|Scientific Name:||Leucoraja circularis|
|Species Authority:||(Couch, 1838)|
Raja circularis Couch, 1838
|Taxonomic Notes:||Formerly called Raja circularis. Early papers often confused Leucoraja circularis and Leucoraja naevus.|
|Red List Category & Criteria:||Endangered A2bcd ver 3.1|
|Assessor(s):||McCully, S., Ellis, J., Walls, R. & Fordham, S.|
|Contributor(s):||Ungaro, N., Serena, F., Dulvy, N., Tinti, F., Bertozzi, M. & Notarbartolo di Sciara, G.|
|Facilitator/Compiler(s):||Walls, R., Lawson, J. & Dulvy, N.|
Sandy Skate (Leucoraja circularis) is a relatively large species found in the Northeast Atlantic and Mediterranean Sea. Historically it was found around 100 m depth on sandy and muddy bottoms, though it is now mainly found in slightly deeper waters along the edge of the continental shelf and upper slope. It is taken as bycatch in multi-species trawl fisheries and offshore bottom longlines.
In the Northeast Atlantic, landings and catch rates for this skate have declined since the early 1990s. The species has completely disappeared from trawl surveys in the North Sea and Celtic Seas in 1996 and 1997, respectively. Scottish surveys still catch it around northwest Scotland and the Porcupine Bank, but at greater depths (180–500 m) than historically reported. This suggests a contraction of the species’ range as a result of trawl fisheries. Records from the outer shelf are scarce, and while survey catch rates have been stable for this species now in the areas it has been considered most abundant since 2001, these rates are very low, therefore do not imply population stability. Misidentification has also prevented reliable estimates of population decline, potentially masking the disappearance of this species from certain areas. For example, Belgium and France are still suspected to be misreporting the species in confusion with Smalleyed Skate (Raja microocellata).
Given the paucity of records from the outer continental shelf, the large declines in landings in recent years, the contracted range to deeper waters, and the very low catch levels seen in the Porcupine Bank survey, Sandy Skate is suspected to have largely in the declined Northeast Atlantic. Fishery independent data for mature individuals are limited and careful monitoring of subpopulations across its range is required to determine accurate population trends for mature individuals.
In the Mediterranean Sea, the occurrence of this species has decreased in the last 60 years. It is no longer encountered in the Gulf of Lions or the Adriatic Sea where it was once relatively common. Mediterranean-wide scientific trawl surveys from 1995–1999 recorded this species in only 12 of 6,336 trawls. Benthic trawl effort has increased significantly during the last 60 years and fishing pressure continues within this species’ depth range.
Given the current rarity of Sandy Skate in the Mediterranean Sea, evidence of potential local extinction from two locations, and its likely low intrinsic rate of increase suggested by its large body size and large size at maturity, together with the declines suspected on the Northeast Atlantic, the species is suspected to have declined overall by more than 50% in the last three generations (29 years). Thus, the species is assessed as Endangered.
|Previously published Red List assessments:|
Given the lack of authenticated records, the exact range of this species is uncertain. In the Northeast Atlantic, it is found in the Norwegian Sea and northern parts of the North Sea, but has not been encountered around the Faroe Islands since prior to 1996 (ICES 2012). It occurs throughout deeper waters west of Ireland and Britain, with the occasional vagrant found in the Celtic Sea. The species is also still landed from the Bay of Biscay and Iberian waters.
This skate was once present throughout the western Mediterranean Sea and as far east as Libya. It is absent from the Black Sea (Stehmann and Bürkel 1984, Bauchot 1987, Notarbartolo di Sciara and Bianchi 1998, Relini et al. 2000, Ragonese et al. 2003, Sion et al. 2003, Serena 2005, Serena et al. 2011), and now considered absent from the Adriatic Sea (Ferretti et al. 2013). Its depth range is 50-800 m.
Native:Albania; Algeria; Bosnia and Herzegovina; Croatia; Egypt (Egypt (African part), Sinai); France (Corsica, France (mainland)); Greece (Greece (mainland)); Iceland; Ireland; Italy; Libya; Montenegro; Morocco; Norway; Portugal (Portugal (mainland)); Slovenia; Spain (Canary Is., Spain (mainland), Spanish North African Territories); Tunisia; Turkey; United Kingdom (Great Britain, Northern Ireland)
|FAO Marine Fishing Areas:|
Atlantic – northeast; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
There are two subpopulations of this species, with different situations for the Northeast Atlantic and Mediterranean Sea. It is likely that there is low connectivity between these two deepwater zones. The overall trend in European waters is of a decline.
This species is rare in the Northeast Atlantic. Accurate determination of abundance trends over the broader area are not possible, as most earlier surveys have focused on shelf fishing grounds, with no long-term, standardised surveys sampling off the edge of the continental shelf. In the southern Northeast Atlantic, French landings data for this species have shown a decline of 92% over about 20 years, from about 500 tonnes per year in the early 1990s to less than 40 tonnes in 2012. French and Portuguese landings data from the Bay of Biscay and Iberian waters across all gears combined have remained low but stable between 1999 and 2011, ranging from around 16–17 tonnes at the beginning and end of the time series, with a peak of 61 tonnes in 2005 (ICES 2012). Again, these data are potentially inaccurate owing to misidentification.
In the northern area of the Northeast Atlantic, English surveys in the North and Celtic Seas have not recorded this species since 1996 and 1997 respectively, although Scottish and Norwegian surveys have recorded it in various surveys around Scotland and along the north coast of Norway since then. Given the low numbers caught in offshore shelf habitats, it is possible that the main part of the range is now in deeper water, such as along the edge of the continental shelf. Indeed, most of the recent captures of this species in Scottish surveys have been from waters of 180–500 m depth. In the Norwegian Sea, the Annual Autumn Bottom Trawl Survey on the north coast of Norway did not report any catches of this skate from 1992 to 2000. From 2000 to 2005 it was encountered in very low numbers (zero to nine individuals per survey), showing no particular trend in abundance (ICES 2012). Given the decline in French landings, and that the range has contracted to deeper waters in the Scottish surveys, it is assumed that the population has declined throughout the Northeast Atlantic. There is uncertainty over the magnitude of the decline in abundance for the population as a whole, owing to the lack of reliable data.
Throughout waters west of Britain and Ireland, the Spanish Porcupine Bank survey (on the western Ireland continental shelf) is the only survey that covers the Northeast Atlantic continental shelf, an important part of this species’ range. This survey recorded peak catches in 2003 and 2007, yet this limited time series has low (e.g., about 0.6 kg per haul in 2011) and variable catch rates, with a stable trend in recent years (ICES 2012). Historically, this species may have been more widely distributed in shelf seas west of Britain and Ireland. It is now encountered rarely in surveys on the inner continental shelf, but still exists in deeper waters along the edge of the continental shelf. Given the reported decreases in survey and landings data, the Northeast Atlantic subpopulation is estimated to be declining.
The occurrence of this species in the Mediterranean Sea has decreased significantly over the last 60 years. It was present in shelf and slope trawl surveys in the Gulf of Lions between 1957 and 1960 but was absent from more recent comparable surveys. Between 1957 and 1960, it was captured in more than 10% of hauls in shelf surveys and in approximately 17% of hauls in slope surveys, whereas between 1966 and 1995 it was not recorded at all from 1,295 hauls in eight trawl surveys (Aldebert 1997).
The International Trawl Surveys in the Mediterranean (MEDITS) cover the northern Mediterranean coast almost continuously, from west Morocco and Spain in the west to the Aegean Sea in the east (Baino et al. 2001). Six trawl surveys were carried out each year in the coastal areas of four arbitrary geographically defined areas: Western (Morocco, Spain, France), Western Central (Tyrrhenian, Corsican, Sardinia and Sicily coasts), Eastern Central (Adriatic, Ionian and Albanian coasts) and Eastern (Aegean Sea). A total of 6,336 tows were completed between 1994 and 1999 at depths ranging from 10 to 800 m. This skate was recorded in only 12 hauls, all in the western area of the Mediterranean Sea (Baino et al. 2001). The evidence that this species may now be scarce in the western Mediterranean Sea points to a substantial reduction in area of occurrence. Its depth range also appears to have contracted, as it was previously found on shelf and slope bottoms between 70 and 275 m (mainly at around 100 m), but is now found only in deeper waters between 500 and 800 m (Baino et al. 2001). The overall biomass index assessed through MEDITS in the west, north and eastern Mediterranean Sea was 0.1 kg per km2 (Baino et al. 2001).
Other records in the Mediterranean also show a decline in capture rates. In the south Ligurian Sea and north Tyrrhenian Sea this species is considered rare based on low capture rates. From 1985–2005 only 10 specimens were caught in the bathyal zone (352–566 m depth) (Serena et al. 2005). In 1948, it was recorded in 3.2% of trawl samples from the Adriatic Sea but has been absent from all trawl survey data in this area since then (Ferretti et al. 2013). It can be inferred that the Mediterranean subpopulation is decreasing given reported declines in capture rates from trawl survey data.
In European waters, the species is suspected to have declined overall by more than 50% in the last three generations (29 years).
|Current Population Trend:||Decreasing|
|Habitat and Ecology:|
This benthic skate occurs in offshore shelf waters and on upper slopes from 50–800 m depth. Historically it was found around 100 m depth on sandy and muddy bottoms, although it now seems more abundant in deeper waters where habitat preferences are currently unknown.
This species is oviparous with egg cases 88–90 by 50–60 mm (Stehmann and Bürkel 1984, Mnsari et al. 2009). The spawning period is unknown (Bauchot 1987, Notarbartolo di Sciara and Bianchi 1998). Maximum recorded size is 120 cm total length (TL), but most individuals caught are between 70 and 80 cm TL (Serena 2005, Ebert and Stehmann 2013). Age at maturity, longevity, size at birth, reproductive age, gestation time, reproductive periodicity, fecundity, rate of population increase and natural mortality are unknown. Its congener L. naevus has a generation lengh of 9.7 years based on a longevity of 12 years, and an estimated age at maturity of 6.8-7.4 years. Thus, the generation length of L. circularis is also 9.7 years.
|Generation Length (years):||9.7|
|Use and Trade:||Large individuals may be landed for human consumption.|
This species is a bycatch in multi-species trawl fisheries operating in the outer parts and edge of the continental shelf. It may also be taken as bycatch in gillnet fisheries targeting anglerfish and longline fisheries targeting hake, though data on the catches in these fisheries are poor. If deepwater commercial fisheries expand into this species’ range they could pose a threat, although there is currently no indication of such expansion. European deepwater fisheries have decreased since 2008, but their effort and extent should be monitored. The relatively large body size would also indicate that it is vulnerable to overfishing. Due to its offshore habitat, it is of no importance to recreational fisheries.
Belgium and France are thought to still record Smalleyed Skate (Raja microocellata) landings erroneously as landings of this species, owing to the shared common name, ‘Sandy Ray’, which hampers the interpretation of some data (ICES 2012).
This skate is a bycatch in multi-species trawl fisheries and offshore bottom longlines. Demersal trawl effort has increased both numerically and technologically in the shelf and slope area of the Mediterranean Sea over the last 50 years. For example, the Gulf of Lions area was initially exploited by small-scale benthic trawl fisheries comprising 27 small low powered boats with a total nominal horsepower of 2,700 hp. More recently effort has increased to a total of 19,940 hp (1974–1987) and more than half of the fishing effort has been displaced to target 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). Although little is known of the life history of this species, it is presumed from similar species that it is slow growing with low fecundity and large juveniles, making it especially vulnerable to fishing exploitation (Brander 1981, Walker and Hislop 1998, Dulvy et al. 2000, Dulvy and Reynolds 2002). Moreover, although only large individuals may be landed for consumption, most size classes including the egg cases are caught in fishing nets, as the legal mesh size used in much of the Mediterranean Sea is about 20 mm. Currently, the contents of the cod end are retained and the 20 mm mesh size commonly used in the Mediterranean Sea means that all life stages of this species are fished.
The main intergovernmental decision-making body on fishery management in the Mediterranean Sea, the General Fisheries Commission for the Mediterranean (GFCM), has made the decision to refrain from expanding deepwater fishing operations beyond the limit of 1,000 m. This is still within the range of this species, as it is not known to occur below 800 m.
In 1999, the European Union (EU) introduced a Total Allowable Catch (TAC) for skates and rays of 6,060 tonnes (t) for fisheries operating in the Norwegian Sea and North Sea (International Council for the Exploration of the Sea [ICES] Division IIa and Subarea IV) based on landing statistics from the previous five years. This TAC has been progressively reduced by 8−25% annually to the current level of 1,256 t. As part of the TAC, the bycatch quota for vessels over 15 metres was set at 25% of live weight of catch retained on board per trip. For much of this period (1999–2014), the TAC was higher than reported landings and therefore was not effectively managing catches. In 2009, skate and ray TACs were established for other EU waters, including the Skagerrak and Kattegat (ICES Division IIIa) and from the northwest coast of Scotland and Northern Ireland to Portuguese waters (ICES Subareas VI–IX) and have also been gradually reduced each year.
In 2006, the European Commission (EC) imposed a permanent ban on all deepwater gillnet fisheries operating at depths greater than 600 m, and imposed maximum limits on the length of nets deployed and the soak time in the remaining fisheries at depths less than 600 m (EC Regulation No. 41/2006). These restrictions may have been of some benefit to this skate. Additionally, since 2008 the EC obligated member states to provide species-specific landings data for the major North Sea species, including this species, in order to improve understanding of skate populations in the area (CEC 2008). In 2009, this obligation was extended to other ICES divisions, including the Celtic Sea (CEC 2009), and has been ongoing since 2008 (CEC 2013).
This skate was listed in Annex III of the Barcelona Convention in 2012, therefore any event of incidental catch and release should be recorded by masters of fishing vessels in the fishing logbook referred to in Article 14 of Regulation (EC) No 1224/2009, in Mediterranean waters.
Moving forward, this species may benefit from more generic management measures for demersal fisheries, for example mesh size regulations and effort reduction. Appropriate non-trawling areas should be defined to protect a proportion of both the adult population and this skate’s eggs (which are often found in the trawl cod-end) (Ragonese et al. 2001). Further research should be conducted on the population size and trend of the species.
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Baino, R., Serena, F., Ragonese, S., Rey, J. and Rinelli, P. 2001. Catch composition and abundance of Elasmobranchs based on the MEDITS program. Rapp. Comm. int. Mer Mèdit 36: 234.
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Ferretti, F., Osio, G.C., Jenkins, C.J., Rosenberg, A.A. and Lotze, H.K. 2013. Long-term change in a meso-predator community in response to prolonged and heterogeneous human impact. Scientific Reports 3 : 1057.
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Mnsari, N., Boumaïza, M. and Capapé, C. 2009. Morphological data, biological observations and occurrence of a rare skate, Leucoraja circularis (Chondrichthyes: Rajidae), off the northern coast of Tunisia (central Mediterranean). Pan-American Journal of Aquatic Sciences 4(70-78).
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Ragonese, S., Zagra, M., Di Stefano, L. and Bianchini, M.L. 2001. Effect of cod-end mesh size on the performance of the deep-water bottom trawl used in the red shrimp fishery of the Strait of Sicily (Mediterranean Sea). Hydrobiologia 449: 279-291.
Relini, G., Biagi, F., Serena, F., Belluscio, A., Spedicato, M.T., Rinelli, P., Follesa, M.C., Piccinetti, C., Ungaro, N., Sion, L. and Levi, D. 2000. Selachians fished by otter trawl in the Italian Seas. Biologia Marina Mediterránea 7(1): 347-384.
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|Citation:||McCully, S., Ellis, J., Walls, R. & Fordham, S. 2015. Leucoraja circularis. The IUCN Red List of Threatened Species 2015: e.T161464A48938919.Downloaded on 26 June 2017.|