Stock assessment of Pacific saury (Cololabis saira) in the Western North Pacific Ocean

The stock assessment update consisted of running the Bayesian state-space surplus production model for the Pacific saury in the Western North Pacific Ocean (WNPO) with the most recent summary of available fishery-dependent and fishery-independent data. Commercial catches of Pacific saury from Japan, Chinese Taipei, Korea, China, Russia and Vanuatu in the WNPO area were collected from 1950 to 2016. Relative abundance indices available for WNPO saury consisted of standardized catch-per-unit effort (CPUE) of stick-held dip net fisheries from Japan (1980-2016), Chinese Taipei (2001-2016), Russia (2001-2016), Korea (2001-2015), and China (2003-2016); and biomass survey from Japan (2003-2017). Three base case models, differing in catchability of the biomass survey index, developed in the previous assessment were updated through 2016. The results of updated stock assessment indicated that the base case model 3 with survey catchability (q) prior being defined from 0 to larger than 1 gave the lowest biomass estimates compared to the  models 1 (survey q < 1) and 2 (survey q = 1). Biomass estimates were sensitive to the updated input data for the model 3, but not found in other models. The stock status is the same as the previous assessment (i.e., not overfishing and not overfished).  It should be noted that the biomass estimates of Western North Pacific saury were relative lower during 2015 to 2016 compared to the average of biomass estimates during 2010 to 2016.