Overview

Comprehensive Description

Raja radula ZBK Delaroche, 1809

Sea of Marmara : 2600-38 (1 spc.), 19.05.1989 , Shore of Florya , trammel net , N. Meriç . Aegean Sea : 2600-588 (1 spc.), August 2000 , Bozcaada Island , trammel net , 30 m, L. Eryilmaz ; 2600-39 (1 spc.), 14.08.1989 , Goekova Bay , trawl , 65 m, N. Meriç .

  • Nurettin Meriç, Lütfiye Eryilmaz, Müfit Özulug (2007): A catalogue of the fishes held in the Istanbul University, Science Faculty, Hydrobiology Museum. Zootaxa 1472, 29-54: 32-32, URL:http://www.zoobank.org/urn:lsid:zoobank.org:pub:428F3980-C1B8-45FF-812E-0F4847AF6786
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Biology

Range from coastal waters to about 300 m depth (Ref. 3167). Feed on all kinds of bottom animals (Ref. 3167). Oviparous. Distinct pairing with embrace. Young may tend to follow large objects, such as their mother (Ref. 205). Eggs are oblong capsules with stiff pointed horns at the corners deposited in sandy or muddy flats (Ref. 205). About 80-154 eggs are laid by an individual in a year (Ref. 41305).
  • McEachran, J.D. and K.A. Dunn 1998 Phylogenetic analysis of skates, a morphologically conservative clade of elasmobranchs (Chondrichthyes: Rajidae). Copeia 1998(2):271-290. (Ref. 27314)
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Distribution

Range Description

Occurs throughout the Mediterranean Sea, mainly in the western part and absent from the Black Sea (Serena 2005). The distribution may extend into the Atlantic Ocean, where it is reported from off Portugal and the northern coasts of Morocco, but these records require verification and may be misidentifications of other Raja species.
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Eastern Atlantic: known only from the Mediterranean but may penetrate through the Strait of Gibraltar and possibly to northern Morocco. Some Atlantic records probably misidentifications of Raja naevus and/or Raja africana.
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Eastern Atlantic: Mediterranean Sea and adjacent coast of Portugal.
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Physical Description

Size

Maximum size: 700 mm TL
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Max. size

70.0 cm TL (male/unsexed; (Ref. 4426))
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Raja radula is found from coastal waters to about depths of about 300 m (Stehmann and Bürkel 1984). In the Balearic Islands, this species is relatively common at less than 40 m depth.

Like all skates, reproduction is oviparous. About 80–154 paired eggs are laid per skate, per year (Walker 1998). Egg-cases measure 5.1–5.7 cm and are laid throughout the year, mainly in spring and summer and embryos develop in about four months (Serena 2005, Stehman and Bürkel 1984). Females mature at 34 cm DW and males at 30 cm DW (Serena 2005, Fischer et al. 1987). Maximum size to about 70 cm TL (Serena 2005, Fischer et al. 1987). Most captured specimens in the Balearic Islands measure about 30–50 cm TL (G. Morey unpub. data).

Systems
  • Marine
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Environment

demersal; marine; depth range ? - 300 m (Ref. 4426)
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Depth range based on 9 specimens in 1 taxon.
Water temperature and chemistry ranges based on 9 samples.

Environmental ranges
  Depth range (m): 21 - 98
  Temperature range (°C): 16.259 - 19.203
  Nitrate (umol/L): 0.756 - 2.333
  Salinity (PPS): 36.454 - 37.656
  Oxygen (ml/l): 4.841 - 5.477
  Phosphate (umol/l): 0.112 - 0.246
  Silicate (umol/l): 2.245 - 3.318

Graphical representation

Depth range (m): 21 - 98

Temperature range (°C): 16.259 - 19.203

Nitrate (umol/L): 0.756 - 2.333

Salinity (PPS): 36.454 - 37.656

Oxygen (ml/l): 4.841 - 5.477

Phosphate (umol/l): 0.112 - 0.246

Silicate (umol/l): 2.245 - 3.318
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Depth: 0 - 300m.
Recorded at 300 meters.

Habitat: demersal. Occurs on the shelf and upper slope waters. Feeds on all kinds of bottom animals. Oviparous, spawns throughout the year with maximum number of egg-cases laid in late spring and summer, embryos developing in about 4 months.
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Trophic Strategy

Ranges from coastal waters to about 300 m depth. Feeds on all kinds of bottom animals.
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Life History and Behavior

Life Cycle

Oviparous, paired eggs are laid. Embryos feed solely on yolk (Ref. 50449). Spawns throughout the year with maximum number of egg-cases laid in late spring and summer, embryos developing in about 4 months (Ref. 3167). Distinct pairing with embrace. Young may tend to follow large objects, such as their mother (Ref. 205).
  • Breder, C.M. and D.E. Rosen 1966 Modes of reproduction in fishes. T.F.H. Publications, Neptune City, New Jersey. 941 p. (Ref. 205)
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Raja radula

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 7
Species With Barcodes: 1
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
DD
Data Deficient

Red List Criteria

Version
3.1

Year Assessed
2009

Assessor/s
Morey, G., Serena, F. & Mancusi, C.

Reviewer/s
Valenti, S.V. & Musick, J.A. (Shark Red List Authority)

Contributor/s

Justification
This relatively small skate (to 70 cm TL) may be endemic to the Mediterranean Sea. Records from off Portugal and the northern coasts of Morocco require verification and may be misidentifications of other Raja species. The Rough Ray (Raja radula) occurs from coastal waters to 300 m depth, but appears to be more common at less than 40 m depth in some areas, such as the Balearic Islands. Where recorded in scientific trawl surveys in the northern Mediterranean, this species appears rare. In northern Mediterranean wide MEDITS scientific trawl surveys from 1994–1999 (at 50–800 m depth) the Rough Ray was captured in only 21 of 6,336 tows. It is the most abundant skate in shallow waters off the Balearic Islands (<40m depth), comprising about 25% in abundance and 12% in biomass of total elasmobranch catch in the trammel net fishery there. The Rough Ray is taken as bycatch of demersal trawl, gillnet, trammel net and bottom longline fisheries, although no specific data are available on catches. Given that this species appears to be restricted to the Mediterranean Sea and fishing pressure is relatively intensive in areas of its range, this species’ status may be of concern. At present insufficient information is available from across its range to assess it beyond Data Deficient. Further investigation is required to determine this species’ full range, abundance, interaction with fisheries and population trends.
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Population

Population
Recorded in low numbers where data are available from trawl surveys in the Mediterranean Sea, however it may be more common in shallow waters (<40 m depth) which were not sampled by some of the surveys mentioned below.

In comparable trawl surveys of the Gulf of Lions (France) from 1957–1960, 1980–1984, 1992–1995, (from the coast to 800 m depth) this species was only captured during the period 1980–1984, on the shelf and slope (Aldebert 1997). In northern Mediterranean wide MEDITS scientific trawl surveys from 1994–1999 (at 50–800 m depth) R. radula was captured in only 21 of 6,336 tows (Baino et al. 2001). In surveys conducted in Italian waters, it occurred in only 3.31% of 9281 hauls performed between 1985 and 1998 (at 0–800 m depth). It was only present in two areas (Sardinian and Sicilian waters) and was absent elsewhere in these surveys (Relini et al. 2000). It was not recorded during trawl surveys in the Adriatic Sea in 1948 or 1998 (Jukic-Peladic et al. 2001).

At least in the Balearic Islands, Spain, western Mediterranean, the species appears to be common in shallow waters. It was not recorded in 131 hauls during trawl surveys there from 1996–2001, at depths of 40–1,800 m (Massuti and Moranta 2003). However, it is the most abundant skate in shallow waters off the Balearic Islands (<40 m depth), comprising about 25% in abundance and 12% in biomass of total elasmobranch catch in the trammel net fishery there (Morey et al. 2006). Therefore the absence of this species from trawl surveys deeper than 40 m, at least off the Balearic Islands, is considered a result of its preference for shallow waters and perhaps the sampling gear.

Population Trend
Unknown
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Threats

Major Threats
This species is taken as bycatch of demersal trawl, gillnet, trammel net and bottom longline fisheries. There is a high level of exploitation over the continental shelf and upper slope in the Mediterranean Sea (Massuti and Moranta 2003, Aldebert 1997). In some areas, such as the Balearic Islands, this species is more common in shallow waters, where it is taken in trammel net (targeting cuttlefish Sepia officinalis and teleost fishes), gillnet (targeting Lobster (Palinurus elephas) and Red Mullet (Mullus surmuletus)) and bottom longline fisheries (targeting groupers Epinephelus spp. and Sparidae) (Morey et al. 2006). Trawl fisheries operating on the upper shelf, targeting red mullet Mullus surmuletus, caramel Spicara smaris and small hake Merluccius merluccius in this area also partially overlap with its range. Species specific data are not available because landings of skates are grouped as ‘rays’.
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Data deficient (DD)
  • IUCN 2006 2006 IUCN red list of threatened species. www.iucnredlist.org. Downloaded July 2006.
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Management

Conservation Actions

Conservation Actions
None in place. Research is required to determine this species’ full range, abundance, interaction with fisheries and population trends.
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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial
  • Schneider, W. 1990 FAO species identification sheets for fishery purposes. Field guide to the commercial marine resources of the Gulf of Guinea. Prepared and published with the support of the FAO Regional Office for Africa. Rome: FAO. 268 p.
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