Update of joint CPUE indices for the bigeye tuna in the Indian Ocean based on Japanese, Korean and Taiwanese longline fisheries data up to 2021

Joint CPUE standardization was conducted for the Indian Ocean bigeye tuna based on Japanese, Korean
and Taiwanese longline fisheries data up to 2021 to provide the WPTT with information on abundance
indices for use in the 2021 stock assessment for this stock. The intention was to produce combined
indices by increasing the spatial and temporal coverage of fishery data. Due to the limitation of remote
access to the data, an approach adopted among the three members for the previous analyses of tropical
tunas for IOTC and ICCAT was used to share only aggregated data. To account for the inter-annual
changes of the target in each fishery, information on the HBF or clustering result was used in each
region. For standardizing the catch-per-unit-effort data, the conventional linear models and deltalognormal
linear models were employed for the shared aggregated data of monthly and 1° grid
resolution in each region. Broadly, the trend of CPUE was similar to that for the previous stock
assessment with some dissimilarity in Region 3. The models were diagnosed by the standard residual
plots and influence analyses.