Southern bluefin tuna spawn between September and April each year in the only known spawning grounds in the Indian Ocean, between the north-west Coast of Australia and Indonesia. The eggs are estimated to hatch within two to three days, and over the next two years attain sizes of approximately 15 kilograms; this size is the principal wild catch of the Australian SBT industry. It is believed that SBT become sexually mature between 9 and 12 years in the wild, which highlights the major negative impact of removing pre-spawning populations from the wild.