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).
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Distribution

Range Description

This species 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 off Portugal and the northern coasts of Morocco suggest that its range may extend into the eastern Atlantic, but these records require verification as they may be misidentifications of other Raja species. The species is found roughly at depths to 350 m.

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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

This skate is found in coastal waters at depths of ~350 m (Stehmann and Brkel 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 5.15.7 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 Brkel 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 3050 cm TL (Morey et al. 2009).

From the Gabs Gulf, 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 estimated to beabout nine years.

Systems
  • Marine
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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
 
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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
 
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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).
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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
EN
Endangered

Red List Criteria
A4b

Version
3.1

Year Assessed
2015

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

Reviewer/s
Farrell, E., Walls, R. & Kemp, J.R.

Contributor/s
Dulvy, N., Buscher, E. & Bradai, M.N.

Justification

Rough Skate (Raja radula) is a medium-sized species (up to 70 cm total length) that may be endemic to the Mediterranean Sea. It appears rare in the northern Mediterranean Sea but is locally abundant in the Balearic Islands and Tunisia. It occurs from coastal waters to 300 m depth, but appears to be more common at < 40 m depth in some areas, such as the Balearic Islands. Records from off Portugal and the northern coasts of Morocco require verification and may be misidentifications of other Raja species. This 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 appears to be restricted to the Mediterranean Sea where it has recently declined in certain regions, and ongoing relatively intense fishing pressure overlaps with parts of its range, Rough Skate is assessed as Endangered under Criterion A4b as a decline of >50% is estimated for the three generation period in the European region. Further investigation is required to determine this species full range, abundance, interaction with fisheries, and population trends.


History
  • 2009
    Data Deficient (DD)
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Population

Population

Trawl surveys have recorded this species in the Mediterranean Sea in low numbers, although it may be more common in shallow waters (< 40 m depth) that are not sampled by some surveys. The International Trawl Survey in the Mediterranean (MEDITS) programme in the northern Mediterranean Sea captured this species in 21 of 6,336 tows between 1994 and 1999 at 50800 m depth (Baino et al. 2001). In the Gulf of Lion, trawl surveys conducted from the coast to 800 m depth in 19571960, 19801984, 19921995 only captured this species on the shelf and slope during the period 19801984 (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 4574 m in this area. MIGJORN and MEDITS surveys performed around the Balearic Islands at depths of 36755 m in subsequent years (20012009) caught this species in 12% of 647 hauls (343 specimens) all at depths of 36172 m (Gouraguine et al. 2011).

In the western Mediterranean Sea, this species was not recorded in 131 hauls during trawl surveys from 19962001 at depths of 401,800 m (Massut and Moranta 2003). This 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. This species was not caught in 170 hauls off Algeria at depths of 45779 m (Echwikhi et al. 2012).In the Aegean Sea, a decline of 58% for the 1995-2000 and 2003-2006 periods was estimated, with an inferred decline of 79% for 2007-2015 and a projected decline of 89% into the future for the period 2016-2023, covering the three-generation period (27 years). However, it is unknown whether this trend is representative of the wider Mediterranean distribution, and the decline of Rough Ray in European waters is therefore estimated to be of >50% over 27 years.


Population Trend
Decreasing
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Threats

Major Threats

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, Massut and Moranta 2003). In some areas such as the Balearic Islands, this species 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 its range. In Tunisian waters (mainly in the Gulf of Gabs), this species is taken as bycatch by trawlers at depths of 2050 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 (trammel net, gillnet and bottom longline, mainly), this species 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 to catch this species (Morey et al. 2006, 2009).

Species-specific data are commonly not 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 are a more significant threat.

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Data deficient (DD)
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Management

Conservation Actions

Conservation Actions

No species-specific management or conservation measures are in place in the Mediterranean Sea. If this species 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 this species full range, abundance, interaction with fisheries, and population trends.

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Relevance to Humans and Ecosystems

Benefits

Importance

fisheries: commercial
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