MESH SELECTIVITY OF UNMARKETABLE TRASH FI SH BY A SMALL TRAWL FISHERYIN THE SETO INLAND SEA

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, Acentrog obius pflaumii, Cryptocentrus filifer, and Repomucenus valenciennei, m esh selectivities are obtained from a covered-net fishing experiment u sing a shrimp beam trawl with codends of six mesh sizes. This paper us es a modified version of Tokai and Kitahara's method of determining th e 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 m esh perimeter, respectively. The master curves of mesh selectivity are determined as a logistic function by the maximum likelihood method fo r the six unmarketable fish species. If the mesh size of the codend is increased from 20.6 mm commonly used in this area to 24.9 mm, the cat ch 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 save s the labor required to sort usable fish.