UNIT 22 

 MARINE MAMMALS OF THE ALASKA REGION 



-**;i*^ 







Northern fur seal bull, cow, 

 and pup. Saint Paul Island, 

 eastern Bering Sea. 



NORTHERN FUR SEAL: 

 EASTERN PACIFIC STOCK 



Stock Definition 



and Geographic Range 



Northern tur seals are found l"rom southern 

 CaHfornia north to the Bering Sea and west to the 

 Okhotsk Sea and Honshu Isktnd, japan. During 

 the breeding season, approximately 74% of the 

 worldwide population is found on the I'ribilot Is- 

 lands in the southern Bering Sea, with the remain- 

 ing animals spread throughout the North Pacific. 

 Of the seals in U.S. waters outside of the Pribiloh, 

 appro.ximately 1% ot the population is found on 

 Bogoslot Island in the southern Bering Sea and 

 San Miguel Island off southern t^alitornia. Fur 

 seals may temporarily haul out onto land at other 

 sites in Alaska, British Cohmibia, and on islets 

 along the coast of the continental United States, 

 but generally outside ol the breeding season. 



Adults usualh' are found on shore during the 

 6-month reproductive season (June-November), 

 then migrate south and spend the next 6 months 

 at sea. Adult females and pups from the Pribilof 

 Islands migrate through the Aleutian Islands into 

 the North Pacific, often to the Oregon and Cali- 



fornia offshore waters. Pups may remain at sea for 

 22 months before returning to their rookery of 

 birth. Adult males generally migrate only as far 

 south as the Gulf of Alaska and the Kamchatka 

 coast. Iwo separate stocks of northern fur seals 

 are recognized within U.S. waters: an eastern Pa- 

 cific stock, and a San Miguel Island stock. 



Population Size 



Ihe population estimate for the eastern Pa- 

 cific stock of fur seals is calculated as the estimated 

 number of pups at rookeries multiplied by a series 

 of different expansion factors determined froin a 

 life table analysis to estimate the number of year- 

 lings, 2-year-olds, 3-year-olds, and animals at least 

 4 years old. The expansion factors are based on a 

 sex and age distribution estimated after the har- 

 vest of juvenile males was terminated. The result- 

 ing population estimate is equal to the pup count 

 multiplied by approximately 4.47'i. As the great 

 majority of pups arc born on the I'ribilof Islands, 

 pup estimates are concentrated on these islands, 

 though additional counts are made on Bogoslof 

 Island. A total population estimate for the north- 

 ern Pacific stock based on recent pup counts was 

 1,002,516 seals. 



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