I

I C

(fidTJ I/i

University of Alaska

Coastal Marine Institute

Feeding Ecology of Maturing Sockeye Salmon

(Oncorhynchus nerka) in Nearshore Waters

of the Kodiak Archipelago

Principal Investigators:

Albert V. Tyler, University of Alaska Fairbanks

Charles 0. Swanton, Alaska Department of Fish and Game

Bruce C. McIntosh, University of Alaska Fairbanks

Final Report

August 2001

OCS Study MMS 2001-059
CMI contact information

E-mail: cmi@sfos.uaf.edu

Phone: 907.474.7707

Fax: 907.474.7204

Postal: Coastal Marine Institute

School of Fisheries and Ocean Sciences

University of Alaska Fairbanks

Fairbanks, AK 997757220

This study was funded in part by the U.S. Department of the Interior, Minerals Management Service

(MMS), through Cooperative Agreement No. 1435-0l-98-CA-30909, Task Order No. 15160, between

the MMS, Alaska Outer Continental Shelf Region, and the University of Alaska Fairbanks.

The opinions, findings, conclusions, or recommendations expressed in this report or product are those

of the authors and do not necessarily reflect the views of the Minerals Management Service, nor does

mention of trade names or commercial products constitute endorsement of recommendation for use

by the Federal Government.
OCS Study MMS 2001-059

Final Report

Feeding Ecology of Maturing Sockeye Salmon

(Oncorhynchus nerka) in Nearshore Waters

of the Kodiak Archipelago

Albert V. Tyler1

Charles 0. Swanton2

Bruce C. McIntosh1

Principal Investigators

1

School of Fisheries and Ocean Sciences

University of Alaska Fairbanks

Fairbanks, AK 99775-7220

2

Alaska Department of Fish and Game

1300 College Road

Fairbanks, AK 99701-I 599

E-mail:ffavt@uaf.edu

charles_swanton@fishgame.state.ak.us

fsbcml @uaf.edu

August 2001
Table of Contents

List of Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... iv

List of Figures .,,,,,.........,.......................................................................................................... V

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . ............................,,,,,,.........,*.........*,........*****., 1

Objectives ................................................................................................................................. 4

Methods .................................................................................................................................... 4

Incidence of feeding ............................................................................................................. 6

Diet ...................................................................................................................................... 7

Results ..................... ................................................................................................................. 9

Incidence of feeding ............................................................................................................. 9

Prey analysis ...................................................................................................................... 1 8

Sample size ........................................................................................................................ 20

Digestive state .................................................................................................................... 20

Stomach content weight ...................................................................................................... 2 1

Prey composition ................................................................................................................ 2 3

Diversity ............................................................................................................................ 28

Discussion ....................................................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Acknowledgements . . . . . . . . . . . . . .................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Study Products ........................................................................................................................ 32

References .............................................................................................................................. 32

. . . 111
List of Tables

Table 1.

Table 2.

Table 3.

Table 4.

Table 5.

Table 6.

Table 7.

Table 8.

Table 9.

Table 10.

Table 11.

Table 12.

Table 13.

Table 14.

Table 15.

Table 16.

Table 17.

Table 18.

Table 19.

Study sample areas by classification and corresponding ADF&G descriptions ........................ 4

ADF&G statistical week and corresponding calendar dates ....................................................... 6

Feeding proportions for 1998 samples ....................................................................................... 1 0

Feeding proportions for 1999 samples ....................................................................................... 11

Incidence of feeding in migration corridors, with significance testing, 1998 .......................... 13

Incidence of feeding in migration corridors, with significance testing, 1999 .......................... 1 4

Incidence of feeding as sockeye salmon move towards their natal streams,

with significance testing, 1998 ................................................................................................... 15

Incidence of feeding as sockeye salmon move towards their natal streams,

with significance testing, 1999 ................................................................................................... 1 6

Incidence of feeding of early and late runs, 1998 ..................................................................... 1 8

Incidence of feeding of early and late runs, 1999 ..................................................................... 1 8

Prey of adult sockeye salmon ..................................................................................................... 1 9

Digestive state of stomach contents from each area with samples pooled by year .................. 2 1

Mean, minimum and maximum stomach content weights ........................................................ 22

Frequency of occurrence and percent composition by number of prey categories;

areas pooled by year ................................................................................................................... 24

Frequency of occurrence (percent) of prey categories for individual samples ........................ 25

Percent composition by number of prey categories for individual samples ............................. 26

Results of Tukey’s HSD test comparing overall prey usage between areas ............................ 27

Effect of period on prey contents ............................................................................................... 28

Shannon-Weaver diversity indices (H? for mean individual and pooled samples ................. 2 9

iv
List of Figures

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6.

Figure 7.

Figure 8.

Figure 9.

Figure 10.

Life energetics of hypothetical age 1.2 Babine Lake sockeye salmon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Locations and boundaries of sampling areas ,,,,.........................................................................,. 5

Location of Cape Alitak, Moser Bay and Olga Bay areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Interpretation of Tokeshi plot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Proportion of feeding sockeye salmon in migration corridors, 1998 and 1999 . . . . . . . . . . . . . . . . . . . . . . . 1 2

Proportion of sockeye salmon actively feeding as they move towards their natal

streams-from Cape Alitak through Moser Bay and into Olga Bay, 1998 and 1999 . . . . . . . . . . . . . . 17

Distribution of sampling effort during 1998 and 1999 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Cumulative prey taxa and categories represented from pooled stomach

contents a s a function of sample size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 1

Overall frequency of occurrence and percent by number for sockeye

prey items, 1998 and 1999 ..,...................................................................................................... 23

Tokeshi plots of Shannon-Weaver diversity indices (H? of diet,

contrasting mean individual and pooled-sample values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

V
Abstract

The diet and feeding behavior of maturing sockeye salmon (Oncorhynchus nerka) were investigated

during the final marine phase of the spawning migration, immediately prior to re-entry into natal streams.

The stomach contents of commercially caught sockeye salmon, migrating through the nearshore waters

of the Kodiak Island Archipelago during 1998 and 1999, were examined to determine level of feeding

activity and taxa of dominant prey items. Representative samples were collected throughout the majority

of the migration (early June to late August) from areas known to be principally migration corridors, and

from areas proximate to several natal streams. Dominant prey of sockeye salmon were decapod larvae,

Pacific sandlance (Ammodytes hexapterus), and the pteropod Limacina helicina. Feeding levels and

dominant prey varied between areas and within areas over time. Feeding levels for the population appear

to gradually diminish, rather then ceasing abruptly, prior to entering freshwater.

Introduction

The Kodiak Archipelago is located in the western Gulf of Alaska approximately 400 km southwest of

Anchorage. The archipelago extends approximately 296 km from the Barren Islands in the north to

Tugidak and Sitkinak Islands at the south end. The islands consist of approximately 13,000 km2

 in surface

area, with roughly 4,000 km of shoreline. The island group lies 60 km due south of the entrance to Cook

Inlet and is separated from the Alaska Peninsula on the west by Shelikof Strait. Kodiak Island proper, at

9,300 km2

, is the second largest island in the United States.

Five species of Pacific salmon are commercially harvested in Kodiak Archipelago waters. Second only

to pink salmon (Oncorhynchus gorbuscha) in abundance, sockeye salmon (0. nerka) are the economic

mainstay nf the Kodiak commercial salmon fishing industry. As the principal targeted species of the

fishery, sockeye landings accounted for approximately 6 1% ($19,014,000) of the total ex-vessel value

for salmon in the Kodiak area during the period 1994 to 1998 [ADF&G 1999].

Sockeye salmon are anadromous, typically spending their first one to three years rearing in freshwater

lakes, then out-migrating to the marine environment where they will spend another one to three years

feeding [Foerster 1968]. During the final spring at sea, as maturing adults, they begin a directed migration

back to their natal streams to spawn [French et al. 1976]. The role of the freshwater environment for

sockeye salmon production is well understood [Koenings and Burkett 1987; Stockner 1987], but

knowledge of marine life history suffers from numerous data gaps, except in the areas of ocean

distribution and offshore food web dynamics [Pearcy et al. l988; Brodeur 1990; Burgner 1991 ].

An array of research efforts has focused on the feeding ecology of juvenile sockeye salmon in the

nearshore marine environment [Brodeur and Pearcy 1990; Landingham et al. 19981 and immature

sockeye salmon in offshore Gulf of Alaska waters [Allen 1956; Pearcy et al. 1988; Walker and Myers

19941. In Brodeur’s [ 19901 review of the feeding habits of salmon, oceanic phase sockeye fed on a variety

of organisms including squid, fish, euphausiids, amphipods and pteropods, while maturing sockeye

salmon within coastal waters were predominantly zooplanktivores, feeding largely on euphausiids,

hyperiid amphipods, and decapod larvae.

The final stages of maturation in salmon are critical to successful reproduction. During the last four

months of ocean life, prior to re-entering fresh water, the fish will consume as much food as in all

previous months combined, doubling their body weight during the last 5-6 months of life [Brett 1983;

Figure 11. Growth is directed towards both storage of energy reserves and production of gonadal tissue

[Brett 19951. The fish cease feeding at some point during the final stage of the spawning migration, while

at the same time undergoing stress associated with changes in osmoregulation, upstream migration and
b a 0 0 0 0 0 Cumulative Energy (kcal) 1')

K molt oastal Phase Offshore Mig Alaskan G

the partitioning of somatic cncrgy into gonadal growth [Durgner 19911. At the time of spawning, the fish

have depleted a majority of energy stores and die shortly thereafter [Brett 19951. Perturbations from

human activities can increase metabolic demands, decrease prey diversity and reduce prey abundance,

adversely affecting growth and available energy stores [Brett 1983; Brett 1995; Higgs et al. 19951.

20,000

16,000

Energetics of Sockeye Salmon (age 1.2) i?

g .E

c & 5

o> $

5:,e tn

$

3rd winter

,te*

t Energy consumed

z #/

+ Energy expended -5‘j;

8

0

i

P

2nd winter

1 st winter

Life History Stage (by month)

Figure 1. Life energetics of hypothetical age 1.2 Babine Lake sockeye salmon. Adapted from

Brett [ 19831.

Current knowledge of the nearshore feeding ecology of mature sockeye is limited to several research

efforts, spanning an area from Oregon to the Sea of Okhotsk, and depicts sockeye salmon as opportunistic

feeders. This precludes generalization to other locations, as most studies are site specific [Andrievskaya

1966; Nishiyama 1977; Beacham 1986; Helton 199 11. A recurrent theme in these studies is that

euphausiids, fish larvae, decapods and amphipods are the major dietary components of maturing fish in

coastal waters. Beacham [ 19861 reported that for sockeye >55 cm FL (fork length) sampled from Juan de

Fuca Strait (between Washington State and British Columbia), dominant prey (by volume) were

euphausiids, amphipods, crab larvae, and mysids. Helton [ 199 11 found that stomach contents of maturing

sockeye near Port Moller were dominated by fish larvae, euphausiids and crab zoea. In offshore areas of

Bristol Bay, Nishiyama [ 19771 reported that the diet of maturing sockeye salmon sampled in the “basin”

area was comprised of squid, fish larvae, amphipods, and euphausiids, whereas for sockeye from the

“continental shelf’ area diet was predominately euphausiids. In Andrievskaya’s [ 19661 research in the

coastal waters of the Sea of Okhotsk, squid were the dominant food item in sockeye stomachs, followed

by fish, decapod larvae, and euphausiids.

While mature sockeye salmon cease feeding when they near and finally ascend their natal streams

to spawn, the environmental cues and timing that lead to feeding cessation are at present not well

2
understood. The incidence of feeding (proportion of the population actively feeding) varies by time and

geographic location. Helton [ 19911 found that the occurrence of empty stomachs ranged from 16% to

38% in maturing Bristol Bay bound sockeye salmon sampled during June and July 1988-90. In the Juan

de Fuca Strait, Beacham [ 19861 found a 300/n occurrence of empty stomachs from maturing sockeye

sampled during 1967-1968.

Evaluation of the food web dynamics and feeding habits of mature salmon is necessary to understand

potential ingestion pathways for hydrocarbon contamination, especially in areas swept by currents from

potential oil exploration and drilling. Kodiak waters make up such an area. Prey taxa, identified in various

studies in coastal areas, exhibit varied life history strategies including habitat utilization. Assessment

of differences (temporal and spatial) in contamination of these habitats should lead to a more concise

evaluation of the impact on sockeye salmon once their prey utilization is known. Identification of feeding

incidence and the stage of cessation provides a clearer understanding of contamination potential via

ingestion.

Since no published information existed on the diet of maturing sockeye salmon from Kodiak waters, the

Alaska Department of Fish aud Game (ADF&G) initiated a stomach conteut study during 1994. The

objective was to determine whether commercially harvested sockeye salmon from the east and west sides

of the Kodiak Archipelago were feeding and, if so, what were their dominant prey.

In July 1994, stomach samples were collected from the Eastside and Westside sections of Kodiak Island.

During early July, a majority (63%) of sockeye salmon sampled were found to be feeding, while in late

July the incidence of feeding was sharply reduced to 24%. For both periods combined, an estimated 36%

of Eastside and 44% of Westside fish stomachs examined were found to contain food. Of the identifiable

prey categories, pooling all areas and periods, sandlance Ammodytes hexapterus were found in 26% of

feeding sockeye salmon, pteropods Limacina helicina in 2 l%, euphausiids Thysanokssa spinijkra in 16%,

and crab glaucothoe in 34%. Both time and area effects on feeding incidence and dietary content were

found to be significant.

Research areas addressed in the present study include the feeding incidence of maturing fish as they

migrate along the nearshore coast, the migration stage of feeding cessation as they approach their natal

streams, and the identification of major prey taxa consumed by actively feeding sockeye salmon. The

results obtained from the initial study in 1994 indicated that a broader-scale sampling effort, both spatially

and temporally, was needed to address these objectives adequately. Unlike some locations such as Bristol

Bay, local stocks of sockeye salmon are present in Kodiak waters from May through October, with the

majority of catch and escapement occurring in June, July and August. Several major stocks exhibit bimodal run timing, with early run fish present through mid-July and late run fish present mid-July through

October. Although the major migration pathways of returning sockeye salmon are well known, variations

in migration patterns and timing can occur between years [D. Prokopowich, ADF&G, Kodiak, personal

communication]. To provide a comprehensive picture of sockeye feeding behavior, sampling was

designed to cover the major nearshore migration areas in the Kodiak Management Area and occurred on

a weekly basis during the months of June, July and August. To allow for this scope of coverage, stomach

samples were collected from the commercial fleet already fishing in these waters during this time frame.

The North Shelikof Strait lease area is important for maturing sockeye salmon of Kodiak origin, as well

as from other regions. Prevailing currents in lower Cook Inlet and Shelikof Strait potentially extend

impacts from oil and gas development throughout the inshore areas of the Kodiak Archipelago and

the eastern Alaska Peninsula. The results of this research should be applicable to oil and natural gas

exploration and development, contingency planning for spill mitigation, as well as establishment of

pre-impact baseline measures.

3
IObjectives

1 . Determine the percentage of sockeye salmon that were feeding from three locations known

to be migration corridors (Eastside Kodiak, Westside Kodiak, and Alaska Peninsula areas)

on a weekly basis during June through August.

2 . Determine the percentage of sockeye salmon that were feeding in an area ~5 km from their

natal stream terminus (Moser-Olga Bay sections) weekly during June through August.

3 . Identify and quantify the major prey taxa in sockeye salmon stomachs within the migration

corridors and determine if location or period has an effect on prey types utilized.

4 . Identify potential mechanisms of indirect effects on sockeye salmon, through prey

utilization, due to development in oil and gas lease areas.

Methods

Ihis study was conducted in conjunction with the existing ADF&G salmon catch sampling program All

,;ockeye salmon in this study were collected from deliveries of the commercial catch during the 1998 and

1933 fishing seasons. Commercial fishing periods arc set in-season by ADF&G, based on estimates of

Lish abundance and escapement counts. The initial commercial salmon opening begins 9 June and fishing

lxcurs through September. The Kodiak commercial salmon fishing area is comprised of all Alaska statute

waters south of 58’ 52’N, west of 15Oo W, north of 55’ 30’N, and east of a line extending south from

156” 20’13” W.

Waters were classified as either migration corridors (no significant sockeye systems, < 20 km distance).

.erminal harvest areas (waters in vicinity of natal stream mouth) or transition areas (waters intermediate

Jetween migration and terminal harvest areas). To facilitate sampling, the boundaries of these study areas

corresponded to ADF&G management districts and sections (Table 1). This allowed the use of harvest

icket data to verify date, location and species composition of the delivered catch prior to sampling. Based

lpon historical catch and tagging studies [Moser 1898; Tyler et al. 198 1; Barrett and Nelson 19941, five

*ireas were identified as migration corridors, one as a terminal harvest area, and one as a transition area for

nclusion in this study (Figure 2).

Table 1. Study sample areas by classification and corresponding ADF&G descriptions.

Classification Sample Area ADFBG District ADFBG Section(s) ADF&G Statistical Area(s)

Migration Westside Kodiak Northwest Kodiak Central 254-10,40; 253-11,

14,31-35

Migration Eastside Kodiak Eastside Kodiak Sitkalidak, Two-Headed

& Seven Rivers 258 - IO through 70

Migration Mainland Mainland Katmai, Alinchak Bay

& Cape lgvak 262-60 through 95

Migration

Migration

Transition

Terminal

Ayakulik

Cape Alitak

Moser Bay

Olga Bay

Southwest Kodiak

Alitak Bay

Alitak Bay

Alitak Bay

Inner 8. Outer Ayakulik

Cape Alitak

Moser-Olga Bay

Moser-Olga Bay

256-10, 15,20

257- IO,20

257-41

257 -40

4
40 D

Alaska

Peninsula

Cape AlitakF

Eastside

Port

Sample Area

Figure 2. Locations and boundaries of sampling areas. Samples were collected and

examined at Alitak.

Stomachs were collected on a weekly basis, dependent upon availability, through the last week of August.

Sample periods corresponded to ADF&G statistical weeks (Table 2). Fish were not always available each

period for sampling for several reasons, including area closures, inclement weather, and a lack of sockeye

in areas open to fishing. Fish were harvested in the five migration areas with purse seines exclusively; the

transition and terminal areas are legally restricted to the use of set-gillnets only. Samples consisted of 100

sockeye stomachs (minimum) obtained from a single area and weekly period. All fish were assumed to be

mature and of predominately local origin. No prior selection was made for size, condition factor or sex

of the fish. Prey were assumed to be equally available to all fish within a single sample. All stomachs

were obtained at the Ward’s Cove fish processing facility, located in Alitak, Kodiak Island, during the

course of normal processing. Plant employees headed the fish and whole, intact digestive tracts (from the

esophagus to the pyloric sphincter) were recovered on the processing line immediately after evisceration.
Table 2. ADF&G statistical week and corresponding calendar dates.

ADF&G

Statistical Week Calendar Dates

2 4 7Jun - 13Jun

2 5 14Jun - 20Jun

2 6 21Jun - 27Jun

2 7 28 Jun - 4 Jul

2 8 5Jul - 11 Jul

2 9 12 Jut - 18 Jul

3 0 19 Jul - 25 Jul

3 1 26 Jul - 1 Aug

3 2 2Aug - 8Aug

3 3 9Aug - 15Aug

3 4 16 Aug - 22 Aug

3 5 23 Aug - 29Aug

Incidence of feeding

Stomachs collected from all seven areas were examined for incidence of feeding. The proportion of fish

in a sample exhibiting evidence of active feeding was termed incidence of feeding. The digestive tract

was incised and examined on site for presence or absence of prey items; stomachs containing prey items,

regardless of type or quantity, were classified as feeding. Stomachs without evidence of any food items

were classified as non-feeding.

Differences in incidence of feeding within areas and among time periods. and differences among areas

during the same time period were tested for significance with contingency tables using log-likelihood

(G) statistics [Zar 1996]. Sockeye salmon are physically constrained to migrate sequentially from Cape

Alititak through Moser Bay and into Olga Bay on the way to their natal streams (Figure 3). Differences

in incidence of feeding among these areas and periods were used to examine the question of feeding

cessation.
Fraser Lake

L LI

Uppet Station

$ Port

a Sample Area

Figure 3. Location of Cape Alitak, Moser Bay and Olga Bay areas. Fraser Lake

and Upper Station Lakes are the major sockeye systems in Olga Bay.

Diet

Prey analysis was performed on samples collected from three migration corridors: the Mainland (Alaska

Peninsula), Eastside Kodiak and Westside Kodiak sections (Figure 1). Subsamples of stomachs showing

evidence of feeding, based on external characteristics, were collected whole and intact for further analysis

of the actual prey items. An attempt was made to collect n = 30 stomachs from each sample. These

stomachs were frozen on site and were examined in laboratory facilities located at the University of

Alaska Fairbanks. Freezing avoided the use of hazardous chemicals around human food. Similar to other

studies [Allen and Aron 1958; Dell 1963], comparative trials early in this project showed that freezing

resulted in samples with equal or less degradation than samples preserved with standard fixatives. In the

laboratory, stomachs were thawed, weighed whole, opened, and the contents rinsed into a beaker. The

empty stomach was re-weighed, with the difference between the whole and empty weights taken as the

stomach content weight.

Digestive state of the stomach contents was rated subjectively, on a scale of one to four. A rating of one

indicated the contents were largely digested-typically with fish remains consisting primarily of skeletal

parts and invertebrate remains consisting of the carapace and detached appendages. A rating of four

indicated the remains were fresh and largely undigested-fish had intact skin and fins and invertebrates

had all appendages present. The digestion rating was based on the dominant taxa (by volume) found in

the stomach.

7
Prey were identified and counted under a dissecting microscope to the lowest practical taxa. The number

of each taxa found in each stomach was recorded. In the case of highly digested prey items, counts were

nade of uniquely identifiable parts, e.g., eye capsules or urostyles. For statistical analysis, prey were

assigned to one of seven major categories: fish, pteropod, decapod, amphipod, cumacean, euphausiid or

other [Nishiyama 1968; Nishiyama 1977; Pearcy et al. 1984; Beacham 1986; Pearcy et al. 1988; Brodeur

and Pearcy 1990]. According to Bowen [ 1996], large numbers of individual prey species can result in

undue emphasis on taxonomic, rather than functional differences between prey items. Use of higher

evels of classification is statistically more efficient [Crow 1982]. Due to the several orders of magnitude

difference in size of prey items and varying degrees of digestion, weights of individual prey items would

b e subject to large errors [Berg 1979; Hyslop 1980; Tirasin and Jorgensen 1999] and as such were not

recorded.

To assess the adequacy of sample sizes (e.g., n = 30) used in characterizing the breadth of diet, all

individual fish diets were pooled into a single unit and sampled randomly. The cumulative number of

prey taxa and prey categories accounted for were then plotted against sample size [Landingham et al.

1998; Hurtubia 1973]. This random sampling continued until an asymptote and stability was reached. Ten

runs each were made, and the median values were used to assess sample sizes.

Prey contents for each sample were initially characterized using frequency of occurrence (FOcc) and

percent composition by number (%N) [B owen 1996]. Frequency of occurrence is the proportion of fish

in a sample that contained one or more items of a particular prey category, and provides a measure of the

uniformity of diet selection. It does not indicate dietary importance because a single item is weighted

equally to a numerous item. Percent composition hy number is the mlmher of items from a prey category

expressed as a proportion of the total number of prey items in the sample. Although it does not account

for differences in size of prey items, and thus the energy contribution, it does provide a measure of

selectivity for a particular prey category. Differences in the degree of feeding among samples were

compared using analysis of variance to examine differences in mean prey weights.

(Contingency table analysis of prey category counts, using G-statistics, was used to test for overall

differences in food habits among areas during the same time period, and within areas across time.

. Although counts do not necessarily reflect relative importance of prey in the diet, they do indicate

(differences in the food habits themselves [Crow 1982]. The Kruskal-Wallis procedure, a non-parametric

equivalent of one-way ANOVA [Conover 1980], was used to test for area and period effects on utilization

of individual prey categories, again using counts. When significant differences were detected, post-hoc

comparisons were made using Tukey’s honestly significant difference test [HSD; Zar 1996] at a

familywise error rate of p = 0.05. Bias, due to size differences between prey, is minimal when using

counts among similarly sized organisms.

Commonly classified as opportunistic, the question of homogeneity or heterogeneity in feeding strategies,

for both the individual and the population, was examined. The diversity of diet for the sampled population

(Hi,,,,) was calculated using the Shannon-Weaver diversity index [Pielou 1975]:

H’p*p = - ~ ~j log~j (1)

i=l

where Pti is the proportion of prey category i in thejth predator. The mean individual diversity (HQ was

c,alculated:

8
I GnraIit

N/n

H' = I1ogF /N jl\ i1

( Generalist

)

Heterogeneous

feeding

where N is the total number of predators. When diet is represented by a single prey category, H’= 0.

Diversity is at maximum when all prey categories are represented equally. Use of the Shannon-Weaver

index provides a relatively objective indication of niche breadth [Marshall and Elliott 19971. To

graphically examine differences in individual versus population feeding habits Tokeshi plots [Tokeshi

19911 were constructed, plotting mean individual diet diversity against group diet diversity (Figure 4).

Homogeneous feeding

Figure 4. Interpretation of Tokeshi plot. A population with a low individual diversity

and a low population diversity corresponds to a specialist, whereas a

population with a high individual diversity and a high population diversity

indicates a generalist with a homogenous feeding regime.

Results

Incidence of feeding

From the seven areas identified for this study. a total of 52 samples were collected in 1998 (Table 3), and

49 in 1999 (Table 4). This represents 11,702 individual sockeye stomachs examined for incidence of

feeding. The proportion of fish in any one sample exhibiting evidence of active feeding varied greatly

within area and time strata, ranging from 0% to 97% (Figure 5). The highest proportion of fish feeding

were found in the Mainland migration corridor samples in 1999, the lowest proportions were during 1998

and 1999 in Olga Bay, the terminal harvest area.

9
Tahle 3. Feeding prnpnrtions for 1998 samples.

1998 Sample Catch Sample Sample Number Proportion C.I. (95%)

Area Date(s) Period Size Feeding Feeding Upper Lower

Migration

Corridors

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitek

Eastside

Eastside

Mainland

Westside

Westside

Westside

Westside

Westside

Westside

Westside

14 Jun 2 5 114 5 0.044 0.090 0.017

20-21 Jun 2 6 114 4 7 0.412 0.494 0.334

27-29 Jun 2 7 101 4 2 0.416 0.503 0.333

6-9 Jul 2 8 126 8 6 0.683 0.751 0.608

14-16 Jul 2 9 113 9 2 0.814 0.872 0.744

27-29 Jul 3 1 129 7 7 0.597 0.670 0.521

IO-11 Aug 3 3 144 4 2 0.292 0.360 0.230

IO-12 Aug 3 3 120 7 6 0.633 0.707 0.555

18 Aug 3 4 119 6 7 0.563 0.640 0.483

20 Aug 3 4 125 8 2 0.656 0.727 0.580

9-10 Jun 2 4 117 3 7 0.316 0.394 0.245

17-18 Jun 2 5 103 6 7 0.650 0.729 0.566

28 Jun 2 7 104 7 3 0.702 0.775 0.620

6 Jul 2 8 9 6 5 4 0.563 0.649 0.473

16 Jul 2 9 142 5 5 0.387 0.459 0.319

20-21 Jul 3 0 121 4 7 0.388 0.467 0.314

3-4 Aug 3 2 116 3 9 0.336 0.415 0.264

4 Aug 3 2 110 5 1 0.464 0.546 0.382

13 Aug 3 3 124 9 1 0.734 0.798 0.661

22 Aug 3 4 125 8 6 0.688 0.756 0.613

27 Aug 35 112 25 0.223 0.298 0.160

7-8 Jul 2 8 164 125 0.762 0.816 0.701

14-16 Jul 2 9 116 8 6 0.741 0.807 0.666

21-22 Jul 3 0 157 6 0 0.382 0.450 0.317

20-22 Jun 2 6 103 6 9 0.670 0.746 0.586

27-28 Jun 2 7 6 4 3 6 0.563 0.668 0.452

5 Jul 2 8 112 8 5 0.759 0.824 0.683

1617Jul 2 9 123 64 0.520 0.597 0.442

11-12 Aug 3 3 138 105 0.761 0.820 0.694

16-18 Aug 3 4 162 4 5 0.278 0.342 0.220

25-26 Aug 3 5 8 6 11 0.128 0.203 0.073

Transition Moser Bay 14-15 Jun 2 5 107 7 0.065 0.119 0.031

Area Moser Bay 27-29 Jun 2 7 8 6 2 4 0.279 0.369 0.200

Moser Bay 5-6 Jul 2 8 8 7 1 9 0.218 0.304 0.148

Moser Bay IS 16 Jul 20 131 24 0.103 0.240 0.130

Moser Bay 20-21 Jul 3 0 112 3 6 0.323 0.401 0.249

Moser Bay 27-28 Jul 3 1 7 8 4 0.051 0.114 0.018

Moser Bay 5 Aug 3 2 123 1 0 0.081 0.134 0.045

Moser Bay IO-12 Aug 3 3 111 2 4 0.216 0.290 0.164

Moser Bay 20-21 Aug 3 4 127 3 0 0.236 0.306 0.175

Moser Bay 22 Aug 3 4 110 4 1 0.373 0.455 0.296

Moser Bay 25-27 Aug 3 5 119 1 4 0.118 0.178 0.073

Terminal Olga Bay 14-15 Jun 2 5 117 0 0.000 0.025 0.000

Harvest Olga Bay 20-21 Jun 2 6 117 5 0.043 0.088 0.017

Area Olga Bay 27-29 Jun 2 7 7 3 2 0.027 0.084 0.005

Olga Bay 6-7 Jul 2 8 9 8 4 0.041 0.091 0.014

Olga Bay 20-21 Jul 3 0 137 4 0.029 0.066 0.010

Olga Bay 30 Jul 3 1 144 1 4 0.097 0.148 0.060

Olga Bay 3-A Aug 32 119 25 0.210 0.281 0.150

Olga Bay IO-II Aug 3 3 104 9 0.087 0.146 0.046

Olga Bay 20-21 Aug 3 4 104 11 0.106 0.169 0.060

Olga Bay 25-26 Aug 3 5 102 1 6 0.157 0.228 0.101

10
Table 4. Feeding proportions for 1999 samples.

1999 Sample Catch Sample Sample Number Proportion C.I. (95%)

Area Date(s) Period Size Feedina Feeding Upper Lower

Migration

Corridors

Transition

Area

Terminal

Harvest

Area

Ayakulik

Ayakulik

Ayalwllk

Ayakulik

Ayakulik

Ayakulik

Ayakulik

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Cape Alitak

Eastside

Eastside

Eastsida

Fart&In

Eastside

Eastside

Eastside

Eastside

Mainland

Mainland

Mainland

Mainland

Mainland

Westsidc

Westside

Westside

Westside

Westside

Westside

15-16 Jun 2 5 120 5 7 0.475 0.568 0.383

15-16 Jun 2 5 120 4 2 0.350 0.442 0.265

28-30 Jun 2 7 110 8 0 0.727 0.808 0.634

13-14 Jul 2 9 120 9 6 0.800 0.867 0.717

27-29 Jul 3 1 135 7 1 0.526 0.612 0.438

5-7 Aug 3 2 106 4 9 0.462 0.562 0.365

5-7 Aug 3 2 102 4 4 0.431 0.533 0.334

25-26 Jun 2 6 125 9 6 0.768 0.839 0.684

25-26 Jun 2 6 106 6 4 0.792 0.865 0.703

22 Jul 3 0 135 7 1 0.526 0.612 0.438

28 Jul 3 1 109 5 8 0.532 0.628 0.434

5 Aug 3 2 127 7 1 0.559 0.647 0.468

11 Aug 3 3 108 8 4 0.778 0.852 0.688

24 Aug 3 5 160 131 0.819 0.875 0.750

22-23 Jun 2 6 115 5 4 0.470 0.565 0.376

7-9 Jul 2 8 108 4 5 0.417 0.515 0.323

8-9 Jul 2 8 110 2 2 0.200 0.287 0.130

13-15 Jul 2 9 110 7 1 0.645 0.734 0.549

4-5 Aug 3 2 141 112 0.794 0.858 0.718

13 Aug 3 3 100 5 0 0.500 0.602 0.398

14 Aug 3 3 100 4 7 0.470 0.572 0.369

17-18 Aug 3 4 104 5 3 0.510 0.609 0.410

15-17 Jun 2 5 119 7 2 0.605 0.693 0.511

25 Jun 2 6 106 9 9 0.934 0.973 0.869

14 Jul 2 9 100 9 7 0.970 0.994 0.915

19-22 Jul 3 0 103 9 5 0.922 0.966 0.853

27-29 Jul 3 1 108 9 8 0.907 0.955 0.836

17-20 Jun 2 5 120 108 0.900 0.947 0.832

23 Jul 3 0 128 7 9 0.617 0.702 0.527

27-30 Jul 3 1 122 7 3 0.598 0.686 0.506

4-7 Aug 3 2 104 6 5 0.625 0.718 0.525

4-7 Aug 32 121 6 6 0.545 0.636 0.452

18-19 Aug 3 4 117 5 6 0.479 0.573 0.385

Moser Bay 9-10 Jun 2 4 125 7 7 0.616 0.702 0.525

Moser Bay 10 Jun 2 4 125 8 2 0.656 0.739 0.566

Moser Bay 22-23 Jul 3 0 124 4 5 0.363 0.454 0.278

Moser Bay 27-28 Jul 3 1 125 5 0 0.400 0.491 0.313

Moser Bay 3-4 Aug 3 2 120 3 9 0.325 0.417 0.242

Moser Bay II-12 Aug 3 3 149 6 9 0.463 0.547 0.381

Moser Bay 22-24 Aug 3 5 140 6 0 0.429 0.515 0.345

Olga Bay 20-21 Jun 2 6 106 11 0.104 0.178 0.053

Olga Bay 21 Jun 2 6 105 1 2 0.114 0.191 0.060

Olga Bay 26 Jun 2 6 109 11 0.101 0.173 0.051

Olga Bay 22-23 Jul 3 0 101 6 0.059 0.125 0.022

Olga Bay 27-29 Jul 3 1 106 2 4 0.226 0.318 0.151

Olga Bay 3-4 Aug 3 2 112 1 9 0.170 0.252 0.105

Olga Bay II-12 Aug 3 3 130 4 0 0.308 0.395 0.230

Olga Bay 11-12 Aug 3 3 9 7 3 9 0.402 0.507 0.304

Olga Bay 22-23 Aug 3 5 103 1 8 0.175 0.262 0.107

1 1
I ri Iii

a 1.00

0

Q- 0.B0-

0.60-

1n - I III

I 1111111111111111

Mainland

0.80 -

0.60 -

0.40 -

E 0.20 -

. -

$_ 0.00 I I I

IL” 14 21 28 ' 5 12 19 26 ' 2 9 16 23

s

'S

b 1 .x3

Ayakulik

8

0.60

0.40

0.20

0.00

14 21 28 5 12 19 26 ' 2

!

9 16 23

Eastside

1.00

0.80 -

0.60 -

0.40 -

F 0.20 -

3

z 0.00

1 1

14 21 28 5 1 12 I 19 , 26 I 2 I 9 I 16 23

Westside

Jun JUI

Week of Catch

*ug

Figure 5. Prnpnrtion of feeding sockeye salmon in migration corridors, 1998 and 1999.

Ir the migration corridors, results of contingency table analysis showed highly significant differences

within each area in incidence of feeding during both 1998 (Table 5) and 1999 (Table 6). Only the two

sc quential samples taken from the Eastside in 1998 were not significantly different. Examining amongaxea differences in incidence of feeding, during weeks when two or more comparable samples were

a\,ailable, again resulted in highly significant differences in the majority of comparisons made during

1098. In 1999 only the Eastside and Westside areas, during the week of 23-29 August, were not

si gificantly different.

12
rable 5. Incidcncc offccding in migration corridors, with significance testing, 1998. G = G-statistic,

p = probability. Period is week catch occurred. Percentages are proportion of sockeye salmon

with prey in the stomach.

Period Ayakulik Cape Alitak Eastside Mainland Westside

7-13Jun

14-20Jun

21-27Jun

28Jun-4Jul

5-11 Jul

12-18Jul

19-25Jul

26 Jul-1 Aug

2-8Aug

9-15 Auy

16-22Aug

23-29Aug

4.4%

41.2%

41.6%

68.3%

81.4%

59.7%

03.3%

65.6%

31.6%

65.0%

70.2%

56.3%

38.7%

38.8%

46.4%

73.476

68.8%

22.3%

76.2%

74.1%

38.2%

67.0%

56.3%

75.9%

52.0%

76.1%

27.8%

12.8%

G = 101.4

p < 0.001

G = 14.6

p < 0.001

G = 17.3

p < 0.001

G = 13.3

P = 0.004

G = 63.4

p < 0.001

G = 0.0

P = 0.915

G = 5.4

P = 0.067

G = 63.2

p c 0.001

G = 3.1

P = 0.080

G = 209.1 = 82.3 = 0.2 = 166.7

P c 0.001 < 0.001 = 0.691 c 0.001

13
Table 6. Incidence of feeding in migration corridors, with significance testing, 1999. G = G-statistic,

p = probability. Period is week catch occurred. Percentages are proportion of sockeye salmon

with prey in the stomach.

Period Ayakulik Cape Alitak Eastside Mainland Westside

7-13Jun

14-20Jun 47.5% 60.5% 90.0%

21-27Jun 76.8% 47.0% 93.4%

28Jun-4Jul 72.7%

6-Il Jul 20.0%

12-18Jul 80.0% 64.5% 97.0%

19-25 Jul 52.6% 92.2% 61.7%

26JuLlAug 52.6% 53.2% 90.7% 59.8%

2-8Aug 46.2% 55.9% 79.4% 54.5%

9-15Aug 77.8% 50.0%

16-22Aug 51.0% 47.9%

23-29Aug 81.9%

G = 50.8 - 57.2 = 101.6 = 72.9 = 60.9

P < 0.001 < 0.001 < 0.001 < 0.001 < 0.001

G = 56.4

p < 0.001

G = 64.6

p c 0.001

G = 40.2

p c 0.001

G = 51.1

p < 0.001

G = 54.7

p c 0.001

G = 34.8

p < 0.001

G = 17.7

p < 0.001

G = 0.2

p = 0.646

Sockeye salmon moving towards their natal streams through the waters off Cape Alitak, Moser Bay and

into Olga Bay exhibited highly significant differences in incidence of feeding within each area during

both 1998 (Table 7) and 1999 (Table 8). Comparisons among the three areas during the same weekly time

periods also resulted in highly significant differences in all but two weeks (26 July - 1 August and 23-29

llugust 1998). In most periods, feeding appcarcd to taper off rather then cease ablupLly (Figure 6), with

more Cape Alit& fish feeding than Moser Bay fish, and Moser Bay fish generally feeding at a higher rate

than Olga Bay fish. Only during three periods in late July and August 1998 did the incidence of feeding in

(>lga Bay surpass that in Moser Bay.

1 4
Table 7. Incidence of feeding as sockeye salmon move towards their natal streams, with

significance testing, 1998. G = G-statistic, p = probability. Period is week catch

occurred. Percentages are proportion of sockeye salmon with prey in the stomach.

Period Cape Alitak Moser Bay Olga Bay

7-13 Jun 31.6%

14-20 Jun 65.0% 6.5% 0.0%

21-27 Jun 4.3%

28Jun-4 Jul 70.2% 27.9% 2.7%

5-11 Jul 56.3% 21.8% 4.1%

12-18 Jul 38.7% 18.3%

19-25 Jul 38.8% 32.1% 2.9%

26 Jul- 1 Aug 5.1% 9.7%

2-8 Aug 46.4% 8.1% 21.0%

9-15Aug 73.4% 21.6% 8.7%

16-22 Aug 68.8% 23.6% 10.6%

23-29Aug 22.3% 11.8% 15.7%

G = 140.9 = 59.1 = 55.5

P < 0.001 < 0.001 c 0.001

G = 164.7

p < 0.001

G = 101.5

p < 0.001

G = 73.7

p < 0.001

G = 14.1

p < 0.001

G = 65.1

p < 0.001

G = 1.5

p = 0.215

G = 47.8

p < 0.001

G = 124.4

p < 0.001

G = 99.6

p c 0.001

G = 4.7

p = 0.096

15
Table 8. Incidence of feeding as sockeye salmon move towards their natal streams, with

significance testing, 1999. G = G-statistic, p = probability. Period is week catch

occurred. Percentages are proportion of sockeye salmon with prey in the stomach.

Period Cape Alitak Moser Bay Olga Bay

7-13Jun 61.6%

14-20Jun 10.4%

21-27 Jun 76.8% 10.1%

28Jun-4Jul

5-11 Jul

12-18Jul

19-25Jul 52.6% 36.3% 5.9%

26Jul-I Aug 53.2% 40.0% 22.6%

2-6Aug 55.9% 32.5% 17.0%

9-15 Aug 77.8% 46.3% 30.8%

16-22&q 42.9%

23-29Aug 81.9% 17.5%

G=115.9

p < 0.001

G = 66.2

p < 0.001

G = 21.9

p < 0.001

G = 41.3

p < 0.001

G = 36.9

e p

< 0.001

G = 113.0

p c no01

G = 57.2 = 26.4 = 36.1

P < 0.001 c 0.001 c 0.001

1 6
Moser Bay

Olga Bay

P1

r

4

'I

I I I

1998

1.00

5 0.80

a,

I? 0.60

z

'F 0.40

2.

2 0.20

a

0.00

7 1 4 2 1 28 5 12 19 26 2 9 1 6 23

Jun Jul Aug

1999

1.00

F

-D 0.80

ti

L L 0.60

5

'E 0.40

0

I28 0.20

0.00

7 1 4

Jun

2 1 28 5 1 2 1 9 26 2

Jul Aug

Week of Catch

9 1 6 23

Figure 6. Proportion of sockeye salmon actively feeding as they move towards their natal

streams-from Cape Alihk ~111uugh Moser Day and into Olga Bay, 1998 and 1999.

The incidence of feeding exhibited a hi-modal pattern in 1998, with greater proportions in late June and

mid-August, corresponding to the timing of the dominant early run Fraser Lake stock (June through midJuly) and the late run Upper Station stock (late July through August). Low returns of salmon in 1999

during June and early July resulted in extended fishing closures, and thus a lack of samples during this

time period. When the incidence of feeding in these three areas was examined within either the early

run (pre-19 July) or late run (post-l 8 July), early-run Olga Bay fish exhibited no significant differences

among time periods in either 1998 (Table 9) or 1999 (Table 10). Early-run and late-run Cape Alitak (1998

and 1999), late-run Olga Bay (1998 and 1999), and late-run Moser Bay (1998) fish were all significantly

different when examined among periods. The 1999 late-run Moser Bay fish did not exhibit any significant

differences in incidence of feeding.

17
Table 9. Incidence of feeding of early and late runs, 1998. G = G-statistic, p = probability. Period is week

catch occurred. Percentages are proportion of sockeye salmon with prey in the stomach.

Early Run Cape

Period Alitak

Moser

Bay

Olga

Bay

Late Run

Period

Cape

Alitak

Moser

Bay

Olga

Bay

7-13 Jun 31.6% 16-25 Jul 38.8% 32.1% 2.9%

14-20 Jun 65.0% 6.5% 0.0% 26 Jul- 1 Aug 5.1% 9.7%

21-27 Jun 4.3% 2-a Aug 46.4% 8.1% 21.0%

28 Jun-4 Jul 70.2% 27.9% 2.7% 9-15 Aug 73.4% 21.6% 8.7%

5-11 Jul 56.3% 21.8% 4.1% 16-22 Aug 68.8% 23.6% 10.6%

12-18 Jul 38.7% 18.3% 23-29 Aug 22.3% I 1.8% 15.7%

G = 51.7 = 17.9 = 3.6 G = 82.4 = 41.2 = 25.4

P c 0.001 c 0.001 = 0.314 P < 0.001 < 0.001 < 0.001

Table 10. Incidence of feeding of early and late runs, 1999. G = G-statistic, p = probability. Period is

week catch occurred. Percentages are proportion of sockeye salmon with prey in the stomach.

Early Run

Period

Cape

Alitak

Moser

Bay

Olga

Bay

Late Run

Period

Cape

Alitak

Moser

Bay

Olga

Bay

7-13 Jun

14-20 Jun

21-27 Jun

2 8 Jun-4 Jul

5-11 Jul

12-18 Jul

76.8%

61.6%

10.4%

10.1%

16-25 Jul

26Jul-I Aug

2-a Aug

9-15 Aug

16-22 Aug

23-29 Aug

52.6%

53.2%

55.9%

77.8%

81.9%

36.3%

40.0%

32.5%

46.3%

42.9%

5.9%

22.6%

17.0%

30.8%

17.5%

G = 0.005

P = 0.945

G = 50.3 = 6.5 = 26.0

P c 0.001 = 0.164 c 0.001

Prey analysis

I;or prey analysis, 26 samples were obtained from three areas (Eastside, Westside and Mainland) during

the 1998 and 1999 seasons. From a total of 647 stomachs examined, at least 25 taxa are represented by

seven prey categories (Table 11). The Eastside and Mainland areas were not well sampled in 1998 due to

1 imited fishery openings and fishing effort, but all three areas were well represented in the 1999 samples

(Figure 7).

1 8
1.00 Olga Bay

Pa

1 I rr

111111..;: ISIIIililh ur'

1998 0 Cape Alitak

El Moser Bay

.-P

u

0.80

ii

u- 0.60 r

5

.f 0.40

0

68 0.20

0.00

1 .oo

.-

P

-0 0.80

ii

LL 0.60

5

.f 0.40

E

g 0.20

a

0.00

7 14 21 28 5 1 2 1 9 2 6 2 9 1 6 2 3

Jun Jul Au9

r

7 14 2 1 28 5 12 1 9 2 6 2 9 1 6 2 3

Jun Jul Au9

Week of Catch

Figure 6. Proportion of sockeye salmon actively feeding as they move towards their natal

streams-from Cape Alitak through Moser Bay and into Olga Bay, 1998 and 1999.

The incidence of feeding exhibited a bi-modal pattern in 1998, with greater proportions in late June and

mid-August, corresponding to the timing of the dominant early run Fraser Lake stock (June through midJuly) and the late run Upper Station stock (late July through August). Low returns of salmon in 1999

during June and early July resulted in extended fishing closures, and thus a lack of samples during this

time period. When the incidence of feeding in these three areas was examined within either the early

run tire-19 July) or late run (post-18 July), early-run Olga Bay fish exhibited no significant differences

among time periods in either 1998 (Table 9) or 1999 (Table 10). Early-run and late-run Cape Alitak (1998

and 1999), late-run Olga Bay (1998 and 1999), and late-run Moser Bay (1998) fish were all significantly

different when examined among periods. The 1999 late-run Moser Bay fish did not exhibit any significant

differences in incidence of feeding.

1 7
Table 11. Prey of adult sockeye salmon. Categnry is the classification

used in analyses.

Category Prey Taxa

Fishes Ammodytidae

Gndidae

Decapods

Anomura

Brachyura

Euphausiids

Cumaceans Diastylopsis dawsoni

Pteropods Gastropoda

Amphipods

Other Copepoda

Mysidacea

Chaetognatha

Larvacea

Crustacea

Fish eggs

lnsecta

Ammodytes hexapterus

Gadus SW.

unidentified fishes

unidentified decapod zoea

unidentified decapod decapodid

unidentified anomuran zoea

unidentified ammuran glaucothoe

Pagurus spp. zoea

Pagurus spp. glaucothoe

unidentified brachyuran zoea

unidentified brachyuran megalopa

Chionoecetes spp. megalopa

Hyas lyratus megalopa

unidentified Oregoniinae megalopa

Telmessus cheiragonus megalopa

Cancer spp. zoea

Cancer spp. megalopa

unidentified Pinnotheridae zoea

unidentified euphausiid

Thysanogssa inermis

Thysano&sa spinifera

Thysanodssaspp.

Limacina helicina

unidentified hyperiid

unidentified gammarid

unidentified calanoid

unidentified

Sagiffa elegans

Oikopleura spp.

unidentified

unidentified

unidentified

1 9
Prey Samples by Date

Mainland

-

I - n

A .A A - A

* 4

Eastside

0 : A a * 0

Westside

14 Jun 21 Jun 28 Jun 5 Jul 12 Jul 19Jul 26 Jul 2 Aug 9 Aug 16Aug 23 Aug

Catch Date

Figure 7. Distribution of sampling effort during 1998 and 1999. Catch date represents the first day

fish were caught. Open marker = 1998, solid marker = 1999.

!iample size

In random sampling from pooled stomach content data, only 18 of 28 prey taxa (64%; the median of 10

random samples) were represented at a sample size of n = 30 stomachs, the target sample size for this

s,tudy (Figure 8). By increasing the sample size to n = 200,25 of 28 prey types (89%) were represented.

In contrast, when sampling prey oatcgorics rather than individual ploy Laxa, all seven prey CategOriCS WeTe

present at a sample size of n = 22. By using prey categories rather than individual taxa in analyses, diet

breadth could be adequately characterized with a smaller sample size than that used in this project.

Digestive state

Overall digestive state for all samples was X = 2.5, indicating relatively recent feeding. Digestive

state ranged from a minimum x ’ = 1.9 for Eastside samples during 22-23 June 1999 to a maximum

c f X = 3.53 for Mainland samples caplured un 25 June 1999. There were no significant differences

between areas when samples were pooled over 1998 and 1999 (F = 1.003; p = 0.367; Table 12).

2 0
8

7- Categories

(1, U) 6-

/ Taxa

. 3-

2 V

Prey Represented in Sample Size

(median of 10 random runs)

3 0

2 5

cu

2Q 2

l-

$

1 5 :

2

3

1 0 z

0’

5

0 I I I I 1 I I I 0

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 60 9 0 100110120130140150160170160190200

Number of Stomachs

Figure 8. Cumulative prey taxa and categories represented from pooled stomach contents

as a function of sample size. Line represents the median value of 10 random runs.

Table 12. Digestive state of stomach contents from each area with samples pooled by year.

Digestive state was subjectively rated for each stomach examined, on a scale of

1 to 4. A score of 1 = highly digested; 4 = minimal digestion. UC1 = upper 95%

confidence interval; LCI = lower 95% confidence interval.

Year Area n Mean LCI (95%) UCI (95%) Median

1998 Mainland 3 0 2.5 2.1 2.9 2.8

1999 Mainland 142 2.6 2.5 2.7 3.0

1998 Eastside 5 5 3.1 2.9 3.3 3.0

1999 Eastside 136 2.2 2.0 2.3 2.0

1998 Westside 124 2.4 2.3 2.6 2.5

1999 Westside 160 2.6 2.5 2.7 3.0

Stomach content weight

Overall mean weight for total stomach contents was X = 8.15 g, ranging by sample from X = 4.19 g

(Westside, 27-28 June 1998) to a maximum of X = 21.49 g (Mainland, 19-22 July 1999). The minimum

weight for an individual stomach with prey was 0.12 g and the maximum individual weight was 65.98 g.

(Table 13). Stomach content weights exhibited a log-normal distribution and were transformed prior to

analysis with ANOVA.

2 1
Table 13. Mean, minimum and maximum stomach content weights (g). UC1 = upper 95% confidence

interval; LCI = lower 95% confidence interval.

Year Area Catch Date n MeallVtCpg;tent LCI (95%) UCI (95%) Minimum (g) Maximum (g)

1998 Mainland 21-22Jul 3 0 12.24 6.78 17.71 0.52 53.99

1999 Mainland 15-17Jun 2 9 6.90 5.34 8.47 1.20 16.86

25Jun 3 0 9.34 7.39 11.28 4.73 24.89

14Jul 3 0 10.15 7.62 12.68 1.38 29.32

19-22Jul 2 3 21.49 12.59 30.40 0.81 65.98

27-29Jul 3 0 14.25 10.94 17.57 2.05 34.50

1998 Eastside 7-8Jul 2 6 13.30 8.29 18.31 0.20 47.99

14-16 Jul 2 9 8.65 6.67 10.63 1.48 21.16

1999 Eastside 22-23Jul 1 1 7. IO 2.88 11.31 1.30 20.75

7-9Jul 2 0 6.93 3.69 10.18 1.07 23.56

13-15Jul 2 8 8.70 3.30 14.09 0.41 55.68

4-5Aug 3 0 6.19 4.51 7.88 1.39 21.09

13-14Aug 3 4 5.59 4.28 6.90 1.45 18.30

17-18Aug 1 7 5.07 3.68 6.46 1.43 10.86

1998 Westside 20-22Jun 1 7 5.73 2.43 9.04 0.15 23.69

27-28Jun 1 4 4.19 2.21 6.18 0.12 13.67

5 Jul 3 0 7.30 4.56 10.03 0.14 29.50

1%17Ju\ 2 0 5.99 4.07 7.91 0.81 19.68

ll-12Aug 3 0 5.97 4.61 7.32 1.10 13.66

16-18Aug 1 4 4.75 2.74 6.76 0.28 10.54

1999 Westside 17-20Jun 3 0 6.30 4.72 7.88 0.98 18.61

23Jul 3 0 4.90 3.74 6.05 0.53 12.19

27-3OJul 3 0 8.62 5.21 12.03 0.98 41.27

4-7Aug 2 9 4.37 2.78 5.96 0.84 16.81

4-7Aug 2 7 5.31 3.68 6.94 0.34 15.21

18-19Aug 1 4 7.78 2.41 13.16 1.02 32.13

Sample data were initially pooled by area over both 1998 and 1999 (Mainland, X = 12.06 g; Eastside,

X = 7.80 g; Westside, X = 6.01 g) and showed the effect of area to be highly significant (F = 35.67.

p << 0.001). Post-hoc comparisons of the three areas using Tukey’s HSD test showed all three to be

significantly different (p < 0.01) in terms of fullness by weight. When examined for year and area effects,

area (F = 23.36; p << 0.001) and the interaction with year (F = 6.33; p = 0.002) were highly significant.

The interaction effect was due to a decrease in mean weights in the Eastside samples and an increase in

weights in the Mainland samples in 1999. Year effect was not significant.

Tests of between area differences in 1998 were hampered by the small number of samples obtained from

the Mainland and Eastside. The 1999 samples were well balanced among areas and the results of a oneway ANOVA for 1999 weights were highly significant (F = 34.78; p << 0.001). Tukey’s HSD showed

that stomach content weights from the Mainland area differed significantly (p -;c 0.001) from the Eastside

and Westside areas, which were not significantly different from each other. The mean weight of stomach

contents in 1999 Mainland samples (X = 12.02 g) was nearly twice that found in the Eastside (Z = 6.56 g)

and Westside (X - 6.08 g) areas.

Within each area, only the Mainland samples exhibited highly significant differences among periods

(F = 3.98; p = c1.002). Tukey’s HSD showed this was due to the high 19-22 July 1999 (.F = 21.49 g) and

22
Jill! !J1 1

0.4

0.2

0.0 111111111

27-29 July 1999 (Z = 14.25 g) values in comparison to the low 15-16 June (K = 6.90 g) weights. Mean

stomach content weights were positively correlated with higher incidence of feeding (r2 = 0.212,

p = 0.02, n = 26).

Prey composition

Overall, the principal prey of sockeye salmon were decapod larvae, pteropods and fish (Figure 9).

Pteropods were comprised exclusively of L. helicina and fish were predominately (86% by number)

Pacific sandlance, of which 94% were < 70 mm FL. In the Eastside and Westside areas, when pooled over

the course of the season, decapod larvae were both the most frequently occurring and numerous prey item

(Table 14). In Mainland samples pteropods and fish were the most frequently occurring prey, with

decapods and pteropods the most numerous.

1.0

0.8

0.6

1998

Frequency of Occurrence

Mainland Eastside Westside

1998

Percent by Number

0.6

0.2

0.0

Mainland Eastside Westside

I .Q

0.6

0.6

1999

Frequency of Occurrence

Mainland Eastside Westside

1999

Percent by Number

z Fish

3 Decapod ’

-

0.8

0.6

E Pteropod

Amphipod

Mainland Eastside Westside

Figure 9. Overall frequency of occurrence and percent by number for sockeye prey items, I998

and 1999.

2 3
Table 14. Frequency of occur-rencc and pcrccnt composition by number of prey categories; areas pooled

by year. An entry of “-” indicates a value < 1%.

Frequency of occurrence Prey Category

Year Area Fish Decapod Euphausiid Cumacea Pteropod Amphipod Other

1998 Mainland 60% 17% 20% 57% -

Eastside 49% 89% 2 % 9 % 49% 2% -

Westside 22% 83% 23% 5 % 46% 3 % 8 %

1999 Mainland 74% 56% 32% 59% 12% 10%

Eastside 47% 78% 22% 25% 5 % 4 % 7 %

Westside 56% 74% 15% 1 % 41% 1 % 8 %

overall 51% 71% 21% 7 % 40% 5% 7%

Percent Composition by Number

Year Area Fish Decapod Euphauslld Cumacea Pteropod Amphipod Other

1998 Mainland 5 % - - 94% -

Eastside 1 % 77% - 9 % 13% -

Westside - 69% 5 % 1 % 24% -

1999 Mainland 10% 44% 3 % 43%

Eastside 52% 5 % 41% -- 1 %

Westside 1 % 66% 2 % 3 % 28%

overall 3% 59% 3 % II % 23%

Prey use varied between areas, and within each area between periods. Only fish and decapods were found

ill all samples. Fish percent composition by number (O/ON) was greatest in the Mainland area in July 1999

vith the percent frequency of occurrence (FOcc) approaching 100% (Table 15). In June 1999 FOcc for

t’ish in Mainland sockeye diets varied from 7% to 72% while FOcc for decapods and pteropods fell in July

Corn high June levels. Although fish occurred in all Eastside and Westside samples, %N values in these

areas were always low, varying from < 1% to 5% (Table 16).

2 4
Table 15. Frequency of occurrence (percent) of prey categories for individual samples. An entry of “-”

indicates a value < 1%.

Frequency of Occurrence (percent) Prey Category

Year Area Catch Date n Fish Decapod Euphausiid Cumacea Pteropod Amphipod Other

1998 Mainland

1999 Mainland

1998 Eastside

1999 Eastside

1998 Westside

1999 Westside

21-22Jul

15-17Jun

25Jun

14Jul

19-22Jul

27-29Jul

7-8Jul

14-16 Jul

22-23Jun

7-9Jul

13-15Jul

4-5Aug

13-14Aug

17-18Aug

20-22Jun

27-28Jun

5 Jul

16-17 Jul

ll-12Aug

16-18Aug

17 20Jun

23Jul

27-3OJul

4-7Aug

4-7 Aug

18-19Aug

3 0 60%

2 9 72%

3 0 7 %

3 0 97%

2 3 1 OOYO

3 0 100%

2 6 65%

2 9 35%

1 1 45%

2 0 42%

2 8 92%

3 0 57%

3 4 18%

1 7 25%

1 7 31%

1 4 36%

3 0 30%

2 0 10%

3 0 7 %

1 4 29%

3 0 47%

3 0 47%

3 0 73%

2 9 55%

2 7 48%

1 4 79%

17%

69%

80%

27%

22%

73%

85%

93%

73%

47%

58%

100%

91%

81%

69%

57%

93%

85%

93%

77%

67%

57%

87%

72%

81%

86%

20%

31%

30%

23%

35%

40%

4 %

36%

16%

-

30%

23%

37%

25%

29%

20%

25%

13%

43%

17%

13%

27%

17%

7 %

-

-

15%

3%

-

47%

35%

10%

21%

37%

12%

-

13%

-

-

57% -

86% 28%

90% 10%

53% -

22% 4%

37% 17%

35% -

62% 3%

27% -

- 10%

8% -

7 % 10%

-

- 6 %

69% -

71% -

80% 7 %

60% -

- 7 %

90% 3 %

47% -

37% -

17% -

30% 4 %

- -

10%

-

20%

-

17%

-

9 %

10%

11%

12%

-

25%

-

13%

7 %

23%

-

13%

7 %

25
Table 16. Percent composition by number of prey categories for individual samples. An entry of “-”

indicates a value < 1%.

Percent Composition by Number Prey Category

Year Area Catch Date n Fish Decapod Euphausiid Cumacea Pteropod Amphipod Other

1998 Mainland

1999 Mainland

1998 Eastside

1999 Eastside

1998 Westside

1999 Westside

21-22 Jul 3 0

15-17 Jun 2 9

25 Jun 3 0

14 Jul 3 0

19-22 Jul 2 3

27-29 Jul 3 0

7-8 Jul 2 6

14-16 Jul 2 9

22-23 Jun 1 1

7-9 Jul 2 0

13-15 Jul 2 8

4-5 Aug 3 0

13-14 Aug 3 4

17-18 Aug 1 7

20-22 Jun 1 7

27-28 Jun 1 4

5 Jul 3 0

16-17 Jul 2 0

II-12Aug 3 0

16-18 Aug 1 4

17-20 Jun 30

23 Jul 3 0

27-30 Jul 3 0

4-7 Aug 2 9

4-7 Aug 2 7

18-19 Aug 1 4

4 %

4 %

41%

54%

15%

4 %

-

2 %

3 %

-

4 %

2 %

2 %

-

-

1 %

2 %

4 %

1 %

5 %

-

14%

55%

13%

21%

77%

76%

77%

69%

1 %

94%

71%

53%

76%

13%

54%

46%

98%

60%

58%

43%

42%

85%

71%

95%

4 %

2 %

4 %

15%

2 %

-

11%

3 %

6 %

21%

6 %

5 %

2 %

40%

8 %

9 %

3 %

-

-

-

-

19%

5 %

97%

94%

2 %

20%

26%

6 %

-

8 %

94%

76%

43%

41%

9 %

5 %

2 %

17%

16%

14%

84%

38%

48%

- -

-

-

-

- -

1 %

-

2 %

- -

3 %

-

-

-

-

-

-

-

-

Decapods were found in all samples, with euphausiids and pteropods occurring in all Mainland samples

and nearly all Eastside and Westside samples. Decapods always outnumbered euphausiids, with the

highest decapod %N found in the Westside and Eastside area diets. Cumaceans occurred primarily in

sockeye sampled from the Eastside. In early July 1999 cumacean FOcc ranged from 35% to 47% and %N

from 94% to 97%. Cumaceans occurred in only three Westside samples; there were no cumaceans in any

Mainland stomachs. In those Westside samples, the cumacea %N ranged from < 1% to 8%. Although

amphipods (approximately 80% gammarids) occurred in nearly half the samples obtained, they were

always < 1% by number. Taxa in the category “other” (primarily unidentified crustaceans) were also

found in approximately half the samples, but rarely accounted for more than 1% of prey items by number.

Contingency table analysis, using the number of prey items in each category, showed highly significant

differences in patterns of overall prey usage. The categories “amphipod” and “other” were not included in

those tests to avoid the confounding effect of sparse data. For both 1998 and 1999 all tests of differences

within areas/between periods, and between areas, resulted in p-values < 0.001.

Patterns in consumption of individual prey categories were tested for within- and between-area

differences using the Kruskal-Wallis ANOVA by ranks. In examining areas pooled by year, only the

26
category “other” was not significantly different between areas. Tests of all remaining categories showed

highly significant differences (p < 0.001) between areas.

Post-hoc comparisons among these pooled areas (by prey category), using Tukey’s HSD, show the

greatest number of significant comparisons occurred in the decapod category (Table 17). Within-year

comparisons of decapod consumption were non-significant only for Eastside and Westside sockeye

in 1998 and 1999, all other comparisons being significantly different. Fish consumption differed

significantly between years within both the Westside and Mainland areas. In 1998 the Westside area

had significantly lower fish consumption than the Mainland and Eastside areas; in 1999 the Mainland

area had higher fish consumption than the Westside and Eastside areas.

Table 17. Results of Tukey’s HSD test comparing overall prey usage bt;tween areas. 11.s; not significant

at p = 0.05, *: p < 0.05.

Fish

Decapod

1998 Mainland

Eastside

Westside

1999 Mainland

Eastside

Westside

1998 1999

Mainland Eastside Westside Mainland Eastside Westside

n.s.

* l

* * l

n.s. n.s. n.6. l

n.s. ns. l l ns.

1998 Mainland

Eastside *

Westside *

1999 Mainland l

Eastside *

Westside l

n.s.

* *

* l *

* l * n.s.

Euphausiid 1998 Mainland

Eastside

Westside

1999 Mainland

Eastside

Westside

n.s.

n.s. n.s.

n.s. l ns.

n.s. n.6. n.s. ns.

n.s. n.s. n.s. n.s. n.s.

Pteropod 1998 Mainland

Eastslde n.s.

Westside n.s. n.s.

1999 Mainland n.s. n.s. n.s.

Eostsidc * l l *

Westside n.s. ns. n.s. * *

In 1998 there were no significant differences among areas in pteropod consumption. In contrast, in 1999

all between-area comparisons were significantly different. Within-area/between-year differences in

pteropod consumption were significant only for Eastside sockeye. Euphausiid consumption appears to be

relatively uniform in all within-year/between-area, and between-year/within-area tests. The significance

of this prey category in the initial Kruskal-Wallis test is due only to differences between the Eastside

27
1998 and Mainland 1 YYY sockeye. Cumacean consumption was not significantly different between years

for any area, and in 1999 only the Eastside sockeye differed from Mainland and Westside sockeye.

Period effects on prey consumption were tested for each area by year (Table 18). Due to the small number

of samples, the 1998 Eastside area (only two sequential samples) and the 1998 Mainland area (one

sample) were not included. In all areas the effect of period on prey consumption was most notable for

decapods and pmupods. Only in the 1998 Westside samples did period not have a significant effect on

fish consumption. Overall, the most pronounced effect of period, found in the majority of prey categories

tested, occurred in the 1999 Eastside samples.

Table 18. Effect of period on prey contents. n.s: not significant at p = 0.05, *: 0.05 <p ~0.01,

**: p dO.01.

Year Area Fish Decapod Euphausiid Cumacea Pteropod AmphipOd Other

1998

1999

Westside n.s. ** n.s. n.s. ** ns. n.s.

Mainland ** l * n.s. n.s. l * l n.s.

Eastside l * ** ** ** l * ns. ns.

Westside l * ns. n.s. l * n.s. **

Diversity

The maximum potential diversity value (I?‘-) for any sample, given equal consumption of the seven

Jrey categories, is H’= 0.85. Measurements of diversity in samples (Table 19) ranged from H’= 0.047 to

Y’= 0.509 for the pooled population (H&) and II’= 0.015 to H’= 0.260 for the mean individual (&d).

The largest values for H;K)p and H6d occurred in the 1999 Mainland samples, with the lowest values

occurring in the 1998 Westside samples. In only the two July 1999 Eastside samples did the values of

Y&d exceed H&,.

2 8
Table 19. Shannon-Weaver diversity indices (H’) for mean individual

and pooled samples. H’,, = 0.0; H’,, = 0.85.

Year Area Catch Date n H’ pooled H’ individual

1998 Mainland

1999 Mainland

1998 Eastside

1999 Eastside

1998 Westside

1999

21-22Jul 3 0 0.106 0.074

15-17Jun 2 9 0.348 0.198

25Jun 3 0 0.337 0.099

14Jul 3 0 0.505 0.161

19-22Jul 2 3 0.509 0.144

27-29Jul 3 0 0.336 0.260

7-8Jul 2 6 0.312 0.135

14-16Jul 2 9 0.295 0.088

22-23Jun 1 1 0.402 0.188

7-9Jul 2 0 0.066 0.118

13-15Jul 2 8 0.130 0.207

4-5Aug 3 0 0.134 0.086

13-14 Aug 3 4 0.327 0.072

17-18Aug 1 7 0.451 0.149

20-22Jun 1 7 0.347 0.176

27-28 Jun 14 0.223 0.095

5 Jul 3 0 0.422 0.210

16-17Jul 2 0 0.377 0.089

II-12Aug 3 0 0.047 0.024

16-18Aug 1 4 0.298 0.015

17-20Jun 3 0 0.330 0.134

23 Jul 30 0.437 0.127

27-3OJul 3 0 0.470 0.212

4-7Aug 2 9 0.235 0.132

4-7Aug 2 7 0.345 0.052

18 IQAuQ 14 0.085 0.075

No clear trends over time were apparent for any area. There was a significant correlation between Hiop

and Hind (r* = 0.19; p = 0.03). When values of H& were plotted against Hiop all sample areas tended to

cluster in the region corresponding to a specialist feeding mode with a heterogeneous diet (Figure 10).

2 9
n

0

O oc, 0 oo

0 C)

0.2 0 00

U U LI 0

0 0

0.8

0.6

Diversity

(all samples) Mainland

0.8

0.6

3

E

5 0.4

.E

‘r

0.2

0

0 0.2 0.4 0.6 (

Eastside

P

::I

3

b 0.4 -

.E

‘r

1

0.2

1

q u

0 0

q

q 00

01

0 0.2 0.4

H ‘pooled

0.6

i

0.8

0.8

0.6

0.4

0.2

P

n

q

#

0 q

I0 0.2 0.4 0.6 0.8

Westside

O’*r------

0.6 -

0.4 -

0 0.2 0.4 0.6 0.8

H ‘pooled

Figure 10. Tokeshi plots of Shannon-Weaver diversity indices (H’) of diet, contrasting

mean individual and pooled-sample values. H’,, = 0.0; H’,, = 0.85.

Discussion

Sockeye in the nearshore waters function as both filter and particle feeders. The feeding behavior of

sockeye salmon, as they enter the final stages of their homeward migration, is neither uniform nor

easily characterized. This study allowed for a fairly comprehensive examination of this behavior in the

nearshore environment, and the results point to significant spatial and temporal variation in the incidence

of feeding, the amount consumed and the types of prey eaten.

Most of the sockeye in the Mainland area are a substantially greater distance from their natal streams than

those caught in the vicinity of Kodiak Island. It was the feeding behavior for these fish that was most

noticeably different from all other sample areas. The high levels of incidence of feeding, greater mean

stomach content weights, and reliance on sandlance as prey contrasted sharply with fish caught adjacent

to Kodiak Island. The diets of migrating sockeye in the Westside and Eastside areas were characterized

by consumption of zooplankton (principally larval decapods). However, the diets in these two areas

contrasted in the other types of zooplankton eaten; Westside sockeye utilized pteropods extensively while

3 0
Eastside sockeye were unique in consuming relatively significant numbers of cumaceans. These

differences could be due either to selective feeding or contrasts in the available prey base.

For the Westside and Eastside areas the low individual dietary diversity and appearance of sequential

layering of one dominant taxa in stomachs suggest sockeye in these areas are exploiting concentrated prey

patches. The fish had low individual diversity relative to population diversity. By looking at several

feeding areas we could see a breadth of feeding habits not evident in any one location.

Copepods, and to a lesser extent euphausiids, were conspicuous in their absence. Larval decapods were

consistently abundant, with the broad range of decapod species found indicating that these organisms

function as a preferred prey type independent of individual taxa. Although not directly sampled for this

project, four other species of salmon (pink, 0. gorbuxha; chum, 0. keta; coho, 0. kisutch; Chinook,

0. tshawytscha) were caught in the same areas during the same time periods and examined concurrently

with these sockeye. Subjective observations during this investigation were that sockeye appeared to be

the least piscivorous of the five species of salmon. Chinook salmon stomachs in particular were often

distended to the point of bursting with sandlance, leading to the conclusion that sandlance were also

readily available to, but ignored by, sockeye in the Kodiak island areas.

In all areas though, sockeye feed on organisms that utilize a variety of different habitats. The potential

exists for hydrocarbon transport from either sediments OI- the water column. In addition, filter feeding

necessitates some indiscriminate filtering of the water column, as evidenced by the occasional piece

of pumice, grass or feather found in stomachs. If sockeye are exploiting hydrographic features

that concentrate zooplankton prey [Pingree et al. 19781, these may also be areas that concentrate

hydrocarbons. The published evidence is not clear on the degree to which migrating salmon avoid

hydrocarbons in the water [Weber et al. 1981; Martin et al. 1989; Purdy 19891. In the study areas the fish

are making a dircctcd migration through coastal waters. If they are preferentially exploiting prey in areas

that also concentrate contaminants, avoidance of these areas (and thus their preferred prey) would have an

unknown, but likely detrimental, effect on sockeye reproductive fitness. Likewise, deleterious impacts on

the prey base itself (changes in abundance, size or species composition) may increase intra- and interspecific competition, reducing rations, due to the limited scope of these areas.

Incidence of feeding appears to taper off rather than cease abruptly, as does quantity of prey consumed,

as sockeye near their natal streams. This is evidenced by the progressive decreases in stomach contents as

fish moved from Cape Alitak through Moser Bay and into Olga Bay. The early-run sockeye in Olga Bay

are predominately bound for the Fraser Lake system, with the stream mouth proximate to the fishery.

There was a small but significant increase in incidence of feeding for Olga Bay sockeye as the late-run

Upper Station stock entered the area. The Upper Station system lies approximately 20 km from the Olga

Bay fishery.

Higher levels of feeding are associated with greater distances or travel time from natal streams, indicating

that non-local sockeye would be at greater risk of contamination via ingestion than local fish. The further

from their natal stream, the larger the meal size and the greater number of fish actively feeding in a

population. We conclude that sockeye proximate to their natal stream would be at the least risk, as

feeding has nearly ceased.

31
Acknowledgements

Financial support for this project was provided by:

Coastal Marine Institute, University of Alaska Fairbanks

Alaska Department of Fish and Game, Kodiak

School of Fisheries and Ocean Sciences, University of Alaska Fairbanks

This project would not have been possible without the cooperation of Ward’s Cove Packing - Alitak.

Study Products

Quarterly reports starting July 1998.

Annual reports for 1998-l 999, 1999-2000.

Presentations at CM1 Annual Research Reviews on 23 February 1999 and 9 March 2000.

Poster presentation, Alaska Chapter - American Fisheries Society annual meeting, Kodiak,

9-l 1 November 1999.

Seminar - Minerals Management Service, Anchorage, 30 November 1999.

35-mm slides representative of fieldwork submitted to MMS.

Final report: Tyler, A.V., CO. Swanton and B.C. McIntosh. 2001. Feeding Ecology of Maturing

Sockeye Salmon (Oncorhynchus nerka) in Nearshore Waters of the Kodiak Archipelago OCS Study

MMS 200 l-059, University of Alaska Coastal Marine Institute, University of Alaska Fairbanks, 34 p.

References

ADF&G. 1999. Various Alaska commercial salmon harvests, ex-vessel values, historical data and graphs.

Alaska Department of Fish and Game.

Allen, G.H. 1956. Food of sockeye salmon (0. nerka). Special Scientific Report - Fisheries, University of

Washington Depamnenr of uceanography, Seattle. 23 p.

Allen, G.H., and W. Aron. 1958. Food of salmonid fishes of the western North Pacific Ocean. Special

Scientific Report - Fisheries, University of Washington Department of Oceanography, Seattle. 11 p.

4ndrievskaya, L.D. 1966. Food relationships of the Pacific salmon in the sea. Vopr. Ikhtiol. 6:&l-90.

Barrett, B.M., and P.A. Nelson. 1994. Estimated run timing of selected sockeye salmon stocks on the west

and east sides of Kodiak Island. Alaska Department of Fish and Game, Kodiak. 53 p.

3eacham, T.D. 1986. Type, quantity, and size of food of Pacific salmon (Oncorhynchus) in the Strait of Juan

de Fuca, British Columbia. Fish. Bull. 84:77-89.

3erg, J. 1979. Discussion of methods of investigating the food of fishes, with reference to a preliminary study

of the prey of Gobiusculusflavescens (Gobiidae). Mar. Biol. 501263-273.

.3owen, S.H. 1996. Quantitative description of the diet, p. 513-532. In B.R. Murphy and D.W. Willis [eds.],

Fisheries Techniques. American Fisheries Society, Bethesda, Maryland.

13rett, J.R. 1983. Life energetics of sockeye salmon, Oncorhynchus nerka, p. 2966. In W.P. Aspey and

S.I. Lustick [eds.], Behavioral Energetics: The Cost of Survival in Vertebrates. Ohio State University

Press, Columbus.

3 2
Brett, J.R. 1995. Energetics, p. l-68. In C. Groot, L. Margolis and W.C. Clarke [eds.], Physiological Ecology

of Pacific Salmon. UBC Press, Vancouver.

Brodeur, R.D. 1990. A synthesis of the food habits and feeding ecology of salmonids in marine waters of the

North Pacific. Fisheries Research Institute, University of Washington, Seattle. 38 p.

Brodeur, R.D., and W.G. Pearcy. 1990. Trophic relations of juvenile Pacific salmon off the Oregon and

Washington coast. Fish. Bull. 88:617-636.

Burgner, R.L. 1991. Life history of sockeye salmon Oncorhynchus nerka, p. 3-l 17. In C. Groot and

L. Margolis [eds.], Pacific Salmon Life Histories. UBC Press, Vancouver.

Conover, W.J. 1980. Practical Nonparametric Statistics. Wiley, New York. 493 p.

Crow, M.E. 1982. Some statistical techniques for analyzing the stomach contents of fish, p. 8-15. In C.A.

Simenstad and G.M. Cailliet [eds.], Gutshop ‘81. Washington Sea Grant, University of Washington

Press, Seattle.

Dell, M.B. 1963. Oceanic feeding habits of the sockeye salmon, Oncorhynchus nerka (Walbaum), in Aleutian

waters. M.S. thesis, University of Michigan, Ann Arbor. 40 p.

Foerster, R.E. 1968. The Sockeye Salmon, Oncorhynchus nerku. Fisheries Research Board of Canada,

Ottawa. 422 p.

French, R., H. BilCon, M. Osako and A. Hartt. 1976. Distribution and origin of sockeye salmon

(Oncorhynchus nerka) in offshore waters of the North Pacific Ocean. International North Pacific

Fisheries Commission, Vancouver. 113 p.

Helton, D.R. 199 1. An analysis of the Port Moller offshore test fishing forecast of sockeye and chum salmon

runs to Bristol Bay, Alaska. M.S. thesis, University of Washington. 122 p.

Higgs, D.A., J.S. MacDonald, C.D. Levings and B.S. Dosanih. 1995. Nutrition and feeding habits in relation

to life stage, p. 161-315. In C. Groot, L. Margolis and W.C. Clarke [eds.], Physiological Ecology of

Pacific Salmon. UEK Press, Vancouver.

Hurtubia, J. 1973. Trophic diversity measurements in sympatric predatory species. Ecology 54:885-890.

Hyslop, E.J. 1980. Stomach contents analysis-a review of methods and their application. J. Fish. Biol.

17:41 l-429.

Koenings, J.P., and R.D. Burkett. 1987. Population characteristics of sockeye salmon (Oncorhynchus nerka)

smolts relative to temperature regimes, euphotic volume, fry density, and forage base within Alaska

lakes, p. 216-234. In H.D. Smith, L. Margolis and C.C. Wood [eds.], Sockeye Salmon (Oncorhynchus

nerka j Population Biology and Future Management. Canadian Special Publications in Fisheries and

Aquatic Sciences.

Landingham, J.H., M.V. Sturdevant and R.D. Brodeur. 1998. Feeding habits of juvenile Pacific salmon in

marine waters of southeastern Alaska and northern British Columbia. Fish. Bull. 96:285-302.

Marshall, S., and M. Elliott. 1997. A comparison of univariate and multivariate numerical and graphical

techniques for determining inter- and intraspecific feeding relationships in estuarine fish. J. Fish. Biol.

5 1:526-545.

Martin, D.J., C.J. Whitmus, A.E. Nevissi, J.M. Cox and L.A. Brocklehurst. 1989. Effects of petroleum

contaminated waterways on migratory behavior of adult pink salmon. National Oceanic and

Atmospheric Administration and Minerals Management Service, Final Report NTIS-PB90-120478.258 p.

Moser, J.F. 1898. The salmon and salmon fisheries of Alaska. Bulletin of the United States Fish Commission.

U.S. Fish Commission, Washington, D.C. 178 p.

Nishiyama, T. 1968. Tentative estimation of daily ration of sockeye salmon (Oncorhynchus nerka) in Bristol

Bay prior to ascending migration. Bull. Faculty of Fisheries, Hokkaido University 20:265-276.

3 3
Nishiyama, T. 1977. Food-energy requirements of Bristol Bay sockeye salmon Oncorhynchus nerka

(Walbaum) during the last marine life stage, p. 289-320. In Research Institute North Pacific Fisheries,

Faculty of Fisheries, Hokkaido University Special Volume.

Pearcy, W.G., R.D. Brodeur, J.M. Shenker, W.W. Smoker and Y. Endo. 1988. Food habits of Pacific salmon

and steelhead trout, midwater trawl catches and oceanographic conditions in the Gulf of Alaska,

1980-1985. Bull. Ocean Res. Inst. Univ. Tokyo 26:29-78.

Pearcy, W.G., T. Nishiyama, T. Fujii and K. Masuda. 1984. Die1 variations in the feeding habits of Pacific

salmon caught in gill nets during a 24-hour period in the Gulf of Alaska. Fish. Bull. 82:391-399.

Pielou, E.C. 1975. Ecological Diversity. John Wiley & Sons, New York. 165 p.

Pingree, R.D., M.J. Bowman and W.E. Esaias. 1978. Headland fronts, p. 78-86. In M.J. Bowman and W.E.

Esaias [eds.], Oceanic Fronts in Coastal Processes, Springer-Verlag, New York.

Purdy, J.E. 1989. The effects of brief exposure to aromatic hydrocarbons on feeding and avoidance behaviour

in coho salmon, Oncorhynchus kisutch. J. Fish. Biol. 34:621-629.

Stockner, J.G. 1987. Lake fertilization: The enrichment cycle in lake salmon production, p. 198-215. In H.D.

Smith, L. Margolis and C.C. Wood [eds.], Sockeye Salmon (Oncorhynchus nerka) Population Biology

and Future Management. Canadian Special Publications in Fisheries and Aquatic Sciences.

Tirasin, E.M., and T. Jorgensen. 1999. An evaluation of the precision of diet description. Mar. Ecol. Prog.

Ser. 182:242-252.

Tokeshi, M. 1991. Graphical analysis of predator feeding strategy and prey importance. Freshwater Forum

1:179-183.

Tyler, R. W., L. Malloy, D. Prokopowich and K. Manthey. 198 1. Migration of sockeye salmon in the Kodiak

Archipelago, 198 1. Alaska Department of Fish and Game, Kodiak. 59 p.

Walker, R.V., and K.W. Myers. 1994. Salmonid food habits in offshore waters of the Gulf of Alaska,

June-July, 1994. Fisheries Research Institute, University of Washington, Seattle. 10 p.

Weber, D.D., D.J. Maynard, W.D. Gronlund and V. Konchin. 1981. Avoidance reactions of migrating adult

salmon to petroleum hydrocarbons. Can. J. Fish. Aquat. Sci. 38:779-781.

Zar, J.H. 1996. Biostatistical Analysis. Prentice-Hall, Englewood Cliffs, New Jersey. 662 p.

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U)

The Department of the interior Mission

As the Nation3 principal conservation agency, the Department of the Interior has responsibility

for most of our nationally owned public lands and natural resources. This includes fostering

sound use of our land and water resources; protecting our fish, wildlife, and biological diversity;

preserving the environmental and cultural values of our national parks and historical places;

and providing for the enjoyment of life through outdoor recreation. The Department assesses

our energy and mineral resources and works to ensure that their development is in the best

interests of all our people by encouraging stewardship and citizen participation in their care.

The Department also has a major responsibility for American Indian reservation communities

and for people who live in island territories under U.S. bdministration.

The Minerals Management Service Mission

As a bureau of the Department of the Interior, the Minerals Management ServiceB (MMS)

primary responsibilities are to manage the mineral resources located on the NationB Outer

Continental Shelf (OCS), collect revenue from the Federal OCS and onshore Federal and

Indian lands, and distribute those revenues.

Moreover, in working to meet its responsibilities, the Offshore Minerals Management

Program administers the OCS competitive leasing program and oversees the safe and

environmentally sound exploration and production of our NationB offshore natural gas, oil and

other mineral resources. The MMS Royalty Management Program meets its responsibilities

by ensuring the efficient, timely and accurate collection and disbursement of revenue from

mineral leasing and production due to Indian tribes and allottees. States and the U.S. Treasury.

The MMS strives to fulfill Its responslDWes tnrough the general guiding prlnCipalS of: (1) being

responsive to the public6 concerns and interests by maintaining a dialogue with all potentially

affected parties and (2) carrying out its programs with an emphasis on working to enhance the

quality of life for all Americans by lending MMS assistance and expertise to economic

development and environmental protection.