Bigeye Tuna (Thunnus obesus) is a highly migratory species distributed throughout the tropical and subtropical waters of the Pacific, Indian and Atlantic Oceans. Genetic-based studies (e.g., allozymes, mtDNA and microsatellites) have not observed evidence of spatial structuring in bigeye tuna from differing locations in the Pacific Ocean, or between the Pacific Ocean and Indian Ocean sampling locations, suggesting that a lack of structuring is consistent with broad-scale panmixia among bigeye tuna in the region but also recognising that additional sampling and alternative techniques may be required to further investigate population structure. Based on genetic or non-genetic studies (e.g., tagging) it is suggested that the stock structure of bigeye tuna in the Pacific Ocean remains unresolved and is associated with high uncertainty (Moore et al. 2020). 

There is likely one stock of bigeye tuna across the Pacific Ocean. Regular stock assessment is developed by the Inter-American Tropical Tuna Commission (IATTC), the same entity that sets conservation and management measures for this stock in this region. The assessment in the EPO is conducted assuming there is a single population for management purposes (Aires-da-Silva and Maunder 2014) (Xu et al. 2020).