Appropriate combinations of mesh sizes for research gillnets

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  • 調査用刺網における適切な目合の組み合わせについて

Abstract

<p>　Research gillnets use combinations of different gillnet mesh sizes to avoid the effect of mesh selectivity on the body length distribution of fish caught. In this study, pooled relative sampling efficiencies (PRSEs) for body length were obtained by assuming various gillnet selectivity curve parameters when the common ratio or common differences between mesh sizes were held constant in the available gillnet mesh sizes for research gillnets, and the conditions under which the PRSEs were kept nearly constant over the length range of target fish species for survey were examined. As a result, the PRSEs for body length were observed to be constant to some extent only when the common ratio between mesh sizes remained constant in the cases of gillnet selectivity parameters with large optimum relative length (6.0 to 7.0) and a medium 50%-selection relative length range (2.5 to 4.5). In the cases of narrow 50%-selection relative length range, the PRSEs for body length often showed a multimodal shape. Possible countermeasures in such cases include using a smaller common ratio between mesh sizes, adjusting the number of gillnets of a given mesh size, or correcting the length composition of the fish caught by mesh selectivity.</p>

Journal

  • NIPPON SUISAN GAKKAISHI

    NIPPON SUISAN GAKKAISHI 90 (2), 95-104, 2024-03-15

    The Japanese Society of Fisheries Science

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