The small otter trawl fisheries in Osaka Bay use cod-end of small mesh size of about 20mm in stretch measure, since their target species are white-spotted conger Conger myriaster and small shrimps e. g. the southern rough Shrimp Trachypenaeus curvirostris. Many juveniles, which play an important role for future resource control, are caught and discarded at sea immediately after net hauling because most of these juveniles are smaller than the commercial size.
This paper describes the mesh selectivity for white-spotted conger. Fishing experiments were carried out using an existing trawl with cover net in July and October 1991. The trawl used had a cod-end of four mesh sizes (21.2, 22.5, 25.0, and 27.0mm) and the mesh size of the cover net was 15.3mm.
Mesh selectivity for white-spotted conger is shown as a function of G/P (body girth/mesh perimeter). Mesh selectivity increases at G/P=1, reaching 100% at a G/P of about 1.25. This indicates that white-spotted conger can pass through a mesh of slightly smaller perimeter than their own body girth.