|Scientific Name:||Glaucostegus obtusus (Müller & Henle, 1841)|
Rhinobatos obtusus Müller & Henle, 1841
|Taxonomic Source(s):||Last, P., White, W., de Carvalho, M., Séret, B., Stehmann, M. and Naylor, G. 2016. Rays of the World. CSIRO Publishing, Clayton.|
|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).
Reports of G. obtusus from South Africa are probably based on another species of guitarfish (Compagno and Last 1999).
|Red List Category & Criteria:||Vulnerable A2bd+3d+4d ver 3.1|
|Assessor(s):||Compagno, L.J.V. & Marshall, A.D.|
|Reviewer(s):||Kyne, P.M., Heupel, M.R. & Simpfendorfer, C.|
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.
A moderate-sized (to 93 cm total length) inshore and offshore guitarfish distributed primarily in the Indian Ocean and known from Pakistan, India, Sri Lanka, Bangladesh, Myanmar, Malaysia, Indonesia and Thailand. Glaucostegus obtusus was once moderately abundant throughout its relatively wide range but is now only irregularly caught in local fisheries. It is susceptible to capture in a variety of fishing gear including trawl, gillnet, line and seine net and its occurrence along inshore areas of the continental shelf makes these rays an easy target for such fisheries. Target fisheries for guitarfish currently exist in several countries particularly in the Indo-West Pacific (including Malaysia and Indonesia). This species is impacted by direct and indirect fishing pressure and the flesh is utilised. Habitat requirements are not well understood, but inshore areas are important as nursery areas and these are being impacted upon by fishing activities and environmental degradation/pollution. The entire range of G. obtusus is subject to generally unregulated, unmonitored and often intense inshore fisheries and fishing pressure is consistently increasing in these areas. Although exact catch data are not available this species is seen less regularly than it was previously and declines of greater than 30% are expected to have already occurred, while fishing pressure continues unabated over this species' range and habitat. The limited biological characteristics of rhinobatid rays (usually annual reproductive cycle with 2 to 16 pups per litter) will restrict the species' ability to recover from population depletion.
|Previously published Red List assessments:|
|Range Description:||Primarily an Eastern Indian species.|
Native:Bangladesh; India; Indonesia; Malaysia; Myanmar; Pakistan; Sri Lanka; Thailand
|FAO Marine Fishing Areas:|
Indian Ocean – western; Indian Ocean – eastern; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Population trends not clear but Glaucostegus obtusus was once moderately abundant throughout its relatively wide range but is now only irregularly caught in local fisheries.|
|Current Population Trend:||Decreasing|
|Habitat and Ecology:||Inshore and offshore distribution along coastal shelves. Benthic. Nothing known of the species' biology, but Glaucostegus species are aplacental viviparous with litter sizes ranging 2 to 16 and an annual reproductive cycle. |
Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (total length): 93 cm TL (Compagno and Last 1999).
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.
Glaucostegus obtusus was once moderately abundant throughout its relatively wide range but is now only irregularly caught in local fisheries. Coastal rhinobatids are susceptible to capture in a variety of fishing gear including trawl, gillnet, line and seine net and their occurrence along inshore areas of the continental shelf makes these rays an easy target for such fisheries. Target fisheries for guitarfish currently exist in several countries particularly in the Indo-West Pacific (including Malaysia and Indonesia) and declines in some species have been documented. For example, Pseudobatos horkelii has been significantly impacted by heavy inshore fishing pressure where it occurs in Brazil. Similarly declines are now been observed in species in Southeast Asia, for example G. granulatus and others. Species are impacted by direct and indirect fishing pressure where the flesh is utilised and the demand for fins for the international fin trade could be a factor in the switch from subsistence fisheries to more directed, commercial export fisheries of especially the larger guitarfish in areas such as Indonesia and the Philippines. Habitat requirements are not well understood, but inshore areas are important as nursery areas and these are being impacted upon by fishing activities and environmental degradation/pollution. Reproductive biology of rhinobatids is reasonably well studied compared with other batoid groups. Rhinobatos and Glaucostegus species tend to have an annual reproductive cycle producing a single litter per year of between two and 16 pups. Landings of aggregations of gravid females, which was a factor in the decline of P. horkelii in Brazil and which was observed for R. formosensis in Taiwan, is cause for great concern. These observations likely mirror trends elsewhere where inshore rhinobatids are fished.
The entire range of G. obtusus is subject to generally unregulated, unmonitored and often intense inshore fisheries and fishing pressure is consistently increasing in these areas. Although exact catch data are not available this species is seen less regularly than it was previously and declines of greater than 30% are expected to have already occurred, while fishing pressure continues unabated over this species' range and habitat.
There is a need to acquire accurate catch data from fisheries throughout the species' distribution. Better understanding of habitat requirements and critical area/habitats is required to establish best amelioration processes.
Future management will need to consider harvest and trade management with a focus on resource stewardship and livelihood alternatives.
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 elasmobranch species. See Anon. (2004) for an update of progress made towards development and implementation of National Plans of Action for countries across the range of R. obtusus.
Anonymous. 2004. Report on the implementation of the UN FAO International Plan of Action for Sharks (IPOA–Sharks). AC20 Inf. 5. Twentieth meeting of the CITES Animals Committee, Johannesburg (South Africa), 29 March–2 April 2004.
Compagno, L.J.V. 2005. Checklist of living Chondrichthyes. In: S.L. Fowler, M. Camhi, G.H. Burgess, G.M. Cailliet, S.V. Fordham, R.D. Cavanagh, C.A. Simpfendorfer, and J.A. Musick (eds) Sharks, rays and chimaeras: the status of the chondrichthyan fishes. IUCN SSC Shark Specialist Group. IUCN, Gland, Switzerland and Cambridge, UK.
Compagno, L.J.V. and Last, P.R. 1999. Rhinobatidae. In: K.E. Carpenter and V.H.Niem (eds) FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Volume 3. Batoid fishes, chimaeras and bony fishes part 1 (Elopidae to Linophyrnidae). FAO, Rome, pp. 1423-1430.
IUCN. 2016. The IUCN Red List of Threatened Species. Version 2016-3. Available at: www.iucnredlist.org. (Accessed: 07 December 2016).
IUCN SSC Shark Specialist Group. Specialist Group website. Available at: http://www.iucnssg.org/.
Last, P.R., Séret, B. and Naylor, G.J.P. 2016a. 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.
|Citation:||Compagno, L.J.V. & Marshall, A.D. 2016. Glaucostegus obtusus. The IUCN Red List of Threatened Species 2016: e.T60170A104015272.Downloaded on 25 November 2017.|
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