Atlantic bluefin tuna
| Atlantic bluefin tuna | |
|---|---|
 | |
| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Scombridae |
| Tribe: | Thunnini |
| Genus: | Thunnus |
| Species: | T. thynnus |
| Binomial name | |
| Thunnus thynnus (Linnaeus, 1758) | |
The Atlantic bluefin tuna (Thunnus thynnus) is a species of tuna in the Scombridae family. It is variously known as the northern bluefin tuna (mainly when including Pacific bluefin as a subspecies), giant bluefin tuna (for individuals exceeding 150 kilograms or around 330 pounds) and formerly as the tunny. Atlantic bluefin are native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea. Atlantic bluefin have become extinct in the Black Sea. The Atlantic bluefin tuna is a close relative of the other two bluefin tuna species—the Pacific bluefin tuna and the southern bluefin tuna.
Atlantic bluefin tuna are capable of reaching well over 450 kilograms (990 lb) in weight, and rival the black marlin, blue marlin and swordfish as the largest Perciformes. Throughout recorded history, the Atlantic bluefin tuna has been highly prized as a food fish. Bluefin have been a valuable commercial catch from the time of the ancient Greeks and Phoenicians to the modern era. Besides their commercial value as food, their great size and the speed and power they display as apex predators has attracted the admiration and respect of both ancient and modern fishermen, as well as writers, sport anglers and scientists.
The Atlantic bluefin tuna has been the foundation of one of the world's most lucrative commercial fisheries. Medium-sized and large individuals are heavily targeted for the Japanese raw fish market, where all bluefin species are highly prized for sushi and sashimi. This commercial importance has led to severe overfishing. The International Commission for the Conservation of Atlantic Tunas (ICCAT) affirmed in October 2009 that Atlantic bluefin tuna stocks have declined dramatically over the last 40 years, by 72% in the Eastern Atlantic, and by 82% in the Western Atlantic.[2] On October 16, 2009, Monaco formally recommended Endangered Atlantic bluefin tuna for an Appendix I CITES listing and international trade ban. In early 2010, European officials, led by the French ecology minister, increased pressure to ban the commercial fishing of bluefin tuna internationally.[3] European Union nations, who are responsible for most bluefin tuna overfishing, later abstained from voting to protect the species from international trade.[4]
Bluefin are captured for the commercial market by professional fishermen using purse seine gear, assorted hook-and-line gear, most importantly the longline, and in certain areas by harpooners. Atlantic bluefin are also taken commercially by heavy rod and reel gear. Since the 1930s the bluefin tuna has long been one of the most important big-game species sought by sports fishermen, particularly in the United States but also in Canada, Spain, France and Italy.
Taxonomy
The Atlantic bluefin tuna is most closely related to the Pacific bluefin tuna (Thunnus orientalis) and the southern bluefin tuna (Thunnus maccoyii), and more distantly to the other large tunas of the genus Thunnus - the bigeye tuna (Thunnus obesus) and the yellowfin tuna (Thunnus albacares).[5] For many years the Pacific and Atlantic bluefin tuna species were considered to be the same, or subspecies, and referred to as the "northern bluefin tuna".[5] This name occasionally gives rise to some confusion as the longtail tuna (Thunnus tonggol) can in Australia sometimes be known under the name "northern bluefin tuna".[6][7] This is also true in New Zealand and Fiji.Bluefin tuna were often referred to as the common tunny, especially in the UK, Australia and New Zealand. The name tuna, a derivative of the Spanish atún, was widely adopted in California in the early 1900s and has since become accepted for all tunas, including the bluefin, throughout the English-speaking world. In some languages the bluefin's name refers to its red meat: atún rojo (Spanish), tonno rosso (Italian), amongst others.
Description
The body of the Atlantic bluefin tuna is rhomboidal in profile and robust. The head is conical and the mouth rather large. The head contains a "pineal window" that allows the fish to navigate over its multiple thousands of mile range.[8] The color is dark blue above and gray below with a gold coruscation covering the body and bright yellow caudal finlets. Bluefin tuna can be distinguished from other family members by the relatively short length of their pectoral fins. Their livers have a unique characteristic in that they are covered with blood vessels (striated). In other tunas with short pectoral fins, such vessels are either not present or present in small numbers along the edges.Fully mature adult specimens average 2–2.5 metres (6 ft 7 in–8 ft 2 in) long. The species can reach a maximum length of almost 4.6 metres (15 ft).[9] The largest recorded specimen taken under International Game Fish Association rules was caught off Nova Scotia, an area renowned for huge Atlantic bluefin, by Ken Fraser and weighed 679 kilograms (1,500 lb). The longest contest between man and tuna fish occurred near Liverpool, Nova Scotia in 1934, when 6 men, taking turns, fought the 795 pounds (361 kg) tuna in a terrific battle that lasted sixty-two hours.[10]
Atlantic bluefin tuna reach maturity relatively quickly. In a survey that included specimens up to 2.55 metres (8 ft 4 in) in length and 247 kilograms (540 lb) in weight, none was believed to be older than 15 years.[11] However, very large specimens may, at least theoretically, be up to 50 years old.[11]
The bluefin possesses enormous muscular strength which it channels through a pair of tendons to its lunate shaped caudal fin. In contrast to many other fish, the body stays rigid while the tail flicks back and forth, increasing stroke efficiency.[12]
Thermoregulation
To keep its core muscles warm (used for power and steady swimming), the Atlantic bluefin uses countercurrent exchange to prevent heat from being lost to the surrounding water. The heat in the arterial blood transfers to the venous blood. This keeps the core muscles warm so they can function efficiently.[13]All members of the tuna family are warm-blooded (have the ability to thermoregulate). This ability, however, is more highly developed in bluefin tuna than in any other fish, allowing them to seek food in the chilly waters of the north Atlantic.[8]
Circulation
Bluefin tuna have a very efficient circulatory system. It possesses one of the highest blood hemoglobin concentrations among fish, which allows them to efficiently deliver oxygen to their tissues; this is combined with their exceptionally thin blood-water barrier to ensure rapid oxygen uptake.[13]Behavior
Bluefin dive to depths of 1,000 metres (550 fathoms).[14] They can reach speeds of 40 miles per hour (64 km/h).[8]Diet and foraging
The Atlantic bluefin tuna typically hunts small fish and invertebrates such as sardines, herring, mackerel, squid and crustaceans.
Conservation
In 2010, Greenpeace International added the northern bluefin tuna to its seafood red list.[22]
On March 18, 2010 the United Nations rejected a U.S.-backed effort to impose a total ban on Atlantic Bluefin tuna fishing and trading.[23] The Convention on International Trade in Endangered Species (CITES) vote was 68 to 20 with 30 European abstentions. The leading opponent, Japan, claimed that ICCAT was the proper regulatory body.[4]
In 2011, the USA's National Oceanic and Atmospheric Administration (NOAA) decided not to list the Atlantic bluefin tuna as an endangered species. It is still considered a "species of concern," but NOAA officials claimed that the more stringent international fishing rules created in November 2010 would be enough for the Atlantic bluefin tuna to recover. NOAA agreed to reconsider the species endangered status in 2013
- Article Source: http://en.wikipedia.org/
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