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Southern Bluefin Tuna
(Thunnus maccoyii)
Appearance
Southern Bluefin Tuna (SBT) is a large silver-white fish with a blue-black upper body and
yellow tinged fins. It grows up to 2m and 200kg in size, but more commonly adults tend to be
around 1.6m in length.
Distribution & Life Cycle
SBT are mainly found between latitudes 20°S and 50°S, in Australian fishing waters south from
northern New South Wales around to the northern waters off Western Australia (spawning
grounds). SBT migrate southwards from the spawning grounds, and juvenile fish tend to
remain near the coasts. Adults from about 3 years of age generally move out to sea, to live a
pelagic (oceanic) life. SBT live to about 20 years of age, and become mature at
about 8 years old, at which time they are about 130cm in length. Tuna must keep moving (at least their body-length every second) to ensure a flow of water over their gills. Their body shape, muscles and heart are all adapted to their high speed (up to 70 km/hr), continuous swimming. Tuna mainly feed on fish, squid, small crustaceans, and krill. Natural predators of the tuna include seabirds, larger tuna, sharks and killer whales.
Aquaculture in the Region
In Australian waters, both Australian and Japanese fishing takes place. Methods include longlines, pole and line, purse seine nets, trolling, and farming. Tuna farming is now well-established, with the fish netted in the Southern Ocean, transferred to cages and slowly towed to Pt Lincoln. The SBT are kept in a an enclosure consisting of a large (up to 80m) diameter floating ring, from which a net of about 15m depth is suspended. They are fed a controlled diet for a period from 3 to 8 months to improve their condition and fattem them. Until recently, that diet was almost entirely pilchards, most of which were imported. However, a grain-based pelletised food has been developed by staff working at the LMSC, and these pellets are now rapidly being introduced. The pellets have many advantages over pilchards, including increased feeding efficiency, ease of storage, reduced reliance on imports, reduced wastage, quality control, etc. Most of the farmed Southern Bluefin Tuna are exported to the Japanese Sashimi market. ('Sashimi' means uncooked or raw food.)
References
Kailola, P.; Williams, M.J.; Stewart, P.C.; Reichelt, R.E.; McNee, A.; Grieve, C. 1993,
Australian Fisheries Resources
Bureau of Resource Sciences, Dept. of Primary Industries and Energy, and Fisheries Resource and Development Corporation, Canberra Australia.
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