Tuna: Bluefin (Southern)

Kuromaguro, Atun de aleta azul, Horse mackerel

The southern bluefin is a large, cold-water tuna of the southern hemisphere. Its only known spawning ground is located in the Indian Ocean, in an area south of Java and off northwest Australia. Juveniles migrate southwards along Australia’s west coast and congregate in the coastal waters off south Australia. As the fish mature, they extend their distribution to cover the circumpolar area throughout the Pacific, Indian and Atlantic Oceans. The largest southern bluefin on record weighed 157 kg, although the average weight of individuals caught is approximately 7 kg. They are believed to become sexually mature at about 8 years, at a length of about 155 cm, and to have a maximum lifespan of 42 years.

Southern bluefin tuna have limited distribution (in comparison to other tunas), fidelity to particular spawning grounds, and are slow to mature. These traits make southern bluefin tuna moderately vulnerable to fishing pressure.

The southern bluefin tuna is in recognized decline throughout its range. An outdated stock assessment (1998) shows spawning biomass in decline, and recruitment at approximately 1/3 of the 1970 level. Unreported fishing by nations not a members of the Convention for the Conservation of Southern Bluefin Tuna (CCSBT) has resulted in a slow recovery of this species. According to Australia’s Bureau of Rural Sciences, the southern bluefin is fished at 30% above the total allowable catch limits set by the CCSBT. The stock status of this species has a high conservation concern.

Longlining is a preferred method to catch southern bluefin tuna. Monitoring of this fleet is sparse to non-existent. Pelagic longlines are known to capture several species of turtles and seabirds, many of which are endangered. Bycatch in southern Bluefin tuna fisheries is a high conservation concern.

Pelagic longlining has no direct habitat impact and therefore is a low conservation concern.

Although regional management of southern bluefin tuna is attempted through the Convention for the Conservation of Southern Bluefin Tuna. There has been an increase in unreported catch by non-member nations. Anticipated benefits of the Convention have not been realized due to illegal fishing. The Convention itself has provisions for monitoring and setting catch quotas, however, overall this species is poorly managed due to illegal fishing and is a high conservation concern.

Am I eating bluefin tuna?

Consumption advisory due to mercury.

No.