台湾海峡における底曳網の角目袋網の網目選択性

抄録

This paper analyzes the mesh selectivity of square and diamond condends of bottom trawl nets. Recently, the catch per unit effort of bottom trawls in the Taiwan Straits has declined and the mean body length of the major species has become smaller and smaller, which suggests overfishing. As one way of controlling demersal fish resources in the Taiwan Straits, it is necessary to study square mesh selectivity which is reported to be effective for simple key species trawl fishery as seen in Europe. A series of cover-net fishing experiments was carried out in the waters of the Taiwan Straits with square mesh and diamond mesh codends. The covernet used was 32mm square mesh and the two codends, square mesh and diamond mesh, were made with 45, 54, 60, and 70mm meshes in internal stretched measure (2 bars and 1 knot). Of the mesh selectivity of six major species obtained, the square mesh codend had a larger selection factor (SF) with a smaller selection span (SP) within the same mesh size category. This result shows that the square mesh codend, as compared with the diamond mesh codend, is more effective for the protection of immature fishes.