Open water species that occurs in large schools in subtropical and temperate waters. Two other tunas also commonly occur in the region, the albacore Thunnus alalunga, a species with very long pectoral fins extending back behind the second dorsal fin, and the yellowfin tuna T. albacares, a species with yellow dorsal and anal fins. The southern bluefin tuna spawns in the Indian Ocean off northwestern Australia, with juvenile fish migrating down the western and then along the southern coasts, gaining in size as they travel. Heavy fishing along this migratory route during the past four decades has reduced stocks to a small fraction of former levels.

• Habitat: Open ocean

• Threats: By-catch, Exploitation
• IUCN Threat Status: Vulnerable
• Occurrence: Rare (1% of sites)
  Occurrence describes how often the species is found on surveys within its distribution. It is calculated as the % of reef sites surveyed by RLS divers across all the ecoregions in which the species has been observed
• Abundance: Several (9 per transect)
  Abundance is calculated as the average number of individuals recorded per RLS transect, where present.