SWARTZMAN and HAAR: INTERACTIONS BETWEEN FUR SEALS AND FISHERIES 



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7 years 



6 years 

 5 years 



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Jan Feb Mar Apr May June July Aug See Oct Nov Dec 



Figure 1.— Seasonal pattern of growth in mean length (cm) of 

 nonpregnant female fur seals of age 1-7. Curves are drawn by 

 inspection with the restriction of no downward curvature. An x 

 designates <10 seals. From Lander (1981). 



Sampling on the Fur Seal Rookeries 



The herds on the Pribilof Islands (St. Paul and 

 St. George Islands and Sea Lion Rock) are esti- 

 mated to comprise 80% of the total world fur seal 

 population. Every year from 1912 to 1924 and 

 since 1950 some census of pup births has been 

 made. Dead pup counts have also been made. 

 Harvests of subadult males on the island hauling 

 grounds have yielded information on weights, 

 lengths, and age composition of these animals as 

 well as limited food data from stomach samples. 

 An estimate has also been made annually of num- 

 bers of harem bulls. 



From 1956 to 1968 almost 300,000 females 

 were harvested from St. Paul and St. George 

 Islands, presumably to increase the sustained 

 productivity of the herds. The herd subsequently 

 failed to achieve a higher sustained productivity 

 as was postulated from higher pregnancy and 

 survival rates predicted from population projec- 

 tions (Abegglen et al. 1956 9 ). 



From 1912 to 1924, pup populations were esti- 

 mated from direct counts. Fur seal populations 

 increased steadily over this period at an 8% an- 

 nual rate, as they recovered from heavy losses 



due to pelagic sealing in the late 19th and early 

 20th centuries. Direct counts were discontinued 

 from 1924 to 1948, but an 8% annual population 

 increase was assumed. However, estimates of 

 pups in 1948 showed that the 8% increase had not 

 continued. In 1947, tagging studies were set up to 

 estimate pups and were continued until 1961. 

 In 1960 an estimation procedure involving pup 

 shearing and direct counts was initiated to re- 

 place the tagging method. Estimates of the num- 

 ber of pups born were computed by adding live 

 pup estimates to dead pup counts. 



The 1951-61 tagging studies are presently 

 thought to have greatly overestimated actual 

 pup abundance because of procedural difficul- 

 ties and lost tags (Chapman 1973). The pup shear- 

 ing procedure, although shown to be unbiased by 

 comparing pup estimates with direct counts on 

 small rookeries (Chapman and Johnson 1968), 

 may be biased for large rookeries in such a 

 way as to underestimate actual pup numbers 

 (Fowler 10 ). 



Age-specific survival and weight at age were 

 estimated from the weighing and aging of the 

 preadult males harvested annually on the rook- 

 eries. Male harvest was discontinued on St. 

 George Island in 1972 to study the effect of the 

 male population density on seal population dy- 

 namics. Recent pup survival on St. George Island 

 appeared lower than on St. Paul Island (Lander 

 1981), and this has been linked to the increased 

 abundance of idle males on the rookeries (Fowler 

 footnote 10). 



Bering Sea Fish Data 



Data on commercially important Bering Sea 

 fish stocks by species have been compiled by the 

 NWAFC. Catch data from Japanese, Russian, 

 Korean, Polish, United States, and Canadian 

 fishing operations have been included. The ma- 

 jor species (in order of magnitude of catch) are 

 walleye pollock, Theragra chalcogramma; yel- 

 lowfin sole, Limanda aspera; Pacific herring, 

 Clupea harengus pallasi; Pacific salmon, Onco- 

 rhynchus spp; Pacific cod, Gadusmacrocephalus; 

 sablefish, Anoplopoma fimbria; Pacific halibut, 

 Hippoglossus stenolepis; other flatfish (rock sole, 

 flathead sole, Alaska plaice, Greenland turbot, 



9 Abegglen, C. F., A. Y. Roppel, and F. Wilke. 1956. Alas- 

 ka fur seal investigations, Pribilof Islands, Alaska. Manuscr. 

 rep., 143 p. Northwest and Alaska Fisheries Center National 

 Marine Mammal Laboratory, National Marine Fisheries Ser- 

 vice, NOAA, 7600 Sand Point Way NE., Seattle. WA 98115. 



10 C. W. Fowler, Head, Fur seal investigations group, North- 

 west and Alaska Fisheries Center National Marine Mammal 

 Laboratory, National Marine Fisheries Service, NOAA, 7600 

 Sand Point Way NE., Seattle, WA 98115, pers. commun. June 

 1980. 



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