2018 Northern Fur Seal Pup Production and Adult Male Counts on the Pribilof Islands, Alaska

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.