Catch sampling and estimation in the Federal groundfish fisheries off Alaska

Abstract

We document the methodologies used by the National Marine Fisheries Service (NMFS) to estimate total catch in the Federal groundfish fisheries in waters off Alaska.  A combination of industry and onboard observer information is used to estimate total catch.  Industry-reported data consists of catch and processed product amounts that are electronically recorded and submitted to NMFS.  An extensive observer program is in place and provides information on catch.  The observer data are collected using a stratified sample design where strata are defined by vessel size and gear fished.  Within each stratum, a multi-stage sampling design is used to sample the species composition of the catch, length distribution of select species, and other catch components.  We describe the current NMFS catch estimation procedures, and include formulas that would characterize the uncertainty associated with the estimates.  Estimates of variance for catch and bycatch are not currently available.  The equations to estimate variances are provided to guide efforts towards their eventual use.

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