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 population size of thornback ray in this stock is unknown but the stock size has been fluctuating without trend since 2010 and the biomass of thornback rays appears to be similar to the values at the beginning of the time-series. Fishing mortality remains to be unknown.

The landing obligation will be fully in place in 2019, which requires that all species with catch limits should be retained. However, skate and rays are exempt from the landing obligation due to their assumed high discard survival rates. 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. Further management of the species is advised e.g. through fishery closures to allow them to reproduce.

Both demersal otter trawls and beam trawls are associated with captures of Endangered, Threatened and Protected 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 population size of thornback ray in this stock is generally unknown but the stock size has been fluctuating without trend since 2010. The UK-Q1-SWBeam survey has shown that that the biomass of thornback rays in the area is greater in 2014-2017 than at the beginning of the time-series. However, preliminarily values from 2018 show values similar to those at the beginning of the time-series. Therefore, there is no concern for biomass.

Landings have increased from 2011, however the level of discards and discard mortality is unknown and therefore, fishing mortality is unknown. In 2017, ICES species-specific landings minimum estimate based on reported landings was 371 tonnes whilst the landings corresponding to advice 212 tonnes. Therefore, there is concern for fishing mortality. Low Resilience.

Management

Criterion score: 0.75 info

There is no direct management plan for skates and rays in these waters. They are usually caught as bycatch in otter and beam trawl fisheries, which target finfish (including flatfish and gadoids).

Skates and rays are managed under five regional quotas (called TACs) which are applied to a group of species, rather than individual skate and ray species. This has been deemed as an unsuitable method for protecting individual species, but species-specific quotas may increase discarding.

The European Commission have considered that skates and rays caught in the Northwest waters (ICES subareas 6 and 7) with all fishing gears, should be exempt from the landing obligation, based on their assumed high survivability rates. However, Member States harvesting the stocks should supply data to STECF to review the effectiveness of the exception and, by the 31 May each year produce a roadmap to increase survivability, fill in the data gaps identified by STECF and produce annual reports on the progress on survivability programmes. Any skates and rays that are discarded are required to be released immediately and below the sea surface. Any vessels fishing using bottom trawls or seines, with catches comprising more than 10% of haddock, cod and skates and rays combined, are required to use, either a) a 120 mm cod-end, or b) an eliminator trawl with 600 mm large mesh panels and a 100 mm cod-end. For vessels fishing using bottom trawls or seines with catches comprising less than 10% of haddock, cod and skates and rays combined, vessels are required to use a cod-end mesh size of 100 mm with a 100 mm squared mesh panel, except for vessels with catches comprising over 30% of Norway lobster. (European Commission 2018b).

Other management methods are currently being considered at an EU level, fishing gear modifications, education, conservation measures (such as closed seasons during spawning times). Some protected areas have been designated in these waters but offshore areas are not sufficiently managed. There are no official minimum landing sizes except for some IFCAs, which, mandate a minimum landing size (40-45 cm disc width) in inshore waters in England and Wales.

Gill nets: Under EU law, where skates are rays are targeted with gillnets, a minimum mesh size of 22 cm (when catching >70% skates and rays) is required in the Celtic Sea.

Monitoring
ICES conduct assessments for most skate and ray species on a biennial basis. There are a lack of reference points for the stock, which prevents the development of management plans (Mangi et al. 2018). Data-limited approaches have been used (using some survey and landings data) but there are important information gaps. Projects including the Fisheries Science Partnership, Sustainable Management of rays and Skates (SUMARiS), National Evaluation of Populations of Threatened and Uncertain Elasmobranch Stocks (NEPTUNE) have been collecting data to close these data gaps. Discarding is known to occur, however the amount that are discarded dead is unknown and therefore, the total fishing mortality is unknown. Fishery-independent surveys have been conducted in Lyme Bay (through the Carhelmar survey) and the UK-Q1-SWBeam survey (conducted from 2006-present).

Enforcement
Surveillance legislation is underpinned by EU Law, which require that 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. There is direct management of fishing effort for vessels since 2003, which allocates effort in kW-days to vessels of >15 m. However, the inshore (smaller) fleets are generally not managed by effort to the same extent.

Capture Information

Criterion score: 0.5 info

Thornback ray is one of the most commercially important skate species in this area. It is normally caught in trawl and net fisheries. 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
The landing obligation will be fully implemented into our seas from 2019. Skates and rays will be exempt from the landing obligation, due to their higher likelihood of survival when discarded. Member states will be required to report on skate and ray catches and discards, and any improvements in selectivity programmes. it’s difficult to avoid catching skates and rays in nets and because of their peculiar shape and size; it’s also difficult for them to escape the net once captured. Therefore, selectivity programmes are in place reduce skate and rays catches and their survival rates.

Discard rates of skates and rays vary dramatically (30 - 70%), depending on the marketability and management measures in place. For example, nearly all skates below 30 cm LT are discarded by English vessels (Silva et al., 2012). Bycatch can include juvenile skate as they can hatch from their egg cases at sizes of 10-20 cm LT and therefore, may be able to escape through the nets (Ellis et al. 2018). Their survival rates upon discarding is extremely variable, depending on the fishing and handling methods used to capture them. Elasmobranchs have the potential for relatively high survival rates because they do not have swim bladders (and thereby are not as impacted by pressure changes), they can have thick and abrasive skins and thorns (which protect them) and some have spiracles and a buccal-pump respiratory which excrete a mucus, which allows the skate or ray to ventilate and acquire oxygen when out of the water (Ellis et al. 2018). Tag-recapture studies suggest that thornback rays that there are significant differences in their condition between different gear types. They were found to be in a significantly better condition when caught using longlines and tangle nets, compared to when they were captured using otter trawl or drift trammel net. Overall, when captured with tangle nets, skate condition was significantly better during shorter (17-28 hours) soak times, compared with (42-48 h soak time)(Ellis et al. 2018). There are a lack of studies available on long-term skate and ray survival when they are released into the wild (Ellis et al. 2018).

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 how accustomed the seabed is to natural disturbance.

Thornbacks prefer hard, coarse, mixed, and unknown sediments.

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. 2018. Thornback ray (Raja clavata) in Division 7.e (western English Channel). Available at: http://ices.dk/sites/pub/Publication%20Reports/Advice/2018/2018/rjc.27.7e.pdf. Published 5 October 2018;

Ellis, J. R., Burt, G.J., Grilli, G., McCully Phillips, S.R., Catchpole, T.L., Maxwell, D.L. 2018. At-vessel mortality of skates (Rajidae) taken in coastal fisheries and evidence of longer-term survival. Journal of Fish Biology. 92, 1702-1719. doi:10.1111/jfb.13597

Mangi, S., Kupschus, S., Mackinson, S., Rodmell, D., Lee, A., Bourke, E., Rossiter, T., Masters, J., Hetherington, S., Catchpole, T. and Righton, D. 2018. Progress in designing and delivering effective fishing industry science data collection in the UK. Fish 00:1-21. https://doi.org/10.1111/faf.12279

Shephard, S. Reid, D.G.,Gerritsen, H.D, Farnsworth, K.D. Estimating biomass, fishing mortality, and total allowable discards for surveyed non-target fish, ICES Journal of Marine Science, Volume 72, Issue 2, 1 January 2015, Pages 458-466, https://doi.org/10.1093/icesjms/fsu146

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.