AUKE BAY LABORATORY (ABL) (cont.)

Groundfish Assessment Program

Southeast Alaska Steller Sea Lion Prey Study, Demersal Prey Survey

During late February 2004, the second of three demersal prey studies was completed as part of a larger study to assess the seasonal prey field of Southeast Alaska Steller sea lions. The survey was conducted by ABL scientists J. J. Vollenweider and Dave Csepp under chief investigator Mike Sigler. The survey used the chartered fishing vessel San Juan and consisted of 15 longline sets, each composed of 3 skates with 100 hooks/skate. Sets were stratified across an area within a 20-km radius of the Brothers Islands in Frederick Sound, about 90 km south of Juneau. Frederick Sound is inhabited by a year-round population of roughly 1,200 sea lions that frequently haul out at the Brothers Islands.

Total catch biomass of fish was 5,250 kg, 750 kg less than in the previous survey from September 2003. Species composition of the winter catches included 19 species, similar to composition (23 species) from the fall survey. During both time periods, catches were dominated by Pacific halibut (~50%) on a relative weight basis. Between the two sampling periods, the relative importance of sablefish and Pacific cod changed, with sablefish increasing from 9% to 27% of the catch and Pacific cod decreasing from 20% to 11% of the catch. Arrowtooth flounder decreased from 9% to 1% of the catch, while spiny dogfish increased from less than 1% to 5% of the catch. Sandpaper skates remained at 3% of the catch during both time periods. Other species of interest caught in amounts less than 1% of the total catch included several species of rockfish, other skate species, Pacific sleeper shark, sole, sculpins, and spotted ratfish.

In addition to estimating species-specific biomass near the sea lion haulouts, catches were subsampled for nutritional analyses. Species selected were among the dominant prey species consumed by local sea lions, as determined by seasonal scat analyses in a related study conducted by ABL contract biologist J. Womble. One hundred eight fish samples were retained and frozen, including sets of Pacific halibut, Pacific cod, sablefish, sandpaper skates, arrowtooth flounder, and rougheye rockfish.

By Johanna Vollenweider


Southeast Alaska Steller Sea Lion Prey Study, Pelagic Prey Surveys

Four cruises were conducted during the first quarter of 2004 to sample pelagic prey of Steller sea lions. These cruises were completed as part of a study to assess the seasonal prey field of Southeast Alaska Steller sea lions near two haul-out areas for these animals: Lynn Canal (northern Southeast Alaska) and Frederick Sound (central Southeast Alaska). The first cruise was an acoustic survey of Frederick Sound in January using the marine vessel Alaska Adventurer, with Dave Csepp (ABL) and Dave Gummeson (University of British Columbia). The second cruise was a midwater trawl of Lynn Canal and Frederick Sound in January-February 2004 from the research vessel Medeia, with ABL scientists Mike Sigler, Dave Csepp, and J. J. Vollenweider. The third cruise was an acoustic survey of Frederick Sound in March from the Alaska Adventurer, with Mike Sigler. The fourth cruise was a midwater trawl of Lynn Canal and Frederick Sound in March using the Medeia, with J. J. Vollenweider and Dave Csepp.

In addition to estimating species-specific biomass near the haulouts, midwater trawl catches were subsampled for nutritional analyses. The March 2004 cruises mark the last of 12 quarterly sampling periods of Frederick Sound for the 3-year Southeast Alaska Steller Sea Lion Prey Study. The study will conclude in May 2004 following the last monthly acoustic cruises (of 36) of Lynn Canal.

By Michael Sigler


Southeast Alaska Estuarine Habitat Surveys

Work to define essential fish habitat (EFH) in Alaska’s coastal areas continued in 2004. The data generated by this work, although limited to northern Southeast Alaska, have been incorporated into a geographical information system (GIS) database that is already in use for EFH consultations.

Mitch Lorenz presented the results of ABL estuarine fish distribution and habitat classification surveys at the Coastal Experts Workshop in Juneau during February 2004. The workshop goal was to coordinate various efforts to classify and map coastal resources. Representatives of federal and state agencies and private interests attended, with constituent issues ranging from biodiversity protection to coastal development.

Data from the ABL surveys on fish distribution mapping in relation to current estuarine mapping protocols were presented, along with an improved mapping protocol. To date, 34 (more than one-third) of all Alaska species managed by the National Marine Fisheries Service (NMFS) have been documented in estuarine survey areas, and more than half of these species are abundant in estuaries. The presentation also noted high temporal and spatial variability of estuarine fish distribution and outlined the resulting shortfalls of current EFH mapping. Finally, methods to groundtruth an improved habitat classification protocol were discussed. Additional estuarine habitat surveys are planned for the 2004 field season.

By Mitch Lorenz

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AFSC Quarterly Research Reports Jan-March 2004