FISHERY BULLETIN: VOL. 84, NO. 4 



Eastern Bering Sea 



Walleye pollock was the most important food for 

 northern fur seals in the eastern Bering Sea, par- 

 ticularly around the Pribilof Islands and in other in- 

 shore waters during July to September (Fig. 11 A, 

 B, C). Capelin was the main food near Unimak Pass 

 during June to October. The squids, Berryteuthis 

 magister and Gonatopsis borealis, were the primary 

 prey species of fur seals in the oceanic areas (Fig. 

 11C). Deep-sea smelts (Bathylagidae) were eaten off- 

 shore, mainly in association with squid. The relative 

 importance of each prey species was not markedly 

 affected by the energy content adjustments (Fig. 

 11A). 



Effect of Energy Value of Prey 



In general, the ranking of prey species in the diet 



of northern fur seals was similar when using either 

 modified volume or modified volume weighted for 

 the energy content of prey. However, caloric values 

 affected relative importance in regions where high 

 energy foods (e.g., Pacific herring, northern an- 

 chovy, salmonids), or where low energy foods (e.g., 

 market squid, Pacific whiting) were commonly 

 eaten. In such cases, the adjustment shifted impor- 

 tance of a prey species in the same direction as the 

 relative value of their caloric content compared with 

 other prey in the diet. A species with high energy 

 content increased in importance, but this caused 

 others to decrease because the relative values of 

 prey species in the diet all totaled 100%. 



DISCUSSION 



The results of earlier investigations on the diet 

 of northern fur seals indicated that basically the 



UNIMAK PRIBILOF BERIN BEROFF 

 N 543 308 1017 732 



Figure 11.— Composition (percent) of diet of northern fur seals 

 by prey species in the eastern Bering Sea during 1958-74 (A) for 

 pooled June-October samples (N = 1,749), using modified volume 

 (dark bars) and energy-adjusted modified volume; (B) by month 

 using modified volume; and (C) by subregion, with pooled June- 

 October samples using modified volume. A dark line separates 

 squid and fish categories in the latter two figures. Key: ATK = 

 Atka mackerel; BER = Berryteuthis magister; CAP = capelin; 

 DEE = deep-sea smelts; GTP = Gonatopsis borealis; HER = 

 Pacific herring; MF = miscellaneous fish species; OP = other prey; 

 POL = walleye pollock. 



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