204 



R. R. STRATY AND R. E. HAIGHT 



In our discussion, we mainly consider pre- 

 dation by birds on commercial fish and com- 

 petition between birds and commercial fish 

 for food. The extent of these interactions de- 

 termines the potential for birds and fish to in- 

 fluence each other's abundance. The extent of 

 the interactions also determines the impact of 

 man's commercial harvest of fish on the abun- 

 dance of birds or of the bird's harvest on the 

 abundance of fish. 



The extent of the interaction between 

 marine birds and commercial fish depends on 

 the abundance, distribution, feeding habits, 

 and life history of the fish species of concern. 

 We have limited our discussion to examples of 

 the major commercial pelagic and demersal 

 fish and shellfish of the eastern Bering Sea. 

 We also use as examples those species of 

 marine birds whose abundance in the eastern 

 Bering Sea and feeding habits give them the 

 greatest potential for influence on, or being in- 

 fluenced by, fish abundance. 



Abundance and Feeding Habits 



of Marine Birds in the 



Eastern Bering Sea 



Information on the general abundance and 

 distribution of the most important marine 

 birds in the eastern Bering Sea in the summer 

 and winter is scattered among many pub- 

 lished and unpublished reports: Shuntov 

 (1961, 1966), Sanger (1972), Bartonek and 

 Gibson (1972), and Ogi and Tsujita (1973); and 

 surveys by D. T. Montgomery and W. E. Oien 

 ("Bristol Bay waterbird survey, 1972," un- 

 published report of the U.S. Bureau of Sport 

 Fisheries and Wildlife, Alaska area) and by 

 J. G. King and D. E. McKnight (1969, "A 

 waterbird survey in Bristol Bay and pro- 

 posals for future studies," unpublished report 

 of the U.S. Bureau of Sport Fisheries and 

 Wildlife and the Alaska Department of Fish 

 and Game, Juneau, Alaska). 



In summer, the most abundant birds appear 

 to be the procellariids, mainly the slender- 

 billed shearwater (Puffinus tenuirostris) and 

 Pacific fulmar (Fulmarus glacialis); the al- 

 cids, mainly the common murre (Uria aalge), 

 thick-billed murre (U. lomvia), tufted puffin 

 (Lunda cirrhata), horned puffin (Fratercula 



corniculata), and the ancient murrelet (Synth- 

 liboramphus antiquus); and the larids, mainly 

 the glaucous- winged gull (Larus glaucescens) 

 and the black-legged kittiwake (Rissa 

 tridactyla). 



In winter, the alcids and larids appear to be 

 the most abundant groups, the procellariids 

 having been reduced by the departure of the 

 slender-billed shearwaters for breeding 

 grounds in the southern hemisphere. The se- 

 lection of the types of food to be consumed by 

 these marine birds is a function of their mor- 

 phological and physiological adaptations and 

 of the resultant feeding behavior. Ashmole 

 (1971) classified the feeding behavior of 

 various genera of marine birds and the rela- 

 tive importance of the kinds of food eaten by 

 each group; this information for some of the 

 Bering Sea bird species occurring in the 

 genera listed by Ashmole (1971) is sum- 

 marized in Fig. 5. 



Fish and invertebrates are evidently of 

 moderate to major importance in the diet of 

 these marine birds (Fig. 5). The extent to 

 which a given fish species is fed upon by or is 

 in competition with marine birds for food is 

 determined by the life history of the fish. 

 Most pelagic and some demersal fish and 

 shellfish are more subject to predation by pur- 

 suit diving birds than by birds restricted to 

 the near-surface waters. Invertebrates appear 

 to be equal to or more important than fish in 

 the diets of birds feeding in near-surface 

 waters (Fig. 5). 



Predation by Marine Birds 



The literature contains numerous accounts 

 of marine birds feeding on marine fish and 

 shellfish of commercial importance. Some 

 studies quantify the impact of some bird 

 species on certain species of commercial fish 

 (Outram 1958; Shaefer 1970; Wiens and Scott 

 1976) and shellfish (Glude 1967). Other 

 studies have shown that in some regions the 

 value of guano produced by birds may exceed 

 the value of the commercial fish they consume 

 (Jarvis 1970). Some fish of worldwide com- 

 mercial importance that are important in the 

 diets of marine birds are listed in Table 2. 



The significance of bird predation on pelagic 

 or demersal fish and shellfish (Fig. 5) depends 



