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April-June 2006
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Groundfish Assessment

Aleutian Islands Bottom Trawl Survey Under Way

Groundfish Assessment Program scientists began the 2006 bottom trawl survey of Aleutian Islands groundfish and invertebrate resources at the beginning of June, meeting and setting up the chartered vessels Gladiator and Sea Storm in Dutch Harbor, Alaska. The survey involves the two vessels sampling 366 assigned stations between Unimak Pass (long. 165˚W) and Stalemate Bank (170˚40'E) in waters as deep as 500 m. The Gladiator's 50-day charter is divided into two legs, while the Sea Storm's 70-day charter is divided into three legs. Charters begin and end in Dutch Harbor and all other leg breaks will be in Adak. Scientists will collect information on species composition of catches and biological data and specimens from the catch.

By Mark Wilkins

Annual Eastern Bering Sea Shelf Bottom Trawl Survey

On 30 May 2006, the fishing vessels Arcturus and Northwest Explorer began charters lasting 60 days to sample 405 stations on the eastern Bering Sea (EBS) shelf. This annual bottom trawl survey extends the time series of bottom trawl surveys, begun in 1971, for collecting data on distribution, abundance, and population biology of key groundfish, crab, and other invertebrate species within the EBS continental shelf ecosystem.

The first large-scale survey of the EBS shelf was conducted in 1975 in response to a need for baseline data to assess the potential impact of proposed offshore oil exploration and development on fishery resources. During this baseline survey, sampling was conducted between the 20-m and 200-m isobaths and from the Alaska Peninsula north to approximately 62°N. The spatial coverage of the annual surveys varied until 1979 when the most comprehensive survey of the EBS shelf and continental slope was undertaken in cooperation with the Japan Fisheries Agency. Subsequent annual bottom trawl surveys have essentially resampled the stations established during the 1975 shelf survey, with slight modifications each year.

Commercial groundfish and crab fisheries of the EBS shelf are vital to the Alaska economy. Results from this survey series are integral elements in the stock assessments of numerous crab, invertebrate, and groundfish species that are updated annually by the North Pacific Fishery Management Council per the requirements of the Magnuson-Stevens Fishery Conservation and Management Act.

In addition to the regular sampling, special studies are being conducted during the survey to investigate: 1) the effect of trawl speed through the water on catch rates and trawl performance; 2) groundfish feeding ecology; 3) use of highly quantitative acoustic data to supplement trawl survey catch data; 4) in situ light levels and pollock distribution; 5) reducing variance of trawl performance indices with net swapping procedures; 6) stationary seabird surveys; 7) incidence of bitter crab disease and black mat syndrome; 8) life history of Bering flounder, three Myoxocephalus species, and the yellow Irish Lord; 9) population structure of Enteroctopus dofleini; 10) fur seal sampling strategies; 11) parasites as indicators of ecosystem change; 12) Ichthyophonus in walleye pollock; 13) DNA-base identification of fish prey items, and 14) summer zooplankton biomass on the EBS shelf.

Preliminary results from this year's survey show water temperatures are the coldest since 1999. The pool of water with bottom temperatures less than 2˚C extended all the way into Bristol Bay compared to last year when the cold pool extended to north of the Pribiloff Islands. Interannual variability in bottom temperatures is important because it can affect the distribution and behavior of crab and fish populations.

By Robert Lauth


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