Northern bluefin tuna

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Northern bluefin tuna
Conservation status
Critically Endangered (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Perciformes
Family:	Scombridae
Genus:	Thunnus
Species:	T. thynnus
Binomial name
Thunnus thynnus (Linnaeus, 1758)

The northern bluefin tuna (Thunnus thynnus), or giant bluefin tuna, is a species of tuna native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea and the Black Sea. Although not native to the Pacific Ocean, the species is now commercially cultivated off the Japanese coast. Bluefin tuna are caught by sports fishermen using heavy-duty rod and reels and by commercial fishermen using purse seine gear. The northern bluefin is an important commercial species, especially for sushi. This commercial importance has led to severe overfishing.

On October 16th 2009 Monaco formally recommended Endangered Atlantic bluefin tuna for an Appendix I CITES listing and international trade ban. The International Commission for the Conservation of Atlantic Tunas (ICCAT) affirmed that Atlantic bluefin tuna stocks are declining dramatically, by 72% in the Eastern Atlantic, and by 82% in the Western Atlantic.^[1]

Contents 1 Taxonomy 2 Description 2.1 Thermoregulation 2.2 Circulation 3 Behaviour 4 Reproduction 5 Uses 6 Footnotes 7 References 8 External links

[edit] Taxonomy

The species was in the past called the common tunny. It is often ambiguously referred to simply as "bluefin" or "bluefin tuna", which also refers to the southern bluefin tuna (Thunnus maccoyii) and the Pacific bluefin tuna (T. orientalis). Even the preferred name, northern bluefin tuna, is not unambiguous, because this is sometimes used for the longtail tuna T. tonggol. In Australia, canned T. tonggol is legally sold under the name "Northern bluefin tuna". This is also true in New Zealand and Fiji, although canned tuna is less common there.

[edit] Description

The body of the northern bluefin tuna is rhomboidal in profile and robust. The head is conical and the mouth rather large. Northern bluefin tuna can live for 30 years. Due to overfishing, few known specimens grow to a mature age. Typical specimens average 2–2.5 metres (6 ft 7 in–8 ft 2 in) long and around 350 kilograms (770 lb) in weight. The largest recorded specimen was caught off Nova Scotia and recorded at 680 kilograms (1,500 lb). The species can reach a maximum length of about 4.3 metres (14 ft). The color is dark blue above and gray below with a gold coruscation covering the body and bright yellow caudal finlets. Northern bluefin tuna can easily 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.

The bluefin possesses enormous muscular strength which it channels through a pair of tendons to the sickle shaped tail. In contrast to many other fish, the body stays rigid while the tail flicks back and forth, increasing stroke efficiency.^[2]

[edit] Thermoregulation

To keep its core muscles warm (used for power and steady swimming), the northern 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.^[3]

[edit] 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.^[3]

[edit] Behaviour

The northern bluefin tuna typically hunts small fish and invertebrates such as sardines, herring, mackerel, squid and crustaceans.

The tetraphyllidean tapeworm Pelichnibothrium speciosum parasitizes this species (Scholz et al. 1998). As the tapeworm's definite host is the blue shark which does not generally seem to feed on tuna^{[citation needed]}, it is likely that the northern bluefin tuna is a dead-end host for P. speciosum. This fish is also a host to 72 parasites, 9 of them host-specific.

Bluefin dive to depths of 1,000 metres (550 fathoms)^[4]

[edit] Reproduction

Each female produces 40 million eggs. They frequent spawning grounds in the eastern Mediterranean and the Gulf of Mexico. They mature at different ages depending on what population they're from.^[4]

[edit] Uses

The northern bluefin tuna is an important source of seafood, providing most of the tuna used in sushi. It is a particular delicacy in Japan where at one auction, a single giant tuna sold for more than $100,000 on the Tsukiji fish market in Tokyo[1][2]. It is also popular in Taiwan, particularly in the town of Tungkang. As a result, many fisheries are now heavily overfished. The bluefin's slow growth rate and late sexual maturity compound this problem. The Atlantic population of the species has declined by nearly 90 percent since the 1970s.^[5] The bluefin species are consequently listed as ones to "Avoid" on the Monterey Bay Aquarium Seafood Watch program.

Despite alarm among scientists, however, overfishing continues. In 2007, researchers from the International Commission for the Conservation of Atlantic Tunas, or ICCAT — the regulators of Northern bluefin fishing — recommended a global quota of 15,000 tons. ICCAT then set the limit at twice that number, since dropping it to 22,500 tons. Their scientists now say that 7,500 tons is the sustainable limit. The fishing industry continue to harvest 60,000 tons of northern bluefin yearly. Bluefin tuna are a $7.2 billion industry. In January 2009, a 440 pounds (200 kg) bluefin sold for $173,000.^[6]

Numerous ranches across the Mediterranean catch juvenile bluefin before they are old enough to reproduce,^[who?] fattening them offshore before harvesting to improve the quality of meat. The industry is worth 220 million US$ annually. Bluefin ranches pose a serious risk to the remaining bluefin population, because they prevent reproduction.^{[citation needed]}

In 2009, aquaculturists for the first time succeeded in breeding bluefin in captivity and keeping them alive through their development from larvae to fingerlings to young juveniles.^[6] This raises the possibility, still remote, that the seemingly inevitable collapse of natural populations can be offset by cultivation. Many issues remain, such as that bluefin must consume enormous amounts of baitfish to thrive and grow.

The northern bluefin tuna is depicted on the reverse of the Croatian 2 kuna coin, minted since 1993.^[7][8][9]

[edit] Footnotes

[edit] References

• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7
• Safina, C. 1993. Bluefin Tuna in the West Atlantic: Negligent Management, and the Making of an Endangered Species. Conservation Biology 7:229-234.
• Safina (1996). Thunnus thynnus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 12 May 2006.
• Safina, C. 1998. "Song For The Blue Ocean." Henry Holt Co. New York.
• Safina, C and D. Klinger. 2008. Collapse of Bluefin Tuna in the Western Atlantic. Conservation Biology 22: 243–246.
• "Thunnus thynnus". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
• Scholz, Tomáš; Euzet, Louis & Moravec, František (1998): Taxonomic status of Pelichnibothrium speciosum Monticelli, 1889 (Cestoda: Tetraphyllidea), a mysterious parasite of Alepisaurus ferox Lowe (Teleostei: Alepisauridae) and Prionace glauca (L.) (Euselachii: Carcharinidae). Systematic Parasitology 41(1): 1–8. doi:10.1023/A:1006091102174 (HTML abstract)

[edit] External links

Wikimedia Commons has media related to: Northern bluefin tuna

Wikispecies has information related to: Northern bluefin tuna

• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.
• IUCN Redlist entry for Northern Bluefin Tuna
• Bluefin Tuna at Seafood Watch
• Greenpeace article on tuna at Greenpeace
• MarineBio article on tuna at MarineBio
• brochure on bluefin tuna tagging at Tag-a-Giant Foundation

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