Alaska Fisheries Science Center Quarterly Report : January, Febuary, March, 1996
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Alaska Fisheries Science Center Quarterly Report : January, Febuary, March, 1996
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  • Alternative Title:
    Estimating Trawl Catchability
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  • Description:
    Swept-area estimates of groundfish biomass, the primary product of Alaska Fisheries Science Center (AFSC) bottom trawl surveys, require knowledge of the proportion offish captured within the swept area of a trawl (Q). Until recently, Q, also known as catchability, had never been estimated for any species sampled by bottom trawl surveys and was assumed to equal Q in the calculation of biomass. Recent studies by both Norwegian and Canadian investigators, however, have shown that the processes of fish herding and escapement often lead to values of Q that are quite different from unity. Because departures of Q from unity can result in biased estimates of biomass and possibly faulty advice for fishery management, the Groundfish Assessment Task of the AFSC Resource Assessment and Conservation Engineering (RACE) Division initiated a study designed to experimentally estimate the value of Q for several species sampled with the 83-112 bottom trawl (Fig. 1) used on the annual National Marine Fisheries Service (NMFS) surveys of the eastern Bering Sea
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