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Auke Bay Laboratory

Workshop on Role of Contaminants in Steller Sea Lion Decline

The Auke Bay Laboratory (ABL) sponsored a workshop in Anchorage, Alaska, on 5-6 September 2001 to evaluate the possible role of contaminants in the decline of the Steller sea lion population.  Participants included representatives from the Alaska Department of Fish and Game (ADF&G),  National Marine Mammal Laboratory (NMML),  National Institute for Status and Trends, Canada Department of Fisheries and Oceans, World Wildlife Federation, and several universities.  Presentations included 1) an evaluation of the nutritional limitation  hypothesis; 2) contaminant trends in murres, sea lions, seals, and killer whales from the northern Gulf of Alaska,  3) impacts of contaminants on immune function in marine mammals; and 4) discussion of other biomarkers that may be useful indicators of exposure.

The meeting will produce a proceedings and provide NMFS with a basis for developing a detailed science plan for a focused research effort.  The primary consensus was that low-level but widespread atmospheric pollution is present in the North Pacific Ocean, and for those species with long lives and fish as a major prey item, pollution may well be a contributing cause of recruitment problems. Systematic data collections are rare, but the few data points available for Steller sea lions indicate that they have contaminant loads.   Steller sea lions have a biology consistent with this potential problem.  There was consensus among the workshop participants that pollutants should be seriously considered as a threat to these species and that further research is warranted.

By Stan Rice.

Second Frederick Sound Cruise of Southeast Alaska Steller Sea Lion Prey Study Completed

The second cruise in Frederick Sound for the Southeast Alaska Steller sea lion prey study was completed during 4 - 17 September 2001 using the chartered fishing vessel Solstice.  The purpose of the Frederick Sound Steller sea lion prey study is to test the hypothesis that juvenile sea lion prey diversity and seasonality are related to Steller sea lion population trends and to provide a comparison to a similar study conducted off Kodiak Island by the University of Alaska.  During the September cruise, prey abundance was measured using echo-integration and a midwater trawl.  Scat was collected from sea lion haul-out areas for diet analysis.  Fish also were collected for proximate and free fatty acid analysis.  Prior to the cruise, ADF&G staff tagged sea lions in the area with radio tags.  The location information from these tagged animals was very helpful for conducting the cruise.  Mostly juvenile walleye pollock and Pacific herring were found at depths less than 75 m, adult walleye pollock were found from 75 to 250 m, and Pacific whiting were found deeper than 250 m.

Both day and night sampling were conducted to determine if fish available at sea lion foraging depths were affected by time of day. Unlike the previous cruise in  May 2001, there was a substantial difference in the day-night depth distribution found during the September 2001 cruise.  During the day in September, relatively few fish were found at depths less than 75 m, but during the night juvenile herring and pollock were found at these depths.  Sea lions were found at two haulouts in Frederick Sound near The Brothers (Sail Island and Southwest Brothers Island); the number hauled out totaled about 600 animals.  The sea lions were at the haulouts during day, leaving the haulouts at night to feed in near-surface waters (based on two nights observation at Southwest Brothers Island).  Quarterly sampling is planned for the Frederick Sound study area;  the next cruise is scheduled for December 2001.

By Mike Sigler.

Sleeper Shark - Steller Sea Lion Predation Cruise Completed

A sleeper shark - Steller sea lion predation study is being conducted to determine whether sleeper sharks prey on Steller sea lions and, if they do, to estimate the predation rate. The first cruise was conducted by ABL scientists from 30 July to 11 August 2001. The chartered fishing vessel Norska deployed longline gear to capture sleeper sharks adjacent to Steller sea lion rookeries at Seal Rocks, Outer Island, Sugarloaf Island, and Marmot Island in the central Gulf of Alaska (GOA).  Samples were collected for diet analysis, and archival tags were deployed to investigate sleeper shark habitat utilization.  One hundred eight sleeper sharks were caught and ninety-nine sacrificed for samples during the August 2001 cruise. Archival tags were attached to nine sharks; three were programmed to release from the tagged sharks on 1 November 2001, three on 1 February 2002, and three on 1 July 2002.  The archival tags will provide time, depth, and temperature data over several months and will detail the diurnal and seasonal behavior of individual sharks of the GOA in a way never before possible. Stomach contents and tissue samples were frozen for subsequent analysis. Preliminary onboard stomach analysis revealed no sea lion tissue. Eleven percent of the sleeper shark stomachs contained what appears to be cetacean tissue. Unknown marine mammal tissue samples will be sent to the Southwest Fisheries Science Center for micro-satellite DNA analysis for species determination. Stomachs collected during the cruise will be processed during fall 2001. The next cruise for this study is scheduled for May 2002.

By Lee Hulbert and Mike Sigler.

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