Dipturus batis 

Scope: Mediterranean
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Chondrichthyes Rajiformes Rajidae

Scientific Name: Dipturus batis (Linnaeus, 1758)
Regional Assessments:
Common Name(s):
English Common Skate, Blue Skate, Flapper Skate, Grey Skate
French Flotte, Pocheteau Gris, Pochette
Spanish Noriega, Raya Noruega
Dipturus cf. flossada (Risso, 1827)
Raja batis Linnaeus, 1758
Taxonomic Notes: Currently, this listing for Dipturus batis represents a species complex. A recent taxonomic review indicates that D. batis will soon be split into two separate species (Iglésias et al. 2010).

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A2b (Regional assessment) ver 3.1
Year Published: 2016
Date Assessed: 2016-03-25
Assessor(s): Dulvy, N.K., Notarbartolo di Sciara, G., Serena, F., Tinti, F., Ungaro, N., Mancusi, C. & Ellis, J.R.
Reviewer(s): Walls, R.H.L. & Allen, D.J.
Contributor(s): Walls, R.H.L.
Facilitator/Compiler(s): Walls, R.H.L.

Geographic Range [top]

Range Description:The historical range of the Common Skate covered much of the continental shelf of the Mediterranean Sea. It is now considered scarce in the western area of the basin (Stehmann and Bürkel 1984). It is absent from the Levantine basin to the east (Serena 2005). This skate's depth range is zero to 600 m.
Countries occurrence:
France (Corsica, France (mainland) - Possibly Extinct); Greece (Greece (mainland)); Italy (Italy (mainland) - Possibly Extinct, Sicilia); Morocco; Spain (Baleares, Spain (mainland), Spanish North African Territories)
Possibly extinct:
Albania; Algeria; Bosnia and Herzegovina; Croatia; Montenegro; Slovenia; Tunisia
FAO Marine Fishing Areas:
Mediterranean and Black Sea
Additional data:
Lower depth limit (metres):600
Range Map:39397-3

Population [top]

Population:A time series of comparative trawl surveys in the Gulf of Lion between 1957 and 1960 indicate that the Common Skate was historically present in both shelf and slope trawl surveys. It was captured in 10% of hauls (n=27) in shelf surveys (coast–150 m depth) and in ~17% of hauls (n=37) in slope surveys at 150–800 m depth (Aldebert 1997). In contrast, comparable surveys carried out from 1966–95 in the Gulf of Lions (totalling 1,295 hauls) did not record this species (Aldebert 1997). 

In the Adriatic Sea, the "Hvar" 1948 trawl survey (based on 138 valid hauls taken in the spring-summer of 1948) caught the Common Skate in 3.2% of hauls. In a comparable survey conducted in the spring-summer of 1998 (127 valid hauls) (the International Trawl Survey in the Mediterranean: MEDITS) it was not recaptured, suggesting possible absence from this area (Jukic-Peladic et al. 2001). The MEDITS began in 1994 while another study of the Adriatic Sea had begun in 1985 (GRUND), with each project carrying out one survey per year. A single individual was captured in the first GRUND survey of 1985 and since then no specimens have appeared in the Adriatic in either of these surveys (Marano et al. in press). The Common Skate is now regarded as locally extinct in the Adriatic Sea (Tinti et al. 2003). Bottom trawl surveys spanning the Alboran to Aegean Sea (i.e., northern Mediterranean coastal waters) between 1994 and 1999 at 10–800 m depth (MEDITS) only caught the Common Skate once throughout the survey (Baino et al. 2001). This indicates local extinction from the entire heavily fished northern coastal waters of the Mediterranean Sea. Although these surveys are exhaustive, it should be noted that the MEDITS net is thought to have a low sampling efficiency of truly benthic species (Jukic-Peladic et al. 2001). Along the Algerian coast from 1996–97, regular systematic surveys of elasmobranchs present in markets have been undertaken. Although eight species of skate have been recorded, the Common Skate has not (Hemida 1998). Tunisian fisheries use prawn trawl and larger "French" trawls, which frequently capture skates and demersal sharks. Although this species was documented from Tunisian waters in the early part of the 20th century, it has not been recorded there since 1971 and it is now presumed absent from this area (Bradaï 2000). 

The former range of this skate included much of the west, north, and eastern shelf and slope habitat of the Mediterranean Sea. These survey data suggest that this species may only be found in the western area of the Mediterranean basin now (Morocco, Spain, and France) representing a substantial reduction in area of occurrence of this species. The species is inferred to have undergone a regional decline of at least 80% based on numerous localized disappearances.
Current Population Trend:Decreasing
Additional data:

Habitat and Ecology [top]

Habitat and Ecology:This demersal species is found from shallow coastal waters down to depths of 600 m, although it is primarily within the 200 m depth range (Stehmann and Bürkel 1984, Bauchot 1987, Serena 2005). 

Although there is almost no life history and ecological information specific to the Mediterranean Sea, it can be inferred as similar to the following. This is the largest species of skate attaining a total length (TL) of >250 cm. The age and growth of the Common Skate has been reported by Du Buit (1976) and more recently by Fahy (1991) who examined the vertebrae of 75 individuals landed in Ireland. Du Buit (1976) gave the following growth parameters: maximum size 253.73 cm TL; k = 0.057; t0 = -1.629. Males are thought to mature at 125 cm TL (Du Buit 1976) and although the size at maturity has not been accurately determined for females, an estimate of 150 cm TL was presented in the 2000 Red List assessment. Du Buit (1976) determined age at maturity as 11 years and longevity as 50 years. The overall sex ratio is reportedly ~1:1, although this may differ geographically and seasonally (Fulton 1903, Steven 1933). The fecundity has not been accurately determined but was estimated at 40 eggs per year over the spawning season (Brander 1981) and the rate of reproduction has been calculated at 0.38.

This skate is oviparous, with large egg-cases covered with close-felted fibres (150–250 mm long and 80–150 mm wide reported in the Mediterranean Sea (Serena 2005). The egg-cases are deposited in spring and summer in the Mediterranean Sea (Serena 2005). The young hatch at a lengths of up to 21.2–22.3 cm (Clark 1926). There is no detailed information on the developmental time.
Generation Length (years):7.5

Use and Trade [top]

Use and Trade: There is no current use or trade information for the Common Skate in the Mediterranean Sea, possibly because it has largely disappeared from the region.

Threats [top]

Major Threat(s): The Common Skate is probably captured as part of the bycatch of multi-species trawl fisheries, despite its low frequency of occurrence in the Mediterranean Sea. Benthic trawl effort has increased both numerically and in technological terms in the shelf and slope area of the Mediterranean Sea over the last 50 years. For example, the Gulf of Lion area was initially exploited by small-scale benthic trawl fisheries comprising 27 small low powered boats (total nominal horse power of 2,700 hp), more recently effort has increased to a total nominal horse power of 19,940 hp (1974–87). Since then half of the fishing effort has been displaced to targeting small pelagic fish (Aldebert 1997). The Adriatic Sea is subject to trawling mainly by Italian, Croatian, Slovenian, and Albanian fleets; however, no landings data are available (Jukic-Peladic et al. 2001).

The large body size, slow growth, low fecundity, and large size of juveniles of this species makes it especially vulnerable to fishing exploitation when compared to other rajids (Brander 1981, Walker and Hislop 1998, Dulvy et al. 2000, Dulvy and Reynolds 2002). Moreover, although only large individuals tend to be landed for consumption, most size classes are taken in fishing nets, including the eggs (which are often found in the trawl cod-end; Ragonese et al. 2003), as the legal mesh size used in much of the Mediterranean Sea is only ~20 mm. Considering the large size at maturity (~130 cm TL) this means that the exploitation of juveniles is likely to be high.

Conservation Actions [top]

Conservation Actions: There are no species-specific measures in the Mediterranean Sea. It is recommended that suitable non-trawling areas are defined to protect both adults and deposited eggs as these are both susceptible to capture by trawling gear. 

The MEDLEM project was adopted at the last SAC meeting (FAO, Rome 2005) for data collection within the Mediterranean basin on large elasmobranches. The Bern Convention encourages research programs aimed at the assessment of the conservation status of chondrichthyans in the Mediterranean Sea (Serena et al. 2002). In Italy a national action plan (PAN-SHARKS) was co-ordinated by ICCRAM (Central Institute for Marine Research) within the guidelines of the Bern Convention and FAO IPOA-Sharks (Serena et al. 2002, Vacchi and Notarbartolo di Sciara 2000). The Barcelona Convention proposed this species for urgent legal protection under its Mediterranean Action Plan.

Citation: Dulvy, N.K., Notarbartolo di Sciara, G., Serena, F., Tinti, F., Ungaro, N., Mancusi, C. & Ellis, J.R. 2016. Dipturus batis. The IUCN Red List of Threatened Species 2016: e.T39397A16527753. . Downloaded on 22 September 2018.
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