|Scientific Name:||Amblyraja radiata (Donovan, 1808)|
Raja radiata Donovan, 1808
|Taxonomic Source(s):||Eschmeyer, W.N. (ed.). 2015. Catalog of Fishes. Updated 5 March 2015. Available at: http://researcharchive.calacademy.org/research/ichthyology/catalog/fishcatmain.asp. (Accessed: 5 March 2015).|
|Taxonomic Notes:||McEachran and Dunne (1998) moved this species from genus Raja to Amblyraja.|
|Red List Category & Criteria:||Least Concern (Regional assessment) ver 3.1|
|Assessor(s):||Kulka, D.W., Sulikowski, J., Gedamke, J., Pasolini, P. & Endicott, M.|
|Contributor(s):||Ellis, J., Fordham, S., Walls, R. & Dolgov, A.|
|Facilitator/Compiler(s):||Walls, R., Dulvy, N. & Lawson, J.|
European regional assessment: Least Concern (LC)
Thorny Skate (Amblyraja radiata) is found in the Northeast Atlantic at depths of 18–1,400 m, but is most common from 27–439 m. This species is common in the northern region of the Northeast Atlantic. It is the most abundant skate in the central and northern North Sea, and showed a marked increase in abundance between 1970 and 1983 in the central North Sea and from 1982–1991 in English groundfish surveys. More recent surveys, from 1991–2011, indicated a decline in the North Sea, but this is believed to be due to a change in survey gear, rather than an actual change in abundance. This species is only occasionally landed as bycatch in southern and southeast North Sea demersal fisheries, and its distribution lies outside the main beam trawling areas in this region. It is also the most abundant skate species in the Barents Sea, where it is a common bycatch species of demersal fisheries. It reaches first maturity at a relatively small size (44 cm total length) and demographic modelling suggests it is less susceptible to fishing mortality in this region than larger skate species. For these reasons Thorny Skate is assessed as Least Concern in European waters.
In the Northeast Atlantic, this skate’s northern range extends to Svalbard, the Barents Sea, and off Greenland and Iceland (ICES 2013), and southwards to the Kattegat (Denmark), Ireland and the southern North Sea. It is found in abundance throughout the Norwegian Sea between latitudes of 62 and 72oN (Williams et al. 2008).
Some reports of this species are likely to be inaccurate, owing to confusion with Thornback Skate (Raja clavata). In particular, nominal reports of this species from the Faeroe Islands, English Channel (Martin et al. 2010) and Celtic Seas (Silva et al. 2012) are believed to be inaccurate.
Its depth range is 18-1,400 m.
Native:Belgium; Denmark; Faroe Islands; Iceland; Ireland; Netherlands; Norway; Svalbard and Jan Mayen; United Kingdom (Great Britain, Northern Ireland)
|FAO Marine Fishing Areas:|
Atlantic – northeast
Generally, this species is thought to be stable in European waters, although changes in trend are apparent. In the North Sea, which is the southern limit of this species’ range, long-term survey trends have shown an overall increase in abundance followed by a more recent decrease. The International Bottom Trawl Survey (IBTS, 1979–present) and survey data collected in Dutch coastal waters between 1951 and 1994 reported that this is the most abundant skate species over the wider North Sea, and has shown a marked increase in the central North Sea between 1970 and 1993 (Bergstad 1990, Heessen and Daan 1996, Walker and Heessen 1996). In research cruises carried out in the northeast North Sea and Skagerrak from 1984–1987 and 1995–1996 the species was caught in 269 of a total of 639 trawls (41%). More recent IBTS survey data from 1991–2011, showed a gradual decrease in the first quarter from almost eight individuals per hour effort in 2000, to approximately one individual per hour in 2011, representing a > 85% decrease, whereas the third quarter IBTS showed stable catch rates following a distinct peak of approximately 6.5 individuals per hour in 2001 (ICES 2012). This decline is believed to be a result of a change in survey gear (Ellis et al. 2005), rather than reflecting an actual change in abundance. Total biomass of this species in the North Sea has been estimated in the order of 100,000 tonnes (t) (Sparholt and Vinther 1991) but sampling effort was restricted by depth and area, omitting the deeper northeast part of the North Sea and the Skagerrak. While the overall North Sea stock is thought to be stable, there are concerns about confusing this species with Thornback Skate (ICES 2013).
In the Norwegian Sea, annual mean abundance of Thorny Skate has been stable (mean catch rates of about 55 individuals per km2) between 1994 and 2005 (Williams et al. 2008), but decreased in the Barents Sea from 1999–2012. The Barents Sea population was originally considered stable at current fishing levels (Drevetnyak et al. 2005), comprising > 90% of skate biomass caught across the Barents Sea (Dolgov et al. 2005, Byrkjedal and Høines 2007). However, from 1999-2012 mean catches of this species decreased in a Russian demersal trawl survey from 5.0–6.2 individuals per hour in 2001–2002 to 3.2–3.3 individuals per hour in 2011–2012, which represents a 42% decline in abundance over this decade. In the Norwegian Sea, trawl catch rates for this species were higher than trawl catch rates in the Barents Sea (61 kg per 100 trawl hours for the Norwegian Sea and 43 kg per 100 trawl hours for the Barents Sea), but lower for longline catches (119 kg per 10,000 hooks and 135 kg per 10,000 hooks, respectively; ICES 2012).
Scottish trawl surveys in the central and northern North Sea for the period 1929–1956 and 1981–1995 show that this species was caught throughout the two periods and increased in abundance between 1981 and 1995 with an unchanged length-frequency pattern over both periods (Greenstreet and Hall 1996, Walker and Hislop 1998). English groundfish surveys from 1982–1991 also showed a marked increase in catches (Ellis et al. 2005). In Iceland, this species has historically been discarded from a variety of fishing gears. A recent increase in landings, from nine tonnes in 1982 to 1,352 tonnes in 2011, suggests increased retention driven by local consumption (ICES 2012). It is estimated that the population is stable in European waters.
|Current Population Trend:||Stable|
|Habitat and Ecology:|
The depth range of Thorny Skate is approximately 18–1,400 m but it is most common at 27–439 m (McEachran and Musick 1975, McEachran 2002, Kulka and Miri 2003). It is found over a wide variety of bottom types from sand, gravel, broken shell and pebbles, to soft mud (McEachran 2002). Off the west coast of Norway, shallow areas are probably used as nurseries (Skjæraasen and Bergstad 2000) and the Barents Sea is a spawning ground (ICES 2006).
This egg laying skate may reproduce throughout the year (del Río and Junquera 2001, del Río 2002, Sulikowski et al. 2005a, b) and produces between 10–45 eggs (Templeman 1987, Walker 1998). Size at birth is 8–12 cm total length (TL; Berestovskii 1994, Walker 1998, Kulka and Miri 2003). In the North Sea, Skjæraasen and Bergstad (2000) reported a size at maturity of 44 cm total length (TL) for both males and females. Also in the North Sea, McCully et al. (2012) reported length at 50% maturity as 36.2 cm TL for males and 38.2 cm TL for females. The largest specimen of Thorny Skate reported by McCully et al. (2012) was 49 cm TL. Again, this is markedly smaller than the maximum size reported from the Norwegian Sea of 90 cm TL, and from the central North Sea of at least 60 cm TL (Walker 1998).
|Use and Trade:||In the northwest Atlantic, the wings of this species are exported to Europe for human consumption. In the northeast Atlantic, Thorny Skates are taken as incidental bycatch in trawl fisheries, but there (North Sea, Irish Sea, Barents Sea), the species is not considered as desirable and thus it is not targeted.|
This species is occasionally landed as bycatch in Northeast Atlantic demersal fisheries, but is likely less sensitive to exploitation in this region than other skates because of its small length at maturity. It is also distributed outside the major beam trawling areas in the southern and southeast North Sea (Walker and Heessen 1996). In the Barents Sea this skate was found to be the dominant skate species, comprising 90–95% of the total weight of skates caught in both survey and trawl fisheries bycatch data (Dolgov et al. 2005, ICES 2013). Relative catch per unit effort (CPUE) in this region indicates that biomass and abundance increased from 1997–2003 (Dolgov et al. 2005, ICES 2006), and remained almost unchanged from 1998–2001, suggesting stable stocks in this region (Dolgov et al. 2005, Drevetnyak et al. 2005, ICES 2006). In the Norwegian Sea, this species dominated catches (and presumably discards) from depth range of 60–400 m in 2008–2009 (Vollen 2010). These catches consisted of large individuals (36-55 cm TL) of both sexes, and were caught by Russian commercial bottom trawl and demersal longline fisheries (Vinnichenko et al. 2010). This species may be confused with Thornback Skate in some reports.
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 (International Council for the Exploration of the Sea [ICES] Division IIa) and North Sea (ICES sub-area 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 sub-areas VI−IX). These TACs have also been gradually reduced since then. In 2013, the TAC for all skate and ray species grouped was 21,800 tonnes (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 this species, 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).
Monitoring of the harvest trends is encouraged.
|Citation:||Kulka, D.W., Sulikowski, J., Gedamke, J., Pasolini, P. & Endicott, M. 2015. Amblyraja radiata. The IUCN Red List of Threatened Species 2015: e.T161542A48945123.Downloaded on 17 November 2017.|
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