|Scientific Name:||Leucoraja naevus|
|Species Authority:||(Müller & Henle, 1841)|
Raja naevus Müller & Henle, 1841
|Taxonomic Notes:||This species was previously referred to as Raja naevus. Early papers often confused Cuckoo Ray with Sandy Ray (Lecoraja (Raja) circularis).|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Assessor(s):||Ellis, J., Dulvy, N. & Walls, R.|
|Contributor(s):||Fordham, S., Ungaro, N., Serena, F., Tinti, F., Bertozzi, M., Pasolini, P., Mancusi, C. & Notarbartolo di Sciara, G.|
|Facilitator/Compiler(s):||Walls, R., Frazer, K., Dulvy, N. & Pardo, S.A.|
This small-bodied skate is relatively widespread and endemic to the Northeast Atlantic and Mediterranean Sea. It occurs at depths between 20 and 500 m, and is more common at about 200 m in the Mediterranean Sea. It is taken as bycatch in mixed demersal fisheries through much of its range and used in some areas. It is apparently rare in the Mediterranean Sea and has disappeared in some areas, remaining in areas less intensively trawled. It may have some capacity to withstand moderate fishing pressure compared with larger skates that are highly sensitive to rapid depletion as a result of their limiting life-history characteristics.
Abundance trends from the Northeast Atlantic are inconsistent as there is considerable spatial and temporal variability in catch. This species seems to have increased in some areas following previous declines, while in other areas the opposite pattern is seen.However the total Northeast Atlantic population is not considered to have declined significantly. However, there have been observed declines in heavily trawled areas of the Mediterranean Sea, although there are other areas where it is less heavily fished, and there is a lack of new information on trends.
Based on the apparent ability of this skate to withstand higher levels of fishing than other larger elasmobranchs, and the lack of negative trend data throughout the majority of its European range, the species is assessed as Least Concern. More information on stock identity is required, and the status of stocks in those areas where it is exploited most in the Northeast Atlantic (e.g., Celtic Sea and Bay of Biscay) need to be better assessed and monitored.
From the Northeast and Eastern Central Atlantic, Cuckoo Skate (Leucoraja naevus) occurs off coasts northward from the Shetland Isles and southern Norway in the north, to Morocco in the south (Stehmann and Bürkel 1989). It is common in the North Sea ecoregion, especially in the northwest area and occurs in low numbers around the Faroe Islands. It occurs throughout the Celtic Seas, including the Irish Sea, outer Bristol Channel, and outer western English Channel. In the Spanish survey of Porcupine Bank, west of Ireland, it is found mainly around the central mound of the bank (ICES 2013).
In the Mediterranean Sea this skate occurs in northern, western and central-eastern waters, excluding the Adriatic Sea. It has been recorded in waters off Algeria, France, Greece, Italy, Malta, Morocco, Spain (including the Balaeric Islands) and Tunisia (Bauchot 1987, Stehmann and Bürkel 1989, Bertrand et al. 2000, Relini et al. 2000, Baino et al. 2001, Jukic-Peladic et al. 2001, Tinti et al. 2003, Serena et al. 2011, Valls et al. 2011). Its depth range is 20-500 m.
Native:Algeria; France (Corsica, France (mainland)); Greece (East Aegean Is., Greece (mainland)); Israel; Italy (Italy (mainland), Sicilia); Libya; Malta; Morocco; Norway; Portugal (Portugal (mainland)); Spain (Baleares, Spain (mainland), Spanish North African Territories); Tunisia; United Kingdom
|FAO Marine Fishing Areas:||
Atlantic – northeast; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
Northeast and Eastern Central Atlantic
This is a relatively small-bodied species that is most abundant on offshore grounds and forms a relatively high proportion of skate landings in those areas where it is abundant. The catch rates below refer to all individuals (not just mature fish) and are typically nominal CPUE trends. Observed increases or declines tend to be of a moderate magnitude, but signals are inconsistent across surveys.
The highest catch rates of this species are found off the east coast of Scotland and around Orkney and Shetland. It is abundant in the northern North Sea, off northwest Scotland, the Irish Sea, the Celtic Seas, and is also one of the dominant skates around the Iberian Peninsula (ICES 2006). It is only rarely observed in the inner parts of the Bristol Channel and in the eastern English Channel and southern North Sea. Preliminary stock assessments were made for the Celtic Sea stock during the Development of Elasmobranch DELASS project (Heessen 2003), though the results were inconclusive.
Mean abundance of this skate in the North Sea ecoregion appears to have increased from the late seventies to early eighties, followed by a sharp decline (Daan et al. 2005), and then by stabilisation in recent years at very low levels (ICES 2012). Fishery-independent mean catch per unit effort (CPUE) of the species for quarter one of the international bottom trawl survey in the North Sea was ~0.5 individuals per hour from 2010 to 2011, falling above the mean for the period 2005 to 2009, having increased by ~60% in three to four years from a low of ~0.2 individuals per hour in 2007 (ICES 2012). The stock is concentrated in the northern and central parts of the North Sea. For quarter three of the survey, mean CPUE for 2010 and 2011 was also higher than the mean for the period 2005 to 2009, having increased by ~53% in three to four years from a low of approximately 0.38 individuals per hour in 2007, to approximately 0.8 individuals per hour in 2011 (ICES 2012). The exploitation level of the North Sea stock is still unknown. It should be noted that survey catch rates are based on all individuals, rather than adults alone.
The stock structure of this skate in the Celtic Seas and waters west of Britain is insufficiently known, which makes the interpretation of catch rates in the various surveys more problematic (ICES 2012). As an offshore species that is also present in the Bay of Biscay (VIII) and northern North Sea (IVa), it is possible that the stock or stocks extend out of the Celtic Seas ecoregion. The French EVHOE survey of this ecoregion suggested peaks in relative abundance in 2001, 2002, 2007-2008 with the lowest catch in 2000 (ICES 2012).
The Spanish survey on the Porcupine Bank indicated recent decreases in catch rates over a four year period both in terms of biomass (~50%) and abundance (~81%) (from ~0.5 kilograms or 0.75 individuals per haul in 2007 to ~0.25 kilograms or 0.25 individuals in 2011), although catch rates in the last few years are comparable to those observed at the start of the time-series (ICES 2012). Earlier analyses of Scottish survey data from waters west of Scotland suggested stable or increasing catch trends (ICES 2012), although more recent data were not available. The English and Welsh beam trawl survey in the Irish Sea indicated a decline in mean CPUE of ~42% over 19 years from ~2.4 individuals per hour in 1993 to ~1.4 in 2011, with the mean catch rates from 2010 and 2011 lower than those from 2005 to 2009 (ICES 2012). From the Irish Groundfish Survey of this area, trends in abundance are not apparent, with variable annual catches and a mean CPUE of approximately one individual per hour, falling within the lower margin of the mean CPUE for the period 2005 to 2009 (ICES 2012).
The biomass indices reported by Spanish fishery-independent trawl surveys of Spanish Atlantic waters show annual variation of ~60% between 0.2 and 0.5 kilograms per haul, with an overall increase in catch rates (ICES 2012). Fishery-independent data for Portuguese waters are too limited to gauge longer-term trends.
The landings per unit effort (LPUE) of this skate from the Bay of Biscay between 2002 and 2011 show constant values between 50 and 68 kilograms per day, excluding the lowest values of approximately 34 tonnes overall for 2004 and 48 tonnes in 2010 (ICES 2012). The relationship between Cuckoo Skate populations in the Celtic Seas and Bay of Biscay region is unknown.
This skate appears to have always been relatively uncommon in the Mediterranean Sea; it was rarely caught in the International Trawl Survey in the Mediterranean (MEDITS) from 1994-1999. The MEDITS covers 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 are 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 performed between 1994 and 1999 at depths ranging from 10-800 m. This species was recorded in only 42 of 6,336 tows during this survey (frequency of occurrence of 1%) and was more frequently captured in the eastern area (Baino et al. 2001). A time series of comparative trawl surveys in the Gulf of Lions indicate that this skate was historically present in both shelf and slope trawl surveys in 1957-1960 and in 1980-1984 (150-800 m), but was not present on the shelf or slope in comparable surveys in 1992-1995 (Aldebert 1997), indicating local extinction from this area.
This species does not appear to have been captured in historical and recent trawl surveys of the Adriatic Sea (Jukic-Peladic 2001). Massuti and Moranta (2003) reported it in relatively recent trawl surveys off the Balearic Islands. Little is known of its current distribution and abundance along northwest African coastlines, except that it now appears to be uncommon in Tunisian waters.
The overall population trend of the species in European waters is unknown.
|Habitat and Ecology:||
The species is found on the continental shelf and slope at depths of 20-500 m, and more commonly at about 200 m in the Mediterranean Sea (Serena 2005). It is typically an offshore species, occurring further offshore than, for example, Spotted Skate (Raja montagui) and Thornback Skate (Raja clavata). It is abundant on coarse sand and gravel substrates in the Irish Sea and western English Channel.
The size at maturity is estimated at 55 cm total length (TL) for both males and females (Walker 1999) with a maximum size of about 72 cm TL (Stehmann and Bürkel 1984, Ellis et al. 2005). In the Mediterranean Sea, the maximum size recorded is about 70 cm TL and size at first maturity is 60 cm TL in females (Serena 2005). Age at maturity for females and males is estimated at 7.4 and 6.8 years, respectively, in the North Sea (Walker 1999), and age at 50% maturity is just over four years in the Irish Sea (Gallagher et al. 2005). Around the British Isles, males and females first mature at 48 and 45 cm TL, respectively (McCully et al. 2012). Additionally, length at 50% maturity (L50) is estimated as 56.3 cm (males) and 59.4 cm (females). There is a significant difference in the L50 for both sexes between the North Sea and Celtic Seas ecoregions, with females and males in the North Sea 6.2 to 6.5 cm smaller at this stage than in the Celtic Seas. The estimated L50 in Portuguese waters is 56.5 and 56 cm TL for females and males, respectively (Maia et al. 2012). Longevity is reported at 12 years (Du Buit 1976b), which in conjunction with an age at 50% maturity of four years would indicate a generation time of eight years for individuals in the Irish Sea.
In Portuguese waters, actively spawning females and males can be found throughout the year, though the percentage of actively spawning individuals is higher between January and May (Maia et al. 2012). The maximum potential fecundity is estimated between 60 and 63 mature follicles for spawning-capable and actively spawning females, respectively. Batch fecundity was estimated as seven follicles per batch, with nine reproductive episodes per female. Other studies have indicated that females produce about 90 eggs per year after an eight month gestation period (Clark 1922, Du Buit 1976a, Bauchot 1987).
|Use and Trade:||
In the Northeast Atlantic, when caught, this species is landed and sold (Holden 1977, Dulvy et al. 2000).
The species is taken as bycatch in mixed demersal fisheries through much of its range and usually retained. Due to occurring further offshore than other skates, this species is less important to recreational fisheries. Increasing fuel prices are thought to have resulted in some fisheries operating closer to port, which may benefit offshore skates.
Skates are an important component of the demersal fisheries of northwest Europe; when caught, this species is landed and sold (Holden 1977, Dulvy et al. 2000). Off the Bay of Biscay it is mainly landed by polyvalent trawlers and longliners operating further offshore (ICES 2013). It may be an important component in mixed demersal fisheries where abundant, and is landed as a bycatch in trawl fisheries throughout its Atlantic range, though smaller individuals tend to be discarded (Silva et al. 2012). This skate is one of the more frequent species landed by the commercial fisheries operating in the Celtic Sea and Iberian waters. Craven et al. (2013) found it to be the dominant bycatch species of scallop dredge fisheries in the northern Irish Sea around the Isle of Man, constituting around 27% of total bycatch.
The situation in the Mediterranean Sea may be similar to that in the Northeast Atlantic: this species may be part of the bycatch of multispecies trawl fisheries typical in the shelf seas of the Mediterranean basin. Demersal trawl effort has increased both numerically and in technological terms in the shelf and slope areas of the Mediterranean Sea over the last 50 years. The continental shelf and upper slope are highly exploited, with intensive commercial trawling occurring at depths ranging from 50-800 m (Colloca et al. 2003, Massuti and Moranta 2003). Although only adult individuals may be landed for consumption, most size classes are likely to be taken in fishing nets as the legal mesh size used in much of the Mediterranean Sea is approximately 20 mm. The relatively small size of this skate suggests that its life history and demography may allow some capacity to withstand moderate fishing pressure (Dulvy et al. 2000, Stevens et al. 2000).
Though there are no species-specific management measures in place, there is a Total Allowable Catch (TAC) for skates and rays in the Northeast Atlantic, and this species may benefit from more generic management measures for demersal fisheries (e.g., mesh size regulations and effort reduction). More information on stock status is required, and the status of stocks in those areas where this species is exploited most (e.g., Celtic Seas) need to be better assessed.
In 1999, the European Union (EU) introduced a 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 meters 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 not effectively constraining catches. Skate and ray TACs were established for other EU waters in 2009, including the Skagerrak and Kattegat (ICES Division IIIa) and from the northwest coast of Scotland and North Ireland to Portuguese waters (ICES Subareas VI-IX) and have also been gradually reduced since then. In 2013, the TAC for all skate and ray species grouped was 21,800 t (regulations are available online at http://faolex.fao.org).
Since 2008, the European Commission has obliged member states to provide species-specific landings data for the major North Sea species, including Cuckoo Skate, in order to improve understanding of skate stocks in the area (CEC 2008). In 2009, this obligation was extended to other ICES divisions, including the Celtic Seas (CEC 2009), and has been ongoing since 2008 (CEC 2013). EC Council Regulation 43/2012 that established a TAC of 4,222 t in 2012 for skates (all species in the family Rajidae) in ICES Subareas VIII and IX (Bay of Biscay and Iberian waters) also indicated that catches of Cuckoo Skate and Thornback Skate should be reported separately (ICES 2013).
Further research should be conducted on the population size and trend of the species.
|Citation:||Ellis, J., Dulvy, N. & Walls, R. 2015. Leucoraja naevus. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 03 September 2015.|
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