Preliminary updates of stock assessment for Pacific saury in the North Pacific Ocean up to 2023

This working paper presents the preliminary results of update of stock assessment for the North Pacific Ocean Pacific Saury stock using the Bayesian state-space production model. The assessment was conducted based on the model specification (2 base cases) updated in the 9th Meeting of the Small Scientific Committee on Pacific saury. The model parameters were estimated based on Bayesian framework with a Markov chain Monte Carlo method. The assessment results were diagnosed with the Gelman and Rubin’s statistic, standardized residual plots, and the shapes of posterior distributions for key parameters. The main preliminary assessment results were concluded as follows: 
The estimated median B2022 from the two base case scenarios was 353,700 (80%CI 182,200-552,900) and 564,200 (80%CI 162,400-963,700) metric tons, respectively. The median B2022/BMSY and F2022/FMSY over the two base case scenarios were 0.31 (80%CI 0.17-0.48) and 0.81 (80%CI 0.50-1.78), respectively. In terms of biomass estimates, a decreasing trend was found from 2018 to 2020, followed by an increase from 2021 to 2023. The probability of the population being in the yellow Kobe quadrant in 2022 was estimated to be greater than 66%.