| Bigeye tuna | |
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| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Order: | Perciformes |
| Family: | Scombridae |
| Genus: | Thunnus |
| Species: | T. obesus |
| Binomial name | |
| Thunnus obesus (Lowe, 1839) |
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The bigeye tuna, Thunnus obesus, is an important food fish and highly sought after recreational game fish. It is a member of the true tunas 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[1].
Bigeye tuna are found in the open waters of all tropical and temperate oceans, but not the Mediterranean Sea. Its length is between 60 and 250 cm (23 and 93 inches). Maximum weight probably exceeds 400 lb, with the all-tackle angling record standing at 392 lbs.
A longer-lived fish than the closely related yellowfin tuna, the bigeye tuna is thought to have a lifespan of up to 12 years, with individuals achieving sexual maturity at the age of four. Spawning has been recorded as taking place in June and July in the northwestern tropical Atlantic, and in January and February in the Gulf of Guinea in the eastern Atlantic, which is, so far, the only known nursery area for Atlantic bigeye tuna.
Bigeye tuna 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 fin. There are 13 or 14 dorsal spines.
Feed items include both epipelagic and mesopelagic species, with deep diving behaviour during the day thought to be related to the seeking of prey.
Satellite tagging has shown that bigeye tuna often spend prolonged periods cruising deep below the surface during the daytime, sometimes making dives as deep as 500 metres. These movements are thought to be in response to the vertical migrations of prey organisms in the deep scattering layer. Physiological adaptations to foraging in these cold (bigeye tuna have been tracked entering water as cold as 5 degrees Celsius) and oxygen-poor subsurface waters include blood that is highly efficient in extracting oxygen from the water, even in oxygen-poor conditions, and vision that is highly adapted for effective function in low light conditions. The heart of bigeye tuna also has an unusual ability to function effectively at the low ambient temperatures encountered while foraging in cold subsurface water. Nonetheless, bigeye tuna must make return trips to warmer surface waters to warm themselves up.
Overfishing
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 extremely susceptible to purse seine fishing in conjunction with man-made fish aggregation devices. Bigeye mature at a later age than other commercially important tuna species, such as skipjack and yellowfin tuna, and the removal of large numbers of juvenile bigeye before they reach breeding age is a major concern to fisheries managers, scientists and sport fishermen.
References
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Wikimedia Commons has media related to: Thunnus obesus |
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Wikispecies has information related to: Thunnus obesus |
- Uozumi (1996). Thunnus obesus. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on 11 May 2006. Listed as Vulnerable (VU A1bd v2.3)
- Thunnus obesus (TSN 172428). Integrated Taxonomic Information System. Retrieved on 18 April 2006.
- "Thunnus obesus". FishBase. Ed. Ranier Froese and Daniel Pauly. January 2006 version. N.p.: FishBase, 2006.
- Tony Ayling & Geoffrey Cox, Collins Guide to the Sea Fishes of New Zealand, (William Collins Publishers Ltd, Auckland, New Zealand 1982) ISBN 0-00-216987-8
- Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7
- Richard W. Brill1, Keith A. Bigelow, Michael K. Musyl, Kerstin A. Fritsches, Eric J. Warrant,
'BIGEYE TUNA (THUNNUS OBESUS) BEHAVIOR AND PHYSIOLOGY AND THEIR RELEVANCE TO STOCK ASSESSMENTS AND FISHERY BIOLOGY'. ICCAT, 2005. http://www.soest.hawaii.edu/pfrp/reprints/iccat_bigeye.pdf
- ScienceDaily (Dec. 3, 2007), 'Turning A Blind Eye To Bigeye Tuna'. http://www.sciencedaily.com/releases/2007/11/071126144222.htm
- National Marine Fisheries Service, 'Atlantic Bigeye Tuna'. http://www.nmfs.noaa.gov/habitat/habitatprotection/profile/hms/atlantic_bigeye_tunahome.htm
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