Pacific bluefin tuna

Taxobox
name = Pacific bluefin tuna
status = DD
status_system = IUCN


image_width = 250px
regnum = Animalia
phylum = Chordata
classis = Actinopterygii
ordo = Perciformes
familia = Scombridae
genus = "Thunnus"
species = "T. orientalis"
range_

range_map_caption=
binomial = "Thunnus orientalis"
binomial_authority = (Temminck and Schlegel, 1844)

Pacific bluefin tuna, "Thunnus orientalis" are some of the biggest and fastest fish in the Pacific Ocean.Fact|date=June 2008 Evolution has streamlined the tuna's body to reduce water resistance and conserve energy for trans-Pacific migrations. Retractable fins also allow a freer flow of water when navigational changes do not require their use.

Temperature regulation

Most fish are cold-blooded (exothermic).Fact|date=June 2008 However, all tunas and the Mackerel Sharks are warm-blooded, in the sense that they can regulate their body temperature. Warm-blooded fish 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. Fish from warmer water elevate their temperature a few degrees whereas those from cold water may raise it as much as 20°C (68°F) warmer than the surrounding sea.

The Tuna's ability to increase and maintain body temperature has several definite advantages over other sea life. Such a fish need not be selective in its range because of different water temperatures, nor is it as affected by geological or climactic changes in its environment. The additional heat supply to the muscles is also advantageous because of the resulting extra power and speed. Bluefin Tuna have been clocked in excess of 30 mph during 10 to 20 second sprints. Such a fast swimming predatory fish finds an abundance of food in the form of squid, herring, mackerel, etc., that slower predators cannot capture.

Distribution

Pacific bluefin tuna spawn in the Western Pacific between Okinawa and the Philippines and probably the Sea of Japan, then migrate over 6,000 nautical miles (11,112 km) to the Eastern Pacific, and eventually return to their birth waters to spawn again.

Life history

Bluefin Tuna mature slowly and can live up to 30 years.Fact|date=June 2008 They reach up to 10 ft (3 m) in length and can weigh 1,200 lbs (555 kg). They eat smaller fish, krill, pelagic red crab, and squid.

Conservation status

Pacific Bluefin Tuna are overfished throughout the world.Fact|date=June 2008 They are hooked on long lines or illegally netted everywhere they swim, and many young bluefins are captured before they reproduce. Creating effective fishing policies for bluefin tuna is difficult because they are highly mobile and swim through the territorial waters of many different nations. Data about their movements and high levels of international cooperation are needed to ensure sustainable bluefin tuna populations.

External links

* [http://topp.org/features/topp_and_bluefin_tuna/ 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.