AN ABSThAC OF THE IHESIS OF
Willard Waldo Wakefieldfor the degree of Master of Science
in Oceanography presented on February 6, 1984
Title: FEEDING RELATIONSHIPS WITHIN ASSEMBLAGES OF NEARSHORE
AND MIDCONTINENTAL SHELF I3ENTHIC FISHES OFF OREGON
Abstract approved: Redacted for Privacy ,. Prof. H. F. Frolander
The food habits of 22 species of benthic fishes occurringon
the Oregon continental shelf were investigated from specimens
collected by trawling nearshore (9 and 22 m sta.) and midshelf
(73 m sta.) depths during spring 1979.
Two generalized feeding types were identified: fishes that prey solely on pelagic crustaceans and fishes, and fishes that feed on infaunal invertebrates, including polychaetes, nemerteans, amphipods, cumaceans and molluscs.
In the nearshore environment, pelagic and/or epifaunal feeders included Psettichthys melanostictus (sandsole) which dominated the catch numerically, Citharichthys stigmaeus(speckled sanddab), Microgadus proximus (Pacific tomcod), Spirinchusstarksi
(night smelt), and Allosmerus elongatus (whitebait smelt). These fishes fed mainly on crustaceans; with mysids composing40% of the weight of their stomach contents. Diet overlap was intermediate to high within this predator group, ranging from 22to 73%.
Within the same assemblage, epifaunal and/or infaunalfeeders were
Rala binoculata (big skate), Hydrolagus colliei (ratfish),
Platichthys stellatus (starry flounder), Isopsetta isolepis (butter sole), and Parophrys vetulus (English sole). The skate,
R. binoculata, ranked first in biomass, and together with H. colliei, fed largely on Cranon stylirostris and Cancer magister.
Ammodytes hexapterus (sand lance) and juvenile . stigmaeus were also important in the skate's diet. Parophrys vetulus had the most diverse diet, feeding primarily on infaunal polychaetes, amphipods, nemerteans, and cumaceans. Epibenthic invertebrates
were more important in the diets of . stellatus and I. isolepis than in the diet of P. vetulus. Diet overlap within this group ranged from low to intermediate ranging from 1 to 37%.
At the midshelf site, both Citharichthys sordidus (Pacific sanddab), the most abundant species, and Eopsetta .iordani (petrale sole), fed on or above the substrate, but C. sordidus fed more on pelagic prey. Citharichthys sordidus consumed euphausiids, copepods, pteropods, a pelagic mysid and salps. A size related shift was observed in the diet of E.jordani with small individuals preying on mysids, Crangon, and newly settled pleuronectiforms, and larger individuals feeding on larger juvenile pleuronectiforms. Six common species of pleuronectiforins at this site were found to feed on a mixture of epibenthos and infauna. Four, P. vetulus, Microstomus pacificus (Dover sole),
Glyptocephalus zachirus (rex sole), and I. isolepis fed primarily, but in varying degrees, on polychaetes and amphipods.
Polychaetes were the only prey of Pleuronichthys decurrens
(curifin sole). The remaining pleuronectid, Lepidopsetta bilineata (rock sole), preyed on recently settled pleuronectiforms, Crangon, and amphipods. Within these six flatfishes, diet overlap ranged from 0 to 28%.
To siimmarize the trophic relationships within the assemblages inhabiting the two continental shelf areas, two food webs were constructed, combining information from both the literature and the current study. FEEDING RELATIONSHIPS WITHIN ASSEMBLAGES OF NEARSHORE
AND MIDCONTINEZ4TAL SHELF BE24ThIC FISHES OFF OREGON
by
Willard Waldo Wakefield
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of
Master of Science
Completed February 6, 1984
Commencement June 1984 APPROVED:
Redacted for Privacy Professor of Oceanography in charge of major
Redacted for Privacy Dean of College of Oceanography
Redacted for Privacy
Dean of Gra'iite School
Date thesis is presentedFebruary 6, 1984
Typed by Waldo Wakefield for Willard Waldo Wakefield ACKNOWLEDGE1IENTS
I gratefully thank my committee members Drs. Herbert
Frolander, William Pearcy, Carl Bond, and Robert Morris. A special thanks belongs to Dr. Pearcy for his guidance and support throughout the various stages of this thesis. Dr. Al Tyler participated as my minor professor in the earlier stages of the research. Dr. Ellen Pikitch provided helpful criticism during the final stages.
Many individuals, outside my committee have helped me along the way, and I would like to acknowledgeas many as possible.
A group of fellow graduate students in my "year class" provided a supportive environment for learning and living, in particular, Chip Hogue, Kathy Fisher, Marc Willis, Hal Batchelder,
Dave Strehlow, and Tom DeYries.
The field samples were collected from two commercial fishing vessels. Credit goes to the captain and crew of the M/V MiToi and
M/V Olympic. Two 24 hour sampling efforts at sea were made possible, because of the hard work of Chip Hogue, Wayne Laroche and Andy Rosenberg in May, and Wendy Gabriel, Mary Yokiavich,
Betsy Washington, Marc Willis and Andy Rosenberg in August.
Howard Jones and Jamie Trautman donated a great deal of time to help with polychaete and amphipod taxonomy. Dr. Robert Olson identified gut parasites, and provided interesting discussion on fish parasitology.
Dr. Andrew Carey and Howard Jones provided unpublished data from Moolack Beach box core samples. A number of close friends within the OSU Oceanography community, not previously mentioned, added to my graduate education experience, Joanne Laroche, Bruce Mundy, Joe and
Madeline Fisher, Bill Peterson, Dave Stein, Barb Dexter, Dena
Gadomski, Jim Harvey, Robin Brown, Denise Herzing, Rebecca
Simpkins, Rick Brodeur, Jon Shenker, John Kern, and John Kalish.
Dr. Charlie Miller, a good friend and exceptional teacher, greatly enriched my learning experience in the field of Biological
Oceanography.
Andy Rosenberg, and Chip and Barbry Hogue saw me through good and bad times, and I could not have completed this work without them.
To Clare, thanks for your loving support in these recent years.
To my parents, thanks for all that you have given me.
This research was sponsored by Oregon State University Sea
Grant College Program supported by NOAA, Office of Sea Grant. TABLE OF CONTENTS ThThOD1JCION. 1Page
SAMH.. ING AREA AND METHODS .3 Sampling Area and Program ...... 3 Laboratory Methods ...... 7 Data Presentation and Diet Overlap Index ...... 8
RESULTS ...... 11 Species Composition ...... 11 Bicimass ...... 15 Length Frequency ...... 17 Food Habits ...... 17 9 m Station ...... 23 22 m Station ...... 29 73 m Station ...... 34 SizeRelated Trends ...... 41 Diet Similarity ...... 45 Prey Availability ...... 51
DISCUSSION...... 57 Fish Assemblages ...... 57 Food Habits ...... 59 The Food Habits of Nearshore Benthic Fishes ...... 61 The Food Habits of Midshelf Benthic Fishes ...... 63 Trophic Relationships ...... 65 Concluding Remarks ...... 71
BIBLIOGRAPHY...... 73
APPENDICES ...... 78 LIST OF FIGURES
Figure Page
1 Trawl tracks for May and August 1979 4
2 Average percent composition by weight of trawl 16 catch at three depths off Moolack Beach
3 Frequency distribution of lengths for fishes 18 collected at the 9 m station during May 1979
4 Frequency distribution of lengths for fishes 19 collected at the 22 m station during May 1979
5 Frequency distribution of lengths for fishes 20 collected at the 73 m station during May 1979
6 Cumulative number of prey taxa as a function 22 of number of stcinach samples analyzed for fish species
7 Diagram of benthic food web in the nearshore 67 area off Moolack Beach, Oregon
8 Diagram of benthic food web in the 69 midcontinental shelf area off Moolack Beach, Oregon LIST OF TABLES
Tables Page
1 Trawl and catch information for May and August 6 1979
2 Summary of overall species composition and 12 ranking of 10 most numerically abundant fishes captured during May 1979
3 Summarization of the number of each fish 21 species examined, proportion of empty stanachs, and stcinach fullness by station
4 Average percent composition by weight of major 24 prey (weights of lower taxa summed) in the diets of fishes collected at the 9 m station off Moolack Beach, Oregon, May 1979
5 Percent frequency of occurrence (FO), and 26 average percent composition by weight (W) and numbers (#) of principal prey for pelagic and/or epifaunal feeding fishes collected at the 9 m station (May 1979)
6 Percent frequency of occurrence (FO), and 27 average percent composition by weight (W) and numbers (#) of principal prey for epifaunal and/or infaunal feeding fishes collected at the 9 m station (May 1979)
7 Average percent compositionbyweight of major 30 prey (weights of lower taxa summed) in the diets of fishes collected at the 22 m station off Moolack Beach, Oregon, May 1979
8 Percent frequency of occurrence (FO), and 31 average percent composition by weight (W) and numbers (#) of principal prey for pelagic and/or epifaunal feeding fishes collected at the 22 m station (May 1979)
9 Percent frequency of occurrence (FO), and 32 average percent composition by weight (W) and numbers (#) of principal prey for epifaunal and/or infawial feeding fishes collected at the 22 m station (May 1979)
10 Average percent composition by weight of major 35 prey (weights of lower taxa summed) in the diets of fishes collected at the 73 m station off Moolack Beach, Oregon, May 1979 11 Percent frequency of occurrence (FO), and 36 average percent composition by weight (W) and numbers (#) of principal prey for pelagic and/or epifaunal feeding fishes collected at the 73 m station (May 1979)
12 Percent frequency of occurrence (FO), and 39 average percent composition by weight (W) and numbers (#) of principal prey for epifaunal and/or infaunal feeding fishes collected at the 73 m station (May 1979)
13 Percent frequency of occurrence (FO), and 42 average percent composition by wet weight ('WT) of dominant prey in stcinachs of Psettichthys melanostictus less than or equal to and greater than 200 mm standard length (SL)
14 Percent frequency of occurrence (FO), and 44 average percent composition by wet weight (WT) of dominant prey and parasitic Trelatoda (Otodistomum velipoum) in stcinachs of Raia binoculata grouped into four length stanzas: standard length (SL mm)< 400 (193 398), 400 599, 600 799,> 800 (870 1320)
15 Percent frequency of occurrence (FO), and 46 average percent composition by wet weight (WT) of dominant prey in stcinachs of Eopsetta jordani less than and greater than 200 mm standard length (SL)
16 Similarity in the diets of eight species of 47 fish collected at the 9 m station based on percentage of major taxa in their diets on a wetweight basis, and on percentage of taxa identified to the lowest taxoncmiic unit (usually species)
17 Similarity in thediets of ten species of 48 fish collected atthe 22 m station based on percentage of major taxa in their diets on a wetweight basis,and on percentage of taxa identified to thelowest taxonxiic unit (usually species)
18 Similarity in the diets of eleven species of 49 fish collected at the 73 m station based on percentage of major taxa in their diets on a wetweight basis, and on percentage of taxa identified to the lowest taxoncinic unit (usually species) 19 Numerical abundance and average composition 52 of invertebrates in box core samples from 22 m station
20 Abundance of invertebrates and fishes in beam 54 trawis at the 22 m station off Moolack Beach on 2 and 29 May 1979 FEEDING RELATIONSHIPS WITHIN ASSEMBLAGES OF NEARSHORE
AND MIDCONTINENTAL SHELF BENTHIC FISHES OFF OREG(4
IN TR ODE cr ION
There is increasing interest in the field of fisheries to go beyond single species management and to consider entire fish assemblages in areas where mixed species fisheries predominate
(Gulland, 1977; Tyler, Gabriel and Overholtz, in press). On the basis of species composition, Gabriel (1983) identified seventeen regional fish assemblages for the mid to outercontinental shelf and upper slope along the west coast of the United States for the area extending from Cape Blanco, Oregon to Cape Flattery,
Washington. The Oregon groundfish fishery targets a number of different nearshore, mid and outer continental shelf assemblages that include mixtures of pleuronectiforms (flatfishes),
scorpaenids (rockfishes), and Anoplopoma fimbria (sablefish)
(Gabriel and Tyler, 1980). Eight major pleuronectid species are harvested off Oregon, accounting for over 40% of the annual trawl landings (Jackson, 1981). The group of pleuronectiform fishes was selected for studies of their ecology off Oregon by investigators involved in the project, "Pleuronectid Production System and its
Fishery", sponsored by Oregon State University Sea Grant.
Management of multispecies fisheries requires information on the biology of members of the assemblage, in particular, knowledge of potential interactions among all commercial and noncommercial fishes within a given assemblage. A first step is to describe the trophic structure of these fish assemblages. Three recent studies 2 have examined feeding relationships within pleuronectid assemblages on the mid and outer continental shelf off Oregon
(Kravitz et al., 1977; Pearcy and Hancock, 1978; and Gabriel and
Pearcy, 1981). However, they have not examined food habits of cooccurriung, nonpleuronectid fishes within the area studied.
In addition, little work has been done in nearshore, open coast areas off Oregon.
The objectives of this study were to:
1) characterize fish assemblages inhabiting a nearshore and
midshelf area off Oregon,
2) describe and compare the food habits of fishes belonging
to these assemblages,
3) identify potential pleuronectiform predators, and
4) construct a partial food web in an attempt to summarize
important fish feeding interactions on the continental
shelf.
I report here the results of this study, and summarize the knowledge of trophic relationships of fishes important commercially and ecologically on the Oregon continental shelf. 3
SAMPLING AREA AND METhODS
Sampling Area and Program
The study area lies off Moolack Beach on the central Oregon
Continental shelf (Figure 1). This site was one of several selected for studies by investigators involved in the project,
"Pleuronectid Production System and its Fishery". Previous work in the Moolack Beach nearshore has focused on recruitment, growth, and feeding ecology of juvenile pleuronectids in an open coast nursery ground (Jackson, 1981; Rosenberg, 1982; Hogue and Carey,
1982; and Krygier and Pearcy, unpubl. manuscr.).
Stations reported here were sampled in the nearshore at depths of 9 and 22 in,and at a midshelf depth of 73 in. The 9 and
22 m stations are separated bathymetrically by a rock reef that rises from a depth of 15into 6inbelow the sea surface and extends from Cape Foulweather to Yaquina Head. The sediments in this shelf area consist of fine sands that decrease in mean grain size offshore (Roush, 1970 and Kuhn et al.., 1975). A greater mud content at midshelf (50 70 in)is attributed to increased sedimentation of fines and bioturbation as evidenced by burrowing in the sediments (Kuhn et al., 1975).
Fishes were collected on two dates utilizing two types of commercial trawls. An Atlantic Western IVA otter trawl was fished from the dragger F/V Mi Toi on 20 May 1979. This trawl was constructed of 12.7 cm mesh (all mesh measurements are stretch mesh) in the belly and lower half of the wings, and 20.3 cm mesh in the square and upper half of the wings. A 29 mm mesh liner was I (Pau/wec//er / / L6Cm0
44°45 N4 (/11.! x N
440 4Q
ewp
I I I I i if /ILI. 124°15W 124°IO 124005
Figure 1.Trawl tracks for May and August 1979. sewn into the cod end to facilitate retention of juvenile fishes.
This 24 m foot rope trawl was assumed to have a 12 m spread
between the wings (assuming that spread equals 1/2 foot rope
length (Dennis Lodge, pers. comm.)). Rubber disc lower bridles
and hose wrapped tow lines increased the effective fishing width
by herding fishes into the trawl's path (Henunings, 1973; Main and
Sangster, 1981). Paired 27.4 m shrimp box trawls were fished from
the 25.9 m shrimper F/V Olympic on 6 August 1979. This shrimp
trawl was constructed of 38 mm mesh throughout the body and the
wings. A 29 mm mesh cod end liner was sewn into the cod end.
The 27.4 m foot rope was assumed to have an effective fishing
width of 13.7 m (again, assuming that spread equals 1/2 foot rope
length). The bridles and tow lines of a shrimp trawl are not
designed to herd fish as in an otter trawl. In addition, shrimp
trawls are not designed to fish on the bottom. For this reason,
chain ballast was added to the leadline so that it dragged along
the bottom.
On each sampling date, single tows were made during day and
night at each station. On 20 May a duplicate tow was made at the
22 m station to investigate tow to tow variability. Tow duration was 20 and 30 minutes in May and August, respectively. Loran C
position fixes at the beginning and end of each tow were used to measure relative distance covered during each tow. These
distances agreed with estimates based on tow times plus ship's
speed. Tow distances ranged from 1330 to 1590 m in May, and 620
to 1750 m in August (see Table 1 for a summary of trawling
information). Table 1. Trawl and catch information for May and August 1979. 9iri STATION 22m 73m AREATIME OFSAMPLED DAY (hrs) 1600 0333night 1324 day(1) 0048 y(2) night1852 1000 night2255 BIOMASSNO. FISH (g/10 m2) (m2) 19190 272 53 16710 147905 17953 641149 16890 672129 17110 475922 18520 2352 138 15970 586 41 AUGUSTTIME OF DAY (his) 0855 0358 1622 - 0040 1848 2210 TOTALAREA SAMPLEDBIOMASS (m2) (g/10 m2) 26820 33 16940 28 55040 7 -- 33880 11 35280 43 48000 57 7
The entire catch was sorted into baskets by species. The
catch of each species was counted (May only) and then weighed on a
45 kg capacity spring scale. A subsample of fishes less than 300
mm standard length (SL) was promptly preserved in 10% buffered
formalin at the time of capture. The coelom of fish greater than
150 mm were opened to enhance preservation of stomach contents.
The stomachs of most individuals greater than 300 mm (SL) were
removed at sea and preserved in buffered formalin. Each stomach
had a label which included information on tow number, species and
fish length.
Fish biomass estimates were calulated from catch weights
determined at sea, t distances, and estimates of the effective
fishing width of the trawls.
Laboratory Methods
Stomach contents were analyzed for the May cruise only.
Prior to laboratory examination, all fish subsamples were
transferred to 40% isopropyl alcohol. In the laboratory, fish were selected randomly from these subsamples and standard lengths were taken on a maximum of fifty fish. From these same fish,
stomach contents were examined (contents anterior to the pyloric valve). Stomachs were ranked according to fullness: empty, 1/3,
2/3, 3/3 full to distended. Food items were identified to species whenever possible, or when not possible, to the lowest taxa practical, and counted. In making counts on fragmented organisms, only fragments representing whole prey were counted; for example, polychaete heads, mysid telsons, ophiuroid discs, etc. As a measure of prey quantity, each prey taxon was grouped, blotted, and weighed to the nearest 0.01 g (wetpreserved weight) on a
Mettler balance. Prey that were too small to be weighed individually were assigned wetpreserved weights derived from weighing a number of similar sized individuals of the taxon in question. In many instances, stomachs contained prey fragments and well digested prey that could not be identified. This material was grouped together under the category of unidentified material, and weighed. The proportion of unidentified material is included at the bottom of each principal prey or complete diet summary table. Although wetweights for molluscs and echinoderms may overestimate nutritional value when compared to those for crustaceans and softbodied prey, no correction was attempted. A range for total length was taken for each invertebrate prey taxon for each fish stomach (carapace width for brachyurans). Standard lengths (SL) were taken on all fish prey.
Data Presentation and Diet Overlap Index
A diet summary table for each station was constructed by combining (summing) the wetweight percent composition of lower taxa under major taxonomic headings (usually class or order). In addition, the species composition of principal prey taxa (FO >
15%) in the diet of each fish species at each station was summarized as percent frequency of occurrence (FO), average percent wetpreserved weight, and average percent numeric abundance. A complete diet summary appears in the appendices. Percent similarity as a measure of dietary overlap was calculated using the index described by Whittaker (1952) (see also, Bray and Curtis, 1957) for predators A and B as:
percent similarity (PS) = l0Omin (at, b)
wherea1and bare the percent wetpreserved weight for the ith prey taxa in the diets of fish species A and B, respectively, and s is the total number of prey taxa in the diets of predators A and B. Percent similarity is a biased statistic, which tends to underestimate similarity.The bias decreases with increasing sample size and decreasing diversity of the population (Miller, 1970).Diet similarity was calculated in two ways:on the basis of comparisons made at the major taxa level (eg. polychaete, amphipod, etc.) and at the lowest taxonanic unit level (usually species). In calculating percent overlap, if some prey were only identified to higher taxonomic levels due to advanced state of digestion, then infOrmation on true proportions of different types of prey will be lost, and errors in percent overlap will result. This potential error was overcome by apportioning of the total wetpreserved weight contributed by the higher taxa prey among lowest taxoncinic units within that taxon.The weight contribution of these unidentified higher taxa was apportioned according to the relative weights of the lower taxa identified from stomachs of a given fish species on a sampling date.The following example illustrates how prey that could not be identified to lower 10 tazonanic levels was apportioned to lower taxonnic levels:
unapportioned apportioned %WT %WT
Polychaeta 22.5 Capitellidae 8.7 Spiochaetoiterus costarum 2.7 22.0 Cirratulidae 6.5 Chaetozone setosa 3.0 18.4 Nephtydae Nephtys sp. 3.2 6.2
total % 46.6 46.6 11
RESULTS
Species Composition
A total of 6350 fishes representing 34 species were collected in seven tows off Moolack Beach during May (only species composition by weight was taken for August). Average species richness (number of species) in collections at the 22 m station was higher (18.3) than at the 9 m or 73 m station (10.5 and 14.0, respectively) (Table 2).
The ranks of the 10 most numerous fishes captured in each tow during May (Table 2) show that Psettichthys melanostictus (sand sole), was usually numerically dominant at the two nearshore stations, where it comprised 50 and 30 % (daynight average) of the 9 and 22 m catch, respectively. Raia binoculata (big skate), was also abundant, composing 18 and 15 % of the catch at the 9 and
22 m stations. Isopsetta isolepis (butter sole), ranked secondor third at 9 and 22 m. Catch of Microgadus proximus (Pacific tcincod), ranked first in abundance in the nighttime tow at 9 m, but was less abundant in other tows. Platichthys stellatus
(starry flounder) and Hydrolag colliei (ratfish), were also common in collections from the nearshore area. Of the additional species captured at the 22 m station, two flatfishes, C. stigmaeus and P. vetulus, and the osmerid, A. elongatus were common.
At the 73 m midshelf station, Citharichthys sordidus
(Pacific sanddab), ranked first in abundance, comprising 65 % of the total catch. Microstomus pacificus (Dover sole), I. isolepis,
Parophrys vetulus (English sole), Eopsetta jordani (petrale sole), 12
Table 2. Summary of overall species composition andranking of the 10 most numerically abundant fishes captured during May 1979(""indicates presence,"-"indicates absence). Table 2 Station 73 m Isop8ett.a isopelia Species 2 3 day (1) 2 day (2) 2 ng 2 3 night 3 Raja binoculata butter sole 4 1 3 1 Microgadus proximus Pacificbig skate tomcod - 8 +9 3 8+ 89 ParophrysI'settichthys vetulus melanostictus sand sole 9 1 92 61 81 64 2 7 Citharichthys sordidus PacificEnglish sanddab sole - - - - - 1 1 Hydrolagus colliei ratfish 8- -5 5 - 4 - 5 - 10 EopseMicrotomus t ta jordani pacificus Dover sole - - - - - 4 5 2 Glyptocephalus zachirue petrale sole - - - - - 4 Lepidop8etta bilineata rex sole - - + + + 76 56 rock sole - - - Citharichthys otigmaeus speckled sanddab 3 6 74 3 - Platiiohthys stellatus starry flounder 5 + 9 57 +8 - + Spirinchus starksi night smelt - - - 6 - - + OphiodonAllosmerus elonatus elongatus white bait smelt - - + - - 9 - Pleuronichthys decurrens lingcodcurlfin sole - - - - + + () Table 2 cont'd. Station 22 m 73 m llhlrPPTrO8OpOfl anale spotfin surtperch 6 gin 8 day ifi 10 !y_tI+ !j& +. night kija ,hin,i a k!ai d' I longsandpaper nose skate skate 10 4 + ScorpaenichthysOcella verrucosa ,nannoratus cabezonwarty poacher -7 10 7 + + + AnaPrhichthysSte henna xyoeterna ace ihatus wolf-eelpricklebreast poacher 10 - + 10 + 7 MerlucciusLeptocottus productus an7r tus Pacificstaghorn hake culp1n + + 9+ Be! as tea mebanopa black rockfish - - I0 !'ollaina barbata tubenose poacher + - + L)nbiotocaLyopsetta laterahis exiZs stripedslender surfperchsole - - + KnophrysHexaqramua bison deoagz'an,nua buffalokelp greenling sculpin - - - + + LipanisSpirinchus pubchehlus thaleiohthys showynight smelt snailfish - - + + II 15 and Glyptocephalus zachirus (rex sole), ranked second through sixth, respectively.
Biomass
Estimates of total biomass are listed in Table 1 for May and
August tows. Figure 2 stmimarizes the species composition in terms of weight. Total fish biomass ranged from 41 475 and 7 57 g/1O m2 among the tows for May and August, respectively. Herding by tow lines and bridles may cause an overestimate of biomass
(Main and Sangster, 1981). Conversely, trawl avoidance by fish would cause underestimation of biomass. Sector scanning sonar studies of otter trawl avoidance have shown the probability of capture for Pleuronectes platessa, plaice, located between the doors, to be about 0.5 (Harden Jones, 1974). Therefore, the biases caused by herding and avoidance may tend to offset each other. The large differences between May and August could be attributed to the gear change between those two months, or to displacement of fish by large concentrations of the medusae,
Chrysaora fusescens which were encountered at 9 and 22m during
August.
Raja binoculata dominated fish biomass at the 9 and 22 m stations, composing an average of 33% of the biomass (Figure 2).
Psettichthys melanostictus and P. stellatus were also important by weight at these stations (12 26% of biomass, respectively).
Isopsetta isolepis composed 34% of the 22 m station catch.
Citharichthys sordidus was dominant by weight as well as number at the 73 m station, composing an average of 54% of the catch (range 16
9mSTATION 22m STATION 73m STATION
Iscpsettc tJ ,So/eo,s I * Rcjc b,nocu/ctc I
M,croqradus prox/mus
Pserficnrnys ' rne/onost,CtuS
Poroplrys C vetu/us * / CrnoricM/'ys I sord,dus
41,croslomus pacificus
jordofl
Glyptoceotlo/us zocfl,,vs
LepI/240settc 41/'neolc
Ctflorrcht/iys st/qmoeus * =75 Ii C
0her
20 40 20 40 0 20 40 60 AVERAGE%COMPOSITION OFCATCH
Figure 2. Average percent composition by weight of trawl catch at three depths off Moolack Beach (hatched area = May, open area = August,* = present at <2% of total of fish catch of a tow). 17
31 71%). The proportion of total catch contributed
individually by P. vetulus, 6. zachirus, M. pacificus, and E.
Jordani averaged only 6 7%.
Length Frequency
Length frequency distributions for fish species common in May
collections and those examined for stomach contents are shown in
Figures 3, 4 and 5 for each station.
Food Habits
The number of each species of fish examined, proportion of
empty stomachs, and stomach fullness are summarized by station in
Table 3 for the May cruise. Of the 714 fish stomachs examined,
16.5% were empty. The amount of food material that could not be
identified because of its advanced state of digestion ranged from
0 71.6% by weight of the total stomach contents for most fishes.
Two species had a relatively high proportion of unidentifiable
stomach contents: H. colliei (9 m sta., 71.6%; 22 m sta., 54.0%)
and C. sordidus (73 m sta., 47.4%). This information is listed
at the bottom of each principal prey table and the bottom of each
summary table in the appendices.
Cumulative prey curves were constructed to investigate diet
diversity and whether a sufficient number of stomachs was examined
to identify the principal prey spectrum (Cailliet, 1977). For
common predator species at each station, cumulative number of prey
is plotted against number of fish stomachs examined (taken randomly) (Figure 6). In general, curves for all predators were P/otichThys ste/Ictus
i: 5
0 Psettic/ithys Hydrolaqus co/i/el rne/cnostictus 0I Roja /nocu/ctcnight
:
Re/c binocu/oto day
2; STANDARD LENGTH (mm)
Figure 3. Frequency distribution of lengths for fishes collected at the 9 m station during May 1979. Hatched area represents the distribution of lengths for fishes used in stcinach content analysis (the maximum number shown for each size group represents the sum of fishes measured). 19
Cifhcrichlhys Sp/r'nc/nis A //osmerus Mlcroqoo'us 40 s/iqmceus s/C,ksl elongotus prOxrn7l/S 3J
I V I
0' "
P/atichrnys /sopsetto I$/4IS 0 steiotuS
o, Psetticflt/'ys Pcropflrys /flC/0fl05//CIU5 yeW/us 0 1 gin_rE
/ ' 'p 1.0' t' P' 1.0'
Hjdro/ogus coil/el
: I
Rap b/noculo/o day
0 45 ,49 1.' , 0 ' . P P c STANDARD LENGTH (mm)
Figure 4. Frequency distribution of lengths for fishes collected at the 22 m station during May 1979. Hatched area represents the distribution of lengths for fishes used in stcinach content analysis (the maximum number shown for eachsize group represents the sum of fishes measured). Is onset/c Op/'iodon elon go/us 20
10
0 L
Pcrophrys Ci/horichthys ye/u/us sordidzis I0 j
/
0 Micros/ornus Eopse/tc jOrdQfli
11.1
20 G/yptocep/clus Lep/dopsetta
zchirus 1 A 0 c STANDARD LENGTH (mm)
Figure 5. Frequency distribution of lengths for fishes collected at the 73 m station during May 1979. Hatched area represents the distribution of lengths for fishes used in stxiach content analysis (the maximum number shown for each size group represents the sum of fishes measured). Table 3. emptySummarization stomachs, of and the stomach number fullnessof each fishby station. species examined, proportion of aminedN ex- Empty9m % STATION 1/3 Stomach Fullness 213 3/3 amlnedN ex Empty22m % STATION1/3Stomach Fullness 2/3 3/3 aminedN ex- Empty73in % STATION1/3 Stomach Fullness RajubinoculataRaja kino.aidii (22) 13 0 (0.0) 0.0 (22.7) (77.3) 0.0- 46.1 - 53.9(0.0) - (35) 29 0 (11.4) -0.0 (25.7) 37.9 - (42.9) (20.0)44.8 - 17.3 - 23 0.0 0.0 50.0t,6.1 2/3 _f 50.033.3 Hyh'olagu8Raja rhina aolliei (12) 0 (0.0) - (83.3) (16.7) - - (0.0) - 16 0 0.0- 87.4 - 12.6 - 0.0- 04 0.0- -0.0 1,0.0 - 50.0 - b'pirinchuoAIioa,nerua at.arkojelongates 60 0.0- 66.7 - 33.3 - 0.0- 5033 60.634.0 28.024.3 12.0 9.1 26.0 6.0 0 - - - - MiarogadmmsNyperprosopon proximus anale (5) 3 (0.0)0.0 100.0 (7.4) (100.0) 0.0 (0.0) 0.0 19 0 21,0 - 47,4 15,8 - 15,8 - 0 - - - - StellerinuxyosternaSoorpueniohthys mmn'n,ozutus (3) 2 0.0 0.0 (66.7) 0.0 100.0(33.3) 5 1 0.0 40.0 0.0 100.0 40.0 10.0 0.0 0 - - - - - CithuriohthyaOphiodon elongates sordi4ua 0 - - - - 0 - - - - - 51 5 23.520.0 33.320.0 47.1 0.0 60.015.7 EopaettaCztharm.chthys jardani stgmv.wua 0 - - - - - 33 0 -6.1 3.0- 51.5 - 39.4 - 33 0 12.1 - 21.2 - 39.4 - - laopaett.aGlyptocephaius isolepia aaohirua 13 0 23.0 - 38.5 - 38.5 - 0.0- 33 0 30.3 - 27.3 - 33.3 9.1- 3237 9.10.0 31.310.8 31.343.2 28.027.346.0 Miapostomu,Lepidopsetta j,aaiJicus bilineata 0 ------0 - - - - - 2729 11.1 6.9 25.917.2 51.944.8 11.131.0 PlmtihthysPu'ophrys stellatua vetulua 20 0 60.0 - 0.0- 20.0 - 20.0 - 14(5)16 28.6(0.0) 6.3 42.9(0.0) 6.3 (20.0) 21.4 0.0 (80.0) 87.5 7.1 35 0 -2.9 14.3 - 74.3 - -3.6 PsettichthymmPleuronohthya melanom,ti,tua decurrenaTOTAL 138 39 0 25.6 - 38.5 - 15.4 - 20.5 - 313 30 0 36.7 - 16.7 - 20.0 - 26.6 - 263 05 -0.0 0.0- -0.0 100.0 - [:17:1 72 50
40
30
. 20-i x ,Pstel
l0 Ls::ISiIs9 P mel. > uJ 0
0 22m. 22m. 20 M prox P
eta C. Sn g
elan ': z
73m. 73 vet LiJ 60
I- 50
J zac /0 40
(-) 30 pa c C ear
E or
01
0 0 20 30 40 0 0 20 30 40
NUMBEROF FISH
Figure 6. Cumulative number of prey taxa as a function of number of stomach samples analyzed for each fish species (A. elon.= A. elongatus, C.sor. = C. sordidus, C.stig. =
. stigmaeus, E. jor. = . jordani, G. zac. = . zachirus, H. col. = H. colliei I.iso. = I. isolepis, L. bi. = L. bilineata, M.prox. = It!. proximus, M. pac. = M. pacificus, P. vet. = P. vetulus, P. mel. = P. melanostictus, R. bi.= K. binoculata, S.star. = Spirinchus starksi). 23
asymptotic, with the exception of . isolepis and P. stellatus at the 9 m station, and G. zachirus and L. bilineata at the 73 m
station, indicating that in most cases the number of stomachs examined was adequate to include the principal prey.
Shape and height of cumulative prey curves may yield some information on feeding habits. A steep curve rising to a high asymptote implies a great diversity in individual diets. In the case of P. vetulus, 50 60 unique prey were encountered from only
8 12 stomachs. A curve gradually increasing to a high asymptote implies a broad diet with lower diversity in individual stomachs
(suggesting greater selectivity) (eg. G. zachirus and L. bilineata). In contrast, R. binoculata, P. melanostictus,
Citharichthys stigmaeus (speckled sanddab), Allosmerus elongatus
(whitebait smelt), and Spirinchus starksi (night smelt) reached a low asymptote (< 10 prey) after 5 10 stomachs, indicating a low diet diversity. The remaining species were intermediate, requiring about 20 stomachs to reach an asymptote.
In the following three sections, food habits data will be presented for fish species collected at each station. The results will begin with a generalized station by station description of major prey types followed by specific details for major prey species.
9 rn Station
The average percent composition of major prey taxa in the diets of fishes collected at the 9 m station are presented in
Table 4. Two general feeding types can be recognized: pelagic and/or epifaunal feeders, and epifaunal and/or infaunal feeders. Table 4. AverageOregon,summed) Mayinpercent 1979the diets of composition("0" by = numberfishes of stomachs weightcollected of major at prey the 9 mexamined). stationtaxa (weights off Moolack Beach, of lower taxa
< 4 0 .çP ' /;.. . I0I.Y('IlAlTA 28.7 0.2 .1 0.0 day 0.0 night 0.0 0.7 0 0.0 3.2 .'< '1' MYSl0Al1APII.ECYI'()1)AM01,1.LISCA SIPhON 0.1)0.00.0 <0.145.2 0.1 0.00.11.5 0.00.0 0.10.02.7 10.8 0.50.0 48.3 0.0 40.4 0.07.4 77.6 0.0 i Psettichthys melanostictus, M. proximus and S. starksi fed mainly on pelagic mysids representing over 40% of the diet; decapods and fishes were also important. Epifaunal and for infaunal feeders included R. binoculata, H. colliei, Scorpaenichthys marmoratus . (cabezon), . isolepis and stellatus. This second group of fishes preyed upon a broad spectrum of epifauna and infauna including polychaetes, molluscs, amphipods, decapods, Dendraster excentricus (sanddollar) and fishes. More detailed information on species composition of principal prey (FO > 15%) in diets of fishes are summarized by feeding type of the predator (e.g. pelagic and/or epifaunal) in Tables 5 and 6. The group of pelagic feeding fishes fed on five mysid species, but one, Neomysis kadiakensis, was most important (Table 5). Additional common prey of M. proximus were surface tube dwelling amphipods and small Crangon (< 40mm). Crab zoea were common in the stomachs of . starksi. A detailed description of the diet of P. melanostictus will be presented in a section on size related changes in diet. Stomachs of a few smaller fishes, less common in commercial trawl catches, were examined: the agonid, Ocella verrucosa, and embiotocid, Hyperprosopon anale both had mysids, particularly Neomysis kadiakensis, as a major dietary component (50 100%). Raja binoculata and . colliei fed largely on Crangon stylirotris, a sand shrimp (20 50 mm TL) and Cancer magister, Dungeness crab (20 - 50 mm) (Table 6). Crangon stylirostris occurred in > 95% of R. binoculata stomachs. One fish, Ammodytes hexapterus (sand lance) was a common prey of R. binoculata (FO = Table 5. Percentfishes(W) and frequency collectednumbers (1/) ofat occurrence theof principal9 m station (FO), prey (Mayand for average1979). pelagic percent and/or compositionepifaunal feeding by weight melanostsand sole ictus 1. tijh thy pPosunusMicioadiPacific tomcod Spirinchiw SF0 SW %# SF0 SW St - SF0night smelt tcirksi SW St GastropodaPolychaeta Olit',ZIa sp. 20.0 7.43.2 1.4 Mysidacea Aa?zOimy$Aintho,rsi1 Dendraster excentricus (sanddollars) (2 25 mm test diameter), and amphipods of the species Ampelisca agassizi and Atylus tridens. In a small sample of three S. marmoratus, Cancer magister were observed to be a major prey (61%) (Table 6). 22 m Station Psettichthys melanostictus, C. stigmaeus, M. proximus, S. starksi, and A. elongatus fed primarily on pelagic and/or epibenthic crustacea. As in the case of the 9 m station, pelagic mysids were the major prey, representing over 50% of the diet by weight and number (Table 7). Neomysis kadiakensis comprised over 70 and 85% of P. melanostictus and C. stigmaeus diets (Table 8). In contrast, M. proximus fed on three different mysids in more even proportions (Table 7). Two . stigmaeus had eaten recently settled I. isolepis (19 20 mm) (Appendix III). Raja binoculata and H. colliei were two common epifaunal predators at 22 m. They fed on Crangon stylirostris (20 50 mm) and on Cancer magister sp.(20 50 mm) (Table 9). In addition to Ammodytes hexapterus (a common prey of Raja at 9 m), the flatfish, C. stigmaeus was also important. When C. stigmaeus occurred in skate stomachs, it was common to find 10 20 individuals ranging in size from 30 50 mm. Three flatfishes were characterized by epibenthic and/or infaunal feeding at the 22 m station (Table 7). Parophrys had a diverse diet, feeding primarily on infaunal polychaetes, Table 7. Oregon,Averagesummed) percentMay in 1919the composition diets("0" =of numberfishes by weight ofcollected stomachs of major at examined). the 22 prey taxa (weights of lower taxa m station off Moolack Beach, ') 43 Q Ql: b ' day ni yht z, NEII ME RI INEA )l,Y( Ii AEI'A 20.923.8 0.77.6 0.711.3 0.0 0.0 0.04.1 0.0 0.01.5 $ 0.01.4 0.00.0 0.0 AMPIIP13W)I,ILJSCA .E( I YP0l)A l'()I)A S I PIION 23.8 5.01.9 11.110.1 3.7 12.9 0.00.3 0.00.2 0.90.01.0 25.312.5 1.1 0.0 0.30.0 15.5 0.0 0.00.0 0.50.0 (IJMA(MIS I'EA SUPUIIAI l)A('lA 0.11.99.5 2.90.82.2 0.10.00.3 0.10.0 0.00.25.0 0.90.11.5 72.4 0.0 86.8 0.00.4 5(1.6 0.00.0 50.0 0.00.0 84.5 (1,00.0 I0:(AIUI)Al)l.(AI'OI)AI ON )I( ASIE l.ALIVAE II 8.41.7 21.418.7 9.6 32.244.7 8.4 76.8 0.0 73.2 0.0 47.3 0.0 0.0 0.00.1 10(118.1 0.0 (1.00.0 (1(70.0 (YFIIObTL 1:11 ICIITIIY 1S 0.00.31.? 4.86.3 0.0 22.7 0.0 19.6 0.0 13.20.0 27.5 0.00.1 0.03.11.8 0.04.4 23.816.7 1.2 11.8 0.0:1.2 0 Table 8. Percentfishes(W) and frequencycollected numbers ofat(//) occurrencethe of 22principal m station (FO), and(May 1979). prey for pelagic and/or epifaunal feeding average percent composition by weight PB t tt(th thy8 Ci thai'ichlhya Micro yadus Al los,ntius Spiiinqhus Nysidacea SF0melc4nostictuasand sole SW SI speckledatijmcieusSF0 sanddab SW 50510 proxsmusPacific tc'mcod SW 50 whitebaitSF0elon.qatus snielt SW SI SF0night smelttarksi SW SI .4cinth.e!iaAcant1iiqsiaMysldae Lwii 85.0 1(1.1 /3.5 100.0 85.8 13.3 40.066.126.133.3 22.312.36.35.8 10.142.5 5.04 9 50.0 50.0 50.0 26.5/3.5 62.910.4 59.114.6 Decapoda ?&o.,yoinNconyaie kiliiknaie zyii 20.0 18.1 14.4 20.1 8.5 9.0 Osteichth3les PaguridaePorcellanidaeBracIyura(vinqo,I etyiiIoatkia megalops zoea 30.0 22.4 17.4 41.9 3.0 19.2 20.0 2.2 1.5 16.116./ 16.7 8.8 16.1 9.4 UnidentifiedOther material 1.61.5 9.1 18.211.2 7.5 18.233.0 21.0 24.5 0.0 23.9 18.2 6.0 17.3 Table 9. fishesPercent(W) and collected frequency numbers at (#)of the occurrenceof 22principal m station (FO), prey (May and for 1979).average epifaunal percent and/or composition infaunal feedingby weight P(wophra110English sole SW SF0 lcpa.tbutter soletJoZ)i.Li SW SF0P1starry.Jtellutu8 flounder t ih thyt SW SF0 SWJay &i.Ja binoiu lz tci bl 9 5 a e kSF0 t night SW Hydzoratfish lujiw SW Polychaeta 60.0 0.10.8 3.7SI - II Ia XI 11510 It N.phtyaGlyaindeGlyindaCha.tozon, as,niwru piata ,.toaait'na eaculdta ap.sp. 20.066.760.046.7 '0.1 0.50.13.00.3 0.30.23.217 20.0 0.1 0.1 Spijh.uwaflalu,w.,aaEt.oneAnitid.aOrbIniIdaeNreia bombyx spino&l bp. sp. 93.375.340.020.046.7 11.7 5.90.1 12.3 1.80.60.50.8 PelecypodaGas tropoda OjjpoLLi sp. 46.753.0 3.50.1 0.50.8 20.0 0.1 1.4 Hysldacea TellInIdaeSiIiqiJPelecypoda sIphon patul4 26.1 1.1 0.3 20.0 0.2 2.0 26.0 25.3 6.4 Cianacea N..c.nVaiaAohaonyuiMysldae Icadjak.en,ja zbnitakii 53.346.7 0.41.4 0.41.7 15.020.0 0.52.0 4.22.6 20.020.0 0.1 1.30.4 44.916.7 3.60.7 8.86.4 26.7 1.4 9.4 1ioiilaripiopaDist1opa&aOistgjliaAnüiiocotorus ep. Juijooni ap. 60.080.026.793.0 2.32.08.44.6 6.60.36.43.3 16.0 0.2 2.2 Isopoda J/Hi,iut.a biouupida 18.8 0.9 2.1 tJ Table 9 cont'd. Parophrya Iaopaetta Piatichthya Raja binoculata Iiydrclagua Aiiiphlpoda SF0Englishvetuiva sole SW SI SF0 butteriaoiepi.a sole SM SI 510starryatellatua flounder SW SI 510 day SW bi SI skate SF0 night SW SI SF0ooflz.ei.ratfish SW SI .4qeliaeaAn5,oli,aGaRmlarldea&,llauatoriud niarocBphataajaaaiai ae,ajllu 66.793.3 8.82.41.2 10.010.5 3.0 36.0 0.97.0 8.13.0 20.030.0 12.4 0.1 11.4 1.4 20.0 1.0 3.4 konou1odeePhotial'hotiaSy.wheiidiwi apinipe8 breulpea p. aFio.ni&ri 47.186.720.033.3 0.20.11.5 1.20.20.53.7 RhepuxynivakhepoxyniwakindibulophoxuaFoxiphaluaPhoxocephafldae epzatomua ui9itthJu UflijQt8tfl4tUd l,tu3ideflS 80.0 0.60.26.9 2.41.41.73.1 15.0 2.5 1.8 Oecapoda CwuevnegioterCaunJon atylix.oatria 33.320.0 1.00.6 0.50.4 20.0 17.0 11.5 20.0 1.3 0.4 62.115.9 32.143.1 14.246.3 62.0/2.4 29.144.0 18.834.5 66.1 25.6 36.2 PorcelianldaePorcellenldaePlnnotheridaePlniiother$daePtnnotherldae megalopsmeyaiopszoea bee 46.720.033.3 '0.1 0.1 0.60.10.5 20.0 9.4 12.9 30.060.020.0 14.3 9.32.10.11.1 21.021.4 2.61.65.4 Echinodermata L)enfratazPagutidae megaiops exoentriaua 80.0 8.4 3.6 46.0 18.7 14.9 40.030.0 44.1 6.4 22.6 2.7 HeaierteaOphluroldea 93.380.0 20.9 1.1 1.5 - 30.0 4.8 4.3 - 20.0 0.7 - Osteichthyes Citharichthpa ati0ewua odyta hex pterua 44.821.611.2 17.3 3.91.0 22.3 7.42.6 30.023.3 11.7 2.1 13.6 2.4 UnidentifIedOther materIal 19.9 5.9 6.5 37.0 4.2 28.5 ii0.1 4.3 14.7 3.6 9.8 9.68.8 15.5 54.045.9 42.6 amphipods, nemerteans, and cumaceans (Table 9). Frequency of occurrence was high (< 60%) for most principal prey, indicating that each stomach contained many prey taxa (average across all prey taza = 22 taxa/stoinach). The polychaete, Si,ioihanes bombyx and amphipods, Ampelisca and Eohaustorius were particularly important by weight. Isopsetta isolepis had a diet similar to P. vetulus, but included more epifaunal prey (Crangon and Cancer), and fewer infaunal polychaetes and amphipods. Platichthys stellatus fed on decapod larvae and small sanddollars (Dendraster excentricus) which were found intact along the length of its tubular gut. Bivalve siphons (Siligua patula), an important food of P. stellatus at 9 m, were not observed in stomachs of fish collected at 22 in. However, large Siligua appeared to inhabit the 22 m station area, because whole individuals were commonly observed in stomachs of H. colliei (Table 9). 73 m Station Diets for the midshelf (73 in)fishes are summarized by major prey taxa in Table 10. Two flatfishes, E.jordani and C. sordidus fed both on and above the substrate. Citharichthys sordidus had the most pelagic food habits of any fish collected at the 73in station. Its prey included: the pelagic mysid, Caesaromysis vanclevei, the pteropod Limacina, copepods, hyperiid amphipods, the euphausiid Thysanoessa spinifera, salps, and chaetognaths (Table 11) . In addition, . sordidus consumed a recently settled flatfish, I. isolepis. Principal prey of E. jordani included juvenile pleuronectiform fishes, Crangon alaskensis, and the mysid, Acanthomysis sculpta (Table 10 and 11). A more detailed Table 10. Oregon,Averagesummed) percentMay in 1979the composition diets("0" =of numberfishes by weight ofcollected stinachs of major at examined). the prey 73 taxam station (weights off ofMoolack lower Beach, taxa J -' .' '4fr ,J' '4 F,,. I'Ol,YCIIAI!lA 86.2 20.4 21.3 \?J 7.5 17.0 100.0 0.0 '0.1 0.0 0.0 I 0.0 (iAIIIIAIIOII)EA1)ASTh0I'ODAPEI.ECYI'01)A 15.2 2.06.4 26.5 1.67.0 36.0 0.02.1 9.30.01.3 19.1 0.0 0.0 '0.1 0.0 0.00.21.9 0.00.1 0.0 0.0 UY8I1)ACACUMACEAIi01'00A '0.110.0 1.0 0.08.91.7 0.36.71.5 3.91.11.4 2.00.07.6 0.0 10.40.0 14.7'0.1 1.5 0.00.0 0.00.0 00.0 00.0 clayECIIINOIIEIII4ATAA3CII)KACEA PEI.l.E'3 2.40.32.2 24.5 0.00.4 0.601.5 1 0.0 14.4 0.02.2 0.0 0.0 0.0 0.0 0.0 0.0 C01EI'0I)AIlYPI11IJEAI'II310I01)A 0.00.3 0.40.00.0 0.00.01.2 0.00.0 0.00.1 0.0 0.00.0 10.44 7.43.9 0.00.0 0.00.0 0.0 0ECAI00AELJPHAIJSIACEAAl.I'A 0.02.8 5.80.0 25.4 0.0 46.8 0.0 31.0 0.0 0.0 111.6 0.0 1(1.2 9,35 8 25.6 (1.00.0 0.02.2 0.0 OSTEIC(1T(1(ESCI4AEi0t,NAlIIA 0.0 0.0 01)0.02.1) 0.0 0.03.7 0.00.0 '14.3 0.0 19.6 5.0 14.30.0 97.8 0.0 400.0 0.0 (1441134 2.2 5.9 I .1) (.9 2.9 0.0 1.7 44.0 0.0 0.0 UI) Ui('3 Table 11. Percentfishes(W) and collected frequency numbers at (#)of the occurrenceof 73principal m station (FO), prey (May and for 1979).average pelagic percent and/or compositionepifaunal feeding by weight 1'ops t ta Ci than ch thy2 Raja kaja ii kaja Oplu udon Polychaeta SF0jordanipetrale sole SW S SF0Pacific sanddabordidus SW St SF0binocubig skateiota SW St SF0sandpaperk in cajd skate SW St SF0 rhinolongnose skate SW St SF0elongallngcod tuu SW St CopepodaGas tropoda L,injaain sp. 38.5 10.8 12.2 33.3 0.1 26.7 Mysidacea (lParny53a 1,nua ' lwnchpua t)u,wlevei 25.638. 5 13.8 6.7 18.8 9.5 Aitiph lpooa Ilyperidea4wtharnyai; ne1hro;hraialrna 51.7 10.4 29.8 15.4 2.10.9 3.6 100.0 0.3 11.5 DecapodaEuphus1 iacea 1J,ynocau tqinifera 20.5 16.2 12.3 (ran;on( Za1JOfl a 1 ha alaBkn8i8sp. 51.7 14.7 15.3 33.3 0.7 7.7 100.0 100.0 50.0 25.819.8 7.8 15.639.6 3.1 50.0 1.7 18.0 iiPa9ur idae a c hyu raaIIfl I/ it,is 33.3 0.23.2 12.82.67.7 50.0 7.8 3.1 25.0 <0.1 0.4 1.3 ChaetounathaSalpa P(.i'i, nnotheridae ,,szjis taz 20.5 5.09.2 5.93.7 21.6 50.0 4.7 4.2 Osteichthyes Agonidae ,a jirnbia 17.2 5.8 7.8 33.3 35.735.4 2.8 33.3 2.62.2 75.0 46.3 41.6 75.0 15.0 75.0 m(a Table 11 cont'd. FJopsetta Citharichthys Raja Raja Raja Ophiodon SF0jordanipetrale sole SW SI SF0 Pacificsordidus sanddab SW SI SF0 binoculatabig skate SW SI SF0sandpaperkincaidii skate SW SI SF0 longnoserhina skate. llngcod SW SI SF0 elongatus SW SI MicronGlyjCi laopmettaO:ii toc(qhaP1 tof,rus euroneti lam pacificumisolepia machiram formes lh.ar nordilun 17.320.724.1 12.913.217.212.7 10.5 6.36.87.8 16.0 8.9 3.8 33.3 0.20.1 2.2 100.0 33.8 22.9 25.050.0 20.825.4 4.21.2 19.7 1.36.39.7 25.0 20.8 4.2 14.310.7 UnidentifiedOther material 10.813.1 16.0 47.426.4 26.6 7.80.0 0.0 20.6 0.0 0.0 9.50.0 0.0 0.0 0.0 -4 38 description of the diet of E.iordani appears in the section entitled: "Sizerelated Trends". A few individuals of three skate species were captured at the 73 m station. Small Raja kincaidii, sandpaper skate, preyed on crangonid shrimp and juvenile C. sordidus (Table 11). Fish comprised the majority of the diet of two larger skates, Raja rhina, longnose skate, and R. binoculata. Raja rhina fed on C. sordidus, G. zachirus and I. isolepis. One large . binoculata (1300 mm) had eaten a 450 mm Anoplopoma fimbria (sablefish), plus two large pleuronectiforms. Ophiodon elongatus, iingcod, fed exclusively on fishes. With the exception of C. sordidus, most Ophiodon prey were in an advanced state of digestion, and therefore, unidentifiable (Table 11). Six species of flatfishes at this station had fed on both epifauna and infauna (Table 10). Four of them, Parophrys vetulus, M. pacificus, G. zachirus and I. isolepis, fed in varying degrees primarily on inlaunal polychaetes and amphipods. A small sample size of stomachs from a fifth, Pleuronichthys decurrens (curlfin sole), contained just the onuphiid polychaete, Nothria irridescens (Table 12). Dietary differences among these four species are clear. Polychaetes were more important in the diet of P. vetulus on a weight basis than in the diets of the other three pleuronectids (56% vs. 17 21%), and P. vetulus fed on a more diverse assemblage of polychaetes (28 taxa vs. 7 14). Cumaceans were also more common in the diet of P. vetulus than in those of the other fishes. Prolate spheroid and spheroid clay Table 12. Percentfishes(W) and collected atnumbersfrequency of occurrence (FO), (/1) ofthe principal 73 m station (May prey forand 1979).averageepifaunal and/or infaunal feeding percent composition by weight vetuZuPai'ohrgEnglish sole pacifiouMicrostomwDover sole zachirusG1yptocepha1urex sole bilineatarockLepidopsetta sole Ibopettaiaolepi8butter sole decurrenaPleuronichthyscurlfin sole 71.49109W 25.1 91 - 91037.5 SW15.6 SI - 35.1SF0 6.4SW SI - 21.9SF0 2.59W SI - SF013.8 4.6SW SI - 50.0910 SW2.1 SI Polychaeta ChaetopteridaeCapitellidae 20.040.017.1 1.01.62.7 6.11.8 11.2 3.4 5.5 Spiu.:etopt'.ew(JkwMa1dnidaeNqty2GlL sp. cotaeu,n town wmijera s tosc 51. 1 45.731.4 2. 12.30.51.6 7.96.51.21.4 18.9 2.1 1.6 Terebellidae.lnaitida,T,','iijia[Wit h,, a j ii desc,ens sp. jiyasp. 25.717.1 12.52.0 1.51.9 20.8 0.8 4.5 18.5 3.0 3.0 100.0 97.9 100.0 G2 s tropoda OlioeilaC5,lichnaiit1 sp. 51.4 4.2 4.8 16.7 6.3 3.6 24.3 2.0 2.3 CopepodaPel ecypoda AetediwB pacificu 17.3 0.3 1.6 35.1 1.2 6.4 Mysidacea Aeanthomysia nephrophChalrna . 48.2 1.1 9.5 CuijiaceaIsopoda IIcmila'npvupa sp. 51.417.1 8.40.2 12.6 1.1 29.2 1.7 5.7 18.9 0.4 3.6 25.9 0.2 4.4 Aisphi poda :;/i1,t1 ep. 33.4 5.5 8.3 29.7 6.4 3.9 17.2 7.0 4.1 A,reliaGai,inaridea na'o,e1ha1a aJ,auiui 62.917.1 4.80.40.6 8.00.91.1 29.2 1.9 5.5 81.116.227.0 13.1 Li0.9 15.7 1.23.5 66.118.5 8.10.2 16.2 2.2 31.020.1 8.91.9 11.88.1 Table 12 cont'd. Parophry8 Mioroatomus Glyptocephalus Lepidopsetta Iaopaetta Pieuronichthya ye tuSF0English lus sole SW SI SF0 Doverpacificue sole SW SF0zachirex rue sole SW SF0rockhi iinea sole ta SW SF0 butter1.80 iepis sole SW curifindecurreneSF0 sole SW RhachtropisRohau.9torj inflat. sp. 40.0 0./ 2.4 SI 21.6 0.6 SI2.0 22.2 0.3 SI1.8 SI SI Re1oxyniwillip.m.ionI.ysianassidaeIhoti8 sp sp.p. 31.428.6 2.0L/ 2.26.1 70.8 19.6 39.5 35.121.648.729.1 4.00.47.22.2 5.35.22.57.8 17.2 2.2 6.0 Decapoda CrunqonRhepcxyniva sp. epiatofm4z 17.1 0.3 0.9 46.140.5 4.01.7 5.94.6 48.0 11.4 9.1 24.1 14.3 3.6 OphiuroideaPinnotheridaePaguridae 45.717.1 1.62.2 2.62.0 40.5 12.1 6.6 20.131.0 12.2 2.2 5.09.9 EllipsoidSpheroid pellets pell.ts Ascideacea 17.1 2.4 20.854.2 21.6 2.9 31.0 14.4 16.5 Osteichthyes (.itho.richthyePleuronectlfonnesI8og8ett aordidua i&1epi 31.025.9 24.2 4.2 10.7 3.5 UnidentifiedOther material 23.316.9 19.0 24.110.8 32.9 21.733.6 21.9 59.3 20.024.8 3.3 20.718.9 28.9 3.7 29.5 0.0 0.0 0 41 particles (1 1.5 mm diam.) were common in the stcinachs of M. pacificus (24.5% by weight). The origin of these particles could not be ascertained, 'but they are probably benthic invertebrate feces or pseudofeces. The nutritional value of these particles is also uncertain. Of the ten amphipod taxa consumed by Microstomus, the genus Photis was most important with greater than 70% FO. Ainphipods and pinnotherid crabs were dominant prey of G. zachirus. The diet of I isolepis was distinguished by the presence of an unidentified, sediment dwelling ascidian, and two decapods: Crangon and pagurid crabs. The remaining pleuronectid, Lepidopsetta bilineata, had a diet distinct from the above five species. The major prey of Lepidopsetta were recently settled pleuronectiform fishes (53%), including ç. sordidus (30 40 mm) and j. isolepis (20 25 mm) that were eaten in relatively equal proportions. Crangon, gammarid amphipods, and polychaetes were also common prey. Sizerelated Trends Three species showed striking changes in diet with size: . melanostictus at 9 and22 m, R. binoculata at 9, 22 and 73 m, and E. jordani at 73 m. At the 9 and 22 m station . melanostictus was represented in the catch by two modal size groups (Figure 3 and 4). A comparison of diets between the small (< 200 mm) and large (> 200 mm) groups showed an increase in the proportion of fish in the diet of Psettichthys with increasing predator size (Table 13). Mysids were the most important dietary component of individuals < 200 mm (73 %), replaced by fish in individuals > 200 mm. The most common Table 13. 200PsettichthyscompositionPercent mm standard frequency bymelanostictus wetweightlength of occurrence (SL) (WT) less of than(FO), dominant or and equal averageprey to in and percentstomachs greater of than (9 and 22 In stations combined). prey taxa SL < 200n = 31 %WT %F0 SL ) = 200%WT20 MysidaceaAmphipoda 83.8%F019.4 73.0 2.1 55.0 0.0 34.0 0.0 DecapodaCrczngon sy larvae Ziros tris 25.8 6.5 1.16.5 15.0 0.0 0.03.4 otherOsteichthyes 25.8 - 16.9 0.4 60.0 - 58.7 3.9 43 fish prey identified for . melanostictus was Microgadus proximus ( 100 mm). The dependency of Raja's prey spectrum on size of individual is outlined in Table 14. Food habits data from all three stations were combined, and then grouped by four predator length stanzas. Crangonid shrimp were the dominant prey of . binoculata within the two smallest length stanzas (< 600 mm). Small Cancer magister (< 40 nun), and Ammodytes hexapterus were also common prey. Intermediate size R. binoculata (600 799 mm) preyed on a mixture of Crangon, Cancer, aid small pleuronectiform fish (< 75 mm), primarily ç. stigmaeus. Skate within the largest size class (870 1320 mm) consumed large C. magister (90 130 mm), plus pleuronectiform (150 275 mm) and nonpleuronectiform fishes. Adult parasitic treniatodes (Otodistomum velii,orum) were common in the stcinachs of R. binoculata (Table 14). The amount of infestation increased with increase in skate length. Frequency of infestation and percent composition of parasites by weight of total stanach contents is reported for the four length stanzas described above. Off Oregon, the metacercaria of 0. veliporum are the most common digenetic trematode parasites of Parophrys vetul and presumably other pleuronectiforms (Olson, 1978). Olson suggests that . binoculata become infested with 0. veliporum when feeding on intermediate pleuronectid hosts. Therefore, trematode infestation may indicate relative importance of pleuronectids in the diet of a given size class of R. binoculata. Table 14. Percent frequency of occurrence (FO), and average percent composition by wet-weight1320).standardin stomachs length of dominantof prey Raja and (SL mm)binoculata grouped into four < 400 (193 parasitic 398), Trematoda400 (Otodistomuin 599,length 600 stanzas: 799, veliporum)> 800 (870 SL < n =400 22 mm 400 n = 33 599 mm 600 n ± 29 799 mm SL > 800 = 9 mm CancerCranjonprey taxa magister 45.595.5% FO 74.411.9% WT 51.590.9% FO % 12.976.4WT 62.179.3% FO % 37.036.4WT 77.811.1% FO 45.3% WT 1.2 PleuroiiectiformesPleuronectiformes A size related shift in the diet of E. jordani occurred at approximately 250 mm (Table 15). Individuals less than 250 mm fed on mysids, the sculpin Radulinus asirellus (50 mm), and two species of recentlysettled, juvenile flatfish: C. sordidus (30 50 mm) and I.isolepis (25 35 mm). Larger . jordani (> 250 mm) fed on Crangon and 75 130 mm juvenile flatfishes, including C. sordidus, M. pacificus and G. zachirus. Diet Similarity Percent similarity values (PS) as a measure of within diet overlap (wetweight basis) are presented for fish collected at each station in Tables 16 18. Percent similarity depends in part on the taxonomic level used in the comparison. For fishes collected simultaneously, overlap measured primarily at the level of species utilizes all the available information, and therefore should be a representation of short term or immediate feeding relationships. Conversely, diet overlap measured at major taxonomic levels (e.g. class, order, etc.) results in a loss of specieslevel information, but may provide a more general picture of potential food resource overlap (assuming that species within a major taxon are equally available). At all stations, similarities based on comparisons made at the level of major prey taxa (Tables 16 18, below diagonal) usually were much greater than those at the lowest taxon (above diagonal). In general diet overlaps were highest within the two major feeding types of fishes: 1) those that preyed on (a mixture of) pelagic and epifaunal prey, and 2) those that preyed primarily on infauna (unless otherwise stated, all overlaps discussed below are based on comparisons made at the Table 15. EopsettacompositionPercentlength frequency(SL)jordani by collected wetweight less of occurrencethan at (WT)the 73of (FO), mdominant station. and averageprey in percentstomachs and greater than 250 mm standard of 250 250 prey taxa 69.6% FO SL< n=23 13.1% WT % FO 0.0 SL> n=6 % WT 0.0 PleuronectiformesCrczngonMysidacea < 50 mm 65.256.5 45.618.7 0.0 0.00.0 otherPleuronectiformes Osteichthyes >< 7550 mmmm 4.4 1.55.7 16.783.3 76.7 3.1 other Osteichthyes > 75 mm 0.0 - 15.4 0.0. 16.7 - 18.6 1.6 Table 16. unitbasisstationSimilarity (usually (lower based in left),species) onthe dietsand (upper on of eight right). species of fish collected percentage of major prey taxa in their diets on a wetweight percentage of taxa identified to the lowest taxonomic at the 9 m )çj Q\J A c S . c. . . c. S ScorpaenichthysRczjcz binocul-ata marmoratus 98 37 5928 11 2930 1211 2521 20 PlatichthjsJIjdro lagus co .stel2atus 1 l-iei 60 3 60 2 i3 12 23 9 11 2 16 3 0 PsettichthysIsopsetta isolep-to rnelanostictus 1429 1428 4253 22 9 38 13 2823 36 0 Spirinc1usMicro gadus starksi proxirnus 27 3 27 4 43 4 14 3 52 5 5471 45 20 -4 Table 17. unitbasisstationSimilarity (usually (lower based in left), species)theon percentagediets and (upper onof percentageten of right). speciesmajor preyof of taxa fishtaxa identified collectedin their todietsat thethe on lowest22 a mwetweight taxonoinic >cp A . "() / o c ,° N . . . . HydrolagusRaja binoculata colliei 55 33 7 3321 42 1 21 18 9 < 1 2 <1 2 IsopsettaPlatichthjs isolepis stellatus 28 9 4910 50 37 2412 < 1- 2 < 1 3 131-2 1220 67 PsettichthysParophrjs vetulus rnelanostictus 23 2 1516 < 1 25 43 9 2 < 1 73 1 22 9 < 1 50 < 1 72 MicrogadusCitharichthys proxirnus stigrnaeus 23 8 2711 32 4 4815 21 5 5580 60 25 5025 3072 AllosI7lerusSpirinchus elongatusstarksi 17 3 15 5 1224 1619 2 6776 9161 64 65 60 OD Table 18. unitbasisstationSimilarity (usually (lower based in left),species) theon percentage dietsand (upper on of percentage eleven right).of major species of prey taxa oftaxa identifiedfish in collectedtheir to diets the at lowestonthe a 73wetweight taxonomic m ' ' c. 6/ / C; O / 6; Q V "ç I .° RajaOphiodon rhina elongatus 98 9 <1<1 14 0 3623 3424 2 00 0 I0 34 RajczCitharichthys binoculata sordidus 1974 2277 26 3 24 1 18 1 61 03 0 21 51 EopsettaLepidopsetta jordani bilineata 5571 5774 7488 3036 73 64 21<1 82 0 15 2 2820 MicrostorausGlyptocephalus pacificus zachirus 02 24 27 6 13 6 19 6 2742 64 18 03 2022 2128 ParophrysPleuronichthys vetulus decurrens 0 20 30 81 40 26 8 4621 5220 56 0 26 0 Isopsetta isole1yzs 4 6 29 13 20 43 72 53 17 41 50 lowest taxonomic level). At the 9 m station, diet overlaps were intermediate within two groups of fishes: 1) P. melanostictus, M. proximus, and S. starksi (20 36%), and 2) R. binoculata, H. colliei, and S. marmoratus (28 59%) (Table 16). The degree of overlap within the first group can be attributed to mutual utilization of mysids and decapod shrimp living both on and above the substrate. Overlap within the second group was due to their feeding on Cancer magister. The diet of I. isolepis overlapped moderately with all fish collected (9 30%) with the exception of the pelagic feeding smelt, S. starisi. As stated earlier, the species composition of the group of pelagic and/or epifaunal feeders at the 9 and 22 m stations was similar except for the addition of C. stigmaeus and A. elongatus at 22 m. Maximal values for diet overlaps were somewhat higher (22 73%) within this group at 22 m when compared to 9 m. In part, the higher values reflect a greater utilization of mysids (primarily . kadiakensis) at 22 m. Diet similarity between small P. melanostictus and other fishes preying on small pelagic and/or epibenthic crustacea could be expected to be larger than the tabulated values because of size related predation on mysids by . melanostictus. Of the remaining five species, P. vetulus, P. stellatus, and I. isolepis, all epibenthic and/or infaunal feeders, showed a low to intermediate degree of overlap (12 37%). These similarities were the result of consumption of an assortment of crustacean prey plus Dendraster in the case of.. isolepis and . stellatus. Intermediate levels of similarity 51 were observed between R. binoculata and H. colliel (37%). Similarities at the 73 m station ranged from 0 64% (Table 18). High diet similarity within the upper left corner of the table corresponds to those fishes that preyed on juvenile pleuronectiforms and/or decapod crustaceans (Cancer and Crangon living on the substrate. Citharichthys sordidus had more pelagic food habits than other fishes within this group, and therefore a lower diet overlap. Low to intermediate diet overlaps (12 28%) were observed for the group of fishes which feed primarily on infauna and appear in the lower right corner of the table (Q. zachirus, M. pacificus, P. decurrens, P. vetulus, and I. isolepis). For example, P. vetulus and G. zachirus had a diet overlap of 22%, resulting primarily from consumption of the same species of polychaetes and especially the amphipods, Ampelisca macrocephala (Table 11). Prey Availability A limited amount of data on available prey exists for the 22 m station from box core and small beam trawl samples that were collected as part of the Pleuronectid Production Project. These data will be used to make a qualitative comparison between fish food habits and the benthic organisms living in each area. Benthic infauna were sampled within the study area in 25 mwater depth during July (4 cores), August (4 cores) and October (5 cores) 1978, about a year before the fish collections with a 0.25 m2 boxcorer (Carey, unpubl. data). Data from all cores were summed and are listed as total counts, densities and percent composition in Table 19. Sampled seven months prior to the fish 52 Table 19. Numerical abundance and average percent composition of invertebrates in box core samples from 22 m station. TAXA TOTAL COUNTS NUMBER/rn2 * % NUMBER ** !4aalonasaccuZ.ata 2337 947 23.6 Spiophtrnes bombyx 1498 866 15.1 Eohau.storiva sencillus 1437 702 14.5 z4mpeiisca agassizi 716 543 7.2 unident amphipoda 610 - 6.1 Olivella sp. 453 216 4.5 Cuinacea 331 137 3.2 Rhepoxynius vigitegus 216 122 2.2 Nernertea 212 98 2.1 Anrpelisca rnacrocephala 185 112 1.9 7lycinde picta 172 118 1.7 Thalessa spinosa 158 99 1.6 Foxiphalus obtusidens 138 78 1.4 Nephtys caecoides 123 74 1.2 Scolop7.oscromiger 101 47 1.0 Dend.raste2' excentricus 100 72 1.0 Chaetozone setosa 84 49 0.9 Mdibulohoxus unicirostratus 75 39 0.8 Syllidae 75 - 0.8 Phoronida 73 - 0.7 Tellirta rnodesta 62 - 0.6 Anaitides sp. 43 - 0.4 CyZichna attonsa 42 - 0.4 Odostemia sp. 41 - 0.4 Nothricz iridescens 41 - 0.4 Ophiuroidea 40 - 0.4 Synchelidiumsp. 38 - 0.4 Pelecypoda (unident.) 36 - 0.4 Monoculoides sp1n1pes 36 - 0.4 Spiophes berkeyeyorum 33 - 0.3 Neinatoda 25 - 0.3 Glycinde az'migera 24 - 0.3 Nereis procera 21 - 0.2 53 Table 19 cont'd. Het.romastus filiformis 20 0.2 Macoma sp. 19 0.2 Phoxocephalidae 18 - 0.2 Pholoe rninuta 17 - 0.2 Other 258 - 2.6 * average for July and August ** based on total counts 54 Table 20. Abundance of invertebrates and fishes in beam trawis at the 22 m station off Moolack Beach on 2 and 29 May 1979. TAXA 2May 29May % weight % number % weight % number Invertebrates Neornys-is kodia7 Citharichths stiamaeus 40.5 26.2 Parophrys vetulus 7.6 30.7 Ocella verrucosa 20.4 9.7 !icroadus proxipus 17.1 5.9 Isoetta isolepis 1.2 14.4 Stellerina xyosterna 5.7 9.8 Psettichthzjs melanostictus 6.8 1.2 Liaris puZcheilus - 0.7 Oohiodon eonc7atus 0.7 0.4 Odontopuxis trispinosa - 0.4 Allosmerus elonaatus - 0.4 *juveniles <20mm 55 collections, these data give a general representation of the available prey in the nearshore. Only taxa representing greater than 0.1% of the numeric total are listed. A total of 9940 invertebrates representing 75 taxa were sampled. Polychaetes were the major group and comprised 50.8% of the organisms sampled. Of the polychaetes present, Magelona (23.6%) and Spiophanes bombyx (15.1%) were numerically dominant. In addition, Glycinde picta, Thalanessa spinosa, Nephtys caecoides and Scoloplos armiger were abundant. Amphipods were the second most abundant group (34.9%). The amphipod, Eohaustorius sencillus plus amphipods of the families Ampeliscidae and Phoxocephalidae were particularly important. Caceans were not identified to species, but the group as a whole ranked seventh in abundance. Nemertea and Dendraster excentricus were also important. A comparison can be made between prey of infaunal feeding fishes and an estimate of available prey from box core data by comparing Tables 8 and 19. For example, six of the ten most abundant prey in box cores were also abundant in . vetulus stomachs. This evidence further supports a nonselective feeding strategy for P. vetulus whereby it utilizes a broad array of infaunal prey. The remaining two potential infaunal feeders, P. stellatus and I. isolepis were more selective and did not utilize prey in even approximate proportion to their abundance in the box core sediments. Beam trawl samples taken in the study area provide information on available epifaunal prey at the 22 in station. Epifaunal invertebrates and small fishes were sampled from 18 and 56 22 m water depth on 2 and 29 May 1979 with a 1.5 m beam trawl (6 mm mesh liner) (Krygier and Pearcy, unpubi. manuscr. and data). Invertebrates and fishes are listed in order of relative abundance by average percent composition (Table 20).Neomysis kadiakensis and Crangon stylirostris were the most abundant invertebrates on a niimieric and biomass basis.Juvenile pleuronectiform fishes, including C.stigmaeus, P. vetulus and I.isolei,is were most abundant in the beam trawl collections.These flatfishes ranged in size from 20 50 mm. Juvenile M. proximus, plus newly settled agonids (20 40 mm), Ocella verrucosa andStellerina xyosterna, were also abundant, and P. melanostictus was common. Neomysis kadiakensis was an important prey for a large group of pelagic feeding fishes at the 9 and 22 m stations, including . melanostictus, C. stigmaeus and M. proximus, and two osmerids (Tables 4 and 7). R. binoculata fed heavily on the most abundant of the larger available prey, C. stigmaeus and C. stylirostris (Tables 5 and 8).Juvenile M. proximus were abundant in the beam trawl and an important prey of large P. melanostictus. The remaining juvenile fishes: agonids, P. vetulus and I. isolepis were not found as prey.The number of prey types available to fishes feeding on or above the substrate appears to be limited, resulting in the high diet overlaps observed in the pelagic and/or epifaunal feeders (previous section). 57 DISCUSSION Fish Assemblages After studying species composition and relative abundance of benthic fishes collected in this study, I propose that the nearshore and midshelf areas off Moolack Beach, Oregon are characterized by two fish assemblages. There is justification for combining information from the 9 and 22instation, and considering fish collected over that depth range as belonging to the same assemblage. Catches at the two nearshore stations were dominated by . melanostictus and . binoculata. Other fishes common to these stations were P. stellatus, I.isolepis, C. stigmaeus, H. colliei, M. proximus and . starksi. Catch composition at both stations was almost identical. Any differences could be attributed to the limited number of trawis. The species composition of benthic fishes found in this study agrees with the results of earlier studies off Oregon. Monthly beam (1.5 in) and otter trawl (7 in)sampling in the same area, over the same depth range yielded a catch composition that encompasses both stations (Krygier and Pearcy unpubl. manusc.). The small sized beam and otter trawis preferentially sampled the smaller fishes. Demory et al.(1976) found I. isolepis, P. melanostictus, and P. stellatus restricted to shallow depths (< 50 in) and sand sediments in his 1971 1974 otter trawl surveys over the entire width of the Oregon shelf from the Columbia River to Cape Blanco. The midshelf assemblage discussed in this paper corresponds to a 74 102in"sandy bottom" assemblage, dominated by C. sordidus, and observed off Heceta Head, Oregon by Pearcy (1978). 58 Other important members of Pearcy's assemblage were . zachirus and . pacificus. Demory et al. (1976) found C. sordidus, P. vetulus, G. zachirus, E. jordani, Raja sp., H.c.olliei, M. pacificus, and Squalus acanthais (spiny dogfish) to constitute a midshelf (35 - 110 m) assemblage in areas of sand with a low "mud content". In analysis of west coast fish assemblages based on National Marine Fisheries Service groundfish survey data, Gabriel (1983) identified an Oregon midshelf assemblage area extending from Cape Falcon to near Coquille Point, Oregon at an average depth of 113 m. The catch in this region was dominated by Merluccius productus (Pacific hake). Other common (FO > 50%) members of the assemblage were G. zachirus, M. pacificus, Thaleichthys pacificus (euchalon), E.jordani, P. vetulus, Atheresthes stomias (arrowtooth flounder), and C. sordidus. The high vertical opening NMFS groundfish survey net was rigged with roller gear. This type of net design is selective for nektobeuthic fishes and selective against flatfishes. Therefore, the type of gear used could account for the dominance of . productus observed by Gabriel. How does the size spectriun of fishes representing the two assemblages in the current study compare to the commercial fishery?The nearshore area is not a typical fishing ground. Pleuronectid fishes from the nearshore assemblage covered a broad size range, including both juveniles and commercial sized adults. With the exception of P. vetulus, pleuronectid fishes collected at the 73 m station were generally smaller (150 250 mm) than those targeted in the commercial fishery (Alverson et al. ,1964; Barss, 59 1976; Hosie, 1976; Eyck and Demory, 1975). Regions of high catch for commercially important flatfishes are located to the south in the vicinity of Heceta Bank, to the north off the Columbia River, and generally further offshore. However, the fishery for . vetu].us is centered at midshelf. In addition, E.jordani and M. pacificus are fished seasonally at midshelf depths (Hewitt, 1980). Food Habits The fishes examined from both the nearshore and midshelf areas form a continuum between two extremes in feeding types: fishes that prey solely on pelagic invertebrates and fishes, and fishes that feed exclusively on infaunal invertebrates including polychaetes, amphipods, cumaceans, and molluscs. Between these two extremes are fishes which eat varying proportions of epifaunal prey including both invertebrates and fishes. As collections were obtained with bottom trawls it is important to emphasize that all fishes examined have benthic or nektobenthic affinities. For pleuronectiform fishes, de Groot (1971) developed three major feeding types based on digestive system morphology (esophagus and stomach, intestinal loop, and gill rakers) and direct observations of food habits: fish feeders (type I), crustacean feeders (type II) and polychaete - mollusc feeders (type III). In an earlier study, Hatanaka et al.(1954) after a study of mouth parts, characterized pelagic feeding species as having large symmetrical jaws (directed forward) with well developed teeth on both blind and eyed sides (often with a double row on the upper jaw), large stomachs, short intestines, and large gill rakers. Tsuruta and Omori (1976) expanded on the work of Hatanaka et al., and arrived at a set of feeding types, similar to those of de Groot based on mouth morphology and behavior. These were pelagic, epibenthic and infaunal feeders. They observed that the mouths of some pelagic feeding flatfishes are asynmmetrical upward (Tsurata and Omori, 1976). In contrast, flatfishes that feed on infauna have small asymmetrical jaws directed toward the blind side (where teeth are more developed), small stomachs, long intestines (complicated intestinal loop), and small gill rakers. It is not uncommon for these infaunal predators to have teeth limited almost entirely to the blind side( Hatanaka et al., 1954). In the current study, the mixed pelagic and epibenthic feeding E.jordani, C.sordidus, C. stigmaeus, and P. melanostictus have large, almost symmetrical mouths with well developed teeth on both sides of the jaw, large stomachs, simple looped intestines, and large gill rakers (Clemens and Wilby, 1967; Hart, 1973; and Wakefield,personal observation). Parophrys vetulus, M. pacificus, 6. zachirus, and P. decurrens fall into the infaunal feeding group (de Groot's type III) having small, asymmetrical, downwarddirected mouths, teeth limited to the blind side, long intestines and small gill rakers (Clemens and Wilby, 1967; Hart, 1973; Wakefield, personal observations). Lepidopsetta bilineata, P. stellatus, and I. isolepis are intermediate between both groups, but lie closer to the infaunal feeding group. These species have a small asymmetrical mouth directed only slightly downward, moderately sized stomach and intestines (a tubular gut 61 in the case of P. stellatus), and stout gill rakers. Isopsetta isolepis and P. stellatus have short but well developed teeth on both sides of the head, whereas L. bilineata has teeth limited to the blind side. The above three species appear to fall into the intermediate catagory of epibenthic feeder (or de Groot type II). The Food Habits of Nearshore Benthic Fishes Few studies have been published on the biology of nearshore opencoast fishes in the northeast Pacific. Ambrose (1976) (see also Cailliet et al., 1979) studied the food habits of four pleuronectiforms (P. vetulus, C. stigmaeus, P. melanostictus and P. stellatus) at a nearshore station near Monterey, California. The food habits of these four species were very similar to those collected in the nearshore off Moolack Beach. Psettichthys melanostictus and C. stigmaeus both consumed pelagic mysids, and in the case of C. stigmaeus, motile epibenthic amphipods. At both Moolack Beach and the Monterey site piscivory increased with size in P. melanostictus. Similarily P. stellatus, both off Monterey and Oregon fed on polychaetes, decapod crustaceans, and pelecypod siphons. The results of Ambrose (1976) and the current study characterize P. vetulus as a nonselective generalist, feeding on a diverse spectrum of infaunal polychaetes, amphipods, cumaceans, whole (and siphons of) pelecypods. Rogue and Carey (1982) found that juvenile flatfishes (17 88 mm)(P. vetulus, I.isolepis, C. stigmaeus and P. melanostictus) fed on different specific food items at the nearshore Moolack Beach site, however, the functional feeding relationships for the juveniles mirrored that of the adults, 62 ranging from pelagic to infaunal feeders. Cropped off body parts were also an important prey of juvenile . vetulus and I. isolei,is. Cropping of tissue that can regenerate has been documented in the nearshore areas of the North Sea for Pleuronectes platessa, and Platichthys flesus. Both ate pelecypod siphons (Tellina) and Arenicola "tails" (Trevallion, 1971; de Vlas, 1979). Pleuronectes platessa and Platichthys flesus are very similar in body morphology, general biology and food habits to the North Pacific Paroprhys vetulus and Platichthys stellatus, respectively. Both of these species share pelecypod siphons as a major prey group. Of the nonpleuronectiform fishes studied here, big skate, R. binoculata, and the chimarid, H. colliei, were abundant and composed much of the fish biomass at the nearshore stations. Raja binoculata consumed primarily decapod crustaceans and pleuronectiforms. Hart (1973) lists crustaceans and fishes as primary food for R. binoculata. McEachran et al.(1976) studied feeding relationships within two coOccurring species pairs of in the North Atlantic. One species pair, R. radiata and R. senta fed heavily on decapod crustaceans and euphausiids, but included some fishes as a secondary component of their diet. Most of northeast Atlantic skates (12 species) feed primarily on decapod crustaceans (both shrimps and crabs) and fishes including flatfishes (Wheeler, 1969). The largest northeast Atlantic skate, R. batis, attains the size of R. binoculata, is similar morphologically, and feeds mainly on fishes with decapods as a secondary component (Wheeler, 1969). 63 Hydrolagus colliei stcinachs contained a large proportion of shell fragments and unidentifiable welldigested material. At the 9 and 22 m stations, Hydrolagus fed on molluscs, crangonid shrimp and fish (mainly C. stigmaeus). Johnson and Horton (1972) had similar findings in their analysis of H. colliei food habits from four locations off Oregon. Of the identifiable material, shrimp, molluscs and echinoderms were principal prey. The Food Habits of Midshelf Benthic Fishes The majority of benthic fish food habits studies off Oregon have emphasized mid and outer continental shelf areas and focused on pleuronectiform fishes (Pearcy and Vanderploeg, 1973, Kravitz et al., 1977; Pearcy and Hancock, 1978 and Gabriel and Pearcy, 1981). In combination, these studies provide information for comparison with the current study site at midshelf. Generally, the above investigators recognized the same feeding types, pelagic and benthic, but there were some differences in their results. Kravitz et al. (1977) examined stomachs of P. vetulus, G. zachirus, L. bilineata, E. jordani and C. sordidus from a 95 - 106 in station in close proximity (44°42' N, 124°24') to my 73 m station. The diet of E. jordani, a pelagic and/or epibenthic feeder in the current study, was similar to the observations of Kravitz et al. (1977), but differed as far as prey types. In both studies, E. jordani fed on juvenile flatfishes, other beuthic fishes, decapod crustaceans, and mysids. Engraulis mordax (northern anchovy) was an important prey of C. sordidus (Kravitz et al., 1977; see also Barss, 1976), where as, pelagic invertebrates and recently settled I. isoplepis were important in 64 the current study. Of the infaunal feeders studied by Kravitz et al.(1977), P. vetulus had the most diverse diet, including 63 prey taxa. The amphipod Ampelisca macrocephala had the highest frequency of occurrence for both studies (60 and 63%). In both that and the current study, . vetulus consumed primarily polychaetes and amphipods, and each individual stcxiach contained many different prey taxa. Glyptocephalus zachirus, another infaunal feeder, showed the same pattern, but with amphipods as dominant prey and polychaetes secondary in importance. Amphipods were also the primary prey of M. pacificus at the midshelf station. However, near Heceta Bank, Pearcy and Hancock (1978) found polychaetes to be the major prey of . pacificus and . zachirus at their deeper stations (100 - 195 m), where as amphipods were secondary. In a separate study on feeding selectivity, Gabriel and Pearcy (1981) observed that polychaetes, ophiuroids and molluscs were the most important prey of M. pacificus with positive selection for polychaetes and ophiuroids. Although this collective evidence shows these fishes feeding on the same general types of infauna, diet overlaps between species were low. The diet of L. bilineata differed between the current study and that of Krasritz et al.(1977). Principal prey of L. bilineata at the 73 m station were recently settled flatfishes, where as in the earlier study ophiuroids were the principal prey. Shubnjj.son and Lisovenko (1964), and Forrester and Thomson (1969) both describe L. bilineata as feeding on a combination of benthic invertebrates and fishes. 65 In a comprehensive study of softbottczn fish communities of the Southern California Bight, Allen (1982) placed P. vetulus, M. tacificus and G. zachirus into three different feeding guilds. He based his conclusion on morphology, stanach content analysis, and prey availability. M. pacificus was classified as a visual "extracting benthivore", P. vetulus as a "excavating benthivore", and G. zachirus as a "nonvisual benthivore" (utilizing subdermal sense organs located on the head). All of the above observations indicate that food resources are partitioned among these benthophagus fishes. In general, the results of this study show similar food habits to previous studies, especially at the level of major prey groups. Its limitation is that sampling for food habits was restricted to a single portion of the coast, and to a single day. The lack of seasonal, bathymetric, and coast wide coverage as well as interannual differences could account for some of the differences between the current study and and those studies cited above. If combined, however, past and current results are useful in examining trophic relationships between the benthic fishes studied. This is demonstrated below. Trophic Relationships Food webs have been constructed for both the nearshore and midshelf fish assemblages, synthesizing information from the current study, previously cited literature and unpublished information on the distribution and food habits of northwest coastal fishes. A general view of feeding relationships within the meio and macrobenthic invertebrate community is derived from review of the literature (Arntz, 1978; Barnes, 1980; Fenchel, 1978; Fenchel and Jørgensen, 1977; Jones, pers. comm.; Mills and Fournier, 1979; Simenstad et al., 1979; Tyler, 1974) A partial food web for the nearshore benthic enviromient is depicted in Figure 7. The transfer arrows in the diagram signify food resource linkages. Relative importance of each linkage is indicated by the type of line. The nearshore habitat is a high energy wave zone, characterized by a well sorted sand substrate. Production in this enviroimient is based on phytoplankton, benthic microalgae, and terrestrial and aquatic organic detritus. Energy flows from detritus and phytoplankton through bacteria and/or meiofauna to macroinfauna and epifauna, and in turn to the benthic fishes (generally three or four trophic levels). The food web identifies the importance of the nearshore open coast as a nursery area for four pleuronectiforms plus juvenile M. proximus, Engraulis mordax, osmerids and agonids. As stated earlier, feeding relationships within the group of zeroage flatfishes is functionally similar to the adults inhabiting the same area. A diverse group of macroinvertebrates are prey to benthophagus fishes feeding within the sediment and at the sedimentwater interface of the nearshore. Major prey items are polychaetes, nemerteans, amphipods, caceans, molluscs and echinoderms. Two crustaceans, Crangon and Cancer, plus juvenile pleuronectiforms and Ammodytes hexapterus are important epibenthic prey of the skate, Rala binoculata. The chimarid, Hydrolagus colliel, has similar food habits. Dietary differences exist within ,, Hbo.] I [ LIL 7 - - -0. I 51 26-50% 5 100% 25% Figure 7. TransferDiagram arrowsof bcnthjc indicate food foodweb inresource the nearshore linkages area (see off text Moolack for description). Beach, Oregon. the group of benthophagus fishes, and these differences are consistant with other studies. In addition, these dietary differences show a relationship to patterns in functional morphology (eg. Platichthys as a polychaete mollusc feeder and sc*newhat of a specialist, vs Parophrys as a polychaete feeder and a generalist). For any given species, comparisons between areas indicate that these fish are each enough of a generalist to alter their predatory tactics to utilize the available prey. A second group of fishes feeds primarily at the interface or in the water column in close association with the substrate. Mysids (and to a lesser extent Crangon) were the dominant prey of this group. These detritivoreherbivore crustaceans represent a major linkage in the nearshore food web. Two pelagic osmerids, cmon nearshore fishes, also fed heavily on this resource. Food resource overlap within the group of pelagic and/or epibenthic feeders was high. Mysids and Crangon are known to be very abundant year round in the nearshore area, and this may explain their large proportion in the diets of so many fishes. In terms of resource partitioning, high diet overlaps may occur when resources are abundant; conversely, during periods of reduced food availability, overlap may be low (Zaret and Rand, 1971; MacPhearson, 1981). The midshelf food web appears in Figure 8. This area is also characterized by a sand substrate, but the mud content is greater. The beuthic invertebrate community as well as the resident fish assemblages are quite different from the nearshore shelf area. As in the case of the nearshore, the midshelf (in .a [a / J 0 27 \- k - -. N ri-i. / , - - )1-.c 't- / \ I ..'L -v - 7=== _---- / / 1 1 1I M I I if ..- / I I / - % f r / / ;.,d - ,/ \4 a.. N lb 2:1 Figure 8. Diagram of benthic food web in the midcontinental shelf area off Moolack 51-100% Beach,text forOregon. description). Transfer arrows indicate food resource linkages (see t'Dm 70 combination with the outershelf) is probably a major nursery for resident flatfishes (Pearcy et al., 1977; Demory et al., 1976). The overall trophic structure is similar to that of the nearshore, based on phytoplankton and detritus with fishes occupying third and fourth trophic levels, but there are differences which are apparent in the two food webs (Figures 7 and 8). The pelagicfeeding Citharichthys sordidus is a dominant feature of the inidshelf. Two additional pleuronectids and three species of Raia prey heavily on juvenile to subadult pleuronectiforms plus epibenthic decapods. Although Raja was not very abundant in the current study, other investigators have found it to be abundant in midshelf areas (Gabriel, 1983; Demory et al., 1976). Mysids, a major epibenthic food resource is less important here, while Crangon continues to be an important prey. Infaunal feeding fishes are more numerous in number and species at the midshelf. Six pleuronectiforms dominated the catches. Diet overlap within the group of infaunal feeders was low to intermediate. Dietary differences do exist within this group of benthophagus fishes, and these differences show a relationship to patterns in functional morphology. These functional differences permit enough flexibility for fishes to alter their predatory tactics to utilize available prey. The observed overlap was probably a result of a combination of distinct feeding types and the diverse nature of the available prey. 71 Concluding Remarks This study of benthic fish feeding relationships builds on the existing biological information and fills information gaps on trophic structure. The food web analysis points to the complexity of the system and diverse nature of potential interactions within the shelf community. Interactions occur in many segments of the community, but those most conspicuous are in the areas of food resource overlap, and predation among species which are part of the same multispecies fishery. During periods of food resource limitation, competition between cooccurring fishes could reduce fish growth rates and/or reproductive output. Of the eleven flatfishes examined as part of the current study, four benthic feeding flatfishes had intermediate diet overlaps: P. vetulus, I. isolepis, M. pacificus and G. zachirus. Of these four, M. pacificus and G. zachirus have the broadest overlapping depth range (Alverson et al., 1964), and cooccur as important components in the multispecies trawl fishery on the Oregon shelf. These two flatfishes could potentially interact trophically to limit one or the other's production. At shallower depths, the commercially important P. vetulus and noncommercial flatfish, I. isolepis, co occur over a broad shallow to intermediate depth range, and throughout both juvenile and adult life history stages. These two species might also compete for food resources during periods of food limitation. A diverse group of fishes were identified as potential predators on flatfishes, including, at the midshelf station, L. 72 bilineata, E.jordani, 0. elongatus, and two skates, R. binoculata and R. rhina. Many of the flatfishes consimied were commercially important species. In the nearshore area, R. binoculata preyed on stigmaeus, a noncommercial bothid. Raja binoculata juvenile . might be an important predator on other juvenile flatfishes utilizing the nearshore nursery area. In general, the broad size range of the flatfishes eaten (20 250 mm) suggests that this source of mortality to pleuronectiforms would not be limited to a single time period during settlement. In addition, skates appear to be a predator on the commercially important crab, Cancer rn!ister. The large number and biomass of skates known to inhabit the nearshore and midshelf indicates that this little studied group may play an important role in the continental shelf benthic community as a dominant predator. Additional coast wide studies during all seasons are needed to identify the importance of these predators in contributing to flatfish and Dungeness crab mortality. '-5 B IBLIOGRAPHY Allen, M. 1. 1982. Functional structure of softbottom fish communities of the southern California shelf. Ph.D. Thesis, Univ. of California San Diego, La Jolla, CA. 576 p. Alverson, D. L., A. T. Pruter and L. L. Ronholt. 1964. A study of demersal fishes and fisheries of the northeasternPacific Ocean. H. R. MacMillan Lectures in Fisheries, Inst. Fish., Univ. of British Columbia. 190 p. Ambrose , D. A. 1976. 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Summary of food habits data collected for Psettichthys melanostictus, sand sole; Microgadus proximus, Pacific toincod; and Spirinchus starksi, night smelt, collected at the 9 m station, May 1979 (FO = frequency of occurrence, W wetweiught, # = number). Appendix I. meianostictu3Psttichthy8%0 tW % SF0proxitrivaMicrog4dua SW s SF0Spirincthusato. LE 81 Appendix II. Summary of food habits data collected for Isopsetta isolepis, butter sole; Platichthys stellatus, starry flounder; Scorpaenichthys marmoratus, cabezon; Raja binoculata, big skate; and Hydrolagus colliei, ratfish, collected at the 9 m station, May 1979 (FO = frequency of occurrence, W = wetweight, /1 = number). Appendix II. isolepiaSF0rsopaetta SW SI ateliatuaSF0Platichthya SW SI SF0max,noratuaScor'paenichthyB SW SI SF0 SWday Raja binoculata SI SF0 night SW SI collieiSF0Ilydrolagus SW SI Polychaeta St$wnalaiaSigal lonldae tertiaglabra 20.0 6.0 - 11.3 0.2 1.1 7.7 0.1 - Gas tropoda NothriaOnuiThidae irideecena 30.0 22.7 20.9 NaaaapivaNassarildaeOli'.lla01 ivldae Sp. foaaatua 11.1 0.1 3.1 33.0 0.1 3.0 Pe 1 ecypoda SiliquaSolenldae)iiiqsa pat4Za patula siphon 44.4 45.2 35.8 4.5 2./ 1.5 23.1 10.8 5.1 MysidaceaHalOctopoda lacostraca: Peracarida 4.5 2.1 1.5 NeorniJBiaArchaeomyaiaAaanthornyaiaMysldae Ia54ii grebni dauiai taki I 11.1 eO.l 0,1 33.3 1.5 1.0 13.1 0.1 0.8 15.4 7.7 0.10.4 4.22.0 Isopodahiiphipoda .'..ynidoteaIdote idae sp. 11.1 0.1 0.1 iajiiiiiaridea AtyluaAtyl idae tridena 20.010.0 0.91.9 12.4 1.3 33.3 24.3 32.8 1.7 <0.1 0.6 1.7 0.1 1.2 Phoxoceptiafldae1!ipponcdonLysanassdae deut r'j 0 93 Appendix V. Summary of food habits data collectedfor Eopsetta jordani, petrale sole; Citharichthyssordidus, Pacific sanddab; Raja binoculata, big skate;Raja kincaidii, sandpaper skate; Raja rhina, longuoseskate; and phiodon elongatus, lingcod, collected at the 73 m station, May 1979 (FO = frequency ofOccurrence, W = wetweight, # = number). Appendix V. Eopsetta CitharichthyaBOrdidUu Raja Raja Raja Ophiodon Polychaeta SF0jordani SW %ä SF0 2.6 0.1SW SI - SF0 binoo.ulata SW SI SF0 kincaidii SW SI rhinaSF0 SW SI SF0eiongatua SW SI Thecoso4naGastropoda ta 3.5 <0.1 06 38.5 10.8 12.2 33.3 0.1 26.7 Neogastropoda OIIvldaetü,<.,ina sp. 6.9 0.3 1.3 OstracodaCephalopoda OiioelZaSquid S. 3.5 0.4 0.8 2.6 0.12.7 0.30.6 Copepoda CalanuaCaZapudaCalanldae plwn