2014 Northern Fur Seal Pup Production and Adult Male Counts on the Pribilof Islands, Alaska
Northern fur seal pup and adult male counts
Numbers of northern fur seal, Callorhinus ursinus, pups were estimated using a mark-recapture method, shearsampling, on the Pribilof Islands during August 2014. We estimated 91,737 (SE = 769, Table 1) pups were born on St. Paul Island and 18,937 (SE = 308, 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. Since 2006 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 3.0% on St. Paul Island and 2.7% on St. George Island. Pup production was estimated on Sea Lion Rock, a small island approximately 500 m from St. Paul Island in 2014 resulting in an estimate of 5,250 (SE = 293) pups born. The 2014 Sea Lion Rock estimate was 22.1% lower than the previous estimate in 2008. The 2014 pup production estimate for St. Paul Island is 5.2% less than the estimate in 2012 (Figure 1). The 2014 pup production estimate for St. George Island is 17.0% greater than the estimate in 2012. Overall pup production for the Pribilof Islands decreased approximately 2.1% from 2012 to 2014. Since 1998 pup production on St. Paul Island declined 49.0%, or at an annual rate of 4.25% (SE = 0.48), while pup production on the Pribilof Islands (St. Paul and St. George Islands combined) declined 45.0%, or at an annual rate of 3.7% (SE = 0.48).
Adult male northern fur seals on St. Paul and St. George Islands (Table 2) were counted over the period July 7 to 15, 2014. Counts of territorial males with females (class 3; "harem" males) on St. George Island decreased by 8.1% compared to 2013. Idle males (classes 2 and 5, Table 2) on St. George Island increased in comparison to 2013 by 21.1%. On St. Paul Island the "harem" males decreased by 11.4% and the idle males decreased by 13.3% (Figure 2). Overall, the total number of adult males counted on the Pribilof Islands in 2014 decreased by 8.8% from 2013 to 8,850. The total number of “harem” males decreased by 10.7% on the Pribilof Islands.