Joint CPUE standardization of the Pacific saury in the Northwest Pacific Ocean during 2001-2019 by using the conventional and geostatistical approaches

Reliable indices of population abundance are an important type of data for stock assessment. We applied a Vector-Autoregressive Spatio-Temporal Model (VAST) to conduct index standardization by using the joint CPUE (catch-per-unit-effort) data of the Pacific saury in the Northwest Pacific Ocean during 2001 and 2019. The joint CPUE data of stick-held dip net fisheries was collected from each member including Chinese Taipei, China, Japan, Korea, Russia, and Vanuatu in the North Pacific Fisheries Commission (NPFC). Furthermore, we provided a comparison of the CPUE standardization between VAST and the conventional generalized linear model. The objective is to make a suggestion for the appropriate specification of the joint CPUE index to be used in the Pacific saury stock assessment. The results indicated that VAST performs better than the GLM with higher R2 value, less residuals depart from zero, and smaller residual variance. We recommend using VAST for deriving the standardized joint index as improved input data in the stock assessment. The analysis we presented is generally applicable and should be considered as a standard tool in the CPUE standardization.