|Scientific Name:||Raja radula Delaroche, 1809|
|Red List Category & Criteria:||Endangered A4b (Regional assessment) ver 3.1|
|Assessor(s):||Mancusi, C., Morey, G & Serena, F.|
|Reviewer(s):||Farrell, E.D., Walls, R.H.L. & Kemp, J.R.|
|Contributor(s):||Dulvy, N.K., Buscher, E. & Bradai, M.N.|
|Facilitator/Compiler(s):||Walls, R.H.L. & Dulvy, N.K.|
Mediterranean regional assessment: Endangered (EN)
The Rough Skate (Raja radula) is medium-sized (up to 70 cm total length) and may be endemic to the Mediterranean Sea. It appears rare in the northern basin but is locally abundant around the Balearic Islands and Tunisia. It occurs in coastal waters to 300 m depth, more commonly found at <40 m depth in some areas such as the Balearic Islands. Records from Portugal and the northern coasts of Morocco require verification and may be misidentifications of other Raja species (skates). The Rough Skate is commonly taken as bycatch of demersal trawl, gillnet, trammel net, bottom longline, and purse seine fisheries, although no species-specific catch data are available. Given that it i) appears to be restricted to the Mediterranean Sea where it has recently declined in certain regions, and ii) ongoing relatively intense fishing pressure overlaps with parts of its range, the Rough Skate is assessed as Endangered under Criterion A4b. A decline of >50% is estimated for the three generation period (27 years) in the European region. Further investigation is required to determine this species’ full range, abundance, interaction with fisheries, and population trends.
The Rough Skate occurs throughout the Mediterranean Sea, but mainly in the western region and around the Balearic Islands. It is absent from the Black Sea (Serena 2005). Reports from Portuguese waters and the northern coasts of Morocco suggest that this skate's range may extend into the eastern Atlantic, but these records require verification as they may be misidentifications of other Raja species. The Rough Skate is found at depths to approximately 350 m.
Native:Albania; Algeria; Bosnia and Herzegovina; Croatia; Cyprus; Egypt (Egypt (African part), Sinai); France (Corsica, France (mainland)); Greece (East Aegean Is., Greece (mainland), Kriti); Israel; Italy (Italy (mainland), Sardegna, Sicilia); Lebanon; Libya; Montenegro; Palestinian Territory, Occupied; Slovenia; Spain (Baleares, Spain (mainland), Spanish North African Territories); Syrian Arab Republic; Tunisia; Turkey (Turkey-in-Asia, Turkey-in-Europe)
|FAO Marine Fishing Areas:|
Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
Trawl surveys have recorded this species in the Mediterranean Sea in low numbers, although it may be more common in unsampled shallow waters (<40 m depth). The International Trawl Survey in the Mediterranean (MEDITS) in the northern Mediterranean Sea captured the Rough Skate in 21 of 6,336 tows between 1994 and 1999 at 50–800 m depth (Baino et al. 2001). In the Gulf of Lion, trawl surveys conducted from the coast to 800 m depth in 1957–60, 1980–84, 1992–95 only captured this species on the shelf and slope during the period 1980–84 (Aldebert 1997). In surveys conducted in Italian waters, it occurred in 3.31% of 9,281 hauls performed between 1985 and 1998 at zero to 800 m depth, which were all from Sardinian and Sicilian waters (Relini et al. 2000). This skate was not caught by trawl surveys in the Adriatic Sea conducted in 1948 or 1998 (Jukic-Peladic et al. 2001).
This species appears to be more common in shallow waters off the Balearic Islands (Morey et al. 2009). Ordines et al. (2011) found it in 37 of 104 bottom trawl hauls in a survey conducted at depths of 45−74 m in this area. MIGJORN and MEDITS surveys performed around the Balearic Islands at depths of 36−755 m in subsequent years (2001−09) caught this species in 12% of 647 hauls (343 specimens) all at depths of 36–172 m (Gouraguine et al. 2011).
The species seems to be uncommon in the Levantine basin, as reported by Golani (2006) and Keskin and Karakulak (2006), who listed it as rare off Israel and north Aegean Sea coasts, respectively. It was not caught in 170 hauls off Algeria at depths of 45−779 m (Echwikhi et al. 2012). In the Aegean Sea, a decline of 58% for the 1995–2000 and 2003–06 periods was estimated, with an inferred decline of 79% for 2007–15 and a projected decline of 89% into the future for the period 2016–23, covering the three-generation period (27 years). However, it is unknown whether this trend is representative of the wider Mediterranean range, and the decline of the Rough Skate in this region is therefore suspected to be >50% over 27 years.
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|
This skate is found in coastal waters to depths of ~350 m (Stehmann and Bürkel 1984, Serena 2005). Around the Balearic Islands it is relatively common at <40 m depth.
Like all skates, this is an egg-laying species. Egg cases are 5.1–5.7 cm long and are laid throughout the year (Kadri et al. 2013), though mainly in spring and summer. Embryos develop in about four months (Stehman and Bürkel 1984, Serena 2005). Females mature at 34 cm disc width (DW) and males at 30 cm DW in the Mediterranean Sea (Fischer et al. 1987, Serena et al. 2010). Maximum body size is ~70 cm total length (TL) (Fischer et al. 1987, Serena et al. 2010). Most captured specimens off the Balearic Islands measure about 30–50 cm TL (Morey et al. 2009).
From the Gulf of Gabès, length at maturity is reportedly 47.05 cm TL for males and 56.48 cm TL for females (Kadri et al. 2013). The age at 50% maturity was estimated to be 4.47 and 5.89 years for males and females, respectively. Maximum age and length were 12 years and 80 cm TL for females, and nine years and 65 cm TL for males. The generation length of this species is therefore estimated to be about nine years.
|Generation Length (years):||9|
|Movement patterns:||Not a Migrant|
|Use and Trade:||
The Rough Skate is not exploited or traded commercially.
This species is taken as bycatch of demersal trawl, gillnet, trammel net, bottom longline, and purse seine fisheries. There is a high level of exploitation over the continental shelf and upper slope in the Mediterranean Sea (Aldebert 1997, Massutí and Moranta 2003). In some areas such as the Balearic Islands this skate is more common in shallow waters where it is taken in: trammel net fisheries targeting Cuttlefish (Sepia officinalis) and teleosts (bony fish); gillnet fisheries targeting Lobster (Palinurus elephas) and Red Mullet (Mullus surmuletus); and bottom longline fisheries targeting Grouper (Epinephelus spp.) and Sparidae (Morey et al. 2006). Trawl fisheries targeting Red Mullet, Picarel (Spicara smaris) and Small Hake (Merluccius merluccius) on the upper shelf also overlap with parts of the Rough Skate's range. In Tunisian waters (mainly in the Gulf of Gabès), this species is taken as bycatch by trawlers at depths of 20−50 m and by gillnets at depths of <20 m (Echwikhi et al. 2012, Kadri et al. 2013). Females outnumbered males in sampled catches in gillnets; 80% of the females and 57% of the males were mature (Echwikhi et al. 2012).
In a multigear small-scale fishery (mainly trammel net, gillnet, and bottom longline), the Rough Skate made up 12% in abundance of the elasmobranch capture at four to 160 m depth between 1998 and 2008 (Mallol et al. 2009). Trammel nets are the most likely gear to catch this species (Morey et al. 2006, 2009).
Species-specific data are not usually available because landings of skates are grouped as “rays” or “skates”. Despite this, a monitoring program conducted at the Palma de Mallorca landing site showed that this species was the sixth most marketed elasmobranch on the island, at an estimated biomass of 6.3 tonnes in 2009. With 66.5% of this biomass coming from bottom trawlers and only 33.5% coming from small-scale fisheries (Morey and Navarro 2010), commercial fisheries appear to be a more significant threat in this region.
No species-specific management or conservation measures are in place in the Mediterranean Sea. If this skate occurs in Portuguese waters (International Council for the Exploration of the Sea sub-area IX), a Total Allowable Catch (TAC) measure is in place for all skate and ray species. In 2013, the TAC was 3,800 tonnes for this sub-area and the Bay of Biscay (sub-area VIII) combined (regulations are available online at http://faolex.fao.org).
Research is required to determine the Rough Skate's full range, abundance, interaction with fisheries, and population trends.
|Citation:||Mancusi, C., Morey, G & Serena, F. 2016. Raja radula. The IUCN Red List of Threatened Species 2016: e.T161339A16527984.Downloaded on 21 June 2018.|
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