2016 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 2016. We estimated 80,641 (SE = 717) pups were born on St. Paul Island and 20,490 (SE = 460) pups were born on St. George Island (Table 1). 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 2.7% on St. Paul Island and 1.1% on St. George Island. Pup production was not estimated on Sea Lion Rock, a small island approximately 500 m from St. Paul Island in 2016. The 2016 pup production estimate for St. Paul Island is 12.1% less than the estimate in 2014 (Figure 1). The 2016 pup production estimate for St. George Island is 8.2% greater than the estimate in 2014. Overall pup production for the Pribilof Islands decreased by approximately 8.6% from 2014 to 2016. Since 1998 pup production on St. Paul Island declined 55.0%, or at an annual rate of 4.12% (SE = 0.40), while pup production on the Pribilof Islands (St. Paul and St. George Islands combined) declined 49.7%, or at an annual rate of 3.5% (SE = 0.40). Estimated pup production on St. Paul has not been this low since before 1915 at which time the population was recovering from pelagic sealing at approximately 8% annually.
Adult male northern fur seals on St. Paul and St. George Islands were counted over the period July 10 to 19, 2016 (Table 2). Counts of territorial males with females (class 3; "harem" males) on St. George Island decreased by 9.2% compared to 2015. Idle males (classes 2 and 5,) on St. George Island decreased in comparison to 2015 by 14.5%. On St. Paul Island the "harem" males increased by less than 1.0% and the idle males decreased by 28.1% (Figure 2). Overall, the total number of adult males counted on the Pribilof Islands in 2016 decreased by 13.7% from 2015 to 7,515. The total number of “harem” males decreased by 1.4% on the Pribilof Islands.