PEARCY and HANCOCK: FEEDING HABITS OF FOUR FLATFISH SPECIES 



sand bottom dominated by slender sole and rex 

 sole. 



Shallow-water and deep-water associations are 

 therefore evident at these stations, based on pre- 

 vious studies of benthic invertebrates and verte- 

 brates, as well as the composition of the diet of 

 Dover sole in this study. Because surface sed- 

 iments were fairly similar at our three deep 

 stations, sediment vs. depth effects could not be 

 separated here. The lack of precise similarities of 

 sediment types for station pairs also weakens this 

 part of our study. Nevertheless, stations with the 

 most similar sediment types often had low similar- 

 ity of benthic fauna. We conclude that depth- 

 related factors may have greater influence than 

 sediment type on the composition of benthic fishes, 

 fish food, and invertebrate fauna within the 

 boundaries of our study area. This conclusion 

 must be tempered, however, by the realization 

 that other sediment parameters besides texture 

 and percent organic matter may be important, and 

 we simply did not study the proper sediment 

 characteristics. We agree with Peterson ( 1918): "It 

 is clear then that the character of the bottom is of 

 fundamental importance for the presence or ab- 

 sence of epifauna. Nevertheless, the succession of 

 the various types of epifauna and of the com- 

 munities belonging to the level bottom cannot be 

 explained by the character of the bottom alone." 



Bertrand ( 1971) estimated the "edible" biomass 

 of infauna ( >1.0 mm) for demersal fishes (i.e., all 

 infauna less holothurians, echinoids, echiurids, 

 and burrowing anemones) at these stations from 

 0. 1-m'^ Smith-Mclntyre grab samples taken on the 

 same cruises. He detected no seasonal variations 

 in the wet or ash-free dry weight of this biomass 

 fraction. The ash-free dry weights per square 

 meter for polychaetes, mollusks, and crustaceans 

 given by Bertrand for the seven stations are shown 

 in Table 8. Crustacean biomass was consistently 

 low at all stations, probably because of the ineffec- 

 tiveness of the grab to sample epibenthic and 

 motile amphipods, major food items of Dover and 

 rex soles. There was no direct or consistent rela- 

 tionship between the biomass per square meter of 



T.\BLE 8. — Ash-free dry weights in grams per square meter of 

 macro-infaunal fish food at the seven stations (from Bertrand 

 1971). 



Taxa 



Stn 22 



23 



15 



8 



Polychaetes 



Mollusks 



Crustaceans 



Total 



0.04 17 0.30 008 0.17 0.14 0.19 



4.50 1.10 1.74 209 0.20 0.16 0.07 



0.006 0.005 001 0004 0.008 0.004 0.003 



4 55 1.28 2.04 2.17 38 0.30 26 



"edible" fish food and the biomass of all fish or 

 Dover sole. Stations with similar standing stocks 

 of infaunal food had widely different standing 

 stocks of benthic fishes. 



Station 22, the beach sand station — with the 

 lowest organic carbon in the sediment of all 

 stations — supported a fairly low biomass of fish, 

 but the largest biomass of edible fish food, 4.55 

 g/m^, and the largest biomass of invertebrate mac- 

 robenthos. Conversely, Wigley and Mclntyre 

 (1964) found the largest biomass in finer sedi- 

 ments off Massachusetts, and Lie and Kisker 

 (1970) found that the shallow-water sand com- 

 munities off Washington had a lower average 

 standing stock of infauna than deeper com- 

 munities on the shelf. The large biomass at Sta- 

 tion 22 is composed primarily of the bivalves Acila 

 castrefhsis and secondarily of Tellina salnwnea. 

 Both of these mollusks were principal prey of 

 Dover sole only at Station 22 (Table 5). Although 

 the frequency of occurrence of these two mollusks 

 in Dover sole stomachs was only 107^ , mollusks 

 composed 58^f by weight of the food of Dover sole 

 at this station. Thus Dover sole are versatile pred- 

 ators, changing their diets opportunistically in re- 

 sponse to changes of prey availability. 



The dominant fish at Station 22 was Pacific 

 sanddab, primarily a pelagic feeder. Mollusks 

 were not principal prey. Acila and other burrow- 

 ing animals are unavailable as food for fishes 

 adapted for pelagic feeding, illustrating a basic 

 reason for the lack of any direct relationships be- 

 tween edible fish food and fish biomass. 



The average biomass of Dover sole was directly 

 related to the biomass of their principal food, 

 polychaetes, at the seven stations (Figure 6). Sta- 

 tion 22, where Dover sole consumed principally 

 mollusks, had the lowest biomass of both 

 polychaetes and Dover sole; intermediate values 

 of biomass of both fish and food are found at the 

 three deep stations (2, 6, 8). The three stations at 

 about 100 m (2, 7, and 15) differed markedly in 

 standing stocks of both polychaetes and Dover 

 sole. This positive correlation (r = 0.73) of stand- 

 ing stocks of predator and prey implies that Dover 

 sole selected habitats within our study area where 

 their prinicpal preferred food was most abundant 

 regardless of depth and bottom type. Of more fun- 

 damental interest is the fact that standing stocks 

 of polychaetes may indicate the amount of food 

 available to Dover sole, and perhaps the produc- 

 tion rates of polychaetes at the different stations. 

 Similar direct relationships between standing 



649 



