Joint CPUE indices for the albacore Thunnus alalunga in the Indian Ocean based on Japanese, Korean and Taiwanese longline fisheries data

Joint CPUE standardization was conducted for the Indian Ocean albacore tuna based on Japanese,
Korean and Taiwanese longline fisheries data up to 2020 to provide the WPTmT with information on
abundance indices for use in the coming stock assessment for this stock. The intention was to produce
reliable indices by increasing the spatial and temporal coverage of fishery data. Due to the limitation
of remote data access, an approach adopted among the three counties for the previous analyses of
tropical tunas for IOTC and ICCAT was used to share only aggregated data. As an underlying analysis,
a clustering approach was applied to account for the inter-annual changes of the target in each fishery
in each region. For this purpose, a hierarchical clustering method with “fastcluster” was used, and the
outputs of the finalized cluster were then used to assign the cluster label on fishery target to each
catch-effort data. For standardizing the catch-per-unit-effort data, the conventional linear models and
delta-lognormal linear models were employed for the shared aggregated data of monthly and 1° grid
resolution in each region. The models were diagnosed by the standard residual plots and influence
analysis.