|Scientific Name:||Hexanchus nakamurai|
|Species Authority:||Teng, 1962|
|Taxonomic Notes:||The species has often been misidentified as the larger Bluntnose Sixgill Shark, H. griseus leading to confusion and poor knowledge of its distribution, and little to no knowledge of population trends.
Ebert (1990) conducted a detailed systematic review of this species and redescribed it. On comparison of the type specimen from the U.S. National Museum Natural History, Smithsonian with material from Taiwan, Ebert (1990) concluded they were the same species, and resurrected the name H. nakamurai, reducing H. vitulus to a junior synonym.
|Red List Category & Criteria:||Data Deficient ver 3.1|
|Assessor/s:||Ebert, D.A., Serena, F. & Mancusi, C.|
|Reviewer/s:||Cavanagh, R.D., Heupel, M.R., Simpfendorfer, C.A. & Valenti, S.V. (Shark Red List Authority)|
The Bigeyed Sixgill Shark (Hexanchus nakamurai) is a little known, moderately large (to 180 cm TL), primarily deepwater cow shark with a patchy distribution in tropical and warm temperate waters in the northeast and central Atlantic; the Mediterranean Sea; the northwest, western central and southwest Pacific; and the Indian Ocean. Probably mesopelagic to benthic in shelf and slope waters from 90-621 m with possible excursions to the surface. The species has often been misidentified as the larger Bluntnose Sixgill Shark (Hexanchus griseus), leading to confusion and poor knowledge of its distribution and no knowledge of any population trends. It is uncommonly taken by bottom trawl and longline gear and is of relatively small importance to fisheries. Due to insufficient information this species cannot be assessed beyond Data Deficient at present. Species-specific catch data are required to better define the distribution, population trends, if any, and threats to the species.
|Range Description:||Widely but patchily distributed in warm temperate and tropical seas, but possibly absent from the eastern Pacific (Ebert 1990, Compagno et al. 2005, Compagno in prep). Records from Mauritius, Madagascar, southern Mozambique, KwaZulu-Natal, South Africa, and the island chains, Geyser and Zelee Banks, east of Diego Suarez, Castor and Cordeliere Banks, were originally referred to as H. griseus, but Ebert (1990) re-identified these specimens as H. nakamurai.
Western Indian Ocean: off southern Africa (KwaZulu-Natal), Aldabra Island group (Aldabra, Diego Suarez, Castor and Condeliere Banks), Mauritius, Madagascar, Kenya, Geyser and Zeleé Banks (Ebert 1990). Eastern Indian: Australia (Western Australia) (Ebert 1990).
Western central Atlantic: off Florida, USA and the Bahamas, northern Cuba, Cayman and Virgin Islands, Yucatán and Gulf coast of Mexico, Nicaragua, Costa Rica, Venezuela and the Guyanas (Ebert 1990). Northeast Atlantic: Gulf of Gascony and Bay of Biscay, off France, Spain and Gibraltar. It occurs from the Straits of Gibraltar to Italy in the Mediterranean Sea (Ebert 1990). Eastern central Atlantic: Morocco and possibly Ivory Coast and Nigeria (Ebert 1990).
Northwest Pacific: off Taiwan Island, Japan (including Kochi, Ogasawara Islands and Okinawa). Western central Pacific: the Philippines (Negros, possibly Luzon), Australia (Queensland), New Caledonia, French Polynesia (Tahiti) (Ebert 1990). Southwest Pacific: Australia (northern New South Wales) (Ebert 1990).
Native:Australia (New South Wales, Queensland, Western Australia); Bahamas; Cayman Islands; Costa Rica; Cuba; France (France (mainland)); French Polynesia (Society Is.); Gibraltar; Guyana; Italy; Japan (Nansei-shoto, Ogasawara-shoto, Shikoku); Kenya; Madagascar; Mauritius; Mexico (Yucatán); Morocco; Mozambique; New Caledonia; Nicaragua (Nicaragua (mainland)); Philippines; Seychelles (Aldabra); South Africa (KwaZulu-Natal); Spain (Spain (mainland)); Taiwan, Province of China; United States (Florida); Venezuela, Bolivarian Republic of; Virgin Islands, British; Virgin Islands, U.S.
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Atlantic – southeast; Atlantic – western central; Indian Ocean – eastern; Indian Ocean – western; Mediterranean and Black Sea; Pacific – northwest; Pacific – southwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Uncommon to rare where it occurs (Compagno in prep, Ebert 1990). Number and size of populations is unknown. Rare in the Mediterranean Sea (Serena 2005, Ebert 1990). Misidentification with H. griseus has prevented a better understanding of this species' distribution.|
|Habitat and Ecology:||Primarily a deepwater species, found on the continental and insular shelves and slopes from 90–621 m depth, usually on or near bottom, but occasionally moving to near the surface or inshore in the tropics (Compagno in prep, Ebert 1990). May be more restricted in habitat and distribution than H. griseus and less tolerant of conditions beyond offshore continental habitat in warmer seas (Compagno in prep.). Size at maturity is 142–178 cm in males and 123–157 cm in females (Compagno in prep., Ebert 1990). Maximum size is approximately 180 cm (Compagno in prep, Ebert 1990). Reproduction is ovoviviparous, with 13–26 pups per litter, measuring 40–45 cm TL at birth (Whitehead et al. 1984, Compagno et al. 2005, Compagno in prep, Ebert 1990). Probably feeds on small to medium-sized bony fishes, including hairtails (Trichiuridae), small tuna (Euthynnus), and crustacea (Compagno in prep, Ebert 1990).|
Apparently uncommonly taken on line gear and in trawls, and considered of relatively minor importance to fisheries (Compagno in prep.). Small numbers are caught off Campeche Bank, Yucatán in Mexican shark fisheries, as bycatch of snapper fisheries in the Cayman Islands, and as bycatch of trawl fisheries off Taiwan (Ebert 1990). The species has also been recorded in very low numbers in catches of the artisanal deepwater long-line fishery operating off eastern Indonesia, where all landed elasmobranchs are utilised (White et al. 2006).
It probably is a minor component of offshore demersal trawl and line fisheries elsewhere where it occurs, but no catch statistics are available (Compagno in prep.).
The species may be under growing pressure with the expansion of deep water fisheries and there is an urgent need to collect species-specific catch data to determine accurate population trends.
|Conservation Actions:||There are no species-specific conservation measures in effect or proposed at this time. Like many deeper water species more information on biology, ecology and importance in fisheries are required to assess the threat status and any future conservation needs. Where taken, catches require monitoring, particularly as deepwater fisheries expand worldwide. The development and implementation of management plans (national and/or regional e.g., under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks) are required to facilitate the conservation and management of all chondrichthyan species in the region.|
Compagno, L.J.V. 1984. FAO species catalogue. Vol. 4. Sharks of the world. An annotated and illustrated catalogue of shark species known to date. Part 1. Hexanchiformes to Lamniformes. FAO, Rome.
Compagno, L.J.V., Dando, M. and Fowler, S.L. 2005. Sharks of the World. Harper Collins.
Compagno, L.J.V. In prep.. Sharks of the World. An annotated and illustrated catalogue of the shark species known to date. FAO, Rome.
Ebert, D.A. 1990. The taxonomy, biogeography and biology of cow and frilled sharks (Chondrichthyes: Hexanchiformes). Unpub. Ph.D. thesis. Rhodes University, Grahamstown.
IUCN. 2009. IUCN Red List of Threatened Species (ver. 2009.2). Available at: www.iucnredlist.org. (Accessed: 3 November 2009).
Serena, F. 2005. Field identification guide to the sharks and rays of the Mediterranean and Black Sea.
Springer, S. and Waller, R. A. 1969. Hexanchus vitulus, a new sixgill shark from the Bahamas. Bulletin of Marine Science 19(1): 159-174.
Teng, H.T. 1962.. Classification and distribution of the Chondrichthyes of Taiwan..
Tortonese, E. 1985. Gli squali mediterranei del genere Hexanchus. Atti della Societa Italiana di Scienze Naturali e del Museo Civico di Storia Naturale di Milano 126(3-4): 137-140.
Vacchi, M. and Notarbartolo di Sciara G. 2000. I pesci cartilaginei nei mari italiani, una risorsa che richiede urgenti misure di tutela. Biologia Marina Mediterranea 7((1):): 296-311.
|Citation:||Ebert, D.A., Serena, F. & Mancusi, C. 2009. Hexanchus nakamurai. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 11 March 2014.|
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