瀬戸内海における小型底曳網の非有用投棄魚に対する網目選択性

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This paper describes mesh selectivity curves of unmarketable fish as a means of decreasing by-catch. For six main unmarketable fish species, Engraulis japonicus, Apogon lineatus, Leiognathus rivulatus, Acentrogobius pflaumii, Cryptocentrus filifer, and Repomucenus valenciennei, mesh selectivities are ob-tained from a covered-net fishing experiment using a shrimp beam trawl with codends of six mesh sizes. This paper uses a modified version of Tokai and Kitaharas method of determining the mesh selectivity curve. In this modified method, mesh selectivity is approximated by a function of G/P, where G and P are body girth and mesh perimeter, respectively. The master curves of mesh selectivity are determined as a logistic function by the maximum likelihood method for the six unmarketable fish species. If the mesh size of the codend is increased from 20.6mm commonly used in this area to 24.9mm, the catch numbers of these unmarketable fish are reduced from 53.4% to 16.7% without reducing the catch of the main target species, small shrimps, e.g., southern rough shrimp Trachypenaeus curvirostris. This also saves the labor required to sort usable fish.
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