Dynamics of two sailfin sandfish (Arctoscopus japonicus) stocks in the Sea of Japan, and their management

Abstract

The dynamics of the northern and western Sea of Japan sailfin sandfish ( Arctoscopus japonicus ) stocks (NSJ and WSJ, respectively) varied simultaneously until the mid-1970s but differently thereafter. To identify the mechanisms underlying these dynamics, we evaluated the impact of environment and harvesting on NSJ by developing a recruitment model and simulating NSJ dynamics. The model was constructed based on egg production, density effect, and water temperatures in winter and spring, which correlated significantly and positively with the estimated surface mixed-layer depth. Winter water temperatures and egg production were variables common to the two stocks. Our results suggest that simultaneous dynamics resulted from similarities in variations in winter water temperatures for each stock and the difference in dynamics resulted from NSJ depletion caused by overfishing. We suggest management strategies to prevent NSJ depletion caused by unfavorable environmental conditions and overfishing, as well as to allow improved biomass recovery while taking advantage of favorable environmental conditions, and avoid further exploitation of previously depleted NSJ.