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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)

A northern bluefin tuna at the Osaka Aquarium Kaiyukan, Japan

The Atlantic bluefin tuna (Thunnus thynnus), also known as the northern bluefin tuna, giant bluefin tuna (for larger individuals exceeding 150 kilograms or around 300 pounds) and formerly as the tunny, is a species of tuna native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea. Atlantic bluefin have been recorded in the Black Sea in the past, but are now believed to be extinct there. 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 a thousand pounds in weight, and rival the black marlin and blue marlin as some the largest known bony fish. 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 Greeks and Phoenicians to the modern era. Besides their value as food and in commerce, the great size that the bluefin can attain and the speed and power they display in their ecological role as apex predators has attracted the admiration and respect of both ancient and modern fishermen, as well as writers, sport anglers and scientists.

Today, the Atlantic bluefin tuna is 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 species of bluefin are highly prized for 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 are declining dramatically, by 72% in the Eastern Atlantic, and by 82% in the Western Atlantic.^[1] 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. ^[2]

Bluefin are captured for the commercial market commercial fishermen using purse seine gear, assorted hook-and-line gear, most important the longline, and in certain areas by harpooners. Atlantic bluefin are also taken commercially by heavy rod and reel gear. The bluefin tuna has long been one of the most important big-game species sought by sports fishermen. Sport fishing for the Atlantic bluefin tuna has existed since the 1930s and continues to be popular to this day, 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). 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'. This name occasionally gives rise to some confusion as the longtail tuna Thunnus tonggol can in Australia be legally sold as canned tuna under the name "northern bluefin tuna". This is also true in New Zealand and Fiji, although canned tuna is less common there.

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 'atun' 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. Many Latin names for the bluefin refer to its red meat - atun roja (Spanish); and tonno rosso (Italian) amongst others.

Description

The body of the northern bluefin tuna is rhomboidal in profile and robust. The head is conical and the mouth rather large. 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.

Atlantic bluefin tuna can live for 30 years, but due to heavy fishing mortality, few known specimens grow to a mature age.

Fully mature adult specimens average 2–2.5 metres (6 ft 7 in–8 ft 2 in) long and around 350 kilograms (770 lb) in weight. The species can reach a maximum length of about 4.3 metres (14 ft). 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 (1,497 lb). According to Gordon Johnston's 'It Happened in Canada' ^[3] "The longest contest between men and a tuna fish occurred near Liverpool, Nova Scotia in 1934, when 6 men, taking turns, fought the 795-lb tuna in a terrific battle that lasted sixty-two hours.

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.^[4]

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.^[5]

All members of the tuna family 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.

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.^[5]

Behaviour

Diet and foraging

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

Bluefin dive to depths of 1,000 metres (550 fathoms)^[6]

Parasites

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.

Reproduction

Female bluefin are thought to produce up to 40 million eggs.

Atlantic bluefin tuna spawn in two widely separated areas. One spawning ground exists in the western Mediterranean, particularly in the area of the Balearic Islands. The other important spawning ground of the Atlantic bluefin is the Gulf of Mexico. Pop-up satellite tracking results appear to confirm in large measure the belief held by many scientists and fishermen that although bluefin spawned in each area may forage widely across the Atlantic, they return to the same area to spawn.

Atlantic bluefin group together in large concentrations to spawn, and at such times are highly vulnerable to commercial fishing. This is particularly so in the Mediterranean where the groups of spawning bluefin can be spotted from the air by light aircraft and purse seines directed to set around the schools.

The western and eastern populations of Atlantic bluefin tuna are thought to mature at different ages. It is thought that bluefin born in the east reach maturity a year or two earlier than those spawned in the west.^[6]

Fisheries and conservation

This tuna is one of the most highly-prized fish used in Japanese raw fish dishes. Bluefin tuna sashimi 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^[7][8]. Bluefin tuna are a $7.2 billion industry. In January 2009, a 440 pounds (200 kg) bluefin sold for $173,000. In January 2010, a 232 kilograms (510 lb) bluefin sold for nearly 180,000$ at auction in Toyko, Japan.^[9] The very highest prices in the Japanese market have tended to be from Pacific bluefin tuna caught in Japanese waters, but high-grade Atlantic bluefin, particularly those from Canada and Boston, also fetched high prices. Prices were highest in the late 1970s and 1980s. The entry of many North African Mediterranean countries, such as Tunisia and Libya, into the bluefin tuna market in the 1990s, along with the increasingly widespread practice of tuna farming in the Mediterranean and other areas such as southern Australia (for southern bluefin tuna) has brought down prices. One result is that fishermen who had already invested in the fishery must now catch up to twice as many fish.

Atlantic bluefin populations probably remained stable until the 1960s. Prior to that period, bluefin fisheries were relatively small in scale. Although a number of local stocks, such as those in the North Sea, were probably decimated by unrestricted commercial fishing, commercial fishing pressure at the time was insufficient to eliminate the species in its entirety. However, in the 1960s purse seiners catching fish for the canned tuna market in United States coastal waters eliminated huge numbers of juvenile and young Western Atlantic bluefin, taking out several entire year classes. The rise in demand for bluefin sashimi led to higher prices for medium and giant adult fish in the 1970s, placing pressure on the remaining breeding stocks that continued into the 2010s. In their eastern range, Mediterranean fisheries have historically been poorly regulated and catches from this area under-reported, with French, Spanish, Italian fishermen competing with North African nations for a diminishing population.

A large proportion of juvenile and young Mediterranean fish are taken to be grown on tuna farms. Tuna farming began as early in the 1970s when Canadian fishermen in St Mary's Bay confined giant bluefins in pens, taking them to Japan at the end of the season when their market value was at its highest. Tuna farming enables farmers to respond to high market prices and to exploit the unpredictable supply of wild-caught fish. Besides the tuna farms located off South Australia, which grow on the related southern bluefin tuna, numerous ranches across the Mediterranean grow bluefin offshore. This industry is worth 220 million US$ annually. Because the young tuna captured for the tuna farms are taken before they are old enough to reproduce, bluefin farming is considered to be one of the most serious threats to Atlantic bluefin tuna.^{[citation needed]}

The bluefin's slow growth and late sexual maturity compound its problems. The Atlantic population has declined by nearly 90 percent since the 1970s.^[10] The bluefin species is listed as "Avoid" on the Monterey Bay Aquarium Seafood Watch program.

Overfishing continues despite repeated warnings. 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 chose twice that number, later 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 yearly.

In 2010, Greenpeace International has added the northern bluefin tuna to its seafood red list. "The Greenpeace International seafood red list is a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."^[11]

On March 18, 2010 the United Nations rejected a US-backed effort to impose a total ban on Northern Bluefin tuna fishing^[12]

Captive breeding

In 2009, aquaculturists succeeded in breeding bluefin in captivity and keeping them alive through their development from larvae to fingerlings to young juveniles.^[13] 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 the carnivorous bluefin must consume baitfish to thrive and grow.

Culture

The northern bluefin tuna is depicted on the reverse of the Croatian 2 kuna coin, minted since 1993.^[14]

Footnotes

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
• Newlands, Nathaniel K. 2002. Shoaling dynamics and abundance estimation : Atlantic bluefin tuna (Thunnus thynnus). PhD thesis, Resource Management and Environmental Studies/Fisheries Centre, University of British Columbia, Vancouver, Canada. 602pp, https://dspace.library.ubc.ca/handle/2429/13501
• Newlands, N.K., Lutcavage, M. and Pitcher, T. 2006. Atlantic Bluefin Tuna in the Gulf of Maine, I: Estimation of Seasonal Abundance Accounting for Movement, School and School-Aggregation Behaviour. Environmental Biology of Fishes, Volume 77, Number 2 / October, 2006, http://www.springerlink.com/content/v8417th6pnh7k176/
• Newlands, N.K., Lutcavage, M. and Pitcher, T. 2007. Atlantic bluefin tuna in the Gulf of Maine, II: precision of sampling designs in estimating seasonal abundance accounting for tuna behaviour. Environmental Biology of Fishes, Volume 80, Number 4 / December, 2007, 405-420, http://www.springerlink.com/content/33l5754335260608/
• Nathaniel K. Newlands1 , Molly E. Lutcavage2 and Tony J. Pitcher (2004) Analysis of foraging movements of Atlantic bluefin tuna ( Thunnus thynnus): individuals switch between two modes of search behaviour. Population Ecology, Volume 46, Number 1 / April, 2004,39-53, http://www.springerlink.com/content/mhywt3radfc9qlcb/
• Newlands, Nathaniel K., Porcelli Tracy A. (2008) Measurement of the size, shape and structure of Atlantic bluefin tuna schools in the open ocean. Fisheries Research, 2008, vol. 91, no1, pp. 42-55. http://cat.inist.fr/?aModele=afficheN&cpsidt=20301569
• 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.
• Froese, Rainer, and Daniel Pauly, eds. (2006). "Thunnus thynnus" in FishBase. January 2006 version.
• 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)

External links

• 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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