|Scientific Name:||Dipturus oxyrinchus|
|Species Authority:||(Linnaeus, 1758)|
There is a possibility that this species is a complex, similar to the Dipturus batis-complex (Iglesias et al. 2010), but further taxonomic work is required.
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Ellis, J., Abella, A., Serena, F., Stehmann, M.F.W. & Walls, R.|
|Contributor(s):||Ungaro, N., Tinti, F., Bertozzi, M., Mancusi, C., Notarbartolo di Sciara, G. & Fordham, S.|
|Facilitator/Compiler(s):||Frazer, K., Lawson, J. & Dulvy, N.|
Longnosed Skate (Dipturus oxyrinchus) is a demersal species found on sandy or muddy bottoms at depths of 90−900 m. The large body size and inferred low intrinsic rate of population increase suggests that this skate will be highly sensitive to exploitation. Two genetically distinct subpopulations exist in the Mediterranean Sea and Northeast Atlantic. In the Northeast Atlantic, the depth range of this species extends down the continental slope to 900 m, but it is rarely encountered on the outer continental shelves. There are limited data on occurrence in Norwegian waters, the Faroes Grounds and the French and Iberian Atlantic shelves but nothing is known of current population trends in the Northeast Atlantic region. Historically, this species may have been more widely distributed in shelf areas.
In the Mediterranean Sea, this species is found at depths > 200 m and is most frequently captured at depths of 200−500 m in research surveys. It is moderately abundant in the central and eastern Mediterranean Sea, but is now absent from the west. While there has been no indication of a decline in abundance for the last 20 years in Italian waters, it has been absent from research surveys from the Gulf of Lions since 1984 and it is now rarely captured in the shelf areas of the Adriatic Sea.
The species is assessed as Near Threatened as, considering the status of other Dipturus species in the European region, the low catch levels in surveys and fisheries and the slow life history of the species, D. oxyrinchus is suspected to have declined by nearly 30% over the past 30 years (three-generation span), therefore being close to qualify as threatened under criterion A2bd. Further research is required to understand the taxonomic and population status of this species in both areas and management and monitoring are required.
In the Northeast Atlantic this skate occurs on the outer continental shelf and continental slope from central Norway southwards (Heintz 1962, Stehmann and Bürkel 1984). It is found in the Barents Sea, in the Norwegian Sea mainly along the coastline south of latitude 65°N, and in very low numbers in the North Sea (Williams et al. 2008, ICES 2012). The species was last encountered in trawl surveys around the Faroe Islands in 2001, and is only occasionally caught on the Rockall Survey in offshore waters west of Scotland (ICES 2012). In the Bay of Biscay, Iberian waters, and the Azores and mid-Atlantic ridge, it is still encountered by fisheries and trawl surveys in low numbers.
This skate was historically found throughout the Mediterranean Sea in both shelf and slope areas (Stehmann and Bürkel 1984), with the greatest survey catches occurring around the Corsica, Sardinia and Malta Islands, and throughout the eastern part of the basin including Dodecanese waters. By contrast it is not present in the western Mediterranean Sea, along the French and Spanish coasts, and the Northern Adriatic Sea (Serena et al. 2011). Its depth range is 90-900 m.
Native:Albania; Algeria; Bosnia and Herzegovina; Cyprus; Denmark; Egypt (Sinai); Faroe Islands; France (Corsica, France (mainland)); Greece (East Aegean Is., Greece (mainland), Kriti); Guernsey; Ireland; Israel; Italy (Italy (mainland), Sardegna, Sicilia); Lebanon; Libya; Malta; Montenegro; Morocco; Norway; Portugal (Azores, Madeira, Portugal (mainland), Selvagens); Spain (Canary Is., Spain (mainland)); Syrian Arab Republic; Tunisia; Turkey (Turkey-in-Asia); United Kingdom (Great Britain, Northern Ireland)
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – northeast; Mediterranean and Black Sea
|Range Map:||Click here to open the map viewer and explore range.|
Two genetically distinct subpopulations exist in the Mediterranean Sea and the Northeast Atlantic.
Little is known of the subpopulation status or trends in abundance in the Northeast Atlantic, but it is suspected to have declined or contracted in range. Between the late 1960s and 2002 United Kingdom groundfish surveys occasionally reported this species in the northern North Sea and Celtic Sea at depths of 111−159 m. Catch rates over this time period were very low ranging between 0.01 and 0.11 individuals captured per hour of trawling (Ellis et al. 2005). In the Annual Autumn Bottom Trawl Surveys of the northern Norwegian Coast, 54 individuals were reported in 1994, and only two individuals were reported in 2005 (Williams et al. 2008). Along the northern coast of Norway from 1992−2005, Williams et al. (2008) caught a mean of 7.7 individuals per square kilometre. The catches in this study were relatively high, indicating that although the species is somewhat rare, local aggregations may occur. In and around the Bay of Biscay catches showed large fluctuations, ranging from zero tonnes in 1999, to 16 tonnes in 2002, and decreasing again to zero tonnes in 2010 (ICES 2012). Although information is limited, the sensitive life history characteristics and available data suggest that this subpopulation is declining in Northeast Atlantic waters.
In the Mediterranean, the International Trawl Survey in the Mediterranean (MEDITS) preformed 6,336 tows between 1994 and 1999 over the entire European Mediterranean area and Morocco at a depth of 10−800 m. This species was the second most abundant skate in this survey and was recorded in 3% of hauls in this area. It was found at depths ranging from 50 to 800 m, but was caught most frequently between 200 and 500 m in the western central Mediterranean Sea and eastwards in the Aegean Sea (Baino et al. 2001, Serena 2005, Serena et al. 2010). A longline survey in 2004 confirmed the presence of this species in the southeast Aegean Sea, around Rhodes between 300 and 400 m depth (Corsini-Foka 2009). This species was historically present in the Gulf of Lions, northwest Mediterranean Sea, where it was captured in 10% (n=27) of hauls, occurring between 1959 and 1972 (coast to 150 m depth) and was also present in the catches of surveys performed between 1980−1984. It was subsequently absent from 628 scientific tows done in the same area in the period 1985−1995 (Aldebert 1997). Similarly, in the Adriatic Sea, historical trawl surveys from 1948 showed that this species was present in 3.2% of hauls carried out on the continental shelf, while in a comparable MEDITS survey in 1998 reported that this species was absent from all hauls on the continental shelf (Jukic-Peladic et al. 2001). In the south Ligurian and north Tyrrhenian Seas this species has been found at depths ranging from 164−750 m, and was mostly concentrated on the outer margin of the slope from 300−400 m. Over this survey period, biomass has reportedly decreased while abundance remained stable. This suggests a change in population structure, with an increasing presence of juveniles in catches. Given the sensitive life history characteristics, evidence of significant population declines and apparent disappearance in some localised areas (likely due to fisheries pressure), this subpopulation is considered to be decreasing throughout the Mediterranean Sea.
Considering the status of other Dipturus species in the European region, D. oxyrinchus is also inferred to be in decline, although to a lesser extent due to its smaller size, and it is suspected that the species has declined by nearly 30% over the past 30 years (three-generation span).
|Habitat and Ecology:||
This demersal skate is found on sandy or muddy bottoms at depths ranging from 90−900 m, and appears to be most abundant from 200−500 m (Stehmann and Bürkel 1984, Baino et al. 2001).
This egg laying skate has a spawning period from February to May (Stehmann and Bürkel 1984, Bauchot 1987, Notarbartolo di Sciara and Bianchi 1998, Serena et al. 2010), and produces egg cases between 10 and 15 cm in length. Size at birth is 17 cm total length (TL; Ebert and Stehmann 2013). Estimated length at 50% maturity was 83.2 cm TL for males and 104.4 cm TL for females (Serena et al. 2011). Both sexes are estimated to reach sexual maturity between six and eight years. Stehmann and Bürkel (1984) reported a maximum size of 150 cm TL. The generation length of this species is inferred from that of Barndoor Skate (which is slightly larger) to be around 10 years.
|Use and Trade:||The species is not used or traded commercially.|
This is one of the larger bodied species of skate and it is thought to have declined from shelf areas, although this would be the shallower fringe of the bathymetric distribution. The large body size (150 cm), and presumably slow growth and later maturation and likely low intrinsic rate of population increase of this species render it especially vulnerable to exploitation such as trawling and at risk of local extinction (Walker and Hislop 1998, Dulvy et al. 2000, Dulvy and Reynolds 2002).
There are no specific data available on threats, however it is inferred that, similar to other large-bodied skates, this species may be retained as bycatch in demersal trawl and longline fisheries, particularly in deeper waters. Although only large individuals may be landed for consumption, most size classes are likely to be taken in fishing nets. This species is caught and landed from offshore fisheries as reported by the United Kingdom, but data are unreliable. These landings are likely the result of misidentification or incorrect use of species codes (ICES 2012). Given recent restrictions on landing other members of this genus, recent data indicating increasing catches of this skate are questionable due to possible reporting of other species as Longnosed Skate (Dipturus oxyrinchus; ICES 2013).
This skate is captured as bycatch in bottom trawl fisheries targeting Norway Lobster (Nephrops norvegicus) or Red Shrimp (Aristeus antennatus) and by offshore bottom longlines. Over the last 50 years, trawl effort has increased numerically and technologically in the shelf and slope area of the Mediterranean Sea. For example, the Gulf of Lions area was historically exploited by small-scale benthic trawl fisheries composed of 27 small, low-powered boats with a total of 2,700 horse power (hp), between 1974 and 1987 effort has increased to a total of 19,940 hp. In particular, fishing effort targeting small pelagic fish has increased (Aldebert 1997). The Adriatic Sea is subject to trawling by Italian, Croatian, Slovenian, and Albanian fleets, however, no landings data are available (Jukic-Peladic et al. 2001). The General Fisheries Commission for the Mediterranean (GFCM), the main intergovernmental decision-making body on fishery management in the Mediterranean Sea, has made the decision to refrain from expanding deepwater fishing operations beyond the limit of 1,000 m. However this species occurs mostly from 200-500 m, thus deepwater fisheries development within the depth range of this species remains a cause for concern.
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).
Further research should be conducted on the population size and trend of the species.
|Citation:||Ellis, J., Abella, A., Serena, F., Stehmann, M.F.W. & Walls, R. 2015. Dipturus oxyrinchus. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 30 July 2015.|
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