Southern Bluefin Tuna, Thunnus maccoyii (Castelnau 1872)


Other Names: Bluefin, Japanese Central Pacific Bluefin Tuna, SBT, Southern Tuna, Southern Tunny

Southern Bluefin Tuna, Thunnus maccoyii, in pontoons off Port Lincoln, South Australia. Source: Ben Endean. License: All rights reserved

Summary:

Large, powerful fast-swimming oceanic predators with an advanced circulatory system that keeps the body temperature above that of the surrounding seawater.

Identifying features:
Blackish-blue above, silvery-white below; caudal keels yellow (colour may be missing in larger adults); Second dorsal-fin, caudal fin and finlets tinged with yellow, anal fin dusky; body robust, streamlined, pectoral fins relatively short.

Southern Bluefin Tuna (SBT) are highly valued in global markets, being the most expensive fresh seafood in the world. About 95% of the SBT catch is consumed in high-end Japanese sashimi market.

SBT live up to 40 years, and migrate long distances from their southern feeding areas to breed in tropical waters near Java, Indonesia each year. Almost all of the Australian SBT catch is now farmed. Juveniles, caught in purse seine nets in the Great Australian Bight, are slowly towed to Port Lincoln in South Australia. They are fattened up in floating sea cages off tehe coast, before being harvested at 30-40 kg.

Images of SBT at the ARKive website.

Video of SBT in pens at Port Lincoln, South Australia

Video of SBT being harvested from tuna pens at Port Lincoln, South Australia


Cite this page as:
Dianne J. Bray & Martin F. Gomon, Thunnus maccoyii in Fishes of Australia, accessed 20 Nov 2018, http://fishesofaustralia.net.au/home/species/732

Southern Bluefin Tuna, Thunnus maccoyii (Castelnau 1872)

More Info


Distribution

Circumglobal in temperate and cold temperate waters of the southern hemisphere, ranging across the Pacific, Indian, Southern and south-eastern Atlantic oceans, mostly between 30°S and 50°S, to almost 60°S (rare in the Eastern Pacific). 

Southern Bluefin Tuna breed between October and March in an area off Java, Indonesia and migrate down the Western Australian coast during their first year. Some then head westwards into the Indian Ocean, while others head eastwards into the Great Australian Bight.

Recorded from every state in Australia except the Northern Territory.  Absent from coasts of the Northern Territory and northern Queensland, and very rare in central and western Bass Strait along the south coast.

Features

Meristic features: Dorsal-fin XII-XIV +  13-16 + 8-10 finlets; Anal-fin 12-15 + 7-10 finlets; pectoral fin 33-36; caudal-fin 17; Pelvic fin I, 5; Lateral line about 270; Gill rakers 26-34.

Body fusiform, of moderate depth (25- 28% FL), greatest depth near middle of first dorsal fin, robust, tapering abruptly to very slender caudal peduncle; each side of caudal peduncle with prominent lateral keel and smaller keels above and below it.  Head of moderate size (approx. 29% FL); eyes moderately small (13-18% HL); mouth moderately small, terminal, angled obliquely, gape extending to below middle of eyes; teeth small, conical, single row in each jaw, smaller teeth on palatines and vomer; preopercles rounded.  

Two dorsal fins situated close together, first dorsal highest anteriorly, length of base slightly less than head length, posterior edge of fin concave; second dorsal triangular, of moderate height (8-15% FL), base shorter than that of first dorsal; anal fin about same size and shape as second dorsal-fin, located below and slightly behind it; caudal fin lunate.  Pectoral fins rather short (not more than 80% HL in specimens 65-145 cm). Pelvic fins thoracic, originating under pectoral fins.

Scales cycloid, small over main part of body, slightly larger in pectoral regions; lateral line moderately arched.

Size

SBT can reach a length of more than 2 metres, and a weight of over 200 kg. They live for up to forty years.

Colour

Dark blue above, silvery below; caudal keels yellow, though colour may be missing in larger adults; second dorsal fin, caudal fin and finlets also tinged with yellow.

Feeding

Juvenile Southern Bluefin Tuna feed on planktonic crustaceans. Adults are opportunistic predators feeding mainly on pelagic fishes, but also on crustaceans and squid.

Biology

The sexes are separate and fertilization is external. Adult Southern Bluefin Tuna migrate to their only spawning ground off northwestern Australia, breeding from September to April each year. Individuals may live to 40 years and mature females may spawn many times, releasing millions of eggs, before returning to colder waters.

The pelagic eggs hatch after a few days and the larvae metamorphose after about 20 days. Studies have shown that the eggs and larvae move south from the spawning grounds off Java, and juveniles are often seen south of Perth, Western Australia, during their first year. By two to three years of age, juveniles are seen in surface waters off southern Australia, and in the Tasman Sea.

Fisheries

Southern Bluefin Tuna are an extremely valuable and highly prized commercial species. The flesh is medium-flavoured and most fish are sold in the Japanese Sashimi market. The worldwide fishery is estimated to be worth more than 1 billion dollars.

Southern Bluefin Tuna were heavily fished in the past with catches reaching 80,000 tonnes per year during the 1960’s. By the 1980's the catch had drammatically declined to half that amount, resulting in the imposition of voluntary quotas by the main fishing nations (Australia, Japan and New Zealand). Despite this, Southern Bluefin Tuna stocks continued to decline and the Commission for the Conservation of Southern Bluefin Tuna was established in 1994 to manage the global fishery.

Except in Australia, most Southern Bluefin Tuna are caught on longlines. In Australian waters most fish are farmed in captive aquaculture programs.

From September to March, schools of mostly immature fish (aged 2-4 years) are enclosed in purse seines in the Great Australian Bight. The schools are then slowly towed towards the mainland where they are transferred to floating sea cages anchored to the sea floor.

The majority of Australia’s SBT quota is farmed in Spencer Gulf near Port Lincoln, South Australia where fish are fattened up over several months before being harvested at 30-40 kg.

SBT are also targeted by game fishers off southwestern Victoria. Bag/possession limit : 2 Landed whole or as a carcass per person.

Conservation

  • EPBC Act 1999 : Conservation Dependent
  • IUCN Red List : Critically Endangered
  • NSW Fisheries Management Act 1994 : Endangered
  • Victorian Flora and Fauna Guarantee Act 1988 : Threatened

    SBT are highly vulnerable to overexploitation, especially as genetics have shown there is a single population worldwide, and they all spawn in one place in Indonesia between Australia and Java. The species has been under considerable fishing pressure, with a recent paper suggesting that the fish stocks have essentially crashed. The current adult biomass is considered to be about 5% of the estimated original biomass (Collette et al 2011). 

  • Remarks

    Although Southern Bluefin Tuna spend part of their life cycle in cool waters, they are ‘warm-blooded’. This means that their core body temperature may be 4 degrees higher than the surrounding water temperature.

    Similar Species

    Similar in appearance to Longtail tuna (Thunnus tonggol), differing in having shorter pectoral fins and darker caudal keels.

    Etymology

    The species maccoyi is named for Professor Frederic McCoy, the first director of the National Museum of Victoria, Australia. http://museumvictoria.com.au/caughtandcoloured/mccoy.aspx

    Species Citation

    Thynnus maccoyii Castelnau 1872, Proc. Zool. Acclim. Soc. Vic. 1: 104, Melbourne market, Victoria, Australia.

    Author

    Dianne J. Bray & Martin F. Gomon

    Resources


    Southern Bluefin Tuna, Thunnus maccoyii (Castelnau 1872)

    References


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    Quick Facts


    CAAB Code:37441004

    Conservation:IUCN Critically Endangered; EPBC Act Conservation Dependent

    Depth:0-600 m

    Fishing:Commercial, recreational fish

    Max Size:225 cm (FL); 200 kg

    Species Image Gallery

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    CAAB distribution map