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​Bottom Trawl Surveys of the Aleutian Islands Characterize Demersal Fish and Invertebrate Populations

Every two years, NOAA scientists conduct a comprehensive bottom trawl survey of marine waters surrounding the Aleutian Islands.  The purpose of the survey is to provide a fishery-independent time series of fish abundance that began in 1980 and to characterize the distributions and biological conditions of important benthic fishes and invertebrates.    The survey area extends from Unimak Pass to west of Attu Island, and 420 stations are sampled based upon a stratified-random design of previously sampled stations.  Two commercial fishing vessels are chartered and fitted with research bottom trawls, and the survey is stratified based upon region, sub-region, and depth to 500 m.  The bottom trawl is for 15 minutes, and precise data are taken on distance traveled, net width, depth, and temperature.  The catch is brought on board, identified, measured, and biological samples are removed for laboratory analysis. The densities of fishes and invertebrates are calculated, averaged among stations, and are used to estimate the relative abundance for the stratum.   Estimates are incorporated in groundfish stock assessments that are used to define species statuses and trends, demography, and fishery potential.  In addition, the survey results are used to describe the Aleutian ecosystem including temperature patterns and population trends for forage fish, benthic invertebrates, and miscellaneous fish species.  The trawl survey also serves as a platform for special studies and collections for the scientific community, and these collaborations have resulted in descriptions of new fishes and invertebrate species, habitat characterizations, and understanding food webs.