Bigeye tuna Thunnus obesus
Bigeye tuna inhabit the tropical and subtropical Pacific, Atlantic and Indian Oceans and are one of the most valuable components of tropical and subtropical tuna fisheries globally. They live about 15 years and grow to two metres and more than 200 kilograms. They reach maturity at about three years, spawning in waters warmer than 26°C and can spawn year round in equatorial waters. In the western Pacific they spend most of their time during the day at 400–600 m, making regular excursions into shallower, warmer waters to reheat themselves. At night they migrate into waters shallower than 200 m, following the daily migrations of their prey which, is a mixture of squid and fish. Archival tagging studies have found that bigeye tuna in the Coral Sea are mostly residential, with little mixing between populations across the larger Pacific Ocean. A small proportion of individuals undertake cyclic migrations between areas off north-eastern Australia and eastern parts of the western Pacific Ocean.