacuation rate at 14oC for YOY chinook salmon was
greater than that obtained by Kolok and Rondorf (1987) at the same temperature, our
estimate compared favorably to that observed by Elliott (1975) for juvenile brown
trout (Salmo trutta) at 15oC (Table 2.4).
25
Table 2.4. Comparison of evacuation rate and daily ration among various salmonine
species (—, not reported).
Study
Species
Mean wet
weight (g)
Evacuation rate
(R:h-1)
Daily ration
estimate
O. tshawytscha
0.6
—
20% of dry
weight at 10oC
Brett (1971)
O. nerka
4
—
17% of dry
weight
Elliott (1975)
Salmo trutta
1
0.283 at 15oC
16.4% of dry
weight at 15oC
—
10-18% of dry
weight
0.152 at 14oC
5.5 kcal.g-1 at
14oC
Davis &
Warren (1968)
Healey (1979)
Kolok &
Rondorf
(1987)
O. keta
O. tshawytscha
age-0
17
Sagar & Glova
(1988)
O. tshawytscha
4
0.152 at 14 C
Principe
(2004)
O. tshawytscha
1.6
0.271 at 14oC
o
8.3% of dry
weight at 14oC
25.4% of dry
weight at 12oC
One possible explanation for this difference in evacuation rate estimates is that
our evacuation rates were estimated, as were Elliott’s (1975), using controlled
laboratory feeding experiments on conditioned fish, which exhibited minimal signs of
stress in their behavior. Conversely, Kolok and Rondorf (1987) estimated evacuation
rate from field observations, which could have resulted in lower estimates of
evacuation rate. Freshly captured fish are often highly stressed, which tends to
suppress evacuation rate (Swenson and Smith 1973; Thorpe 1977).
Because of the variability of methods for estimating and reporting mean daily
ration (e.g., dry weight vs. weight wet of fish) and the overall lack of information
26
regarding daily consumption of YOY chinook salmon in the literature, few studies are
available with which to directly compare our daily ration estimates. Our estimate of
mean daily ration (25.4% of dry body weight at 12oC) for out-migrated, YOY chinook
salmon in Lake Ontario was greater than estimates obtained by Sagar and Glova
(1988) in New Zealand (8.3% of dry body weight at 14oC). However, our estimate of
daily ration is comparable to those predicted by Davis and Warren (1968) for YOY
chinook salmon (about 20% of dry body weight at 10oC) and by Elliott (1975) for
YOY brown trout (16.4% of dry body weight at 15oC) (Table 2.4).
Some of the dissimilarity between the results of our study and estimates from
Sagar and Glova (1988) can be explained by three important differences. First, their
estimate of daily ration is based on a much lower evacuation rate (0.152·h-1 at 14oC
from Kolok and Rondorf 1987), than that predicted by our model at 14oC (0.271·h-1),
thus resulting in a much lower daily ration estimate for Sagar and Glova (1988).
Second, the mean gut fullness for YOY chinook salmon in the Rakaia River, where
Sagar and Glova (1988) conducted their study, was about 2.4 g dry·100 g dry-1, much
lower than our average gut fullness of 3.9 g dry·100g dry-1 over the six-week sampling
period. Some of this difference in gut fullness is probably due to our use of the
heavier CDT contents, rather than the stomach only, as used by Sagar and Glova
(1988). More importantly, however, this difference in gut fullness could likely be
attributed to differences in prey availability, as a number of researchers have
suggested that food supply may be the limiting factor in daily ration in young salmon.
For example, Healey (1979) estimated daily consumption to be approximately 10 –
18% of dry body weight for age-0 chum salmon (O. keta) in the Nanaimo Estuary,
British Columbia, while Godin (1981) estimated daily consumption to be about 6.6%
of dry body weight for juvenile pink salmon (O. gorbuscha) in Hammond Bay, British
27
Columbia. In both cases, the authors suggested that these daily consumption estimates
were greatly suppressed due to limited food supply.
Finally, Sagar and Glova (1988) used chinook salmon that were almost
threefold heavier than those used in our study (4 g versus 1.6 g; Table 2.4). Daily
ration decreases substantially as a function of size, such that larger fish, as used by
Sagar and Glova (1998), would have a much lower estimated daily ration than smaller
fish (Brett 1971; Elliott 1975). For example, Brett (1971) estimated a daily ration of
about 17% of dry body weight for a 4 g juvenile sockeye salmon (O. nerka), but only
4.3% for a 216 g fish. Similarly, Elliott (1975) found that a 1 g brown trout would
consume about 16.4% of dry body weight per day, while a 200 g brown trout would
consume only 4.8% of dry body weight.
Our growth estimate of 0.65 (± 0.02) mm·day-1 compares favorably to high
growth rates exhibited by YOY chinook salmon residing in food-rich estuarine
environments along the Pacific coast of the U. S. For instance, Kjelson et al. (1982)
estimated growth rates of approximately 0.53 – 0.86 mm·day-1 in the Sacramento –
San Joaquin River Estuary and Federenko et al. (1979) estimated growth rates of about
0.62 mm·day-1 in the Nitinat River Estuary. However, Kjelson et al. (1982) noted that
tagged chinook salmon fry grew faster in the estuary than in the river. Although
observed growth rates for YOY chinook salmon in Lake Ontario are similar to those
found in estuarine environments, it is difficult to know how these growth rates
compare to chinook salmon from other freshwater environments, since there is a
paucity of information regarding YOY chinook growth in freshwater (Healey, 1991).
However, if our growth rates are indeed higher than those found in other freshwater
environments, particularly riverine habitats, some of that difference could be
explained by the higher daily rations found in our study than in those conducted in
riverine environments (i.e., Sagar and Glova 1988).
28
Results from this study show that recently out-migrated naturally produced
YOY chinook salmon occupying the near-shore waters of Lake Ontario had an
exceptionally high daily ration and exhibited rapid growth rates. This high food
consumption rate, as many authors have suggested, is most likely the result of
excellent food availability in the near-shore habitat. Clearly, rapid growth of young
chinook salmon entering the harsh near-shore environment of Lake Ontario would
greatly enhance the survival of these vulnerable fish, as they would quickly attain a
large enough size to emigrate offshore, thus escaping near-shore predation and
improving their ability to consume piscine prey, such as alewife and rainbow smelt.
Furthermore, as previous studies have suggested (e.g., Kitchell and Crowder 1986;
Stewart and Ibarra 1991; Rand et al. 1994), overexploitation of fluctuating alewife
populations in the Great Lakes by overstocked salmonines could lead to an inability to
sustain current salmonine population levels. Lakewide declines in the salmonine sport
fishery would have a considerable negative impact on the local economy of the lake
communities. For this reason it is imperative that the contribution of naturally
produced chinook salmon to the lakewide salmonine fishery be assessed prior to the
planning of future annual chinook salmon stocking programs in Lake Ontario.
CHAPTER THREE
DIET AND PREY SELECTION OF OUT-MIGRATED AGE-0 CHINOOK
SALMON (ONCORHYNCHUS TSHAWYTSCHA) IN LAKE ONTARIO
Introduction
Alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) are the
predominant prey of large chinook salmon (Oncorhynchus tshawytscha) throughout
the Laurentian Great Lakes (Brandt 1986; Jude et al. 1987; Diana 1990; Rand and
Stewart 1998). Although it has been documented that small young-of-the-year (YOY)
chinook salmon tend to remain in shallow (< 2 m) near-shore waters in the Great
Lakes for several weeks immediately following out-migration from spawning
tributaries before dispersing offshore (Johnson and Ringler 1981; Elliott 1994), very
little is known about the sub-yearling chinook’s food habits during this critical period.
However, the food habits of YOY chinook salmon have been studied
extensively in riverine and estuarine habitats throughout the Pacific Northwest (e.g.,
Becker 1973; Reimers et al. 1978; Levy and Northcote 1981; Kjelson 1982) and in
New Zealand (e.g., Sagar and Glova 1987; 1988). In the Pacific Northwest, several
researchers have found that out-migrating chinook salmon tend to remain in estuaries
to feed on aquatic and terrestrial invertebrates for a period of time before emigrating to
the ocean (e.g., Reimers et al. 1978; Healey 1980; Kjelson et al. 1982). Moreover,
most of these studies have shown that juvenile chinook salmon are opportunistic,
diurnal feeders, preying on crustaceans, amphipods, and insects in the water column
and at the surface. For example, Becker (1973) reported that adult chironomids (5863%) and larval chironomids (17-18%) comprised the majority of the diet of YOY
chinook salmon in the Columbia River. Similarly, Levy and Northcote (1981)
reported that larval and adult chironomids were the most dominant prey of YOY
29
30
chinook salmon occupying the Fraser River marshes. On the other hand, Kjelson
(1982) found that YOY chinook salmon fed extensively on zooplankton, including
cladocerans and copepods, and adult insects, such as dipterans and homopterans, in the
Sacramento-San Joaquin River delta. Contrary to other studies, Bottom (1984)
observed that YOY chinook salmon fed actively at night on amphipods
(i.e., Corophium and Eogammarus) in the Sixes River estuary.
In New Zealand, where introduced chinook salmon have reproduced naturally
since the early 1900s (Unwin 1986), studies have shown that YOY chinook tend to be
opportunistic, diurnal feeders, preying on aquatic insects in the spring, especially
Deleatidium nymphs, and emerging terrestrial insects in the summer (Sagar and Glova
1987; 1988).
Much like the literature from the Pacific Northwest and New Zealand, diet
studies of YOY chinook salmon in the Great Lakes suggest that sub-yearling chinook
rely on aquatic and terrestrial insects during the first summer following emergence.
For example, Johnson (1981) reported that YOY chinook salmon in a tributary of the
Salmon River at the eastern end of Lake Ontario fed primarily on aquatic prey, mainly
ephemeropterans (64%) in May, but switched to a diet of mostly terrestrial insects
from June – September. Johnson (1983) later found that recently stocked chinook
salmon fed primarily on aquatic and terrestrial insects, such as adult dipterans and
coleopterans, as well as fish eggs, while occupying the shallow, near-shore areas of
Lake Ontario in early summer. Similarly, Elliott (1994) found that out-migrated YOY
chinook salmon in the near-shore waters of Lake Michigan fed primarily on terrestrial
insects in the spring and summer, with Bythotrephes and larval fish becoming an
important diet item by late summer.
The goal of this study was to describe the feeding habits of recently outmigrated YOY chinook salmon occupying the shallow near-shore waters of Lake
31
Ontario. The objectives of this study were to: 1) examine the diet and prey selection
of YOY chinook salmon in two geographically distinct regions of Lake Ontario (i.e.,
near the mouth of the Salmon River, near Pulaski, NY and near the mouth of Sandy
Creek, near Rochester, NY); and 2) identify diel feeding patterns of out-migrated
YOY chinook salmon near the mouth of the Salmon River, in Lake Ontario.
Methods
Study Site
From April – July of 2000, out-migrated YOY chinook salmon, along with
potential macroinvertebrate prey items, were sampled biweekly at two near-shore sites
in Lake Ontario. The first site was near the mouth of the Salmon River, just west of
Pulaski, New York and the second site was located near the mouth of Sandy Creek,
approximately 50 km west of Rochester, New York (Figure 3.1). Both sites consisted
of four sampling stations distributed along the shoreline, with two stations on either
side of the tributary mouth. In 2001, weekly diet and prey sampling was conducted
from April – July at the Salmon River site only.
32
Figure 3.1. Chinook salmon seining stations (1-4) along the southern coast of Lake
Ontario. The Sandy Creek site, west of Rochester, NY was sampled in 2000, while
the Salmon River site, located near Pulaski, NY was sampled in both 2000 and 2001.
At both sites, Station 4 was situated approximately 2500 meters from Station 3.
Prey Collection, 2000
Mid-water and surface prey sampling was conducted at dusk using a 4.88 m
neuston net, with a mouth opening of 0.5 x 1 m, and a mesh size of 1000 µm. The
neuston net was pulled by hand across the surface and parallel to the shoreline, in
water about one meter deep, for a distance of approximately 35 m and at a rate of
approximately 0.5 m·sec-1. Two replicate tows, each separated by approximately
100 m, were conducted at the two stations closest to the mouth of both the Salmon
33
River and Sandy Creek tributaries and the contents of each tow were placed
immediately in 70% ethanol for preservation. The prey specimens were later
separated by major taxonomic groupings (Borror et al. 1989) and individual head
capsules were counted using a stereo microscope at 10X or 20X magnification.
Fish Collection, 2000
Fish sampling at both the Salmon River and Sandy Creek sites began in midApril and continued through late-July and was conducted approximately biweekly at
the two sites for a total of 16 weeks, beginning with Sandy Creek on April 15th (Table
3.1). Out-migrated, age-0 chinook salmon were captured using a 1.2 x 36 m delta
knotless bag seine, with 0.95 cm mesh in the first 10.7 m of each wing and 0.32 cm
mesh in the remainder of the seine. The seine was hauled in a semicircular fashion,
with one end held at the beach. Three replicate seine hauls, each separated by
approximately 100 m, were conducted at each sampling station (i.e., 12 seine hauls per
night) beginning about 30 minutes after sunset and continuing throughout the night
until all replicates were completed (i.e., typically between 0300 and 0500). A random
sample of YOY chinook salmon were retained for diet analysis from each replicate
seine haul and placed immediately on dry ice to avoid further digestion of stomach
contents. Usually about 12-24 hours after each sampling effort, YOY chinook total
length was measured to the nearest mm (TL), wet weights were taken (0.1g), and
stomachs were removed and placed in 90% ethyl alcohol. All ingested prey were later
identified to major taxonomic groups (Borror et al. 1989) and counted using a stereo
microscope at 10X or 20X magnification. For macroinvertebrate prey items, only
individual head capsules were counted.
34
Table 3.1. Number and size of out-migrated age-0 chinook salmon collected from
Lake Ontario for stomach examination in 2000 (―, no sampling; n/a, not applicable).
Sandy Creek
Salmon River
Total Length (mm)
Mean ± s.d. Range
―
―
―
Week of
18-April
No.
―
No. Empty
―
24-April
1
0
41
n/a
11-May
20
1
76.2
16-May
―
―
22-May
14
30-May
Total Length (mm)
Mean ± s.d. Range
37.0
1.9
34-39
No.
6
No. Empty
0
n/a
―
―
―
―
―
5.0
68-86
―
―
―
―
―
―
―
―
19
1
46.9
9.1
38-74
0
74.7
5.5
65-88
―
―
―
―
―
―
―
―
―
―
20
0
51.3
8.7
39-82
7-June
38
0
79.2
5.4
62-88
―
―
―
―
―
13-June
―
―
―
―
―
20
0
62
7.4
48-75
19-June
12
0
91.8
7.6
74-100
―
―
―
―
―
27-June
―
―
―
―
―
20
0
72.5
4.5
60-79
29-June
5
0
93.4
11.7
75-103
―
―
―
―
―
11-July
―
―
―
―
―
6
1
74.3
8.2
65-87
24-July
―
―
―
―
―
6
0
82.0
7.0
74-93
90
1
79.9
9.42
62-103
97
2
59.5
14.5
34-93
Prey Collection, 2001
Mid-water and surface prey were sampled, preserved, sorted, and counted
using the same techniques as in 2000. However, to assess changes in prey availability
throughout the day, two replicate neuston hauls were conducted at Station 2, just south
of the Salmon River mouth, on May 21, June 6, June 12, June 18, and June 25, during
each of the three distinct chinook sampling periods (i.e., dawn, midday, and dusk).
35
Fish Collection, 2001
Sampling was conducted approximately once per week at the Salmon River
site from mid-April to mid-July, for a total of 13 weeks. Out-migrated YOY chinook
salmon were captured using the same techniques as in 2000, except that only two
replicate seine hauls were performed at each of the four seining stations, instead of
three (i.e., eight seine hauls per night). In addition to dusk sampling, daytime
collections were made at Station 2 on five dates (i.e., May 21, June 6, June 12, June
18, and June 25). On these five dates, a random sample of 10 chinook were retained
for diet analysis at three distinct time periods: approximately 30-60 minutes after
sunrise (dawn); about 1400 (mid-day); and about 30 minutes after sunset (dusk; Table
3.2). Chinook retained for diet analysis were placed immediately on dry ice to avoid
further digestion of stomach contents. All ingested prey were later identified to major
taxonomic groups and counted using the same methods as in 2000.
36
Table 3.2. Number and size of out-migrated age-0 chinook salmon collected with a
seine near the mouth of the Salmon River in Lake Ontario in 2001 (d=dawn;
m=midday; dk=dusk).
Date
Total Length (mm)
Mean
± s.d.
Range
No.
No. empty
16-April
3
1
67.0
51.2
36-126
23-April
6
0
39.2
1.5
37-41
30-April
13
0
64.2
32.5
37-117
7-May
9
0
51.9
25.1
38-118
16-May
4
0
46.0
5.4
40-53
21-May (d)
10
0
49.3
5.8
41-61
21-May (m)
8
0
54.1
11.2
41-72
21-May (dk)
10
0
66.4
7.7
50-80
1-June
20
0
47.9
4.7
40-58
6-June (d)
10
0
50.3
5.6
42-61
6-June (m)
10
0
51.4
5.8
47-62
6-June (dk)
10
0
51.9
4.1
46-58
12-June (d)
10
0
53.1
4.1
47-62
12-June (m)
10
0
58.6
6.0
50-68
12-June (dk)
10
0
62.2
5.3
55-68
18-June (d)
10
0
62.9
5.4
55-68
18-June (m)
10
0
63.9
5.6
57-77
18-June (dk)
10
2
63.2
4.5
56-70
25-June (d)
10
0
60.1
5.9
49-68
25-June (m)
10
0
63.7
4.8
56-72
25-June (dk)
10
0
67.9
5.4
56-75
16-July
21
4
74.1
7.3
61-87
23-July
4
0
73.3
7.1
66-83
228
7
58.8
14.4
36-126
37
Prey Selectivity
Strauss’s (1979) linear index of food selection was used to assess prey
selection by age-0 chinook salmon in Lake Ontario because of the often extremely low
sample sizes of prey captured in the neuston net in 2000 and 2001 relative to the
number of prey found in the age-0 chinook stomachs. Strauss' index is well suited for
these situations because of the inherent normal distribution of the linear index that
exists even in situations where the prey and diet samples are very unequal (Strauss
1979). Thus, as Lechowicz (1982) reported, Strauss’ index is not prone to skewness in
the sampling distributions and is less likely to give extreme selectivity values in the
presence of low sample sizes, as do other commonly used indices (e.g., Ivlev 1961,
Chesson 1978, and Vanderploeg and Scavia 1979).
Strauss (1979) described the calculation of the linear index of food selection
(L) in equation 1:
(1) L = ri – pi
where, ri is the proportion of prey in class i in the diet and pi is the proportion of prey
in class i in the environment. Possible values range from +1 to –1, with positive
values indicating active selection and negative values indicating avoidance or
inaccessibility. Strauss (1979) also described the estimated sample variance of L in
equation 2
(2) s2(L) = ri(1-ri)/nr + pi(1-pi)/np
where nr is the total number of prey found in the diet and np is the total number of prey
found in the environment (df = nr + np-2).
For all selectivity analyses performed in this study, the most commonly
consumed taxa, mature chironomidae, was pooled with larval chironomidae, while all
other taxa were considered non-chironomidae. However, only chironomidae index
38
values were reported, since results are mirrored (e.g., +0.35 and –0.35) when only two
taxa are used in Strauss’ selectivity index.
Results
Nocturnal Feeding, 2000
In order to determine the extent of nocturnal feeding and to assess the need for
mid-season changes in sampling protocol, I examined the stomachs of 80 YOY
chinook (M = 44.1 mm TL; Range = 38-74 mm) salmon captured between 2120 and
0.025
50
0.020
40
0.015
30
Weight
% Empty
0.010
0.005
20
10
0.000
Percentage of Empty Stomachs
Wet Weight (g)
0410 at the Salmon River site on May 16, 2000 (Figure 3.2).
0
21:20
23:45
1:50
4:10
Time
Figure 3.2. Mean wet weights of stomach contents and percentage of empty stomachs
of out-migrated YOY chinook salmon captured after dusk on May 16, 2000 near the
mouth of the Salmon River in Lake Ontario, NY. Error bars represent 95%
confidence intervals.
39
Subsequent analyses showed that stomach wet weight declined significantly after dusk
(F3,59 = 3.82; p = 0.01; ANOVA) and that there was also a significant decline in
stomach wet weight between 2345 and 0150 (F1,59; p = 0.01). Moreover, the
percentage of empty stomachs increased sharply as the night progressed (i.e., 2120 =
0%; 0410 = 45%). In general, stomach contents were also unidentifiable in fish
captured after midnight, indicating a cessation of fresh prey consumption after dark.
Therefore, based on these data, it was concluded that out-migrated YOY chinook
salmon did not feed actively at night in Lake Ontario. Subsequently, only chinook
salmon captured during the day through 2300 were used for diet analyses in 2000 and
2001 (including May 16, 2000 samples).
Prey, 2000
Mature chironomidae were the most abundant taxa collected in the neuston
tows on all dates at the Sandy Creek site in 2000, with the exception of June 29, when
larval and emerging chironomidae were the most prevalent invertebrates captured
(69.6%; Table 3.3). Prey samples taken on April 24 at Sandy Creek were disregarded
because of fouled neuston samples due to malfunctioning field equipment.
40
Table 3.3. Relative abundance (%) of prey items sampled at dusk using a 1000 µm
neuston net near Sandy Creek in Lake Ontario in 2000 (n, total number of prey items;
—, not present).
11-May 22-May 7-June 19-June 29-June
n = 22
n = 13 n = 24 n = 177 n = 56
Prey type
Aquatic Organisms
Amphipoda
Collembola
Diptera
Chironomidae £
Chironomidae
Other £
Cercopagis spp.
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Leptodora
Oligochaeta
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Ephemeroptera
Hemiptera
Homoptera
Hymenoptera
Odonata
Trichoptera
Total % terrestrial
22.7
—
—
—
—
—
—
—
—
—
9.1
68.2
—
—
—
—
—
—
—
—
—
—
100
7.7
69.2
—
—
—
—
—
—
—
—
—
—
76.8
8.3
62.5
—
—
—
—
—
—
—
8.3
—
—
79.1
12.4
61.0
1.1
—
—
—
—
—
—
—
—
—
74.5
69.6
23.2
—
—
—
—
—
—
—
1.8
—
—
94.6
—
—
—
—
—
—
—
—
—
0
7.7
15.4
—
—
—
—
—
—
—
23.2
—
12.5
—
4.2
—
—
4.2
—
—
20.9
1.1
8.5
—
—
11.9
—
1.1
—
2.8
25.5
—
—
—
—
5.4
—
—
—
—
5.4
£ Indicates taxa that were either larvae, nymphs, or pupae
In contrast to the Sandy Creek site, prey samples at the Salmon River site in
2000 were more variable, with amphipoda dominating in May (84.1% on May 16 and
44.4% on May 30) and Leptodora becoming more prevalent in June and July (Table
41
3.4). Prey samples taken on April 18 were disregarded because of fouled neuston
samples due to malfunctioning field equipment.
Table 3.4. Relative abundance (%) of prey items sampled at dusk using a 1000 µm
neuston net near the Salmon River in Lake Ontario in 2000 (n, total number of prey
items; —, not present).
16-May 30-May 13-June 27-June 11-July 24-July
n = 44
n = 36
n = 36
n = 20 n = 687 n = 22
Prey type
Aquatic Organisms
Amphipoda
Collembola
Diptera
Chironomidae £
Chironomidae
Other £
Cercopagis spp.
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Leptodora
Oligochaeta
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Ephemeroptera
Hemiptera
Homoptera
Hymenoptera
Odonata
Trichoptera
Total % terrestrial
84.1
—
44.4
—
—
—
—
15.0
1.0
—
—
—
2.3
—
—
—
—
—
—
13.6
—
—
—
—
100
—
41.7
—
2.8
—
—
—
—
8.3
—
—
—
97.2
2.8
58.3
—
—
—
—
—
—
30.6
—
—
—
91.7
5.0
45.0
—
—
—
—
—
—
5.0
—
—
—
70.0
1.2
54.3
0.6
—
—
—
—
0.3
2.6
—
—
—
60.1
—
22.7
—
13.7
—
—
—
4.5
59.1
—
—
—
100
—
—
—
—
—
—
—
—
—
0
—
—
2.8
—
—
—
—
—
—
2.8
—
—
8.3
—
—
—
—
—
—
8.3
—
10.0
—
—
—
5.0
10.0
—
5.0
30.0
0.1
2.9
1.6
0.1
29.0
0.4
3.5
0.1
2.2
39.9
—
—
—
—
—
—
—
—
—
0
£ Indicates taxa that were either larvae, nymphs, or pupae
42
Diet, 2000
A total of 187 out-migrated YOY chinook salmon captured at the Sandy Creek
(90) and Salmon River (97) sites were examined for stomach analysis in 2000, with
chinook captured at the Sandy Creek site being much larger (M = 79.9 mm TL; S.E. =
8.4) than the fish captured at the Salmon River site (M = 59.5 mm TL; S.E. = 6.1;
Table 3.1). However, chinook captured at both sites fed almost exclusively on aquatic
taxa, with mature chironomidae constituting the bulk of the diet throughout the study
period (Tables 3.5 and 3.6). Chinook salmon captured on June 27 at the Salmon River
site were the only exception, as they consumed 58.8% terrestrial prey and fed on a
wide array of taxa, including hemiptera (29.4%), hymenoptera (24%) and amphipoda
(10.7%; Table 3.6).
43
Table 3.5. Relative abundance (%) of prey items consumed at dusk by out-migrated
age-0 chinook salmon near Sandy Creek in Lake Ontario in 2000 (n1, total number of
fish examined; n2, total number of prey items; *, <0.1%; —, not present).
24-April 11-May 22-May
7-June
19-June 29-June
n1 = 1
n1 = 20 n1 = 14 n1 = 38
n1 = 12
n1 = 5
n2 = 7 n2 = 427 n2 = 535 n2 = 1419 n2 = 648 n2 = 437
Prey type
Aquatic Organisms
Amphipoda
Cladocera
Diptera
Chironomidae £
Chironomidae
Other £
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Hemiptera
Homoptera
Hymenoptera
Total % terrestrial
—
—
—
—
0.2
—
—
—
0.5
—
—
—
—
100
—
—
—
—
—
—
—
100
0.2
97.2
0.2
—
—
—
0.2
—
—
97.8
—
96.1
—
—
—
—
—
—
—
96.3
0.1
89.8
—
—
—
—
—
*
—
89.9
0.1
65.6
—
—
—
—
—
—
—
66.2
—
94.2
—
—
—
—
—
—
—
94.2
—
—
—
—
—
—
0
—
1.2
—
0.5
—
0.5
2.2
—
0.9
1.3
—
—
1.5
3.7
0.2
2.7
2.1
1.6
0.5
3.0
10.1
0.9
4.6
0.9
23.5
1.4
2.5
33.8
—
0.5
1.6
0.5
0.2
3.0
5.8
£ Indicates taxa that were either larvae, nymphs, or pupae
44
Table 3.6. Relative abundance (%) of prey items consumed at dusk by out-migrated
age-0 chinook salmon near the Salmon River in Lake Ontario in 2000 (n1, total number
of fish examined; n2, total number of prey items; *, <0.1%; —, not present).
18-April
n1 = 6
n2 = 20
Prey type
Aquatic Organisms
Amphipoda
—
Cladocera
—
Diptera
Chironomidae £
50.0
Chironomidae
50.0
Other £
—
Coleoptera £
—
Ephemeroptera £
—
Fish eggs
—
Fish larvae
—
Trichoptera £
—
Zygoptera £
—
Total % aquatic
100
Terrestrial Organisms
Arachnida
—
Coleoptera
—
Diptera
—
Hemiptera
—
Homoptera
—
Hymenoptera
—
Total % terrestrial
0
16-May
n1 = 19
n2 = 638
30-May
n1 = 20
n2 = 563
13-June
n1 = 20
n2 = 549
27-June
n1 = 20
n2 = 1084
11-July
n1 = 6
n2 = 124
24-July
n1 = 6
n2 = 178
0.5
69.0
3.2
—
—
—
10.7
—
2.4
—
2.2
—
0.9
27.6
0.9
—
—
—
—
—
—
98.9
—
92.5
0.7
—
—
—
—
—
—
96.5
—
96.0
—
—
—
—
—
—
—
96.0
17.6
12.9
—
—
—
—
—
—
—
41.2
1.6
79.8
—
—
—
—
—
—
—
83.8
1.7
93.8
—
—
—
—
—
—
—
97.8
—
—
0.3
0.5
—
0.3
1.1
—
1.2
0.9
0.9
—
0.5
3.5
—
1.3
0.9
0.9
—
0.9
4.0
0.2
3.2
—
29.4
1.9
24.0
58.8
—
3.2
0.8
8.9
—
3.2
16.1
—
—
1.1
1.1
—
—
2.2
£ Indicates taxa that were either larvae, nymphs, or pupae
Chinook salmon feeding at dusk at both Sandy Creek and the Salmon River
sites in 2000 ate predominantly mature chironomidae, even though prey samples
indicated that mature chironomidae were not always the most abundant prey item in
neuston samples collected from near-shore waters (Figures 3.3-3.4).
45
100
Terrestrial
A
80
Other aquatic
60
Chiro-M
Percent composition
40
20
Chiro-L
Ap
0
100
B
80
60
40
20
29-Jun
22-Jun
15-Jun
8-Jun
1-Jun
25-May
18-May
11-May
0
Time
Figure 3.3. Relative abundance (%) of amphipods (Ap), mature chironomids
(Chiro-M), chironomid larval/pupae (Chiro-L), all other identified aquatic prey, and
all terrestrial organisms in both the field (A) and the stomachs (B) of YOY chinook
salmon sampled at dusk near Sandy Creek in Lake Ontario during May-June 2000.
46
100
A
Terrestrial
80
Other Aquatic
60
Percent composition
40
Chiro-M
Amphipods
20
Chiro-L
0
100
B
80
60
40
18-Jul
4-Jul
27-Jun
20-Jun
13-Jun
6-Jun
30-May
23-May
16-May
0
11-Jul
20
Time
Figure 3.4. Relative abundance (%) of amphipods, mature chironomids (Chiro-M),
chironomid larval/pupae (Chiro-L), all other identified aquatic prey, and all terrestrial
organisms in both the field (A) and the stomachs (B) of YOY chinook salmon sampled
at dusk near the Salmon River in Lake Ontario during May-June 2000.
Prey, dusk 2001
Mature chironomidae were the most abundant taxa in the dusk prey samples at
the Salmon River site in 2001, with the exception of late June and July, when larval
fish, Cercopagis, oligochaeta, and Leptodora became noticeably more abundant
(Table 3.7).
47
Table 3.7. Relative abundance (%) of prey items sampled at dusk using a 1000 µm
neuston net near the Salmon River in Lake Ontario in 2001 (n, total number of prey
items; —, not present).
7-May
Prey type
n = 72
Aquatic Organisms
Amphipoda
—
Collembola
—
Diptera
Chironomidae £
—
Chironomidae
94.4
Other £
—
Cercopagis spp.
—
Coleoptera £
1.4
Ephemeroptera £
—
Fish eggs
—
Fish larvae
—
Leptodora
—
Oligochaeta
—
Trichoptera £
—
Zygoptera £
—
Total % aquatic
95.8
Terrestrial Organisms
Arachnida
—
Coleoptera
1.4
Diptera
2.8
Ephemeroptera
—
Hemiptera
—
Homoptera
—
Hymenoptera
—
Odonata
—
Trichoptera
—
Total % terrestrial
4.2
21-May
n = 21
6-June
n=9
12-June
n = 39
18-June
n = 21
25-June
n = 11
16-July
n = 47
23-July
n = 94
23.8
—
—
—
2.6
—
—
—
—
—
—
—
—
—
—
47.6
—
—
—
—
—
—
14.3
—
—
—
85.7
33.3
66.7
—
—
—
—
—
—
—
—
—
—
100
7.7
28.2
—
—
—
—
—
—
—
10.3
2.6
—
51.3
—
71.4
—
—
—
—
—
—
—
—
—
—
71.4
—
27.3
—
—
—
—
—
—
9.1
27.3
—
—
63.6
—
25.5
—
4.3
—
—
—
42.6
6.4
14.9
—
—
93.6
8.5
2.1
—
14.9
9.6
—
—
7.4
23.4
28.7
—
—
94.6
—
—
14.3
—
—
—
—
—
—
14.3
—
—
—
—
—
—
—
—
—
0
—
15.4
15.4
—
7.7
10.3
—
—
—
48.7
—
—
14.3
—
—
4.8
9.5
—
—
28.6
27.3
—
9.1
—
—
—
—
—
—
36.4
—
—
4.3
—
—
—
2.1
—
—
6.4
2.1
—
—
—
—
1.1
1.1
—
1.1
5.4
£ Indicates taxa that were either larvae, nymphs, or pupae
Prey, daytime 2001
Amphipods dominated during dawn and midday periods in the May prey
samples, while the remainder of the daytime prey samples were quite variable, with
either mature chironomidae, homoptera, or chironomidae larvae/pupae dominating the
prey samples in June and July (Table 3.8).
48
Table 3.8. Relative abundance (%) of prey items sampled at dawn and midday (time,
1400) using a 1000 µm neuston net near the Salmon River in Lake Ontario in 2001
(n, total number of prey items; —, not present).
21-May
6-June
12-June
dawn midday dawn midday dawn midday
n = 89 n = 38 n = 37 n = 127 n = 42 n = 72
Prey type
Aquatic Organisms
Amphipoda
69.7
Collembola
—
Diptera
Chironomidae £
2.2
Chironomidae
23.6
Other £
—
Cercopagis spp.
—
Coleoptera £
—
Ephemeroptera £
—
Fish eggs
—
Fish larvae
—
Leptodora
1.1
Oligochaeta
—
Trichoptera £
—
Zygoptera £
—
Total % aquatic
96.7
Terrestrial Organisms
Arachnida
—
Coleoptera
—
Diptera
2.2
Ephemeroptera
—
Hemiptera
1.1
Homoptera
—
Hymenoptera
—
Odonata
—
Trichoptera
—
Total % terrestrial
3.3
50.0
—
—
—
—
—
2.4
—
4.2
—
10.5
28.9
—
—
—
—
—
—
2.6
2.6
—
—
94.7
8.1
86.5
—
—
—
—
—
2.7
—
—
—
—
98.3
0.8
94.5
—
—
—
—
—
—
—
—
—
—
95.2
40.5
23.8
—
2.4
—
—
—
—
—
14.2
—
—
83.3
16.7
38.9
—
—
—
—
—
—
—
4.2
4.2
—
68.1
2.6
2.6
—
—
—
—
—
—
—
5.3
—
—
—
—
—
—
2.7
—
—
2.7
—
—
1.6
—
—
0.8
2.4
—
—
4.8
2.4
—
7.1
—
—
4.8
2.4
—
—
16.7
1.4
2.8
4.2
—
13.9
8.3
1.4
—
—
31.9
49
Table 3.8 (Continued)
18-June
25-June
dawn midday dawn midday
n = 177 n = 27 n = 15 n = 94
Prey type
Aquatic Organisms
Amphipoda
Collembola
Diptera
Chironomidae £
Chironomidae
Other £
Cercopagis spp.
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Leptodora
Oligochaeta
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Ephemeroptera
Hemiptera
Homoptera
Hymenoptera
Odonata
Trichoptera
Total % terrestrial
1.1
—
3.7
—
—
—
2.1
—
2.3
20.3
—
—
—
—
—
—
—
—
1.1
—
24.8
18.5
63.0
—
—
—
—
—
—
—
3.7
—
—
88.9
13.3
60.0
—
6.7
—
—
—
—
—
—
—
—
80.0
12.8
45.7
—
4.2
—
2.1
—
1.1
—
22.3
—
—
90.4
—
14.7
14.7
—
—
39.0
6.8
—
—
75.2
3.7
3.7
—
—
—
—
3.7
—
—
11.1
—
—
6.7
—
13.3
—
—
—
—
20.0
—
—
6.4
—
—
3.2
—
—
—
9.6
£ Indicates taxa that were either larvae, nymphs, or pupae
50
Diet, dusk 2001
Out of a total of 228 (M = 58.8 mm TL; Range 36-126 mm) out-migrated
YOY chinook salmon captured at the Salmon River site in 2001, 130 (Range 36-126
mm TL) were sampled after dusk and examined for diet analysis. As in 2000, chinook
collected after dusk consumed mostly aquatic organisms (> 74%; Table 3.9).
Table 3.9. Relative abundance (%) of prey items consumed at dusk by out-migrated
age-0 chinook salmon near the Salmon River in Lake Ontario in 2001 (n1, total number
of fish examined; n2, total number of prey items; —, not present).
16-April
n1 = 3
n2 = 27
23-April
n1 = 6
n2 = 86
30-April
n1 = 13
n2 = 615
7-May
n1 = 9
n2 = 482
16-May
n1 = 4
n2 = 50
21-May
n1 = 10
n2 = 322
1-June
n1 = 20
n2 = 118
40.7
—
1.2
—
—
—
0.2
—
—
—
21.7
—
—
—
7.4
40.7
—
—
—
—
—
—
—
88.9
—
97.6
—
—
—
—
—
—
—
98.8
—
98.9
—
—
—
—
—
—
—
98.9
—
98.0
—
—
—
—
—
—
—
98.2
—
94.0
—
—
—
—
—
—
—
94.0
—
76.4
—
—
—
—
—
—
—
98.1
19.5
77.1
—
0.8
—
—
—
—
—
97.5
—
—
—
7.4
—
3.7
11.1
—
—
1.2
—
—
—
1.2
—
—
1.0
—
—
0.1
1.1
—
—
1.6
—
—
0.2
1.8
—
—
6.0
—
—
—
6.0
—
—
1.9
—
—
—
1.9
—
—
0.8
—
0.8
0.8
2.5
Prey type
Aquatic Organisms
Amphipoda
Cladocera
Diptera
Chironomidae £
Chironomidae
Other £
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Hemiptera
Homoptera
Hymenoptera
Total % terrestrial
51
Table 3.9 (Continued)
6-June
n1 = 10
n2 = 428
12-June
n1 = 10
n2 = 402
18-June
n1 = 10
n2 = 176
25-June
n1 = 10
n2 = 284
16-July
n1 = 21
n2 = 115
23-July
n1 = 4
n2 = 7
—
—
2.2
—
4.5
—
6.0
—
4.3
—
—
—
12.6
86.0
—
—
—
—
—
—
—
98.6
5.7
86.1
—
—
—
—
—
—
—
94.0
17.6
47.2
—
3.4
—
1.1
—
—
0.6
74.5
8.8
65.8
—
13.0
—
—
—
—
—
93.6
0.9
77.4
—
1.7
—
—
—
—
—
84.3
—
100
—
—
—
—
—
—
—
100
—
—
1.2
0.2
—
—
1.4
0.3
0.8
1.7
2.4
—
0.8
6.0
—
1.1
—
24.4
—
—
25.5
—
1.4
0.4
3.2
—
1.4
6.4
—
1.7
0.9
—
0.9
12.2
15.7
—
—
—
—
—
—
0
Prey type
Aquatic Organisms
Amphipoda
Cladocera
Diptera
Chironomidae £
Chironomidae
Other £
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Hemiptera
Homoptera
Hymenoptera
Total % terrestrial
£ Indicates taxa that were either larvae, nymphs, or pupae
Moreover, dusk chinook ate predominantly mature chironomidae, even though
prey samples indicated that mature chironomidae were not always the most abundant
prey item in neuston samples collected from near-shore waters, especially in the midsummer months (Figure 3.5).
52
100
Terrestrial
A
80
60
Chiro-M
Other Aquatic
40
Chiro-L
Percent composition
20
Amphipods
0
100
B
80
60
40
23-Jul
9-Jul
2-Jul
25-Jun
18-Jun
11-Jun
4-Jun
28-May
21-May
14-May
7-May
0
16-Jul
20
Time
Figure 3.5. Relative abundance (%) of amphipods, mature chironomids (Chiro-M),
chironomid larval/pupae (Chiro-L), all other identified aquatic prey, and all terrestrial
organisms in both the field (A) and the stomachs (B) of YOY chinook salmon sampled
at dusk near the Salmon River in Lake Ontario during May-July 2001.
Diet, daytime 2001
The chinook (N = 98; Range 41-77 mm TL) sampled during the dawn and
midday intervals at the Salmon River site in 2001 also consumed predominantly
aquatic prey (> 71%), with mature chironomidae constituting the bulk of the diet
(Table 3.10). The only exceptions were the two dawn samples on May 21 and June
53
12, when larval fish (40.4%) and chironomidae larvae/pupae (49%), respectively were
also abundant in the diet samples.
Table 3.10. Relative abundance (%) of prey items consumed at dawn and midday
(time, 1400) by out-migrated age-0 chinook salmon near the Salmon River in Lake
Ontario in 2001(n1, total number of fish examined; n2, total number of prey items;
—, not present).
21-May
6-June
12-June
dawn midday
dawn
midday
dawn
midday
n1 = 10 n1 = 8 n1 = 10 n1 = 10 n1 = 10 n1 = 10
n2 = 47 n2 = 51 n2 = 376 n2 = 444 n2 = 400 n2 = 304
Prey type
Aquatic Organisms
Amphipoda
14.9
Cladocera
—
Diptera
Chironomidae £
—
Chironomidae
44.7
Other £
—
Coleoptera £
—
Ephemeroptera £
—
Fish eggs
—
Fish larvae
40.4
Trichoptera £
—
Zygoptera £
—
Total % aquatic
100
Terrestrial Organisms
Arachnida
—
Coleoptera
—
Diptera
—
Hemiptera
—
Homoptera
—
Hymenoptera
—
Total % terrestrial
0
9.8
—
—
—
—
—
—
—
0.7
—
—
74.5
—
—
—
—
13.7
—
—
98.0
5.3
93.1
—
—
—
0.3
—
—
—
98.7
18.0
77.3
—
—
—
1.6
—
—
—
96.9
49.0
47.2
—
0.3
—
—
0.3
—
—
96.8
5.9
83.9
—
1.0
—
—
—
—
—
91.5
—
—
—
—
2.0
—
2.0
—
—
1.0
0.3
—
—
1.3
—
—
1.3
1.8
—
—
3.1
—
0.5
—
2.0
—
0.7
3.2
—
1.0
1.3
4.9
0.3
1.0
8.5
54
Table 3.10 (Continued)
18-June
25-June
dawn
midday dawn midday
n1 = 10 n1 = 10 n1 = 10 n1 = 10
n2 = 729 n2 = 485 n2 = 79 n2 = 828
Prey type
Aquatic Organisms
Amphipoda
Cladocera
Diptera
Chironomidae £
Chironomidae
Other £
Coleoptera £
Ephemeroptera £
Fish eggs
Fish larvae
Trichoptera £
Zygoptera £
Total % aquatic
Terrestrial Organisms
Arachnida
Coleoptera
Diptera
Hemiptera
Homoptera
Hymenoptera
Total % terrestrial
—
—
3.1
—
17.7
—
1.4
—
0.8
71.3
—
—
—
20.4
—
—
—
92.6
16.7
50.3
—
0.2
—
—
—
—
1.2
71.6
—
73.4
—
—
—
—
3.8
—
2.5
97.4
1.0
92.0
—
0.5
—
—
—
—
—
94.9
—
1.1
0.8
5.1
0.3
0.1
7.4
0.2
0.6
0.6
26.0
1.0
—
28.4
1.3
—
—
1.3
—
—
2.6
—
0.1
1.1
2.7
0.4
0.8
5.1
£ Indicates taxa that were either larvae, nymphs, or pupae
Prey Selectivity, dusk 2000-2001
Strauss’s (1979) index of food selection (L) showed that out-migrated, YOY
chinook feeding at dusk at the Sandy Creek site in 2000 exhibited only a slight feeding
preference for chironomids (i.e., L values near zero), while chinook feeding at dusk at
the Salmon River site in both 2000 and 2001 strongly preferred chironomids (i.e., L
values approaching one) throughout most of the sampling period (Figure 3.6).
55
1
SC (00)
SR (00)
SR (01)
0.8
L value
0.6
0.4
0.2
0
-0.2
-0.4
4
23
-2
6
ly
Ju
Ju
ly
11
-1
529
ne
2
Ju
819
Ju
ne
1
213
ne
1
Ju
Ju
ne
6
-7
0
21
-3
ay
M
M
ay
M
ay
11
-1
6
7
-0.6
Date
Figure 3.6. Pattern of selectivity of chironomidae by YOY chinook salmon captured
at dusk near Sandy Creek in 2000 and the Salmon River in 2000 and 2001 using
Strauss’ linear index (L). Vertical lines represent 95% confidence intervals.
Prey Selectivity, diel 2001
Diel prey selection analysis at the Salmon River site from May 21 – June 25,
2001 revealed that out-migrated, YOY chinook showed a somewhat consistent pattern
of low-moderate preference for chironomidae both throughout the day and over the
entire six-week study period (Figure 3.7). However, there were two dates (i.e., June 6
and June 18) where chironomids were eaten rather opportunistically (i.e., L values
approaching zero), especially later in the day.
56
0.6
Dawn
0.5
Midday
Dusk
0.4
L value
0.3
0.2
0.1
0.0
-0.1
-0.2
21-May
6-June
12-June
18-June
25-June
Date
Figure 3.7. Diel pattern of selectivity of chironomidae by YOY chinook salmon near
the Salmon River in 2001 using Strauss’ linear index (L). Vertical lines represent 95%
confidence intervals.
Discussion
Young chinook salmon in Lake Ontario were primarily diurnal feeders as
indicated by both a decrease in gut content wet weight and the lack of identifiable prey
in stomach samples examined after midnight. Although, Sagar and Glova (1987)
suggested that a lack of nocturnal feeding in the Rakaia River was most likely due to
turbid conditions, it was unlikely that turbidity was a relevant factor in near-shore
Lake Ontario waters because the substrate in the near-shore areas of both Sandy Creek
and Salmon River was clearly visible in less than two meters of water on calm
evenings. A more likely explanation for the lack of nocturnal feeding in the near-
57
shore areas of Lake Ontario stems from the abundance of large piscivorous predators,
especially yellow perch (Perca flavescens) and smallmouth bass (Micropterus
dolomieu), which although entirely absent during daytime sampling efforts, comprised
much of the bycatch in our evening seine hauls. The presence of these predators
would likely suppress surface feeding activity by young chinook that might seek to
avoid predation by hiding among the cobble substrate rather than risk exposure near
the water’s surface (Vehanen 2003).
Many studies in the Pacific Northwest and in New Zealand have shown that
aquatic taxa, such as, zooplankton, amphipods, and mayfly nymphs tend to have
significant importance in the diets of YOY chinook salmon, especially in early spring
(e.g., Rondorf et al. 1990; Sagar and Glova 1987). Results from this study also show
that out-migrated YOY chinook occupying the shallow near-shore areas near Sandy
Creek and the Salmon River fed heavily on aquatic taxa, with mature chironomidae
constituting the bulk of the diet. Even though YOY chinook were significantly larger
at Sandy Creek (M = 80 mm TL) in 2000 than the chinook captured at the Salmon
River site in both 2000 (M = 60 mm TL) and 2001 (M = 59 mm TL), fish at both
locations displayed similar feeding patterns. For instance, young chinook feeding at
dusk at the Sandy Creek site consumed at least 66% aquatic taxa, especially adult
chironomidae, on all sampling dates, while chinook feeding at dusk at the Salmon
River location in both 2000 and 2001 ate at least 74% aquatic taxa on all but one
sampling date (i.e., June 27, 2000, 41% aquatic). Moreover, daytime samples at the
Salmon River site in 2001 showed similar results, as aquatic taxa were consumed at
least 71% of the time, with the most predominant prey being mature chironomidae.
Johnson (1983) found similar results, as recently stocked YOY chinook fed heavily on
aquatic organisms near the Salmon River in Lake Ontario, with as much as 63% of
their diet being adult chironomidae.
58
In addition, zooplankton were essentially absent in the chinook diets at both
locations, even though large taxa such as Leptodora and Cercopagis were abundant in
many of the late summer prey samples. In fact, only one chinook out of 415 fish
examined ate zooplankton (i.e., Daphnia spp., Salmon River, May 16, 2000). This is
in stark contrast to chinook salmon residing in the Pacific Northwest, where estuarine
and reservoir chinook tend to feed heavily on cladocerans and calanoid and cyclopoid
copepods at some point during the season (Kjelson 1982; Rondorf et al. 1990). Some
of the absence of larger predatory zooplankton, such as Cercopagis, in the diets of
sub-yearling chinook in Lake Ontario could be the result of limited spatial overlap or
because of the extremely long caudal spine of some species, such as Cercopagis
pengoi (Bushnoe et al. 2003).
Johnson (1981) found that in a tributary of the Salmon River in Lake Ontario
recently emerged chinook salmon ate 96% aquatic organisms in May, but switched to
a diet of mostly terrestrial prey in late summer as terrestrial insects became more
abundant. However, we observed no evidence of a seasonal diet shift in the nearshore waters of Lake Ontario. For example, although aquatic taxa such as amphipods
were relatively abundant in early prey samples at the Salmon River site in both years,
prey selectivity analysis showed that non-chironomidae taxa were typically avoided
(L < -0.5) in favor of chironomids.
In addition, prey selection indices also show that the chinook in the near-shore
waters of Lake Ontario displayed little evidence of a diel shift in food preference.
During both the daytime and dusk sampling periods at the Salmon River site and at
dusk at the Sandy Creek site, chinook moderately selected (L = 0.2-0.5) for
chironomids, while most often avoiding other available taxa. However, because of the
low sample sizes of the neuston samples, especially during the day hauls, it is difficult
to make a clear case for negative selection of other potential prey items. For example,
59
aquatic taxa, such as amphipods and larval fish, which were at times abundant in the
diet, particularly at the Salmon River site, were most often absent in the neuston
samples. Several factors may have contributed to the typically low neuston catches,
including a large mesh size (1000 µm), a slow haul rate (about 0.5 m·sec-1), or choppy
water surface conditions caused by wave and/or wind action.
The feeding behavior of out-migrated YOY chinook salmon in Lake Ontario is
quite similar to that of juvenile chinook residing in tributaries and rivers, in that both
tend to feed on a large variety of prey types, whether in the water column or at the
water’s surface (Johnson 1981; Sagar and Glova 1987). Moreover, the chinook
examined in this study showed a moderate to strong preference for chironomidae both
at the air-water interface and in the water column, while at the same time typically
avoiding non-chironomid taxa. This ability to adapt to the often harsh, scoured nearshore environment of Lake Ontario should enhance the chinook’s ability to thrive after
out-migration, thus attaining a large enough smolt size (i.e., about 100 mm TL; Elliott
1994) to emigrate offshore in late summer as near-shore water temperatures approach
hazardous levels (i.e., > 23oC; Scott and Crossman 1973). This bodes well for
chinook salmon in Lake Ontario, especially those that are naturally produced, as they
would seem to have an excellent head start in becoming successfully recruited to the
lake’s adult chinook salmon population.
BIBLIOGRAPHY
Amundsen, P.A. and Klemetsen, A. 1988. Diet, gastric evacuation rates and food
consumption in a stunted population of Arctic charr, Salvelinus alpinus L., in
Takvatn, northern Norway. Journal of Fish Biology 33: 697-709.
Angradi, T.R., and Griffith, J.S. 1990. Diel feeding chronology and diet selection of
rainbow trout (Oncorhynchus mykiss) in the Henry’s Fork of the Snake River,
Idaho. Canadian Journal of Fisheries and Aquatic Sciences 47: 199-209.
Bajkov, A.D. 1935. How to estimate the daily food consumption of fish under natural
conditions. Transactions of the American Fisheries Society 65: 288-289.
Becker, C.D. 1973. Food and growth parameters of juvenile chinook salmon,
Oncorhynchus tshawytscha, in central Columbia River. U.S. Fisheries
Bulletin 71: 387-400.
Boisclair, D., and Leggett, W.C. 1985. Rates of food exploitation by littoral fishes in
a mesotrophic north-temperate lake. Canadian Journal of Fisheries and
Aquatic Sciences 42: 556-566.
Boisclair, D., and Leggett, W.C. 1988. In situ experimental evaluation of the Elliott
& Persson and the Eggers models for estimating fish daily ration. Canadian
Journal of Fisheries and Aquatic Sciences 45: 138-145.
Boisclair, D., and Leggett, W.C. 1989. Among-population variability of fish growth:
I. Influence of the quantity of food consumed. Canadian Journal of Fisheries
and Aquatic Sciences 46: 457-467.
Boisclair, D., and Marchand, F. 1993. The guts to estimate fish daily ration.
Canadian Journal of Fisheries and Aquatic Sciences 50: 1969-1975.
Borror, D.J., Triplehorn, C.A., Johnson, N.F. 1989. An introduction to the study of
insects, 6th edition. Saunders College Publishing, Philadelphia, PA. 875 p.
Bowen, S.H. 1996. Quantitative description of diet, pages 513-532 in B.R. Murphy
and D.W. Willis, editors. Fisheries Techniques, 2nd edition. American
Fisheries Society, Bethesda, Maryland.
Brandt, S.B. 1986. Food of trout and salmon in Lake Ontario. Journal of Great Lakes
Research 12(3): 200-205.
60
61
Brett, J.R. 1971. Satiation time, appetite, and maximum food intake of sockeye
salmon (Oncorhynchus nerka). Journal of the Fisheries Research Board of
Canada 28: 409-415.
Buckel, J.A., and Conover D.O. 1997. Movements, feeding periods, and daily ration
of piscivorous young-of-the-year bluefish, Pomatomus saltatrix, in the Hudson
River estuary. U.S. Fishery Bulletin 95: 665-679.
Bushnoe, T.M., Warner, D.M., Rudstam, L.G., Mills, E.L. 2003. Cercopagis pengoi
as a new prey item for alewife (Alosa pseudoharengus) and rainbow smelt
(Osmerus mordax) in Lake Ontario. Journal of Great Lakes Research 29: 205212.
Carl, L.M. 1982. Natural reproduction of coho salmon and chinook salmon in some
Michigan streams. North American Journal of Fisheries Management 4: 375380.
Carl, L.M. 1984. Chinook salmon (Oncorhynchus tshawytscha) density, growth,
mortality, and movement in two Lake Michigan tributaries. Canadian Journal
of Zoology 62: 65-71.
Chesson, J. 1978. Measuring preference in selective predation. Ecology 59: 211-215.
Christie, W.J. 1974. Changes in the fish species composition of the Great Lakes.
Journal of the Fisheries Research Board of Canada 31: 827-854.
Davis, G.E., and Warren, C.E. 1968. Estimation of food consumption rates, pages
204-225 in W.E. Ricker, editor. IBP Handbook No. 3. Methods for
Assessment of Fish Production in Fresh Waters. Blackwell Scientific
Publications, Oxford and Edinburgh.
Diana, J.S. 1990. Food habits of angler-caught salmonines in western Lake Huron.
Journal of Great Lakes Research 16(2): 271-278.
Eckert, T.H. 1999. Lake Ontario stocking and marking program 1999. NYSDEC
Lake Ontario Annual Report 1999. 10 p.
Eggers, D.M. 1977. Factors in interpreting data obtained by diel sampling of fish
stomachs. Journal of the Fisheries Research Board of Canada 34: 290-294.
Elliott, J.M. 1972. Rates of gastric evacuation in brown trout, Salmo trutta L.
Freshwater Biology 2: 1-18.
62
Elliott, J.M. 1975. Number of meals in a day, maximum weight of food consumed in
a day and maximum rate of feeding for brown trout, Salmo trutta L.
Freshwater Biology 5: 287-303.
Elliott, R.F. 1994. Early life history of chinook salmon in Lake Michigan. Pages
286-308 in anonymous editor. Michigan sport fish restoration program annual
reports for projects F-35-R19 and F-53-R-10, April 1, 1993 to March 31,1994.
Michigan Department of Natural Resources, Fisheries Division, Lansing.
322 p.
Fedorenko, A.Y., Fraser, F.J., and Lightly, D.T. 1979. A limnological and salmonid
resource study of Nitinat Lake: 1975-1977. Fisheries Marine Service (Canada)
Technical Report 839: 86 p.
Godin, J-G.J. 1981. Daily patterns of feeding behaviour, daily rations, and diets of
juvenile pink salmon (Oncorhynchus gorbuscha) in two marine bays of British
Columbia. Canadian Journal of Fisheries and Aquatic Sciences 38: 10-15.
Goyke, A.P., and Brandt, S.B. 1993. Spatial models of salmonine growth rates in
Lake Ontario. Transactions of the American Fisheries Society 122: 870-883.
Hartig, J.H., Kitchell, J.F., Scavia, D., and Brandt, S.B. 1991. Rehabilitation of Lake
Ontario: the role of nutrient reduction and food web dynamics. Canadian
Journal of Fisheries and Aquatic Sciences 48: 1574-1580.
Hayward, R.S., and Margraf, F.J. 1987. Eutrophication effects on prey size and food
available to yellow perch in Lake Erie. Transactions of the American Fisheries
Society 116: 210-223.
Hayward, R.S. 1991. Bias associated with using the Eggers model for estimating fish
daily ration. Canadian Journal of Fisheries and Aquatic Sciences 48: 11001103.
Healey, M.C. 1979. Detritus and juvenile salmon production in the Nanaimo Estuary:
I. Production and feeding rates of juvenile chum salmon. Journal of the
Research Board of Canada 36: 488-496.
Healey, M.C. 1980. Utilization of the Nanaimo River estuary by juvenile chinook
salmon, Oncorhynchus tshawytscha. U.S. Fishery Bulletin 77: 653-668.
Healey, M.C. 1991. Life history of chinook salmon (Oncorhynchus tshawytscha), p.
313-393 In: C. Groot and L. Margolis (eds.) Pacific Salmon Life Histories.
UBC Press, Vancouver, BC, Canada.
63
Heese, J.A. 1994. Contribution of hatchery and natural chinook salmon to the eastern
Lake Michigan Fishery, 1992-1993. Masters Thesis. Michigan State
University, East Lansing, Michigan.
Ivlev, V.S. 1961. Experimental ecology of the feeding of fishes. Yale University
Press. New Haven, Connecticut.
Johnson, J.H. 1981. Comparative food selection by coexisting subyearling coho
salmon, chinook salmon, and rainbow trout in a tributary of Lake Ontario.
New York Fish and Game Journal 28(2): 150-161.
Johnson, J.H. 1983. Food of recently stocked subyearling chinook salmon in Lake
Ontario. New York Fish and Game Journal 30(1): 115-116.
Johnson, J.H., and Ringler, N.H. 1981. Natural reproduction and juvenile ecology of
Pacific salmon and rainbow trout in tributaries of the Salmon River, New
York. New York Fish and Game Journal 28(1): 49-60.
Johnston, T.A., and Mathias, J.A. 1996. Gut evacuation and absorption efficiency of
walleye larvae. Journal of Fish Biology 49: 375-389.
Jones, M.L., Koonce, J.F., and O’Gorman, R. 1993. Sustainability of hatcherydependent salmonine fisheries in Lake Ontario: the conflict between predator
demand and prey supply. Transactions of the American Fisheries Society
122:1002-1018.
Jude, D.J., Tesar, F.J., Deboe, S.F., and Miller, T.J. 1987. Diet and selection of major
prey species by Lake Michigan salmonines, 1973-1982. Transactions of the
American Fisheries Society 116: 677-691.
Kitchell, J.F. and Crowder, L.B. 1986. Predator-prey interactions in Lake Michigan:
model predictions and recent dynamics. Environmental Biology of Fishes 16:
205-211.
Kjelson, M.A., Raquel, P.F., and Fisher, F.W. 1982. Life history of fall-run juvenile
chinook salmon, Oncorhynchus tshawytscha, in the Sacramento – San Joaquin
estuary, California, pages 393-411 in V.S. Kennedy, editor. Estuarine
comparisons. Academic Press, New York, NY.
Kwain, W., and Thomas E. 1984. The first evidence of spring spawning by chinook
salmon in Lake Superior. North American Journal of Fisheries Management 4:
227-229.
Lechowicz, M.J. 1984. The sampling characteristics of electivity indices. Oecologia
(Berl) 52: 22-30.
64
Levy, D.A., and Northcote, T.G. 1981. The distribution and abundance of juvenile
salmon in marsh habitats of the Fraser River estuary. Westwater Research
Center University of British Columbia Technical Report 25: 117 p.
Lindbergh, J.M. 1982. A successful transplant of Pacific salmon to Chile.
Proceedings of the Gulf Caribbean Fisheries Institute 34: 81-87.
Major, R.L., Ito, J., Ito, S., and Godfrey, H. 1978. Distribution and origin of chinook
salmon (Oncorhynchus tshawytscha) in the offshore waters of the North
Pacific Ocean. International North Pacific Fisheries Commission Bulletin 38:
54 p.
Mason, D.M., Goyke, A.P., and Brandt, S.B. 1995. A spatially explicit bioenergetics
measure of habitat quality for adult salmonines: Comparison between Lakes
Michigan and Ontario. Canadian Journal of Fisheries and Aquatic Sciences
52: 1572-1583.
McGurk, M.D. 1984. Effects of delayed feeding and temperature on the age of
irreversible starvation and on the rates of growth and mortality of Pacific
herring larvae. Marine Biology 84: 13-26.
McPhail, J.D., and Lindsey, C.C. 1970. Freshwater fishes of northwestern Canada
and Alaska. Bulletin of the Fisheries Research Board of Canada 173: 381 p.
Mills, E.L., and Forney, J.L. 1981. Energetics, food consumption, and growth of
young yellow perch in Oneida Lake, New York. Transactions of the American
Fisheries Society 110: 479-488.
Mills, E.L., Ready, R.C., Jahncke, M., Hanger, C.R., and Trowbridge, C. 1984. A
gastric evacuation model for young yellow perch, Perca flavescens. Canadian
Journal of Fisheries and Aquatic Sciences 41: 513-518.
Mills, E.L., Roseman, E.F., Rutzke, M., Gutenmann, W.H., and Lisk, D.J. 1993.
Contaminant and nutrient element levels in soft tissues of zebra and quagga
mussels from waters of southern Lake Ontario. Chemosphere 27:1465-1473.
Neilson, J.D., and Geen, G.H. 1986. First-year growth rate of Sixes River chinook
salmon as inferred from otoliths: effects on mortality and age at maturity.
Transactions of the American Fisheries Society 115: 28-33.
Noble, R.L. 1973. Evacuation rates of young yellow perch, Perca flavescens
(Mitchell). Transactions of the American Fisheries Society 102: 759-763.
65
O’Gorman R., Bergstedt, R.A., and Eckert, T.H. 1987. Prey fish dynamics and
salmonines predator growth in Lake Ontario, 1978-84. Canadian Journal of
Fisheries and Aquatic Sciences 44 (Supplement 2): 390-403.
O’Gorman R., Johannsson, O.E., and Schneider, C.P. 1997. Age and growth of
alewives in the changing pelagia of Lake Ontario, 1978-1992. Transactions of
the American Fisheries Society 126: 112-126.
Parrish, D.L., and Margraf, F.J. 1990. Interactions between white perch (Morone
americana) and yellow perch (Perca flavescens) in Lake Erie as determined
from feeding and growth. Canadian Journal of Fisheries and Aquatic Sciences
47: 1779-1787.
Parrish, D.L., and Margraf, F.J. 1990b. Gastric evacuation rates of white perch,
Morone Americana, determined from laboratory and field data. Environmental
Biology of Fishes 29: 155-158.
Parsons, J.W. 1973. History of salmon in the Great Lakes, 1850-1970. No. 68
Technical Papers of the Bureau of Sport Fisheries and Wildlife. U.S. Fish and
Wildlife Service. 88 p.
Persson, L. 1979. The effects of temperature and different food organisms on the rate
of gastric evacuation in perch (Perca fluviatilis). Freshwater Biology 9:
99-104.
Persson, L. 1982. Rate of food evacuation in roach (Rutilus rutilus) in relation to
temperature, and the application of evacuation rate estimates for studies on the
rate of food consumption. Freshwater Biology 12: 203-210.
Powell, M.J., and Miller, M. 1990. Shoal spawning by chinook in Lake Huron.
North American Journal of Fisheries Management 10: 242-244.
Rand, P.S., Lantry, B.F., O’Gorman, R., Owens, R.W., and Stewart, D.J. 1994a.
Energy density and size of pelagic prey fishes in Lake Ontario, 1978-1990:
Implications for salmonine energetics. Transactions of the American Fisheries
Society 123: 519-534.
Rand, P.S., Stewart, D.J., Seelbach, P.W., Jones, M.L., and Wedge, L.R. 1994b.
Modeling steelhead population energetics in Lakes Michigan and Ontario.
Transactions of the American Fisheries Society 122: 977-1001.
Rand, P.S., and Stewart, D.J. 1998. Dynamics of salmonine diets and foraging in
Lake Ontario, 1983-1993: a test of a bioenergetic model prediction. Canadian
Journal of Fisheries and Aquatic Sciences 55: 307-317.
66
Rand, P.S., and Stewart, D.J. 1998b. Prey fish exploitation, salmonine production,
and pelagic food web efficiency in Lake Ontario. Canadian Journal of
Fisheries and Aquatic Sciences 55: 318-327.
Reimers, P.E., Nicholas, J.W., Downey, T.W., Halliburton, R.E., and Rodgers, J.D.
1978. Fall chinook ecology project. Federal aid progress report fisheries
AFC-76-2. Oregon Department of Fish and Wildlife, Portland, Oregon. 52 p.
Rondorf, D.W., Gray, G.A., and Fairley, R.B. 1990. Feeding ecology of subyearling
chinook salmon in riverine and reservoir habitats of the Columbia River.
Transactions of the American Fisheries Society 119: 16-24.
Ruggerone, G.T. 1989. Gastric evacuation rates and daily ration of piscivorous coho
salmon, Oncorhynchus kisutch Walbaum. Journal of Fish Biology 34:
451-463.
Rybicki, R.W. 1973. A summary of the salmonid program (1969-1971). p. 33-42 in
Michigan’s Great Lakes trout and salmon fishery 1969-1972. Michigan
Department of Natural Resources, Fisheries Management Report 5, Lansing,
Michigan.
Sagar, P.M., and Glova, G.J. 1987. Prey preferences of a riverine population of
juvenile chinook salmon, Oncorhynchus tshawytscha. Journal of Fish Biology
31: 661-673.
Sagar, P.M., and Glova, G.J. 1988. Diel feeding periodicity, daily ration and prey
selection of a riverine population of juvenile chinook salmon, Oncorhynchus
tshawytscha (Walbaum). Journal of Fish Biology 33: 643-653.
Schaner, T., Bowlby, J.N., Daniels, M., and. Lantry, B.F. 2000. Lake Ontario
offshore pelagic fish community. 7 p. Part I. Fish Communities. In Lake
Ontario Fish Communities and Fisheries: 1999 Annual Report of the Lake
Ontario Management Unit. Ontario Ministry of Natural Resources, Picton,
Ontario, Canada.
Scheffe, H. 1953. A method of judging all contrasts in the analysis of variance.
Biometrika 40: 87-104.
Schelske, C.L. 1991. Historical nutrient enrichment of Lake Ontario:
paleolimnological evidence. Canadian Journal of Fisheries and Aquatic
Sciences 48: 1529-1538.
Scott, W.B., and Crossman, E.J. 1973. Freshwater fishes of Canada. Fisheries
Research Board of Canada Bulletin 184.
67
Seelbach, P.W. 1985. Smolt migration of wild and hatchery-raised coho and chinook
salmon in a tributary of northern Lake Michigan. Michigan Department of
Natural Resources, Fisheries Division, Research Report 1935. 19 p.
Seelbach, P.W. 1993. Population biology of steelhead in a stable-flow, low-gradient
tributary of Lake Michigan. Transactions of the American Fisheries Society
122: 179-198.
Smith, S.H. 1968. Species succession and fishery exploitation in the Great Lakes.
Journal of the Fisheries Research Board of Canada 25(4): 667-693.
Stewart, D.J. and Ibarra, M. 1991. Predation and production by salmonine fishes in
Lake Michigan, 1978-1988. Canadian Journal of Fisheries and Aquatic
Sciences 48: 909-922.
Stewart, D.J., Kitchell, J.F., and Crowder, L.B. 1981. Forage fishes and their
salmonid predators in Lake Michigan. Transactions of the American Fisheries
Society 110: 751-763.
Strauss, R.E. 1979. Reliability estimates for Ivlev’s electivity index, the forage ratio,
and a proposed linear index of food selection. Transactions of the American
Fisheries Society 108: 344-352.
Swenson, W.A. 1977. Food consumption of walleye (Stizostedion vitreum vitreum)
and sauger (S. canadense) in relation to food availability and physical
environmental conditions in Lake of the Woods, Minnesota, Shagawa Lake,
and western Lake Superior. Journal of the Fisheries Research Board of Canada
34: 1643-1654.
Swenson, W.A. and Smith, L.L. Jr. 1973. Gastric digestion, food consumption,
feeding periodicity, and the conversion efficiency in walleye (Stizostedion
vitreum). Journal of the Fisheries Research Board of Canada 30: 1327-1336.
Taube, C.M. 1974. Transfer releases of coho salmon and trout in an upper part of
Platte River, and observations of salmonid spawning. Michigan Department of
Natural Resources, Fisheries Research Report 1815, Lansing, Michigan.
Thorpe, J.E. 1977. Daily ration of adult perch, Perca fluvialitis L. during summer in
Loch Leven, Scotland. Journal of Fish Biology 11: 55-68.
Unwin, M.J. 1986. Stream residence time, size characteristics, and migration patterns
of juvenile chinook salmon (Oncorhynchus tshawytscha) from a tributary of
the Rakaia River, New Zealand. New Zealand Journal of Marine and
Freshwater Research 20: 231-252.
68
Vanderploeg, H.A. and Scavia, D. 1979. Two electivity indices for feeding with
special reference to zooplankton grazing. Journal of the Fisheries Research
Board of Canada 36: 362-365.
Vehanen, T. 2003. Adaptive flexibility in the behaviour of juvenile Atlantic salmon:
short term responses to food availability and threat from predation. Journal of
Fish Biology 63: 1034-1045.
Wahl, D.H., and Stein, R.A. 1991. Food consumption and growth of three esocids:
field tests of a bioenergetic model. Transactions of the American Fisheries
Society 120: 230-246.
Wallace, R.K. 1981. An assessment of diet-overlap indexes. Transactions of the
American Fisheries Society 110: 72-76.
Walsh, G., Morin, R., and Naiman, R.J. 1988. Daily rations, diel feeding activity, and
distribution of age-0 brook char, Salvelinus fontinalis, in two subarctic streams.
Environmental Biology of Fishes 21: 195-205.
Wetzel, R.G. 2001. Limnology: lake and river ecosystems, 3rd edition. Academic
Press, San Diego, CA. 1006 p.
Zafft, D.J. 1992. Migration of wild chinook and coho salmon smolts from the Pere
Marquette River, Michigan. Masters Thesis. Michigan State University, East
Lansing, Michigan.
Zar, J.H. 1999. Biostatistical Analysis, 4th edition. Prentice-Hall, Upper Saddle
River, NJ. 663 p.