Stock assessment of albacore tuna in the Indian Ocean using Bayesian State-Space Surplus Production Model

A Bayesian state-space production model with the Pella and Tomlinson function was developed to assess the stock status of albacore tuna (Thunnus alalunga) in the Indian Ocean. The catch data used span from 1950 to 2017, and the joint standardized CPUEs of longline fleets were used as the abundance indices. As a result, for the base case which used CPUE of R34 with the initial year of 1950 and no increase in catchability, the median estimates of carrying capacity (K), maximum sustainable yield (MSY), B_MSY, and F_MSY were 290,003 ton, 93,933 ton, 128,890 ton and 0.748/year, respectively. And the ratios of B₂₀₁₇/B_MSY, and F₂₀₁₇/F_MSY for the base case were respectively estimated as 1.589, and 0.259, which indicate that the stock is not overfished and not subject to overfishing. However, in sensitivity analyses, the scenarios using CPUE of R3 showed that the stock is overfished and not subject to overfishing.