SWARTZMAN and HAAR: INTERACTIONS BETWEEN FUR SEALS AND FISHERIES 



Table 2. — Fur seal dietof walleye pollock from pelagic samples in theeastern 

 Bering Sea. (Unpubl. data (text footnote 16).) 



crease in total stock biomass, mostly in the youn- 

 ger age classes, can account both for the increased 

 fur seal diets on (mostly smaller) pollock and the 

 continued high yield of the fishery after over 10 

 yr of heavy fishing pressure. 



Table 2 indicates that both fur seals and the 

 fishery may have exploited the same pollock re- 

 source, since both show a drop in size of "catch" 

 over time. We suspect that the trend toward 

 greatly increased abundance of pollock juveniles 

 in the Bering Sea has also resulted in larger 

 schools (patches) of juvenile pollock, which has 

 made them an easier target for the fur seals and 

 also the fishery, than previously. One possible, 

 dangerous consequence of future increased fish- 

 ing pressure on pollock, however, is that most of 

 the catch will be of premature individuals. With 

 continued heavy fishing pressure, this might re- 

 sult in inadequate recruitment to maintain the 

 stock. 



A possible alternative explanation for why pol- 

 lock were so consistently taken by fur seals in 

 1973-74 is that these were relatively cold years 

 with pollock aggregating more on the outer shelf 

 than in warmer years (Pereyra et al. footnote 5). 

 Another possible explanation is that the Pribilof 

 area, where the bulk of the 1973 and 1974 stom- 

 ach samples were taken (unlike the earlier sam- 

 ples which did not focus as heavily on this area), 

 is a nursery area for young-of-the-year pollock, 

 which may account for the reduced average size 

 and increased abundance of pollock in fur seal 

 stomachs during 1973 and 1974. Despite these 

 possible alternatives, the most plausible hypothe- 

 sis is that pollock has increased in importance in 



fur seal diets since the initiation of the pollock 

 fishery. 



Energetics Approach to 

 Fur Seal Food Consumption 



The total amount of food consumed by fur seals 

 (and other marine mammals as well) in the east- 

 ern Bering Sea has been estimated by a num- 

 ber of individuals (Laevastu and Larkins 1981; 

 McAlister and Perez 1976 17 ; Anonymous 1979 18 ). 

 McAlister and Perez (footnote 17) estimated that 

 fur seals eat 378,000 t of fish and squid every 

 year. They used an estimated feeding rate of 7.5% 

 body weight daily while Miller ( 1978) 19 suggested 

 that 14% body weight daily may be more appro- 

 priate to support seals at 7°C, the average sum- 

 mer temperature in the Bering Sea. Miller based 

 his arguments on metabolic studies in which he 

 recorded oxygen consumption at different tem- 

 peratures in the laboratory for a number of juve- 

 nile seals and also conducted feeding studies 

 using food most commonly found in the diet of 



"McAlister, W. B., and M. A. Perez. 1976. Preliminary 

 estimates of pinniped-finfish relationships in the Bering Sea. 

 Background paper for the 19th meeting of the North Pacific 

 Fur Seal Commission, 29 p. Northwest and Alaska Fisheries 

 Center National Marine Mammal Laboratory, National Ma- 

 rine Fisheries Service, NOAA, 7600 Sand Point Way NE., 

 Seattle, WA 98115. 



18 Anonymous. 1979. Draft environmental impact state- 

 ment of the Interim Convention on Conservation of North Pa- 

 cific Fur Seals. U.S. Dep. Commer., NOAA, Natl. Mar. Fish. 

 Serv., Seattle, Wash., 39 p. 



19 Miller, L. K. 1978. Energeticsof the northern fur seal in 

 relation to climate and food resources of the Bering Sea. U.S. 

 Marine Mammal Commission Report MMC-75/08, 27 p. 



129 



