The Thornback Skate has been confused with the related Biscuit Skate (Raja straeleni) in overlapping parts of their range (Heemstra et al. 2022). Further studies are needed to delineate the geographic range of both species.

The Thornback Skate (Raja clavata) is a medium-sized (generally up to 115 cm total length, but with occasional larger individuals to 130 cm) skate found in the Northeast Atlantic, and Eastern Central Atlantic, from Iceland and Norway to Northwest Africa, including the Azores, Mediterranean Sea, and Black Sea. The species is also reported from the Southeast Atlantic and Southwest Indian Oceans (including South Africa, Madagascar, and Mauritius), although taxonomic confusion with the Biscuit Skate (Raja straeleni) requires additional studies to better delineate its geographic range along the coast of Africa. Thornback Skate occurs on the continental shelf and slope at depths from 5–1,020 m, but is most common on the continental shelf from close to the shore to <300 m depth. The Thornback Skate is an important commercial species across its range, and is taken as targeted catch and retained as bycatch in demersal trawl, set net (gillnet and trammel), and longline fisheries. Since the implementation of catch quotas in European Union (and United Kingdom) Atlantic waters in 2009, the Thornback Skate appears to be increasing in the Northeast Atlantic. There are contrasting population trends in the Mediterranean Sea, with some regions showing signs of increase in abundance and other regions showing declining trends in abundance. Elsewhere, there are few data available. However, in the Eastern Central Atlantic, sharks and rays have been exploited by semi-industrial fisheries since the 1950s. Over the years, targeted shark and ray fisheries have expanded across many countries in this region, and are likely increasing fishing pressure on this species. There is high distribution overlap with intensive fishing pressure, reported declines in part of its range but increasing trends in others, and a lack of species-specific management across most of its range. The Thornback Skate is inferred to have undergone a population reduction of 20–29% over the past three generations (33 years) based on abundance data and actual levels of exploitation, and it is assessed as Near Threatened (close to meeting Vulnerable A2bd).

The Thornback Skate is found in the Northeast Atlantic and northern part of the Eastern Central Atlantic, from Iceland and Norway to Northwest Africa, including the Azores, Mediterranean Sea, and Black Sea (Last et al. 2016, Ebert and Dando 2021). The species is also reported from the Southeast Atlantic and Southwest Indian Oceans (including South Africa, Madagascar, and Mauritius, Last et al. 2016). The Thornback Skate, has been confused with Biscuit Skate (Raja straeleni, Heemstra et al. 2022) and more detailed studies of its distribution along the western coast of Africa are required to better delineate its geographic range, and its southernmost limits.

There are no data available on the absolute global population size of the Thornback Skate. Genetic results suggest there are strong regional differences between the Mediterranean basin, the Azores, and the European continental shelf (Chevolot et al. 2006). In the Mediterranean Sea, the eastern Mediterranean and Adriatic appear to be a distinct population from the western Mediterranean, with further subdivision in this region (Melis et al. 2023).

Population trend data are available from two sources: (1) the Northeast Atlantic (Marandel et al. 2019, Santos et al. 2020, ICES unpub. data); and (2) Mediterranean Sea (MEDITS unpub. data). The trend data from each source were analysed over three generation lengths using a Bayesian state-space framework (a modification of Sherley et al. 2020, Winker et al. 2020). This analysis yields an annual rate of change, a median change over three generation lengths, and the probability of the most likely IUCN Red List category percent change over three generations (see the Supplementary Information).

Within the Northeast Atlantic, the International Council for the Exploration of the Sea (ICES) provide advice for stocks of Thornback Skate in the following areas: (1) North Sea and eastern Channel, (2) Western Channel (3) North-west Scotland, (4) Irish Sea and Bristol Channel, (5) Bay of Biscay, (6) Cantabrian Sea, and (7) Iberian waters of Division 9.a. With the exception of the Western Channel, all stocks have accepted assessments undertaken using one or more survey indices. The longest running surveys encompass three generations (ca 30-years) while the short running survey index considered is 13-years. All of the combined normalised or individual surveys used in the ICES assessments show an increasing trend across the time series, although noting that some of these started from a low level (Marandel et al. 2019, ICES 2021). It should be noted that some surveys use data for only the ‘exploitable biomass’ (>50 cm total length, TL), which is below length at maturity. Therefore, these biomass trends are not fully representative of the adult population and should be viewed with caution. The trend analysis of the North Atlantic modelled biomass for 1950–2021 (71 years) revealed annual rates of increase of 0.66%, with the highest probability of no major reductions in population over the past three generation lengths (33 years).

In the Mediterranean Sea, data are collected during the MEDiterranean International Trawl Survey (MEDITS) and these data have generally been analysed and reported in a range of publications with differing spatial and temporal scales. Population trends appear to differ across the region. Population abundance for Thornback Skate have shown increasing trends around the Balearic Islands (1994–2015) and in the South Ligurian and North Tyrrhenian Seas (1994–2004) (Serena et al. 2005, Ramírez-Amaro et al. 2020), while catch rates in the Adriatic Sea (1996–2006) suggested declining trends and a pronounced change in the distribution and abundance compared to an earlier expedition in 1948–1949 (Krstulović Šifner et al. 2009). In the Aegean Sea, catch rates showed a declining abundance trend from 1998 to 2004, with a subsequent increase after 2004, though the catch rates at the end of the time-series analysed had not reached the levels observed at the start of the time-series (Maravelias et al. 2012). The species is still the most common Rajidae reported in landings in terms of volume (Giovos et al. 2021). The trend analysis of the Mediterranean Sea modelled biomass for 1994–2021 (27 years) revealed annual rates of increase of 1.98%, with the highest probability of no major reductions in population over the past three generation lengths (33 years).

The Thornback Skate is the only member of the order Rajiformes that occurs in the Black Sea (Yankova et al. 2014), and so landings data for Thornback Skate and Rajiformes from the Black Sea, as collated by FAO (1970–2020) were considered. By decade, mean annual reported landings were 1,589 t (1970–1979), increased to 2,128 t (1980–1989), and then declined to 640 t (1990–1999), 418 t (2000–2009), and 164 t (2010–2020). This would equate to a population reduction of 88% over the past three generation lengths (33 years). While reported landings may not be indicative of populations trends, the regional stock assessments present signs of overexploitation of various species, including reduced fish size, localized extinctions, and catch-per-unit-effort (CPUE) of important commercial stocks declining by more than 90% between 1967 and 2016 (Ulman et al. 2020). Consequently, it is likely that the Thornback Skate has experienced population decline in the Black Sea.

In the Eastern Central Atlantic, both overall catch and effort have continued to rise in the major shark and ray fishing countries, including Mauritania, Nigeria, and Ghana. Across West Africa, total artisanal fishing effort increased 10-fold between 1950–2010, while the CPUE of artisanal and industrial vessels declined by 34% over this period (Belhabib et al. 2018). Many regional fisheries are now characterised by severe overexploitation and declines in abundance of marine resources (e.g., Gascuel et al. 2007). Trawl surveys carried out across the Gulf of Guinea from 1977 to 2000 showed a decline in fish biomass of approximately 50% (Brashares et al. 2004). Further, the total demersal biomass of inshore stocks is estimated to have declined by 75% since 1982 (Meissa and Gascuel 2015). While these levels of declines are not species-specific, they are informative for understanding the broader levels of decline in sharks in the region. In Mauritania, landings of all skates (family Rajidae) from the Spanish trawl fishery for Black Hake (Merluccius senegalensis and M. polli) operating in depths of 140–750 m fell from 18 t in 1992 to 9 t in 2001 (Fernández et al. 2005). This would equate to a population reduction of more than 99% over the past three generation lengths (33 years) at fishing locations. However, it is important to note that these declines could be attributed to changes in the fishing fleet, economics, and likely overexploitation of both the target and bycatch species (Fernández et al. 2005).

Due to estimated and suspected declines in part of its range (parts of the Mediterranean Sea, Black Sea and Eastern Central Atlantic) but increasing trends in others, and high levels of exploitation, a global population reduction of 20–29% was inferred over three generation lengths (33 years) based on abundance data and actual levels of exploitation. Therefore, the Thornback Skate is assessed as Near Threatened (close to meeting Vulnerable A2bd).

The Thornback Skate is demersal on the continental shelf and slope depths from 5–1,020 m, though mostly occurs at depths of less than 300 m in at least European waters (Last et al. 2016, Ebert and Dando 2021). It reaches a maximum size of ~130 cm total length (TL), but generally only attains about 115 cm TL. Male maturity occurs at 60–77 cm TL and female maturity occurs at 60–85 cm TL and at 5–8 years of age. Reproduction is oviparous. Accurate fecundity estimates are lacking, but it is thought to be in the range of 48–160 eggs per year (Ellis and Shackley 1995, Ellis et al. 2015). Size-at-hatching is ~10–13 cm TL (Last et al. 2016). Female age-at-maturity is 7 years and maximum age is 15 (Walker et al. 1999, Kadri et al. 2014). This results in a generation length of 11 years.

The Thornback Skate is an important commercial species, particularly in inshore fisheries operating in the Celtic Seas (Irish Sea and Bristol Channel), English Channel, southern North Sea, Bay of Biscay and Iberian waters. It is taken in target fisheries, fisheries targeting the wider skate complex and as a marketable bycatch in mixed demersal fisheries, being caught by demersal trawl, set net (gillnet and trammel), and longlines (ICES 2023). In the Northeast Atlantic, skates have been landed since the 1800s, and became increasingly marketable by the late 1800s/early 1900s (Ellis et al. 2010). Fisheries were largely unregulated, and fishing quotas for skates in the North Sea were only introduced in 1999, and further applied to all vessels operating in European Union Atlantic waters in 2009 (EC 1999, 2009, 2024). Earlier management efforts treated skates as one skate complex, and species-specific measures were only first introduced in 2007 (Ellis et al. 2010). Long-term extensive and intensive fishing pressure has led to documented population reductions, localized extinctions, and widespread changes to the shark and ray community structure across the range of the Thornback Skate in the Northeast Atlantic (Dulvy and Reynolds 2002, Marandel et al. 2019). The effects of fishing have been greatest on large-bodied species (Dulvy et al. 2000, Ellis et al. 2010). The sensitive life histories of these species meant that they could not withstand the pressure of overexploitation and large-bodied skate species were replaced in the marine environment by more productive, small-bodied species like the Thornback Skate (Ellis et al. 2010). The Thornback Skate is now amongst the most abundant skate species reported in regional research surveys (ICES 2023).

In the Mediterranean and Black Sea, the Thornback Skate has been subject to extensive and intensive fishing across much of the species' known depth and spatial distribution. The Thornback Skate is the most widespread and landed skate species in the Mediterranean Basin and is caught with demersal trawl, trammel net, and longline gear (Carbonara et al. 2020, Ferragut-Perello et al. 2023). Across the Mediterranean Basin and the Black Sea, the Thornback Skate has been found to have low genetic diversity, with lowest diversity in the Black Sea, suggesting that the species has undergone high fishing exploitation and population reduction over past decades (Chevolot et al. 2006, Ferragut-Perello et al. 2023). Large sized Thornback Skates captured in demersal trawl fisheries in the Black Sea are often retained while smaller individuals are discarded (Yildiz and Karakulak 2017). Post-release mortality estimates for Thornback Skate are variable but suggest the species has relatively high release survival (Ellis et al. 2017, ICES 2023).

There is little information available for the Thornback Skate across the remainder of its range. However, in the Eastern Central Atlantic, sharks and rays have been exploited by semi-industrial fisheries since in the 1950s (Walker et al. 2005). Over the years, this has expanded into targeted shark and ray fisheries across many countries and is likely increasing fishing pressure on this species (Walker et al. 2005, Diop and Dossa 2011). In general, fishing effort and the number of fishers has intensified in recent decades across the range of this species. Reports indicate that the diversity and average body size of many important commercial coastal, demersal, and pelagic fishery species have markedly declined with many stocks now considered to be overexploited (CCLME 2016, Polidoro et al. 2017). The direct cause of decline for many of these stocks has been attributed to overcapacity within both the industrial and artisanal fisheries and destructive fishing practices (GCLME 2006, CCLME 2016).

Climate change may influence the distributions of various European fish populations, including the Thornback Skate, in a manner that may influence the assessment of population trends and the potential viability of subpopulations (Simpson et al. 2011, Sguotti et al. 2016). Analyses of the Northeast Atlantic International Council for the Exploration of the Sea (ICES) research trawls over 24 years (1997–2020) revealed that the habitat suitability has been altered by ongoing climate change for Thornback Skate. Currently, the suitable habitat increases at an annual rate of 1,886 km² in the Western Channel and the southern and eastern North Sea, extending northwards (Coulon et al. 2024).

The Thornback Skate is utilized for its meat and is commercially valued for its wings. In some of its Northeast Atlantic distribution, it is one of the most commercially important shark and ray species (ICES 2021). Products of the Thornback Skate may be marketed under a generic "ray" or "skate" label or mislabelled as a different species, and in Greece, the species is commonly sold as angel shark wings (Griffiths et al. 2013, Giovos et al. 2020, Giagkazoglou et al. 2022). Unmarketable parts of the ray may be used to supply bait for pot fisheries (Bullimore et al. 2001).

The species is likely to be used across the remainder of its range where retention is allowed or unregulated. Skate meat is consumed across West Africa where it may also be dried, or dried and smoked and exported across West Africa to supply countries such as Guinea, Ghana, Nigeria, Mali, and Burkina Faso (e.g., Jabado et al. 2021).

Within the Skagerrak and Kattegat (ICES Division 3.a), the Thornback Skate is listed as Prohibited Species on European Union (EU) fisheries regulations (EC 2024). It is prohibited for EU vessels to target, retain, tranship, or land the species, and it is recommended that fishers use handling practices that encourage rapid and safe release (ICES 2023). Elsewhere in the EU and United Kingdom waters of the ICES area, the exploitation of Thornback Skate is managed largely through catch quotas for skates and rays (Rajiformes). There are some local and national management measures in place across the species range. For example, there is a minimum conservation reference size (or minimum landing size) of either 40 cm or 45 cm (disc width) for skates and rays caught in the inshore waters of parts of the coasts of England and Wales. In Portugal, there is a limit on landing skates (Rajidae) in the nominal May-June spawning period, whereby skates and rays should not be landed (except where skate and ray landings are less than 5% of the landings). Portugal also has a minimum landing size (52 cm total length) for all Raja spp. Potential nursery areas for the Thornback Skate have been identified in Shetland, eastern and western Irish Sea, Cardigan Bay, Bristol Channel, and Greater Thames Estuary (Ellis et al. 2012, McAllister et al. 2023). Further information is required on its distribution, ecology and life history, as well as interactions with fisheries across its distribution around Africa.