|Scientific Name:||Glaucostegus thouin|
|Species Authority:||(Anonymous [Lacepède], 1798)|
Raja thouin Anonymous [Lacepède], 1798
Rhinobatos thouin (Anonymous [Lacepède], 1798)
|Taxonomic Source(s):||Last, P.R., Séret, B. and Naylor, G.J.P. 2016. A new species of guitarfish, Rhinobatos borneensis sp. nov. with a redefinition of the family-level classification in the order Rhinopristiformes (Chondrichthyes: Batoidea). Zootaxa 4117(4): 451-475.|
|Taxonomic Notes:||Some recent changes in the systematics of Rhinobatus have elevated the subgenus Glaucostegus to full generic status and placed this genus into a family of its own: Glaucostegidae (Compagno 2005, Last et al. 2016).|
|Red List Category & Criteria:||Vulnerable A2abd+3bd+4abd ver 3.1|
|Assessor(s):||White, W.T. & Marshall, A.D.|
|Reviewer(s):||Kyne, P.M., Heupel, M.R., Simpfendorfer, C. & Cavanagh, R.D.|
This is an amended version of the 2006 assessment to accommodate recent taxonomic revision of the genus Rhinobatus, and the former subgenus Glaucostegus being raised to genus level.
Glaucostegus thouin has a widespread distribution in the Indo-West Pacific. It was once moderately abundant but is now irregularly caught as bycatch in local fisheries throughout its range, especially in the Western Central Pacific. It is a large species (>300 cm TL), vulnerable to gillnets, inshore trawl fisheries and even line fishing. Rhinobatids are taken by multiple artisanal and commercial fisheries throughout their range as a target species and as bycatch, and population declines in many guitarfish species have been observed in areas of the Indo-Pacific. Local population depletion can be inferred from Indonesia where the target gillnet fishery fleet declined from a maximum of 500 boats in 1987 to 100 in 1996, due to declining catch rates (Chen 1996). Flesh is sold for human consumption in Asia and the fins from large animals fetch particularly high prices, creating a significant incentive for bycatch to be retained (the value of rhinobatid and rhynchobatid fins far exceeds that of other sharks and rays). Demands for dried fins for the international fin trade could be a factor in the switch from subsistence fisheries to more directed fisheries, although their flesh is also highly sought after. Very little is known about the biology or population status of G. thouin. Their existence along coastal inshore areas of the continental shelf makes them an easy target for fisheries and it is likely that habitat degradation in these areas may also be affecting nursery areas. Population declines are inferred from observed declines in bycatch numbers in local fisheries and given its susceptibility to capture by multiple fishing gear types and its high value fins, it is probable that numbers have been locally reduced by fishing throughout its range. This species meets the criteria of A2abd+3bd+4abd for Vulnerable due to the population decline outlined above and the remaining very high level of unmanaged exploitation in Southeast Asia.
|Previously published Red List assessments:|
|Range Description:||Widespread Indo-West Pacific distribution. Possibly Suriname and the Mediterranean (Compagno and Last 1999).|
Native:Bangladesh; Djibouti; Egypt; Eritrea; Ethiopia; India; Indonesia (Jawa, Kalimantan, Sumatera); Iran, Islamic Republic of; Iraq; Japan; Kuwait; Malaysia; Myanmar; Oman; Pakistan; Papua New Guinea; Qatar; Saudi Arabia; Singapore; Somalia; Sri Lanka; Sudan; Thailand; United Arab Emirates; Viet Nam; Yemen
|FAO Marine Fishing Areas:|
Present - origin uncertain:
Atlantic – western central; Indian Ocean – western; Indian Ocean – eastern; Mediterranean and Black Sea; Pacific – western central; Pacific – northwest
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||No information available.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Benthic ray found in inshore waters, typically less than 60 m depth over soft sandy substrate. |
Aplacental viviparous, attaining at least 300 cm TL but nothing known of its biology.
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (total length): >300 cm TL.
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Unknown.
Average annual fecundity or litter size: Unknown.
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Taken by multiple artisanal and commercial fisheries throughout its range as a target species and as bycatch. Fished using nets, line and hook, and trawls throughout its range. Large species, extremely powerful but still vulnerable to gillnets and to a lesser extent inshore trawl fisheries and lines. The fins from Rhinobatos and Glaucostegus spp. are widely considered as being amongst the most valuable of elasmobranchs (i.e., white-fin) and there is a significant incentive for fishers to remove the fins from large individuals when they are taken as either target catch or bycatch. G. thouin is commonly landed as bycatch in fisheries in Indonesia (Chen 1996, White unpublished data). Fisheries targeting the rhynchobatids in eastern Indonesia, e.g., Aru Islands and Merauke (Papua), often catch this species but generally in low numbers. Also recorded as trawl bycatch in Sabah and Sarawak (R. Cavanagh, pers. comm).
Since juveniles of this species inhabit shallow sand flats and mangrove estuaries (White, unpubl. data), intensive fishing pressures, e.g., gill, trap and seine nets, in such inshore areas throughout Indonesia (e.g., Merauke, Papua) are most likely having a high level of impact on this species.
Not known to have specific habitat requirements but young may require specific inshore nursery areas that have been affected by human activities resulting in habitat degradation, as destructive fishing practices and pollution are significant factors affecting marine resources in parts of this species' range.
Local population depletion can be inferred from Indonesia where the target gillnet fishery fleet declined from a maximum of 500 boats in 1987 to 100 in 1996 due to declining catch rates (Chen 1996).
Further research into the population structure, biology and ecology of G. thouin is required to assess the extent to which fishing pressure, particularly in relation to finning, and habitat destruction is influencing this species within its range. Improved species composition data from all fisheries that take shovelnose rays and guitarfish is necessary.
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. See Anon. (2004) for an update of progress made by nations in the range of G. thouin.
Future management may involve difficult decisions affecting communities adjacent to these areas.
|Citation:||White, W.T. & Marshall, A.D. 2016. Glaucostegus thouin. The IUCN Red List of Threatened Species 2016: e.T60175A104017154.Downloaded on 22 February 2017.|
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