Bigeye tuna
Encyclopedia
The bigeye tuna, Thunnus obesus, is an important food fish
and prized recreational game fish. It is a true tuna of the genus
Thunnus
, belonging to the wider mackerel
family
Scombridae
.
In Hawaiian
, it is one of two species known as ahi; the other is yellowfin tuna
.
s, but not the Mediterranean Sea
.
. They display 13 or 14 dorsal
spines.
-poor subsurface waters. Their blood
extracts oxygen efficiently even in oxygen-poor conditions. Their vision functions well in low light conditions. The heart has an unusual ability to function effectively while foraging in cold subsurface water. Nonetheless, they must periodically return to warmer surface waters to warm up.
, which is the only known Atlantic nursery area.
Satellite tagging showed that bigeye tuna often spend prolonged periods diving deep below the surface during the daytime, sometimes reaching 500 metres (1,640.4 ft). Bigeye have been tracked entering water as cold as 5 °C (41 °F). These movements are thought to be in response to vertical migrations of prey organisms in the deep scattering layer
.
In 2010, Greenpeace International has added the bigeye tuna to its seafood red list. "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."
For the first time ever, NOAA closed the western and central Pacific bigeye fishery to the Hawaii
-based longline fishing fleet for the final three days of 2009, having reached the internationally-agreed catch limit of 3673 metric tons (3,615 LT). This limit is 30% lower than that of earlier years and will also apply to 2010. The ban does not apply to yellowfin tuna
and other fishes or bigeye in the eastern Pacific.
The United States and the eight island nations that are part of the so-called Nauru Agreement are negotiating an extension of the 1987 Multilateral Treaty, which allows the United States
40 vessels with no limit on fishing days. That treaty expires on 2013. The island nations want the U.S. to reduce the number of days its boats fish each year and lower quotas by 20-30%. Since 2004, quotas on longline fishing have reduced bigeye fishing by 10 percent.
Hawaii's longline fishing vessels virtually stopped 2010 bigeye fishing in the central and western Pacific as of Nov. 22 after reaching their quota. They continued fishing in nontraditional waters in the eastern Pacific, where trips are longer and tuna may be scarce.
The Western Pacific Regional Fishery Management Council acts as a policy adviser to the U.S. Secretary of Commerce. The council supports a reduction in the use of purse seine nets at fish aggregation devices—open-ocean buoys—because too many juvenile bigeyes are taken before they become sexually mature and can propagate.
At a conference in April, Nauru countries banned purse seine fishing by vessels under license to the group in some high seas around their nations as of January. 1. That agreement covers an estimated 25 percent of the world's tuna catch.
The "Nauru countries" are the Federated States of Micronesia, Kiribati, the Republic of the Marshall Islands, Nauru, the Republic of Palau, Papua New Guinea, Solomon Islands and Tuvalu. Other commission members include Australia, China, Canada, the Cook Islands, the European Union, Fiji, France, Japan, South Korea, New Zealand, Niue, the Philippines, Samoa, Taiwan, Tonga, the United States and Vanuatu.
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and prized recreational game fish. It is a true tuna of the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Thunnus
Thunnus
Thunnus is a genus of ocean-dwelling fish in the family Scombridae, all of which are tuna, although other tuna species are found in other genera. The name of the genus is the Latinized form of the Greek θύννος, thýnnos, tuna, the word being first mentioned in Homer...
, belonging to the wider 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...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Scombridae
Scombridae
Scombridae is the family of the mackerels, tunas, and bonitos, and thus includes many of the most important and familiar food fishes. The family consists of about 55 species in 15 genera and two subfamilies...
.
In Hawaiian
Hawaiian language
The Hawaiian language is a Polynesian language that takes its name from Hawaii, the largest island in the tropical North Pacific archipelago where it developed. Hawaiian, along with English, is an official language of the state of Hawaii...
, it is one of two species known as ahi; the other is yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...
.
Range and habitat
Bigeye tuna are found in the open waters of all tropical and temperate oceanOcean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
s, but not the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
.
Anatomy
Bigeye tuna vary up to 250 centimetres (98.4 in) in length. Its maximum weight probably exceeds 400 pounds (181.4 kg), with the all-tackle angling record standing at 392 pounds (177.8 kg). They are large, deep-bodied, streamlined fish with large heads and eyes. The pectoral fins are very long, reaching back as far as the second dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
. They display 13 or 14 dorsal
Dorsum (biology)
In anatomy, the dorsum is the upper side of animals that typically run, fly, or swim in a horizontal position, and the back side of animals that walk upright. In vertebrates the dorsum contains the backbone. The term dorsal refers to anatomical structures that are either situated toward or grow...
spines.
Physiology
The bigeye forages in cold and oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
-poor subsurface waters. Their blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
extracts oxygen efficiently even in oxygen-poor conditions. Their vision functions well in low light conditions. The heart has an unusual ability to function effectively while foraging in cold subsurface water. Nonetheless, they must periodically return to warmer surface waters to warm up.
Life history
Longer-lived than the closely related yellowfin tuna, the bigeye has a lifespan of up to 12 years, with sexual maturity at age four. Spawning takes place in June and July in the northwestern tropical Atlantic, and in January and February in the Gulf of GuineaGulf of Guinea
The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean between Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian is in the gulf....
, which is the only known Atlantic nursery area.
Satellite tagging showed that bigeye tuna often spend prolonged periods diving deep below the surface during the daytime, sometimes reaching 500 metres (1,640.4 ft). Bigeye have been tracked entering water as cold as 5 °C (41 °F). These movements are thought to be in response to vertical migrations of prey organisms in the deep scattering layer
Deep scattering layer
The deep scattering layer, sometimes referred to as "The Sound Scattering Layer"; is the name given to a layer in the ocean consisting of a variety of marine animals. It was discovered through the use of sonar, as ships found a layer that scattered the sound and was thus sometimes mistaken for the...
.
Feeding
Feed items include both epipelagic and mesopelagic species, with deep diving behaviour during the day thought to be related to the seeking of prey.Fishery
Bigeye tuna are amongst the tuna species most threatened by overfishing. Juvenile bigeye tuna associate closely with floating objects such as logs, buoys and other flotsam, which makes them susceptible to purse seine fishing in conjunction with man-made fish aggregation devices. The removal of large numbers of juvenile bigeye, before they reach breeding age, is a major concern to fisheries managers, scientists and sport fishermen. Most seafood sustainability guides encourage consumption of other types of tuna.In 2010, Greenpeace International has added the bigeye tuna to its seafood red list. "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."
Western and central Pacific
The central and western Pacific provides about 54 percent of the world's tuna, amounting to about 1.3 million tons annually.For the first time ever, NOAA closed the western and central Pacific bigeye fishery to the Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
-based longline fishing fleet for the final three days of 2009, having reached the internationally-agreed catch limit of 3673 metric tons (3,615 LT). This limit is 30% lower than that of earlier years and will also apply to 2010. The ban does not apply to yellowfin tuna
Yellowfin tuna
The yellowfin tuna is a species of tuna found in pelagic waters of tropical and subtropical oceans worldwide.Yellowfin is often marketed as ahi, from its Hawaiian name ahi although the name ahi in Hawaiian also refers to the closely related bigeye tuna. The species name, albacares can lead to...
and other fishes or bigeye in the eastern Pacific.
The United States and the eight island nations that are part of the so-called Nauru Agreement are negotiating an extension of the 1987 Multilateral Treaty, which allows the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
40 vessels with no limit on fishing days. That treaty expires on 2013. The island nations want the U.S. to reduce the number of days its boats fish each year and lower quotas by 20-30%. Since 2004, quotas on longline fishing have reduced bigeye fishing by 10 percent.
Hawaii's longline fishing vessels virtually stopped 2010 bigeye fishing in the central and western Pacific as of Nov. 22 after reaching their quota. They continued fishing in nontraditional waters in the eastern Pacific, where trips are longer and tuna may be scarce.
The Western Pacific Regional Fishery Management Council acts as a policy adviser to the U.S. Secretary of Commerce. The council supports a reduction in the use of purse seine nets at fish aggregation devices—open-ocean buoys—because too many juvenile bigeyes are taken before they become sexually mature and can propagate.
At a conference in April, Nauru countries banned purse seine fishing by vessels under license to the group in some high seas around their nations as of January. 1. That agreement covers an estimated 25 percent of the world's tuna catch.
The "Nauru countries" are the Federated States of Micronesia, Kiribati, the Republic of the Marshall Islands, Nauru, the Republic of Palau, Papua New Guinea, Solomon Islands and Tuvalu. Other commission members include Australia, China, Canada, the Cook Islands, the European Union, Fiji, France, Japan, South Korea, New Zealand, Niue, the Philippines, Samoa, Taiwan, Tonga, the United States and Vanuatu.