The White Skate (Rostroraja alba) is a large skate (to 240 cm total length) with a temperate range along the Eastern Atlantic coast from the southern British Isles to South Africa, and in the southwest Indian Ocean, including Madagascar and the Seychelles archipelago. It also occurs throughout most of the Mediterranean. It is demersal on the continental shelf and slope at depths of 10–750 m. The White Skate's large size in combination with its life history parameters and population demography allow little capacity for it to withstand exploitation by fisheries. The species is incidentally caught mainly by multispecies trawl fisheries but also by multiple fishing gears including gillnet and set nets, which operate over the continental shelf and slope across its range. In the Mediterranean, available information indicates that the White Skate was captured frequently in the north-western Mediterranean during the 1960s and off Tunisia and Morocco in the early to mid-1970s, but is now regionally absent or rarely caught except for in the Balearic Islands where it shows signs of recovery following protection. The species has undergone a significant decline in both population size and extent of occurrence in the Mediterranean, and is inferred to have undergone a population reduction of 50–79% over the past three generation lengths (90 years) and is assessed as Endangered in the Mediterranean. Similar declines in geographical range have also occurred in the Northeast Atlantic, along with dramatic population reductions; severe declines are documented from both the Irish Sea and English Channel. It is suspected that similar population declines have occurred in the Bay of Biscay and Atlantic Iberian waters. Therefore, the White Skate is inferred to have undergone a population reduction of >80% over the past three generation lengths (90 years) and is assessed as Critically Endangered in the Northeast Atlantic. In the Eastern Central and Southeast Atlantic some fisheries catching sharks and rays have collapsed, there have been intense increases in fishing pressure, and documented declines of 75% in inshore demersal fisheries stocks. Based on this, it is suspected that the White Skate population has undergone a reduction of 50–79% over the past three generation lengths (90 years) and is assessed as Endangered in the Eastern Central and Southeast Atlantic. Overall, across all regions, the White Skate is suspected to have undergone a population reduction of 50–79% over the past three generation lengths (90 years) based on suspected regional and local extinctions due to levels of exploitation and habitat degradation, and a decline in its extent of occurrence, and it is assessed as Endangered A2cd.

The White Skate occurs along the Eastern Atlantic Ocean, from the western and southern coasts of the British Isles south to South Africa it extends to the southwestern parts of the Indian Ocean, including Madagascar and the Seychelles archipelago (Last et al. 2016, Fricke et al. 2018). It occurs throughout the Mediterranean Sea, except from some restricted areas such as Lebanon, as well as the Black Sea (Serena et al. 2020, Ebert and Dando 2021, Giovos et al. 2021a, M. Lteif pers. comm. August 2022). Its presence in Indian waters is questionable (Akhilesh et al. 2014) and no validated records exist in the northern Northeast Atlantic Ocean.

Limited quantitative data are available on the population size and trend of the White Skate over much of its range.

Northeast Atlantic: the available data suggests that this species has undergone a significant reduction in abundance and is now considered rare in the Northeast Atlantic. The species was common in historical trawl surveys in the late 1800s, with rays, including this species, accounting for up to a quarter of the catch until the 1920s. However, by the 1990s rays accounted for less than 0.5% of the catch and the species is now only reported infrequently, indicating that the population has markedly declined (Moreau 1881, Quéro and Cendrero 1996, Dulvy et al. 2000, Rogers and Ellis 2000, ICES 2021). Targeted fisheries for White Skate, in the English Channel and off Brittany collapsed over the past 100 years with declines also documented from both the Irish Sea and English Channel (Brander 1981, Dulvy et al. 2002, Ellis et al. 2010, ICES 2021). White Skate were considered relatively frequent in recreational fisheries on the west coast of the Ireland in the 1980s (Quigley 1984), but the population has declined to a level where only two locations have yielded confirmed reports of this species from 2005–2014 (Clarke et al. 2016). Considering the comparison of historical data with the widespread contemporary absence from many recent data sources, ICES considers White Skate to be depleted and near-extinct from various parts of the Celtic Sea and Biscay-Iberian ecoregions (ICES 2021). Overall, the White Skate is inferred to have undergone a population decline of >80% over the past three generation lengths (90 years) and it is assessed as Critically Endangered in the Northeast Atlantic.

Mediterranean: historically, White Skate was captured frequently in different parts of the Mediterranean (Serena et al. 2020). Much of the currently available data comes from the MEDIterranean Trawl Survey (MEDITS) project, which has operated since 1994. This survey covers all European Mediterranean coasts from southern Spain in the west to the Aegean Sea in the eastern Mediterranean, and involves ten nations (France, Greece, Italy, Spain, Slovenia, Croatia, Albania, Malta, Montenegro, and Cyprus). Some sampling is also carried out in non-European waters (Morocco), with the survey coordinated in the frame of the FAO regional projects (e.g., AdriaMed, CopeMed, etc.; Spedicato et al. 2019). Overall, the MEDITS covers 543,000 km² with, on average, about 1,300 sampling stations per year (Bertrand et al. 2000). In almost 30 years of MEDITS trawl surveys from 1994–2021, only 77 White Skate specimens in total were recorded (excluding the Balearic Islands; see below) (F. Serena unpub. data 2023). Most of the specimens came from the continental shelf of the western-central Mediterranean (FAO-GSA 5 and 16; 50 individuals in total) and the Aegean Sea (GSA 22; 11 individuals). The remaining 16 individuals were from the wider survey area (GSAs 1,8,9,15,17,18 and 25).

North-western Mediterranean (Balearic Islands, Spain): in the Balearic Islands, the White Skate is showing signs of recovery. Serrat et al. (2022) indicated there has been an increase in the species area of distribution and abundance since 2002, and in the proportion of mature individuals since 2006 (based on data from the MEDITS surveys). Landings data from Majorca in 2009 resulted in ~100 individuals captured around the island (Morey and Navarro 2010). Moreover, the White Skate is very abundant off the southernmost islands of the archipelago, where a targeted fishery existed until 2015, when the species became legally protected in Spanish Mediterranean waters. Preliminary monitoring of that fishery in 2010 showed a mean catch-per-unit-effort of 0.9 individuals/100 of trammel net (range: 0.3–3.3), with a mean total length (TL) of 131 cm (range: 67–171 cm), including adult females carrying near-term eggcases (G. Morey pers.comm. 2010). No further monitoring of that small-scale fishery has been conducted but many interviews with fishers suggests that the species is very abundant, which is perceived as a problem due to competence as a top predator. This abundance seems to be confirmed by very recent observations (10 individuals caught in a single trammel net 500 m long; i.e., 2 individuals/100 m; G. Morey, pers. obs. 2023). Finally, there are some other locations where the species is regularly caught along the Balearic Islands (G. Morley pers. comm. 2023).

North-western Mediterranean: the White Skate was relatively frequent in the commercial demersal trawl catches in the North-western Mediterranean (1965), French coast (1950 to 1960s), and Italian seas (1972) (Capapé 1976, Serena et al. 2010). However, a time-series of comparative trawl surveys from 1957–1995 in the Gulf of Lions (Western basin of the Mediterranean) did not show any catch of White Skate (Aldebert 1997). The surveys analysed consisted of eight separate cruises, conducted by four survey vessels. A total of 1,359 tows were conducted on both shelf and slope areas extending from the coastal area to 800 m depth (thus covering the known depth range of the species). More recent data from the MEDITS programme suggests White Skate is now rare in most of the north-western Mediterranean (with the exception of the Balearic Islands). In particular, from the surveys carried out in the past in the Gulf of Lions, the contemporary occurrence of White Skate along the French coast was in doubt, with Aldebert (1997) reporting it to be absent from the Gulf of Lions. The French element of the MEDITS collected some seven specimens in GSA 8, but all from the eastern area of Corsica (Tyrrhenian Sea), a site with limited trawling, it is noted that some problems of species misidentification may have occurred. From other research programs collecting data from commercial landings, two specimens of White Skate were recorded from bottom trawlers from Livorno in 2003 (Serena et al. 2010).

North-eastern and Central Mediterranean: at the end of 1950s, White Skate was considered common in the Adriatic Sea (eastern Mediterranean), and was captured frequently (Fortibuoni 2009). The limit of its eastern distribution is reported as the Turkish coasts, in particular Iskenderun Bay (Bi̇lecenoğlu et al. 2014), but excluding Lebanese waters (M. Lteif pers. comm. August 2022). In the Adriatic Sea, early trawl surveys indicated that White Skate was considered to be captured relatively frequently (given the more limited fishing effort at that time) as it occurred in 4% of the hauls of the "Hvar" 1948 survey (based on 138 valid hauls with bottom trawl at depths down to 400 m). Two subsequent survey series have provided more contemporary data for the Adriatic Sea. The first one being the trawl surveys carried out by the Italian Group for Demersal Resource Evaluation (GRUND) that began in 1982 (Relini 2000), and the second one being the ongoing international MEDITS programme, that began in 1994 (Bertrand et al. 2000). White Skate was captured sporadically in both surveys, typically in <2.6% of the hauls in any year (Baino et al. 2001). During the GRUND surveys, White Skate was captured in approximately 1.7% of hauls in the central, northern, and southern Adriatic Sea (Marano et al. 2003). Further south, a single White Skate individual was reported in 1997 from the North-western Ionian Sea (Sion et al. 2003). The species is still present in the Aegean Sea though it is rare (Damalas and Vassilopoulou 2011, Giovos et al. 2021b).

Southern Mediterranean: historically, White Skate was captured frequently along the northern coast of Africa, including off Tunisia in the mid-1970s and the coast of Morocco in the early 1970s (Capapé 1976). Whilst White Skate was caught regularly in Tunisian fisheries, especially in the northern area (Capapé 1976), captures of this species are now rare along the whole Tunisian coast (Bradai 2000).

Across the entire Mediterranean, the White Skate has undergone significant population reduction and reduction in extent of occurrence, except for in the Balearic Islands where it showing signs of recovery following protection. Thus, it is inferred to have undergone a population reduction of 50–79% over the past three generation lengths (90 years), and it is assessed as Endangered in the Mediterranean.

Eastern Central and Southeast Atlantic: in South Africa, species-specific population trend data are available from National Research Survey of biomass over 29 years (1991–2019) (C. da Silva unpubl. data 2023). 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 generation lengths (see the Supplementary Information). The trend analysis revealed an annual rate of decrease of 0.11% with the highest probability of a <30% reduction over three generation lengths (90 years); Least Concern obtained the highest probability (42%) but as it is less than 50%, the Near Threatened category was assigned as the most likely status. This probability is over a very long period of three generations (90 years); it has incorporated the relatively stable but slightly declining annual trend from one generation length of data and projected an estimated trend based on those reductions for a considerable period beyond that of the time-series and thus indicates a trend of decline over the long time frame of 90 years rather than stability. In South Africa, there was a temporal decline in relative contribution of this species to catches of recreational shore anglers in False Bay (Best et al. 2013). However, this may be due to distributional shifts linked to climate change, habitat destruction, fishing or a combination thereof shown for other demersal species such as the Biscuit Skate (Raja straeleni) and Slime Skate (Dipturus pullopunctatus) (Currie et al. 2020). Although population trend data from Eastern Central and Southeast Atlantic are lacking from elsewhere, the threats in those regions are significant, with the collapse of some fisheries catching sharks and rays, intense increases in fishing pressure, and documented declines of 7% over the past 40 years in total demersal biomass of inshore stocks. Therefore, it is suspected that the White Skate has undergone a population reduction of 50–79% over the past three generation lengths (90 years) and is assessed as Endangered in the Eastern Central and Southeast Atlantic.

Across all regions, it is assumed that the current spatial distribution of White Skate now represents only a small fraction of its former range. It can be inferred that this species, especially in the Northeast Atlantic and Northwestern Mediterranean, has undergone a substantial decline in abundance and geographic extent, except for in the Balearic Islands where there are signs of recovery following protection. White Skate was a regionally important commercial species in the past (e.g., English Channel and off Brittany), but is now scarce. Due to its size and morphology, White Skate is susceptible to capture in a range of demersal fisheries, and with a late age-at-maturity and an estimated longevity of 35 years, recovery is expected to be slow. For these reasons, it is thought to no longer occur in large areas of former range (or reduced to such a low population size that surveys have a very low probability of capture). White Skate is now absent in the captures of many research surveys undertaken in parts of its former range and very rare in commercial catches (ICES 2021). Overall, the White Skate is suspected to have undergone a population reduction of 50–79% over the past three generation lengths (90 years) due to suspected regional and local extinctions due to levels of exploitation and habitat degradation, and a decline in its extent of occurrence.

The White Skate is demersal on the continental shelf and slope at depths of 10–750 m (Weigmann 2016, Ebert and Dando 2021). It occurs on sandy and muddy substrates and in some areas, close to rocky areas (Du Buit 1974, Serena et al. 2010, Last et al. 2016). Size parameters vary regionally with larger sizes in South Africa than the Mediterranean. In South Africa, maximum size is 240 cm total length (TL) and males mature at 152–170 cm TL and females mature at 195 cm TL (Last et al. 2016). In the Mediterranean, maximum size is 200 cm TL and males mature at 75–119 cm TL and females mature at 80–129 cm TL (Capapé 1976, Yıgın and Ismen 2010, Kadri et al. 2014). Reproduction is oviparous with litter sizes of 55–158 egg cases, an incubation period of approximately 15 months, and size-at-birth of 25–30 cm TL (Stehmann and Burkel 1984, Bor 2002, Serena 2005, Kadri et al. 2014, Ebert and Dando 2021, Mancusi et al. 2021, Marongiu et al. 2021). In the Mediterranean, male age-at-maturity is estimated as 20 years, female age-at-maturity is estimated as 24 years, and maximum age estimated as 35 years (Kadri et al. 2014). Generation length is therefore 30 years.

The White Skate is subject to fishing pressure across its range. It was historically targeted in some regions and is currently taken incidentally in industrial and artisanal fisheries with mainly trawl and also multiple fishing gears including gillnet and set nets.

Northeast Atlantic: skates form an important component of demersal fisheries in the Northeast Atlantic (Holden 1977) and the White Skate would be landed and sold if caught. The species would have traditionally been landed and marketed in mixed demersal fisheries and fisheries targeting the skate assemblage. Historically, fisheries targeting White Skate existed in some areas, although these fisheries ceased after localised depletion of the species. Such targeted fisheries, including those using demersal longline, occurred in the English Channel and off Douarnanez (Brittany) (Rogers and Ellis 2000, Ellis et al. 2010, ICES 2021). White Skate will still be caught in a range of demersal fisheries that operate over its bathymetric and geographical range, such as off the Iberian Peninsula. Since 2009, White Skate should be discarded as European Union, and United Kingdom, fishing regulations require that this species cannot be fished for, retained or landed. The survival rate of discarded White Skate is unknown.

Mediterranean: the White Skate is incidentally caught in multi-species trawl fisheries operating within its range. The fishing effort has progressively increased from the post-war period until today, in particular on the shelf and slope area of the Mediterranean. This increase in effort is despite decreases of 46% in the number of trawlers over the same period (Cataudella and Spagnolo 2011). Ferretti et al. (2013) analysed trawl surveys by various research programs carried out in the area over the last six decades, and detected a structurally depleted elasmobranch community reporting that as many as 11 species disappeared from the historical list with a possible extinction in the area. Aldebert (1997) reports a similar situation for the Gulf of Lions where initially the area was exploited by small-scale demersal trawl fisheries. Since then, effort increased to a high total nominal horsepower causing decrease in abundance of many elasmobranch species The degree of compliance with the European Union measure of non-retention since 2009 across the Mediterranean is uncertain, especially as many active fishers may not be familiar with the species, given its rarity.

Eastern Central and Southeast Atlantic: the White Skate is likely taken as bycatch in industrial and artisanal fisheries with mainly trawl, and multiple fishing gears including gillnet, set nets, tangle nets, and trammel nets. Information on discards and associated mortality is not available. Sharks and rays have been exploited in this region by semi-industrial fisheries since the 1950s (Walker et al. 2005). While these fisheries gradually collapsed, the demand for dried salted shark meat (for export to Ghana) and shark fins in the 1980s drove the development of artisanal targeted shark fishing across much of the region (Diop and Dossa 2011, CCLME 2016, Seto et al. 2017, Moore et al. 2019). 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 most of the range of this species. In West Africa, reports indicate that the diversity and average body size of many commercial demersal and pelagic fishery species have markedly declined with many stocks now considered to be overexploited (CCLME 2016, Polidoro et al. 2016). In Mauritania, the total demersal biomass of inshore stocks is estimated to have declined by 75% since 1982 (Meissa and Gascuel 2015). The direct cause of decline for many of these stocks has been attributed to overcapacity within both the industrial and artisanal fisheries in addition to destructive fishing practices (GCLME 2006, CCLME 2016). Overall, between 1950–2010, the total artisanal fishing effort increased by 10-fold with an estimated 252,000 unregulated artisanal and 3,300 industrial vessels operating in this region by 2010 (mostly distant water fleets from Europe and East Asia operating under ‘access agreements’ that take sharks and rays as bycatch) (Walker et al. 2005, Diop and Dossa 2011, Belhabib et al. 2018). In South Africa, White skate is caught incidentally in the demersal trawl hake and monkfish fisheries (da Silva et al. 2015). Landings of White Skate have been estimated to be 11–100 tons per annum; White Skate catches are aggregated with other skates and landings are estimated with the use of National Research survey data (da Silva et al. 2015).

Mixed fishery bilateral agreements between the European Union and the West African nations (Sustainable Fisheries Partnership Agreements, SFPAs) involve payments to third party countries in exchange for access to marine resources and sectorial support aimed at promoting sustainable fisheries development in the partner countries (European Commission 2023). Under SFPAs, there are a number of European distant-water industrial vessels using demersal trawls to capture deep-water shrimps at depths of 400–950 m in Mauritania and 150–850 m in Guinea-Bissau (Sobrino et al. 2017, Fernandez Peralta et al. 2019). In Mauritania, there are demersal trawl fisheries for black hake (Merluccius senegalensis and M. polli) that operate mainly at depths 500–700 m (Fernandez Peralta et al. 2019). In these trawl fisheries, unidentified deep-water sharks and rays have accounted for approximately 10% of landings (Fernandez Peralta et al. 2019), but further information on bycatch species in these fisheries is largely unknown.

Destructive fishing practices including intensive inshore and offshore trawling with increasing incursions into coastal areas, the use of explosives and chemicals in inshore areas, and the use of small-sized beach and purse seine nets in both nearshore and offshore regions, have contributed to depleted fish stocks across the Eastern Central Atlantic region and which covers most the species' range (GCLME 2006, Gascuel et al. 2007). China’s West African fleet has rapidly increased in recent years with an estimated 518 vessels (82% of them trawlers) currently operating in the Eastern Central Atlantic (mostly between Morocco and Gabon; Gutiérrez et al. 2020). This region also has some of the highest levels of Illegal, Unreported, and Unregulated (IUU) fishing in the world and it is estimated that illegal catches exceed more than 40% of the reported legal catch (Pauly and Zeller 2016, Welch et al. 2022). Indirect and sublethal sources of mortality include habitat destruction and degradation, and pollution (e.g., heavy metals).

The species is retained for its meat that is marketed in Europe. While there is no species-specific information available in West Africa, the meat of skates is consumed fresh across many coastal communities in the region as an important source of protein. It is also dried or dried and smoked and exported across West Africa to supply countries such as Ghana, Guinea, Nigeria, Mali, and Burkina Faso (P. Doherty, R.W. Jabado, I. Seidu, and A.B. Williams pers. comm. 2020). In South Africa, the White Skate meat is exported to Spain, the Republic of Korea, Australia, France, and Portugal (Louw and Burgener 2022) with a small amount consumed locally.

Northeast Atlantic: White Skate is a protected species in United Kingdom (UK) territorial waters, through listing in the Wildlife and Countryside Act. Under European Union (EU) (and UK) fishing regulations, White Skate is a prohibited species that cannot be fished for, retained, landed or sold. Such measures have been in place since 2009, with this now enacted through Article 10(2) and Annex I of Regulation (EU) 2019/1241. Consequently, it is prohibited for fishing vessels to “fish for, retain on board, tranship, land, store, sell, display or offer for sale”. The White Skate in ICES Areas 6-10, and specimens of White Skate “shall not be harmed and specimens shall be promptly released back into the sea”. The White Skate is included in OSPAR Recommendation 2010/6 to further the protection and restoration of the species in the OSPAR maritime area which includes recommendations for national protection legislation conservation measures in key areas for the species, and promotion for inclusion of the species as a protected species in Europe and international biodiversity conventions. ICES (2019) advised that there should be zero catches in each of the years 2020–2023 based on a precautionary approach.

Mediterranean: the White Skate was legally protected in Spanish Mediterranean waters in 2015. For the conservation of chondrichthyans within the Mediterranean region, the FAO SAC Subcommittee on the Environment and Ecosystem (2002) recommended that all fishing states implement a Mediterranean Action Plan for the Management and Conservation of chondrichthyans, in line with IPOA sharks (International Plan of Action on the management and conservation of chondrichthyans). White Skate is listed in Appendix III of the Bern Convention (Convention on the Conservation of European Wildlife and Natural Habitats); this Appendix III requires "regulation of species populations to keep them out of danger". The Bern Convention encourages research programs aimed at the assessment of the conservation status of chondrichthyans in the Mediterranean Sea. In this sense, the monitoring programs are very important tools to reach this goal such as the GFCM Data Collection. In particular, MEDLEM project adopted at the FAO-SAC meeting in 2005, evaluates the large elasmobranchs as bycatch within the Mediterranean and Black Sea (Mancusi et al. 2020, Carpentieri et al. 2021). The White Skate is also listed under the Barcelona Convention for the Protection of the Mediterranean Sea, this Convention concerns specially protected areas and biological diversity within the Mediterranean Sea. It lists White Skate in Annex II (List of endangered or threatened species) whose fishing is forbidden in the Mediterranean and the Black Sea and the reporting of any incidental catch to the GFCM is mandatory. In fact, this species is also considered in the Recommendations GFCM/36/2012/3 and GFCM/42/2018/2.

Eastern Central and Southeast Atlantic: there are no known conservation measures in place for this species. In South Africa, one of the major goals within the newly released National Plan of Action Sharks South Africa II (2022) is to improve species level reporting in all fisheries, this will be achieved through the release of identification guides (Cliff et al. 2022) and improved observer effort on various levels. Although countries across the species range have legislation concerning fisheries activities (including gear restrictions, and no-trawling zones in coastal waters), fisheries taking the White Skate are generally unmanaged, and it is unlikely that pressure will decrease in the near future. A number of countries have either adopted a Regional Plan of Action for the Conservation of Sharks (Sub-Regional Fisheries Commission countries from Mauritania to Sierra Leone, including Cape Verde) or are currently working on developing a National Plan of Action to conserve sharks and rays and manage their fisheries for sustainability under the Food and Agriculture Organization of the United Nations (FAO) International Plan of Action for the Conservation and Management of Sharks (IPOA). However, progress towards the implementation of these actions have stalled since 2011 due to lack of funding and support (M. Diop pers.comm. 2020). The Regional Marine Protected Areas Network in West Africa (RAMPAO) was set up in 2007 across six countries (Mauritania to Sierra Leone) to conserve representative samples of critical habitats and protect threatened species but many of these protected areas lack capacity, funding, infrastructure, and governance for effective enforcement and conservation (Polidoro et al. 2016). Therefore, it is unlikely that they provide a refuge for this species.

To conserve the population and to permit recovery, a suite of measures will be required which may include species protection, spatial management, bycatch mitigation, and harvest and trade management measures (including international trade measures). Effective enforcement of measures will require ongoing training and capacity-building (including in the area of species identification). Catch monitoring is needed to help understand population trends and inform management.