Tuna - SpeedyLook encyclopedia

Tuna species

One fishes in the world, per annum, 2,5 million tons of tunas. This family of swift swimmers (with records of 80 km/h) and voracious eaters (each day up to 30% of their weight in small fish or shellfish) account a dozen species:

the blue fin tuna ( Thunnus thynnus ) is largest and can reach up to 1000 kg. It is consumed and sold fresh.
the long fin Tuna or albacore ( Thunnus alalunga ) is smaller than blue fin tuna and lives with this last. It is fished on the surface and is appreciated in Conserve.
the obese tuna or blackfin tunny ( Thunnus obesus ) is appreciated believed by the Japanese.
the yellow tuna or yellowfin tuna ( Thunnus albacares ) is a tropical tuna very much used in Conserve. It was observed in diving with depths higher than 1.000 m than broad of the Seychelles
the striped bonito or listan or listao ( Katsuwonus pelamis ) is a tropical tuna also used out of preserve.
the Ravil (Euthynnus allettaratus), tropical tuna.

Description

The tunas, from their big size, their hydrodynamism and their good vision, are very fast swimmers. Although they are Poïkilotherme S, they are the only fish, with certain large sharks, which have a system of exchangers of heat enabling them to preserve at the heat their muscles and their internal organs. This system is based on the contact between capillary venous, whose Sang is heated by the muscular activity, and of the arterial capillaries, whose cold blood coming from the gills is heated in contact with the venous capillaries. However this system is not also elaborate at all the tuna species and is not as developed in the young people as in the adults. In fact the large blue fin tunas (being able to exceed 4 meters and to weigh more than 600 kg) are able to attend the coldest water, they are fished besides until in Iceland. Contrary to the majority of the fish species which have the white flesh that of tunas is often pink, because of their important vascularization. The tunas are the predatory ones nourishing small fish primarily, of cephalopod S and Krill. Because of its position of Predatory, and because it contains many Lipide S, the blue fin tuna tends to accumulate pollutants such as the mercury, metal very toxic.

The tuna is untiring a migrating and attends only warm water, which makes it possible to locate it at the time of the fishing years. The benches or mattes gather several thousands of individuals continuing of the benches of Sardine S, of anchovy, Sprat S or Maquereau X of which they are nourished.

Food characteristics

The tuna is a source of Protéine and contains few Cholestérol. The tuna abounds in nutritive elements, whose Phosphore, the Sélénium, the Vitamine S.A. and D, like those of the group B. the blue fin tuna dissociates long fin tuna by its high percentage of fatty-acids omega-3 of which eicosapentanoïque acid (EPA) and docosahexanoïque acid (DHA). Studies show that the tuna consumption has favorable effects on cardiovascular health and would reduce mortality by cardiovascular disease.

The tuna is generally consumed out of preserve. In the Asian countries, the tuna is consumed in the form of Sushi. This kind of food is in vogue in the European countries but can present serious food risks for the fragile people.

Economic issue and Surpêche

The tuna has a great commercial value and interests of many international fisheries. They are industries of the congelation and the canning facility which regulate its exploitation. Fishing with tuna is a very old practice and was only one auxiliary fishing until the years 1950. With the development of more powerful tools, certain countries developed industrial fleets in the principal oceans: Indian Ocean, Pacific Ocean and Atlantic Ocean. The various fleets are devoted to a competition without mercy to run out their production.

The current level of fishing of blue fin tuna is evaluated with 50.000 tons annual in the Atlantic and the Mediterranean (for a quota of 29.500 tons), whereas the rate of catches allowing the renewal is estimated at 15.000.

Techniques of fishing

The madrague

The Madrague is a technique of fishing to blue fin tuna traditional in the Mediterranean. It consists in trapping fish benches during their migration S along the coasts. Large-sized nets, called tunny nets or tunny nets or thonares , are laid out so as to form a trap and to direct tunas towards the “room of death”. The nets are anchored to the bottom and are retained on the surface by floats. When fish are taken, from the Bateau X come to place all around the room of death, then the nets are gradually raised so as to tighten tunas on a few square meters and the setting with dead ( matanza in Italian) intervenes. This artisanal fishing, but which requires means and organization, is practiced in spring and in summer, in particular off the coasts of Sicily and Tunisia.

Drifting nets

Fishing with thonidés using drifting nets (or gill nets) was prohibited by the European Union starting from January 1st, 2002. They are floating nets very big length (several kilometers) whose meshs were widened to capture the species of big size like tunas. One reproaches them their lack of selectivity (they take as well the Dauphin S and the tortoises marinades S) and their too great effectiveness, dangerous for the maintenance of the resources. Initially, the European Union had regulated their length by fixing a maximum of 2,5 km, following in that the recommendations of UNO. This measurement, moreover badly respected, proved to be ineffective.

Alive soft foods

This fishing, created with the Portugal in 1926, was then developed in California before developing in Europe in the years 1950, in particular with the Basque Country. This technique of fishing consists in capturing and preserving alive small fish such as sardines or anchovies, which one will use as soft foods after having located a tuna bench. The tunas are thus fished with the cane.

The goal is to attract blue fin tuna more close to the boat and to maintain it there while launching alive sardines or anchovies. The fishermen mingle with their soft foods with the hooks without Ardillon at the end of lines. The chair-caners can then shoe their prey. Water jets sprinkle water surface simulating the wriggling of sardines and dissimulating the fishermen. The excited tunas become easier to catch. Fishing with the cane tends to disappear in France, but remains practiced in Africa or in the countries of the Pacifique which has great alive soft food resources.

The seine

See also: Seine (halieutic)

It is the fishing machine used mainly under the Tropique S by the flotillas of Thonier s-senneurs freezers. They are powerful ships from 50 to 120 meters provided with engines of 4 000 cv. They spin 16 nodes and are equipped to detect the tuna benches thanks to electronics (Radar, Sonar), nests of magpie and sometimes of the Hélicoptère S.

The seine used is a gigantic net released in arc of circle around the boat. It can cover up to 21 hectares is twice the surface of the Place of the Harmony. Only the quays of Dakar, Abidjan or of Black Pointe (in West Africa) are enough vast to deploy them in the event of great repairs. The fishing year can last up to 45 days (of the thousands of Thousand S traversed). The tuna benches are often located by men provided with powerful Jumelle S in their nests of magpie (the men of crew locate the birds which gather with the top of the benches, or the tunas which jump to the top of surface. The modern radars manage to detect the birds at very long distance). Once located, the tuna boat must be placed at less than 10 m on the line of the bench in the same direction and at the same speed. At the good moment, the tuna boat releases its Skiff, actuating the seine and tries to circumvent the bench. Surrounding and the capture in general last more than one hour. The net is maintained with water and the fish are recovered using a large scoop which one calls the salabarde, it is operated by a Palan. The fish then are immediately plunged in the tanks of the boat, filled with cooled Saumure. Only one blow of seine can make it possible to capture up to 200 tons of tunas and the hard operation up to 3 p.m.

This technique developed in the years 1950 pennies the impulse of some French fishermen. The season of the passage of tuna in coastal water of the the Bay of Biscay is short and lasts only 4 to 5 months. It is on this report that three Basque chair-caners decided in 1955 to go towards the Senegal where the Sardine and the Albacore are abundant in winter. As of 1956, they are 25 crews which put the course at the south accompanied by a Chalutier being used as freezer. In 1961, the " Curlinka" use the first seine and in 1963, the first tuna boat-senneur " Island of Faisans" be equipped with the back with a strong boat, the Skiff , intended for the operation of the net. It is the beginning of the industrial fishing of tuna. The European market consumed of them in 1960 160.000 tons. Spaniards and French produced of them 110.000 tons, there was thus a market of 50.000 tons to conquer. It was the race with the investments. But, very quickly, the market becomes saturated and the course of tuna collapses. The resources becoming exhausted on the coasts of West Africa, the French fleet redeploys in 1985 in the Indian Ocean.

The line

The tuna can be sinned with the trailing line. One speaks about fishing to the drag. This technique of fishing was very much used by the fishermen of the Basque Country which knew where to trail their lines thanks to several signs:

the boiling of the surface of to the movements of tunas at the time of their huntings for sardines.
the slapping of the tuna wake in the Vague S.
like an oil task, the bench of tunas tightened on the surface slows down the clapot sea.

The long fin tuna is tracked from May to September in the Atlantique. The ligneurs traverse the the Bay of Biscay and the west of the Ireland.

Breeding

The tuna breeding develops even if it is acted in fact of fattening fish collected at the time of the seasons of fishing for then selling them on the market Japan board. The tunas are captured by tuna boats-senneurs then they are installed in circular cages of 200 000 m ³ and nourished with fish fodder (sardines, mackerels). The young tunas have important performances of fattening with a growth of 5 kg per month during the summer. They are maintained in cages of which the density is from 2 to 4 kg per m ³. The Croatia and the Australia are the leaders of this market. The reproduction in captivity is controlled in research but is not applied to large scales.

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