Glaucostegus granulatus

Status_ne_offStatus_dd_offStatus_lc_offStatus_nt_offStatus_vu_onStatus_en_offStatus_cr_offStatus_ew_offStatus_ex_off

Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Glaucostegus granulatus
Species Authority: (Cuvier, 1829)
Common Name/s:
English Sharpnose Guitarfish
Synonym/s:
Rhinobatos granulatus Cuvier, 1829
Taxonomic Notes: Revision of the large genus Rhinobatos is proposing to elevate subgenera Glaucostegus to generic status, thus Rhinobatos granulatus will be referred to as Glaucostegus granulatus (L.J.V. Compagno pers. comm.). However, these changes are not yet published and until such time as they are the species should continue to be referred to as Rhinobatos granulatus.

Often confused with Rhinobatos typus and Pacific Ocean records of R. granulatus are probably R. typus. This effects distribution and catch data as misidentifications are probably quite common.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2bd+3d+4d ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor/s: Marshall, A.D. & Last, P.R.
Reviewer/s: Kyne, P.M., Heupel, M.R. & Simpfendorfer, C.A. (Shark Red List Authority)
Justification:
A large (to 215 cm total length) inshore and offshore guitarfish recorded to depths of 119 m. An Indo-Pacific species with a poorly documented distribution, but with a centre of abundance around India and Sri Lanka. Rhinobatos granulatus was once moderately abundant but is now 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. The species is 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 Asia. 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 known area of occurrence of R. granulatus is impacted by often intense and generally unregulated and unmonitored fisheries. The centre of abundance for this species, off India and Sri Lanka is impacted upon by a high level of resource utilisation, as is most of the Southeast Asian region. Fishing pressure is consistently increasing in these areas and the demand for fins for the international fin trade is helping drive landings of large guitarfish. Although exact catch data are not available this species is seen much 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.

Geographic Range [top]

Range Description:Indo-West Pacific but range not accurately defined. Occurrence in the Western Indian needs better documentation. Possibly occurs off China, Indonesia, Philippines, Papua New Guinea and Australia, but confusion with Rhinobatos typus confounds accurate mapping of range, particularly in the Western Pacific.
Countries:
Native:
Australia; India (Andaman Is.); Indonesia; Kuwait; Myanmar; Pakistan; Papua New Guinea; Philippines; Sri Lanka; Thailand; Viet Nam
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern; Indian Ocean – western; Pacific – western central
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population: Was most abundant off India and Sri Lanka. Once moderately abundant but now irregularly caught in fisheries.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Inshore and offshore to mid-continental shelf down to 119 m. Benthic on soft substrates.

Little known of biology. Aplacental viviparous. Prasad (1951) documented litter sizes of 6 to 10 pups. Reproductive periodicity is annual in examined Rhinobatos species.

Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length cm): Unknown.
Longevity (years): Unknown.
Maximum size (total length): 215 cm TL (Compagno and Last 1999).
Size at birth (cm): Unknown.
Average reproductive age (years): Unknown.
Gestation time (months): Unknown.
Reproductive periodicity: Probably annual (based on other Rhinobatos species).
Average annual fecundity or litter size: 6 to 10 pups/litter (Prasad 1951).
Annual rate of population increase: Unknown.
Natural mortality: Unknown.
Systems: Marine

Threats [top]

Major Threat(s): Rhinobatos granulatus is fished throughout its range, both directly and indirectly. It was once moderately abundant but is now irregularly caught in local fisheries.

This large rhinobatid 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. The species is 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 for Rhinobatos species and these are being impacted upon by fishing activities and environmental degradation/pollution.

The entire known area of occurrence of R. granulatus is impacted by often intense and generally unregulated and unmonitored fisheries. The centre of abundance for this species, off India and Sri Lanka, is impacted upon by a high level of resource utilisation, as is most of the Southeast Asian region. Fishing pressure is consistently increasing in these areas and the demand for fins for the international fin trade is helping drive landings of large guitarfish. 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.

Conservation Actions [top]

Conservation Actions: There is a need to acquire accurate catch data from fisheries throughout the species? distribution and to confirm presence in certain areas where it might have been previously been misidentified. 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. granulosus.

Bibliography [top]

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. 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.

Compagno, L.J.V., Last, P.R., Stevens, J.D. and Alava, M.N.R. 2005. Checklist of Philippine Chondrichthyes. CSIRO Marine Laboratories Report 243.

IUCN. 2006. 2006 IUCN Red List of Threatened Species. www.iucnredlist.org. Downloaded on 04 May 2006.

IUCN SSC Shark Specialist Group. Specialist Group website. Available at: http://www.iucnssg.org/.

Prasad, R.R. 1951. Observations on the egg-cases of some ovoviviparous and viviparous elasmobranchs, with a note on the formation of the elasmobranch egg-case. Journal of the Bombay Natural History Society 49:755–762.

Randall, J.E. and Compagno, L.J.V. 1995. A review of the guitarfishes of the genus Rhinobatos (Rajiformes: Rhinobatidae) from Oman, withe description of a new species. Raffles Bulletin of Zoology 43(2):289–298.

Citation: Marshall, A.D. & Last, P.R. 2006. Glaucostegus granulatus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 24 April 2014.
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