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'''Tuna''' are ocean-dwelling [[carnivorous]] [[fish]] in the family [[Scombridae]], mostly in the genus ''[[Thunnus]]''. Tuna are fast swimmers—they have been clocked at {{convert|70|km/h|mph}}—and include several [[warm-blooded]] species. Unlike most fish, which have white flesh, tuna flesh is pink to dark red, which could explain their odd nick-name, "rose of the sea." The red coloring comes from tuna muscle tissue's greater quantities of [[myoglobin]], an [[oxygen]]-binding molecule. Some of the larger species, such as the [[bluefin tuna]], can raise their blood temperature above water temperature through muscular activity. This ability enables them to live in cooler waters and to survive in a wide range of ocean environments.
Tuna is crap. '''Tuna''' are ocean-dwelling [[carnivorous]] [[fish]] in the family [[Scombridae]], mostly in the genus ''[[Thunnus]]''. Tuna are fast swimmers—they have been clocked at {{convert|70|km/h|mph}}—and include several [[warm-blooded]] species. Unlike most fish, which have white flesh, tuna flesh is pink to dark red, which could explain their odd nick-name, "rose of the sea." The red coloring comes from tuna muscle tissue's greater quantities of [[myoglobin]], an [[oxygen]]-binding molecule. Some of the larger species, such as the [[bluefin tuna]], can raise their blood temperature above water temperature through muscular activity. This ability enables them to live in cooler waters and to survive in a wide range of ocean environments.


While many stocks are managed sustainably, it is widely accepted that bluefin have been severely [[overfishing|overfished]], with some stocks at risk of collapse.<ref>{{cite web
While many stocks are managed sustainably, it is widely accepted that bluefin have been severely [[overfishing|overfished]], with some stocks at risk of collapse.<ref>{{cite web

Revision as of 19:30, 8 October 2009

For other uses, see Tuna (disambiguation).

Tuna
File:Tuna.jpg
Yellowfin tuna, Thunnus albacares
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Actinopterygii
Order:
Perciformes
Family:
Scombridae
Genus:
Thunnus

South, 1845
Species

See text.

Tuna is crap. Tuna are ocean-dwelling carnivorous fish in the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers—they have been clocked at 70 kilometres per hour (43 mph)—and include several warm-blooded species. Unlike most fish, which have white flesh, tuna flesh is pink to dark red, which could explain their odd nick-name, "rose of the sea." The red coloring comes from tuna muscle tissue's greater quantities of myoglobin, an oxygen-binding molecule. Some of the larger species, such as the bluefin tuna, can raise their blood temperature above water temperature through muscular activity. This ability enables them to live in cooler waters and to survive in a wide range of ocean environments.

While many stocks are managed sustainably, it is widely accepted that bluefin have been severely overfished, with some stocks at risk of collapse.[1]

The Eastern Pacific Ocean bigeye is also in need of better management in order to maintain sustainability, leading the world's major canneries involved with the International Seafood Sustainability Foundation (ISSF) to agree to not accept that stock if meaningful conservation measures are not put in place by September 1, 2009.[2]

Taxonomy

Bar chart that states Thunnus thynnus is the largest tuna, at 458 centimetres (180 in) followed by Thunnus orientalis at 300 centimetres (120 in), Thunnus obsesus at 250 centimetres (98 in), Gymnosarda unicolor at 248 centimetres (98 in), Thunnus maccoyii at 245 centimetres (96 in), Thunnus albacares at 239 centimetres (94 in), Gasterochisma melampus at 164 centimetres (65 in), Thunnus tonggol at 145 centimetres (57 in), Thunnus alalunga at 140 centimetres (55 in), Euthynnus alletteratus at 122 centimetres (48 in), Katsuwonus pelamis at 108 centimetres (43 in), Thunnus atlanticus at 108 centimetres (43 in), Allothunnus fallai at 105 centimetres (41 in), Euthynnus affinis at 100 centimetres (39 in), Auxis thazard thazard at 65 centimetres (26 in),Auxis rochei rochei at 50 centimetres (20 in), and Auxis rochei eudorax at 36.5 centimetres (14.4 in)
Maximum reported sizes of tuna species

There are over 48 different tuna species. The Thunnus genus includes 8 species:

Species of several other genera (all in the family Scombridae) have common names containing "tuna":

Biology

A remarkable aspect of Thunnus physiology is its ability to maintain body temperature above than that of the ambient seawater. For example, bluefin can maintain a core body temperature of 75-95°F (24-35°C), in water as cold as 43 °F (6 °C). However, unlike typical endothermic creatures such as mammals and birds, tuna do not maintain temperature within a relatively narrow range.[3]

Tuna achieve endothermy by conserving the heat generated through normal metabolism. The rete mirabile ("wonderful net") the intertwining of veins and arteries in the body's periphery, transfers heat from arterial blood to venous blood via a counter-current exchange system. This reduces surface cooling, maintaining a warmer core. Higher body temperatures allow more efficient muscle use, supporting higher swimming speed with reduced energy expenditure.[3]

Commercial fishing

Photo of larger than human-sized fish lying on a dock with fishermen in background
Tuna being weighed on Greek quay-side
Photo of large tuna being landed on fishing boat
Tuna fishing in Hokkaidō, Japan
Photo of multiple rows of tuna
Tuna at a fish market
Photo of split tuna resting on cutting machine
Tuna cut in half for processing at the Tsukiji fish market in Tokyo, Japan

Tuna is an important commercial fish. Some varieties, such as bluefin and bigeye tuna, are threatened by overfishing, which dramatically affects Atlantic and northwestern Pacific Ocean populations. Other areas seem to support fairly healthy populations—for example, the central and western Pacific skipjack tuna—but there is mounting evidence that overexploitation threatens populations worldwide. The Australian government alleged in 2006 that Japan had illegally overfished southern bluefin by taking 12,000 to 20,000 tonnes per year[citation needed] instead of the their agreed 6,000 tonnes; the value of such overfishing would be as much as USD $2 billion. Such overfishing has severely damaged stocks.[citation needed] According to the WWF, "Japan's huge appetite for tuna will take the most sought-after stocks to the brink of commercial extinction unless fisheries agree on more rigid quotas".[4]

Increasing quantities of high-grade tuna are reared in net pens and fed bait fish. In Australia, former fishermen raise southern bluefin tuna, Thunnus maccoyii, and another bluefin species.[5] Farming its close relative, the northern bluefin tuna, Thunnus thynnus, is beginning in the Mediterranean, North America and Japan.

According to the Foodmarket Exchange, the total tuna catch was 3,605,000 tons in 2000, down about 5.7 percent from 3,823,000 tons in 1999. The main tuna fishing nations are concentrated in Asia, with Japan and Taiwan floating the main fleets. Other important producers in Asia are Indonesia and South Korea. Spain and France are also important producers, with their ships fishing primarily in the Indian Ocean. In southeast Asia, the southern Philippines is an important area, particularly General Santos City and Davao.

Japan remains the main tuna producer in the Pacific. In 2000, Japanese vessels landed 633,000 tons, about 17 percent of the world catch. Taiwan was the second biggest producer at 435,000 tons, or about 12 percent of the world's total catch. Spain supplies most of the yellowfin to European canneries, accounting for 5.9 percent of the total catch, while Ecuador and Mexico dominate the Eastern Pacific Ocean.

Fishing Methods

Recreational fishing

From the 1950s through the 1970s, bluefin were abundant in the waters of Cuba, Bimini and Cat Cay, a few miles off the Florida coast, and were targeted by recreational fishermen, famously Ernest Hemingway and Habana Joe aboard his 1938 40-foot Wheeler named Pilar. Word spread quickly about the exciting new sport of big-game fishing. Despite the growing popularity of the sport, however, the boats of the day were hardly ideal for fighting the prized fish. Most boats used at the time were converted cabin cruisers, which were relatively slow and hard to maneuver.

The Rybovich family of South Florida eventually constructed a boat in 1946 that relaunched the sport and birthed a new industry. This boat, the Miss Chevy II, was the first sportfishing boat the world had ever seen.[6]

Merritt gained particular notoriety during the 1950s through the 1970s with its 37- and 43-foot custom boats, which together with boats like those being built by Rybovich helped fuel the growth of big game fishing around the world.

Association with whaling

In 2005 Nauru, defending its vote at that year's meeting of the International Whaling Commission, argued that commercial whaling is necessary for preserving tuna stocks and that country's fishing fleet.[7]

Association with dolphins

Dolphins swim beside several tuna species. These include yellowfin tuna in the eastern Pacific Ocean, but not albacore or skipjack. The dolphin are believed to use the tuna schools to hide from sharks, which are tuna predators.[8]

Fishing vessels exploit this association by searching for dolphin pods. They encircle the pod with nets to catch the tuna beneath.[9] The nets are prone to entangling dolphins, injuring or killing them. Public outcry has led to more "dolphin friendly" methods, now generally involving lines rather than nets. However, there are neither universal independent inspection programs nor verification of "dolphin safeness", so these protections are not absolute. According to Consumers Union, the resulting lack of accountability means claims that tuna that is "dolphin safe" should be given little credence.

Fishery practices have changed to be dolphin friendly, which has caused greater bycatch including sharks, turtles and other oceanic fish. Fishermen no longer follow dolphins, but concentrate their fisheries around floating objects such as fish aggregation devices that attract large populations of other organisms. The public demand to protect dolphins which are not particularly endangered actually damages endangered species.[10]

Management and conservation

There are five main tuna fishery management bodies: the Western Central Pacific Ocean Fisheries Commission, the Inter-American Tropical Tuna Commission, the Indian Ocean Tuna Commission, the International Commission for the Conservation of Atlantic Tunas and the Commission for the Conservation of Southern Bluefin Tuna.[11] The five gathered for the first time in Kobe, Japan in January 2007. Environmental organizations made submissions[12] on risks to fisheries and species. The meeting concluded with an action plan drafted by some 60 countries or areas. Concrete steps include issuing certificates of origin to prevent illegal fishing and greater transparency in the setting of regional fishing quotas. The delegates are scheduled to meet at another joint meeting in January or February 2009 in Europe.[13]

Canned tuna

Photo of grocery shelves
Canned tuna on sale at an American supermarket
Photo of plate containing grilled tuna and leafy vegetables
Tuna steak served in a French bistro

Canned tuna was first produced in 1903, quickly becoming popular.[14] Tuna is canned in a variety of edible oils or in brine.

In the United States, only Albacore can legally be sold in canned form as "white meat tuna"; in other countries, yellowfin is also acceptable.[citation needed] While in the early 1980s canned tuna in Australia was most likely Southern bluefin, as of 2003 it is usually yellowfin, skipjack, or tongol (labelled "northern bluefin").[14]

As tuna are often caught far from where they are processed, poor quality control leads to spoilage. Tuna are typically eviscerated by hand, then pre-cooked for 45 minutes to three hours. The fish are then cleaned and filleted, canned, and sealed. The sealed can itself is then heated (called retort cooking) for 2 to 4 hours.[15] This process kills any bacteria, but retains the histamine that can produce rancid flavors. The international standard sets the maximum histamine level at 200 milligrams per kilogram. An Australian study of 53 varieties of unflavored canned tuna found none to exceed the safe histamine level, although some had "off" flavors.[14]

Australian standards once required cans of tuna to contain at least 51% tuna, but these regulations were dropped in 2003.[16][17] The remaining weight is usually oil or water. In the US, the FDA regulates canned tuna (see part c).[18] In 2008, some tuna cans changed from 6 ounces (170 g) to 5oz due to "higher tuna costs".[19]

Nutrition and health

Canned tuna is a prominent component in many weight trainers' diets, as it is very high in protein and is easily prepared.

Tuna is an oily fish, and therefore contains a high amount of Vitamin D. A can of tuna in oil contains about the Adequate Intake (AI) of the US Dietary Reference Intake of vitamin D for infants, children, men, and women aged 19–50 - 200 IU.

Canned tuna can also be a good source of omega-3 fatty acids. It sometimes contains over 300 milligrams (0.011 oz) per serving.[20]

Mercury levels

See also: Mercury in fish

The health risks of the relatively low levels of methylmercury in tuna may be dampened by the relatively high selenium levels,[21] although the mechanism and effect of this still is largely unknown.[22]

Due to their high position in the food chain and the subsequent accumulation of heavy metals from their diet, mercury levels can be high in larger species such as bluefin and albacore.

In 2009 a California appeals court upheld a ruling that canned tuna does not need warning labels as the methylmercury is naturally occurring.[23]

In March 2004 the United States FDA issued guidelines recommending that pregnant women, nursing mothers, and children limit their intake of tuna and other predatory fish.[24] However, in January 2009 the FDA released a draft report that found a greater risk to children whose mothers do not eat fish during pregnancy, concluding, "Benefits tend to increase as both fish consumption and exposure to methylmercury increase. The benefits are the size of a fraction of an IQ point through the 95th percentile of exposure to methylmercury (involving the consumption of 44.2 grams of fish per day), but then increases to the size of about 1.5 IQ points at the 99th percentile of exposure (involving the consumption of about 98 grams of fish per day), and to about the size of three IQ points at the 99.9th percentile of exposure (involving 205.7 grams of fish per day).[25]

The Chicago Tribune, cited for its inaccurate reporting on tuna related topics,[26] reported that some canned light tuna such as yellowfin tuna[27] is significantly higher in mercury than skipjack, and caused Consumers Union and other activist groups to advise pregnant women to refrain from consuming canned tuna.[28] This was considered extreme and thus not adopted by leading scientific and governing bodies.

The Eastern little tuna (Euthynnus affinis) has been available for decades as a low-mercury, less expensive canned tuna. However, of the five major species of canned tuna imported by the United States it is the least commercially attractive, primarily due to its dark color and more pronounced 'fishy' flavor. Its use has traditionally been restricted to institutional (non-retail) commerce.

A January 2008 investigation conducted by the New York Times found potentially dangerous levels of mercury in certain varieties of sushi tuna, reporting levels "so high that the Food and Drug Administration could take legal action to remove the fish from the market."[29]

See also

Footnotes

  1. ^ Black, Richard (17 October 2007). "Last rites for a marine marvel?". BBC News Online. Retrieved 2007-10-17.
  2. ^ "International Seafood Sustainability Foundation Resolution 09-02". 2009-01. Retrieved 2009-03-25. {{cite web}}: Check date values in: |date= (help)
  3. ^ a b "Tuna - Biology Of Tuna". Retrieved September 12 2009. {{cite web}}: Check date values in: |accessdate= (help)
  4. ^ McCurry, Justin (Monday January 22 2007). "Japan warned tuna stocks face extinction". guardian.co.uk. {{cite web}}: |access-date= requires |url= (help); Check date values in: |date= (help); Missing or empty |url= (help); Text "http://www.guardian.co.uk/environment/2007/jan/22/japan.conservationandendangeredspecies" ignored (help)
  5. ^ a b Doolette, DJ and Craig, D (1999). "Tuna farm diving in South Australia". South Pacific Underwater Medicine Society journal. 29 (2). ISSN 0813-1988. OCLC 16986801. Retrieved 2008-08-17.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  6. ^ http://www.rybovich.com/RyboHistory.aspx
  7. ^ http://www.abc.net.au/news/newsitems/200506/s1402449.htm
  8. ^ ENSENADA: El Puerto del Atun
  9. ^ [1]
  10. ^ http://southernfriedscience.com/2009/02/16/the-ecological-disaster-that-is-dolphin-safe-tuna/
  11. ^ "WWF demands tuna monitoring system". 2007-01-19. Retrieved 2008-05-19.
  12. ^ "Briefing: Joint Tuna RFMO Meeting, Kobe 2007". 2007-01-23. Retrieved 2008-05-19.
  13. ^ "Conference approves global plan to save tuna stocks". 2007-01-26. Retrieved 2008-05-10.
  14. ^ a b c Choice: Jan/Feb 2004.
  15. ^ "The tuna processing industry". US Dept. of Labor. Retrieved 15 October, 2007. {{cite web}}: Check date values in: |accessdate= (help)
  16. ^ Choice, August 2003.
  17. ^ http://www.choice.com.au/viewArticle.aspx?id=104101&catId=100406&tid=100008&p=2&title=Test:+Canned+tuna+(archived)
  18. ^ http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?fr=161.190
  19. ^ http://foodimportgroup.blogspot.com/2008_05_01_archive.html
  20. ^ "Omega-3 Centre". Omega-3 sources. Omega-3 Centre. Retrieved 2008-07-27.
  21. ^ "Selenium: Mercury's Magnet". Retrieved 2009-07-03.
  22. ^ Watanabe C (2002). "Modification of mercury toxicity by selenium: practical importance?" (PDF). Tohoku J Exp Med. 196 (2): 71–7. doi:10.1620/tjem.196.71. PMID 12498318.
  23. ^ "California Court of Appeals Ruling" (PDF). 2009-03. Retrieved 2009-03-25. {{cite web}}: Check date values in: |date= (help)
  24. ^ "What You Need to Know About Mercury in Fish and Shellfish". 2004-03. Retrieved 2007-05-19. {{cite web}}: Check date values in: |date= (help)
  25. ^ "US FDA Draft Risk and Benefit Assessment Report". 2009-01. Retrieved 2009-03-25. {{cite web}}: Check date values in: |date= (help)
  26. ^ "Bad choices at the Tribune". 2008-10. Retrieved 2009-03-25. {{cite web}}: Check date values in: |date= (help)
  27. ^ "FDA to check tuna". Retrieved 2007-06-21.
  28. ^ "Mercury in tuna". 2006-06. Retrieved 2007-05-19. {{cite web}}: Check date values in: |date= (help)
  29. ^ "High Mercury Levels Are Found in Tuna Sushi". New York Times. January 23, 2008. Retrieved September 11, 2009.

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
  • FAO: Species Catalog Vol. 2 Scombrids of the World. FAO Fisheries Synopsis No. 125, Volume 2. FIR/S125 Vol. 2.ISBN 92-5-101381-0
  • FAO: Review of the state of world marine fishery resources: Tuna and tuna-like species - Global, 2005 Rome.
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