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NOAA Technical Memorandum NMFS-AFSC-241

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Fur seal investigations, 2010 - 2011


Researchers from the Alaska Fisheries Science Center’s National Marine Mammal Laboratory conduct field investigations on the population status of northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Bogoslof Island in the eastern Bering Sea, and on San Miguel Island off the coast of California. This report summarizes these monitoring efforts in 2010 and 2011.

Population parameters monitored on the Pribilof Islands included the size of the subsistence harvest and the number of adult male fur seals. On St. Paul Island 3,974 and 3,829 territorial male seals with females were counted in 2010 and 2011, respectively, and both years represented a 3.6% annual decline from the previous year.  On St. George Island the respective totals were 805 and 873, representing a 4.9% decrease in 2010 and 1.4% increase in 2011. On St. Paul Island, 357 and 322 subadult male seals were harvested in 2010 and 2011, respectively. On St. George Island the respective totals were 78 and 120.  The estimate for the total number of pups born in 2010 was 93,627 (SE = 1,034) on St. Paul Island (not including Sea Lion Rock) and 17,973 (SE = 323) on St. George Island. Pup mortality from birth to late August was 5.3% on St. Paul Island and 5.3% on St. George Island. The number of pups born on St. Paul Island in 2010 was 8.8% less than in 2008 (P < 0.01), while at St. George the number of pups was not significantly different from the 2008 estimate. The overall rate of decline on the Pribilof Islands since 1998 was 4.9%. Both male and female pups on St. George Island were significantly longer and heavier than those on St. Paul Island (P < 0.01) in 2010.

Index counts of territorial bulls on San Miguel Island, California, in 2010 and 2011 were 65 and 148, respectively. In 2010 and 2011, total numbers of pups born at Adams Cove on San Miguel Island were 1,537 (SE = 12) and 1,398 (SE = 4); at nearby Castle Rock the numbers were 1,144 (SE = 27) and 1150 (SE = 8). Pup production in 2010 was near the peak recorded in 1997, just prior to a strong El Niño event, though the recovery since that time has been sporadic.  Pup mortality in recent years has been high, and remained so in 2010 (47%) and 2011 (37%). Pup weights at San Miguel Island in both 2010 and 2011 were near the long-term average. 

The estimated stock size for all fur seals breeding in the United States in 2010 was ~671,000, with the Pribilof Islands population accounting for ~566,000.  
View Online  (.pdf, 1.85 MB).

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