NOAA Technical Memorandum NMFS-AFSC-102

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

August 1999

by

T. W. Buckley, G. E. Tyler, D. M. Smith, and P. A. Livingston

Food Habits of Some Commercially

Important Groundfish off the Coasts

of California, Oregon, Washington, and

British Columbia
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service's Alaska Fisheries Science Center

uses the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Buckley, T. W., G. E. Tyler, D. M. Smith, and P. A. Livingston. 1999. 

Food habits of some commercially important groundfish off the coasts 

of California, Oregon, Washington, and British Columbia. U.S. Dep. 

Commer., NOAA Tech. Memo. NMFS-AFSC-102, 173 p.

 

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
NOAA Technical Memorandum NMFS-AFSC-102

Food Habits of Some Commercially

Important Groundfish off the Coasts

of California, Oregon, Washington,

and British Columbia

by

T. W. Buckley, G. E. Tyler2 D. M. Smith’, and P. A. Livingston’

1Alaska Fisheries Science Center

Resource Ecology and Fisheries Management Division

7600 Sand Point Way N.E., BIN C-15700

Seattle, WA 98115-0070

2

 University of Washington

School of Fisheries

Box 357980

Seattle, WA 98195

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Penelope D. Dalton, Assistant Administrator for Fisheries

August 1999
This document is available to the public through:

National Technical Information Service

U.S. Department of Commerce

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Springfield, VA 22161
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iii

ABSTRACT

This report describes the food habits of some commercially important groundfish

collected off the coasts of California, Oregon, Washington, and British Columbia.

Generally, the groundfish reported on were sampled during three cruises - the triennial

groundfish survey of 1989 and the continental slope surveys of 1991 and 1992. Some

young-of-the-year Pacific hake (also known as Pacific whiting, Merluccius productus)

were examined from 1987 and 1988 surveys. Where possible, the diet of each groundfish

species was examined for possible ontogenetic, latitudinal, depth, and seasonal changes.

Typically, ontogenetic shifts in the diet of the predators examined on this study were

based on the ability of the larger fish to eat larger prey. Effects of latitude, depth, and

season were also detected for some of these species.

The diet of age-0 Pacific hake shifted from copepods to euphausiids with

increasing size (33-128 mm total length) in 1987, but not in 1988. Pacific hake became

increasingly piscivorous with size, and cannibalism was an important diet component in

1991 in the Monterey INPFC (International North Pacific Fisheries Commission)

statistical area. Sablefish (Anoplopoma fimbria) and shortspine thornyhead

(Sebastolobus alascanus) consumed a wide variety of locally abundant prey items

including large amounts of offal from fish-processing operations conducted at sea. The

diet of juvenile sablefish captured over the continental shelf was similar to the diet of

Pacific hake, but the diet of larger sablefish sampled from the upper continental slope

was more similar to the shortspine thornyhead diet. Arrowtooth flounder (Atheresthes

stomias) was the most piscivorous predator examined in this study, consuming mostly

Pacific hake, Pacific herring (Clupea pallasi) and unidentified gadids. Longspine

thornyhead (S. altivelis) consumed a variety of benthic crustaceans, and the presence of

fishery offal in the diet indicated that longspine thornyhead also scavenged the slope

bottom. Giant grenadier (Albatrossia pectoralis) consumed mostly deepwater

crustaceans and fishes in this study, by weight. Pacific grenadier (Coryphaenoides

acrolepis) stomachs contained mostly squid and a variety of crustaceans, by weight. A

majority of the diet of Dover sole (Microstomuspaczjkus) and deepsea sole

(Embassichthys bathybius) was polychaete worms and brittlestars.

V

CONTENTS

ABSTRACT ..................................................... .

INTRODUCTION ................................................ .

METHODS ...................................................... .

RESULTS and DISCUSSION. ...................................... .

Young-of-the-year Pacific Hake ............................... .

Pacific Hake ............................................... .

Sablefish ................................................. .

ShortspineThornyhead ...................................... .

LongspineThornyhead ...................................... .

GiantGrenadier ............................................ .

Pacific Grenadier ........................................... .

Dover Sole ................................................ .

Deepsea Sole .............................................. .

Arrowtooth Flounder ....................................... .

Species Interactions ........................................ .

ACKNOWLEDGEMENTS ........................................ .

CITATIONS .................................................... .

APPENDIX ..................................................... .

Page

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107

123

124

131

INTRODUCTION

The National Marine Fisheries Service (NMFS) is charged with the mission of

conducting scientific research programs to better understand and manage regional fishery

resources. Presently, most of the major species of groundfish off the Pacific coast of the

United States are fully utilized, and control of the excess harvesting capacity and

allocation of the available catch are the two most severe concerns facing managers of the

Pacific coast groundfish fishery (Low 1993). Both of these management concerns are

exacerbated by the complex multi-species nature of the fishery.

Scientific research of species interactions in the Pacific coast groundfish

community will increase our knowledge about the ecosystem and may assist managers in

forecasting the consequences of various management actions. Predation (including

cannibalism) may affect recruitment and population size, and competition for food

resources may affect growth and mortality. Published studies on the feeding habits of

Pacific coast groundfish typically describe the food habits of a few species, usually

within a limited spatial range. The objective of this study was to describe the food habits

of several commercially valuable or potentially valuable groundfish over wide latitudinal

and depth ranges of the Pacific coast.

METHODS

Stomach samples were collected from important groundfish species that occupy

the narrow continental shelf and the upper continental slope of North America. Bottom

trawl surveys of the groundfish resources on the Pacific Coast continental shelf and upper

continental slope are conducted by the National Marine Fisheries Service (NMFS),

Alaska Fisheries Science Center (AFSC), Resource Assessment and Conservation

Engineering Division. Stomachs from several important species of groundfish were

collected during three of these surveys (1989, 1991, and 1992).

Young-of-the-year (YOY) Pacific hake (Merluccius productus) in this study were

caught incidentally during the1987 and 1988 annual juvenile rockfish (Sebastes spp.)

surveys conducted by NMFS, Southwest Fisheries Science Center, Tiburon Laboratory.

Study Area

This study primarily encompasses the continental shelf and upper continental

slope (30-700 fm, 50-1300 m) between Point Conception, California (34°30’N lat.),

through Oregon, Washington, and into British Columbia (50°30’N lat.). This broad

latitudinal range extends over several statistical areas established by the International

North Pacific Fisheries Commission (INPFC). These areas -- Conception (United StatesMexico International Boundary to 36°00’ N lat.), Monterey (36° 00’ to 40° 30’N lat.),

Eureka (40° 30’ to 43° 00’N lat.), Columbia (43°00’ to 47°30’N lat.) and Vancouver

(47°30’ to 50°30’N lat.) -- will hereafter be referred to by name (Fig. 1).

Stomachs from several important species of groundfish were collected in these

INPFC statistical areas during three NMFS bottom-trawl surveys (Fig.1). In 1989, the

fifth triennial groundfish survey was conducted on the continental shelf (30 to 200 fm, or
2

55 to 366 m) from Point Conception, California, to central Vancouver Island, British

Columbia, Canada (34 o 30’ to 49 o 35’N lat.), between 7 July and 29 September

(Weinberg et al. 1994). In 1991, a groundfish survey was conducted on the upper

continental slope (300 to 400 fm, or 550 to 732 m depths) in the Columbia and Eureka

INPFC areas as well as the shelf and slope (100 to 700 fm, or 183 to 1,280 m) in the

Monterey INPFC area between 21 October and 18 November (Lauth et al. 1997). In

1992, a groundfish survey was conducted on the continental shelf and slope (100 to 700

fm, or 183 to 1,280 m) in parts of the Vancouver and Columbia INPFC areas between 16

October and 13 November (Lauth et al. 1997).

Young-of-the-year Pacific hake were collected from midwater trawls in April

1987 and in May 1988. Samples were taken from about Point Sur to Point Reyes and out

to 124° W long. off Point Reyes (Wyllie Echeverria 1990) (Fig. 2).

Sample Collection

Fish stomachs were collected from a core group of species during each of the

three bottom-trawl surveys: sablefish (Anoplopoma fimbria), Pacific hake, shortspine

thornyhead (Sebastolobus alascanus), and Dover sole (Microstomus pacificus). Some

species were not sampled during all three of the surveys because they were not present in

the survey area. Stomachs from arrowtooth flounder (Atheresthes stomias) were

collected in 1989 and 1992. Stomachs from longspine thornyhead (Sebastolobus

altivelis) and deepsea sole (Embassichthys bathybius) were collected in 1991 and 1992.

Stomachs were collected from giant grenadier (Albatrossiapectoralis) and Pacific

grenadier (Coryphaenoides acrolepis) in 1992 only.

The buccal cavities of individual fish were examined before removing the

stomach, and fish showing signs of regurgitation (prey in the mouth or gills, or inverted

or flaccid stomach) or evidence of net feeding were discarded. To minimize a bias

toward sampling empty stomachs, when a fish was discarded due to regurgitation or net

feeding, it was replaced with a fish whose stomach contained food. Stomachs from fish

that met these collection criteria were placed in a cloth bag with a specimen tag

indicating the species, sex, fork length (FL), vessel, survey, haul, and specimen numbers.

When very small fish were encountered, whole specimens were chosen and placed in a

cloth bag with a specimen tag indicating the cruise and haul numbers. Lengths of these

small fish were recorded before the stomachs were removed and processed in the

laboratory. Stomach samples and whole fish were preserved in 10% formalin, rinsed

with water, and stored in 70% ethanol.

Stomach Content Analysis

In the laboratory, samples were rinsed with tapwater and the stomach’s contents

removed and blotted dry. The total weight of the stomach contents was recorded to the

nearest one-tenth (0.1) of a gram. Individual prey were identified to the lowest practical

taxon and, with a few exceptions, the weight and number of prey in each taxon were

recorded. Only fish and crab prey were counted and weighed for Pacific hake collected

in 1989. For each of the remaining prey taxa, the percentage of the total stomach

contents volume was visually estimated. Whenever possible, standard length (SL) of fish

prey and carapace width (CW) of crab prey were measured and recorded to the nearest
3

millimeter. Some of the stomach contents were identified as offal (discarded parts from

commercial fish processing operations) and treated as a single prey type.

Data Analysis

For each predator, the diet was summarized using the percent frequency of

occurrence, the percent number (when possible), and the percent weight of each prey

taxon identified. The diet of YOY Pacific hake was summarized for each year, 1987 and

1988. The diet of each fish species sampled during the bottom-trawl surveys was

summarized separately for 1991, 1992, for the region north of Cape Blanco (Vancouver

and Columbia INPFC areas) in 1989, and for the region south of Cape Blanco (Eureka,

Monterey and Conception INPFC areas) in 1989. Cape Blanco is a prominent coastal

feature that approximately corresponds with a boundary separating regions of the

California Current system with distinct oceanographic characteristics (U.S. GLOBEC

1994). North of Cape Blanco there are larger estuaries, greater freshwater input, and a

relatively broad continental shelf, and the coastline is concave and fairly smooth. South

of Cape Blanco the coastline is generally convex in shape, with large coastal

promontories, and the continental shelf is narrower. Although primary productivity in

both regions is seasonal, there are wind stress reversals that create strong upwelling in

spring and summer north of Cape Blanco. South of Cape Blanco, the prevailing winds

tend to favor upwelling in all seasons with only moderate spring and summer increases.

To examine the variation of diet with bottom depth and latitude for each species,

the diet data were divided into four depth zones within each of the five INPFC areas (30-

99 fm, l00-199 fm, 200-499 fm, and 500-699 fm). The diet data were then aggregated

into broad prey categories for each depth zone and was presented in area-proportional

(doughnut) charts.

To examine the variation of the diet with predator size, diet data from 1991, 1992,

and 1989 south of Cape Blanco and 1989 north of Cape Blanco were divided into

predator length groups for each species. We aggregated the diet data into broad prey

categories, and produced figures that depict changes in the composition of the diet, by

weight, with increasing predator size.

The amount of temporal variability in the diet that could be determined from these

data was limited because in most cases the samples were unique with respect to two or

more of the following characteristics; year, season, area, or bottom depth. However, we

were able to compare autumn diets of shortspine thornyhead, longspine thornyhead, and

Dover sole between 1991 and 1992 in the 200-499 fm depth range of the Columbia

INPFC area.
Figure 1 .--Locations where stomach samples were collected

during the 1989 triennial groundfish survey

(circles) and the 1991 (squares) and 1992

(triangles) slope groundfish surveys.
Figure 2. --Locations where young-of-the-year Pacific hake

stomach samples were collected in 1987 and 1988.
6

YOUNG-OF-THE-YEAR PACIFIC HAKE

Age-O, or YOY, Pacific hake are an important component of the energy flow in

the California Current ecosystem. They are preyed upon by albacore tuna (Thunnus

germo), several species of rockfish (Sebastes sp.) (Best 1963, Livingston and Bailey

1985), and intra-cohort cannibalism has been observed among Pacific hake as small as

5.5 mm in length (Sumida and Moser 1980). Juvenile Pacific hake are preyed upon by

many predatory fishes including bigmouth sole (Hippoglossina stomata), arrowtooth

flounder, sablefish, and larger Pacific hake (Best 1963, Livingston and Bailey 1985).

Marine birds that prey on juvenile hake include the sooty shearwater (Puffinus griseus)

and the western gull (Larus occidentalis) (Livingston and Bailey 1985).

Little is known about the food habits of intermediate sizes of YOY Pacific hake.

The larvae finish yolk absorption and begin feeding at about 3 mm SL (Sumida and

Moser 1980). They feed primarily on copepod eggs, nauplii, copepodites, and adults

through 10.7 mm SL (Sumida and Moser 1980). The diet of larger (10-20 cm FL)

juvenile Pacific hake was found to be dominated by euphausiids (> 90% by weight)

(Livingston 1983, Livingston and Bailey 1985, Fig. 3 of this study). The transition from

a diet of copepods to euphausiids has not been described. The age-0 Pacific hake

collected for this study during juvenile rockfish surveys cover a portion of this size range:

34 to 102 mm FL in 1987 and 33 to 128 mm FL in 1988.

RESULTS

General Diets

Stomachs from 65 YOY Pacific hake collected in 1987 off of central California

were examined. Three (5%) of these stomachs were empty (Table 1). Euphausiids and

calanoid copepods occurred frequently in the diet, but euphausiids dominated the

stomach contents (96%) by weight because of their larger size. For all age-0 Pacific hake

examined from 1987, only 3% of the stomach contents were identified as calanoid

copepods by weight and the average fullness was 0.21 g/fish or 5.5% body weight.

In 1988, 43 (12%) of the 345 stomachs collected off of central California were

empty (Table 2). Similar to the preceding year, euphausiids and calanoid copepods

occurred most frequently in the diet and euphausiids dominated the diet by weight (74%).

However, calanoid copepods contributed more to the diet by weight (19%) and the fish

were less full (0.07 g/fish or 2.6% body weight), on average, than in 1987. One

occurrence of cannibalism by a 128 mm FL Pacific hake was found. Because of the large

relative size of this prey, compared to calanoid copepods and euphausiids, it was over 4%

of the weight of the combined stomach contents.

Variation of the Diet with Predator Size

The juvenile Pacific hake samples were divided into three size groups - small (33-

60 mm FL), medium (61- 90 mm FL), and large (91-128 mm FL). The diet composition,

by weight, was summarized for each size group by year (Fig. 3). In 1987, a decreasing

proportion of the diet was comprised of calanoid copepods as predator-length increased.

In 1988, no decrease in copepod consumption was apparent with length, and the trend
appeared to be the opposite, an increasing proportion of copepods in the diet with

increasing length.

DISCUSSION

Juvenile Pacific hake of the sizes examined here (33-128 mm SL) consumed

primarily calanoid copepods and euphausiids. Given that the diet of larval Pacific hake

(3-10.7 mm SL) consists mainly of calanoid copepods (Sumida and Moser 1980) and the

diet of larger juvenile Pacific hake (10-20 cm FL) consists mainly of euphausiids

(Livingston 1983; Livingston and Bailey 1985; this study, Fig. 3) this result is not

surprising. However, the transition from a diet of calanoid copepods to euphausiids

appears to differ between 1987 and 1988.

The contribution of calanoid copepods to the weight of the diet was greater in

1988 than in 1987 and the average fullness per fish was lower in 1988 than in 1987.

Year-class strength was moderate in these two years with somewhat fewer fish in the

1988 year class, based on recruitment of age-2 Pacific hake into the fishery (Dorn and

Methot 1990). Large swarms of euphausiids were encountered in the study area in 1987

(Smith and Adams 1988). It is possible that euphausiids were less available to the

juvenile Pacific hake sampled in 1988, resulting in less full stomachs and a continued

feeding on calanoid copepods. However, if euphausiids were less available in 1988 than

1987, it did not seem to affect their early growth because Woodbury et al. (1995) found

the growth rates of Pacific hake in these two years to be nearly identical, at least up to 70

mm SL. Further investigation into the transition from calanoid copepods to euphausiids

in the diet of Pacific hake is required, especially during years of differing environmental

conditions.

Previously, intracohort cannibalism by Pacific hake was only known to occur in

the larval stage (Sumida and Moser 1980). The incidence of cannibalism in 1988 is

evidence that this behavior can occur beyond the larval stage. Intracohort cannibalism by

Pacific hake requires substantial differences in size among cohort members. While

differences in individual growth rates may contribute to the differences in individual size,

the broad temporal distribution of spawning dates (October through March - Woodbury

et al. 1995) is probably more of a factor. The potential for intracohort cannibalism may

have significant implications for recruitment, especially during years when prey is scarce.
8

Table 1 .--The percent frequency of occurrence (%F) and percent weight (%W) of the

prey found in the stomachs of age-0 Pacific hake (Merluccius productus)

caught in the spring of 1987.

Prey Name %F %W

Teuthoidea oegopsida (squid) 1.61 0.09

Calanoida (copepod) 41.94 3.05

Mysidae (mysid) 3.23 0.86

Gammaridea (amphipod) 1.61 0.05

Euphausiacea (euphausiid) 14.52 46.61

Euphausiidae (euphausiid) 35.48 6.99

Euphausia pacifica (euphausiid) 35.48 42.24

Unidentified organic material 1.61 0.12

Total prey weight:

Total non-empty stomachs:

Total empty stomachs:

12.92 g

62

3
9

Table 2.--The percent frequency of occurrence (%F) and percent weight (%W) of the

prey found in the stomachs of age-0 Pacific hake (Merluccius productus)

caught in the spring of 1988.

Prey Name %F %W

Crustacea 5.63

Calanoida (copepod) 39.74

Cirripedia (barnacle) 0.33

Peracarida Mysidacea (mysid) 0.66

Hyperiidea (amphipod) 3.64

Eucarida 0.33

Euphausiidae (euphausiid) 54.97

Euphausia pacifica (euphausiid) 31.13

Thysanoessa sp. (euphausiid) 0.66

Thysanoessa spinifera (euphausiid) 12.58

Reptantia (crab) 0.33

Osteichthyes Teleostei (bony fish) 0.99

Merluccius productus (Pacific hake) 0.33

Unidentified organic material 1.99

Unidentified tube 0.33

Total prey weight: 21.86 g

Total non-empty stomachs: 302

Total empty stomachs: 43

0.53

19.23

0.05

0.02

0.66

0.09

33.76

28.84

0.34

10.87

0.00

0.91

4.44

0.21

0.05
10

Figure 3.--Diet composition of age-0 Pacific hake (by length) from the 1987 and 1988

juvenile rockfish surveys south of Cape Blanco. The length-range shown in

each figure may be different. The sample size (n) is shown above each length

group.
11

PACIFIC HAKE

Pacific hake (Merluccius productus), also known as Pacific whiting, is the largest

single groundfish resource found off the U.S. Pacific coast (Dark and Wilkins 1994).

This resource is fully exploited with an average annual catch from 1983 to 1992 of

221,600 metric tons (t) (Dorn 1993). Commercial landings of Pacific hake from 1991 to

1993 in the U.S. were about two-thirds of the total U.S. commercial landings of

groundfish from the Pacific coast (Pacific Fishery Management Council 1994).

Ecologically, Pacific hake is one of the most important fish species on the west

coast of North America (Francis 1983, Livingston and Bailey 1985). It is an important

prey resource for birds, tuna, sharks, groundfish, and several marine mammals (Best

1963, Livingston and Bailey 1985). Adult Pacific hake have been found in the stomachs

of several large piscivorous fish: spiny dogfish (Squalus acanthias) (Tanasichuk et al.

1991), Pacific lancetfish (Alepisaurus richardsoni), northern bluefin tuna (Thunnus

thynnus), sablefish, lingcod (Ophiodon elongatus), soupfin shark (Galeorhinus

zyopterus), great white shark (Carcharodon carcharias), and electric ray (Torpedo

californica) (Best 1963). Also, several marine mammals - California sea lion (Zalophus

californianus), northern fur seal (Callorhinus ursinus), northern sea lion (Eumetopias

jubatus), elephant seal (Mirounga augustirotris), Pacific whitesided dolphin

(Lagenorhynchus obliquidens), and Dall porpoise (Phocoenoides dalli) - prey on adult

Pacific hake (Best 1963, Dorn 1993). Pacific hake is also an important predator in the

Pacific coast ecosystem. The diet of smaller (< 45 cm FL) Pacific hake is typically

dominated by euphausiids, but larger Pacific hake feed more on fish and larger

crustaceans, including commercially important species such as Pacific herring (Clupea

pallasi), northern anchovy (Engraulis mordax), and pink shrimp (Pandalus jordani)

(Francis 1983, Livingston 1983, Livingston and Bailey 1985, Rexstad and Pikitch 1986).

Due to its large biomass, the impact of Pacific hake predation on these commercially

important species can be extensive (Francis 1983, Gotshall 1969, Livingston and Bailey

1985).

RESULTS

General Diets

A total of 1,334 Pacific hake stomachs were examined in the laboratory. Of the

351 stomachs collected south of Cape Blanco in the summer of 1989,49 (14%) were

empty. Fifty-one (7%) of the 745 stomachs collected north of Cape Blanco in the

summer of 1989 were empty. Only 7 (5%) of the 138 stomachs collected in the autumn

of 1991 were empty, but 26 (26%) of the 100 stomachs collected farther north in the

autumn of 1992 were empty.

The diet, by weight, of the Pacific hake sampled in 1989 south of Cape Blanco

was dominated by fish, followed by crustaceans and cephalopods, but crustaceans

occurred most frequently, especially euphausiids (Table 3). The most important fishes in

the diet, by weight and frequency of occurrence, were northern anchovy, followed by

Pacific herring, and rockfish (Sebastes spp.). The most important crustaceans by weight

and frequency of occurrence were euphausiids, especially Euphausia pacifica and
12

Thysanoessa spinifera, but sergestid shrimp also occurred frequently. Gonatid squid

were the most important cephalopods, including Gonatus onyx and Berryteuthis magister.

A similar pattern was found north of Cape Blanco in 1989: fish dominated the diet

composition, by weight, and crustaceans, especially euphausiids, were the most

frequently occurring prey (Table 4). However, the species composition of the diet was

different than south of Cape Blanco and cephalopods comprised a much smaller portion

of the diet by weight. The most important fishes in the diet, by weight and frequency of

occurrence, were Pacific herring and the smelts (family Osmeridae) including eulachon

(Thaleichthyspacijicus) and whitebait smelt (Allosmerus elongatus). The most important

crustaceans in the diet by weight and frequency of occurrence were euphausiids,

dominated by E. pacifica and T. spinifera, and shrimp, especially the pink shrimp,

contributed a larger portion to the diet than they did south of Cape Blanco.

In autumn 1991, Pacific hake stomachs were collected from the outer shelf and

upper slope in the Monterey INPFC area, south of Cape Blanco. The diet, in terms of

weight, was dominated by fish, but crustaceans were most numerous and occurred most

frequently (Table 5). Of the crustaceans, sergestid shrimp were the most frequently

occurring and contributed the most weight, while euphausiids contributed the highest

number of individuals. Myctophids (lanternfishes), followed by Pacific hake, were the

two most frequently occurring and numerically dominant fish in the diet and the vast

majority of the fish weight in the diet was composed of Pacific hake.

North of Cape Blanco in autumn 1992, fish comprised about half the diet by

weight, were few in number, and occurred infrequently (Table 6). Crustaceans

comprised almost half of the diet by weight, were numerically dominant, and occurred

with great frequency. The Pacific saury (Cololabis saira) contributed most to the weight

of fish in the diet, followed by Pacific herring and bristlemouths (family

Gonostomatidae), but the smaller myctophids were the most frequently occurring fish.

Pandalid shrimp contributed most to the weight of crustaceans in the diet, followed

closely by sergestid shrimp. Sergestid shrimp occurred with the highest frequency of all

prey, followed by euphausiids which were the most numerous prey items.

Patterns in Diet Variability

In 1989, the diet of Pacific hake in the Conception INPFC area was dominated by

shortbelly (Sebastes jordani) and stripetail (S. saxicola) rockfish, but in the Monterey

INPFC area and northward, northern anchovy and Pacific herring generally dominated

the biomass of fish eaten (Fig. 4). In the Eureka INPFC area, euphausiids and pink

shrimp comprised nearly the entire diet. Euphausiids were also very important in the

100-l99 fm depth zone in the Columbia and Monterey INPFC areas (Fig. 4). Although

some differences in the diet of Pacific hake with depth were found, especially in the

Columbia and Monterey INPFC areas, the most consistent difference with depth was the

presence of myctophids (included in the “Other fish” category) in the diet of the Pacific

hake caught in deeper water (l00-199 fm).

In 1991, Pacific hake were sampled in the Monterey INPFC area in autumn

Pacific hake from a broad size range co-occurred in this area and a high level of

cannibalism was found (Fig. 4). Although two incidents of cannibalism were found in

the 30-99 fm depth zone in summer of 1989, the diet composition, by weight, was

dominated by northern anchovy and euphausiids in the Monterey INPFC area.
13

The diet of Pacific hake in autumn 1992 appeared to be different from that in

summer -1989 in the Vancouver and Columbia INPFC areas (Fig.4). In the 100-199 fm

depth zone, pink shrimp, and Pacific saury (which was included in the “Other fish”

category) were very important in the Vancouver INPFC area. In the Columbia INPFC

area, sergestid shrimp comprised nearly all of the “Other prey” category. Gonostomatids

and myctophids account for most of the “Other fish” category in the 200-499 fm depth

zone in the Columbia INPFC area.

Diet Variability with Predator Size

In the summer of 1989, euphausiids decreased while fish increased in importance

with increasing length of Pacific hake both north and south of Cape Blanco (Fig. 5). As

noted earlier, the fishes by weight were primarily clupeids north of Cape Blanco and

engraulids south of Cape Blanco. A similar pattern of increasing fish and decreasing

euphausiid biomass in the diet was observed south of Cape Blanco in autumn of 1991.

Cannibalism by larger Pacific hake was the main contributor to this pattern. North of

Cape Blanco in 1992, the length-range of the sampled Pacific hake was too narrow to

show size-related changes in the diet composition.

DISCUSSION

The reliance by Pacific hake on euphausiids as a major food source in the spring

and summer is well documented (Brodeur et al. 1987, Livingston 1983, Tanasichuk et al.

1991), as is their increasing piscivory with size (Livingston 1983, Livingston and Bailey

1985, Rexstad and Pikitch 1986, Tanasichuk et al. 1991). Interannual variability in the

species composition of the diet has been documented (Gotshall 1969, Tanasichuk 1991)

and can be dramatic, especially in strong El Nino years (Brodeur et al. 1987). Due to

northward summer feeding migrations and size-dependent migratory distance, the size of

hake encountered tends to increase with latitude (Francis 1983, Fig. 4 of this study) and

apparent latitudinal differences in the diet may be confounded with the size of the Pacific

hake sampled (Livingston 1983, Livingston and Bailey 1985, Rexstad and Pikitch 1986).

Because most surveys are conducted during the summer months, seasonal

changes in the diet of Pacific hake are not well documented, however stomach samples

were collected year-round by Gotshall (1969) in the Eureka INPFC area. Euphausiids

appear to be most important by volume in the late spring and summer (Gotshall 1969),

with a peak contribution in June or July that declines over the following 3 months in the

Eureka, Columbia, and Vancouver INPFC areas (Brodeur et al. 1987, Gotshall 1969,

Tanasichuk et al. 1991), and less important in autumn, winter, and early spring (Gotshall

1969). Similarly, in this study the contribution of euphausiids in the diet appears to have

been lower in autumn 1991 than in summer 1989 south of Cape Blanco for most sizes of

Pacific hake (Fig. 5). North of Cape Blanco, this same pattern is true for 40-49 cm FL

Pacific hake (the only size adequately sampled in 1992) (Fig. 5). However, the diet of

juvenile Pacific hake (< 20 cm FL) was almost exclusively euphausiids in autumn 1992,

similar to what Livingston (1983) found in October off California. Fish are generally

most important to the weight of the diet of larger Pacific hake in autumn (Gotshall 1969,

Livingston 1983, Tanasichuk et al. 1991), winter (Gotshall 1969), and early spring

(Brodeur et al. 1987, Gotshall 1969). However, adult Pacific hake have been observed to
14

gorge themselves on fish schooling against the shoreline in June of several years (De Witt

1952, Hobson and Howard 1989).

While cannibalism has been noted previously (Best 1963, Bailey et al. 1982), it

has not been quantified and the dynamics of this interaction have only been described as

occurring where the large and small Pacific hake overlap in their distributions (Bailey

et al. 1982). These conditions were rarely sampled during the more rigorous

investigations into the feeding habits of Pacific hake (Livingston and Bailey 1985,

Rexstad and Pikitch 1986). The role of cannibalism in shaping observed recruitment

patterns for this species is unknown. More sampling in this area is needed to determine

the degree of interannual variation in the levels of cannibalism that occur.
15

Table 3.--The percent frequency of occurrence (%F) and percent weight (%W) of the

prey found in the stomachs of Pacific hake (Merluccius productus) caught

south of Cape Blanco in the summer of 1989.

Prey Name %F %W

Gastropoda (snail)

Bivalvia (clam)

Cephalopoda (squid & octopus)

Teuthoidea oegopsida (squid)

Gonatidae (squid)

Gonatus onyx (Oegopsid squid)

Berryteuthis magister (squid)

Crustacea

Calanoida (copepod)

Cumacea (cumacean)

Gammaridea (amphipod)

Euphausiidae (euphausiid)

Euphausia pacifica (euphausiid)

Nematobrachion boopis (euphausiid)

Nematoscelis sp. (euphausiid)

Nematoscelis dzscilis (euphausiid)

Thysanoessa sp. (euphausiid)

Thysanoessa spinifera (euphausiid)

Sergestidae (sergestid shrimp)

Sergestes sp. (sergestid shrimp)

Car-idea (shrimp)

Spirontocaris lamellicornis (shrimp)

Pandalus jordani (shrimp)

Natantia (shrimp)

Echinacea sp. (sea urchin)

Osteichthyes Teleostei (bony fish)

Non-gadoid fish remains

Clupea pallasi (Pacific herring)

Engraulis mordax (northern anchovy)

Osmeridae (smelts)

Mallotus villosus (capelin)

Idiacanthus sp. (black dragonfish)

Myctophidae (lanternfish)

Stenobrachius leucopsarus (northern lampfish)

Merluccius productus (Pacific hake)

0.33 0.00

0.33 0.00

0.33 0.21

0.66 2.18

3.64 3.05

0.33 0.05

0.99 3.65

0.33 0.00

0.99 0.00

0.33 0.00

0.33 0.00

42.05 3.84

30.46 8.14

0.33 0.00

0.66 0.00

0.33 0.01

0.33 0.01

7.28 3.62

0.33 0.00

10.93 0.87

0.66 0.02

0.33 0.92

1.66 0.78

0.33 0.00

0.33 0.00

2.98 0.56

0.03 0.00

1.66 6.57

9.60 53.06

0.33 0.03

0.33 0.17

0.33 0.02

1.32 0.17

0.33 0.01

0.66 1.36
16

Table 3 .--Continued.

Prey Name %F %W

Sebastes sp. (rockfish) 0.33 0.29

Sebastes jordani (shortbelly rockfish) 0.99 3.04

Sebastes saxicola (stripetail rockfish) 0.66 1.87

Zalembius rosaceus (pink surfperch) 0.66 1.70

Icichthys lockingtoni (Medusafish) 0.33 1.41

Pleuronectiformes Pleuronectoidei (flatfish) 0.33 1.40

Bothidae (left-eye flounders) 0.33 0.01

Citharichthys sordidus (Pacific sanddab) 0.66 0.94

Unidentified organic material 0.99 0.01

Total prey weight: 2,514.34 g

Total non-empty stomachs: 302

Total empty stomachs: 49
17

Table 4.--The percent frequency of occurrence (%F) and percent weight (%W) of the

prey found in the stomachs of Pacific hake (Merluccius productus) caught

north of Cape Blanco in the summer of 1989.

Prey Name %F %W

Bivalvia (clam)

Teuthoidea (squid)

Teuthoidea oegopsida (squid)

Gonatidae (squid)

Gonatus onyx (Oegopsid squid)

Crustacea

Peracarida Mysidacea (mysid)

Mysidae (mysid)

Hyperiidea (amphipod)

Hyperiidae (amphipod)

Euphausiidae (euphausiid)

Euphausia sp. (euphausiid)

EuphausiapaciJica (euphausiid)

Thysanoessa sp. (euphausiid)

Thysanoessa longipes (euphausiid)

Thysanoessa spinifera (euphausiid)

Sergestidae (sergestid shrimp)

Sergestes sp. (sergestid shrimp)

Caridea (shrimp)

Pasiphaea pacifica (shrimp)

Hippolytidae (shrimp)

Pandalidae (shrimp)

Pandalus sp. (shrimp)

Pandalus jordani (shrimp)

Crangonidae (shrimp)

Crangon sp. (shrimp)

Crangon communis (shrimp)

Natantia (shrimp)

Galatheidae (pelagic slip crabs)

Cancer sp. (crab)

Cancer magister (Dungeness crab)

Cancer oregonensis (pygmy cancer crab)

Ophiuroidae Ophiurida (brittle star)

Echinacea sp. (sea urchin)

0.14 0.00

0.29 0.00

0.43 0.02

0.86 0.08

1.73 0.24

0.14 0.00

1.15 0.05

0.14 0.00

0.14 0.00

0.29 0.00

55.33 5.46

2.02 0.21

49.57 12.18

3.03 0.61

0.29 0.00

35.73 4.97

0.14 0.00

4.90 0.50

0.29 0.01

0.14 0.03

0.14 0.00

3.03 0.25

2.45 0.71

4.03 2.47

1.15 0.09

1.59 0.18

0.43 0.14

0.29 0.00

0.14 0.00

0.86 0.00

4.32 0.13

1.01 0.00

0.14 0.00

0.14 0.06
Table 4.--Continued.

18

Prey Name %F %W

Osteichthyes Teleostei (bony fish) 0.29 0.00

Non-gadoid fish remains 3.31 0.33

Clupeidae 0.14 0.00

Clupea pallasi (Pacific herring) 11.67 48.42

Engraulis mordax (northern anchovy) 0.86 0.76

Osmeridae (smelts) 6.63 2.34

Thaleichthy spacificus (eulachon) 6.05 4.25

Allosmerus elongatus (whitebait smelt) 2.59 11.18

Myctophidae (lanternfish) 0.58 0.09

Gadidae (gadid fish) 0.43 1.97

Theragra chalcogramma (walleye pollock) 0.14 0.13

Zoarcidae (eelpout) 0.14 0.01

Sebastes sp. (rockfish) 0.14 0.00

Pleuronectiformes Pleuronectoidei (flatfish) 0.58 0.11

Bothidae (left-eye flounders) 0.29 0.08

Citharichthys sordidus (Pacific sanddab) 0.29 0.39

Pleuronectidae (flatfish) 0.29 0.38

Atheresthes stomias (arrowtooth flounder) 0.43 0.85

Pleuronectes bilineatus (rock sole) 0.14 0.05

Eopsetta exilis (slender sole) 0.14 0.05

Unidentified organic material 0.58 0.01

Offal 0.43 0.17

Unidentified algae 0.14 0.03

Total prey weight: 6,069.11 g

Total non-empty stomachs: 694

Total empty stomachs: 51
1 9

Table 5.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Pacific hake (Merluccius

productus) caught south of Cape Blanco in the fall of 1991.

Prey Name %F %N %W

Cephalopoda (squid & octopus) 0.76 0.09 0.02

Teuthoidea (squid) 0.76 0.09 0.00

Loliginidae (squid) 0.76 0.09 0.03

Teuthoidea oegopsida (squid) 4.58 0.63 0.19

Gonatidae (squid) 2.29 0.27 0.06

Gonatus onyx (Oegopsid squid) 1.53 0.27 0.65

Crustacea 0.76 0.09 0.00

Calanoida (copepod) 2.29 0.27 0.00

Peracarida Mysidacea (mysid) 1.53 0.63 0.02

Hyperiidea (amphipod) 0.76 0.18 0.00

Euphausiidae (euphausiid) 25.19 43.33 0.81

Euphausia sp. (euphausiid) 1.53 1.61 0.03

Thysanoessa sp. (euphausiid) 3.82 9.31 0.40

Thysanoessa spinifera (euphausiid) 6.87 15.22 0.76

Decapoda (shrimp & crab) 1.53 0.18 0.00

Sergestes sp. (sergestid shrimp) 51.91 18.35 5.11

Reptantia (crab) 0.76 0.09 0.00

Caridea (shrimp) 0.76 0.09 0.01

Pasiphaeidae (shrimp) 0.76 0.09 0.09

Pasiphaea pacigica (shrimp) 1.53 0.18 0.26

Spirontocaris holmesi (shrimp) 0.76 0.09 0.06

Echinacea sp. (sea urchin) 1.53 0.18 0.03

Osteichthyes Teleostei (bony fish) 2.29 0.27 0.02

Non-gadoid fish remains 3.05 0.36 0.15

Osmeridae (smelts) 0.76 0.09 0.56

Bathylagus pacificus (slender blacksmelt) 0.76 0.09 3.44

Leuroglossus sp. 0.76 0.09 0.67

Leuroglossus schmidti (northern smoothtongue) 1.53 0.18 0.14

Myctophidae (lantemfish) 19.08 2.78 3.44

Stenobrachius leucopsarus (northern lampfish) 1.53 0.18 0.50

Gadidae (gadid fish) 1.53 0.18 1.52

Merluccius productus (Pacific hake) 9.92 1.52 75.94

Sebastolobus sp. (unidentified thornyhead) 0.76 0.09 0.83

Pleuronectiformes Pleuronectoidei (flatfish) 0.76 0.18 0.10

Citharichthys sordidus (Pacific sanddab) 0.76 0.98 4.13

Eopsetta exilis (slender sole) 0.76 0.09 0.02
20

Table 5 .--Continued.

Prey Name

Unidentified organic material 1.53 1.52 0.01

Offal 0.76 0.09 0.02

Total prey number: 1,117

Total prey weight: 986.33 g

Total non-empty stomachs: 131

Total empty stomachs: 7
21

Table 6.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Pacific hake (Merluccius

productus) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Scyphozoa (jellyfish) 1.35 0.04 1.56

Teuthoidea (squid) 1.35 0.04 0.08

Gonatidae (squid) 5.41 0.17 1.04

Gnathophausia sp. 1.35 0.04 0.06

Euphausiidae (euphausiid) 36.49 44.21 3.72

Euphausia pacifica (euphausiid) 5.41 10.54 1.32

Thysanoessa sp. (euphausiid) 8.11 9.34 0.94

Thysanoessa spinifera (euphausiid) 5.41 12.44 1.81

Sergestidae (sergestid shrimp) 2.70 0.08 0.05

Sergestes sp. (sergestid shrimp) 1.35 0.04 0.04

Sergestes similis (Pacific sergestid) 51.35 18.35 14.71

Caridea (shrimp) 2.70 0.08 0.15

Pasiphaeidae (shrimp) 1.35 0.04 0.14

Pasiphaea pacifica (shrimp) 1.35 0.04 0.36

Pandalidae (shrimp) 4.05 0.17 0.85

Pandalus sp. (shrimp) 8.11 0.83 3.69

Pandalus jordani (pink shrimp) 6.76 2.44 18.98

Natantia (shrimp) 1.35 0.04 0.02

Echinacea sp. (sea urchin) 1.35 0.04 0.00

Non-gadoid fish remains 9.46 0.29 0.87

Clupea pallasi (Pacific herring) 2.70 0.08 7.07

Gonostomatidae (bristlemouth or anglemouth) 1.35 0.04 7.63

Myctophidae (lanternfish) 6.76 0.21 2.49

Tarletonbeania crenularis (blue lanternfish) 1.35 0.04 0.16

Cololabis saira (Pacific saury) 2.70 0.21 28.77

Sebastolobus alascanus (shortspine thornyhead) 2.70 0.12 3.22

Offal 1.35 0.04 0.26

Total prey number: 2,420

Total prey weight: 460.71 g

Total non-empty stomachs: 74

Total empty stomachs: 26
22

Figure 4.--Diet composition (by weight) of Pacific hake for each depth zone,

INPFC area and year. The number of nonempty stomachs examined are

shown in each ring. Mean and standard deviation of the fork lengths are

shown in the lower left and right of each box, respectively.
23

Figure 4.--Continued.
24

Figure 5.--Diet composition of Pacific hake (by length) from north and south of Cape

Blanco in 1989, and from the 1991 and 1992 surveys. The total length-range

shown in each figure may be different. The sample size (n) is shown above

each length group.
25

SABLEFISH

Sablefish is a valuable commercial species that has a long history of exploitation,

and it commands a higher price than other groundfish (Dark and Wilkins 1994).

Sablefish ranked fourth in biomass and fifth in relative abundance of groundfish species

in the 1989 triennial groundfish survey (Weinberg et al. 1994).

Sablefish grow rapidly as juveniles, primarily in the pelagic environment, and

may reach a length of 38 cm by age 1.5 years (Methot 1993). By this age, sablefish are

typically demersal and found on the continental shelf in waters less than 200 m deep

(Methot 1993). Sablefish may live over 50 years and grow to a length of over 100 cm

(Methot 1993). Adult sablefish inhabit the outer shelf and continental slope with older

and larger sablefish inhabiting increasingly deeper waters (Cailliet et al. 1988, Methot

1993, Dark and Wilkins 1994). The sablefish range extends northwestward from Baja

California along the continental shelf and slope into the Bering Sea and southwestward to

Hokkaido, Japan (Hart 1973).

The food habits of sablefish have been examined from the eastern Bering Sea

(Shubnikov 1963, Kulikov 1965, Sasaki 1985, Brodeur and Livingston 1988), Aleutian

Islands (Sasaki 1985), Gulf of Alaska (Sasaki 1985, Yang 1993), British Columbia

(Tanasichuk 1997), Washington (Grinols and Gill 1968, Brodeur et al. 1987), Oregon

(Brodeur et al. 1987, Grover and Olla 1987, Laidig et al. 1997), northern California

(Gotshall 1969, Laidig et al. 1997), central California (Cailliet et al. 1988, Laidig et al.

1997) and southern California (Conway 1967). In general, these studies found that

sablefish are opportunistic predators that eat a variety of crustaceans, cephalopods, salps

and fishes.

RESULTS

General Diets

A total of 731 sablefish stomachs were examined in the laboratory. Of the 159

stomachs collected from south of Cape Blanco in the summer of 1989, 30 (19%) were

empty. Only 47 (13%) of the 355 stomachs collected from north of Cape Blanco in the

summer of 1989 were empty. Sixteen (15%) of the 104 stomachs collected in the autumn

of 1991 were empty, but 37 (33%) of the 113 stomachs collected farther north in the

autumn of 1992 were empty.

South of Cape Blanco in 1989, the weight of the sablefish diet was dominated by

fish followed by crustaceans (especially euphausiids) and fishery offal from processing

vessels (Table 7). The most important fish in the diet by weight were Pacific sanddab

(Citharichthys sordidus), shortbelly rockfish (Sebastesjordani), and northern anchovy,

and euphausiids were the most gravimetrically important crustacean. Of all prey,

euphausiids were numerically dominant and occurred most frequently. Other prey

categories with a high frequency of occurrence were (unidentified) bony fish,

unidentified organic material, fishery offal, and polychaetes (Table 7).

The diet of sablefish sampled north of Cape Blanco in 1989 was comprised, by

weight, of fish and fishery offal followed by crustaceans (especially euphausiids) (Table

8). The fish most important to the diet were Pacific herring and unidentified clupeids,
26

hagfish, and flatfish. Euphausiids were numerically dominant followed by pelagic salps

and gammarid amphipods. The most frequently occurring prey types were euphausiids

(including Euphausia spp. and Thysanoessa spp.), fishery offal, Pacific herring,

gammarid amphipods, unidentified organic material, and (unidentified) bony fish.

The diet of the sablefish collected in autumn 1991 from the upper slope (depths

> 199 fm) in the Monterey and Eureka INPFC areas was dominated by fish and fishery

offal by weight, number, and frequency of occurrence (Table 9). In all three measures,

longspine thornyhead (Sebastolobus altivelis) was the largest contributor to the fish in the

diet of these sablefish. Euphausiids were noticeably rare in weight, number, and

frequency of occurrence.

In autumn 1992, the diet of the sablefish collected from the outer shelf and upper

slope in the Columbia and Vancouver INPFC areas was comprised almost exclusively of

fish and fishery offal by weight (Table 10). Longspine thornyhead and Pacific hake

(Merluccius productus) were the greatest contributors to the weight of fish in the diet,

and they had the highest frequency of occurrence. Numerically, however, euphausiids

were the dominant prey type.

Patterns in Diet Variability

The sablefish sampled in the 30-99 fm depth zone of the Conception INPFC area

in 1989 were much smaller on average (mean = 27.9 cm FL) than in the other areas (Fig.

6). Their diet consisted of mostly northern anchovy, by weight. In the 100-l99 fm depth

range, shortbelly rockfish and squid were important In the Monterey and Eureka INPFC

areas, fishery offal (mostly heads of Pacific hake) and euphausiids were most important

to the weight of the diet, but Pacific sanddab, shortbelly rockfish, lithodid crabs,

myctophids, and polychaetes were sometimes important. The diet also included a large

proportion of fishery offal by weight in the Columbia INPFC area, where juvenile

sablefish, pandalid shrimp, salps, and flatfish also contributed significantly to the weight

of the diet. In the Vancouver INPFC area, clupeids and euphausiids were important diet

components, by weight, across the shelf (30-199 fm), but fishery offal and hagfish were

also important in the shallow zone, (30-99 fm).

In 1991, sablefish sampled in the 200-499 fm depth zone in the Monterey INPFC

area ate mostly fishery offal by weight, but squid, longspine thornyhead, Pacific hake,

and unidentified gadids were also part of the diet (Fig. 6). In the 500-699 fm depth zone

of the Monterey INPFC area, the diet of sablefish consisted primarily of longspine

thornyheads, fishery offal, squid, unidentified Chionoecetes sp., and tunicates. In the

Eureka INPFC area, sablefish were sampled only from the 200-499 fm depth zone where

their diet was dominated by fishery offal and scorpaenids (mostly longspine

thornyheads).

In 1992, scorpaenids were an important part of the diet by weight in the

200-499 fm and the 500-699 fm depth zones in both the Columbia and Vancouver INPFC

areas (Fig. 6). These were mostly longspine thornyheads, but some shortspine

thornyheads and Sebastes sp. were identified in the stomachs. Fishery offal was found in

the diet in the l00-199 fm and 200-499 fm depth zones. Pacific hake contributed about

half the weight of the diet in the l00-199 fm and 200-499 fm depth zones of the

Vancouver INPFC area, but considerably less in the 200-499 fm and 500-699 fm depth

zones of the Columbia INPFC area. Pacific herring contributed a third of the weight of
27

the stomach contents in the 100-199 fm depth zone of the Vancouver INPFC area, but it

was minimal or not identified in the other depth zones.

Diet Variability with Predator Size

Taken together, fish were very important prey in the diet of all size groups of

sablefish sampled in the summer of 1989, south of Cape Blanco (Fig. 7). Fishery offal

and scorpaenids (mostly shortbelly rockfish) appeared to be more important in the diet of

larger sablefish than smaller sablefish, while the prey category of “Other fish” (mostly

Pacific sanddab and northern anchovy) displayed the opposite pattern. North of Cape

Blanco in 1989, fishery offal also appeared to be more important to the larger sablefish

than the smaller ones, while the opposite pattern appeared for consumption of

euphausiids. In 1991, scorpaenids (mostly longspine thornyheads) were increasingly

important with size while the prey categories of other fish and fishery offal generally

decreased in importance with sablefish size. In 1992, only a narrow size range of

sablefish was sampled, but herring appeared to be important in the diets of only smaller

(40-49 cm FL) sablefish.

DISCUSSION

The wide variety of prey in the diet of sablefish in this and other studies indicates

that it is an opportunistic predator and scavenger in both pelagic and benthic habitats

(Low et al. 1976). The observed sablefish diet is affected by ontogeny, geographic

location, season, and interannual and daily changes in prey availability (Low et al. 1976),

and these factors have been examined to various extents in other studies. In addition,

Kulikov (1965, cited in Low et al. 1976) described differences in diurnal and nocturnal

prey of sablefish.

The observed changes in the diet with increasing size of sablefish in this study

were generally consistent with changes observed in other studies. As size increases,

sablefish include an increasing amount of benthic prey in their diet and the size of prey

tends to increase (Laidig et al. 1997). Off southern California, sablefish in their first year

eat copepods, euphausiids, and larvaceans; age-2 sablefish eat amphipods, mysids,

euphausiids, gastropods, cephalopods, and fish; sablefish over age-3 eat mostly fish

(especially thornyheads) and cephalopods (Conway 1967). The diet of three size groups

of sablefish were examined by Cailliet et al. (1988) in Monterey Bay. The larger

sablefish occupied a wider and deeper depth range than smaller sablefish, and their diet

reflected this shift in distribution from pelagic fish and cephalopods to a more diverse

diet including demersal fish and crustaceans (Cailliet et al. 1988). Examining sablefish

from two areas off Oregon and California, Laidig et al. (1997) found that small

crustaceans and heteropods decreased and fish increased in the diet of sablefish with

increasing size (from < 30 cm FL to > 60 cm FL). In addition, the species composition of

the fish prey changed, with rockfish and eelpouts decreasing and thornyheads increasing

in their contribution to the diet with the size of the sablefish examined (Laidig et al.

1997). Off Oregon and Washington, larval sablefish eat mostly copepods (Grover and

Olla 1987) and juvenile sablefish (13-41 cm FL) caught by purse seine eat euphausiids,

salps, cnidarians, and fish (Brodeur et al. 1987). Off the southwest comer of Vancouver

Island, Pacific herring and other fish are eaten more often by larger (40-80 cm FL)
28

sablefish than smaller (< 40 cm FL) sablefish, and euphausiids and other invertebrates

decrease in importance in the diet as sablefish size increases (Tanasichuk 1997). In the

Gulf of Alaska, Yang (1993) found very little difference in the diets that could be

attributed to change in sablefish size from 40 to 80 cm FL; however, it appeared that

fishery offal decreased and walleye pollock (Theragra chalcogramma) increased with

predator size. An increasing amount of fish in the sablefish diet with length was found in

the Gulf of Alaska and the Aleutian Islands region for sablefish caught by longline, but

for sablefish caught by trawl in the Aleutian Islands region and the Bering Sea, such an

increase was less evident (Sasaki 1985).

Geographic variation in the diet of sablefish has been recognized on several

scales. In reviewing some diet descriptions from the Bering Sea, Aleutian Islands, Gulf

of Alaska, and British Columbia, Tanasichuk (1997) pointed out that the fish component

of the diets reflected local species compositions. Laidig et al. (1997) found that sablefish

ate more midwater prey, including heteropods and thaliacians, and less fish off central

California than off Oregon. Brodeur et al. (1987) found the diet of smaller (22 cm mean

FL; 13-41 cm FL range), purse-seine caught sablefish to be mostly euphausiids, fish and

pteropods off central Oregon, mostly fish and secondarily cnidarians and decapod larvae

off the Columbia River, and dominated by hyperiid amphipods and euphausiids off

Washington. On a smaller scale, Tanasichuk (1997) found a significant location effect on

the amount of Pacific herring and other fish in their diet off the southwest comer of

Vancouver Island. In our study, it appears that the fish in the diet reflect the locally

available species and, consequently, the latitudinal variation in the diet seems to be more

pronounced on the continental shelf than on the continental slope.

Little is known about the seasonal variation in the diet of sablefish. In the Bering

Sea, it is reported that the sablefish diet consists mostly of fish during the early spring,

switches to shrimp, ctenophores, and some benthic organisms during the summer, and

switches back to fish during autumn (Shubnikov 1963, cited in Low et al. 1976). A

similar pattern in the amount of fish (primarily shortspine thornyhead, Sebastolobus

alascanus, a benthic species) in the diet was found in the southern California Bight

(September through February) (Conway 1967). The pattern in fish consumption may be

related to seasonal changes in preferred habitat. Adult sablefish appear to move into

shallower water during the summer, while in autumn through spring, they occupy deeper

water where they spawn in the winter (Cailliet et al. 1988). We were unable to make

many inferences about the seasonal feeding habits of sablefish because, although we

collected stomach samples from sablefish in summer and autumn months, the depths

sampled and the years sampled were different.

Interannual differences in the diet of larval sablefish have been documented and

were attributed to El Nino conditions in 1983 (Grover and Olla 1987). Similarly,

Brodeur et al. (1987) found interannual differences in juvenile sablefish diets, with the

most difference occurring in 1983. Interannual differences in the frequency and amount

of Pacific herring in the diet of sablefish was linked to the abundance of Pacific herring

stocks around southwest Vancouver Island (Tanasichuk 1997). We were unable to make

interannual comparisons in this study.

Although sample sizes are low in some areas, gross comparison with other studies

conducted in the same area and season and on the same size of sablefish can be made. In

the Conception INPFC area, we found more fish in the summer diet than found by
29

Conway (1967), but northern anchovy was a fairly important diet component in both

studies. In the Monterey INPFC area, we found fishery offal, euphausiids, shortbelly

rockfish and Pacific sanddab were important diet components in the summer (30-

199 fm), and fishery offal, longspine thornyheads, squid, and Chionoecetes sp. crabs

were important diet components in autumn (200-914 fm). The prey reported by Cailliet

et al. (1988) were similar, but ranked differently in importance, perhaps because those

sablefish were taken by traps and were sampled over a 1-year period. Laidig et al. (1997)

collected sablefish in autumn or winter from 1987 through 1992 from a depth range

similar to our autumn samples, and the prey were similar to those we found. Gotshall

(1969) found pink shrimp (Pandalus jordani) and euphausiids in the stomachs of five

sablefish from the Eureka INPFC area in summer. We found euphausiids and fishery

offal dominated the diet by weight, but pink shrimp also occurred in summer in the

Eureka INPFC area. The “northern area” reported on by Laidig et al. (1997) roughly

corresponds to the Eureka and southern portion of the Columbia INPFC areas reported on

in this study. We found the three most important prey, by weight, to be longspine

thomyhead, fishery offal, and Pacific hake in the Eureka and Columbia INPFC areas.

Similarly, Laidig et al. (1997) reported over 80% of the diet volume to be composed of

fish in their northern area with longspine thornyheads and Pacific hake comprising the

majority of fish volume in the diet. In the Vancouver INPFC area, we found euphausiids,

Pacific herring, and fishery offal were important diet components in the summer (30-

99 fm), which, except for the fishery offal, was similar to the diet found by Tanasichuk

(1997) in summer.

The occurrence of fishery offal in the sablefish diet was a consistent difference

between this study and the others. It is possible that fishery offal (mostly heads of Pacific

hake) was 1) not considered a prey item, 2) identified and included as Pacific hake or

unidentified fish, or 3) not present in any of the stomachs examined in other studies.

Fishery offal in the diet of sablefish has also been found in the Gulf of Alaska (Yang

1993) and the eastern Bering Sea (Brodeur and Livingston 1988). Because most of the

fishery offal is comprised of Pacific hake parts, and Pacific hake is already a common

prey of sablefish, the at-sea fish-processing operations may not be disrupting regular food

web linkages. However, the spatial distribution of sablefish may be affected by fish

processing operations because sablefish may be attracted to the area by the odor plume

(Lokkeborg et al. 1995) and remain in the area, feeding on the concentrations of offal.
30

Table 7.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of sablefish (Anoplopoma

fimbria) caught south of Cape Blanco in the summer of 1989.

Prey Name %F %N %W

Polynoidae (polychaete) 7.75 0.33 0.94

Gastropoda (snail) 1.55 0.04 0.01

Teuthoidea (squid) 4.65 0.09 5.41

Teuthoidea oegopsida (squid) 0.78 0.01 0.01

Octopoda (octopus) 3.10 0.06 1.68

Crustacea 0.78 0.03 0.00

Calanoida (copepod) 3.88 1.07 0.01

Gammaridea (amphipod) 3.88 0.49 0.03

Hyperiidea (amphipod) 3.10 0.17 0.01

Hyperiidae (amphipod) 1.55 0.03 0.00

Themisto sp. (amphipod) 0.78 0.01 0.00

Eucarida 1.55 0.03 0.00

Euphausiacea (euphausiid) 5.43 2.40 0.43

Euphausiidae (euphausiid) 25.58 48.30 6.48

Euphausia pacifica (euphausiid) 32.56 38.00 9.76

Stylocheiron Zongicorne (euphausiid) 0.78 0.01 0.00

Stylocheiron maximum (euphausiid) 0.78 0.04 0.01

Thysanoessa Zongipes (euphausiid) 0.78 0.01 0.01

Thysanoessa spinifera (euphausiid) 13.18 6.63 1.62

Sergestes sp. (sergestid shrimp) 3.10 0.07 0.05

Reptantia (crab) 0.78 0.01 0.00

Pandalus jordani (pink shrimp) 0.78 0.01 0.14

Lithodidae (king crab) 0.78 0.01 0.00

Lithodes couesi (couesi king crab) 0.78 0.01 1.98

Cancer sp. (crab) 0.78 0.38 0.01

Echiuridae (marine worm) 0.78 0.01 0.17

Echinodermata (sea star, cucumber, urchin) 0.78 0.01 0.01

Ophiuridae (brittle star) 0.78 0.01 0.00

Echinacea sp. (sea urchin) 3.10 0.06 0.33

Urochordata (tunicate) 1.55 0.03 0.83

Larvacea Copelata 0.78 0.01 0.00

Osteichthyes Holostei (cartilaginous fish) 0.78 0.01 0.05

Osteichthyes Teleostei (bony fish) 23.26 0.49 4.49

Clupeidae 0.78 0.01 0.62

Engraulis mordax (northern anchovy) 3.10 0.09 6.38

Osmeridae (smelts) 0.78 0.01 0.10
3

Table 7.--Continued.

Prey Name %F %N %W

Myctophidae (lantemfish) 2.33 0.04 0.36

Sebastes sp. (rockfish) 1.55 0.03 1.93

Sebastes jordani (shortbelly rockfish) 3.10 0.12 15.57

Peprilus simillimus (Pacific butterfish) 0.78 0.01 3.16

Pleuronectiformes Pleuronectoidei (flatfish) 0.78 0.01 0.04

Citharichthys sordidus (Pacific sanddab) 3.88 0.07 18.42

Pleuronectidae (flatfish) 1.55 0.03 0.31

Unidentified organic material 15.50 0.29 0.30

Offal 15.50 0.29 17.87

Unidentified tube 0.78 0.01 0.00

Unidentified algae 1.55 0.03 0.43

Unidentified material 0.78 0.01 0.03

Total prey number: 6,913

Total prey weight: 1,512.57 g

Total non-empty stomachs: 129

Total empty stomachs: 30
32

Table 8.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of sablefish (Anoplopoma

fimbria) caught north of Cape Blanco in the summer of 1989.

Prey Name %F %N %W

Phaeophyta (brown algae) 0.97 0.02 0.14

Scyphozoa (jellyfish) 1.30 0.03 0.27

Annelida (worm) 0.65 0.02 0.00

Polychaeta (worm) 4.55 0.12 0.40

Polynoidae (polychaete) 0.32 0.01 0.02

Opheliidae (polychaete) 0.32 0.01 0.08

Mollusca 0.32 0.01 0.02

Gastropoda (snail) 4.22 0.18 0.02

Bivalvia (clam) 0.32 0.01 0.00

Cephalopoda (squid & octopus) 0.65 0.02 0.00

Teuthoidea (squid) 4.22 0.31 0.32

Loliginidae (squid) 0.32 0.01 0.07

Loligo opalescens (squid) 0.32 0.01 0.07

Teuthoidea oegopsida (squid) 0.65 0.02 0.02

Octopoda (octopus) 1.30 0.08 0.16

Octopodidae (octopus) 0.32 0.01 0.36

Crustacea 2.27 0.08 0.00

Calanoida (copepod) 0.65 0.02 0.00

Peracarida Mysidacea (mysid) 0.65 0.02 0.00

Isopoda (isopod ) 1.95 0.05 0.01

Gammaridea (amphipod) 14.29 2.79 0.13

Ampeliscidae (amphipod) 0.32 0.01 0.01

Gammaridae (amphipod) 0.32 0.02 0.00

Hyperiidea (amphipod) 4.22 0.32 0.01

Eucarida 1.30 0.50 0.01

Euphausiidae (euphausiid) 24.68 25.71 3.37

Euphausia sp. (euphausiid) 3.90 7.85 1.11

Euphausia pacifica (euphausiid) 23.70 12.06 2.09

Nematoscelis difficilis (euphausiid) 0.32 0.01 0.00

Thysanoessa sp. (euphausiid) 1.30 0.28 0.05

Thysanoessa longipes (euphausiid) 0.97 0.02 0.00

Thysanoessa spinifera (euphausiid) 16.23 38.22 6.80

Decapoda (shrimp & crab) 0.65 0.04 0.00

Sergestidae (sergestid shrimp) 0.32 0.01 0.00

Sergestes sp. (sergestid shrimp) 0.32 0.01 0.01

Reptantia (crab) 0.65 0.02 0.22
33

Table 8.--Continued.

Prey Name %W

Caridea (shrimp)

Pandalidae (shrimp)

Pandalus sp. (shrimp)

Pandalus jordani (pink shrimp)

Crangonidae (shrimp)

Crangon sp. (shrimp)

Argis sp. (shrimp)

Natantia (shrimp)

Anomura (crab)

Galatheidae (pelagic slip crabs)

Munida quadrispina (pinch bug)

Decapoda brachyura (crab)

Cancridae (crab)

Cancer sp. (crab)

Cancer magister (Dungeness crab)

Cancer oregonensis (pygmy cancer crab)

Sipuncula (marine worm)

Echiuroinea (marine worm)

Echiurus sp. (marine worm)

Ophiuroidea (basket & brittle star)

Ophiuridae (brittle star)

Echinoidea (sea urchin and sand dollar)

Echinacea sp. (sea urchin)

Holothuroidea (sea cucumber)

Urochordata (tunicate)

Thaliacea (pelagic salp)

Eptatretus sp.

Eptatretus stouti (Pacific hagfish)

Gnathostomata

Hydrolagus colliei (ratfish)

Osteichthyes Teleostei (bony fish)

Non-gadoid fish remains

Fish eggs

Clupeidae

Clupea pallasi (Pacific herring)

Oncorhynchus sp. (salmon)

Osmeridae (smelts)

Thaleichthys pacificus (eulachon)

2.92 0.08 0.23

3.25 0.34 1.07

2.60 0.31 1.21

2.27 0.09 0.62

1.62 0.05 0.05

0.32 0.01 0.00

0.65 0.02 0.02

2.92 0.07 0.01

0.65 0.02 0.49

3.90 0.41 0.45

0.32 0.02 0.08

0.65 0.02 0.00

0.97 0.03 0.00

0.65 0.06 0.01

1.95 0.06 0.01

0.32 0.01 0.00

1.30 0.03 0.81

0.32 0.01 0.09

0.65 0.04 0.03

2.92 0.12 0.06

1.95 0.21 0.22

0.32 0.01 0.00

0.32 0.01 0.01

0.32 0.01 0.01

0.97 0.04 0.09

9.42 6.23 2.99

0.32 0.01 3.63

0.65 0.02 4.41

0.32 0.01 0.00

0.32 0.01 1.50

11.04 0.28 0.49

6.17 0.15 1.80

0.32 0.44 0.08

1.30 0.06 5.74

17.21 0.76 16.65

0.32 0.02 0.96

0.97 0.03 0.38

0.65 0.02 0.17
34

Table 8.--Continued.

Prey Name %F %N %W

Myctophidae (lanternfish) 0.32 0.02 0.03

Tarletonbeania crenularis (blue lanternfish) 0.32 0.01 0.01

Zoarcidae (eelpout) 0.32 0.02 0.24

Lycodapus sp. (eelpout) 0.65 0.02 0.06

Lycodopsis pacifica (blackbelly eelpout) 0.65 0.02 0.44

Cololabis saira (Pacific saury) 0.32 0.01 1.25

Gasterosteus aculeatus (3-spined stickleback) 0.32 0.01 0.01

Scorpaenidae (rockfish) 0.65 0.02 0.17

Anoplopoma fimbria (sablefish) 0.32 0.02 2.63

Agonidae (poacher) 0.65 0.02 0.32

Stichaeidae (prickleback) 0.65 0.02 0.12

Pleuronectiformes Pleuronectoidei (flatfish) 0.97 0.02 0.03

Bothidae (left-eye flounders) 0.32 0.01 0.19

Citharichthys sordidus (Pacific sanddab) 0.32 0.01 0.10

Pleuronectidae (flatfish) 0.65 0.02 1.34

Errex zachirus (rex sole) 0.65 0.02 2.10

Aves (bird part) 0.32 0.01 0.00

Unidentified organic material 11.36 0.27 0.92

Unidentified worm-like organism 0.32 0.01 0.06

Offal 22.08 0.54 29.81

Overboard material (non-fishery) 0.32 0.01 0.00

Unidentified algae 0.65 0.02 0.02

Unidentified material 0.32 0.01 0.02

Total prey number: 13,104

Total prey weight: 4,792.42 g

Total non-empty stomachs: 308

Total empty stomachs: 47
35

Table 9.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of sablefish (Anoplopoma

Jimbria) caught south of Cape Blanco in the fall of 1991.

Prey Name %F %N %W

Gastropoda (snail)

Bivalvia (clam)

Teuthoidea (squid)

Loliginidae (squid)

Octopoda (octopus)

Peracarida Mysidacea (mysid)

Hyperiidea (amphipod)

Hyperiidae (amphipod)

Euphausiidae (euphausiid)

Sergestes sp. (sergestid shrimp)

Majidae (spider crab)

Chionoecetes sp. (snow and Tanner crab)

Urochordata (tunicate)

Eptatretus sp.

Osteichthyes Teleostei (bony fish)

Non-gadoid fish remains

Bathylagus pacificus (slender blacksmelt)

Chauliodus macouni (Pacific viperfish)

Saganichthys abei (shining tubesnout)

Myctophidae (lanternfish)

Tarletonbeania crenularis (blue lanternfish)

Gadidae (gadid fish)

Merluccius productus (Pacific hake)

Scorpaenidae (rockfish)

Sebastolobus sp. (unidentified thornyhead)

Sebastolobus alascanus (shortspine thornyhead)

Sebastolobus altivelis (longspine thornyhead)

Pleuronectiformes Pleuronectoidei (fiatfish)

Microstomus pacificus (Dover sole)

Unidentified organic material

Unidentified worm-like organism

Offal

Unidentified tube

2.27 1.40 0.00

1.14 0.70 0.00

13.64 8.39 9.63

1.14 0.70 0.80

1.14 0.70 0.06

1.14 0.70 0.00

3.41 2.80 0.00

2.27 1.40 0.08

1.14 0.70 0.00

7.95 4.90 0.10

2.27 1.40 2.62

4.55 3.50’ 3.81

1.14 0.70 3.83

1.14 0.70 0.14

10.23 6.29 0.18

3.41 2.10 0.04

1.14 0.70 0.26

1.14 0.70 1.02

1.14 0.70 0.24

4.55 2.80 0.32

1.14 0.70 0.09

7.95 4.90 2.55

2.27 1.40 3.34

2.27 1.40 0.11

3.41 2.10 1.24

3.41 2.10 3.26

20.45 15.38 24.24

1.14 0.70 0.13

1.14 0.70 2.24

5.68 4.20 1.98

1.14 0.70 0.42

35.23 23.08 37.22

1.14 0.70 0.00
36

Table 9.--Continued.

Total prey number: 143

Total prey weight: 3,352.83 g

Total non-empty stomachs: 88

Total empty stomachs: 16
37

Table l0.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of sablefish (Anoplopoma

fimbria) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Cnidaria 1.32 0.24 0.04

Polychaeta (worm) 2.63 0.94 0.04

Gastropoda (snail) 1.32 0.24 0.04

Bivalvia (clam) 1.32 0.24 0.03

Cephalopoda (squid & octopus) 3.95 0.71 0.04

Teuthoidea (squid) 5.26 1.18 0.87

Teuthoidea oegopsida (squid) 2.63 0.47 0.07

Octopoda (octopus) 2.63 0.47 0.08

Ampeliscidae (amphipod) 2.63 4.48 0.02

Hyperiidae (amphipod) 1.32 2.12 0.01

Euphausiacea (euphausiid) 2.63 0.94 0.00

Euphausiidae (euphausiid) 3.95 64.62 0.23

Euphausia sp. (euphausiid) 1.32 1.18 0.01

Thysanoessa sp. (euphausiid) 1.32 0.47 0.00

Decapoda (shrimp & crab) 1.32 0.47 0.30

Reptantia (crab) 1.32 0.47 0.29

Eualus macrophthalma (shrimp) 1.32 0.24 0.02

Pandalidae (shrimp) 1.32 0.24 0.02

Hyas sp. (lyre crab) 1.32 0.24 0.12

Chionoecetes sp. (snow and Tanner crab) 6.58 1.42 4.16

Echiuridae (marine worm) 1.32 0.24 0.09

Ophiuroidae Ophiurida (brittle star) 2.63 0.47 0.03

Echinacea sp. (sea urchin) 2.63 0.47 0.01

Osteichthyes Teleostei (bony fish) 17.11 3.54 3.77

Non-gadoid fish remains 7.89 1.42 0.24

Clupea pallasi (Pacific herring) 2.63 0.47 3.56

Osmeridae (smelts) 1.32 0.24 0.28

Leuroglossus sp. 1.32 0.24 0.25

Merluccius productus (Pacific hake) 19.74 3.77 20.19

Lycodapus sp. (eelpout) 1.32 -0.24 0.16

Sebastes sp. (rockfish) 1.32 0.24 3.53

Sebastolobus alascanus (shortspine thornyhead) 1.32 0.24 1.84

Sebastolobus altivelis (longspine thornyhead) 25.00 5.42 46.76

Offal 9.21 1.65 12.92
38

Table 10.--Continued.

Total prey number: 424

Total prey weight: 2,875.73 g

Total non-empty stomachs: 76

Total empty stomachs: 37
THIS PAGE INTENTIONALLY LEFT BLANK
40

Figure 6.--Diet composition (by weight) of sablefish for each depth zone, INPFC

area and year. The number of nonempty stomachs examined are shown in

each ring. Mean and standard deviation of the fork lengths are shown in the

lower left and right of each box, respectively.
41

Figure 6.--Continued.
42

Figure 7.--Diet composition of sablefish (by length) from north and south of

Cape Blanco in 1989 and from the 1991 and 1992 surveys. The total

length-range shown in each figure may be different. The sample size (n)

is shown above each length group.
43

SHORTSPINE THORNYHEAD

Shortspine thornyhead (Sebastolobus alascanus) is a component of the deepwater

species complex managed by the Pacific Fishery Management Council (Ianelli et al.

1994). In response to developing Japanese export markets, higher prices, and the

movement of the bottom trawl fishery into deeper water (Jacobson 1993), landings of

shortspine thornyheads in Washington, Oregon, and California have increased from an

average of 250 metric tons (t) per year in the late 1960s to 3,300 t per year in the early

1990s (Ianelli et al. 1994).

The shortspine thornyhead primarily inhabits the continental slope between 300

and 1,100 m, but they can be found as shallow as 90 m and at depths exceeding 1,500 m

(Jacobson 1993). Geographically, shortspine thornyhead range from northern Baja

California to the Bering Sea and to the Commander Islands of the Asiatic mainland

(Jacobson 1993). In the northern portions of the range, shortspine thornyhead can be

found as shallow as 25 m (Jacobson 1993). Sexual maturity is attained by 50% of the

fish at 21 cm total length (TL) or about 12-13 years (Jacobson 1993). In late winter or

early spring, buoyant, bilobate egg masses are spawned that range in length from 15 to 61

cm (Hart 1973, Jacobson 1993). About 14 to 15 months later, juvenile shortspine

thornyhead settle out of their pelagic phase onto the continental shelf at sizes of 22 to 27

mm TL (Jacobson 1993). Shortspine thornyheads seem to move into deeper water as

they grow (Ianelli et al. 1994) because larger individuals tend to be found in deeper water

(Jacobson 1993). Shortspine thornyheads can grow to 75 cm TL (Hart 1973) and, based

on otolith increments, may reach ages approaching 150 years (Ianelli et al. 1994).

However, radiometric methods suggest that maximum ages may be between 50 and 100

years (Ianelli et al. 1994).

The stomach contents of shortspine thornyhead have been described from the

Aleutian Islands (Yang 1996), Gulf of Alaska (Yang 1993), southeastern Alaska (Miller

1985), and Oregon and California (Tom Laidig, personal communication’).

RESULTS

General Diets

Only 30 shortspine thornyhead stomachs were collected south of Cape Blanco in

summer of 1989 and 14 (47%) of them were empty. By weight, fish (94%), especially

Pacific hake, dominated the contents of the stomachs that contained food (Table 11).

Forty-four (26%) of the 170 shortspine thornyhead stomachs collected north of Cape

Blanco were empty. The contents of the stomachs with food in them are described in

Table 12. Caridean shrimp, especially pandalids, dominated the diet by weight and

number (5 1% and 42%, respectively). During the slope survey of autumn 1991,216

stomachs were collected, 18 (8%) of which were empty (Table 13). Tanner crabs

(Chionoecetes spp.) were important in the diet by weight and number (61% and 23%,

respectively). During the slope survey of autumn 1992, 193 stomachs were collected

1

 National Marine Fisheries Service, Southwest Fisheries Science Center, Tiburon Laboratory, 3150

Paradise Drive, Tiburon, CA 94920. Phone: (415) 435-3149.
44

north of Cape Blanco and 60 (3 1%) of them were empty (Table 14). Fish (67%) and

Tanner crabs (18%) dominated the diet by weight, but small crustaceans were more

important numerically. Scorpaenids (rockfishes and thornyheads, 29%) were the most

important type of fish prey by weight.

Variation of the Diet with Location

In the Conception INPFC area, Pacific hake were the dominant diet component of

the shortspine thornyhead sampled, by weight, in the summer of 1989 (Fig. 8). In

addition, most of the “Other fish” category was comprised of gadid fish that could not be

positively identified as Pacific hake (Table 13).

The Monterey INPFC area was only sampled in the autumn of 1991, and the

length of the sampled shortspine thornyheads increased with depth (Fig. 8). The diet also

changed with increasing depth (and length, see below) from mostly “Other prey”

(polychaetes, molluscs, and echinoderms) and fishery offal to scorpaenids, fishery offal,

and some Tanner crab, then to mostly Tanner crab. Scorpaenids seemed to decrease in

importance in the 200-499 fm zone going northward through the Eureka and Columbia

INPFC areas.

Similar diets were observed for shortspine thornyhead sampled in the 200-499 fm

zone in the Columbia INPFC area during both the 1991 and 1992 slope surveys, and thus,

samples from the two years were combined in Figure 8. In the Columbia INPFC area,

scorpaenids, Pacific hake and non-gadoid fish remains (included in “Other fish”) were

important diet components in the 500-699 fm zone in autumn 1992. In the summer of

1989, pandalid shrimp and mud shrimp (Axiopsis sp., included in “Other crustacea”) were

important on the continental shelf.

In the Vancouver INPFC area, “Other crustacea” were most important in the diet

of shortspine thornyhead caught on the continental shelf and included crangonid shrimps,

slip crabs, and decorator crabs in the 30-99 fm zone and mostly slip crabs in the l00-

199 fm zone. Fishery offal was also important in the l00-199 fm zone sampled in

summer 1989. Smaller shortspine thornyheads were sampled in this same depth zone in

autumn 1992, and the composition of the “Other crustacea” included mysids, hyperiid

amphipods, and hippolitid shrimp. In deeper water, fishery offal and Tanner crabs were

important while the fraction of scorpaenids in the diet, by weight, appeared to decrease

(Fig. 8).

Variation of the Diet with Predator Size

Regardless of the area, season, or year sampled, “Other crustacea” seemed to be

the most important component in the diet of small (FL < 20 cm) shortspine thornyhead

(Fig. 9). The importance of “Other crustacea” generally decreased with increasing size.

On the continental shelf in 1989 south of Cape Blanco, predation on juvenile Pacific hake

was important to the few shortspine thornyhead sampled. North of Cape Blanco in

summer of 1989, pandalid shrimp appeared to increase then decrease in importance with

increasing predator size. The diet of shortspine thornyheads sampled in autumn of 1991

included an increasing amount of Tanner crab, by weight, with increasing size, while the

proportion of scorpaenids in the diet increased then decreased with increasing size. The

opposite pattern was true for shortspine thornyheads sampled in autumn of 1992 with the
4 5

proportion of scorpaenids increasing and Tanner crabs increasing then decreasing in the

diet as a function of predator size.

DISCUSSION

The results of this study were generally consistent with the results of other

investigations of the stomach contents of shortspine thornyhead. Around the Aleutian

Islands, fish (65%), shrimp (23%), and crab (9%) were the major components of the diet

by weight (Yang 1996). In the Gulf of Alaska, shrimp (67%) comprised more of the diet

than fish (17%) or crab (11%) by weight (Yang 1993). In a study conducted over a

smaller area in southeastern Alaska, Miller (1985) found fish (42%), shrimp (27%) and

crab (11`%) were volumetrically the most important groups in the diet of shortspine

thornyhead. Off Oregon and California, shortspine thornyhead eat mostly fish, shrimp,

and crab (Tom Laidig, personal communication’). The shortspine thornyhead appears to

be an opportunistic predator that will consume a variety of locally available crustaceans

and fish that are on or near the bottom. Yang (1993) suggests that the large terminal

mouth and the presence of relatively few stout gill-rakers are consistent with this

epibenthic feeding strategy.

The presence in the diet of offal from fish processing activities indicates that

shortspine thornyhead are also scavengers. The offal found in the stomachs of this

species were primarily heads of Pacific hake. It is possible that the biological identity of

undigested parts of fishery offal could be identified (i.e., Pacific hake, gadidae, or fish

remains), but that evidence of it being processed by the fishery would be lacking. If this

were the case, the amount of fishery offal in the diet would be underestimated.

Changes in the diet that occured as a function of predator size were generally in

agreement with other studies. Yang (1996) found a decrease in the proportion of small

crustaceans and an increase in the proportion of fish and larger crustaceans in the diet

with increasing size of Aleutian Islands shortspine thornyheads. Similarly, in an area of

southeastern Alaska, the diet was found to shift from mainly smaller shrimp and

amphipods to mainly larger shrimp (pandalids) and fish (Miller 1985). Laidig’ also

found a shift in the diet from mainly shrimp to mainly fish and crab in Oregon and

northern California.

The observed changes in diet with size may also be a function of prey availability

with depth because, on average, larger shortspine thornyhead are found in deeper water

than smaller individuals (Jacobson 1993). Miller (1985) concluded that the observed

change in diet with size was probably not related to depth, but samples were collected

over a relatively narrow depth range (183-330 m, or 100-l80 fm) when compared to the

depth range inhabited by this species. Larger sample sizes than were taken in this study

would be required to differentiate between the influence of bottom depth and predator

size on the diet of shortspine thornyhead.
46

Table 11 .--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of shortspine thornyhead

(Sebastolobus alascanus) caught south of Cape Blanco in the summer of

1989.

Prey %F %N %W

Polynoidae (polychaete) 6.25 3.70 0.13

Terebellidae (polychaete) . 6.25 7.41 1.07

Malacostraca 6.25 3.70 0.00

Peracarida Mysidacea (mysid) 18.75 14.81 0.50

Gammaridea (amphipod) 6.25 3.70 0.03

Hyperiidea (amphipod) 6.25 3.70 0.10

Euphausia pacifica (euphausiid) 6.25 3.70 0.14

Caridea (shrimp) 6.25 3.70 0.20

Crangon communis (shrimp) 6.25 3.70 2.17

Natantia (shrimp) 12.50 7.41 1.11

Pinnotheridae (pea crab) 18.75 11.11 0.49

Non-gadoid fish remains 6.25 3.70 9.41

Gadidae (gadid fish) 12.50 7.41 17.79

Merluccius productus (Pacific hake) 25.00 22.22 66.85

Total prey number: 27

Total prey weight: 40.07 g

Total non-empty stomachs: 16

Total empty stomachs: 14
47

Table 12.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of shortspine thornyhead

(Sebastolobus alascanus) caught north of Cape Blanco in the summer of

1989.

Prey %F %N %W

Polychaeta (worm)

Aphroditidae (sea mouse)

Polynoidae (polychaete)

Gastropoda (snail)

Bivalvia (clam)

Teuthoidea (squid)

Crustacea

Copepoda

Calanoida (copepod)

Peracarida Mysidacea (mysid)

Isopoda (isopod)

Gammaridea (amphipod)

Hyperiidea (amphipod)

Euphausiidae (euphausiid)

Euphausia paciJica (euphausiid)

Thysanoessa spinifera (euphausiid)

Caridea (shrimp)

Hippolytidae (shrimp)

Spirontocaris sp. (shrimp)

Spirontocaris holmesi (shrimp)

Eualus sp. (shrimp)

Pandalidae (shrimp)

Pandalus sp. (shrimp)

Pandalus jordani (pink shrimp)

Crangonidae (shrimp)

Crangon sp. (shrimp)

Crangon dulli (shrimp)

Crangon communis (shrimp)

Natantia (shrimp)

Axiopsis sp. (mud shrimp)

Galatheidae (pelagic slip crabs)

Munida quadrispina (pinch bug)

Oregonia sp. (decorator crab)

Cherilia longipes (decorator crab)

Pinnotheridae (pea crab)

Echinacea sp. (sea urchin)

0.79 0.25 0.00

1.59 0.50 1.20

2.38 0.76 0.14

0.79 0.25 0.08 

1.59 0.50 0.26

2.38 0.76 0.07

1.59 0.50 0.12

0.79 1.01 0.00

0.79 0.25 0.00

8.73 5.79 0.12

1.59 0.50 0.58

9.52 6.05 0.28

1.59 0.50 0.07

7.94 3.78 0.06

4.76 1.76 0.10

1.59 0.50 0.05

8.73 2.77 1.92

7.94 3.27 0.94

2.38 1.26 0.44

7.94 3.53 2.64

7.94 8.31 0.42

9.52 3.02 4.37

10.32 4.79 16.77

8.73 2.77 17.86

14.29 5.79 1.95

1.59 0.50 0.17

3.17 1.01 1.06

11.11 4.28 2.62

0.79 0.25 0.00

4.76 1.76 10.63

20.63 22.42 10.59

1.59 1.01 0.20

1.59 0.50 0.18

0.79 0.76 0.25

0.79 0.25 0.23

1.59 0.50 0.08
48

Table 12.--Continued.

Prey %F %N %W

Osteichthyes Teleostei (bony fish) 3.17 1.01 0.33

Non-gadoid fish remains 3.17 1.01 0.58

Zoarcidae (eelpout) 1.59 0.50 3.04

Lycodopsis pacifica (blackbelly eelpout) 2.38 0.76 5.57

Scorpaenidae 2.38 0.76 0.18

Sebastes sp. (rockfish) 3.17 1.01 4.63

Agonidae (poacher) 0.79 0.25 1.28

Pleuronectidae (flatfish) 0.79 0.25 0.97

Atheresthes stomias (arrowtooth flounder) 1.59 0.50 0.64

Errex zachirus (rex sole 2.38 0.76 0.05

Offal 1.59 0.50 5.81

Total prey number: 397

Total prey weight: 267.43 g

Total non-empty stomachs: 126

Total empty stomachs: 44
49

Table 13 .--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of shortspine thornyhead

(Sebastolobus alascanus) caught south of Cape Blanco in the fall of 1991.

Prey %F %N %W

Polychaeta (worm) 4.55 1.91 0.04

Aphroditidae (sea mouse) 8.08 4.47 2.07

Euphrosinidae (polychaete) 1.01 0.43 0.09

Neptuneidae (snail) 0.51 0.21 0.83

Bivalvia (clam) 0.51 0.21 0.00

Teuthoidea (squid) 1.01 0.43 1.04

Octopoda (octopus) 1.52 0.64 0.16

Crustacea 1.01 1.06 0.00

Peracarida Mysidacea (mysid) 10.10 7.45 0.08

Cumacea (cumacean) 4.04 7.87 0.01

Isopoda (isopod) 3.03 1.49 0.09

Gammaridea (amphipod) 5.56 2.34 0.01

Hyperiidea (amphipod) 0.51 0.21 0.00

Euphausiidae (euphausiid) 1.01 0.43 0.00

Sergestes sp. (sergestid shrimp) 1.52 0.85 0.06

Reptantia (crab) 0.51 0.21 0.03

Caridea (shrimp) 2.02 0.85 0.04

Pasiphaeidae (shrimp) 1.52 0.64 0.16

Hippolytidae (shrimp) 15.15 9.57 0.36

Spirontocaris sp. (shrimp) 3.03 1.70 0.10

Spirontocaris holmesi (shrimp) 6.57 5.96 0.49

Eualus macrophthalma (shrimp) 0.51 0.21 0.01

Heptacarpus decorus (elegant coastal shrimp) 0.51 0.21 0.01

Pandalidae (shrimp) 0.51 0.43 0.02

Pandalus sp . (shrimp) 0.51 0.21 0.01

Crangonidae (shrimp) 1.52 0.64 0.02

Crangon sp. (shrimp) 1.52 0.85 0.15

Natantia (shrimp) 0.51 0.21 0.00

Calocaris quinqueseriatus (mud shrimp) 1.01 0.43 0.10

Callianopsis goniopthalma (mud shrimp) 1.52 0.64 0.50

Paguridae (hermit crab) 0.51 0.21 0.09

Galatheidae (pelagic slip crabs) 2.02 1.06 0.07

Majidae (spider crab) 2.53 2.34 1.51

Chionoecetes sp. (snow and Tanner crab) 10.61 9.79 14.17

Chionoecetes tanneri (grooved Tanner crab) 22.73 13.62 46.52
50

Table 13 .--Continued.

Prey %F %N %W

Pinnotheridae (pea crab) 0.51 0.21 0.01

Ophiuroidae Ophiurida (brittle star) 2.02 0.85 0.01

Echinacea sp. (sea urchin) 1.52 0.64 0.00

Osteichthyes Teleostei (bony fish) 2.53 1.28 0.07

Non-gadoid fish remains 3.54 1.49 0.21

BathyZagus pacificus (slender blacksmelt) 0.51 0.21 0.19

Myctophidae (lantemtish) 1.52 0.64 0.10

Gadidae (gadid fish) 1.52 0.64 1.66

Merluccius productus (Pacific hake) 0.51 0.21 0.00

Zoarcidae (eelpout) 4.04 1.91 2.44

Lychenhelys sp. (eelpout) 0.51 0.43 2.81

Macrouridae (rattail) 1.52 0.64 2.80

Scorpaenidae 3.54 1.70 0.32

Sebastolobus sp. (unidentified thornyhead) 8.59 3.83 5.56

Sebastolobus alascanus (shortspine thornyhead) 1.52 0.64 0.74

Sebastolobus altivelis (longspine thornyhead) 4.55 1.91 6.00

Icelidae (sculpin) 0.51 0.21 0.09

Offal 6.57 2.77 8.14

Total prey number: 470

Total prey weight: 2,490.71 g

Total non-empty stomachs: 198

Total empty stomachs: 18
51

Table 14.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of shortspine thornyhead

(Sebastolobus alascanus) caught north of Cape Blanco in the fall of 1992.

Prey %F %N %W

Polychaeta (worm) 7.52 4.46 0.23

Euphrosinidae 3.01 1.79 0.16

Nudibranchia dendronotoidea (nudibranch) 0.75 0.45 0.02

Nuculoida (clam) 0.75 0.45 0.00

Cephalopoda (squid & octopus) 0.75 0.45 0.00

Teuthoidea (squid) 0.75 0.45 0.00

Teuthoidea oegopsida (squid) 0.75 0.45 0.71

Crustacea 2.26 1.34 0.01

Copepoda 1.50 1.79 0.00

Peracarida Mysidacea (mysid) 3.01 2.68 0.01

Mysidacea Mysida (mysid) 0.75 0.45 0.01

Cumacea (cumacean) 1.50 0.89 0.00

Isopoda (isopod) 0.75 0.45 0.08

Gammaridea (amphipod) 11.28 9.82 0.04

Gammaridae (amphipod) 0.75 0.45 0.02

Hyperiidea (amphipod) 1.50 1.34 0.01

Caridea (shrimp) 12.78 8.48 0.38

Pasiphaea pacifica (shrimp) 0.75 0.45 0.14

Hippolytidae (shrimp) 18.05 15.63 1.43

Pandalidae (shrimp) 2.26 2.23 0.11

Crangonidae (shrimp) 2.26 1.34 0.07

Crangon sp. (shrimp) 2.26 1.34 0.10

Natantia (shrimp) 3.01 1.79 0.01

Anomura (crab) 2.26 5.36 1.17

Majidae (spider crab) 0.75 0.45 0.58

Chionoecetes sp. (snow and Tanner crab) 5.26 3.13 10.30

Chionoecetes tanneri (grooved Tanner crab) 5.26 3.13 7.64

Pinnotheridae (pea crab) 0.75 0.45 0.03

Echiura (marine worm) 0.75 0.45 0.02

Ophiuroidae Ophiurida (brittle star) 2.26 1.34 0.04

Gnathostomata 0.75 0.45 0.01

Osteichthyes Teleostei (bony fish) 6.77 4.46 1.36

Non-gadoid fish remains 2.26 1.34 18.01

Clupea pallasi (Pacific herring) 0.75 0.45 1.23

Myctophidae (lanternfish) 0.75 0.45 0.20
52

Table 14.--Continued.

Prey Name %F %N %W

Gadidae (gadid fish) 1.50 1.34 16.12

Merluccius productus (Pacific hake) 1.50 0.89 0.54

Zoarcidae (eelpout) 1.50 0.89 0.22

Lycenchelys jordani (shortjaw eelpout) 1.50 0.89 0.33

Cololabis saira (Pacific saury) 0.75 0.45 0.37

Scorpaenidae (rockfish) 12.03 7.14 25.34

Sebastes sp. (rockfish) 2.26 1.34 0.32

Sebastolobus alascanus (shortspine thornyhead) 2.26 1.34 0.62

Sebastolobus altivelis (longspine thornyhead) 4.51 2.68 2.53

Unidentified organic material 1.50 0.89 0.00

Offal 3.01 1.79 9.48

Total prey number: 224

Total prey weight: 1,454.19 g

Total non-empty stomachs: 133

Total empty stomachs: 60
THIS PAGE INTENTIONALLY LEFT BLANK
54

Figure 8.--Diet composition (by weight) of shortspine thornyhead for each

depth zone, INPFC area and year. The number of nonempty stomachs

examined are shown in each ring. Mean and standard deviation of the

lengths are shown in the lower left and right of each box, respectively.
55

Figure 8.--Continued
56

Figure 9.--Diet composition of shortspine thornyhead (by length) from north and

south of Cape Blanco in 1989, and from the 1991 and 1992 surveys. The

length-range shown in each figure may be different. The sample size (n) is

shown above each length group.
57

LONGSPINE THORNYHEAD

Longspine thornyhead (Sebastolobus altivelis) is a component of the deepwater

species complex managed by the Pacific Fishery Management Council (Ianelli et al.

1994). In response to developing Japanese export markets, higher prices, and the

movement of the bottom trawl fishery into deeper water (Jacobson 1993), landings of

longspine thornyheads in Washington, Oregon, and California have increased from an

average of 57 t per year in the late 1960s to 5,200 t per year in the early 1990s (Ianelli

et al. 1994).

The longspine thornyhead primarily inhabits the continental slope between 500

and 1,100 m but can be found from 300 m to depths exceeding 1,750 m (Hart 1973,

Jacobson 1993). Geographically, longspine thornyhead ranges from southern Baja

California to the Aleutian Islands (Hart 1973, Jacobson 1993). Sexual maturity is

attained by 50% of the females at 19 cm TL or about 14 years (Jacobson 1993). In late

winter or early spring, buoyant, bilobate egg masses are spawned (Jacobson 1993), and

about 18 to 20 months later, juvenile longspine thornyhead settle out of their pelagic

phase onto the continental slope at sizes of 40 to 60 mm TL (Jacobson 1993). Unlike

shortspine thornyheads, there is no relationship between depth and length for longspine

thornyheads (Jacobson 1993). Longspine thornyheads can grow to 35 cm TL and, based

on otolith increments, may reach ages approaching 50 years (Jacobson 1993).

RESULTS

General Diets

Seventeen (9%) of the 185 longspine thornyhead stomachs collected in the

autumn of 1991 were empty (Table 15). By weight, fish (26%), crab (24%), and shrimp

(15%) were the most important types of prey in the diet, but cephalopods (8%),

polychaetes (7%), echinoderms (7%), and fishery offal (5%) also contributed.

Numerically, small, non-decapod crustaceans (33%), echinoderms (14%), and polychaete

worms (12%) were the most important groups in the diet.

In 1992,30 (21%) of the 143 longspine thornyhead stomachs collected were

empty (Table 16). Fish (33%), shrimp (29%), and crab (14%) were the most important

diet components, by weight, but cephalopods (9%), fishery offal (6%), and polychaetes

(5%) also contributed. Numerically, the small, non-decapod crustaceans (40%) and

shrimp (18%) were most important in the diet.

Overall, the diet did not seem to be dominated by a particular prey type for either

year that samples were taken. However, most of the prey were benthic organisms.

Variation of the Diet with Location

The Monterey INPFC area was sampled in the autumn of 1991 (Fig. 10). In the

200-499 fm depth zone, Chionoecetes sp. (Tanner crab), other fish (mostly bathylagids

(deepsea smelts) and unidentified fish), other prey (mostly polychaetes and fishery offal),

scorpaenids, and mudshrimp were the most important prey categories by weight. In the

500-699 fin depth zone, other prey (mostly clams, brittlestars, and fishery offal), other

crustacea (mostly isopods), myctophids, and squid were the most important prey
58

categories by weight. In 199 1, fewer longspine thornyheads were sampled from the

Eureka and Columbia INPFC areas and only from the 200-499 fm depth zone. The

stomach contents, by weight, were dominated by mud shrimp in the Eureka INPFC area

and by Chionoecetes sp. in the Columbia INPFC area for the few samples that were

collected.

In 1992, the Columbia and Vancouver INPFC areas were sampled (Fig. 10). In

the 200-499 fm depth zone, fishery offal contributed to the large amount of “Other prey”

and the diet appears considerably different from that seen in 1991. Little, if anything, can

be inferred from this comparison because of the low number of samples taken in 1991.

In the 500-699 fm depth zone, a variety of smaller crustacea (mostly pasiphaeid shrimp)

and other fish (mostly non-gadoid remains) were important in the diet. In the Vancouver

INPFC area, “Other fish” (mostly zoarcids (eelpouts) and bathylagids) contributed about

half the weight to the stomach contents; squid, mud shrimp and Chionoecetes sp. were

also important.

Variation in the Diet with Predator Size

“Other crustacea” decreased in importance in the diet with increasing size of

longspine thornyhead in the areas sampled in 1991 and 1992 (Fig. 11). Squid and

myctophids (lantemfishes) appeared to be more important to the diet of longspine

thornyheads from the areas sampled in 1991. The “Other prey” category (includes offal

and polychaete worms) was important over a wide range of sizes in 1991 and 1992,

illustrating the diversity in the diet. In both years, mud shrimp, Chionoecetes sp., and

“Other fish” became important in the diet of longspine thornyheads at lengths of 20 cm

FL and larger (except for the 30-34 cm FL fish examined in 1992 when only two

longspine thornyheads of that size were sampled.

DISCUSSION

There is very little information on the diet of longspine thornyhead. Off Oregon

and California, longspine thornyhead eat mostly polychaete worms, shrimp, and crab

(Tom Laidig, personal communication1). The longspine thornyhead appears to be an

opportunistic predator that will consume a variety of locally available crustaceans and

fish that are on or near the bottom. The presence of offal from fish processing activities

in the diet, primarily heads of Pacific hake, indicates that longspine thornyhead are also

scavengers. It is possible that the biological identity of undigested parts of fishery offal

could be identified (i.e., Pacific hake, gadidae, or fish remains), but that evidence of it

being processed by the fishery would be lacking. If this occurred, the amount of fishery

offal in the diet would be underestimated.

The changes in the diet that occurred as a function of predator size were generally

in agreement with those found by Laidig’. Laidig found a shift in the diet from mainly

gammarid amphipods and polychaete worms to mainly crabs, shrimp, and fish. In this

study, we found that small crustacea were replaced by small fish and squid, then mud

shrimp, crab, and larger fish as predator size increased. The observed changes in diet

with size were not likely functions of prey availability with depth because there is no

relationship between depth and length for longspine thornyheads (Jacobson 1993).
59

Table 15 .--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of longspine thornyhead

(Sebastolobus altivelis) caught south of Cape Blanco in the fall of 1991.

Prey Name %F %N %W

Polychaeta (worm)

Aphroditidae (sea mouse)

Euphrosinidae (polychaete)

Onuphidae (polychaete)

Gastropoda (snail)

Heteropoda sp. (mollusc)

Bivalvia (clam)

Cephalopoda (squid & octopus)

Teuthoidea (squid)

Teuthoidea oegopsida (squid)

Gonatidae (squid)

Crustacea

Copepoda

Calanoida (copepod)

Peracarida Mysidacea (mysid)

Mysidae (mysid)

Cumacea (cumacean)

Isopoda (isopod)

Gammaridea (amphipod)

Hyperiidea (amphipod)

Caprellidea (amphipod)

Euphausiidae (euphausiid)

Unidentified crimson shrimp

Sergestes sp. (sergestid shrimp)

Caridea (shrimp)

Hippolytidae (shrimp)

Eualus sp. (shrimp)

Crangonidae (shrimp)

Crangon sp. (shrimp)

Natantia (shrimp)

Axiidae (mud shrimps)

Calocaris investigatoris (mud shrimp)

Calocaris quinqueseriatus (mud shrimp)

Callianopsis goniopthalma (mud shrimp)

Paguridae (hermit crab)

16.67 7.43 3.29

0.60 0.27 0.83

4.76 3.45 2.46

1.19 0.80 0.49

0.60 0.27 0.03

1.19 1.06 0.24

3.57 2.12 1.93

1.19 0.53 0.01

2.98 1.33 2.54

5.36 2.39 4.87

0.60 0.27 0.67

4.17 1.86 0.35

1.79 3.98 0.01

1.19 0.53 0.01

1.79 0.80 0.03

7.74 5.84 0.53

2.98 8.22 0.10

4.17 1.86 3.06

12.50 7.96 0.35

1.79 0.80 0.05

1.19 0.53 0.01

2.38 1.06 0.03

2.38 1.06 1.11

2.98 1.59 0.96

1.79 0.80 0.57

2.98 1.59 1.28

0.60 0.27 0.50

0.60 0.27 0.40

0.60 0.27 0.25

1.79 0.80 0.02

1.19 0.53 0.16

0.60 0.27 1.02

3.57 1.59 4.17

1.19 0.53 4.52

1.79 0.80 1.32
6 0

Table 15 .--Continued.

Prey Name % F O/ON % W

Galatheidae (pelagic slip crab) 0.60 0.27 0.01

Munida quadrispina (pinch bug) 0.60 0.27 0.02

Majidae (spider crab) 1.79 0.80 0.57

Chionoecetes sp. (snow and Tanner crab) 2.98 1.59 2.97

Chionoecetes tanneri (grooved Tanner crab) 8.33 5.04 18.21

Cherilia longipes (decorator crab) 0.60 0.27 1.03

Asteroidea (starfish) 1.19 0.53 1.65

Ophiuroidae Ophiurida (brittle star) 14.29 13.00 2.82

Echinacea sp. (sea urchin) 0.60 0.27 0.24

Holothuroidea (sea cucumber) 0.60 0.27 2.24

Urochordata (tunicate) 0.60 0.27 0.04

Osteichthyes Teleostei (bony fish) 1.79 0.80 0.39

Non-gadoid fish remains 4.76 2.39 4.77

Bathylagidae (deepsea smelts) 0.60 0.27 2.94

Myctophidae (lantemfish) 7.74 3.71 10.52

Gadidae (gadid fish) 0.60 0.27 0.88

Zoarcidae (eelpout) 0.60 0.27 1.26

Scorpaenidae (rockfish) 0.60 0.27 0.24

Sebastolobus sp. (unidentified thornyhead) 1.79 0.80 4.72

Unidentified organic material 3.57 1.59 1.08

Unidentified worm-like organism 0.60 0.27 0.04

Offal 5.95 2.65 5.03

Unidentified tube 0.60 0.27 0.15

Unidentified material 0.60 0.27 0.00

Total prey number: 377

Total prey weight: 184.44 g

Total non-empty stomachs: 168

Total empty stomachs: 17
61

Table 16.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of longspine thornyhead

(Sebastolobus altivelis) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Polychaeta (worm) 12.39 6.28 1.69

Aphroditidae (sea mouse) 1.77 0.90 2.31

Maldanidae (polychaete) 1.77 0.90 1.21

Gastropoda (snail) 0.88 0.45 0.00

Bivalvia (clam) 0.88 0.45 0.02

Teuthoidea (squid) 7.08 3.59 2.97

Teuthoidea oegopsida (squid) 1.77 0.90 6.20

Crustacea 7.08 4.48 0.17

Ostracoda 0.88 0.45 0.00

Calanoida (copepod) 1.77 0.90 0.02

Mysidacea Mysida (mysid) 7.08 4.04 0.13

Cumacea (cumacean) 7.08 21.52 0.27

Amphipoda (amphipod) 1.77 0.90 0.03

Gammaridea (amphipod) 10.62 5.83 0.14

Hyperiidea (amphipod) 0.88 0.45 0.02

Caprellidea (amphipod) 1.77 1.35 0.02

Sergestidae (sergestid shrimp) 0.88 0.45 0.13

Sergestes sp. (sergestid shrimp) 3.54 1.79 0.79

Reptantia (crab) 0.88 0.45 0.36

Pasiphaea pac$ca (shrimp) 2.65 1.35 7.15

Hippolytidae (shrimp) 4.42 2.69 1.71

Eualus sp. (shrimp) 2.65 1.35 2.36

Natantia (shrimp) 11.50 5.83 2.08

Axiidae (mud shrimps) 1.77 0.90 0.83

Calocaris investigatoris (mud shrimp) 5.31 3.59 13.41

Paguridae (hermit crab) 1.77 0.90 0.45

Lithodes couesi (couesi king crab) 0.88 0.45 0.56

Majidae (spider crab) 3.54 1.79 2.02

Chionoecetes sp. (snow and Tanner crabs) 2.65 1.79 2.05

Chionoecetes tanneri (grooved Tanner crab) 7.96 4.04 8.73

Ophiuroidae Ophiurida (brittle star) 11.50 8.97 3.36

Echinacea sp. (sea urchin) 0.88 0.45 0.05

Urochordata (tunicate) 0.88 0.45 0.08
6 2

Table 16.--Continued.

Prey Name %F %N %W

Osteichthyes Teleostei (bony fish) 3.54 1.79 0.17

Non-gadoid fish remains 7.08 3.59 10.89

Bathylagidae (deepsea smelts) 0.88 0.45 18.39

Zoarcidae (eelpout) 0.88 0.45 2.60

Scorpaenidae (rockfish) 0.88 0.45 0.96

Unidentified organic material 4.42 2.24 0.17

Offal 0.88 0.45 5.48

Total prey number: 223

Total prey weight: 85.26 g

Total non-empty stomachs: 113

Total empty stomachs: 30
63

Figure lO.--Diet composition (by weight) of longspine thornyhead for each

depth zone, INPFC area and year. The number of nonempty stomachs examined

are shown in each ring. Mean and standard deviation of the lengths are shown

in the lower left and right of each box, respectively.
64

Figure 11 .--Diet composition of longspine thornyhead (by length) from the 1992 survey.

The length-range shown in each figure may be different. The sample size (n)

is shown above each length group.
65

GIANT GRENADIER

Giant grenadier (Albatrossia pectoralis), also known as the pectoral rattail, is

typically the most abundant grenadier (Family Macrouridae) by weight when trawling on

the upper continental slope off Oregon (Parks et al. 1993). Giant grenadier occur along

the continental slope from California through the Bering Sea to Japan and are found from

depths of 200 m to 2,170 m (Iwamoto and Stein 1974). Small, presumably young, giant

grenadier (TL < 50 cm) may be pelagic, but juveniles and adults are typically caught near

the bottom (Novikov 1970). This species is the largest of the grenadiers and may reach a

length of 150 cm TL (Iwamoto and Stein 1974).

Despite their large size and wide availability, the commercial potential of giant

grenadier is limited because of their soft flesh (Matsui et al. 1990). However, large

specimens are occasionally marketed in northern California (Iwamoto and Stein 1974)

and Novikov (1970) considers it to be a valuable food resource because of its high

biomass and the high content of vitamin-rich fats in the roe and liver.

Unlike some other deepwater fishes, the stomach contents of many giant

grenadier have been described from the western Pacific Ocean (Novikov 1970, Okamura

1970), Aleutian Islands, and Bering Sea (Novikov 1970). This is due to its reduced

swimbladder (Iwamoto and Stein 1974) resulting in fewer instances of stomach eversion

as fish are brought to the surface (Matsui et al. 1990). However, the stomach contents of

only a few giant grenadier have been examined from the eastern Pacific Ocean. Pearcy

and Ambler (1974) describe the stomach contents of four giant grenadier caught off the

Oregon coast and Hart (1973) describes the stomach contents of one specimen caught off

British Columbia.

RESULTS

General Diet

Sixty-five (69%) of the 94 stomachs collected from giant grenadier north of Cape

Blanco in 1992 were empty. The contents of the 29 (31%) stomachs with food in them

are described in Table 17. Over 93% of the stomach contents by number, and 65% by

weight, were more than half digested, making identification difficult. Squid remains

(mostly beaks) had the highest frequency of occurrence followed by Gnathophausia sp.

(a large crimson mysid) and unidentified bony fish (usually bones). Squid remains

numerically dominated the diet composition, but Gnathophausia sp. (37%) shrimp

(30%), and fish (25%) were the most important diet components by weight.

Variation of the Diet with Location

It appeared there were differences in the overall diet of giant grenadier from the

Columbia and Vancouver INPFC areas (Fig. 12). A larger portion of the stomach

contents, by weight, was comprised of fish, pasiphaeid shrimp, and other shrimp in the

Columbia INPFC area. Gnathophausia sp. appeared to be more important to the weight

of stomach contents in the Vancouver INPFC area.
66

Variation of the Diet with Predator Size

There appeared to be differences in the diet composition, by weight, with the size

of the giant grenadiers examined (Fig. 13). The proportion of fish in the diet increased

with size while the proportion of crustaceans (Gnathophausia sp., pasiphaeid, pandalid,

and other shrimp) decreased.

DISCUSSION

Most of the information on the food habits of the giant grenadier is from the

northwestern North Pacific Ocean (Novikov 1970, Okamura 1970). Novikov (1970) lists

the stomach contents and their frequency of occurrence in over 2,000 giant grenadier

from several areas - northeastern Bering Sea, Aleutian Islands, Bowers Ridge, Pacific

coast of the Kamchatka Peninsula, northern Kurile Islands, and Sea of Okhotsk.

Although the number of stomachs that contained food is not reported, the data indicate

that the diet is quite different among these areas and consists of a mixture of benthic,

bathypelagic, and pelagic prey. Squid, with a frequency of occurrence greater than 10%

in all areas, appear to be the most consistently important prey type. Other prey with a

frequency of occurrence greater than 10% in at least one area include shrimp, amphipods,

unidentified crustaceans, Lampanyctus sp. (lanternfishes), liparids (snailfishes),

unidentified fish, ctenophores, bryozoans, and unidentified animals. Okamura (1970)

reports the volumetric composition of the stomach contents of four giant grenadier as

37% squid, 24% euphausiids, 20% fish, and 19% prawns (mysids).2

The stomach contents of very few giant grenadier have been examined from the

eastern Pacific Ocean. Four giant grenadier caught off the Oregon coast had eaten

cephalopods (Cranchiidae and Japatella sp.), brittlestars (Ophioctenpacfxum and

Ophiacantha sp.), the sea cucumber Scotoplanes sp., and unidentified fishes (Pearcy and

Ambler 1974). Hart (1973) reports that one of two giant grenadier caught by longline off

British Columbia had two squid beaks in its stomach. Squid remains were also

commonly found in the giant grenadier stomachs examined in this study but contributed

little (7%) to the overall weight of the stomach contents. Crustaceans (67% by weight)

were the gravimetrically dominant type of prey of giant grenadier in this study. This is

similar to the results of Okamura (1970) off Japan where crustaceans (euphausiids and

prawns) were the dominant type of prey by volume (43%), but dissimilar to the results of

Pearcy and Ambler (1974) off Oregon where no crustaceans were found in the diet of

giant grenadier.

Because of the low sample size (see results), differences or trends that occurred

among areas or size classes should be considered preliminary until a larger number of

samples can be analyzed. The differences in the composition of the stomach contents

between the Vancouver and Columbia INPFC areas may indicate differences in the

availability of these prey types between areas. However, the Pacific grenadier

(Coryphaenoides acrolepis) examined in this study show the opposite pattern for fish in

the diet, a higher proportion in the Vancouver INPFC area than in the Columbia INPFC

area (see Fig. 13). Apparent size-related changes in the diet of giant grenadier may have

contributed to the apparent areal differences. These two factors were somewhat

 On page 170, Okamura (1970) uses the term “mysids” parenthetically after the term “prawns” which may indicate that shrimp and

mysids were both included in this prey category, or that the prey were, Gnathophausia, a genus of large mysids.
67

confounded, so no firm conclusion about differences in diet by size or area were possible.

However, increasing fish and decreasing crustaceans (Gnathophausia sp. and shrimp) in

the diet with increasing size is consistent with patterns observed in many other fish.

The importance of Gnathophausia sp. as a prey item in this study (and perhaps

Okamura’s 1970 study, see Footnote 2) and its absence in other studies may be a result of

the prey’s distribution. The northern limit of Gnathophausia spp. in the eastern Pacific

Ocean is apparently southeastern Alaska (Kathman et al. 1986). Other regional

differences in the diet of giant grenadier have been found (Novikov 1970). Giant

grenadier appear to opportunistically prey on the available benthic and mesopelagic fauna

occurring near the continental slope.
68

Table 17.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of giant grenadier

(Coryphaenoides pectoralis) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Cephalopoda (squid & octopus) 3.45 1.67 0.36

Teuthoidea (squid) 75.86 68.33 7.07

Octopoda (octopus) 6.90 3.33 0.03

Crustacea 3.45 1.67 0.04

Gnathophausia sp. (mysid) 13.79 8.33 37.02

PasiphaeapaciJica (shrimp) 6.90 3.33 15.22

Pandalidae (shrimp) 3.45 1.67 1.98

Natantia (shrimp) 3.45 1.67 12.98

Ophiuroidae Ophiurida (brittle star) 3.45 1.67 0.32

Osteichthyes Teleostei (bony fish) 10.34 5.00 13.16

Non-gadoid fish remains 3.45 1.67 4.28

Bathylagidae (deepsea smelts) 3.45 1.67 7.55

Total prey number: 60

Total prey weight: 33.41 g

Total non-empty stomachs: 29

Total empty stomachs: 65
69

Figure12.--Diet composition (by weight) of giant grenadier for each depth zone,

INPFC area and year. The number of nonempty stomachs examined are

shown in each ring. Mean and standard deviation of the lengths are shown

in the lower left and right of each box, respectively.
Figure 13.--Diet composition of giant grenadier (by length) from the

The sample size (n) is shown above each length group.

1992 survey.
71

PACIFIC GRENADIER

Pacific grenadier (Coryphaekoides acrolepis), also known as Pacific rattail, has

the best potential of the eastern North Pacific macrourids (grenadiers or rattails) for

commercial use (Matsui et al. 1990). Grenadiers (Macrouridae) are the most abundant

fish, by weight and number, in deep-water trawl catches off Oregon and Washington

(Pearcy and Ambler 1974), and recently the commercial landings of Pacific grenadier

have been rapidly increasing (Michael Hosie, personal communication3). Pacific

grenadier occur along the continental slope from Baja California through the Bering Sea

to Sagami Bay (near Tokyo), Japan (Hart 1973) and are found from depths of 155 m

(Hart 1973) to 3,000 m (Matsui et al. 1990). Adults are typically caught near the bottom

but are also frequently caught in midwater hauls and are considered by many to be

bathypelagic or mesopelagic animals (Iwamoto and Stein 1974, Simenstad et al. 1977).

Obtaining accurate TL measurements is difficult because the tips of the long, thin

tails are often broken off and some show signs of regeneration (Matsui

et al. 1990). Consequently, length measurements are usually taken from the tip of the

snout to the first anal-fin ray which is known as the pre-anal fin length (PAL). The

relationship of PAL to TL is approximately TL mm = 2.308 x (PAL mm) + 122.158 for

males and TL mm = 2.276 x (PAL mm) + 115.4 for females (Matsui et al. 1990). The

largest specimen of this species measured over 95 cm TL and weighed 4 kg (Matsui et al.

1990).

Spawning appears to occur throughout the year with a peak in spring and early

summer off southern California (Matsui et al. 1990). The length at maturity is

approximately 23.5 cm PAL (65 cm TL) for females and 16.4 cm PAL (50 cm TL) for

males (Matsui et al. 1990).

Currently, information on the food habits of Pacific grenadier is very limited.

Pacific grenadier have a large gas bladder that expands, everting the stomach, when they

are captured at depth and hauled to the surface. Typically, too few stomachs are found

intact for meaningful analysis of their contents (e.g., Matsui et al. 1990). Pearcy and

Ambler (1974) found only 3% (n = 7) of the 216 specimens that they examined still

contained food in the stomachs. There is also little known about the predators of Pacific

grenadier, but the holotype of this species was taken from the stomach of a northern fur

seal (Callorhinus ursinus).

RESULTS

General Diet

The stomachs from 40 Pacific grenadier that appeared to have not regurgitated

were collected north of Cape Blanco in 1992 and examined in the laboratory. Seven

(17.5%) of these stomachs were empty. The contents of the remaining stomachs are

shown in detail in Table 18. Most (68%) of the stomach contents by weight were more

than half digested, making identification difficult. Squid or squid remains (usually beaks)

occurred in the stomachs most frequently followed by polychaete worms, unidentified

bony fishes (usually bones), unidentified organic material, sergestid shrimp, and

3

 Oregon Department of Fish & Wildlife, P.O. Box 5430, Charleston, OR 97420, U.S.A.
72

amphipods. Copepods and squid dominated the numerical composition of the diet. By

weight, squid and crustaceans were the most important components of the diet followed

by fish, unidentified organic material, and polychaetes.

Variation of the Diet with Location

There were differences in the overall diet of Pacific grenadier from the Columbia

and Vancouver INPFC areas (Fig. 14). A larger portion of the stomach contents, by

weight, was comprised of fish and other shrimp in the Vancouver INPFC area. Squid,

mud shrimp, and other crustacea appeared to be more important to the weight of stomach

contents in the Columbia INPFC area.

Variation of the Diet with Predator Size

There appeared to be differences in the diet composition, by weight, with the size

of the Pacific grenadiers examined (Fig. 15). The proportion of fish and squid in the diet

increased with size while the proportion of crustaceans (other shrimp, mud shrimp, and

other crustacea) and polychaetes decreased.

DISCUSSION

The stomach contents of a few Pacific grenadier have previously been reported

from the eastern Pacific Ocean as well as from the Aleutian Islands. The stomach

contents of seven Pacific grenadier caught off the Oregon coast included several species

of cephalopods (Gonatus fabricii, Cranchiidae, Japatella sp., Vampyroteuthis infernalis,

and unidentified squid beaks) fish remains, shrimp (Crangon abyssorum), crab

(Chionoecetes tanneri, and unidentified crab), and amphipods (Pearcy and Ambler 1974).

Matsui et al. (1990) report finding remains of fish, euphausiids, other crustacea, squid

beaks, polychaetes, and sponge spicules in the stomach and intestines of Pacific grenadier

captured off California. In the stomachs of four Pacific grenadier caught in midwater

near Amchitka (an Aleutian) Island, myctophids (lanternfishes) were most important in

frequency of occurrence and weight. Other prey included Pacific viper&h (Chauliodus

macouni), tadpole snailfish (Nectoliparis pelagicus), mysids, isopods, euphausiids,

unidentified decapod crustaceans, and cephalopods (Simenstad et al. 1977).

The results of this study were most similar to those of Pearcy and Ambler (1974)

and Matsui et al. (1990). These studies were conducted in the eastern Pacific Ocean

capturing Pacific grenadier near the bottom. The prey was a combination of benthic (e.g.,

polychaetes, crab and mudshrimp) and pelagic (e.g., squid, hyperiid amphipods, and

sergestid shrimp) organisms. Carcasses of epipelagic organisms may have been eaten

after they had died and sunk to the bottom or Pacific grenadier may swim into the water

column to forage there (Pearcy and Ambler 1974). In addition to their stomach contents,

the evidence for pelagic foraging by Pacific grenadier is their capture in midwater trawls

(Simenstad et al. 1977, Iwamoto and Stein 1974). The stomachs of Pacific grenadier

captured in midwater contain mostly mesopelagic prey (Simenstad et al. 1977).

Although the number of non-empty Pacific grenadier stomachs examined in this

study was higher than in other studies, the sample-size was still too low to reach firm

conclusions regarding area- and size-related trends. Thus, differences or trends that
73

occurred among areas or size classes should be considered preliminary until a larger

number of samples can be analyzed.

The differences in the composition of the stomach contents between the

Vancouver and Columbia INPFC areas may indicate differences in the availability of

these prey types in each area. However, the giant grenadier (Albatrossia pectoralis)

examined in this study show the opposite pattern for fish in the diet, a higher proportion

in the Columbia INPFC area than in the Vancouver INPFC area (see Fig. 14).

The size-related decrease in the proportion of crustaceans and polychaetes and the

increase in the proportion of fish and squid in the diet, by weight, is typical of many

predatory fishes. We can not infer whether this change in diet composition is related to a

change in feeding behavior (i.e., a shift from primarily benthic or pelagic foraging)

because the crustaceans are a mixture of benthic and pelagic types and the fish and squid

may be scavenged from the benthos or eaten in midwater. In addition, mesopelagic or

vertically migrating species that occur in the diet may migrate close to the continental

slope during the day and be consumed there (Pearcy and Ambler 1974).

The results of this study, combined with information from other studies, indicate

that Pacific grenadier are opportunistic predators and scavengers associated with the

continental slope and sometimes the mesopelagic environment. Benthic and pelagic

animals are both important in their diet, but distinguishing the importance of midwater

feeding relative to benthic scavenging will require further investigation.
7 4

Table 18.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Pacific grenadier

(Coryphaenoides acrolepis) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Polychaeta (worm) 45.45 7.08 8.18

Cephalopoda (squid & octopus) 3.03 0.29 0.09

Teuthoidea (squid) 60.61 25.07 29.04

Octopoda (octopus) 6.06 1.18 0.04

Crustacea 18.18 2.95 1.35

Copepoda 6.06 1.77 0.11

Calanoida (copepod) 18.18 32.15 0.31

Mysidacea Mysida (mysid) 18.18 4.72 0.94

Cumacea (cumacean) 3.03 0.29 0.01

Isopoda (isopod) 6.06 1.47 0.12

Gammaridea (amphipod) 27.27 3.83 0.64

Hyperiidea (amphipod) 12.12 2.06 0.52

Caprellidea (amphipod) 6.06 0.59 0.07

Euphausiidae (euphausiid) 9.09 1.18 0.28

Decapoda (shrimp & crab) 3.03 0.29 0.22

Sergestes sp. (sergestid shrimp) 27.27 3.83 8.58

Reptantia (crab) 9.09 1.18 3.35

Caridea (shrimp) 3.03 0.29 0.09

Hippolytidae (shrimp) 9.09 1.47 5.82

Natantia (shrimp) 3.03 0.29 0.40

Axiidae (mud shrimps) 3.03 0.29 0.73

Calocaris investigatoris (mud shrimp) 3.03 0.29 5.21

Chionoecetes sp. (snow and Tanner crab) 3.03 0.29 2.10

Osteichthyes Teleostei (bony fish) 30.30 2.95 14.63

Non-gadoid fish remains 6.06 0.59 4.42

Unidentified organic material 30.30 2.95 11.81

Unidentified worm-like organism 3.03 0.59 0.94

Total prey number: 339

Total prey weight: 35.27 g

Total non-empty stomachs: 33

Total empty stomachs: 7
75

Figure 14--Diet composition (by weight) of Pacific grenadier for each depth zone,

INPFC area and year. The number of nonempty stomachs examined are

shown in each ring. Mean and standard deviation of the fork lengths are

shown in the lower left and right of each box, respectively.
76

Figure 15.--Diet composition of Pacific grenadier (by length) from the 1992 survey.

The sample size (n) is shown above each length group.
77

DOVER SOLE

Dover sole, Microstomus pacificus, is a valuable commercial species with a long

history of exploitation by the bottom trawl fishery (Dark and Wilkins 1994, Turnock

et al. 1994). Landings, centered around the 183 m isobath, began to increase in the late

1940s after the introduction of new techniques to harden the soft flesh and produce a

marketable fillet from what was previously considered a trash fish (Hager-man 1952).

Coastwide landings exceeded 5,000 t per year in the 1950s and increased to a peak of

20,329 t in 1985 (Turnock et al. 1994), due in part to the expansion of the Dover sole

fishery to deep water, especially off northern California (Dark and Wilkins 1994). In

recent years, the fishery has continued to expand into deeper water over the continental

slope (Turnock 1993, Jacobson and Hunter 1993); however, landings declined to 14,300 t

in 1993 (Turnock et al. 1994).

The range of Dover sole extends from northern Baja California to the Bering Sea

(Hart 1973) and occupy depths from 55 m to more than 1,500 m off the west coast of

North America (Jacobson and Hunter 1993). Off Oregon, Dover sole are the most

abundant fish on pure mud bottoms, but they occur in much higher densities on mud and

boulder bottoms (Stein et al. 1992). Following a pelagic larval phase of 1 to 2 years,

Dover sole settle onto the continental shelf as juveniles and gradually move into deeper

water as they age and grow (Hart 1973, Jacobson and Hunter 1993, Tumock 1993).

Superimposed on this ontogenetic increase in depth is a seasonal pattern of movement

where fish migrate to deeper water in the winter to spawn and return to shallower water

in the summer (Hagerman 1952, Jacobson and Hunter 1993, Tumock 1993). Sexual

maturity is attained by 50% of Dover sole males and females at lengths of 32 cm and 35

cm FL, respectively (Hagerman 1952).

Dover sole are known to eat burrowing invertebrates (Hart 1973, Turnock 1993).

Off northern California, Hagerman (1952) found that bivalves and scaphopods were

common prey; sipunculids, polychaetes, sea urchins, brittle stars, and gastropods

occurred in varying quantities; shrimp and other crustaceans were sometimes gorged

upon. Pearcy and Hancock (1978) found a similar array of prey in the diet of Dover sole,

including 11 species of polychaetes considered to be their principal prey off Oregon.

Dover sole were found to select for polychaetes and brittle stars when feeding, and these

prey groups were more important than molluscs and crustaceans off Oregon (Gabriel and

Pearcy 1981).

RESULTS

General Diets

A total of 846 Dover sole stomachs were examined in the laboratory. Of the 279

stomachs examined from south of Cape Blanco in the summer of 1989, 17 (6%) were

empty. Similarly, 20 (7%) of the 281 Dover sole stomachs analyzed from north of Cape

Blanco in the summer of 1989 were empty. Only 4 (3%) of the 120 stomachs collected in

the autumn of 1991 were empty, but 35 (2 1%) of the 166 stomachs collected farther north

in the autumn of 1992 were empty.
78

South of Cape Blanco in 1989, the diet of Dover sole was gravimetrically

dominated by polychaete worms (56%) and brittle stars (26%) (Table 19). These prey

types were also numerically important and occurred frequently in the stomachs

containing food. Gammarid amphipods and bivalves also occurred frequently and were

numerically important, but because of their small size, their contribution to the weight of

the diet was fairly small.

The diet of Dover sole caught north of Cape Blanco in 1989 was also

gravimetrically dominated by polychaetes (42%) and brittle stars (31%) (Table 20).

However, large, soft bodied prey, such as echiurans (marine worms) and holothurians

(sea cucumbers), also contributed substantially to the total weight of the stomach contents

(6% and 4%, respectively). Polychaete worms and brittle stars (especially brittle star legs

without the central disk) occurred in the stomachs of Dover sole very frequently.

Gammarid amphipods and bivalves were also numerically important and had a high

frequency of occurrence, but because of their small size, their gravimetric contribution

was small.

The Dover sole sampled in autumn of 1991 from the outer continental shelf and

upper continental slope fed almost exclusively on polychaetes (85%) by weight (Table

21). Brittle stars (4%), amphipods (3%), and bivalves (2%) also contributed to the

weight of the diet and had a high frequency of occurrence.

In autumn of 1992, the diet of Dover sole sampled from the outer continental

shelf and upper continental slope north of Cape Blanco was dominated by polychaetes

(49%) and brittle stars (35%) by weight (Table 22). These prey types were also

numerically important and occurred very frequently in the stomachs of the Dover sole

sampled. Small crustaceans - gammarid amphipods, caprellid amphipods, and

cumaceans - and bivalves also had a high frequency of occurrence, but because of their

small size, their contribution to the weight of the diet was fairly small. Numerically,

gammarid amphipods (23% by number) were the second most important prey.

Variation in the Diet with Location

In general, polychaete worms were the dominant prey of Dover sole, by weight,

throughout the study area (Fig. 16). In the summer of 1989, polychaetes were over 80%

of the diet, by weight, of Dover sole sampled in the Conception INPFC area. In the

Monterey INPFC area there was more variety in the diet, which included polychaetes,

brittle star legs, brittle stars, crustaceans, and other prey. In the Eureka INPFC area,

brittle star legs and squid (a mollusc) contributed to a diet dominated by polychaetes. In

the Columbia INPFC area, sea urchins (included in other prey, Fig. 16) followed

polychaetes in importance to the diet in the 30-99 fm depth zone, but in the 100-l99 fm

depth zone, polychaetes followed marine worms in importance, by weight. In the

Vancouver INPFC area, brittle stars and polychaetes were the most important

components of the diet in the summer of 1989 (Fig. 16).

In autumn of 1991, the diet of Dover sole caught in deeper water in the Monterey

INPFC area was composed almost entirely (> 85%) of polychaetes, but in the Eureka

INPFC area, brittle stars contributed a significant portion of the diet weight. Dover sole

were sampled from the 200-499 fm depth zone in the Columbia INPFC area in both 1991

and 1992. In 1991; 14 Dover sole stomachs contained 68% polychaetes, 9% molluscs

(mostly clams), 4% brittle stars, 3% crustaceans, and 16% other and unidentified prey, by
79

weight. In 1992, 80 Dover sole stomachs contained 50% polychaetes, 34% brittle stars,

9% crustaceans (mostly galatheids or pinch bugs), 4% marine worms, and 3% other and

unidentified prey, by weight. In the 500-699 fm depth zone of the Columbia INPFC area,

cumaceans and amphipods contributed to the weight of other crustaceans eaten. The

stomach contents of the Dover sole caught in the 100-199 fm depth zone in the Columbia

and Vancouver INPFC areas were dominated by brittle stars and polychaetes.

Diet Variation with Predator Size

In the summer of 1989, south of Cape Blanco, the composition of the diet did not

appear to change very much with increasing size of the Dover sole, but the crustacea in

the diet of the smallest size category (15-l9 cm FL) was replaced by brittle star legs and

“Other prey” in larger sizes of Dover sole (Fig. 17). North of Cape Blanco, the diet also

appears to be fairly consistent for all sizes of Dover sole sampled, but brittle stars appear

to increase in importance with size and marine worms were eaten by the largest fish.

These increases are coupled with a decrease in other types of prey with predator size. In

autumn of 1991, polychaetes were over 80% of the diet by weight for all sizes of Dover

sole sampled. In autumn of 1992, it appears that a decrease in the percentage of

polychaetes in the diet, by weight, was accompanied by an increase in the percentage of

brittle stars and the occurrence of marine worms in the diet of Dover sole 45 cm FL and

larger.

DISCUSSION

The diet of Dover sole is known from previous studies to consist primarily of

benthic invertebrates (Hagerman 1952) especially polychaete worms and brittle stars

(Pearcy and Hancock 1978, Gabriel and Pearcy 1981). The results of our study are in

agreement with this generalization for most areas and depths examined (Fig. 16). Other

studies found Dover sole consuming polychaetes and brittle stars in greater proportions

than they occurred in box core samples, indicating a positive selection for these prey

(Gabriel and Pearcy 1981). However, the contribution of brittle stars to the diet may be

overestimated because brittle star legs may be evacuated very slowly from the stomach

(Gabriel and Pearcy 1981). In addition, the brittle star legs are protected by calcareous

shields (Barnes 1987) which may hinder digestion by raising the pH of the gut (Gabriel

and Pearcy 1981).

Dover sole appear to select habitats with more food (Pearcy and Hancock 1978)

and, although they are the most numerous fish found on mud bottoms, they occur in

much higher densities on bottoms with mud and boulders (Stein et al. 1992). Mud and

boulder bottoms are also occupied by very high densities of rockfishes and other species

(Stein et al. 1992), and might support a higher density of brittle stars and polychaetes

(food for Dover sole) than only mud bottoms because of higher nutrient (fecal) inputs

from the biomass aggregated above this bottom type. Alternatively, Dover sole may

prefer mud and boulder habitat because it provides better refuge than mud bottoms alone.

Seasonal differences in the feeding of Dover sole have been noted, although no

conclusions could be made from the data in this study. Pearcy and Hancock (1978) found

that Dover sole had fewer empty stomachs and a larger number of principal prey taxa in

the summer than in the winter. This corresponds well with higher growth rates in the
80

summer (Demory 1972). However, the summer growth rates increase in feeding intensity

and does not appear to be affected by food availability, which remains fairly constant in

all seasons (Bertrand 1971).

Size-related changes in the diet composition of Dover sole in this study were seen

primarily as an apparent increase in brittle stars and marine worms as predator size

increased (Fig. 17). This is consistent with observations of larger Dover sole eating

larger prey that were buried at increasing depths in the substrate (Gabriel and Pearcy

1981). Pearcy and Hancock (1978) found an increase in the number of polychaete

species eaten with size, and found molluscs and brittle stars to be most important to

intermediate sizes of Dover sole. In this study, we found the importance of molluscs in

the diet to show peaks at intermediate sizes, but the size where the peak occurred was not

consistent among the areas described (Fig. 17).

In general, the diet composition of Dover sole did not appear to be affected by

latitude or depth (Fig. 16). However, this is probably a function of comparing prey

groups at a high taxonomic level (Pearcy and Hancock 1978). Considerable variation in

the species assemblage of polychaetes eaten occurs between stations (Pearcy and

Hancock 1978), but only a small fraction of the polychaetes were identified down to the

family level in this study. Some differences seem to occur when size groups are

compared from north and south of Cape Blanco in summer of 1989 and autumns of 1991

and 1992 (Fig. 17). However, it appears that consistent differences were limited to brittle

star legs being more important in the diet on the continental shelf than on the continental

slope, and brittle stars being more important north of Cape Blanco than south of Cape

Blanco.
81

Table 19.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Dover sole (Microstomus

pacificus) caught south of Cape Blanco in the summer of 1989.

Prey Name %F %N %W

Foraminiferida (protozoan) 1.53 0.08 0.00

Hydrozoa 0.38 0.02 0.01

Polychaeta (worm) 58.02 14.56 33.55

Aphroditidae (sea mouse) 0.38 0.04 1.25

Sigalionidae (polychaete) 0.38 0.04 0.04

Euphrosinidae (polychaete) 14.12 2.83 14.16

Euphrosinidae multibranchiata (polychaete) 0.38 0.21 0.16

Phyllodocidae (polychaete) 4.58 0.34 0.25

Nereidae (polychaete) 0.38 0.06 0.14

Glyceridae (polychaete) 0.38 0.02 0.00

Goniadidae (polychaete) 1.15 0.06 0.08

Onuphidae (polychaete) 1.15 0.06 0.13

Lumbrineridae (polychaete) 1.15 0.11 0.01

Lumbrineris sp. (polychaete) 2.67 0.32 0.05

Flabelligeridae (polychaete) 2.29 0.13 0.62

Scalibregmidae (polychaete) 0.38 0.02 0.01

Opheliidae (polychaete) 0.38 0.04 0.12

Travisia sp. (polychaete) 0.38 0.02 0.60

Sternaspis scutata (polychaete) 4.96 0.51 0.66

Maldanidae (polychaete) 1.15 0.09 0.02

Oweniidae (polychaete) 0.38 0.04 0.03

Pectinariidae (polychaete) 5.34 0.41 0.46

Ampharetidae (polychaete) 1.91 0.55 0.84

Melinna (polychaete) 0.38 0.02 0.04

Terebellidae (polychaete) 4.58 0.41 2.70

Gastropoda (snail) 7.25 0.73 0.08

Aplacophora 1.53 0.08 0.00

Bivalvia (clam) 25.57 5.12 1.27

Scaphopoda 1.53 0.11 0.05

Teuthoidea (squid) 0.38 0.02 1.52

Ostracoda 1.15 0.06 0.00

Myodocopa (ostracoda) 0.38 0.04 0.00

Cirripedia Apygophora (barnacle) 0.38 0.02 0.00

Cumacea (cumacean) 14.89 1.47 0.11

Tanaidacea (peracaridan) 2.29 0.38 0.02
82

Table 19.--Continued.

Prey Name %F %N %W

Gammaridea (amphipod) 46.56 15.84 0.43

Ampeliscidae (amphipod) 0.76 0.04 0.01

Caprellidea (amphipod) 1.91 0.38 0.03

Euphausiacea (euphausiid) 5.73 1.45 2.00

Caridea (shrimp) 0.76 0.04 0.05

Anomura (crab) 0.38 0.02 0.00

Ophiuroidae Ophiurida (brittle star) 29.01 7.16 5.73

Brittle star legs 44.66 40.83 18.45

Ophiura sp. (brittle star) 1.15 0.19 1.47

Echinacea sp. (sea urchin) 0.76 0.04 0.01

Holothuroidea (sea cucumber) 0.38 0.02 0.10

Ascidiacea (sea squirt) 3.44 0.24 0.12

Osteichthyes Teleostei (bony fish) 1.15 0.45 0.00

Unidentified organic material 24.43 1.21 11.47

Unidentified worm-like organism 6.87 0.83 0.64

Unidentified tube 10.31 1.98 0.43

Unidentified algae 2.67 0.30 0.05

Total prey number: 5308

Total prey weight: 166.25 g

Total non-empty stomachs: 262

Total empty stomachs: 17
83

Table 20.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Dover sole (Microstomus

pacificus) caught north of Cape Blanco in the summer of 1989.

Prey Name %F %N %W

Phaeophyta (brown algae) 0.38 0.02 0.02

Foraminiferida (protozoan) 0.77 0.11 0.00

Foraminiferida Textulariina (foraminifera) 0.38 0.02 0.00

Nematoda (worm) 0.38 0.02 0.29

Acanthocephala (parasitic worm) 0.38 0.04 0.72

Polychaeta (worm) 73.18 22.47 17.46

Aphroditidae (sea mouse) 0.38 0.02 0.41

Euphrosinidae (polychaete) 1.53 0.31 0.21

Phyllodocidae (polychaete) 1.92 0.15 0.37

Nereidae (polychaete) 0.77 0.07 0.12

Sphaerodoridae (polychaete) 0.38 0.02 0.01

Glyceridae (polychaete) 1.15 0.15 0.44

Goniadidae (polychaete) 3.83 0.31 0.32

Onuphidae (polychaete) 1.15 0.22 0.57

Eunicidae (polychaete) 0.77 0.04 0.18

Lumbrineridae (polychaete) 5.75 1.03 0.87

Lumbrineris sp. (polychaete) 1.15 0.13 0.00

Paraonidae (polychaete) 0.38 0.02 0.00

Flabelligeridae (polychaete) 1.15 0.11 0.09

Scalibregmidae (polychaete) 0.38 0.02 0.01

Opheliidae (polychaete) 5.36 0.41 5.50

Travisia sp. (polychaete) 4.21 0.35 10.44

Sternaspis scutata (polychaete) 13.41 1.44 1.26

Maldanidae (polychaete) 4.60 0.33 1.50

Oweniidae (polychaete) 0.77 0.04 0.08

Sabellaridae (polychaete) 0.38 0.07 0.23

Pectinariidae (polychaete) 6.13 0.61 0.25

Ampharetidae (polychaete) 3.07 0.26 0.85

Terebellidae (polychaete) 1.53 0.13 0.38

Gastropoda (snail) 4.98 0.37 1.37

Nudibranchia dendronotoidea (nudibranch) 0.77 0.04 0.49

Bivalvia (clam) 28.35 4.19 1.94

Nuculoida (clam) 6.13 1.40 0.82

Scaphopoda 1.92 0.20 0.03

Crustacea 0.38 0.02 0.00

Ostracoda 2.30 0.94 0.02
84

Table 20.--Continued.

Prey Name %F %N %W

Copepoda 1.53 0.11 0.00

Calanoida (copepod) 0.38 0.02 0.00

Cirripedia (barnacle) 0.38 0.11 1.61

Cumacea (cumacean) 13.03 1.70 0.18

Isopoda (isopod) 0.38 0.02 0.09

Gammaridea (amphipod) 40.23 8.60 0.31

Ampeliscidae (amphipod) 2.30 0.28 0.03

Caprellidea (amphipod) 0.77 0.04 0.00

Euphausiacea (euphausiid) 2.30 0.15 0.04

Euphausiidae (euphausiid) 0.77 0.04 0.00

Euphausia pacifica (euphausiid) 0.77 0.04 0.03

Decapoda (shrimp & crab) 0.38 0.02 0.01

Reptantia (crab) 0.38 0.02 0.00

Caridea (shrimp) 1.15 0.09 0.23

Pandalidae (shrimp) 1.15 0.07 0.82

Anomura (crab) 0.77 0.04 0.02

Axiidae (mud shrimps) 0.38 0.02 0.55

Cancer magister (Dungeness crab) 0.38 0.02 0.01

Echiura (marine worm) 1.92 0.20 5.71

Ophiuroidae Ophiurida (brittle star) 25.67 5.35 11.58

Brittle star legs 47.89 23.72 8.93

Ophiura sarsi (brittle star) 7.66 6.37 10.16

Echinoidea (sea urchin and sand dollar) 1.15 0.07 0.01

Echinacea sp. (sea urchin) 3.45 0.20 4.10

Holothuroidea (sea cucumber) 1.15 0.07 0.28

Ascidiacea (sea squirt) 1.15 0.11 0.61

Gnathostomata 0.38 0.09 0.60

Non-gadoid fish remains 0.38 0.04 0.00

Unidentified organic material 17.62 1.03 4.21

Unidentified worm-like organism 22.61 9.73 1.88

Unidentified tube 14.94 5.24 0.70

Unidentified algae 1.53 0.31 0.04

Total prey number: 4583

Total prey weight: 457.24 g

Total non-empty stomachs: 261

Total empty stomachs: 20
85

Table 2 1 .--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Dover sole (Microstomus

pacificus) caught in the fall of 1991.

Prey Name

Foraminiferida Textulariina (foraminifera)

Anthozoa (anemome)

Polychaeta (worm)

Aphroditidae (sea mouse)

Euphrosinidae (polychaete)

Opheliidae (polychaete)

Sternaspis scutata (polychaete)

Maldanidae (polychaete)

Pectinariidae (polychaete)

Mollusca

Gastropoda (snail)

Nudibranchia dendronotoidea (nudibranch)

Bivalvia (clam)

Teuthoidea (squid)

Ostracoda

Copepoda

Calanoida (copepod)

Mysidacea Mysida (mysid)

Mysidae (mysid)

Cumacea (cumacean)

Isopoda (isopod)

Gammaridea (amphipod)

Hyperiidea (amphipod)

Caprellidea (amphipod)

Sergestidae (sergestid shrimp)

Caridea (shrimp)

Natantia (shrimp)

Paguridae (hermit crab)

Majidae (spider crab)

Ophiuroidae Ophiurida (brittle star)

Echinacea sp. (sea urchin)

Osteichthyes Teleostei (bony fish)

Myctophidae (lanternfish)

Unidentified organic material

Unidentified worm-like organism

1.72 0.38 0.01

0.86 0.04 0.39

92.24 33.88 58.41

0.86 0.04 2.02

37.07 8.61 20.29

0.86 0.04 0.00

11.21 1.85 2.56

0.86 0.13 0.59

3.45 0.34 0.63

0.86 0.04 0.01

3.45 0.21 0.16

1.72 0.08 0.05

27.59 2.90 2.46

1.72 0.08 0.01

14.66 8.40 0.91

0.86 0.04 0.00

1.72 0.08 0.00

0.86 0.04 0.00

1.72 0.08 0.00

18.10 2.14 0.21

3.45 0.55 0.19

68.10 23.05 2.33

3.45 1.72 0.12

19.83 8.94 0.59

0.86 0.04 0.34

0.86 0.04 0.04

1.72 0.08 0.16

0.86 0.04 0.16

2.59 0.13 0.06

34.48 5.46 3.77

3.45 0.17 1.27

0.86 0.04 0.00

0.86 0.04 0.22

5.17 0.25 1.89

0.86 0.04 0.13
86

Table 21 .--Continued.

Total prey number: 2382

Total prey weight: 124.41 g

Total non-empty stomachs: 116

Total empty stomachs: 4
87

Table 22.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of Dover sole (Microstomus

pacificus) caught north of Cape Blanco in the fall of 1992.

Prey Name %F %N %W

Foraminiferida Textulariina (foraminifera) 3.82 0.95 0.02

Cnidaria 0.76 0.07 0.13

Hydrozoa Hydroida (hydroid) 0.76 0.14 0.02

Sertulariidae (hydroid) 0.76 0.07 0.52

Anthozoa (anemone) 0.76 0.07 0.31

Polychaeta (worm) 83.97 36.01 44.87

Euphrosinidae (polychaete) 1.53 0.14 2.07

Opheliidae (polychaete) 1.53 0.14 0.02

Sternaspis scutata (polychaete) 5.34 0.48 0.13

Maldanidae (polychaete) 7.63 0.75 1.59

Pectinariidae (polychaete) 2.29 0.27 0.06

Ampharetidae (polychaete) 1.53 0.27 0.39

Terebellidae (polychaete) 0.76 0.14 0.07

Gastropoda (snail) 3.05 0.48 0.15

Polyplacophora 0.76 0.07 0.00

Bivalvia (clam) 21.37 2.79 0.32

Scaphopoda 0.76 0.20 0.06

Teuthoidea (squid) 6.11 0.54 0.05

Crustacea 3.05 0.41 0.05

Ostracoda 1.53 0.20 0.01

Myodocopa (ostracoda) 1.53 0.14 0.00

Copepoda 0.76 0.95 0.01

Calanoida (copepod) 0.76 0.07 0.00

Mysidacea Mysida (mysid) 2.29 0.20 0.01

Cumacea (cumacean) 19.85 5.84 0.46

Tanaidacea (peracaridan) 0.76 0.07 0.00

Isopoda (isopod) 0.76 0.07 0.00

Gammaridea (amphipod) 49.62 23.37 2.20

Hyperiidea (amphipod) 0.76 0.20 0.00

Caprellidea (amphipod) 20.61 3.06 0.18

Decapoda (shrimp & crab) 1.53 0.14 1.20

Sergestes sp. (sergestid shrimp) 2.29 0.20 0.95

Pasiphaeidae (shrimp) 0.76 0.07 0.34

Natantia (shrimp) 0.76 0.07 0.14

Anomura (crab) 0.76 0.07 0.08

Munida quadrispina (pinch bug) 6.11 2.11 5.35

Cancer magister (Dungeness crab) 0.76 0.07 0.01
88

Table 22.--Continued.

Prey Name %F %N %W

Sipuncula (marine worm) 0.76 0.07 0.64

Echiura (marine worm) 0.76 0.07 0.00

Echiuridae (marine worm) 2.29 0.20 2.26

Ophiuroidae Ophiurida (brittle star) 54.96 18.21 34.53

Echinacea sp.(sea urchin) 3.05 0.27 0.26

Unidentified organic material 0.76 0.07 0.08

Unidentified worm-like organism 3.05 0.27 0.47

Total prey number: 1472

Total prey weight: 78.83 g

Total non-empty stomachs: 131

Total empty stomachs: 35
THIS PAGE INTENTIONALLY LEFT BLANK
90

Figure 16.--Diet composition (by weight) of Dover sole for each depth zone, INPFC

area and year. The number of nonempty stomachs examined are shown in

each ring. Mean and standard deviation of the lengths are shown in the

lower left and right of each box, respectively.

92

Figure 17.--Diet composition of Dover sole (by length) from north and south of Cape

Blanco in 1989 and from the 1991 and 1992 surveys. The length-range

shown in each figure may be different. The sample size (n) is shown above

each length group.
93

DEEPSEA SOLE

The deepsea sole, Embassichthys bathybius, is a small-mouthed flatfish occurring

in deep water along the western continental slope of North America. This species was

first described from specimens captured off southern California in the late 1800s

(Hagerman 1950) and the known northern extent of its range has increased over the years

from Eureka, California (Hagerman 1950), to southeast Alaska (Hart 1973) to the Bering

Sea (Matarese et al. 1989). The deepsea sole is the most deeply distributed of the

flatfishes off Oregon and California (Alton 1972, Vetter et al. 1994) and possibly

throughout its range. It is found mixed with Dover sole around depths of 1,000 m off

central California (Vetter et al. 1994), and between depths of 732 to 870 m off Oregon

(Day and Pearcy 1968, Alton 1972). Beyond 1,200 m, the deepsea sole is the only

common flatfish, and its numbers decline with increasing depth by 1,400 m (Vetter et al.

1994). Deepsea sole may occasionally be processed in the Dover sole fishery, where they

co-occur, but no fishery is directed toward its harvest.

Little is known about the life history of the deepsea sole. It can grow to 47 cm in

length (Hart 1973). It spawns in winter through spring, releasing relatively large eggs,

3.0 mm in diameter, and may have a pelagic phase lasting several month (Richardson

198 1). There does not appear to be any ontogenetic shift in its depth distribution, as is

found for Dover sole, based on the similarity of the length distribution throughout its

depth range (Vetter et al. 1994). Deepsea sole is thought to feed on polychaetes and other

benthic invertebrates similar to other small-mouthed flatfish, like the Dover sole (Vetter

et al. 1994).

RESULTS

General Diets

The stomach contents were examined from 17 1 deepsea sole sampled during the

slope surveys in 199 1 and 1992. In 199 1, 10 (16%) of the 62 stomachs collected were

empty (Table 23). Polychaete worms dominated the diet by frequency of occurrence,

numerical composition, and gravimetric composition. Small crustaceans, especially

mysids and amphipods, were commonly encountered in the stomachs, but because of

their small size, they contributed little to the prey weight in the stomachs. Anemones and

brittle stars were the second and third most important prey in terms of weight. In 1992,

30 (28%) of the 109 stomachs collected were empty (Table 24). Polychaete worms

occurred about as frequently and were as important numerically in the deepsea sole diet

in the 1992 survey as in the 199 1 survey, but they contributed less to the weightcomposition of the diet in 1992. A higher percentage of the weight of the diet was

composed of brittle stars in the 1992 survey than the 1991 survey.

Variation in the Diet with Location

Polychaete worms were the dominant prey of deepsea sole, by weight, in most

areas sampled (Fig. 18). In the autumn of 1991 in the Monterey INPFC area,

polychaetetes were the dominant prey, but sea anemones (coelenterates) were also

important in the 200-499 fm depth zone. In the autumn of 1992 in the Columbia INPFC

area, brittle stars were somewhat important, by weight, in the stomachs of deepsea sole,
94

and they were dominant in eight fish from the 500-699 fm depth zone. In the Vancouver

INPFC area, polychaetes were the most important prey type, but unidentified hydrozoans

(coelenterates) also contributed to the weight of the diet in the 200-499 fm depth zone.

Diet Variation with Predator Size

In general, opposite trends occurred in 1991 and 1992 with respect to the diet

composition changes and predator size (Fig. 19). However, molluscs appear to be most

important to intermediate sized deepsea sole and crustaceans appear to decrease in

importance with increasing predator size during both years.

DISCUSSION

Previous descriptions of the food habits of deepsea sole suggest that it feeds on

benthic invertebrates, especially polychaetes, similar to other small-mouthed flatfish

(Vetter et al. 1994). The results of our study confirm this generalization of the food

habits of deepsea sole, and it seems fairly invariant over the latitudes and depths

examined, given the level of identification of the prey items in our study (Fig. 18).

However, considerable between-station variation in the species assemblage of

polychaetes consumed by Dover sole has been found (Pearcy and Hancock 1978).

Diet variation with predator size was very different in the 1991 and 1992 surveys

(Fig. 19). It seems unlikely that the opposite trends in diet composition with predator

size indicate that true differences exist in the availability or selection of prey types for the

different sizes of deepsea sole. It seems more likely that larger deepsea sole would have

a tendency to feed on larger prey that were buried deeper in the substrate than would

smaller deepsea sole, similar to the trend found for Dover sole (Gabriel and Pearcy 1981).

Perhaps if a larger number and a broader size-range of deepsea sole were sampled and the

prey were identified to finer taxonomic categories (Pearcy and Hancock 1978), then more

meaningful dietary changes with predator size could be described.

This is the first description of the diet of deepsea sole that we know of. The diet

is generally similar to other small-mouthed flatfishes, but it may be unique because the

depths at which all sizes of deepsea sole occur is deeper than most, except for the largest

Dover sole.
9 5

Table 23.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of deepsea sole

(Embassichthys bathybius) caught south of Cape Blanco in the autumn of

1991.

Prey Name %F %N %W

Anthozoa (anemone) 7.69 2.60 6.26

Polychaeta (worm) 67.31 46.35 76.09

Sabellidae (polychaete) 5.77 3.13 1.58

Gastropoda (snail) 1.92 1.56 2.93

Crustacea 1.92 0.52 0.00

Calanoida (copepod) 1.92 0.52 0.00

Mysidacea Mysida (mysid) 11.54 5.21 0.35

Gammaridea (amphipod) 25.00 14.06 0.61

Caprellidea (amphipod) 1.92 1.56 0.00

Reptantia (crab) 1.92 0.52 0.09

Callianassidae (mud shrimp) 1.92 0.52 1.74

Ophiuroidae Ophiurida (brittle star) 19.23 14.58 4.94

Urochordata (tunicate) 1.92 3.13 1.35

Ascidiacea (sea squirt) 1.92 0.52 0.31

Unidentified organic material 17.31 4.69 2.43

Unidentified worm-like organism 1.92 0.52 1.31

Total prey number: 192

Total prey weight: 42.31 g

Total non-empty stomachs: 52

Total empty stomachs: 10
9 6

Table 24.--The percent frequency of occurrence (%F), percent number (o/ON), and percent

weight (OhW) of the prey found in the stomachs of deepsea sole

(Embassichthys bathybius) caught north of Cape Blanco in the autumn of

1992.

Prey Name %F %N %W

Hydrozoa 2.53 0.99 5.01

Anthozoa (anemone) 3.80 1.49 0.91

Polychaeta (worm) 63.29 45.05 36.29

Polynoidae (polychaete) 1.27 0.50 2.20

Sabellidae (polychaete) 8.86 7.43 12.70

Nudibranchia dendronotoidea (nudibranch) 1.27 0.50 1.43

Bivalvia (clam) 1.27 0.50 0.05

Calanoida (copepod) 1.27 0.50 0.01

Mysidacea Mysida (mysid) 11.39 4.46 0.51

Gammaridea (amphipod) 17.72 12.38 0.87

Caprellidea (amphipod) 13.92 7.43 0.41

Crangonidae (shrimp) 1.27 0.50 0.03

Galatheidae (pelagic slip crabs) 2.53 0.99 1.01

Majidae (spider crab) 1.27 0.50 0.25

Ectoprocta (bryozoan) 1.27 0.50 0.57

Ophiuroidae Ophiurida (brittle star) 11.39 6.44 22.99

Urochordata (tunicate) 2.53 0.99 1.15

Unidentified organic material 21.52 8.42 12.60

Unidentified tube 1.27 0.50 1.00

Total prey number: 202

Total prey weight: 18.97 g

Total non-empty stomachs: 79

Total empty stomachs: 30
97

Figure 1 S.--Diet composition (by weight) of deepsea sole for each depth zone, INPFC

area and year. The number of nonempty stomachs examined are shown in

each ring. Mean and standard standard deviation of the lengths are shown in

the lower left and right of each box, respectively.
98

Figure 19.--Diet composition of deepsea sole (by length) from north and south of Cape

Blanc0 in 1989, and from the 1991 and 1992 surveys. The length-range

shown in each figure may be different. The sample size (n) is shown above

each length group.
9 9

ARROWTOOTH FLOUNDER

Arrowtooth flounder (&here&es stomias) is a low-value species processed

primarily by the reduction industry, but some is marketed in fillet form (Kabata and

Forrester 1974, Dark and Wilkins 1994). Historically, annual landings of this species

have been a few hundred metric tons for the U.S. Pacific coast (Dark and Wilkins 1994),

but up to 3,180 t per year have been processed in British Columbia, Canada, for mink

feed (Hart 1973). Annual U.S. landings increased in the early 1980s and were 2831

metric tons by 1987 (Dark and Wilkins 1994), and landings from areas off Washington in

1990-92 were higher than any other groundfish species except Pacific hake (Rickey

1995). However, discard rates for arrowtooth flounder are estimated to be 76% off

Oregon and Washington and over 80% in the Gulf of Alaska (Rickey 1995).

Arrowtooth flounder extend from central California to the Bering Sea and inhabit

depths down to 499 fm (900 m) (Hart 1973, Dark and Wilkins 1994). The biomass of

this species is centered in the Gulf of Alaska with the biomass density decreasing

southward, becoming very low in the Eureka and Monterey INPFC areas (Dark and

Wilkins 1994). As with several other flattish species, arrowtooth flounder exhibits a

tendency for larger, older fish to occupy deeper depths and perform seasonal spawning

migrations into deeper waters in the winter (Alton 1972, Kabata and Forrester 1974, Dark

and Wilkins 1994, Rickey 1995). Sexual maturity is attained by 50% of arrowtooth

flounder at lengths of 28 cm FL for males and 37 cm FL for females (Rickey 1995).

The diet of arrowtooth flounder has been described from the eastern Bering Sea

(Yang and Livingston 1986, Yang 1991, Livingston et al. 1993, Lang and Livingston

1996), Aleutian Islands (Yang 1996), Gulf of Alaska (Yang 1993) and the eastern Pacific

Ocean off British Columbia (Hart 1973, Kabata and Forrester 1974) and northern

California (Gotshall 1969). Arrowtooth flounder is primarily piscivorous, consuming

schooling gadids and small, schooling fishes, but it also eats shrimp and euphausiids.

RESULTS

General Diets

The stomach contents of 380 arrowtooth flounder from the 1989 and 1992 surveys

were examined in the laboratory. Of the 341 stomachs collected in the summer of 1989,

163 (47.8%) were empty (Table 25). Euphausiids, especially Euphausiapaczjka and

Thysanoessa spinifera, occurred more frequently in the diet than any other prey types and

they dominated the numerical composition of the diet. However, because of their small

size relative to other prey types, they contributed very little to the gravimetric

composition of the diet. Pacific herring (Clupeapallasi) also occurred fairly often in the

stomachs that contained food, and was of little importance to the numeric composition of

the diet due to the great number of euphausiids. However, Pacific herring was an

important component of the diet, by weight, because of its intermediate size relative to

the other prey types. Unidentified gadids and Pacific hake (Merluccius productus)

dominated the weight of the stomach contents because of their large size (64%

combined), even though they did not occur frequently. Twenty-eight (72%) of the 39

stomachs collected in autumn of 1992 were empty (Table 26). Pacific herring occurred
100

most frequently in the stomachs and was the dominant prey by number. However,

Pacific hake was the dominant prey by weight.

Variation in the Diet with Location

In the Columbia INPFC area, flatfish (pleuronectiformes), pandalid shrimp, and

“Other fish” (mostly unidentified gadids) comprised the bulk of the diet in the 30-99 fin

depth zone in the summer of 1989 (Fig. 20). In the l00-199 fm depth zone, pandalid

shrimp and “Other fish” dominated the diet. Pacific hake was followed by “Other fish”

and clupeids as the three most important diet components, by weight, in the 30-99 fm

depth zone of the Vancouver INPFC area. Euphausiids were the dominant prey of the 14

arrowtooth flounder sampled with food in their stomachs in the 100-199 fm depth zone of

the Vancouver INPFC area in the summer of 1989.

Few arrowtooth flounder sampled during the 1992 autumn survey of the

continental shelf and slope had prey in their stomachs (Table 26 and Fig. 20). Pacific

herring was the only prey type found in four fish from the Vancouver INPFC area in the

l00-199 fm depth zone. Pacific hake was the dominant prey of seven arrowtooth

flounder captured in the 200-499 fm depth zone in the Columbia INPFC area.

Variation in the Diet with Predator Size

The stomach samples collected in 1989 north of Cape Blanco indicated a high

degree of piscivory, even in very small arrowtooth flounder, that is highest for the largest

arrowtooth flounder (Fig. 21). However, fish were less important in the smallest size

categories, reaching a minimum percentage of the stomach contents weight by 30-39 cm

FL, before increasing rapidly with predator size to comprise almost the entire diet.

Euphausiids decreased as a component of the diet, by weight, and pandalid shrimp were

important to intermediate sizes of arrowtooth flounder. Pacific herring, flatfish, and

“Other fish” were important components of the diet over a broad range of size categories

(10-19 to 50-59 cm FL). Pacific hake was an important prey for larger arrowtooth

flounder (FL > 59 cm) in all samples that we examined.

DISCUSSION

The results of this study were generally consistent with the results of other studies

on the food habits of arrowtooth flounder which found that the diet primarily consists of

available schooling fishes. On the continental shelf of the eastern Bering Sea, arrowtooth

flounder consume mostly walleye pollock (Theragra chalcogramma) (56-88%), by

weight, but euphausiids (2-22%), shrimp (0-7%), and Pacific herring (0-3%) are

sometimes important (Yang and Livingston 1986, Yang 1991). Walleye pollock (55%) is

also the primary prey of arrowtooth flounder caught on the continental slope of the

eastern Bering Sea, and Pacific herring (11%) and squid (11%) also contribute to the

weight of the stomach contents when they are available (Lang and Livingston 1996).

Around the Aleutian Islands, Atka mackerel (Pleurogrammus monopterygius) (44%) was

the most important prey, by weight, followed by walleye pollock (11%), lanternfish

(Myctophidae) (7%) and euphausiids (5%) (Yang 1996). In the Gulf of Alaska, walleye

pollock (66%) dominate the weight of the diet followed by Pacific herring (9%) and

capelin (Mallotus villosus) (8%) (Yang 1993). Kabata and Forrester (1974) examined the
101

numerical composition of the arrowtooth flounder diet off British Columbia and found

euphausiids (58%) were most important followed by pandalid shrimp (18%), eulachon

(Thaleichthys pacificus) (6%), and Pacific herring (3%). Walleye pollock and Pacific

hake were both identified in the diet. Given the relative sizes of these prey types, it is

likely that, by weight, fish was the most important prey category followed by pandalid

shrimp and euphausiids. A similar numeric-gravimetric reversal in the order of prey

importance can be seen in Table 25 where euphausiids are dominant numerically and fish

are dominant gravimetrically. Hart (1973) describes the diet of arrowtooth flounder,

presumably from British Columbia, as consisting of shrimp and Pacific herring. Off

northern California, the diet of arrowtooth flounder includes, by volume, fish (mostly

flatfish and small, schooling fish) (47%), pink shrimp (Pandalus jordani) (38%), and

euphuasiids (7%) (Gotshall 1969), and arrowtooth flounder is listed as a predator of

Pacific hake (Best 1963).

The vast majority of the prey are pelagic or semi-pelagic, and we can conclude

that arrowtooth flounder is primarily a pelagic predator off the coasts of Washington and

Oregon, as they are in other areas (Kabata and Forrester 1974, Yang and Livingston

1986). The rare presence of benthic organisms (polychaete worm, snail, starfish, and

algae) in the stomach contents may indicate that arrowtooth flounder occasionally forage

on the bottom. However, these organisms may not normally be preyed upon, and might

only be eaten when they are lifted up from the bottom by the trawl footrope and are

available to arrowtooth flounder in the net (net feeding).

Arrowtooth flounder appears to be an opportunistic and somewhat non-selective

predator of relatively large prey such as fish, shrimp, and squid (Yang and Livingston

1986, Lang and Livingston 1996, Yang 1996). The variety of fishes in the diet (Table

25) and the importance of the “Other fish” category across areas (Fig. 20), as well as the

differing composition of the “Other fish” category among areas, support this conclusion.

This generalization also appears to be applicable over seasonal (Gotshall 1969, Yang

1991, Lang and Livingston 1996) as well as regional scales (Yang and Livingston 1986,

Yang 1996).

Increasing piscivory and decreasing euphausiid consumption with increasing size

of arrowtooth flounder is well documented in northern regions (Yang and Livingston

1986, Yang 1991, Yang 1993, Lang and Livingston 1996, Yang 1996). Similarly, in this

study the percentage of euphausiids, by weight, in the diet decreased with increasing size,

and the percentage of fish in the diet was higher for larger arrowtooth flounder than

smaller ones (Fig. 21). However, a large percentage of the diet, by weight, of the 30-39

cm FL size group was comprised of pandalid shrimp, creating a decrease then increase in

the proportion of fish in the diet with increasing length. It is possible that larger sample

sizes might show a consistent and gradual increase in the proportion of fish in the diet, as

was found in other studies examining a similar size-range of arrowtooth flounder (Yang

and Livingston 1986, Yang 1993, Yang 1996). However, pandalid shrimp may represent

an abundant and appropriately sized prey type for intermediate sizes of arrowtooth

flounder in this area.
102

Table 25.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of arrowtooth flounder

(Atheresthes stomias) caught north of Cape Blanco in the summer of 1989.

Prey Name %F %N %W
103

Table 25.--Continued.

Prey Name %F %N %W

Pleuronectidae (flatfish) 2.25 0.21 0.81

Atheresthes stomias (arrowtooth flounder) 0.56 0.05 0.85

Errex zachirus (rex sole) 1.12 0.10 1.37

Eopsetta exilis (slender sole) 0.56 0.10 2.08

Psettichthys melanostictus (sand sole) 0.56 0.05 1.26

Unidentified organic material 1.69 0.16 0.02

Unidentified algae 0.56 0.05 0.01

Unidentified material 0.56 0.05 0.01

Total prey number: 1925

Total prey weight: 2763.77 g

Total non-empty stomachs: 178

Total empty stomachs: 163
104

Table 26.--The percent frequency of occurrence (%F), percent number (%N), and percent

weight (%W) of the prey found in the stomachs of arrowtooth flounder

(Atheresthes stomias) caught north of Cape Blanco in the autumn of 1992.

Prey Name %F %N %W

Pandalidae (shrimp) 9.09 7.69 0.07

Osteichthyes Teleostei (bony fish) 18.18 15.38 0.00

Clupeapallasi (Pacific herring) 36.36 46.15 13.94

Merlucciusproductus (Pacific hake) 27.27 23.08 83.57

Atheresthes stomias (arrowtooth flounder) 9.09 7.69 2.42

Total prey number: 13

Total prey weight: 659.09 g

Total non-empty stomachs: 11

Total empty stomachs: 28
Figure 20.--Diet compositon (by weight) of arrowtooth flounder for each depth zone, INPFC area and year.

The number of nonempty stomachs examined are shown in each ring. Mean and standard deviation

of lengths are shown in the lower left and right of each box, respectively.
1 0 6

Figure 2 1 .--Diet composition of arrowtooth flounder (by length) from north of

Cape Blanco in the 1989 and 1992 surveys. The length-range shown in

each figure may be different. The sample size (n) is shown above

each length group.
107

SPECIES INTERACTIONS

Species interactions can be between predator and prey or among competitors for

the same prey resource. The first step in examining the potential for competition among

species is to assess the similarity in their diets, Comparisons of various indices of dietary

overlap or similarity indicate that those based on the quantities or proportions of prey

types are generally better than those based solely on the presence or absence of prey

types in the diets (Cailliet and Barry 1979). The Percent Similarity Index (PSI), also

commonly known as Schoener’s (1970) Index, is the simplest, and it has been

independently developed several times since 1938 (Hurlbert 1978, Cailliet and Barry

1979). The PSI can be calculated in two ways:

where p is the percentage (or proportion) of prey i in predators x and y. The value of this

index ranges from 0 to 100 (or 0 to 1 if proportions are used) indicating, respectively, no

similarity to complete similarity of the diets. The PSI performs well (Cailliet and Barry

1979, Linton et al. 1981), responds to both rare and dominant prey types, and is less

sensitive to skewness in prey composition than some other indices (Cailliet and Barry

1979). However, its accuracy decreases when overlap is very low (< 7%) or very high

(> 90%) (Linton et al. 1981). When overlap is very low, an index based on comparison

of prey lists (presence or absence) can be a better measure (Pielou 1974).

METHODS

Predator diet data were pooled into 61 mutually exclusive prey categories, and the

percentage weight composition of the 61 prey categories was calculated for each

predator. The PSI was calculated for each pair of predators using all 61 prey categories

including miscellaneous shrimp, miscellaneous crabs, miscellaneous crustacea,

miscellaneous vertebrata, miscellaneous organic material, and miscellaneous prey. The

“miscellaneous” categories were mostly composed of unidentified prey. By using the

“miscellaneous” prey categories in the calculation of the PSI, an assumption was implied

that the identified and unidentified components of those categories were identical in both

predators. The PSI was also calculated for each pair of predators without using the

“miscellaneous” prey categories, implying that the components of those categories were

assumed to be completely different. When one wants to avoid biasing the PSI estimate

due to improperly assuming predators contain identical prey, the second method of

calculating PSI should be used to generate an estimate of minimum diet overlap. In our

calculations, when the difference between the PSI with “miscellaneous” categories and

the minimum estimate of PSI without “miscellaneous” categories was less than four, the

mean value was presented: otherwise, the range was presented. The amount of diet

overlap was categorized as low (0-24%), moderate (25-49%), high (50-74%), or very

high (75- 100%) based on the mean of the two index values.
108

RESULTS

The percentage weight composition of the diet of each predator, based on the 61

prey categories, was presented for samples collected in the summer 1989 shelf survey

south of Cape Blanco (Table 27) and north of Cape Blanco (Table 28) and the autumn

slope surveys of 1991 (Table 29) and 1992 (Table 30). Using these values, the PSI was

calculated with and without the ‘miscellaneous’ prey categories, as described above.

South of Cape Blanco in the 1989 shelf survey, moderate diet overlap was found

between Pacific hake and sablefish (Table 32). This was due mainly to the consumption

of euphausiids, but cephalopods (mostly squid), engraulids (anchovies), scorpaenids

(rockfishes), and pleuronectiform fish also contributed (Table 27).

North of Cape Blanco in the 1989 survey of the continental shelf, moderate PSI

values were found among Pacific hake, sablefish, and arrowtooth flounder, indicating

moderate diet overlap (Table 31). The diet overlap among Pacific hake, sablefish, and

arrowtooth flounder was due to consumption of clupeids (mostly herring), euphausiids,

and some pandalid shrimp. Pleuronectiform (flat) fish also contributed to the diet overlap

between arrowtooth flounder and sablefish (Table 28).

Among the predators sampled in the 1991 slope survey, moderate diet overlap

was found among sablefish, shortspine thornyhead, and longspine thornyhead, and very

high diet overlap was found between Dover sole and deepsea sole (Table 33). The

overlap in the diets of sablefish and shortspine thornyhead was attributed mainly to

predation on scorpaenids (mostly thornyheads), offal, gadids (mostly hake), and

Chionoecetes sp. (Table 29). Sablefish and longspine thornyhead overlapped in their

consumption of cephalopods, scorpaenids, offal, and Chionoecetes sp. Longspine and

shortspine thornyhead diets had mostly Chionoecetes sp., scorpaenids, offal, and

polychaetes in common. The very high overlap between the diets of Dover and deepsea

soles was attributed to polychaete worms and ophiuroids (brittle stars) (Table 29).

In the 1992 survey, moderate diet overlaps were found between longspine and

shortspine thornyheads, longspine thornyhead and Pacific grenadier, and longspine

thornyhead and giant grenadier (Table 34). High diet overlap was found between

sablefish and shortspine thornyhead and between Dover and deepsea soles (Table 34).

The diets of longspine and shortspine thornyheads overlapped mostly in miscellaneous

vertebrates (mostly unidentified fish), Chionoecetes sp., and offal (Table 30). Longspine

thornyhead mostly consumed miscellaneous vertebrates, cephalopods, thalassinids

(mudshrimp), polychaete worms, and hippolytid shrimp in common with Pacific

grenadier. Longspine thornyhead and giant grenadier diets overlapped mostly in

miscellaneous vertebrates, bathylagids (deepsea smelts), cephalopods, and miscellaneous

shrimp. Shortspine thornyhead and sablefish consumed scorpaenids, gadids, offal,

Chionoecetes sp., miscellaneous vertebrates, and clupeids in common. The very high diet

overlap between Dover and deepsea soles consisted of polychaete worms and ophiuroids

(Table 30).

DISCUSSION

These diet comparisons were made using data combined from all sizes of the

predators examined over large regions. However, this is only a first step in determining
109

the degree of predator interaction that may be taking place. Differences in spatial and

temporal distribution of the predators, available prey, and predator size have a large

effect on the diet. If the diet overlap of two predators was examined only when they were

captured at the same time and location, it is possible that the diets would appear more

similar than would be found over a broad area. In addition, the diet of certain sizes of a

predator might overlap only with certain sizes of another predator, and comparing all

sizes at once may mask some of the intensity of this diet overlap. However, comparisons

of the overall diets provide perspective on the diet overlap and on the potential for

competition among the predator populations in a general sense.

The moderate overlap among the diets of Pacific hake, sablefish, and arrowtooth

flounder north of Cape Blanco and the moderate overlap between the diets of Pacific

hake and sablefish south of Cape Blanco in 1989 is consistent with the results of other

food habits studies. Gotshall (1969) found pandalid shrimp and euphausiids were the

most frequently occurring prey in the stomachs of all three predators off northern

California. Euphausiids were the dominant prey of Pacific hake and juvenile sablefish

off Oregon and Washington (Brodeur et al. 1987). Livingston (1983) recognized

euphausiids as a unifying factor in the diet of Pacific hake because they attract small

schooling fishes (clupeids, osmerids, and engraulids) and invertebrates that also prey on

euphausiids. This phenomenon also appears to be a unifying factor among the diets of

Pacific hake, sablefish, and arrowtooth flounder because euphausiids and schooling fishes

that eat euphausiids, including Pacific hake and rockfish (Sebastes spp.), often

contributed to the diet overlap among these three species. Shortspine thornyhead

sampled during the three NMFS bottom-trawl surveys reported on here, also consumed

Pacific herring, rockfish, and Pacific hake (Table 35).

Pacific hake is recognized as one of the most ecologically important species in the

California Current ecosystem (Bailey et al. 1982, Francis 1983, Livingston and Bailey

1985). In this study, we found Pacific hake eaten by pelagic predators, arrowtooth

flounder, and other Pacific hake, as well as denizens of the upper continental slope,

sablefish, and shortspine thornyhead (Table 35). In addition, much of the fishery offal

eaten by sablefish, shortspine thornyhead, and longspine thornyhead consisted of severed

heads of Pacific hake.

In contrast to 1989, Pacific hake displayed low diet similarity to sablefish in 1991

and to sablefish and arrowtooth flounder in 1992. However, the diets of sablefish and

arrowtooth flounder were almost moderate in similarity (24%, Table 34) due to predation

on Pacific hake and Pacific herring. The 1991 and 1992 surveys of the upper continental

slope were conducted in deeper water than the 1989 survey of the continental shelf.

Smaller sablefish were absent from the samples taken from the 1991 and 1992 surveys

(Fig. 7), and larger sablefish tend to lead a more demersal existence (Dark and Wilkins

1994) while Pacific hake maintain a semi-pelagic lifestyle above the continental slope.

The diet of sablefish was found to exhibit moderate or high similarity to the diet

of shortspine thornyhead in 1991 and 1992 (Tables 33 and 34, respectively). The diet of

longspine thornyhead moderately overlapped with the diets of sablefish and shortspine

thornyhead in 1991, but with only shortspine thornyhead in 1992. The diet similarity

among these three predators was based on consumption of Chionoecetes sp., offal and

scorpaenids in 1991, and of Chionoecetes sp., offal, and miscellaneous vertebrates in

1992. However, the similarity between the diets of shortspine thornyhead and sablefish
110

was based mainly on the consumption of fishes (scorpaenids, gadids, and clupeids) and

offal, while the diet overlap between shortspine and longspine thornyheads was based

largely on the consumption of similar benthic invertebrates (Chionoecetes sp., polychaete

worms, hippolytid shrimp and miscellaneous crabs) in addition to some fish and offal

(Tables 29 and 30).

The longspine thornyhead diet was also moderately similar to the diets of Pacific

grenadier and giant grenadier (Table 34). In addition to diet overlap based on

cephalopods and miscellaneous vertebrates, longspine thornyhead and Pacific grenadier

both consumed an array of benthic invertebrates (thalassinid shrimp, polychaete worms,

hippolytid shrimp, Chionoecetes sp., and miscellaneous crabs) while longspine

thornyhead and giant grenadier both consumed bathylagid fish and miscellaneous

shrimp.

The very high diet overlap between Dover sole and deepsea sole is based mostly

on the broad taxonomic category of polychaete worms in 1991 and 1992 (Tables 29 and

30). Although indices of similarity are higher when prey species are grouped and higher

taxa are compared (Pearcy and Hancock 1978), the polychaete prey category is

representative of a well-defined ecological group. It is likely that some differences in the

diets would be found if families or species of polychaetes were compared.

In general, the species of fish sampled in this study can be grouped into three

major categories based on their dietary habits. The pelagic group - Pacific hake,

arrowtooth flounder, and juvenile sablefish - ate mostly euphausiids and other euphausiid

consumers. The large-mouthed benthic group - adult sablefish, shortspine thornyhead,

longspine thomyhead, Pacific grenadier, and giant grenadier - were omnivorous, eating a

variety of fishes, crustaceans, and other invertebrates. Most, but not all, of these prey

were bottom-dwellers. The small-mouthed flatfish - Dover sole and deepsea sole -

consumed mainly polychaetes and brittle stars.
THIS PAGE INTENTIONALLY LEFT BLANK
112

Table 27.--The percentage weight composition of the stomach contents of groundfish

south of Cape Blanco in the summer of 1989. (HAK = Pacific hake, SAB =

sablefish, SST = shortspine thornyhead, DOV = Dover sole).
113

Table 27.--Continued.
114

Table 28.--The percentage weight composition of the stomach contents of groundfish

north of Cape Blanco in the summer of 1989. (HAK = Pacific hake, ATF =

arrowtooth flounder, SAB = sablefish, SST = shortspine thornyhead, DOV

= Dover sole).

Predator: HAK ATF SAB SST DO V
115

Table 28.--Continued.
116

Table 29.--The percentage weight composition of the stomach contents of’groundfish in

the autumn of 1991. (HAK = Pacific hake, SAB = sablefish, SST =

shortspine thornyhead, LST = longspine thornyhead, DOV = Dover sole,

DSS = deepsea sole).
117

Table 29.--Continued.
118

Table 30.--The percentage weight composition of the stomach contents of groundfish in

the autumn of 1992. (HAK = Pacific hake, ATF = arrowtooth flounder,

SAB = sablefish, SST = shortspine thomyhead, LST = longspine

thornyhead, DOV = Dover sole, DSS = deepsea sole, PGN = Pacific

grenadier, GGN = giant grenadier).
Table 30.--Continued.

119
120

Table 3 1 .--Percent similarity index of dietary overlap among Pacific hake (HAK),

arrowtooth flounder (ATF), sablefish (SAB), shortspine thornyhead

(SST), and Dover sole (DOV) caught north of Cape Blanco in the

summer of 1989.

Table 32.--Percent similarity index of dietary overlap among Pacific hake (HAK),

sablefish (SAB), shortspine thornyhead (SST), and Dover sole (DOV)

caught south of Cape Blanco in the summer of 1989.
121

Table 33 .--Percent similarity index of dietary overlap among Pacific hake (HAK),

sablefish (SAB), shortspine thornyhead (SST), longspine thornyhead

(LST), Dover sole (DOV) and deepsea sole (DSS) caught in the

autumn of 1991.

Table 34.--Percent similarity index of dietary overlap among Pacific hake (HAK),

arrowtooth flounder (ATF), sablefish (SAB), shortspine thornyhead

(SST), Dover sole (DOV), deepsea sole (DSS), Pacific grenadier (PGN)

and giant grenadier (GGN) caught in the autumn of 1992.
Table 35.--Length-ranges of predators and their schooling fish-prey. The predator

length-range includes only the predators, sampled during the bottom-trawl

surveys in 1989, 1991 and 1992, that consumed these schooling fish-prey.

(HAK = pacific hake, SAB = sablefish, SST = shortspine thornyhead, ATF

= arrow-tooth flounder).
123

ACKNOWLEDGEMENTS

The juvenile Pacific hake samples were collected by A. Hollowed in 1987 and T.

Wilderbuer in 1988. Other stomachs were collected primarily by M. Dom, D. Molenaar,

R. Pacunski, and J. Parkhurst in 1989; A. Ward in 1991; and M. Grader and J.

McClelland in 1992. We appreciate their efforts and the efforts of other survey

participants who assisted in collecting the stomach samples.

Our gratitude also extends to those who assisted in the laboratory analysis of the

stomach contents presented in this report. The stomach contents of the 1987 and 1988

juvenile Pacific hake were analyzed by G. Lang and D. Molenaar. The stomach contents

of sablefish, arrowtooth flounder, and some shortspine thornyhead from 1992, as well as

some Dover sole from 1989 were analyzed by K. Craig.

We thank M. Wilkins, B.J. Tumock, G. Duker and J. Lee for their editorial

comments.
124

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APPENDIX

The geographical distributions of important prey groups are illustrated by plotting

their percent frequency of occurrence in all predators sampled at each haul location. The

charts on facing pages show the geographical distribution of a prey group north of Cape

Blanco and south of Cape Blanco. The 200-fm and 500-fm isobaths are shown.










































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93 MURPHY, J. M., N. E. MALONEY, and B. L. WING. 1998. Distribution and abundance of zooplankton

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91 WING, 6. L., and J. J. PELLA. 1998. Time series analyses of climatological records from Auke Bay,

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PACUNSKI, R. E., P. A. LIVINGSTON, and B. S. MILLER. 1998. Food of flathead sole HiDDoalossoides

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89 WILKINS, M. E., M. ZIMMERMANN, and K. L. WEINBERG. 1998. The 1995 Pacific west coast bottom

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FRITZ, L. W., A. GREIG, and R. F. REUTER. 1998. Catch-per-unit-effort, length, and depth distributions

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based on groundfish fishery observer data, 179 p. NTIS No. PB98-139298.

87 SINCLAIR, E. H. (editor) 1997. Fur seal investigations, 1996, 115 p. NTIS No. PB98-131790.