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Rhinobatos obtusus

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Rhinobatos obtusus
Species Authority: Müller & Henle, 1841
Common Name/s:
English Widenose Guitarfish
Taxonomic Notes: Revision of the large genus Rhinobatos is proposing to elevate subgenera Glaucostegus to generic status, thus Rhinobatos obtusus will be referred to as Glaucostegus obtusus. However, these changes are not yet published and until such time as they are the species should continue to be referred to as Rhinobatos obtusus.

Reports of R. obtusus from South Africa are probably based on another species of guitarfish (Compagno and Last 1999).

Assessment Information [top]

Red List Category & Criteria: Vulnerable A2bd+3d+4d ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor/s: Compagno, L.J.V. & Marshall, A.D.
Reviewer/s: Kyne, P.M., Heupel, M.R. & Simpfendorfer, C.A. (Shark Red List Authority)
Justification:
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. Rhinobatos 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 R. 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.

Geographic Range [top]

Range Description: Primarily an Eastern Indian species.
Countries:
Native:
Bangladesh; India; Indonesia; Malaysia; Myanmar; Pakistan; Sri Lanka; Thailand
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: Population trends not clear but Rhinobatos obtusus was once moderately abundant throughout its relatively wide range but is now only irregularly caught in local fisheries.
Population Trend: Decreasing

Habitat and Ecology [top]

Habitat and Ecology: Inshore and offshore distribution along coastal shelves. Benthic. Nothing known of the species? biology, but Rhinobatos 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.
Systems: Marine

Threats [top]

Major Threat(s): Rhinobatos 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, Rhinobatos 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 Rhinobatos 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 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 R. horkelii in Brazil and which has been 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 R. 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.

Conservation Actions [top]

Conservation Actions: 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.
Citation: Compagno, L.J.V. & Marshall, A.D. 2006. Rhinobatos obtusus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 19 April 2014.
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