Bluefin tuna

Bluefin tuna
A northern (or Atlantic) bluefin tuna, Thunnus thynnus
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Order: Perciformes Family: Scombridae Genus: Thunnus
Species
T. orientalis (Pacific bluefin tuna) T. thynnus (northern bluefin tuna) T. maccoyii (southern bluefin tuna)

Bluefin tuna is the common name for three of the eight species of tuna in the Thunnus genus (tribe Thunnini in the family Scombridae): the Pacific bluefin tuna (Thunnus orientalis), the northern bluefin tuna or Atlantic bluefin tuna (T. thynnus), and the southern bluefin tuna (T. maccoyii). They share with other tuna such characteristics as two dorsal fins that are depressible into grooves, finlets behind the second dorsal fin, pelvic fins with six rays placed behind the pectoral fins, a deeply forked tail, and a body that is very narrow right before the tail. These highly migratory, large, pelagic fish are fast swimmers and have a heat exchange system that allows them to elevate their body temperature well above ambient water temperatures; they can tolerate a very broad range of temperatures and inhabit a broad thermal niche.

Pacific bluefin tuna are found in both the western and eastern Pacific Oceans, largely in temperate waters in the North Pacific but their range also includes tropical waters in the southern hemisphere. The northern bluefin tuna is native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea, extending southward to northern Brazil and the Canary Islands. The southern bluefin tuna is found in open southern hemisphere waters of all the world's oceans, mainly between 30°S and 50°S, to nearly 60°S.

Bluefin tuna are important both ecologically and commercially. Ecologically, they are an integral part of marine food chains, preying (depending on whether young larvae, juveniles, or adults) on such organisms such as rotifers, crustaceans, other fish (from larvae to adult), mollusks (such as squid), and macroalgae, and being preyed upon by sharks, large predator fishes, and marine mammals. Commercially, they serve as food for humans and bluefin tuna also are a popular target for sportsfishing.

The bluefin tuna of all three species—northern, southern, and Pacific—are overfished throughout the world. They are hooked on longlines or illegally netted everywhere they swim. Creating effective fishing policies for bluefin tuna is difficult since they are highly mobile and swim through the territorial waters of many different nations. In particular, there is great concern about the overfishing of the Atlantic bluefin. ****** go into details ****

Overview and description

As tuna, bluefin tuna belong to the tribe Thunnini in the subfamily Scombrinae and the family Scombridae (the mackerel family). There are 14 extant species in this tribe (collectively known as tunas), organized into five genera—Thunnus, Euthynnus, Allothunnus, Auxis, and Katsuwonus (Nelson 2006). The bluefin tuna comprise three of the 8 extant species in the Thunnus genus: Thunnus orientalis (Pacific bluefin tuna), T. thynnus (Pacific or Atlantic bluefin tuna), and T. maccoyii (southern bluefin tuna). The Scombrie family overall has about 51 species organized into 15 genera.

Members of the Scombridae family have two dorsal fins that are depressible into grooves. There are five to 12 finlets behind the second dorsal fin and also after the anal fins (Nelson 1994). The first dorsal fin has nine to 27 rays, the pelvic fins have six rays and are placed behind the pectoral fins, which are high on the body (Nelson 2006). Tunas have a deeply forked or crescent-shaped tail, and the body is very narrow right before the tail. Members of the subfamily Scombinae are characterized by scales that are cycloid and minute or are absent (Nelson 2006).

As a general description, bluefin tuna have a pointed snout, small eyes, and the dorsal, pelvic, and pectoral fins fit into slots, which helps to reduce drag as they swim. There is a small space between the two dorsal fins and they have short pectoral fins. The anal fin starts far behind the second dorsal fin.

The three species of bluefin tuna differ from some other members of the Thunnus genus by the fact that they all have striations on the ventral surface of the liver.. For example, there are no such striations in the blackfin tuna (T. atlanticus), yellowfin tuna (T. albacares), or longtail tuna (T. tonggol).. However, the other two species in the Thunnus genus—the bigeye tuna (T. obesus) and the albacore (T. alalunga)—also have the presence of striations on the ventral surface of the liver.

One notable difference from other members of Thunnus is that the bluefin tuna all have very short pectoral fins, shorter than the other species. In other tunas with short pectoral fins, the striations on the ventral surface of the liver (from the blood vessels) are either not present or present in small numbers along the edges.

Bluefin tuna, in general, are the largest of the tunas. In particular, T. thynnus, the Atlantic tuna or northern tuna, is notable for its size and is also known as the "giant bluefin tuna." It achieves a length of up to 4.2 meters and is capable of reaching well over 450 kilograms (992 lb) in weight, rivaling the black marlin and blue marlin as the largest bony fish. The smallest of the bluefin tuna is the southern bluefin tuna, which reaches up to 2.5 meters (8.2 feet) and weighs up to 400 kilograms (882 pounds).

The bluefin tuna species have different distributions in general, with some overlap between T. maccoyii and T. orientalis. T. maccoyii is found solely in the southern hemisphere, being widely distributed below about 30°S in all oceans. T. orientalis is mainly found in the northern hemisphere, in temperate waters, but has been spotted as far south as Australia and New Zealand, as well as near the Galapagos Islands. T. thynnus is found in the Atlantic Ocean and the Mediterranean Sea.

Anatomical differences between bluefin species

The northern bluefin tuna (Thunnus thynnus) and the Pacific bluefin tuna (T. orientalis) are very similar and were for a long time considered subspecies of the same species, T. thynnus, with the Pacific bluefin tuna known as T. thynnus orientalis and the Atlantic or northern bluefin tuna as T. thynnus thynnus. On the other hand, the southern bluefin tuna is much more easily distinguishable.

The southern bluefin tuna was originally differentiated from the Pacific bluefin tuna, with which it range overlaps, based on the position of the first ventrally directed parapophysis, which is on the 8th vertebrae in T. orientalis and on the 9th vertebrae in T. maccoyii. Another character used to differentiate these two is the presence of a muscular protrusion in the dorsal abdominal cavity (a "bust"), which is present in both T. maccoyii and T. thynnus, but not in T. orientalis; it has been confirmed as a reliable character in distinguishing T. maccoyii and T. orientalis in large fish in the field.

Distinguishing the northern bluefin tuna from the Pacific bluefin tuna is more difficult, with most characters indistinguishable. Godsil and Holmberg note five characteristics in which they can be differentiated, however. First, there are generally differences in the shape and length of the air bladder, with T. thynnus having a normal air bladder that extends almost the full length of the body cavity, while T. orientalis has a irregular air bladder, often pear-shaped and generally covering only the front half of the abdominal cavity. Secondly, the northern or Atlantic species has no arterial trunk that connects the No. II and No. III branches of the coeliac mesenteric artery, whereas the Pacific species has the presence of this connecting network. Third, there is a difference in the pelvic girdle in the two forms. Fourth, the gill raker count differs, with T. thynnus typically having a total count of from 39 to 41, whereas T. orientalis has from 32 to 39, with the main difference in the number of the lower limb of the arch (25-28 in the former, and 21-25 in the later). Finally, the most conspicuous difference was found in the shape of the dorsal wall of the body cavity, with this difference particularly striking and consistent in the large fish.

Thermoregulation

Bluefin tuna have very effective lateral heat exchangers, which allows bluefin tuna to conserve metabolic heat, invade cooler waters, tolerate a wide temperature range, and swim faster. The bluefin tuna’s heat exchange system works so well that it can elevate the bluefin’s body temperatures to more than 20°C above ambient water temperatures. .

Essentially, the heat exchange system means that the outgoing veins carrying warm, carbon dioxide-laden blood toward the gills pass the heat over to incoming arteries carrying cold oxygenated blood from the gills. More specifically, tunas possess organs near their muscles called retia mirabilia that consist of a series of minute parallel veins and arteries that supply and drain the muscles. As the warmer blood in the veins returns to the gills for fresh oxygen it comes into close contact with cold, newly oxygenated blood in the arteries. The system acts as a counter-current heat exchanger and the heat from the blood in the veins is given up to the colder arterial blood rather than being lost at the gills. The net effect is an increase in temperature.

All members of the tuna family have the ability to thermoregulate; however, this ability is more highly developed in bluefin tuna than in any other fish. The Atlantic bluefin tuna can tolerate ambient temperature ranges from 2.8°C to 31.0°C, allowing them to spawn in warm water during the summer and forage in cool waters during the summer, giving them the "broadest thermal niche of all species of the family Scombridae."

The heat exchange system also keeps the swimming muscles warm by conserving heat, allowing bluefin tuna to function more efficiently, have extra power, and speed. Bluefin tuna have been clocked in excess of 30 miles per hour (48 km/h) during 10 to 20 second sprints, enabling them to hunt squid, herring, mackerel, and so forth that slower predators cannot capture.

Bluefin tuna also possess 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.

Pacific bluefin tuna

Pacific bluefin tuna, Thunnus orientalis

Conservation status: Vulnerable

Thunnus orientalis, the Pacific bluefin tuna, spawn in the Western Pacific between Okinawa and the Philippines and probably the Sea of Japan/East Sea, then migrate over six thousand nautical miles (11,100 kilometers) to the Eastern Pacific, and eventually return to their birth waters to spawn again. Although T. orientalis is primarily found in the northern hemisphere, specimens have been reported as far south as Australia, New Zealand, and the Galapagos Islands, where their range overlaps with the T. maccoyii, the southern bluefin tuna.

The Pacific bluefin tuna is one of the biggest and fastest fish in the Pacific Ocean. Their streamlined bodies reduce water resistance and conserve energy for trans-Pacific migrations; tetractable fins also allow a freer flow of water when navigation does not require their use.

Bluefin tuna mature slowly, reaching sexual maturity at about 5 years of age, with a maximum lifespan believed to be about 25 years. Pacific bluefin tuna have been recorded to reach 9 feet (2.7 meters) in fork length and can weigh over 1,000 pounds (454 kg). They eat smaller fish, krill, pelagic red crab, mackerel, and squid.

Pacific Bluefin Tuna are overfished throughout their range and the status of their stocks are considered to be of high conservation concern. They are hooked on long lines or illegally netted where they swim, and many young bluefin are captured before they reproduce to be fattened to full size in open net pens for the market. Creating effective fishing policies is difficult because they are migratory, swimming through the territorial waters of many different nations. Data about their movements and high levels of international cooperation are needed to ensure sustainable populations. They have been placed on various endangered species lists and most seafood sustainability guides recommend consumers choose alternatives to bluefin tuna.

Northern bluefin tuna

Northern (or Atlantic) bluefin tuna, Thunnus thynnus

Conservation status: Critically endangered

The northern bluefin tuna (Thunnus thynnus), also known as the Atlantic bluefin tuna and giant bluefin tuna, is native to both the western and eastern Atlantic Ocean, as well as the Mediterranean Sea. In the Western Atlantic Ocean, they range from Labrador in Canada to northern Brazil, including the Caribbean Sea and the Gulf of Mexico. In the eastern Atlantic Ocean, they are found from the Lofoten Islands off of Norway to the Canary Islands and Mauritania in the south, including the Mediterranean Sea.

While many accounts list a subpopulation in the southern part of the Black Sea, where they were once common, they are now believe to be extinct in the Black Sea. Di Natale notes in a 2010 paper that "The bluefin tuna finally disappeared completely from the Black Sea, even from Turkish waters close to the Bosphorus, in 1988." It is also extinct from the Caspian Sea.

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. Fully mature adult specimens average 2–2.5 meters (6 ft 7 in to 8 ft 2 in) long and around 350 kilograms (770 lb) in weight. The species can reach a maximum length of about 4.3 meters (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).

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. Bluefin dive to depths of 1000 meters.

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. According to archaeological findings, the northern bluefin tuna was first exploited over 11,200 years ago in the Mediterranean Sea.

Besides their commercial value as food, their great size and the speed and power they display as predators has attracted the admiration and respect of both ancient and modern fishermen, as well as writers, sport anglers, and scientists. The longest contest between man and 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 northern bluefin tuna typically hunts small fish and invertebrates, such as sardines, herring, eels, mackerel, squid, and crustaceans, with larvae feeding on such organisms as rotifers, brine shrimp, and other fish larvae. They can use their fast speed to chase down prey and use modified filter feeding to catch smaller, slow moving organisms. Predators of the tuna include sharks, marine mammals (killer whales, pilot whales), and large predatory fishes. Bluefin tuna also are host to at least 72 parasites.

Life cycle

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 that were 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, with males and females producing eggs and sperm synchronously nd resulting in many individuals mating at the same time (broadcast spawning).. The tuna are highly vulnerable to commercial fishing at such times. 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.

Female bluefin produce up to 10 million eggs during each spawning period. No parental care is provided. The bluefin tuna become sexually mature between 4 and 8 years old. 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.

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

Threats and conservation

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. The bluefin tuna is particularly prized by Japanese sushi consumers for its fatty belly flesh. The bluefin tuna (including Pacific and Southern fisheries) supports a $7.2 billion industry. The highest prices in the Japanese market tend to be for Pacific bluefin tuna caught in Japanese waters, but high-grade Atlantic bluefin also fetch high prices. In January 2010, a 510 pound (232 kg) bluefin sold for nearly $180,000 at auction in Tokyo, Japan., while in January 2011, a 754 (342 kg) was sold on the Tsukiji fish market in Tokyo for US$396,700.

The commercial importance of the Altantic bluefin tuna has led to severe overfishing of both the Atlantic and Mediterranean stocks. 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. Proposals to ban international trade in Atlantic bluefin tuna, however, were soundly defeated (68 to 20, with 30 abstentions) by the delegates of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), which had gathered March 2010 in Doha, Qatar. Japan had argued that ICCAT should be responsible for regulating the fishery, not the United Nations via CITES. The United States advocated for the ban on international trade in bluefin tuna, while several European Union nations, who have fisheries considered responsible for much of the overfishing, abstained from voting, and many fishing nations voted against the proposal being concerned about this being the first intrusion by CITES into a major commercial fishery.

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.

Prior to the 1960s, Atlantic bluefin fisheries were relatively small scale, and populations remained stable. Although some local stocks, such as those in the North Sea, were decimated by unrestricted commercial fishing, other populations were not at risk. However, in the 1960s purse seiners catching fish in United States coastal waters, largely for the canned tuna market, removed huge numbers of juvenile and young Western Atlantic bluefin, taking out several entire year classes.

Tuna farming began as early as the 1970s. Canadian fishermen in St Mary's Bay captured young fish and raised them in pens. In captivity, they grow to reach hundreds of kilos, eventually fetching premium prices in Japan. Farming enables farmers to exploit the unpredictable supply of wild-caught fish. Ranches across the Mediterranean and off South Australia grow bluefin offshore. However, this method requires the taking of juvenile and young Mediterranean fish to be grown on the tuna farms. Because the tuna are taken before they are old enough to reproduce, tuna farming is a serious threats. The bluefin's slow growth and late sexual maturity compound its problems. In 2009, aquaculturists succeeded in breeding bluefin in captivity and keeping them alive through their development from larvae to fingerlings to young juveniles.

Overfishing continues today despite repeated warnings. In 2007, researchers from ICCAT, the regulators of Northern bluefin fishing, recommended a global quota of 15,000 metric tons (15,000 long tons; 17,000 short tons). ICCAT then chose twice that number, later dropping it to 22,500 metric tons (22,100 LT; 24,800 ST). Their scientists now say that 7,500 metric tons (7,400 LT; 8,300 ST) is the sustainable limit. In November, 2009 ICCAT set the 2010 quota at 13,500 metric tons (13,300 LT; 14,900 ST) and said that if stocks were not rebuilt by 2022 it would consider closing some areas.

In 2010, Greenpeace International has added the northern bluefin tuna to its seafood red list, a list of fish that is commonly purchased in supermarkets and yet have a very high risk of coming from unsustainable fisheries.

Southern bluefin tuna

Southern bluefin tuna, Thunnus maccoyii

Conservation status: Critically endangered

The southern bluefin tuna, Thunnus maccoyii, is a tuna of the family Scombridae found in open southern hemisphere waters of all the world's oceans mainly between 30°S and 50°S, to nearly 60°S. At up to 2.5 m (8.2 ft) and weighing up to 400 kg (882 lbs) it is among the larger bony fishes.

The southern bluefin tuna is a large, streamlined, fast swimming fish with a long, slender caudal peduncle and relatively short dorsal, pectoral and anal fins. The body is completely covered in small scales.

The body color is blue-black on the back and silver-white on the flanks and belly, with bright yellow caudal keels in adult specimens. The first dorsal fin colour is grey with a yellow tinge, the second dorsal is red-brown, and the finlets are yellow with a darker border.

Southern bluefin tuna, like other pelagic tuna species, are part of a group of bony fishes that can maintain their body core temperature up to 10 degrees above the ambient temperature. This advantage enables them to maintain high metabolic output for predation and migrating large distances. The southern bluefin tuna is an opportunistic feeder, preying on a wide variety of fish, crustaceans, cephalopods, salps, and other marine animals.

Harvesting

The onset of industrial fishing in the 1950s, in conjunction with ever improving technologies such as GPS, fishfinders, satellite imagery, etc., and the knowledge of migration routes, has led to the exploitation of southern bluefin tuna across its entire range. Improved refrigeration techniques and a demanding global market saw global SBT catch plummet from 80,000 tonnes a year during the 1960s to 40,000 tonnes a year by 1980. Australian catch peaked in 1982 at 21,500 tonnes, and the total population of SBT has since declined by about 92 percent.

Conservation

The southern bluefin tuna is now classified as Critically Endangered on the IUCN Red List of Threatened species. In 2010, Greenpeace International has added the SBT 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.

There was a pressing obligation to alleviate some of the harvesting pressure on SBT populations, and increasing concerns about sustainability in the mid 1980s led the main nations fishing SBT at the time to manage catches. These nations imposed strict quotas to their fishing fleets, although no official quotas were put in place.

In 1994, the then existing voluntary management arrangement between Australia, Japan and New Zealand was formalised when the Convention for the Conservation of Southern Bluefin Tuna came into force. The Convention created the Commission for the Conservation of Southern Bluefin Tuna (CCSBT). Its objective was to ensure, through appropriate management, the conservation and optimum utilisation of the global SBT fishery. South Korea, Taiwan and Indonesia have since joined or are cooperating with the Commission. The CCSBT is headquartered in Canberra, Australia.

Current quota limits reflect the vulnerable nature of wild stocks, with quotas being reduced for the 2010/2011 seasons to 80% of years previous. Thus the global total allowable catch (TAC) has been reduced from 11,810 tonnes from the previously allocated global TAC to 9,449 tonnes. Australia currently have the highest "effective catch limit" with 4,015 tonnes, followed by Japan (2,261), Republic of Korea (859), Fishing Entity of Taiwan (859), New Zealand (709), and Indonesia (651). However, fishing pressure outside the allocated global TAC is still a major concern, for instance the Australian government stated in 2006 that Japan had admitted to taking more than 100,000 tonnes over its quota; the new quotas reflect this, as Japans was cut by half, as supposed punishment for overfishing.

The quota system has actually increased the value of the catch, where fisherman that once earned $600 a ton selling fish to canneries began making more than $1,000 per fish, selling them to buyers for the Japanese market. The quotas are expensive and are bought and sold like stocks within their national allocations.

Aquaculture

Ranching

The rapidly declining fishery led to Australian tuna fishers investigating the potential for value-adding their catch through aquaculture. All SBT ranching occurs in a small region offshore of Port Lincoln, South Australia; the region comprising almost all of the SBT fishing companies in Australia since the 1970s. This industry was initiated in 1991 and has now developed to be the largest farmed seafood sector in Australia.

Southern Bluefin Tuna spawn between September and April each year in the only known spawning grounds in the Indian Ocean, between the north-west Coast of Australia and Indonesia. The eggs are estimated to hatch within two to three days, and over the next two years attain sizes of approximately 15 kilograms; this size is the principal wild catch of the Australian SBT industry. It is thought that SBT become sexually mature between 9 and 12 years in the wild, which highlights the major negative impact of removing pre-spawning populations from the wild.

Juvenile tuna are mainly caught on the continental shelf in the Great Australian Bight region from December to around April each year, and as mentioned weigh on average 15 kilograms. The tuna that are located are purse seined, and then transferred through underwater panels between nets to specialised tow pontoons. They are then towed back to farm areas adjacent to Port Lincoln at a rate of about 1 knot; this process can take several weeks. Once back at the farm sites, the tuna are transferred from the tow pontoons into 40-50 m diameter farm pontoons. They are then fed bait fish (usually a range of locally caught or imported small pelagic species such as sardines) six days per week, twice per day and "grown out" for three to eight months, reaching an average of 30 to 40 kilograms. Because SBT swim so fast and are used to migrating long distances, they are difficult to keep in small pens. Their delicate skin can be easily damaged if touched by human hands and too much handling can be fatal.

As with most aquaculture ventures, feeds are the biggest factor in the cost-efficiency of the farming operation, and there would be considerable advantages in using formulated pellet feed to supplement or replace the baitfish. However, as yet the manufactured feeds are not competitive with the baitfish.

A further future prospect in enhancing the ranching of SBT is the plan of Long Term Holding. By holding its fish for two successive growing seasons (18 months) instead of one (up to 8 months), the industry could potentially achieve a major increase in volume, greater production from the limited quota of wild-caught juveniles, and ability to serve the market year round. Undoubtedly, this presents several uncertainties, and is still in the planning stage.

At harvest time, the fish are gently guided into a boat (any bruising lowers the price) and killed and flash frozen and predominantly put on Tokyo-bound planes. They are so valuable, that armed guards are paid to watch over them; 2,000 tuna kept in a single pen are worth around $2 million. Australia exports 10,000 metric tons of bluefin worth $200 million; almost all is from penned stocks.

Complete aquaculture

Initially, the notorious difficulties in closing the life cycle of this species dissuaded most from farming them. However, in 2007, using hormonal therapy developed in Europe and Japan (where they had already succeeded in breeding Northern Pacific bluefin tuna to third generation) to mimic the natural production of hormones by wild fish, researchers in Australia managed for the first time to coax the species to breed in landlocked tanks. This was done by the Australian aquaculture company, Clean Seas Tuna Limited. who collected its first batch of fertilized eggs from a breeding stock of about 20 tuna weighing 160 kilograms. They were also the first company in the world to successfully transfer large SBT over large distances to its onshore facilities in Arno Bay which is where the spawning has taken place. This led Time magazine to award it second place in the 'World's Best Invention' of 2009.

The state-of-the-art Arno Bay hatchery was purchased in 2000, and undertook a $2.5 million upgrade, where initial broodstock facilities catered for Kingfish (Seriola lalandi) and Mulloway (Argyrosomus japonicas), along with a live-feed production plant. This facility has more recently been upgraded to a $6.5 million special purpose SBT larval rearing recirculation facility. During the most recent summer (2009/2010), the company completed its third consecutive annual on-shore Southern Bluefin Tuna spawning program, having doubled the controlled spawning period to three months at its Arno Bay facility. Fingerlings are now up to 40 days old with the grow-out program, and the spawning period has been extended from 6 weeks to 12, but as yet, grow-out of commercial quantities of SBT fingerlings has been unsuccessful. Whilst aquaculture pioneers Clean Seas Limited have not been able to grow out commercial quantities of SBT fingerlings from this season's trials, the SBT broodstock are now being wintered and conditioned for the 2010-11 summer production run.

With collaboration secured with International Researchers, in particular with Kinki University in Japan, commercial viability is likely to be achieved in the near future. The successful closing of the SBT life cycle by Clean Seas will therefore potentially produce unrestricted additional tonnages of this valuable fish; supplying the growing global demand for SBT.

Enhancing growth and production

Feeds

Scientists are currently trying to develop less expensive fish feed. One of main obstacles is creating a processed food that doesn't affect the taste of the tuna because what a tuna eats very much affects the taste of its meat. As previously mentioned, SBT are still largely fed fresh or frozen small pelagic fishes, and the use of formulated pellets is not yet viable. This cost is largely due to the expensive diet research costs (the annual costs of diet for research alone is approximately US$100,000), and the problems associated with working with such large, mobile marine animals. Farm raised tuna generally have a higher fat content than wild tuna. A one metre tuna needs about 15 kilograms of live fish to put on one kilogram of fat, and about 1.5 to 2 tons of squid and mackerel are needed to produce a 100 kilogram bluefin tuna. More research must be undertaken in evaluating the ingredients for use in SBT feed, and important information on ingredient digestibility, palatability and nutrient utilisation and interference can improve cost efficiencies.

Dietary supplements

The use of dietary supplements can improve the shelf life of farmed SBT flesh. Results of a study by SARDI (South Australian Research and Development Institute) indicated that feeding a diet approximately 10 times higher in dietary antioxidants raised levels of vitamin E and vitamin C, but not selenium, in tuna flesh and increased the shelf life of tuna. This is important as the frozen baitfish diets are likely to be lower in antioxidant vitamins than the wild tuna diet.

Parasites and pathology

So far the risk of parasite and disease spreading for SBT aquaculture is low to negligible; the modern SBT aquaculture industry has total catch to harvest mortalities of around 2-4%. A diverse range of parasite species has been found hosting the SBT, with most of the parasites examined posing little or no risk to the health of the farms - with some SBT actually showing antibody responses to epizootics - however, blood fluke and gill fluke have the greatest risk factors. Hypoxia is also a significant issue, and can be escalated due to unforeseen environmental factors such as algal blooms. So it seems that pathological risks are low now, however, this is seen as a dynamic process, therefore ongoing monitoring should take place to ensure its control, especially if farming intensifies and stocking levels increase.

Negative impacts

Sustainability is the key issue here, and with feed conversion ratios (feed to tuna growth) of approximately 10:1 or higher, though this is purely a consequence of the carnivorous diet and high metabolic costs of the species. Removing tuna from the wild before they have spawned is another obvious impact, which hopefully the closed life cycles of SBT at Clean Seas will alleviate some of the pressure on declining stocks. Tuna farms are point sources of solid waste onto to the benthos and dissolved nutrients into the water column. Most farms are more than a kilometre off the coast, thus the deeper water and significant currents alleviate some of the impact on the benthos. Due to the high metabolic rates of SBT, low retention rates of nitrogen in tissue is seen, and there are high environmental leaching of nutrients (86-92%).

Other environmental impacts include the use of chemicals on the farms, which can leach into the surrounding environment. These include antifoulants to keep the cages free from colonial algae and animals, and therapeutants to deal with disease and parasitism. Toxicants such as mercury and PCB's (polychlorinated biphenyls) can build up over time, particularly through the tuna feed, with some evidence of contaminants being more elevated in farmed fish than in wild stocks.

Flesh

Southern Bluefin Tuna is a gourmet food, which is in demand for this sashimi and sushi. It has medium flavoured flesh and is regarded by both Japanese and Western chefs as the best eating raw fish in the world. Clean Seas SBT carry the classic three grades representative of high quality: "Otoro – the premium fatty belly is pale white in colour with a full, rich and sweet flavour and soft, buttery texture. Chutoro – is pale pink/white in colour, with a slightly fuller flavour and firmer texture. Akami – is deep rich red in colour with a firm texture."

Market

By far the largest consumer of SBT is Japan, with USA coming in second, followed by China. Japanese imports of fresh bluefin tuna (all 3 species) worldwide increased from 957 tons in 1984 to 5,235 tons in 1993 [7].Template:Full The price peaked in 1990 at $34 per kilogram when a typical 350 pound fish sold for around $10,000. As of 2008, bluefin was selling for $23 a kilogram. The drop in value was due to the drop in the Japanese market, an increase in supply from northern bluefin tuna from the Mediterranean, and more and more tuna being stored (tuna frozen with the special "flash" method can be kept for up to a year with no perceivable change in taste).

The Tsukiji Market in Tokyo is the largest wholesale market of SBT in the world. Tsukiji handles more than 2,400 tons of fish, worth about US$20 million, a day, with pre-dawn auctions of tuna being the main feature. No tourists are allowed to enter the tuna wholesale areas, which they say is for purposes of sanitation and disruption to the auction process. Higher prices are charged for the highest quality fish; bluefin tuna worth over $150,000 have been sold at Tsukiji. In 2001, a 202-kilogram wild tuna caught in Tsugaru Straight near Omanachi I Aomori Prefecture sold for $173,600, or about $800 a kilogram.

References

ISBN links support NWE through referral fees

• Template:FishBase species
• Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
• Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 978-0-09-189780-2
• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.

• Nelson, J. S. 1994. Fishes of the World, 3rd ed. New York: John Wiley & Sons. ISBN 0471547131.

• Nelson, J. S. 2006. Fishes of the World, 4th ed. New York: John Wiley & Sons. ISBN 0471250317.

• 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
• Hogan, C.Michael. 2010. Overfishing. Encyclopedia of Earth. National Council for Science and the Environment. eds. Sidney Draggan and C.Cleveland. Washington DC.</ref>
• 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. [1]. 2006 IUCN Red List of Threatened Species., World Conservation Union. 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.
• Template:FishBase species
• 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. Digital object identifier (DOI): 10.1023/A:1006091102174 (HTML abstract)

External links

• Southern Bluefin Tuna at CSIRO
• Southern Bluefin Tuna at MarineBio.org
• Official homepage of the Commission for the Conservation of Southern Bluefin Tuna

External links

• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.
• Template:IUCNlink
• Bluefin Tuna at Seafood Watch
• Tuna at Greenpeace
• MarineBio article on tuna at MarineBio
• Bluefin tuna and Sushi
• brochure on bluefin tuna tagging at Tag-a-Giant Foundation

External links

Wikispecies has information related to:

Thunnus orientalis

• Bye bye bluefin: Managed to death The Economist. 30 October 2008. Retrieved 6 February 2009.
• TOPP, Tagging of Pacific Predators, a research group that tags and tracks the amazing Pacific bluefin tuna to learn more about it. The site features information, photos, blog posts and multimedia stories about the bluefin tuna.

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