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Alaska Ecosystems Program

Northern Fur Seal Research, Summer 2008

northern fur seal pups on St. Paul Island
Figure 2.  Northern fur seal pups on St. Paul Island, showing those with and without the temporary shear marks used for pup production estimation.
Photo by Kathryn Sweeney.

The Alaska Ecosystems Program (AEP) conducted fieldwork in July–September 2008 in support of the following northern fur seal (Callorhinus ursinus) research projects: 1) Annual Population Assessments, 2) Mortality Studies on St. Paul Island, 3) Summer Foraging Behavior, 4) Vital Rates, and 5) Food Habits of Steller Sea Lions and Northern Fur Seals.

Population assessments of northern fur seals consist of annual counts of adult males and biennial estimates of pup production on the Pribilof Islands (St. Paul and St. George), the primary breeding rookeries for the species in the North Pacific Ocean. Current adult male counts and estimates of pup production on the Pribilof Islands are approximately one-third the numbers estimated during the 1950s, when the population was assumed to be at its peak. Adult male northern fur seals have been counted annually since the early 1900s on the Pribilof Islands and provide an index of population trend; counts on both St. Paul and St. George declined by 37% between 1997 and 2007.

In July 2008, John Bengtson and Robert Caruso (NMML) counted adult males on St. Paul, while Michael Williams (NMFS Alaska Regional Office) counted males on St. George. Pup production is estimated every other year using a mark-resampling technique involving the application of a temporary mark (shearing fur off the top of their heads) to thousands of pups and estimating the ratio of marked to unmarked pups (Fig. 2). This work requires a large field crew, which on St. Paul consisted of Kate Call, Brian Fadely, Sara Finneseth, Tom Gelatt, Carey Kuhn, Rolf Ream, Jeremy Sterling, Kathryn Sweeney, Jim Thomason, and Rod Towell (all of AEP), Robert Caruso (NMML), and others; on St. George, AEP staff included Lowell Fritz, Devin Johnson, Jeremy Sterling, and Jim Thomason.

In August 2008, pup production field crews were on both St. Paul and St. George, and production estimates by rookery will be available in November 2008. Scat samples were also collected at rookeries as part of the Food Habits of Steller Sea Lions and Northern Fur Seals research project.

AEP scientists assess on-land mortality of northern fur seals on St. Paul Island during the summer months. Dead northern fur seal pups, juveniles, and adults were collected at selected sites, and necropsies were conducted by a veterinarian (Dr. Terry Spraker, Colorado State University) to determine the causes of mortality. This research is used to assess factors influencing mortality during the summer months and to identify changes or trends in these factors.

Survival and health of northern fur seals is likely related to the quality of the habitat they occupy and use for foraging. The location and duration of foraging trips by lactating adult females during the summer months in the Bering Sea have been examined using satellite telemetry. After many years of satellite-tag deployments, AEP scientists have generally described the travel routes and summer foraging habitats of adult female fur seals from different rookeries on the Pribilof Islands and have identified the oceanographic features and fish resources associated with these habitats. To obtain more detailed and higher-resolution data on adult female foraging, AEP scientists, led by Carey Kuhn, deployed stomach-pill telemeters in combination with GPS tags on adult female fur seals (with pups) on St. Paul Island in August 2008 to identify the occurrence and precise location of feeding events. Data are stored on these tags and the tagged animals will be recaptured in October 2008.

In fall 2007, AEP scientists, led by Ward Testa and Devin Johnson, initiated a tagging program on St. Paul to allow the estimation of survival and reproductive rates of adult female fur seals. The study was designed to evaluate the use of flipper tags and included the development of new statistical methods to estimate tag loss as well as new resighting methods that were implemented in summer 2008 by Oregon State University graduate student and former AEP scientist Erin Kunisch.

By Lowell Fritz


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