2015 Northern Fur Seal Pup Production Estimate on Bogoslof Island, Alaska
Northern fur seal pup estimates
Numbers of northern fur seal, Callorhinus ursinus, pups were estimated using a mark-recapture method, shearsampling, on Bogoslof Island (Figure 1) during August 10 to 15, 2015. For the 2015 estimate, the island was divided into 4 rookeries instead of 5 as had been done from 2005 to 2011. We no longer considered the Grotto to be a separate rookery due to the near continuous distribution of adults and little physical separation that would prevent an exchange of pups with Northwest rookery. The combination of the Grotto and Northwest will be referred to as Northwest rookery. As the population grows, Southwest rookery may also be merged with Northwest as there is very little separation remaining between the rookery areas.
We estimated that 27,750 (SE = 228, Table 1) pups were born on Bogoslof Island. Dead pups were counted on all breeding areas of Bogoslof Island resulting in an observed pup mortality rate of 2.2%. The 2015 pup production estimate for Bogoslof Island is 21.1% greater than the estimate in 2011 (Figure 2). Since the first pup was observed on Bogoslof Island in 1980 pup production has increased at an annual rate of 33.7% (SE = 2.53) and at an annual rate of 10.1% (SE = 1.08) since 1997.