FISHERY BULLETIN: VOL. 81. NO. 1 



fur seals in the Bering Sea. Using Miller's esti- 

 mate for consumption would give an estimate of 

 705,000 t eaten annually by fur seals. Laevastu 

 and Larkins ( 1981 ) gave an estimate of 513,000 t 

 taken by fur seals annually in the eastern Bering 

 Sea, with an additional 368,000 t taken in the 

 Aleutian region. The latter estimates were based 

 on runs of the PROBUB (prognostic bulk bio- 

 mass) model. Estimates of fur seal populations of 

 the Bering Sea and the Aleutian Islands and 

 their mean consumption rates, given in Table 3 

 (Anonymous footnote 18), were used to compute a 

 total fur seal consumption of 219,000 t. 



These estimates can be compared with annual 

 fish catches in the eastern Bering Sea and Aleu- 

 tian Islands (North Pacific Fishery Management 

 Council 20 ). Between 1968 and 1976, annual fish 

 catches varied between 750,000 and 2,100,000 t 

 in the eastern Bering Sea and between 40,000 

 and 80,000 t near the Aleutian Islands. These fig- 

 ures indicate that fish harvests by marine 

 mammals and by man in the Bering Sea are com- 

 parable and that the marine mammals' harvest 

 exceeds man's in the Aleutian Islands' area. It is 

 important to note, however, that fur seals prey on 

 a larger number of species than man, and thus a 

 part of their harvest is not in direct competition 

 with man's. As a consequence of the fur seals' 



greater ability to switch prey when abundances 

 of preferred prey species are low, total fur seal 

 consumption is probably fairly steady from year 

 to year, while man's is highly variable. 



It has been estimated (Anonymous footnote 18: 

 table 12) that 9.8% of fish standing stock in the 

 eastern Bering Sea and the Aleutian Islands is 

 consumed annually by marine mammals, 5% by 

 man, and 1.8% by birds (1.9% by fur seals). Lae- 

 vastu and Larkins (1981) estimated a total com- 

 mercial fish standing stock of 24,880,000 1 in the 

 Bering Sea and Gulf of Alaska, which implies 

 that 3.5% of all commercial fish stocks are taken 

 by fur seals annually and 10.7% by all marine 

 mammals. The fur seal figures are deceptive, 

 since fur seal impact on fish stocks is relatively 

 localized. Thus, fur seals near the Pribilof Islands 

 are probably consuming considerably more fish 

 than man is, though man may be harvesting 

 some different species than fur seals. This ener- 

 getics computation is inconclusive with respect 

 to fur seal-fishery interaction, except to show 

 that competition between the two is possible. 



DISCUSSION 



Suggested Analyses of Existing Data 

 Population Indices 



-"Data available from North Pacific Fishery Management 

 Council, 333 W. Fourth Ave., Suite 32, P.O. Box 3136DT, An- 

 chorage. AK 96813. 



Following Eberhardt and Siniffs (1977) sug- 

 gestion that a population's response to impact 

 may be reflected by various indices, we suggest 



Table 3. — Fur seal population estimates at sea (June-November) in the eastern Bering Sea 

 and Aleutian area (Anonymous text footnote 18). 



'Average 1969 to 1974. 



2 Based on National Marine Mammal Division, NMFS pelagic research data, 1958-74, N = 13,772, except 

 average weight for pups (10 kg) based on observations in the Pribilof Islands during September; total mean 

 weight based on an effective fishery population 754,000, on time spent on land and at sea for each class 

 during June and September. 



'Weighed by mean animal weight of estimated body weight for animals weighing <10 kg or <45 kg in 

 waters colder than 15°C; 7% for >10 kg on land or >45 kg at sea. 



"Based on the ratio of males to females (0.085) in the eastern Bering Sea during June-November from 

 National Marine Mammal Division, NMFS pelagic research data, 1958-74 (N = 4,451). 



5 8% mortality, pups estimated to feed at sea only 18 d (10% of time) during September-November 



6 These percentages represent proportions of the total population of the respective age class not on the 

 rookeries during the breeding season 



7 Based on percent of time out of 130 d not on rookery. 



8 Effective fishery population (June-November) 



130 



