Abstract:Pacific saury Cololabis saira is one of the most harvested species in the temperate waters of the Northwest Pacific Ocean, and an important part of their fishery industry. In 2014, the yearly catch from mainland China, from more than 40 fishing vessels, reached 620,300 tons. The Pacific saury has also become a dominant fish species of the North Pacific Fisheries Commission (NPFC), and the conservation of saury resources has received increasing attention. It is therefore necessary to assess their stock to ensure that sustainable fishery practices occur, however, there is little previous research in this field. Based on the data of catches from 2003 to 2017, collected by the NPFC and the resource abundance data submitted by China, the stock assessment and risk analysis of alternative management strategies for the Pacific saury were carried out using a Bayesian Schaefer model. During the process, two scenarios, a standard scenario and a sensitivity analysis scenario, were considered. The Schaefer model was chosen not only because of the lack of age structure data for the Pacific saury, but also because the migration mechanisms and stock structures of the Pacific saury are very complex and insufficiently understood. Bayesian analysis is one of the methods which can be used to improve the reliability of stock assessments in data-poor situations, by utilizing information from other species with good-quality data or other known information. The results showed that compared with the results of the two scenarios, those of the posterior distribution of the three parameters are similar. Under the standard scenario, the MSY(maximum sustainable yield) is 752,600 tons. To maintain the MSY, the biomass and fishing mortality should be 2.401 million tons and 320,000 tons, respectively. While, under the sensitivity analysis scenario, the MSY is 700,300 tons. To maintain the MSY, the biomass and fishing mortality should be 2.325 million tons and 310,000 tons, respectively. The status of the Pacific saury stock is currently good and it is not under overfishing. If the harvest rate is set below 0.3, then the stock will be protected and the probability of resource collapse will be very low. The harvest rates from 2003 to 2017 are all close to 0.3, so there is reason to be optimistic for the potential of this resource. We have concluded that in the future, a harvest rate of 0.3 for Pacific saury should be set, as the best and most sustainable management strategy.
