potential prey in short supply is unknown. 



Seasonal intrusions of abundant predators could also result in 

 food resource limitation and competition. Tyler (1972) reported 

 that seasonally abundant species did not, as a group, feed on a 

 unique set of prey species. In the present study 5. chrysops, a sea- 

 sonal species, was similar in diet to U. chuss and M. bilinearis. 

 Ocean pout were only abundant seasonally (in summer), but fed on 

 common prey species shared with other predators. Apparently sea- 

 sonal intrusions of abundant predators do not affect food availabil- 

 ity on the Middle Atlantic Shelf. 



Overlap in diet between closely related species is generally lower 

 than that for unrelated species, suggesting food resource partition- 

 ing among closely related species. Thus the congeners U. chuss and 

 U. regia show a low similarity in prey species and prey size (Fig. 

 29). Seasonally, the bothids Citharichthys arctifrons and Hip- 

 poglossina oblonga were also quite dissimilar in diet. Still , no pred- 

 ator monopolized any trophic resource. This apparent food 

 resource partitioning among closely related species may be due. not 

 to present limited food resources, but to environmental factors and 

 predator community structure during the evolutionary history of 

 these species. 



Although predators demonstrated considerable diet overlap, each 

 predator had a diverse diet and fed selectively on some prey items 

 that were not as important in the diets of other predators. Perhaps 

 each predator has a food refuge in these prey species if competition 

 for food becomes intense. Due to overexploitation by fishing ves- 

 sels, populations of fishes on the outer shelf may be below carrying 

 capacity (Edwards 1976; Clark and Brown 1977; Edwards and 

 Bowman 1979). allowing several dominant species to coexist on 

 similar food resources. At higher population levels, food resources 

 may become a limiting factor and the high level of diet overlap 

 could lead to competition. With reduced fishing pressure due to 

 extended jurisdiction by the United States, fish populations on the 

 outer shelf may increase, and food competition ma) become 

 intense. 



ACKNOWLEDGMENTS 



I thank John A. Musick. my major advisor, for providing assist- 

 ance during this study and for his re\ iew of the manuscript; C. A. 

 Barans. G. C. Grant, and C. A. YVenner for their criticism and 

 review of the manuscript; and the able assistance, in the field and in 

 the laboratory, of many Virginia Institute of Marine Science 

 employees and graduate students. I especially thank R. K. Carpen- 

 ter. J. A. Colvocoresses, E. J. Foell, N. P. Heil. R. W. Middleton, 

 W. G. Raschi. and J. van Montfrans for their assistance on cruises; 

 M. A. Bowen (amphipods). E. L. Wenner and J. van Montfrans 

 (decapods). G. Gaston (polychaetes), G. C. Grant (copepods and 

 chaetognaths), and R O. Smyth (decapod larvae) for help in identi- 

 fying pre\ organisms; and W. R Blystone for the computer pro- 

 grams used in data analysis. This work was supported through 

 funds provided by the Bureau of Land Management, contract 

 AA550-CT6-62. and the Virginia Institute of Marine Science. 



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