1Fisheries Division of Agriculture, Forestry and Fisheries Department Tokushima Prefectural Government, Tokushima 770-8570, 2Department 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 larvae, Engraulis japonica, in the western sea area of the Kii Channel. The current codend is made of minnow netting of which the mesh size, 260 kei (the number of twine in the webbing of 50 cm width) is too fine even for anchovy larvae, and therefore enlargement of the mesh size is required. Experimental cone nets made of minnow netting of three mesh sizes (260, 240, 220 kei) were covered with fine mesh net (mesh material is nylon and mesh size is 0.45 mm). Four towings of each mesh size net, making a total of 12, were carried out. Selectivity curves of each towing for anchovy larvae were estimated with an extended SELECT model for analyzing body size (total length) distributions of the sample from the cone net and cover net catch. In case of a small catch without clogging, the l50 values (the length of 50% retention) of 240 and 220 kei mesh size were 10.5-12.5 mm and 11.0-14.3 mm, respectively. However clogging occurred with large catch volume and then the l50 became smaller than 10 mm, which is equivalent to the l50 of 260 kei mesh size. The boat seine fishing gear has a large cylinder-shaped codend of 1.3 m in diameter and 16 m in length. The cylinder-shaped nets were recognized as being superior for maintaining high filtration efficiency, but clogging over the codend meshes is still unknown. To determine an appropriate mesh size for anchovy larvae, the mesh selectivity should be confirmed under real fishing operation of boat seine fisheries.