Pacific bluefin tuna
Encyclopedia
Pacific bluefin tuna, Thunnus orientalis are some of the biggest and fastest fish in the Pacific Ocean.
They possess streamlined bodies to reduce water resistance and conserve energy for trans-Pacific migrations. Retractable fin
s also allow a freer flow of water when navigation does not require their use.
However, tuna
and mackerel sharks
are warm-blooded
: 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 gill
s 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-change warmer than the surrounding sea.
The tuna's ability to maintain body temperature has several definite advantages over other sea life. It need not limit its range according to water temperature, nor is it dominated by climactic changes. The additional heat supplied to the muscles is also advantageous because of the resulting extra power and speed. Bluefin tuna have been clocked in excess of 30 miles per hour (48.3 km/h) during 10 to 20 second sprints, enabling it to hunt squid
, herring
, mackerel
, etc., that slower predators cannot capture.
. They migrate over 6000 nautical miles (11,112 km) to the Eastern Pacific, eventually returning to their birth waters to spawn again.
, pelagic red crab, mackerel and squid.
They are hooked on long lines or illegally netted where they swim, and many young bluefin are captured before they reproduce. 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.
It is estimated by some that from 1976 to 2006 worldwide stocks of Bluefin Tuna plummeted by 90%. Most seafood sustainability guides recommend consumers choose alternatives to bluefin tuna.
In 2010, Greenpeace International added this population to its seafood red list, saying:
of Japan first successfully farmed already-hatched bluefin tuna in 1979. In 2002, they succeeded in breeding them, and in 2007, the process was repeated for a third generation. This farm-raised tuna is now known as Kindai tuna. Kindai is a contraction of Kinki University (Kinki daigaku). In 2009, Clean Seas, an Australian company with assistance from Kinki University managed to breed Southern Bluefin Tuna in captivity, leading Time Magazine to award it second place in World’s Best Invention of 2009.
They possess streamlined bodies to reduce water resistance and conserve energy for trans-Pacific migrations. Retractable fin
Fin
A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...
s also allow a freer flow of water when navigation does not require their use.
Thermoregulation
Most fish are cold-blooded (ectothermic).However, tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . 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...
and mackerel sharks
Lamniformes
Lamniformes is an order of sharks commonly known as mackerel sharks . It includes some of the most familiar species of sharks, such as the great white shark, as well as more unusual representatives, such as the goblin shark and the megamouth shark.Members of the order are distinguished by...
are warm-blooded
Warm-blooded
The term warm-blooded is a colloquial term to describe animal species which have a relatively higher blood temperature, and maintain thermal homeostasis primarily through internal metabolic processes...
: they can regulate their body temperature. Warm-blooded fish possess organs near their muscles called retia mirabilia
Rete mirabile
A rete mirabile is a complex of arteries and veins lying very close to each other, found in some vertebrates. The rete mirabile utilizes countercurrent blood flow within the net...
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 gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
s 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-change warmer than the surrounding sea.
The tuna's ability to maintain body temperature has several definite advantages over other sea life. It need not limit its range according to water temperature, nor is it dominated by climactic changes. The additional heat supplied to the muscles is also advantageous because of the resulting extra power and speed. Bluefin tuna have been clocked in excess of 30 miles per hour (48.3 km/h) during 10 to 20 second sprints, enabling it to hunt squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, mackerel
Mackerel
Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel , enter bays and can be...
, 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 JapanSea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
. They migrate over 6000 nautical miles (11,112 km) to the Eastern Pacific, eventually returning to their birth waters to spawn again.
Life history
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 m) in fork length and can weigh over 1000 pounds (453.6 kg). They eat smaller fish, krillKrill
Krill is the common name given to the order Euphausiacea of shrimp-like marine crustaceans. Also known as euphausiids, these small invertebrates are found in all oceans of the world...
, pelagic red crab, mackerel and squid.
Conservation status
Pacific Bluefin Tuna are overfished throughout their range.They are hooked on long lines or illegally netted where they swim, and many young bluefin are captured before they reproduce. 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.
It is estimated by some that from 1976 to 2006 worldwide stocks of Bluefin Tuna plummeted by 90%. Most seafood sustainability guides recommend consumers choose alternatives to bluefin tuna.
In 2010, Greenpeace International added this population to its seafood red list, saying:
- "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."
- Effects of protection policies: Some individual countries have put regulations on the fishing of bluefin; the downside is unemployment of local fishermen. There are concerns that arise from attempting to implement an umbrella policy such as Monaco is proposing: Tuna port countries, many of which are found in the southern hemisphere, are concerned for their fishermen, as well as their source of income.
Farming
Japan is both the biggest consumer and the leader in over tuna farming research. Kinki UniversityKinki University
, or , is a private non-sectarian and coeducational university based in Higashiosaka, Osaka, Japan with campuses in five other locations: Nara, Nara; Ōsakasayama, Osaka; Uchita, Wakayama; Higashihiroshima, Hiroshima; and Iizuka, Fukuoka....
of Japan first successfully farmed already-hatched bluefin tuna in 1979. In 2002, they succeeded in breeding them, and in 2007, the process was repeated for a third generation. This farm-raised tuna is now known as Kindai tuna. Kindai is a contraction of Kinki University (Kinki daigaku). In 2009, Clean Seas, an Australian company with assistance from Kinki University managed to breed Southern Bluefin Tuna in captivity, leading Time Magazine to award it second place in World’s Best Invention of 2009.
External links
- 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.