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Rhinobatos nudidorsalis

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RHINOBATIDAE

Scientific Name: Rhinobatos nudidorsalis
Species Authority: Last, Compagno & Nakaya, 2004
Common Name(s):
English Bareback Shovelnose Ray, Nakedback Guitarfish
Taxonomic Notes: A newly described and distinct species.

Assessment Information [top]

Red List Category & Criteria: Near Threatened 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:
Rhinobatos nudidorsalis is a recently described rhinobatid known from a single specimen collected on the Saya de Malha Bank, Mascarene Ridge in the central Western Indian Ocean (another Rhinobatos specimen collected from the Saya de Malha Bank by Russian surveys in 1989 may be this species, although this has not been confirmed). This is an unusual deeper water rhinobatid collected from 125 m depth on a mid-oceanic ridge; most other guitarfish species are coastal. A likely small species (single specimen was a 50.1 cm total length mature male), which is possibly endemic to the Mascarene Ridge. There is no specific information available neither on fishing activities in the species' area of occurrence nor on catches of this ray. However, Saya de Malha Bank is a large, relatively shallow, easily accessible oceanic feature likely to be presently targeted by high seas fishing vessels. There is an increasing trend for fishing vessels operating out of African ports to target such oceanic structures for high value teleosts including wreck bass and toothfish. The fact that this bank is remote and beyond any national Economic Exclusion Zone, and therefore is not governed by fishing regulations or subject to fisheries patrols makes it an appealing fishing zone. High seas fishing is likely to continue to grow in the future as resources within national jurisdictions are depleted and/or as restrictions are placed on national resources/fisheries. Even despite any available catch data, unregulated and unmonitored fishing activities pose a real threat to R. nudidorsalis whose available habitat on the Saya de Malha Bank (calculated as the area between the 50 and 200 m isobaths) is limited to just over 20,000 km². The central Western Indian Ocean, however, is not well surveyed and further survey work may show the species to have a wider distribution (for example, on other banks of the Mascarene Ridge). However, until such time as further information is available, a precautionary approach is taken to this assessment, factoring in present trends of unregulated and unmonitored fisheries on the high seas targeting high value teleost products, the accessibility of the type locality, the low reproductive potential of rhinobatids and the small area of available habitat (inferring a low population size).

Geographic Range [top]

Range Description: Possibly endemic to the Mascarene Ridge (central Indian Ocean) and as presently known has a very restricted range. Available habitat on the entire Saya de Malha Bank is calculated to be 22,000 km² based on the area between the 50 and 200 m isobaths (L.J.V. Compagno unpublished data). Further survey work may show that the species has a wider distribution, for example on the other banks of the Mascarene Ridge (Seychelles Bank, Nazareth Bank and Mauritius Bank), and these areas are where survey work should attempt to locate the species.
Countries:
Native:
Mauritius; Seychelles
FAO Marine Fishing Areas:
Native:
Indian Ocean – western
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Population is inferred to be small based on potentially limited area of available habitat.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Single known specimen (the holotype) is a 50.1 cm TL mature male taken at a depth of 125 m on an oceanic ridge (Last et al. 2004). Likely to be a small to moderate sized species of rhinobatid given that the holotype was mature at 50 cm TL (Last et al. 2004). Nothing known of the species' biology, but Rhinobatos species are aplacental viviparous with litter sizes ranging 2 to 16 and an annual reproductive cycle.

A second Rhinobatos specimen collected by Russian surveys from the Saya de Malha Bank in 1989 is likely to be this species, although this has not been confirmed. This specimen was taken in similar depths as the holotype (87 to 110 m) (M. Stehmann pers. comm.).

Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length): Female: unknown; Male: holotype mature at 50.1 cm TL (Last et al. 2004).
Longevity (years): Unknown.
Maximum size (total length): At least 50 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.
Systems: Marine

Threats [top]

Major Threat(s): There is no specific information available neither on fishing activities in the species' area of occurrence nor on catches of this ray. However, Saya de Malha Bank is a large, relatively shallow, easily accessible oceanic feature likely to be presently targeted by high seas fishing vessels.

There is an increasing trend for fishing vessels operating out of African ports to target such oceanic features for high value teleosts including wreck bass and toothfish. The fact that this bank is remote and beyond any national Economic Exclusion Zone, and therefore is not governed by fishing regulations or subject to fisheries patrols makes it an appealing fishing zone. High seas fishing is likely to continue to grow in the future as resources within national jurisdiction are depleted and/or as restrictions are placed on resources/fisheries under national jurisdiction (Gianni 2004).

Even despite any available catch data, unregulated and unmonitored fishing activities pose a real threat to R. nudidorsalis whose available habitat on the Saya de Malha Bank (calculated as the area between the 50 and 200 m isobaths) is limited to just over 20,000 km². This is an unusual rhinobatid as most other species have a coastal occurrence. The central Western Indian Ocean is not well surveyed and further survey work is required.

A precautionary approach is taken to this assessment, factoring in present trends of unregulated and unmonitored fisheries on the high seas targeting high value teleost products, the accessibility of the type locality, the low reproductive potential of rhinobatids and the small area of available habitat (inferring a low population size).

Conservation Actions [top]

Conservation Actions: Further specimens are required to document the species' range and biology. The Russian collected specimen needs to be compared to the holotype of R. nudidorsalis to see if it represents a second specimen of the species (M. Stehmann pers. comm.). Further survey work should focus on the Saya de Malha Bank as well as other banks along the Mascarene Ridge (Seychelles Bank, Nazareth Bank and Mauritius Bank).

High seas benthic trawling activities are impacting poorly known oceanic environments on a global basis (Gianni 2004). High seas fishing activities require international regulation to ensure endemic fauna is not adversely impacted when taken in directed fisheries or as bycatch.

Citation: Compagno, L.J.V. & Marshall, A.D. 2006. Rhinobatos nudidorsalis. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 23 December 2014.
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