INTERACTIONS AMONG MARINE BIRDS AND COMMERCIAL FISH 



217 



feeding behavior, and food habits of marine 

 birds. 



The most apparent predation by marine 

 birds on fish is on fish large or mature enough 

 that some hard body parts persist and can be 

 found in the stomach samples of birds. 



Little is known of the extent of bird preda- 

 tion on the pelagic eggs and larvae of 

 demersal fish and shellfish in the Bering Sea 

 because of lack of investigation and the rapid 

 digestion of eggs and larvae by birds. 



Predation by marine birds on juvenile 

 salmon is not well documented because of the 

 lack of investigation in areas where both birds 

 and fish are present. 



Marine birds and commercial fish eat simi- 

 lar zooplankton and fish in the eastern Bering 

 Sea. The food exploited by both generally re- 

 flects the relative abundance of the types of 

 food in the area, but food preference is dis- 

 played by some species of fish and birds. 



More is known about the food habits of the 

 commercial fish than of the marine birds of 

 the Bering Sea. 



Sea water temperature may be a major en- 

 vironmental factor in the Bering Sea since it 

 influences both the extent to which fish are 

 vulnerable to predation and the amount of 

 competition with marine birds. Sea tempera- 

 tures may vary greatly from year to year in 

 the Bering Sea, and this may result in varia- 

 tions in the magnitude of predation and com- 

 petition between birds and fish. 



The distribution of marine birds and the 

 various stages in the life history of commer- 

 cial fish are not well known for the eastern 

 Bering Sea. Where these have been studied, 

 they are intimately related. Such knowledge is 

 required to gain some insight into even the 

 potential for predation and competition in the 

 dynamics of the marine bird and commercial 

 fish populations of this region. In two in- 

 stances, it is known that the occurrence of 

 marine birds and the early life history stages 

 of fish coincide so as to result in both poten- 

 tial predation on the fish by the birds and 

 competition for food between the fish and the 

 birds. 



The possibility exists that the commercial 

 fish resources of the eastern Bering Sea will 

 eventually come under the jurisdiction of the 

 United States. This could mean reduced har- 

 vests of fish to restore depleted stocks. Such 



action could result in changes in the abun- 

 dance of the marine birds of this region by 

 creating an increased food supply for some 

 and decreased supply for others. 



Acknowledgments 



We thank J. C. Bartonek and H. R. Carlson, 

 H. Jaenicke, H. Larkins, and B. L. Wing for 

 supplying various materials presented in this 

 paper. 



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