Southern bluefin tuna spend their lives swimming constantly through the oceans cruising at two to three kilometres per hour (5), although they are able to reach speeds of 70 kilometres per hour (6). Individuals swim together in shoals and these migrate vast distances from spawning grounds in the Indian Ocean to feeding grounds in colder southern waters (4). It is thought that females do not spawn until they reach around 1.5 metres in length, which corresponds to at least eight years of age (5). A mature female will produce several million eggs in one spawning period (5). The breeding season runs from September and October until March (4), and occurs in Indonesian waters (5). Juvenile southern bluefin tuna are then known to group together during the summer months in coastal waters off the southern coast of Australia until they reach around five years old, after which they are more consistently associated with deeper waters (5).
These oceanic fish are opportunistic feeders, preying on a wide variety of other fish as well as crustaceans, cephalopods (such as squid and octopus) and other marine animals (7). Southern bluefin tuna are thought to be long-lived with a life expectancy possibly as long as 40 years (6).