Steimle et al.: Predator-prey relationships of Pleuronectes americanus 



61 1 



anthozoan, Ceriantheopsis americanus, a polychaete, 

 Pherusa affinis, and the sand shrimp Crangon 

 septemspinosa varied between 0.96 and 1.00 (n=>26). 

 However, the ratios for calcareous-shelled prey were 

 lower, 0.70 for the bivalve mollusc Nucula proximo 

 (n-50), and 0.77 for the sand dollar Echinarachnius 

 parma (n=30). 



All fish were collected near mid-day; therefore, the 

 effects of digestion on stomach volume estimates were 

 not considered a major factor. Winter flounder are 

 primarily daytime feeders and all but the most soft- 

 bodied prey should remain identifiable in their stom- 

 achs for several hours (MacDonald et al., 1982). 



Results 



Diet spectrum and dominance 



Forty-nine prey taxa were identified in winter floun- 

 der stomachs, although only about 30 taxa were iden- 

 tified in the stomach contents at any individual sta- 

 tion (Table 2). These are conservative estimates be- 

 cause of some uncertainties in identification caused 

 by digestion. This prey spectrum represents about a 

 quarter of the total available benthic macrofaunal 

 taxa identified at station NY6 ( 119 species) and R2 

 (133 species), and about a fifth of the 154 species 

 identified at station NYU. 



Dominant prey, defined as species that composed 

 at least 2% of the total stomach volume of fish from 

 any station, were the polychaetes Pherusa affinis, 

 Asabellides oculata, andNephtys incisa and the tube- 

 dwelling anthozoan Ceriantheopsis americanus. The 

 rhynchocoel Cerebratulus lacteus, juvenile rock crabs 

 Cancer irroratus, and other polychaetes, including 

 Capitel/a sp. and Scoletoma (Lumbrineris) spp., were 

 dominant in the diet at one or two stations (Table 3). 

 Collectively these eight taxa constituted between 76% 

 and 96% of the winter flounder diet by volume at the 

 three stations (Table 3). 



Predation patterns 



The log forage ratio (K) indices were positive for sev- 

 eral dominant species. The K index was consistently 

 high (>+0.25) for the polychaetes, P. affinis and A. 

 oculata. High positive K values were also calculated 

 for other prey, but at only one or two stations (Table 

 3). The K indices were near zero (±0.20) for some 

 dominant species at some stations, such as C. 

 americanus. For other prey or at other stations the 

 K indices were low (<-0.25). This was especially evi- 

 dent for C. americanus, Spio setosa, Glycera sp., and 

 the molluscs (Table 3). 



Comparison of the contributions of these dominant 

 prey species to flounder diets and to macrofaunal 



