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NOAA Technical Memorandum NMFS-AFSC-335

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Estimating confidence in trawl efficiency and catch quantification for the eastern Bering Sea shelf survey

Abstract

The Alaska Fisheries Science Center’s Resource Assessment and Conservation Engineering (RACE) Division has been conducting annual multispecies bottom trawl surveys of the eastern Bering Sea continental shelf using the same standardized gear and trawling procedures since 1982. The data and results from these surveys are available to the general public. However, because the use of these data and results by researchers outside RACE is not monitored, users should be aware of the limitations of this information and design their analyses accordingly. In particular, there are multiple sources of variability in the sampling efficiency of the trawl gear used for the survey, both species- and size-specific, that may affect inferences about the nature of the overall catches and relative animal densities. Furthermore, the quality and specificity of catch quantification (weighing and counting) at sea of many taxa can vary depending on the overall size of the catch and the species composition of the sample, particularly for non-commercial taxa of small size. This document is an assessment of the relative reliability of survey catch weights, numbers, and catch per unit effort estimates derived from the eastern Bering Sea shelf bottom trawl survey and is intended to serve as a guideline for researchers interested in using the survey data and results. Included within is a confidence matrix of sampling efficiency and catch quantification for all fishes and invertebrates identified during the shelf survey.



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