National Marine Mammal Laboratory (NMML)

Alaska Ecosystems Research Program

Northern Fur Seal Research

One of the responsibilities of the Alaska Ecosystem Research Program is investigation of the ecology of northern fur seals. Scientists within the program have been collaborating with investigators from the University of Alaska Fairbanks and Dalhousie University, Nova Scotia, to examine the consequences of northern fur seal foraging strategies at two separate locations in the Bering Sea. This is a collaborative study funded by the North Pacific Research Board and the AFSC. For largely unknown reasons, northern fur seal abundance on the Pribilof Islands (Saint Paul and Saint George) has fallen to less than half of peak numbers present in the 1950s and during the 1990s has continued to decline, while abundance on Bogoslof Island in the eastern Aleutian Islands has increased.

Oceanographic conditions encountered by maternal seals during the summer are substantially different between these islands, but northern fur seals also spend about two-thirds of the year wintering at sea in the North Pacific Ocean. In this study we are tracking maternal fur seals from the Saint Paul and Bogoslof Islands during winter and summer, while measuring their health and condition and subsequent pup growth rates.

The study began in November 2004 when 20 adult female fur seals were captured on Saint Paul Island. Body condition was assessed, and seals were tracked with satellite telemetry in the North Pacific Ocean. In July 2005, the conditions of 20 mother and newborn pup pairs at each island were measured, and maternal foraging behavior in the Bering Sea was tracked via satellite transmitters and dive recorders. The seals will be recaptured in October near the end of the pup-rearing period to measure pup growth rates, maternal condition, and to retrieve the dive recording instruments.

Figure 1.  Estimated number of northern fur seal pups born on Bogoslof Island, Alaska, 1980 - 2005.

The population of northern fur seal pups on Bogoslof Island was estimated using shear-sampling, a mark-recapture method, in August 2005. Staff of the Alaska Ecosystem Program estimated 12,631 (SE = 335) pups were born on Bogoslof Island this past summer. These results indicate that pup production has increased at 12% per year since pups were last counted in 1997 (Fig. 1). Some of the increase in pup production may be a result of emigration of adults from St. Paul and St. George Island rookeries, where pup numbers have been declining.

By contrasting between winter and summer and among rookeries on Saint Paul and Bogoslof Islands, we will quantify effects of foraging in different habitats on maternal condition and ability to raise pups. Additional project information can be found on the web at http://www.nprb.org.

By Tonya Zeppelin and Brian Fadely


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AFSC Quarterly
Research Reports July-Sept 2005