Longtail tuna (Thunnus tonggol) is a neritic tuna species, distributed throughout subtropical and tropical waters from the Western Indian Ocean to the Western Pacific Ocean, between latitudes 47° N and 33° S. It extends from the sub-tropical east and west coasts of Australia, northward to southern Papua New Guinea and Indonesia and northwest through Malaysia and Thailand; it has a continuous distribution to the northeast to south Japan and the northwest through India, Sri Lanka, and Pakistan, to the Persian Gulf and the Red Sea (Willette et al. with Griffiths, Duncan Leadbitter et al. 2020)(AsiaPacific-Fishwatch 2023).

The Indian Ocean Tuna Commission (IOTC) is the responsible body for stock assessment and management for this species in the Indian Ocean and although the stock structure of longtail tuna in this region is unknown, an assessment unit is here considered. Longtail tuna are mostly targeted by the gillnet and, to a lesser extent, coastal purse seine and trolling fleets under the IOTC (IOTC 2017).