Stock assessment of albacore tuna (Thunnus alalunga) in the Indian Ocean using Stock Synthesis

This paper presents a stock assessment of albacore tuna in the Indian Ocean using Stock Synthesis (version 3.30.19.01 http://nft.nefsc.noaa.gov/Download.html).  The albacore tuna assessment model is an age structured (14 years), spatially aggregated (1 region) and two sex model. The catch, effort, and size composition of catch, are grouped into 23 fisheries covering the time period from 1950 through 2020. Fifteen indices of abundance, fourteen of which are  from longline fisheries were considered for this analysis.   The estimated abundance trend is decreasing throughout the time frame of the model, and spawning stock abundance has decreased to approximately 2 times SSBMSY  The fishing mortality has increased   over the model time frame with F2020/FMSY= 0.6.

Albacore tuna are most often caught in long line fisheries in the Indian Ocean tuna fisheries, though some bycatch occurs in the purse seine fisheries as well as other mixed gear fisheries.   

This analysis was developed based on the 2019 assessment along with updates to the data and parameterization.  A the diagnostic case,   is referred to in the main text when presenting the model parametrization and diagnostics.  The upcoming 8^th meeting of the Indian Ocean Tuna Commission Working Party on Temperate Tuna and Bycatch (WPTmT08) will recommend the final parameterization as a base case model for the provision of stock status. Initial analysis based on the sensitivity analysis done with SS3 indicated that the stock is not over fished nor experiencing overfishing.