1Tokushima Agriculture, Forestry and Fisheries Technology Support Center, Tokushima, Tokushima 770-8570, 2Fisheries Division Agriculture, Forestry and Fisheries Department, Tokushima Prefectural Government, Tokushima, Tokushima 770-8570, 3Department of Marine Bioscience, Faculty of Marine Science, Tokyo University of Marine Science and Technology, Minato, Tokyo 108-8477, Japan
The boat seine fisheries target mainly anchovy Engraulis japonica larvae and juveniles, in the western sea area of the Kii Channel. Minnow netting of mesh size 260 kei (unit “kei” means the number of twines in webbing of 50-cm width) is too fine for the codend of the boat seine fishery, because it retains larvae of no commercial value. Four seine-nets with codends made of minnow netting of mesh sizes (260, 240, 220, and 200 kei; 1.36, 1.56, 1.72, and 1.82-mm aperture width, respectively) were towed simultaneously with small-mesh pocketnets attached to the codend. Two experimental parallel hauls were carried out: one towed on a straight line, and the other with one right-angled course change. Selectivity curves were estimated with an extended SELECT model for analyzing the total length distributions of the pockets catch and codend catch sample. The mesh size could be enlarged to 220 kei of which the l50 values were 18-20 mm, because the total length of anchovy larvae and juveniles in the fishing ground is mainly over 15 mm. The loss in the catch is estimated to be 1% with mesh size enlargement to 220 kei, while enlargement to 200 kei probably causes over 10% loss in the catch, and therefore 220 kei minnow netting would be acceptable to the fishermen.