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April-June 2006
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Alaska Ecosystem Research Program

Scientific Successes Amidst Court Ruling

Northern fur seal research:

The National Marine Mammal Laboratory’s (NMML) Alaska Ecosystems Program saw both scientific success in the form of published research and field work completed, as well as cessation of future work during the last quarter.

Several new publications on northern fur seals reflect new information on population trends and foraging ecology of northern fur seals in Alaska. The majority of the world’s northern fur seals breed on two islands of the Pribilof Island group in the Bering Sea. A recent publication in the journal Marine Mammal Science, “Decline in northern fur seal (Callorhinus ursinus) pup production on the Pribilof Islands,” describes a substantial decline in pups born during 1998-2004. Pup production levels have now declined to that observed in 1918 on Saint Paul Island and in 1916 on Saint George Island. It is unknown why pup production has been declining at the Pribilof Islands yet has increased at Bogoslof Island in the eastern Aleutian Islands. This is an area of intensive current research.

Analysis of hard parts found in scats provided the basis for describing northern fur seal foraging habits in a new study published in the Journal of Zoology, “Foraging habitats based on the diet of female northern fur seals (Callorhinus ursinus) on the Pribilof Islands, Alaska.” Dominant prey species consumed by fur seals on the two Pribilof Islands during 1987-2000 were juvenile walleye pollock and gonatid squids, though primary prey also included Pacific sand lance, Pacific herring, northern smoothtongue, Atka mackerel, Pacific salmon, and other squid species. Analysis of diet patterns among the 17 rookeries suggest that rookeries can be clustered into five complexes representing predominant diets associated with specific oceanographic domains. This clustering provides evidence of resource-partitioning among adult female northern fur seals.

Examination of hard parts found in collected scats has been the most common method for estimating diets of seals and sea lions in the wild. In a new study published in the journal Fishery Bulletin, “Application of two methods for determining diet of northern fur seals (Callorhinus ursinus)”; available at http://fishbull.noaa.gov/1043/gudmundson.pdf), estimates of diet in northern fur seals determined from scat analysis were compared with estimates based on remains found in spews (regurgitations). They found that not only did the relative occurrence of primary prey differ between scats and spews, but that hard parts found in scats were biased towards smaller prey items, while parts in spews were biased towards larger prey and cephalopods. Thus many sampling methods should be combined to accurately assess northern fur seal diet, and there may be a much greater overlap in sizes of commercially important prey species, such as walleye pollock, taken by fur seals and commercial fisheries than previously estimated.


Steller sea lion research:

Since the year 2000, NMML has collaborated with the Alaska Department of Fish and Game (ADF&G) to mark Steller sea lion pups with brands or flipper tags at selected rookeries spanning the eastern Aleutian Islands through Southeast Alaska to estimate survival and vital rates. Two cruises covering the eastern Aleutian Islands and the central and eastern Gulf of Alaska were conducted during May 2006 to record locations and behaviors of marked Steller sea lions and to collect scats for diet analysis. Some of these scats were subsampled by a researcher from the University of British Columbia for stress hormone analyses and to test the efficacy of using genetic analysis techniques to determine sea lion diets. Between the two cruises, 173 sea lions marked as pups, and 10 marked as juveniles were observed among 51 sites. The oldest observed was a 19 year old female marked as a pup (from an earlier study) at Marmot Island in 1987.

Unfortunately, the Steller sea lion research planned for June was effectively terminated by a 31 May ruling from the U.S. District Court of the District of Columbia.  The court found that NMFS failed to comply with the National Environmental Policy Act (NEPA) in issuing Steller sea lion research permits last year, and granted the plaintiff (Humane Society of the U.S., HSUS) motion to vacate all permits and suspend Steller sea lion research pending completion of an environmental impact statement (expected to be completed in 2007). As a result, all researchers conducting field work on Steller sea lions in Alaska had their work suspended.  For our program, this included the collection of data to assess population trends and status, survival, reproductive rates, diets, and pup condition.

A subsequent appeal negotiated by NMFS and HSUS and granted by the Court authorized limited low-disturbance research activities to recommence.  Though this authorized aerial surveys to estimate population trends and remote observations to estimate reproductive rates, the reprieve occurred too late for completion of those studies.

By Brian Fadely and Tom Gelatt
 

 

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