About Southern Bluefin Tuna

The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 m (8.2 ft) and weighing up to 400 kg (882 lbs) it is among the larger bony fishes.

The southern bluefin tuna is a large, streamlined, fast swimming fish with a long, slender caudal peduncle and relatively short dorsal, pectoral and anal fins. The body is completely covered in small scales.

The body color is blue-black on the back and silver-white on the flanks and belly, with bright yellow caudal keels in adult specimens. The first dorsal fin color is grey with a yellow tinge, the second dorsal is red-brown, and the finlets are yellow with a darker border.

Southern bluefin tuna, like other pelagic tuna species, are part of a group of bony fishes that can maintain their body core temperature up to 10 degrees higher than the ambient temperature. This advantage enables them to maintain high metabolic output for predation and migrating large distances. The southern bluefin tuna is an opportunistic feeder, preying on a wide variety of fish, crustaceans, cephalopods, salps, and other marine animals.

Physical Description

Southern bluefin tuna weigh over 200kg; and grow over 2m. Lifespan is 20 to 40 years.

Bluefin tuna are built like torpedoes. Not only do they have a hydrodynamic shape, their pectoral (side) fins can be retracted and their eyes are set flush to their body. This means their bodies create little drag as they swim through water. A warm body temperature also helps these fish swim fast, as does a stiff body that channels muscle energy directly to a highly efficient, crescent-shaped tail.

Life History

Thunnus maccoyii are often caught near their spawning grounds in the Indian Ocean. During spawning, large fish migrate to tropical seas, off the west coast of Australia, up to 10°S. Spawning fish and larvae can be found in waters with surface temperatures between 20-30°C. They have a minimum population doubling time of 4.5 - 14 years, making the southern bluefin tuna a prime target for overfishing.

Economic Value

Southern bluefin tuna are exported to Japan, the USA and Canada where it is highly prized for sashimi and sushi. Almost all large bluefins are shipped to Japan where they can fetch very high prices. An individual 444 pound bluefin sold for a record US$173,000 in Tokyo in 2001. The export value of southern blue fin tuna was $7million in 2008.