Stock assessment for swordtip squid, Loligo edulis, in the East China Sea and the southwest sea of Japan

The present study investigates the status of swordtip squid (Loligo edulis) stocks in the southwest sea of Japan and the East China Sea, which are multi-gear and multi-national fishing grounds. Commercial landings of six fisheries for the period 1980-99 and eight research trawl-survey data sets from 1986 from 1999 were used to estimate minimum biomass in each fishing ground. The relationships between stock and recruitment and between catch and fishing effort were estimated using regression analysis. The maximum sustainable yield (MSY) and the corresponding fishing effort for given interspecies relationships are then obtained. Predicted fishing effort rates were estimated from a relative gross profitability for each fishery for the past 5 years and were proposed as an alternative standard to assign the fishing effort to each fishery. Estimates of fishing effort at MSY were above the current fishing effort in the southwest sea of Japan and the East China Sea. However restraint for the increase rate in fishing effort is required in the East China Sea to prevent stock collapse. The present results also suggest that fishing effort for the Chinese offshore trawl fishery should firstly be reduced, if the fishing effort has to be adjusted in the East China Sea.