2018 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, shear-sampling, on the Pribilof Islands during August 2018. We estimated 75,719 (SE = 1,008) pups were born on St. Paul Island and 21,625 (SE = 345) 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 3.0% on St. Paul Island and 1.6% on St. George Island. Pup production was not estimated on Sea Lion Rock, a small island approximately 500 m from St. Paul Island in 2018. The 2018 pup production estimate for St. Paul Island is 6.1% less than the estimate in 2016 (Figure 1). The 2018 pup production estimate for St. George Island is 5.5% greater than the estimate in 2016. Overall pup production for the Pribilof Islands decreased approximately 3.7% from 2016 to 2018. Since 1998 pup production on St. Paul Island declined 57.7%, or at an annual rate of 4.04% (SE = 0.34), while pup production on the Pribilof Islands (St. Paul and St. George Islands combined) declined 51.6%, or at an annual rate of 3.4% (SE = 0.36). Pup production on St. George shows no significant trend in production since 1998 but the last three estimates have all shown an increase in pup production.