FISHERY BULLETIN: VOL. 81. NO. 1 



southern New England. The other major differ- 

 ence between areas was in the quantity of other 

 polychaetes, but a large percentage of this group 

 was unidentified remains (12.93% in southern 

 New England and 11.61% on Georges Bank). The 

 diversity of polychaete prey was very similar in 

 the two areas; 27 families of polychaetes in the 

 stomach contents of fish from southern New Eng- 

 land and 24 different families on Georges Bank. 

 Eleven different genera of polychaetes were iden- 

 tified in each area. Six of these were common to 

 both regions, but only Spiophanes contributed 

 >1% to the total stomach contents weight. 



Amphipods made up almost twice the percent- 

 age of the weight of stomach contents in southern 

 New England than on Georges Bank (18.87% vs. 

 10.23%). The same species were important in 

 both areas (Table 2). There was, however, a 

 slightly greater reliance on Unciolasp. and Lep- 

 tocheirus pinguis in southern New England than 

 on Georges Bank. The diversity of amphipod 

 prey was greater on Georges Bank, 16 genera as 

 opposed to 11 genera, although yellowtail floun- 

 der from the two areas preyed on 9 of the same 

 genera. 



Crustaceans such as C. septemspinosa and D. 

 leptocerus played a minor role in the diet of yel- 

 lowtail flounder as did all other arthropod groups 

 except the amphipods. The only other category of 

 stomach contents that differed substantially be- 

 tween areas was the quantity of sand in the stom- 

 achs. This might be related to the heavy preda- 

 tion on «S. bombyx on Georges Bank, since this 

 polychaete is reported to prefer a fine sand sub- 

 strate (Light 1978). 



The percentage of empty stomachs was virtu- 

 ally the same in southern New England and on 

 Georges Bank, but was less in the Middle Atlan- 

 tic (Table 2). The mean weight per stomach in- 

 creased from the Middle Atlantic to Georges 

 Bank and the mean fish length also increased 

 from south to north(Table2). This size difference 

 did not counterbalance the increase in stomach 

 content weight. The mean weight of stomach con- 

 tents ranged from 0.12% in the Middle Atlantic 

 to 0.14% in southern New England and 0.21% 

 body weight on Georges Bank. 



Yearly, Seasonal, and Diurnal Variation 



Data were collected over a 4-yr period in both 

 the spring and autumn and throughout the day- 

 night cycle. It is, therefore, possible to examine 

 the influence of the time of capture on the com- 



position of the diet as well as on changes in the 

 absolute quantity of prey in the stomachs. 



On a year-to-year basis, polychaete worms were 

 always the most important prey, between 36 and 

 44% of the diet, followed by amphipod crusta- 

 ceans, 10 to 33% of the diet. Within these two taxa 

 the actual percentage composition of the various 

 groups fluctuated, but no systematic changes in 

 diet were discernible. Within the Polychaeta, for 

 example, S. bombyx made up between 2 and 12% 

 of the diet from 1973 to 1974 and ranged from 9 to 

 11% between 1975 and 1976, respectively. At the 

 family level, Spionidae, the range increased from 

 2 to 16% for the first 2 yr and 9 to 18% for the lat- 

 ter 2 yr. When spionids were most important, 

 there was also a very large percentage of sand in 

 the stomachs, 20 and 27% for 1974 and 1976, re- 

 spectively, which probably relates to predation 

 on these particular polychaetes. Among the am- 

 phipods, Unciola sp. showed the greatest fluctua- 

 tion, ranging from 16% of the diet in 1973 to 1% in 

 1975 but increasing to just under 5% in 1976. 



The mean weight of prey showed an increase 

 from 1973 to 1976, but when this was corrected 

 for fish size, there was no pattern evident in these 

 changes. The slightly larger mean fish lengths 

 occurring in 1975 and 1976 counterbalanced the 

 increase in the mean weight of stomach contents. 

 The percentage of empty stomachs also showed 

 no consistent yearly change, fluctuating around 

 the overall mean value of 33%. 



Species composition of the diet showed no dras- 

 tic shift between spring and autumn. Polychaetes 

 were more important in the spring (49%) than in 

 the autumn (35%), and the same was true for am- 

 phipods, 19% vs. 13%. Both of the changes may, 

 however, simply reflect the higher percentages 

 of unidentified animal remains and sand in the 

 fish stomachs collected in the autumn. 



In all years, except 1976, stomachs collected on 

 spring cruises contained a greater mean weight 

 of prey than stomachs from fish collected in the 

 autumn. Although the mean length offish in the 

 spring was only slightly larger (30.0 cm vs. 28.8 

 cm). The 4-yr mean weight of prey in the stom- 

 achs was 0.505 g (0.20% body weight) for the 

 spring and 0.298 g (0.14% body weight) in the 

 autumn. The percentage of empty stomachs was 

 also lower in the spring than the autumn; 22.7% 

 of the 574 stomachs examined from spring 

 cruises versus 46.3% of 447 stomachs examined 

 from autumn cruises. 



An examination of the data for a composite 

 24-h day revealed a diurnal feeding pattern. 



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