Tuna are large oceanic fish in the family Scombridae. They are seasonally migratory, travelling hundreds of miles and sometimes making trans-oceanic journeys. They may be found in variable numbers in almost every temperate, subtropical or tropical waters. Compared to some fishes, tuna are late to mature and can reach ages of 10-25 years, depending on the species. Blue-fin tuna are slower growing than the smaller albacore, skipjack and yellow-fin tunas. An adult Atlantic blue-fin can be more than 2 m long and weigh 500 kg.
All commercially important tunas need warm water to breed, although several species are warm-blooded, enabling them to live in cooler waters. They are fast swimmers and, unlike most fish whose flesh is white, tuna flesh is pink to dark red. Tuna fisheries include both low-value (less than US Dollars 1/kg), high-volume fisheries that supply the canneries, and highvalue (more than US Dollars 500/kg), low-volume fisheries that specialize in fresh tuna. There are seven commercially fished species, including:
Southern blue-fin (Thunnus maccoyii): Found in temperate and cold seas of the southern hemisphere, these fish migrate to the tropics to spawn. They are fished mainly by Japan, Korea, Australia and New Zealand, and consumed mainly by Japan.
Pacific northern blue-fin (Thunnus orientalis): Found mainly in subtropical regions of the north Pacific Ocean, this species is both fished and consumed mainly by Japan.
Northern or Atlantic blue-fin (Thunnus thynnus): This species is found in the northern half of the Atlantic Ocean, the Mediterranean and the southern Black Sea.
Big-eye (Thunnus obesus): Also known as Ahi, Po'onui, Patudo, this is a tropical and subtropical species with separate stocks in the Atlantic, Indian, Western and Central Pacific, and Eastern Pacific Oceans.
Albacore (Thunnus alalunga): Also known as Tombo, canned white tuna, longfin tunny, and albacora, this is a highly migratory fish found in all oceans but less common in the tropics. It is available as canned "white" tuna and fresh and frozen.
Skipjack (Euthynnus or Katsuwonus pelamis): Found throughout the world's tropical and warm temperate waters, catches of this species account for half the annual global tuna supply. Also marketed as aku, canned light tuna, arctic bonito, striped tuna, these fish may be mixed with other species when processed. It is most often sold as canned light tuna (much of which is caught by purse seine), but is sometimes sold fresh and frozen.
Yellow-fin (Thunnus albacares): Found throughout the world's tropical and subtropical seas, except the Mediterranean, this species is also marketed as ahi when fresh and frozen, and canned light tuna. It is the main species for canning and is caught mainly by purse seine fleets.
Three species of tuna are listed on the IUCN Red List:
A fourth species, albacore tuna, is considered Data Deficient, but with stocks considered threatened in the North Atlantic (Vulnerable) and South Atlantic (Critically Endangered). Several conservation issues affect all seven commercially fished tuna species, principally:
Overfishing: World catches of tuna have doubled in the last decade. All species, except some stocks of skipjack, are considered fully exploited, over-exploited or depleted. The popularity of sashimi and sushi is one cause of overfishing, especially of the three species of blue-fin tuna (also known as kuromaguro, atun de aleta azul, thon rouge and horse mackerel), which are the most valuable fish in the world. Overfishing is made worse by the fact that juvenile tunas (e.g. big-eye) are often caught as by-catch in the purse seine fisheries targeted for adult tuna. The long-term effects on marine ecosystems of removing large fish such as tuna are not fully understood.
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