Thornback ray in North Sea and eastern English Channel, Beam trawls
Content last updated
19th Jan 2018
Thornback ray (Raja clavata) in Subarea 4 and in divisions 3.a and 7.d (North Sea, Skagerrak, Kattegat, and Eastern English Channel
Thornback ray (Raja clavata) is one of the commonest skates in European shelf seas and is the most commercially important skate species in this region. This species is widely distributed in the North-eastern Atlantic, from Iceland and Norway to the Azores, Northwest Africa, Mediterranean Sea and Black Sea (Stehmann and Bürkel, 1984). It is a demersal species that occurs on a variety of substrates, including mud, sand and gravel. This species is distributed on the continental shelf and upper slope, but is most common in waters less than 100 m deep (Ellis et al., 2005).
The largest recorded specimen is 130 cm (but specimens >105 cm are rare), and they can live for about 15 years. They spend the winter in slightly deeper water and migrate into shallower coastal areas in the late spring and summer to spawn. Spawning occurs in inshore coastal waters between February and September, peaking in March to June. Eggs are deposited on the seabed and hatch after 4 to 6 months, depending on the water temperature. Juveniles are non-migratory, inhabiting inshore nursery grounds, whilst adults display seasonal migrations and longer movements. Juveniles feed on small crustaceans particularly amphipods and bottom-living shrimps, while adults feed on crabs, shrimps and small fish.
Thornback ray is a target species in some inshore fisheries in the south-western North Sea that use otter trawl, tangle nets and longlines. It is also a bycatch in offshore otter trawl and beam trawl fisheries targeting plaice (Pleuronectes platessa) and sole (Solea solea). Juvenile thornback ray are often discarded (Silva et al., 2012)
The degree of resource competition and species interactions between skate species is poorly understood. Historically, the larger common skate (Dipturus batis) was known to predate on smaller skate individuals, and earlier, longer-term declines in larger skates may have benefited populations of smaller skate species, due to a reduction in predation or competition.
Insufficient information is available to present longer-term trends in species-specific landings for this stock, although the species-specific reporting of skates is improving.
Ellis, J. R., Cruz-Martinez, A., Rackham, B. D., and Rogers, S. I. (2005). The distribution of chondrichthyan fishes around the British Isles and implications for conservation. Journal of Northwest Atlantic Fishery Science, 35: 195–213.
ICES (2015). Report of the Working Group on Elasmobranch Fishes (WGEF), 17–23 June 2015, Lisbon, Portugal. ICES CM 2015/ACOM:19. 711 pp.
Silva, J. F., Ellis, J. R. and Catchpole, T. L. (2012). Species composition of skates (Rajidae) in commercial fisheries around the British Isles, and their discarding patterns. Journal of Fish Biology, 80: 1678–1703.
Stehmann, M., and Bürkel, D. L. (1984). Rajidae. In Fishes of the north-eastern Atlantic and Mediterranean. P. J. P. Whitehead, M-L. Bauchot, J-C. Hureau, J. Nielsen, and E. Tortonese (eds.). UNESCO, Paris. Vol. 1, pp. 163–196.
Thornback ray in the North Sea, Skagerrak and Eastern English Channel (ICES Subarea 4 and Divisions 3a and 7d) has been scored as moderate risk
Thornback ray in the North Sea, Skagerrak and Eastern English Channel (ICES Subarea 4 and Divisions 3a and 7d) has been scored as moderate risk. The state of the stock is uncertain, but abundance appears to be increasing. Catch rates is scientific trawl surveys have strongly increased in the last decade. The advice given by ICES in 2017 was that landings could be increased by up to 20%, and “should be no more than 2574 tonnes in each of the years 2017 and 2018”.
Reference points for long-term sustainability have not been defined for this stock, and therefore cannot be used to derive a risk score. The risk score was calculated using a data-limited approach where the high vulnerability score for thornback ray (72/100; FishBase, 2015) was weighted with an increasing population trend in accordance with the RASS scoring guidelines.
Thornback ray in the North Sea, Skagerrak and Eastern English Channel (ICES Subarea 4 and Divisions 3a and 7d) has been scored a moderate risk
Thornback ray in the North Sea, Skagerrak and Eastern English Channel (ICES Subarea 4 and Divisions 3a and 7d) has been scored a moderate risk. This is because data-derived management controls are in place, albeit under the framework of a generic TAC for all skates (Rajidae) over a broader management area, and that compliance can be patchy. Data-limited assessments and scientific advice for this stock are provided on a biennial basis and a comprehensive regulatory framework is in place.
The bycatch risk of this fishery has been scored a very high risk. This is because beam trawls have the potential to take relatively high quantities of bycatch (> 50% of catch weight) including demersal elasmobranchs and occasionally protected, endangered and threatened (PET) species (e.g. sharks and rays) in certain circumstances. Absolute levels of discards across all fleets have gradually decreased since 2002 (Catchpole et al., 2011) and the incoming EU landings obligation is intended to reduce discarding further.
The habitat risk of this fishery has been scored a high risk. This is because beam trawls interact with the seabed, potentially modifying bottom topography including damage and removal of some biogenic features and interacting with vulnerable marine habitats and benthic communities. However, the risk due to damage to vulnerable marine habitats is likely to be reduced given that most of the footprint of the gear occurs on core fishing grounds.
Some spatial management is in place and is continually being developed, which will restrict the footprint of this gear on the seabed. However, there remains some uncertainty about the location of some sensitive seabed habitats so these remain at risk.
|Current risk status||Outlook||Reason|
|Stock||Moderate||Improving||There is evidence for recent stock increase in the stock, and ICES has advised that landings could be increased Species-specific landings data are improving. Estimates of dead discards are not available, and some landings data are generic. Hence, recent trends in the catches of thornback ray cannot be fully quantified. Ongoing collection of species-specific landings data should improve understanding of stock dynamics.|
|Management||High||Improving||No individual TAC is set for this stock at present and only a data-limited assessment has been produced to provide fisheries advice. No reference points for long-term sustainability have been defined, and no management plans are currently in place. Increasing the quantity and quality of species-specific data will help to improve targeted management techniques|
|Bycatch||Very high||Improving||Bycatch of important commercial and non-commercial species remains high, but absolute levels of discards across all fleets have been gradually decreasing since 2001 and the incoming EU landings obligation is intended to reduce discarding further.|
|Habitat||High||Improving||Beam trawls disturb seabed habitats, but a range of technical and spatial management measures are under development and will likely reduce the habitat risk in the future.|
|Type||Current Risk Status||Outlook||Reason|
There is evidence for recent stock increase in the stock, and ICES has advised that landings could be increased
No individual TAC is set for this stock at present and only a data-limited assessment has been produced to provide fisheries advice.
Bycatch of important commercial and non-commercial species remains high, but absolute levels of discards across all fleets have been gradually decreasing since 2001 and the incoming EU landings obligation is intended to reduce discarding further.
Beam trawls disturb seabed habitats, but a range of technical and spatial management measures are under development and will likely reduce the habitat risk in the future.