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 — Western English Channel
Stock detail

7e


Picture of Ray, Thornback ray, Roker

Sustainability rating five info

Sustainability overview

The stock status is unknown and there is conflicting advice: some areas show a population increase but not enough is known about the population, to show that their populations are increasing throughout the region.

There is no specific management plan for skates and rays in these waters. They are managed under a total allowable catch (TAC) for many skates and rays but greater protection is needed. More data are needed to find out if their population and fishing levels are healthy. There are some protected areas in the inshore region which likely benefit thornback rays, however the offshore protected areas do not receive enough protection.

Both demersal otter trawls and beam trawls are associated with occasional captures of endangered species and beam trawls can pose significant risks to the habitat. However, management can mitigate these risks e.g. with area closures. Management is generally better in inshore waters.

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: 1 info

Stock Area

Western English Channel

Stock information

The state of the stock in this area is unknown. A trawl survey data collected for the stock in 1989 to 2011 which suggested that abundance was stable or increasing in the Lyme Bay area. However, this is not enough information to understand the stock status for the whole area. Scientists advise that landings should be no more than 212 tonnes in each of 2017 and 2018. However, landings in 2015 were estimated at 391 tonnes. 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. However, thornback ray populations have been consistently increasing over the past five years, partly attributable to climate change and reductions in trawling effort.

Little is known about connectivity of thornback ray stocks, yet, connectivity is crucial for managing skates and rays and provides a long-term perspective of their population trends.

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: 0.75 info

Thornback is almost exclusively caught through bottom and beam trawls in this area. Thornback ray is the most commercially important ray species in this ecoregion. It is mainly caught close to shore. Considerable catches are taken in artisanal coastal fisheries in southeast England.

Bycatch
Common bycatch in bottom trawls include mixed crabs, urchins, lesser spotted dogfish, nursehound, Dragonet, starry ray, smelt. Angel shark and common skate (critically endangered, IUCN) were depleted through incidental capture in trawls in this area. Invertebrates such as crabs and urchins are vulnerable to damage.

Discards
Discards from beam and otter trawls are high. Otter trawls appear to catch more thornback rays than beam trawls and are not selective: discards are high among thornback rays <55 cm total length. Beam trawling is generally more targeted than demersal trawls. Because 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 from gill nets after 2 days is 88% whereas its about 25%-100% survived in beam trawl surveys.

Habitat
Thornbacks prefer hard, coarse, mixed, and ‘unknown’ sediments. The level of information is limited for vessels <12m because they are not required to have Vessel Monitoring Systems (VMS). 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. IFCAs ensure bottom trawling occurs in areas where there will be minimal damage to habitats such as mobile sands, however, in offshore areas, bottom trawling can occur over vulnerable habitats. Thornback rays are normally found on mixed sediments and rock or hard 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

ICES 2016. Thornback ray (Raja clavata) in Division 7.e (western English Channel). Available at: http://ices.dk/sites/pub/Publication%20Reports/Advice/2016/2016/rjc-echw.pdf
ICES 2016. ICES Technical Services 2016, Book 11. Request from EU for ICES to review a proposal of an in-year TAC adjustment for 2016 for skates and rays (SRX) in Division 7.d. Available at: http://ices.dk/sites/pub/Publication%20Reports/Advice/2016/Special_Requests/EU_Technical_Service_Review_skate_and_rays.pdf

Sguotti, C., Lynam, C. P., Garcia-Carreras, B., Ellis, J. R. and Engelhard, G. H. (2016), Distribution of skates and sharks in the North Sea: 112 years of change. Glob Change Biol, 22: 2729-2743. doi:10.1111/gcb.13316

Marandel, F., Lorance, P., Andrello, M., Charrier, G., Le Cam, S., Lehuta, S. Trenkel, V.M. 2017. Insights from genetic and demographic connectivity for the management of rays and skates. Canadian Journal of Fisheries and Aquatic Sciences IN PRESS.

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