|Scientific Name:||Hexatrygon bickelli|
|Species Authority:||Heemstra & Smith, 1980|
|Taxonomic Notes:||Several species of sixgill stingrays have been named from the Western Pacific; H. longirostris, H. yangi, H. taiwanensis and H. brievirostra, mainly on snout length and shape. However, these forms may be based on variation with growth and state of preservation (Heemstra 1991, Endo and Machida 2005). The current opinion of the occurrence of a single species of sixgill stingray, H. bickelli based on morphological comparisons, should be confirmed by genetic analyses.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||McCormack, C., Wang, Y., Ishihara, H., Fahmi, Manjaji, M., Capuli, E. & Orlov, A.|
|Reviewer(s):||Valenti, S.V. & Fowler, S.L. (Shark Red List Authority)|
A large (to 168 cm TL) deepsea stingray, known from depths of 500-1,120 m. It has a wide but patchy distribution on continental slopes and seamounts in the Northwest and Central Pacific Ocean, off Australia in the Eastern Indian Ocean and off South Africa in the Western Indian Ocean. While several species of Hexatrygon have been described, a single species H. bickelli is recognized. The species is taken as bycatch in deepwater trawl fisheries although no information is available on the numbers caught. It is of concern that there has been a decline in the numbers landed in Taiwan, Province of China, but no quantitative data are currently available. In other areas of this species' geographic range, such as Hawaii and Indonesia, deepwater trawl fisheries are absent or restricted and globally it is currently listed as Least Concern. Catches and population trends should be monitored and the species' status in the Northwest Pacific should be investigated.
|Range Description:||Northwest and western central Pacific, and eastern Indian Ocean: South China Sea off China, Taiwan (Province of China), Indonesia, Philippines, Australia (Western Australia off Exmouth Plateau to Shark Bay; also from Queensland off Flinders Reef) (Compagno 1998).
Eastern central Pacific: Hawaii (Compagno 1998).
Western Indian Ocean: off the east coast of South Africa (eastern Cape off Port Elizabeth and Port Alfred, possibly western Cape near Cape Agulhas) (Compagno 1998).
Native:Australia (Northern Territory, Queensland, Western Australia); China; Indonesia (Bali, Jawa, Kalimantan, Lesser Sunda Is., Maluku, Papua, Sulawesi, Sumatera); Philippines; South Africa (Eastern Cape Province); Taiwan, Province of China (Taiwan, Province of China (main island)); United States (Hawaiian Is.)
|FAO Marine Fishing Areas:||
Indian Ocean – eastern; Pacific – eastern central; Pacific – northwest; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||A rare species with a patchy, wide distribution.|
|Habitat and Ecology:||
A deepwater, benthic ray, mostly found on the upper continental slopes at depths of 362-1,120 m, although there have been two records of the species stranding on beaches off South Africa and one additional live specimen photographed feeding at about 30 m depth off Japan by divers (Compagno 1998, H. Ishihara pers. obs.). It is found on sandy mud to rocky bottom substrates (B. Séret pers. obs).
The species is ovoviviparous and females have been observed with up to three term fetuses (Compagno 1998). Hexatrygon bickelli reaches a maximum total length of at least 168 cm (adult female). Males are estimated to mature at 110 cm TL and females are estimated to mature at 113 cm TL (Compagno 1998, B. Séret pers. obs.). Size at birth is about 48 cm TL (Compagno 1998).
|Major Threat(s):||Infrequently captured in bottom trawl fisheries (Compagno 1998), however there are no quantitative data on the numbers caught or landed throughout its range. In Taiwan, Province of China, this species forms part of the bycatch in both coastal and offshore bottom trawl fisheries (H. Ishihara pers. obs.). It is of concern that the species appears in the landed bycatch of deep bottom trawl fisheries much less than it did only a few years ago (B. Séret pers. obs.). Hexatrygon bickelli is a large and presumably slow growing species, with a relatively large size at maturity; traits that make the species particularly susceptible to overfishing. In other parts of its geographic range, this species' bathymetric distribution may extend below the range of fisheries.|
Close monitoring of catches in deep bottom trawl fisheries in the species range is required in order to assess the threats to this species.
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 sustainable management of all chondrichthyan species in the region.
|Citation:||McCormack, C., Wang, Y., Ishihara, H., Fahmi, Manjaji, M., Capuli, E. & Orlov, A. 2009. Hexatrygon bickelli. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 01 July 2015.|
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