Ray, Thornback ray, Roker

Raja clavata

Method of production — Caught at sea
Capture method — Demersal otter trawl
Capture area — North East Atlantic (FAO 27)
Stock area — Irish and Celtic Seas
Stock detail

7a,f,g


Picture of Ray, Thornback ray, Roker

Sustainability rating four info

Sustainability overview

Thornback ray abundance for this stock is estimated to have increased substantially in this area in recent years.

There are still major data gaps on discards and fishing levels of Thornback Rays. This information is crucial for better management within the fishery. There is no specific management plan for skates and rays in these waters but there is some improved management in inshore waters. They are managed under a total allowable catch (TAC) for many skates and rays but greater protection is needed.

Demersal otter trawling is also associated with discarding of unwanted fish and occasional catch of endangered species. However, capture rates can be reduced by adapting fishing gear and methods.

Biology

Thornback rays or roker are an inshore to slope species, belonging to the Rajidae family of skates and rays. Thornback rays have been described as showing philopatric behaviour (tendency of a migrating animal to return to a specific location in order to breed or feed). Females can grow to 118cm in length and 18kg in weight, while males can reach 98cm in length. Females mature between 60 and 85cm while males mature between 60 and 77cm (in both cases corresponding to an age of 5 to 10 years). The species has a maximum recorded age of 16 years. There are 13 species of ray and skate Rajidae and 7 to 8 demersal shark species in the North Sea ecoregion.

Stock information

Criterion score: 0.5 info

Stock Area

Irish and Celtic Seas

Stock information

The state of the stock in this area is unknown. Thornback Ray populations have increased by an estimated 10% in the last two years (2014-2015) than the average of the previous five years (2009-2013). Fishing pressure in 2013 was deemed sufficient and landings have since decreased.

Scientists advise that landings in 2017 and 2018 should be no more than 1386 tonnes. The Thornback Ray is assessed as “near threatened” by the IUCN.

Thornback ray are considered relatively sensitive to fishing pressures because of its marketable large size and vulnerable life-history traits. Historically, this species was distributed across the North Sea. However, populations declined due to high levels of fishing pressure from beam trawls, and nursery habitat disruption, therefore, it is now mainly confined to the southwestern North Sea.

Thornback ray populations have been consistently increasing over the past five years, partly attributable to climate change and reductions in trawling effort.

Discarding occurs, although the likelihood of survival is high, assuming responsible fishing and handling methods.

Management

Criterion score: 0.75 info

There are no management plans or objectives for this species. Skates and rays are managed under five regional quotas (called TACs) applied to a group of species. This has been deemed as an unsuitable method for protecting individual species, but species-specific quotas may not be suitable because it may increase unnecessary discarding of skates and rays.

Other management methods are currently being considered at an EU level. Methods to avoid catching rays include closed areas and seasons and modifying fishing gear to observe their escape behaviour and design fishing gear accordingly. However, it is difficult to avoid catching rays in fishing gear (because of their peculiar shape) so fishing gear modifications have been suggested to improve the potential survival of rays so that they can be quickly and safely discarded.

There is no official minimum landing size for many skates and rays outside the 6 nautical mile limit in European waters. However, some inshore areas mandate a minimum landing size (40-45 cm disc width). There is direct management of fishing effort, depending on fishing gear, mesh size and area, however, this only applies to vessels of >15 m and therefore, inshore (generally smaller) fleets are generally not effort managed to the same extent. There are catch composition rules limit the percentage of skates that can be landed by demersal otter trawls (dependent on the mesh size of the net).

More information is needed on skate and ray catches, discard and survival rates. Landings data doesn’t tell scientists much about the health of the stock. The Fisheries Science Partnership project connects fishermen and scientists to fill in important knowledge gaps.

Surveillance legislation is underpinned by EU Law, and requires all vessels above 12m in length use vessel monitoring systems (VMS), and mandate at-sea and aerial surveillance and inspections of vessels, logbooks and sales documents.

Some protected areas have been designated in these waters but offshore areas are not sufficiently managed. Some of these MPAs are designated to protect rays such as the Offshore Overfalls MCZ which is designated partly to protect the undulate ray’s nursery areas. The inshore waters, such as the Isle of White SAC, ensure management, which may provide protection for various life stages e.g. undulate rays. Although the connectivity of these species is unknown and therefore, these waters need sufficient management and protection to prevent over-exploitation of these animals and their habitats.

Capture Information

Criterion score: 0.5 info

Thornback rays from this area are caught as bycatch mainly in bottom trawls and fixed nets. They are also targeted by sea anglers.

Bycatch
Otter trawls are not a very selective gear.

Bycatch
The catch may include a large variety of species such as various soles, plaice, monkfish, haddock, cod, John Dory, red gurnard, horse mackerel, boar fish and grey gurnard, skates, rays and starry smooth-hound.

ETP species can occasionally be caught such as common skate and spurdog in offshore otter trawl fisheries but it is illegal to land these species.

Discards
Since skate and rays are a peculiar shape and size, it is difficult for them to escape from fishing gear once caught. Therefore, other methods must be used to increase their likelihood for survival: Skates and rays are generally a hardly species but their survival rate after discarding is extremely variable depending on fishing and handling methods: discard survival varied between 25%-100% in beam trawl surveys. However, in this specific area, discarding rates and survival is unknown. As part of the cod-recovery plan trawlers have Square Mesh Panels (SMPs) which allows bycatch species to escape the nets including dogfish. Dogfish have really rough skin which harms other species in the net. By allowing them to escape, it means that skates and rays are more likely to be discarded alive. Discards of other species may include undersized or unmarketable fish or because they are choke species. Discards rates vary dramatically (30 - 70%)

Habitat
Bottom trawling has the potential to cause significant impact to habitat such as removing or destroying physical features and reducing biota and habitat complexity. Therefore, the recovery time of the seabed after trawling varies greatly and depends on the fishing gear, the substrate, intensity of the trawl and accustomed the seabed is to natural disturbance. Fishing occurs over a mixture of seafloor types e.g. sandy, muds, gravel. In beam trawls, VMS shows the location of trawling. IFCAs ensure bottom trawling occurs in areas where there will be minimal damage to habitats e.g. by requesting that otter trawls avoid vulnerable features such as ross worm (or sabellaria), however, in offshore areas, bottom trawling can occur over a variety of substrates.

Alternatives

Based on method of production, fish type, and consumer rating: only fish rated 2 and below are included as an alternative in the list below. Click on a name to show the sustainable options available.

Dab
Halibut, Atlantic (Farmed)
Halibut, Pacific
Megrim
Plaice
Sole, Dover sole, Common sole
Sole, Lemon
Turbot (Caught at sea)
Turbot (Farmed)

References

McCully, S. R., Scott, F., and Ellis, J. R. 2012. Lengths at maturity and conversion factors for skates (Rajidae) around the British Isles, with an analysis of data in the literature. -ICES Journal of Marine Science, 69: 1812-1822

ICES. 2016. Thornback ray (Raja clavata) in divisions 7.a, 7.f-g (Irish Sea, Bristol Channel, Celtic Sea North). Available at: http://ices.dk/sites/pub/Publication%20Reports/Advice/2016/2016/rjc-7afg.pdf

Project Inshore MSC Pre-Assessment Database. 2013. Irish and Celtic Sea (VII a/f/g): Thornback ray: Trammel net: Available at: http://msc.solidproject.co.uk/inshore-uoc.aspx?id=8344&s=&a=

Project Inshore MSC Pre-Assessment Database. 2013. Thornback ray: Gill net. Available at: http://msc.solidproject.co.uk/inshore-uoc.aspx?id=8345&s=&a=

Scientific, Technical and Economic Committee for Fisheries (STECF) - 56th Plenary Meeting Report (PLEN-17-03); Publications Office of the European Union, Luxembourg.