MATURITY CHARACTERISTICS OF PACIFIC SAURY DURING FISHING SEASON IN THE NORTHWEST PACIFIC

Pacific saury is a commercially important fish in the Northwest Pacific. This study examined the maturity characteristics, gonadosomatic index (GSI), condition factor (CF), and ovarian developmental stage of the saury stock in three months of the fishing season (from May to December) in the Northwest Pacific. The maturity characteristics of saury varied among these three months (May, July, and October) in 2009. In May, large GSI and CF values with advanced ovarian developmental stages but small knob lengths (KnL) and body weights (BW) were found. Also in this month, the large-sized saury (>29 cm) possessed large GSI values and the medium- and small-sized saury 29 cm) possessed large CF values. The GSI and CF values in July were similar to those in October while the KnLs and BWs of the former were larger than those of the latter. Most ovaries of the medium-sized saury (27-29 cm) developed to early cortical alveoli stage (CA1) and late cortical alveoli stage in July and October, respectively. Few individuals (5 samples) possessed GSI values larger than 1.0. Most saury were found at the CA1 stage, comprising 42.5-57.8% of the monthly samples, and the most advanced ovarian developmental stage was the secondary yolk stage and found only in May, comprising 2.0% of samples in May. From the point of view of maturity characteristics and body size for saury during the fishing season, it is suggested that it is better not to harvest saury early in May and that the fishing effort in July should be controlled in order to give the small and immature saury a couple more months to grow and mature for sustainable fishing.