Dipturus nidarosiensis may be a composite species with a small and large morphotype similar to that seen in Dipturus batis-complex (Iglésias et al. 2010) and Dipturus oxyrinchus-complex. Taxonomic resolution and further genetic research is recommended to comprehensively understand the presence of Dipturus nidarosiensis across its distribution (Ebert and Stehmann 2013, Serena et al. 2020). 

The Norwegian Skate (Dipturus nidarosiensis) is a large (to at least 200 cm total length) deepwater skate found in the found in the Eastern Atlantic Ocean, from Iceland to South Africa, including the Mid-Atlantic Ridge, and the Mediterranean Sea. It occurs on the continental and insular shelves and slopes at depths of 125–1,573 m. In the Northeast Atlantic, the Norwegian Skate is infrequently reported from demersal deepwater trawl and longline fisheries. The species was previously exploited in commercial fisheries either as targeted or incidental catch. Population declines of 90% and even localized extinctions have been documented for skates (Dipturus spp.) across the North Atlantic, and these declines have been greatest in large-bodied species, like the Norwegian Skate. 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 and are likely increasing fishing pressure on this species. There are also a number of European distant-water vessels using demersal trawl and longline to target demersal fish and shrimp species off the coasts of Africa that reach the depth limit of the species. The Norwegian Skate is suspected to be declining in the Northeast and Central Atlantic and Mediterranean Sea where historic and current fishing pressure is high. The species is suspected to have undergone a population reduction of 50–79% over the past three generation lengths (66 years) based on actual levels of exploitation, and it is assessed as Endangered A2d.

The Norwegian Skate is now known to be found in the Eastern Atlantic Ocean, from Iceland and Norway to South Africa, including the Mid-Atlantic Ridge, and the Mediterranean Sea (Last et al. 2016, Carbonara et al. 2021, Ebert and Dando 2021).

Population declines of 90% and even localized extinctions have been documented for skates (Dipturus spp.) across the North Atlantic (Dulvy and Reynolds 2002). These declines have been greatest in large-bodied species, like the Norwegian Skate (Dulvy et al. 2000, Ellis et al. 2010).

In the Northeast Atlantic, the Norwegian Skate has been confused with related species and is part of the "Common Skate" (Dipturus spp.) complex, which also includes the Common Blue Skate (D. batis) and the Flapper Skate (D. intermedius). Research trawl surveys from the Spanish Porcupine Bank Survey between 2001 and 2020 indicate low but increasing catch rates for Dipturus spp., with most of the catch comprised of the Norwegian Skate (Fernández-Zapico et al. 2021). Species-specific data for the Norwegian Skate are available from 2011 onwards, and show a fluctuating trend in abundance and biomass between 2011 and 2020 (Fernández-Zapico et al. 2021). Regional catches of skates have shown large historical declines and evidence of long-term overexploitation. For example, reported landings of skates from the Bay of Biscay strongly declined between 1950 and 2017, with more commonly reported species to be estimated at 20–50% of their carrying capacity, and even as low as 10% for species grouped in a generic skate reporting category (Marandel et al. 2019). The Norwegian Skate is very infrequently reported across its range in fisheries-independent research surveys (e.g., Neat et al. 2015, Fernández-Zapico et al. 2021).

In the Mediterranean Sea, the Norwegian Skate is infrequently recorded from research surveys. Large declines (90%) or the altogether disappearance of other slope species have been documented across the region between 1940/50s–1990s (Aldebert 1997, Ferretti et al. 2005). The Norwegian Skate may have some refuge from fishing in the deeper part of its distribution.

In the Eastern Central Atlantic, both overall catch and effort have continued to rise in the major shark and ray fishing countries of Mauritania, Nigeria, and Ghana. Across West Africa, total artisanal fishing effort increased 10-fold between 1950–2010, while the catch-per-unit-effort (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 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 99% over the past three generation lengths (66 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).

Based on documented declines and localized extinctions of other skates across its range and overlap with past and ongoing fishing pressure, a global population reduction of 50–79% was suspected over three generation lengths (66 years). Therefore, the Norwegian Skate is assessed as Endangered A2d.

The Norwegian Skate is demersal on the continental and insular shelves and slopes at depths of 125–1,573 m, and is most common from 200–1,000 m (Last et al. 2016, Ebert and Dando 2021, Carbonara et al. 2021). It reaches a maximum size of at least 200 cm total length (TL), and possibly 250 cm TL (Last et al. 2016). Maturity occurs at ~120 cm TL (Follesa et al. 2012). Reproduction is oviparous. Nothing else is known of its biology. Maximum age and age-at-maturity are unknown; maximum age is inferred from a congener, the Roughskin Skate (D. trachydermus), with female age-at-maturity is estimated at 17 years and a maximum age of 26 years (Licandeo et al. 2007). This results in a generation length of 22 years.

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). Earlier management efforts treated skates as one skate complex, and species-specific measures were only first introduced in 2007 (Ellis et al. 2010). Previously, the Norwegian Skate was exploited in commercial fisheries either as targeted or incidental catch, but historical catches are difficult to quantify across its range because of identification issues with similar-looking species (Stehmann et al. 2015, ICES 2021). Between 1982 and 1993, reported landings of the Norwegian Skate from the Northeast Atlantic varied from 19 to 393 tonnes, and the species was reported to account for 1% of skate landings sampled at Irish ports from 2001–2007 (Stehmann et al. 2015).

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 Norwegian Skate in the Northeast Atlantic (Duvly and Reynolds 2002, Marandel et al. 2019). The effects of fishing have been greatest on large-bodied species, like the Norwegian Skate (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 species were replaced in the marine environment by more productive, small-bodied species (Sguotti et al. 2016). In the most northern part of its distribution, the Norwegian Skate was reported in Norway during the 1950s, but has rarely been recorded since (Hesthagen et al. 2021). The Norwegian Skate is now infrequently reported from demersal deep-water trawl and longline fisheries (ICES 2021).

There is little information available for the Norwegian 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).

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 deepwater 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 deepwater 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.

Previously, the Norwegian Skate was utilized for its meat in the Northeast Atlantic, and product may have been mislabelled as other skate species (Iglésias et al. 2010). 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 and it may also be dried or dried and smoked and exported across West Africa to supply countries such as Ghana, Guinea, Nigeria, Mali, and Burkina Faso (e.g., Jabado et al. 2021).

The Norwegian Skate is listed as Prohibited Species on European Union (EU) fisheries regulations (EU waters of subarea 6 and Divisions 7.a-c and 7e–h and 7.k) (ICES 2021). 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 2021). The species has been assessed as Vulnerable under the Norwegian Red List (Hesthagen et al. 2021). Taxonomic resolution with Dipturus spp. is required to ensure the Norwegian Skate can be identified and monitored at the species level. Further information is required on its distribution, ecology and life history, as well as interactions with distant-water fleets fishing in African waters. 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.