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Bigeye tuna (Thunnus obesus) is a large pelagic predatory fish found mainly in tropical waters throughout the Indian Ocean where they form a single genetic stock. Bigeye tuna can live for up to 15 years, and reach a maximum size of approximately 250 cm, with a maximum weight of over 210 kg. Sexual maturity is reached at between 100 to 125 cm (approximately three to four years of age).
The stock assessment for bigeye tuna in the Indian Ocean is commissioned every three years, according to the schedule set out within the workplan of the Working Party for Tropical Tunas (WPTT) within the Indian Ocean Tuna Commission (IOTC). In 2025, the stock assessment is based on an update of the 2022 stock assessment model and is a spatially structured age-based integrated model that uses catch rate indices, length-compositions, and tagging data to inform estimates of spawning stock biomass (SSB) and fishing mortality (F), relative to estimated maximum sustainable yield (MSY).
The assessment was completed using Stock Synthesis 3.30 and incorporates all newly available data since the previous assessment, including updated abundance indices, and updated age and length data that informs a newly estimated growth curve for bigeye tuna in the Indian Ocean.
