Sri Lanka,ශ්රී ලංකා,fishing trip on a trawler:Tuna line fishing (19)
Tuna are salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of 70 km/h (43 mph). Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an oxygen-binding molecule, which tuna express in quantities far higher than most other fish. Some larger tuna species, such as bluefin tuna, display some warm-blooded adaptations, and can raise their body temperatures above water temperatures by means of muscular activity. This enables them to survive in cooler waters and to inhabit a wider range of ocean environments than other types of fish.There are over 48 different tuna species. The Thunnus genus includes 9 species:Albacore, Thunnus alalunga (Bonnaterre, 1788).Yellowfin tuna, Thunnus albacares (Bonnaterre, 1788).Blackfin tuna, Thunnus atlanticus (Lesson, 1831). Southern bluefin tuna, Thunnus maccoyii (Castelnau, 1872).Bigeye tuna, Thunnus obesus (Lowe, 1839).Pacific bluefin tuna, Thunnus orientalis (Temminck & Schlegel, 1844).Northern bluefin tuna, Thunnus thynnus (Linnaeus, 1758).Longtail tuna, Thunnus tonggol (Bleeker, 1851).Karasick tuna, Thunnus karasicus (Lesson, 1831). Species of several other genera (all in the family Scombridae) have common names containing tuna:Slender tuna Allothunnus fallai (Serventy, 1948).Bullet tuna Auxis rochei (Risso, 1810) Terriowipet tuna Auxis tongolis (Bonnaterre, 1788).Frigate tuna Auxis thazard (Lacepede, 1800) Kawakawa (little tuna or mackerel tuna) Euthynnus affinis (Cantor, 1849) A remarkable aspect of Thunnus physiology is its ability to maintain body temperature above 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.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 venous blood to arterial blood via a counter-current exchange system. This reduces surface cooling, maintaining warmer muscles. This supports higher swimming speed with reduced energy expenditure.Little tunny (little tuna) Euthynnus alletteratus (Rafinesque, 1810)
Black skipjack tuna Euthynnus lineatus (Kishinouye, 1920)
Dogtooth tuna Gymnosarda unicolor (Rüppell, 1836)
Skipjack tuna Katsuwonus pelamis (Linnaeus, 1758)
Lineside Tuna, Thunnus lineaus (Temminck & Schlegel, 1844). Tuna is an important commercial fish. The International Seafood Sustainability Foundation compiled a detailed scientific report on the state of global tuna stocks in 2009, which includes regular updates. According to the report, Tunas are widely but sparsely distributed throughout the oceans of the world, generally in tropical and temperate waters between about 45 degrees north and south of the equator. They are grouped taxonomically in the family Scombridae, which includes about 50 species. The most important of these for commercial and recreational fisheries are yellowfin (Thunnus albacares), bigeye (T. obesus), bluefin (T. thynnus, T. orientalis, and T. macoyii), albacore (T. alalunga), and skipjack (Katsuwonus pelamis).The report further states:Between 1940 and the mid-1960s, the annual world catch of the five principal market species of tunas rose from about 300 thousand tons to about 1 million tons, most of it taken by hook and line. With the development of purse-seine nets, now the predominant gear, catches have risen to more than 4 million tons annually during the last few years. Of these catches, about 68 percent are from the Pacific Ocean, 22 percent from the Indian Ocean, and the remaining 10 percent from the Atlantic Ocean and the Mediterranean Sea. Skipjack makes up about 60 percent of the catch, followed by yellowfin (24 percent), bigeye (10 percent), albacore (5 percent), and bluefin the remainder. Purse-seines take about 62 percent of the world production, longline about 14 percent, pole and line about 11 percent, and a variety of other gears the remainder 3.The Australian government alleged in 2006 that Japan had illegally overfished southern bluefin by taking 12,000 to 20,000 tonnes per year 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 bluefin stocks.[4] 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.In early 2011, a new record was set at 32.49 million yen for a bluefin tuna weighing 754-pounds (342-kilograms), during an auction in Tsukiji Market, Tokyo.(wikipedia)