Standardizing abundance index for spawning stock biomass of chub mackerel in the Northwest Pacific

We estimated a relative abundance index of spawning stock biomass (SSB) for the Pacific stock of chub mackerel with historical monthly egg survey data. The monthly egg surveys have been conducted from 2005 to 2018 off the Pacific coast of Japan to cover the spawning ground of chub mackerel. We applied the vector autoregressive spatio-temporal (VAST) model to the survey data to derive a relative abundance index of egg density, which should be proportional to SSB. This document provides important references and diagnostics on this standardization according to “CPUE standardization protocol”. Because we found there was no serious problem in the diagnostics and the spatio-temporal data coverage was enough, the estimated index could be utilized as an abundance index for the forthcoming stock assessment of chub mackerel in TWG CMSA.