Journal Article

Effects of fish density distribution and effort distribution on catchability

Nick Ellis and You-Gan Wang

in ICES Journal of Marine Science

Published on behalf of ICES/CIEM

Volume 64, issue 1, pages 178-191
Published in print January 2007 | ISSN: 1054-3139
Published online November 2006 | e-ISSN: 1095-9289 | DOI: http://dx.doi.org/10.1093/icesjms/fsl015
Effects of fish density distribution and effort distribution on catchability

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Ellis, N., and Wang, Y-G. 2007. Effects of fish density distribution and effort distribution on catchability – ICES Journal of Marine Science, 64, 178–191.

The effects of fish density distribution and effort distribution on the overall catchability coefficient are examined. Emphasis is also on how aggregation and effort distribution interact to affect overall catch rate [catch per unit effort (cpue)]. In particular, it is proposed to evaluate three indices, the catchability index, the knowledge parameter, and the aggregation index, to describe the effectiveness of targeting and the effects on overall catchability in the stock area. Analytical expressions are provided so that these indices can easily be calculated. The average of the cpue calculated from small units where fishing is random is a better index for measuring the stock abundance. The overall cpue, the ratio of lumped catch and effort, together with the average cpue, can be used to assess the effectiveness of targeting. The proposed methods are applied to the commercial catch and effort data from the Australian northern prawn fishery. The indices are obtained assuming a power law for the effort distribution as an approximation of targeting during the fishing operation. Targeting increased catchability in some areas by 10%, which may have important implications on management advice.

Keywords: aggregation; catchability; catch and effort data; density distribution; effort distribution; stock assessment

Journal Article.  6548 words.  Illustrated.

Subjects: Environmental Science ; Marine and Estuarine Biology

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