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Alaska Ecosystems

Bogoslof Island Research: 2015

Research Reports
Summer 2015
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Figure 1. Location of Bogoslof Island, Alaska. (The photograph was taken 6 years after the 1992 volcanic eruption).

Bogoslof Island is a small, remote, volcanic island in the Bering Sea, approximately 60 nautical miles west of Dutch Harbor, Alaska (Fig. 1). Despite its small size, Bogoslof Island teems with wildlife and is home to seabird, Steller sea lion, and northern fur seal breeding colonies. Northern fur seals only colonized the island relatively recently, but the species has thrived there over the past three decades. From 1976 to 1982, small numbers of northern fur seals were documented on Bogoslof Island, with only two and three pups recorded in 1980 and 1982, respectively. However, despite significant volcanic activity on Bogoslof Island in 1992, the growth of the northern fur seal population on the island has been rapid and continuous since then, resulting in dense aggregations that are typical for the species at other established breeding colonies (Fig. 2). The most recent northern fur seal pup production estimate for Bogoslof Island  in 2011 was 22,905 pups.

During summer 2015, National Marine Mammal Laboratory (NMML) scientists conducted two research missions at Bogoslof Island to assess the health of the Steller sea lion and northern fur seal populations aggregated on the island for the pupping and breeding season. The first research trip occurred in July, when a team of scientists visited the island to collect morphological and biological samples from Steller sea lion pups. The team also transported camp supplies and scientific equipment to the island in support of research efforts in August to address northern fur seal abundance and foraging ecology, as well as prevalence of disease in the population.

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Figure 2. A small portion of a northern fur seal rookery on Bogoslof Island, Alaska, in 2015.

During 10-15 August 2015, personnel from NMML’s Alaska Ecosystems Program, the Pacific Islands Fisheries Science Center, and the Protected Resources Division at NOAA Fisheries’ Alaska Regional Office conducted studies of northern fur seals from a temporary camp on Bogoslof Island. Shear-sampling, a mark-recapture process, was used throughout the study to estimate pup production, which is the standard index used to assess northern fur seal population trends. Satellite transmitters were attached to 10 adult females and fecal and tissue samples were obtained for studies of northern fur seal foraging behavior and diet. Nasal swabs and blood samples were also collected to evaluate the prevalence of disease in the population.

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Figure 3. Northern fur seal pup production estimates for St. Paul, St. George, and Bogoslof Islands, Alaska.  

Preliminary analysis of the 2015 data indicates continued growth in northern fur seal pup production on Bogoslof Island (Fig. 3). The Pribilof Islands of St. Paul and St. George in the Bering Sea contribute approximately half of the world’s northern fur seal pup production. However, pup production has been declining at approximately 3.71% per year on the Pribilof Islands since 1998. Comparably, northern fur seal pup production on Bogoslof Island has increased 11.7% per year from 1997 to 2011, and estimates of pup production at Bogoslof Island have exceeded those at St. George Island. While immigration to Bogoslof from the Pribilofs has contributed to the growth of the northern fur seal colony at Bogoslof Island, it does not fully explain the population decline on the Pribilof Islands.

By Rod Towell and Rolf Ream





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