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Dipturus crosnieri

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RAJIDAE

Scientific Name: Dipturus crosnieri
Species Authority: (Séret, 1989)
Common Name(s):
English Madagascar Skate
Taxonomic Notes: Synonym = Raja (Dipturus) crosnieri Séret, 1989.

Assessment Information [top]

Red List Category & Criteria: Vulnerable A3d ver 3.1
Year Published: 2006
Date Assessed: 2006-01-31
Assessor(s): Brash, J.M., Séret, B. & Compagno, L.J.V.
Reviewer(s): Kyne, P.M., Cavanagh, R.D., Notarbartolo di Sciara, G. & Haywood, M. (Shark Red List Authority)
Justification:
A relatively small (to at least 61 cm TL), poorly known, rare deepwater skate with a limited distribution in the Western Indian Ocean off the west coast of Madagascar. Benthic on the continental slope at depths of 300 to 850 m. Virtually nothing is known of the biology of the species. Its depth range and narrow continental slope where it occurs results in a restricted area of available benthic habitat. Although its depth range precludes it from capture in most of the industrial trawl fleet targeting shrimp off the west coast of Madagascar, there are presently two boats targeting deepwater shrimp (Heterocarpus spp.) operating out of Nosy Be in NW Madagascar. Although bycatch data are not available, this fishery is likely capturing this species. With no market value this small skate is likely discarded with survivorship from capture at such depths being extremely low. Deepsea demersal resources off Madagascar are considered under-utilised at present and as such there is a high likelihood that deepwater fisheries will develop and expand in the Mozambique Channel, following the global trend in expanding deepwater fisheries, particularly as inshore resources are depleted. The collapse of upper slope chondrichthyan populations after exploitation of these habitats for valuable finfish and/or crustacean resources is well documented (i.e., New South Wales, Australia). The future development of deepsea fishing activities in the area poses a considerable threat to D. crosnieri given its restricted range, limited available habitat and rarity. It is thus assessed as Vulnerable considering both actual and potential levels of exploitation of its habitat. More information is required to better determine distribution, population size and life history, as well as careful monitoring of regional fishing activities.

Geographic Range [top]

Range Description: At present, known from a restricted area in the Western Indian Ocean, Madagascar: off Nosy Be, northwestern coast and off Tulear, southwestern coast (Séret 1989).
Countries:
Native:
Madagascar
FAO Marine Fishing Areas:
Native:
Indian Ocean – western
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: No specific information available. A rare species, presently known only from the type series.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Benthic on the continental slope at depths of 300 to 850 m. A relatively small Dipturus species, with the largest known specimen a 61 cm TL female. Largest immature male was 48.1 cm TL and males 55.4 to 59.7 cm TL were mature. Largest immature female examined was 41.4 cm TL and two females 57.5 and 61.0 cm TL were mature (Séret 1989). Like other skates, this species is oviparous, but nothing else known of its biology.

Life history parameters
Age at maturity (years): Unknown.
Size at maturity (total length): <57 cm TL (Séret 1989) (female); <55 cm TL (Séret 1989) (male).
Longevity (years): Unknown.
Maximum size (total length): to at least 61 cm TL (Séret 1989).
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): Although its depth range precludes it from capture in most of the industrial trawl fleet targeting shrimp off the west coast of Madagascar, there are presently two boats targeting deepwater shrimp (Heterocarpus spp.) operating out of Nosy Be in NW Madagascar. Although bycatch data are not available, this fishery is likely capturing this species. With no market value this small skate is likely discarded with survivorship from capture at such depths being extremely low. Deepsea demersal resources off Madagascar are considered under utilised at present (Anon. 1999) and as such there is a high likelihood that deepwater fisheries will develop and expand in the Mozambique Channel, following the global trend in expanding deepwater fisheries, particularly as inshore resources are depleted. The collapse of upper slope chondrichthyan populations after exploitation of these habitats for valuable finfish and/or crustacean resources is well documented (for example off New South Wales, Australia; Graham et al. 2001). Habitat damage from heavy trawling gear may also indirectly impact upon the species.

The future development of deepsea fishing activities in the area poses a considerable threat to D. crosnieri given its restricted range, limited available habitat and rarity.

Conservation Actions [top]

Conservation Actions: Recommendation: further research required to determine the species' distribution and gain information on population size and life history. The careful monitoring of regional fishing activities is also required.

The development and implementation of a national management plan under the FAO International Plan of Action for the Conservation and Management of Sharks: IPOA-Sharks is required to facilitate the conservation and sustainable management of all chondrichthyan species in Madagascar. At the time of writing Madagascar had not taken any action towards implementing a National Plan of Action (Anonymous 2004).

Citation: Brash, J.M., Séret, B. & Compagno, L.J.V. 2006. Dipturus crosnieri. The IUCN Red List of Threatened Species. Version 2014.2. <www.iucnredlist.org>. Downloaded on 01 September 2014.
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