Southern bluefin tuna Thunnus maccoyii
Southern bluefin tuna (SBT) are large oceanic predators that grow to about 2.2 metres and 200 kilograms. They are supreme hunters and roam the Indian, Southern and Pacific Oceans in waters with surface temperatures of 17–23 degrees Celcius, catching prey from the surface to more than 600 metres deep. They are prized as sashimi in Japan where 95 per cent of the global catch is consumed. CSIRO research since the 1960s has shown that SBT breed in one location off Java, Indonesia, between October and March. The young fish spend their first year migrating south along the west coast of Australia and then head either east and into the Great Australian Bight or west and into the central Indian Ocean. Tagging studies show that juvenile SBT (two-to-five-year-olds) undertake cyclic migrations between the warm waters of the Great Australian Bight (where they are fished for tuna farms at Port Lincoln) and the cooler waters of the Indian Ocean. As they mature, they begin to roam more widely, visiting foraging areas of the east coast of Australia and the west coast of New Zealand in the Tasman Sea in winter and returning to the north-eastern Indian Ocean in summer to spawn.