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Groundfish Assessment Program

Gulf of Alaska Biennial Bottom Trawl Survey

F/V Sea Storm and F/V Gladiator trawlers
F/V Sea Storm and F/V Gladiator, two of the chartered commercial trawlers being used to conduct the 2007 Gulf of Alaska bottom trawl survey, lie at the dock in Sand Point, Alaska, at the end of the first leg of the survey.

Three vessels chartered by RACE Divisionís Groundfish Assessment Program have begun more than 2 months of scientific bottom trawl surveys in the Gulf of Alaska, continuing data-gathering that has gone on every 2-3 years since 1984. These data are used to derive fishery-independent estimates of abundance, distribution, and biological condition for groundfish resources in the Gulf of Alaska.

Scientists on the chartered fishing vessels Sea Storm, Gladiator, and Vesteraalen are expected to complete about 825 survey trawl hauls over a 75-day period along the continental shelf and upper continental slope of the Gulf of Alaska. They started 25 May in Dutch Harbor and are scheduled to end their charters on 7 August in Ketchikan.

The three boats started the survey near the Islands of Four Mountains, about 180 miles southwest of Dutch Harbor, and will work their way eastward to the U.S.-Canada border at Dixon Entrance. Cruise breaks for all three vessels will occur in Sand Point, Kodiak, and Seward. As of the end of June, when crews completed the second of four survey legs, about half of the stations had been sampled and the project is on schedule to be completed successfully.

Each of the three boats holds six researchers plus the skipper and crew. In addition to core staff from the Alaska Fisheries Science Center, scientists from the California Academy of Sciences, the International Pacific Halibut Commission, the University of Washington, the Alaska Sea Life Center (Seward), and the University of Alaska Fairbanks are participating on various legs of the survey.

This biennial survey monitors trends in the distribution and abundance of important groundfish species such as walleye pollock, Pacific cod, flatfish, and rockfish. It also helps us measure various biological and environmental parameters such as sea surface and bottom temperatures and the size, age, and food habits of important groundfish. The survey has been carried out every other year since 1999. Before then, it was conducted every 3 years starting in 1984.

Each vessel makes 15-minute trawl hauls at specific, randomly preselected stations. The trawl catches are sorted, weighed, and enumerated by species. Samples will be collected from selected species to determine fish size and age, sexual maturity, and food habits. Data on the location and depth of the survey tows, the fishing performance of the trawl, and the temperature of the ocean are recorded using a variety of monitoring instruments on the vessel or attached to the trawl headrope. Sample depths will range from depths greater than 15 m near shore to 1,000 m on the continental slope.

Following completion of the survey in early August, scientists will edit and finalize the data they collected on fishing effort, catch rates, and fish size distribution and generate fishery-independent estimates of geographic and depth distribution, abundance, and population size composition by the end of September. Stock assessment modelers will then combine that information with data from the fishery and results of previous surveys to update the stock assessments used by the North Pacific Fishery Management Council to manage the groundfish stocks of the Gulf of Alaska.

By Mark Wilkins

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