HOGUE and CAREY: FEEDING ECOLOGY OF 0-AGE FLATFISHES 



tion on the most important commercial species, 

 emphasis was placed on those trawls which con- 

 tained English sole. Priority was also given to 

 using samples which were collected between 

 July 1978 and September 1979, since quantita- 

 tive meiobenthic samples were also gathered 

 from the study area during that period. We used 

 selected trawl collections from 1977 and 1978 to 

 investigate the between-year repeatability of 

 trends noted in the 1979 data. Finally, only hauls 

 containing specimens 70 mm SL and less were 

 used. 



In the laboratory a size range of juvenile flat- 

 fish was selected from each of the trawls chosen 

 for study. Standard length of each specimen was 

 recorded prior to removal of the gut. Both the 

 stomach and intestinal tract were removed and 

 opened under a dissecting microscope; gut con- 

 tents were identified to the lowest possible taxon 

 and counted. We used a subjective scale ranging 

 between and 4 to quantify the degree of gut full- 

 ness (0 = <5% full, 1 = 5-25% full, 2 =25-50% full, 

 3 = 50-75% full, 4 = 75-100% full). 



Quantitative data for each prey category were 

 summarized in two ways. The frequency of prey 

 occurrence, expressing the proportion of all fish 

 sampled which had a given food item in their gut, 

 was computed for each flatfish species within a 

 trawl. The mean percent composition, based on 

 numerical abundance, was determined also by 

 averaging the percent composition of each indi- 

 vidual fish gut for a given species within a trawl. 

 When more than one trawl was examined from a 

 sampling date, the frequency of occurrence and 

 percent composition from the separate trawls 

 were averaged to give an overall mean. Diversity 

 (/f ) of prey consumed was computed using nat- 

 ural logarithms (Pielou 1969). 



On two sampling dates, 29 May and 30 June 

 1979, English sole were captured at the study 

 site and returned live to the laboratory along 

 with sand collected from the same area using a 

 0.25 m 2 box core. Fish were placed in aquaria 

 with the sediments, and their behavior was mon- 

 itored over several days while they fed on natur- 

 ally occurring prey in the sediments. Fresh sea- 

 water (12°C) was circulating continually through 

 each aquarium. A photoperiod matching that ex- 

 perienced by the fish in the field was maintained 

 using room lighting. 



Quantitative meiobenthic samples were ob- 

 tained from the study area at one site in 25 m of 

 water (Fig. 1). Three replicate 0.25 m 2 box cores, 

 positioned 30 m apart, were collected on each of 



six cruises between July 1978 and May 1979. Box 

 cores were subsampled with at least three ran- 

 domly placed clear plastic cores (1.9 cm internal 

 diameter) which were in turn vertically parti- 

 tioned into six depth increments (0-1 cm, 1-3 cm, 

 3-6 cm, 6-11 cm, 11-18 cm, and >18 cm). These 

 plastic corers were also used to subsample 

 Smith-Mclntyre grabs collected on two cruises 

 in July and September 1979 at the same site. 

 Samples were preserved in 10% buffered Forma- 

 lin and stained with rose bengal. The fauna was 

 extracted from the sediments (well-sorted fine 

 sand) by shaking and decanting followed by 

 three rinses. A 38.5 /jm sieve was used to retain 

 the fauna. Harpacticoid copepods and nematodes 

 were identified to species and enumerated. 



RESULTS 



The data for all four flatfish species are sum- 

 marized in Table 1. A total of 422 guts from re- 

 cently settled fish (17-88 mm SL) were examined, 

 only 16 of which were empty (4%). The guts of an 

 additional 40 late stage IV and early stage V P. 

 vetulus larvae (sensu Shelbourne 1957) were also 

 examined. These metamorphosing individuals, 

 ranging in size from 16 to 18 mm SL, all had 

 empty stomachs and intestinal tracts. 



The 13 prey categories identified (Table 1, top) 

 were placed into three broad groupings based on 

 the size of individual food items and their typical 

 location within the habitat. Small benthic prey 

 were composed of palps from the surface deposit- 

 feeding polychaete Magelona sacculata, juvenile 

 bivalves (predominantly Tellina modesta and 

 occasionally Siliqua patula), siphon tips cropped 

 from tellinid clams, harpacticoid copepods 

 (mainly Halectinosoma spp. and a few Thomp- 

 sonula hyaenae and Rhizothrix curvata), free- 

 living nematodes (Theristus sp. and Mesacan- 

 thion sp.), and tube feet from the sand dollar 

 Dendraster excentricus. These food items were on 

 the order of 0.5-1.5 mm long. Larger benthic 

 prey were amphipods (predominantly Ampelisca 

 spp. and Eohaustoris sp.), cumaceans, decapods 

 (juvenile Cancer magister, pinnotherid crabs, 

 and Callianassa calif omiensis), and polychaetes 

 (Nephtys sp., Glycinde armigera, Magelona sac- 

 culata, Thalenessa spinosa, and Spiophanes bom- 

 byx). These prey were usually juveniles measur- 

 ing 1.5-4 mm in their largest dimension. Species 

 identifications were difficult for this latter 

 group because of their immature status and ten- 

 dency to fragment after being eaten. Examina- 



557 



