For the first time, all scombrid species (tunas, bonitos, mackerels and Spanish mackerels) and billfishes (swordfish and marlins) have been assessed for the IUCN Red List of Threatened Species. Of the 61 known species, 7 are thought to be at serious risk of extinction and are classified in a threatened category. Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations. 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 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.
For the first time, all scombrid species (tunas, bonitos, mackerels and Spanish mackerels) and billfishes (swordfish and marlins) have been assessed for the IUCN Red List of Threatened Species. Of the 61 known species, 7 are thought to be at serious risk of extinction and are classified in a threatened category. Critically Endangered is the highest risk category assigned by the IUCN Red List for wild species. Critically Endangered means that a species' numbers have decreased, or will decrease, by 80% within three generations. 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 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.
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The situation appears particularly grim for tunas – three of the eight species are now classified in a threatened category, including the Critically Endangered southern bluefin tuna and the Endangered northern bluefin tuna, while two species are classified as Near Threatened.
Three species of billfishes were classified in threatened or Near Threatened categories; the blue marlin and the white marlin are both Vulnerable, while the striped marlin is Near Threatened.
As these scombrids and billfishes are at the top of the marine food web, population reductions of these predators may cause negative effects on other species that are critical to the balance of the marine ecosystem and that are economically important as a source of food.
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. 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 in the family Scombridae.
The Australian government alleged in 2006 that Japan had illegally overfished southern bluefin by taking 12,000 to 20,000 tons per year instead of the their agreed 6,000 tons. Such overfishing has severely damaged bluefin stocks.
Japan's Fisheries Research Agency counters that Australian and New Zealand tuna fishing companies under-report their total catches of southern bluefin tuna and ignore internationally mandated total allowable catch totals.
In 2010, Greenpeace International added the albacore, bigeye tuna, blackfin tuna, pacific bluefin tuna, northern bluefin tuna, southern bluefin tuna and the yellowfin tuna to its seafood red list.
While many stocks are managed sustainably, it is widely accepted that bluefin have been severely overfished, with some stocks at risk of collapse. According to the International Seafood Sustainability Foundation, Indian Ocean yellowfin tuna, Pacific Ocean (eastern & western) bigeye tuna, and North Atlantic albacore tuna are all overfished.
For further information: http://blog.arkive.org/2011/07/increased-protection-urgently-needed-for-tunas/
Photo: http://www.britannica.com/EBchecked/media/95850/Bluefin-tuna-in-the-waters-near-Japan
