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Dentiraja flindersi

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA CHONDRICHTHYES RAJIFORMES RAJIDAE

Scientific Name: Dentiraja flindersi
Species Authority: Last & Gledhill 2008
Common Name(s):
English Pygmy Thornback Skate
Taxonomic Notes:

The Pygmy Thornback Skate (Dentiraja flindersi) was first identified as Raja sp. M in Last and Stevens (1994) and is one of the smallest hard-nose skates. It appears to have been confused with other skate species and is a small relative of the Thornback Skate (D. lemprieri). The Pygmy Thornback Skate differs from the Thornback Skate by having an extremely broad interorbital space, nuchal thorns widely separated, and plain colour with fine white spots (Last and Stevens 2009). Some confusion remains with specimens collected from the inner continental shelf off Albany (southwestern Australia), which are most likely to be of a different species (Last and Stevens 2009).

Assessment Information [top]

Red List Category & Criteria: Data Deficient ver 3.1
Year Published: 2011
Date Assessed: 2010-12-21
Assessor(s): Heard, M. & Huveneers, C.
Reviewer(s): Ebert, D.A. & Kyne, P.M.
Justification:

The Pygmy Thornback Skate (Dentiraja flindersi) is a poorly known, small South Australian endemic skate that is believed to be found only in waters adjacent to the Gulfs of South Australia in depths of 27–54 m. Maximum size of this species is about 33 cm TL but there is no information on the population size, ecology or life history of this species. Given its endemism, this species is a key indicator of the Gulfs Province of southern Australia. It is considered to be rare and the population size is likely to be small based on low abundance and narrow range. It has a high encounterability and selectivity to trawl fishing. Commonwealth gillnet, hook and trap fisheries, and South Australian prawn trawl fisheries operate over a portion of the range of this species, although no information on catches is currently available. The South Australian prawn trawl fisheries are managed by traditional methods of limited licences, vessel and gear restrictions as well as seasonal closures and rotation of trawling grounds. Other measures such as bycatch reduction devices and reduced sorting times have also been implemented. Although the area of occurrence is <5,000 km² (Criterion B1), there are no available data on its population or distribution trends. Further information is required on population size/structure, trends, habitat requirements, biology, bycatch and range for this species to assess it beyond Data Deficient; further research is required on the species’ biology, occurrence and capture in fisheries.

Geographic Range [top]

Range Description: The Pygmy Thornback Skate is endemic to South Australian waters and is only known from the Investigator Strait and Backstairs Passage, off Kangaroo Island. However, the distribution map in Last and Stevens (2009) includes Gulf St Vincent for this species – presence here is uncertain (Last and Gledhill 2008, Last and Stevens 2009).
Countries:
Native:
Australia (South Australia)
FAO Marine Fishing Areas:
Native:
Indian Ocean – eastern
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: Population size and trends are unknown for the Pygmy Thornback Skate.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology:

The Pygmy Thornback Skate occurs in waters adjacent to the gulfs of South Australia at depths of 27–54 m (Last and Stevens 2009) There are no specific details on habitat. Maximum size of this species is about 33 cm total length (TL); males mature at about 29 cm TL (Last and Stevens 2009). There is no information on neonatal juveniles or egg cases (Last and Gledhill 2008) and no further information on the ecology or life history of this species.

Systems: Marine

Use and Trade [top]

Use and Trade: The Pygmy Thornback Skate is not known to be traded and is generally too small to be marketed.

Threats [top]

Major Threat(s):

The Pygmy Thornback Skate is a potential bycatch of the Gillnet, Hook and Trap Sectors (GHATS), part of the Commonwealth managed Southern and Eastern Scalefish and Shark Fishery (SESSF). No fishing effort takes place within the South Australian Gulfs, while fishing effort in Backstairs Passage and Investigator Strait is virtually nonexistent and relatively small, respectively (Goldsworthy et al. 2010). Fishing effort off the south and southwest of Kangaroo Island is higher and more likely to impact the Pygmy Thornback Skate if the distribution of the species extends to that area. However, encounterability, post-capture mortality, and catch susceptibility of the Pygmy Thornback Skate were assessed as low for the gillnet fishery of the SESSF (Walker et al. 2008). The actual bycatch level for the species is unknown.

The Pygmy Thornback Skate is also a potential bycatch of South Australian prawn trawl fisheries which operate over a portion of the range of this species. The species has a high encounterability, a high selectivity and a medium post-capture mortality to otter trawl gear. The fishery operates in waters greater than 10 m with demersal, otter-trawl rigged gear. Prawn fishing in the Investigator Strait was closed in 1987 with the buyback of licences for the Investigator Strait prawn fishery. While trawling can still be undertaken by licensees from other areas, fishing effort within Investigator Strait is minimal. No prawn trawling is being undertaken in Backstairs Passage due to unsuitable grounds, effectively providing a refuge area for the Pygmy Thornback Skate (G. Hooper pers. comm. 2011). Similar to Commonwealth catches, no information is currently available on State catches of this species. While the occurrence of the Pygmy Thornback Skate in the South Australian Gulfs is uncertain, Currie et al. (2009) did not report Pygmy Thornback Skate as bycatch in the Spencer Gulf Prawn Fishery in 119 trawls (mostly of 30 minutes duration) possibly indicating the apparent rarity of the species.

No species-specific catch data is available for rays and skates caught by the recreational fishing industry. However, a survey of the South Australian recreational fishery estimated 18,082 rays and skates caught in 2007/08 with 97% of them released (Jones 2009). As such, the South Australian recreational fishery is unlikely to have a strong impact on the Pygmy Thornback Skate.

Conservation Actions [top]

Conservation Actions:

South Australian prawn trawl fisheries are managed by traditional methods of limited licences, vessel and gear restrictions as well as seasonal closures and rotation of trawling grounds. Other measures including bycatch reduction devices such as crab bags (separate cod-end is enclosed within the main cod-end) and crab racks (grates used to sort prawns from larger bycatch) have lead to reduced sorting times. Post release survival of skate species is largely unknown and requires further investigation to gauge the impact of prawn fisheries on the Pygmy Thornback Skate.


Citation: Heard, M. & Huveneers, C. 2011. Dentiraja flindersi. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 27 November 2014.
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