CPUE standardization of albacore tuna caught by Korean tuna longline fishery in the Indian Ocean, 1979-2020

In this study the CPUE of albacore tuna caught by Korean tuna longline fishery in the Indian Ocean was standardized using lognormal constant model and delta lognormal model with added cluster factor as a categorical variable for addressing target changes over time. The data used for the CPUE standardization were catch in number, hooks used, fishing location (5° cell), and vessel identifier by year, quarter, and region. The standardized CPUE in the western subtropical region (R1) decreased from the early 1980s to the early 1990s, after that showed at low level with a fluctuation, and has increased since the 2010s. In the western temperate region (R3), since the early 2000s it has shown an increasing trend. However, we could not estimate the recent trend of the indices for the eastern subtropical region (R2) and the eastern temperate region (R4), because there was no fishing information or missing data.