CPUE standardization for the Pacific saury (Cololabis saira) fishery in the Northwest Pacific

Abstract

In stock assessment and fisheries management, the standardization of catch per unit effort (CPUE) is critical to derive an effective index of the abundance of exploited fish stocks. In addition to developing various statistical models, a method including the relative fishing power (RFP) of individual vessels has been developed from an intuition concept and applied to bottom trawl fisheries using logbook-based data. This is a convenient and straightforward approach for standardizing the catch-effort data of a fishery. The Pacific saury is a pelagic fish species, and its stock in the Northwest Pacific has been targeted by international fleets since the early 1980s; annual production ranged from 328,000 to 630,000 tons during 2001- 2016. The Pacific saury stock has been one of the resources managed by the North Pacific Fisheries Commission (NPFC) since 2015. In this study, the RFP method in CPUE standardization was applied to the Taiwanese Pacific saury fishery in the Northwest Pacific, and the effects of varying the parameters of the model were analyzed. The results indicate that more than 98.8% of the fishing effort can be standardized according to the estimated RFP, with 20 being the minimum number of required comparisons in each of the 4-year periods during 2001-2016. The RFP values of the model generally correlate with the length and gross tonnage of fishing vessels in the saury fishery. The result of the model, applied to the Pacific saury fishery, is robust when the model considers the effects of varying the model parameters (the minimum number of comparisons and standard vessel). This study suggests that first, the RFP method is appropriate for the CPUE standardization of the Pacific saury fishery, and that second, the resulting CPUE can be an effective index of abundance that reflects the annual variability of the Pacific saury stock in the Northwest Pacific.