Assessment of fishery management by using a fishery simulator for bottom otter trawling in Ise Bay

Improving the condition of coastal fishery requires the implementation of effective fishery management practices, as well as development of an assessment system. More efficient and sustainable fishing operations need to be determined considering both the resource and economic conditions. For the bottom trawling, fishery management considering only a single species might not be appropriate, because a wide variety of fish is caught by the trawling net. Thus in this study, we developed a fishery simulator for bottom otter trawling in Ise Bay, Japan, to treat two fish species—conger eel and mantis shrimp—which show distinct biological behaviors. The simulator was based on two models: a fish behavioral model that predicts the spatiotemporal variability of fish biomass and population size and a fishing operations model that predicts the fishing activities of trawling boats. The developed simulator could well reproduce the annual variations of catch per unit effort for conger eel and mantis shrimp. The model was also used to assess the effects of fishery management to control the use of fishing gear and boat number. The mesh size of trawling nets and the period for which these nets need to be used to maximize the total fish catch could be estimated based on the simulations. At the target ports, reduction of boat number could increase the profit because the effect of fixed cost change exceeded the impact of fish catch decrease; however, the optimum reduction rate was different across each port.