High demand for its dark red flesh has made the bluefin tuna the object of intense commercial and recreational fishing efforts and has resulted in a dwindling population of adult fish. This species, as well as its cousin the southern bluefin tuna, is gravely overfished. According to some estimates, the population of the species in the western Atlantic has declined by roughly 87 percent since 1970.
Because bluefin tuna are slow to mature, they are especially vulnerable to overexploitation. Although some catch quotas have been established, the continued landing of small bluefins, as well as large ones (called giants), in some regions; the failure to restrict harvest in others.
The ignorance of restrictions by commercial fishermen of some countries; the lack of punishment or enforcement; and the managerial treatment of bluefins on a separate two-stock basis, instead of on one interpolar migratory one, are leading reasons for both species of bluefin tuna to be further troubled, if not endangered.
In 1996, scientists warned that existing worldwide catch quotas would have to be cut by 80 percent for populations to recover in 20 years, but these were raised instead.
Other Names
Atlantic bluefin tuna, northern bluefin tuna, tunny fish, horse-mackerel; Arabic: tunna; Chinese: cá chan, thu; French: thon rouge; Italian: tonno; Japanese: kuromaguro; Norwegian: sjorjf, thunfisk; Portuguese: atum, rabilha; Spanish: atún aleta azul, atun rojo; Turkish: orkinos.Identification
The bluefin tuna has a fusiform body, compressed and stocky in front. It can be distinguished from almost all other tuna by its rather short pectoral fins, which extend only as far back as the eleventh or twelfth spine in the first dorsal fin. There are 12 to 14 spines in the first dorsal fin and 13 to 15 rays in the second.The anal fin has 11 to 15 rays. The bluefin has the highest gill raker count of any species of Thunnus, with 34 to 43 on the first arch. The ventral surface of the liver is striated, and the middle lobe is usually the largest.
The back and the upper sides are dark blue to black, with a gray or green iridescence. The lower sides are silvery, marked with gray spots and bands. The anal fin is dusky and has some yellow. The finlets are yellow and edged with black. The caudal keel is black at the adult stage but is semitransparent when immature.
Size/Age
Bluefin tuna can grow to more than 10 feet and are commonly found at lengths from 16 to 79 inches. Adults weigh from 300 to 1,500 pounds, although fish exceeding 1,000 pounds are rare. The all-tackle world record is a fish from Nova Scotia that weighed 1,496 pounds when caught in 1979. The species reportedly can live for 40 years.Life history/Behavior
Bluefin tuna are warm blooded and able to maintain their body temperatures up to 18°F above the surrounding water, which makes them superbly adapted to temperate and cold waters. They retain 98 percent of muscular heat, may have the highest metabolism of any known fish, and are among the fastest and most wide-ranging animals on earth. When hunted or hunting, they can accelerate to 35 miles per hour.Bluefins are schooling fish and do congregate by size, although the largest schools are formed by the smallest individuals, and the smallest schools are composed of the largest fish. They swim in a single file, side by side (soldier formation), or in an arc (hunter formation). Extensive migrations appear to be tied to water temperature, spawning habits, and the seasonal movements of forage species.
Bluefins in the western Atlantic are sexually mature at approximately age 8 (80 inches curved fork length) and in the eastern Atlantic at about age 5 (60 inches).
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Food
The diet of bluefin tuna consists of squid, eels, and crustaceans, as well as pelagic schooling fish such as mackerel, flyingfish, herring, whiting, and mullet.Distribution/Habitat
Bluefin tuna occur in subtropical and temperate waters of the north Pacific Ocean and the North Atlantic Ocean and in the Mediterranean and the Black Seas. They are widely distributed throughout the Atlantic.Distribution in the western Atlantic occurs along Labrador and New-foundland southward to Tobago, Trinidad, Venezuela, and the Brazilian coast; they are especially encountered by anglers off Nova Scotia and Prince Edward Island; Cape Cod; Montauk, New York; the canyons offshore of New York and New Jersey; the North Carolina region; and the Bahamas.
Distribution in the eastern Atlantic extends as far north as Norway and Iceland and as far south as northern West Africa. Atlantic bluefin tuna spawn in the Gulf of Mexico between April and June and in the Mediterranean Sea in June and July.
