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Alaska Ecosystems Program

Northern Fur Seal Research

A number of northern fur seal projects were conducted by the Alaska Ecosystems Program (AEP) on St. Paul Island, Alaska, during October and November 2007. In addition to continued satellite-tracking studies investigating the winter distribution of both juvenile and adult female fur seals (see article in the April-June 2007 AFSC Quarterly Report), two studies measuring the vital rates of northern fur seals were initiated. These studies followed recommendations from the Conservation Plan for the Eastern Pacific Stock of Northern Fur Seals and the Northern Fur Seal Tagging and Census Workshop held in September 2005.

The main objective of the first study is to determine whether the survival of fur seals, particularly juvenile fur seals, is a factor in the observed population decline. The first phase of this study aims to evaluate both the field and statistical methodology that will be required to successfully make such estimates, particularly the difficult problem of estimating tag loss rates to avoid bias in survival estimates.

From 6 to 9 November 2007, 131 adult female fur seals were captured on St. Paul Island and tagged with two prospective tag types for comparison of tag retention rates and visibility on the rookeries next summer. Biometricians Devin Johnson (AEP) and Jeff Laake (NMML's California Current Ecosystems Program) are working to develop new statistical estimators that better account for tag loss and determine the feasibility and cost of estimating fur seal survival with the precision needed to adequately address the suggested recommendations and conservation concerns.

The second study investigating fur seal vital rates is the continuation of a successful pilot study conducted in 2005 testing the method of transrectal ultrasonography as a means of determining reproductive condition of northern fur seals prior to their winter departure from St. Paul Island. The objective of the ultrasonography work is to determine whether declining reproductive rates are a contributing factor to the current decline of this population.

From 11 to 16 November 2007, a team from AEP, with collaborating veterinarians Gregg Adams (Western College of Veterinary Medicine, University of Saskatchewan) and Don Bergfelt (U.S. Environmental Protection Agency), used ultrasonography to examine 96 adult female fur seals at Polovina Cliffs rookery to determine how many had ovarian corpora lutea, indicative of ovulation the previous July, and how many had developing embryos in comparison to similar observations made from the lethal collections of fur seals in the 1950s and 1960s.

The animals were released with numbered tags and VHF radio-tags to enable relocating them and estimating their pupping success next summer. From 15 June to 30 August 2008, a VHF receiving and data-logging station will be maintained over the rookery at Polovina Cliffs to monitor the presence of these radio-tagged fur seals.

Visual confirmation of pupping success will be sought for each of the tagged animals that are present, and the attendance pattern from the VHF data logger will be compared to the suckling/foraging patterns of parturient females. Visual searches for flipper tags may also determine pupping success of females that lose their VHF tags during winter.

By Jeremy Sterling and Ward Testa

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