2010 Northern Fur Seal Pup Production and Adult Male counts on the Pribilof Islands, Alaska
Pup production and adult male northern fur seal count
Numbers of northern fur seal, Callorhinus ursinus, pups were estimated using a mark-recapture method, shearsampling, on the Pribilof Islands during August 2010. We estimated 94,502 (SE = 1,120, Table 1) pups were born on St. Paul Island and 17,973 (SE = 323, Table 1) pups were born on St. George Island. To minimize disturbance, dead pup counts were conducted at 4 sample rookeries on St. Paul Island and 3 sample rookeries on St. George Island. As in 2006 and 2008, this dead pup counting procedure resulted in a ratio estimation protocol for the calculation of the estimate of the total number of pups born. The observed pup mortality rates were 5.6% on St. Paul Island and 5.3% on St. George Island. Pup production was not estimated on Sea Lion Rock, a small island approximately 500 m from St. Paul Island in 2010. The 2010 pup production estimate for St. Paul Island is 8.0% less than the estimate in 2008 (Figure 1). The 2010 pup production estimate for St. George Island is 1.0% less than the estimate in 2008. The overall decrease in pup production for St. Paul and St. George Islands combined from 2008 to 2010 is approximately 6.9%. Since 1998 pup production on St. Paul Island has declined at an annual rate of 5.4% (SE = 0.34) and on the Pribilof Islands (St. Paul and St. George Islands) at an annual rate of 4.9% (SE = 0.37).
Adult male northern fur seals on St. Paul, and St. George Islands (Table 2) were counted over the period July 9 to 17, 2010. Counts of territorial males with females ("harem" males) on St. George Island decreased by 4.9% compared to 2009. Idle males on St. George Island increased in comparison to 2009 by 25.0%. On St. Paul Island the idle males decreased by 7.4% and the "harem" males decreased by 3.7% (Figure 2). Overall, the total number of adult males counted on the Pribilof Islands in 2010 decreased by 3.3% from 2009 to 10,674. The total number of territorial males with females decreased by 3.8% on the Pribilof Islands.