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In this study, Bayesian State-Space Surplus Production Model was constructed to assess the status of Bigeye tuna Thunnus obesus stock in the Indian Ocean from 1975 to 2018. This assessment was carried out in the open-source stock assessment environment, JABBA (Just Another Bayesian Biomass Assessment). In the sensitivity analysis, 8 scenarios including joint CPUE (1979-2018) in different regions were tested, and results indicated that model fitting and result, especially for stock status, did not show significant difference. Therefore, joint CPUE in all regions were used for the Base case model. B2018 was estimated to be 607,766 t, while BMSY estimate was 476,817t. Catch in 2018 is 93,515t, while MSY was estimated to be 126,820 (105,576~157,865) t for median and 95% confidence interval. The results of JABBA Base case indicated that the stock of Bigeye tuna in the Indian Ocean is not overfished and does not subject to overfishing. The results of projection also revealed that there is little probability for the stock to violate the MSY-based target or limit reference points in the next 3 or 10 years, when the catches are relative to catches from 2018 (same, ± 10%, and ± 20%).
The join of CPUE from China longline fishery during 2012~2018 did not change the assessment results largely. This process of CPUE standardization from China Bigeye tuna fishery will be improved together with its application in the stock assessment in the future.
