National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa 236-8648, Japan
We estimated the catch rates for each quarterly fishery season and fishery ground, and evaluated the impacts of fisheries on the population dynamics of the Pacific stock of chub mackerel Scomber japonicus during 1970-2006. The catch rates increased when the biomass declined during 1979-1980 and 1986-1990, and the selectivity of the immature fish stock increased. According to the biomass decline, The survival rate of each year-class steadily decreased during 1970-2006. We evaluated the effects of a moratorium at each fishing ground using a population dynamics model with multiple fishery seasons and grounds. The results showed that the moratorium at the area where immature fish were mainly distributed effectively conserved the spawning stock biomass. This result suggests that the management performance could be improved by considering the proper allocation of allowable biological catch (ABC) to each fishery season and ground.