Status Assessment 2021 - Thornback ray
|Assessment of status||Distribution||Population size||Demographics, e.g. productivity||Previous OSPAR status assessment||Status|
|Assessment of key pressures||Fishing pressure||Habitat damage||Threat or impact|
Explanation to table:
Distribution, Population size, Condition
Trends in status (since the assessment in the background document)
↓ decreasing trend or deterioration of the criterion assessed
↑ increasing trend or improvement in the criterion assessed
←→ no change observed in the criterion assessed
? trend unknown in the criterion assessed
Previous status assessment: If in QSR 2010 then enter regions where species occurs ( ○) and has been recognised by OSPAR to be threatened and/or declining (● ). If a more recent status assessment is available, then enter ‘poor’/’good’
red – poor
green – good
Blue cells –? status unknown, insufficient information available,.
NA - Not Applicable
*applied to assessments of status of the feature or of a criterion, as defined by the assessment values used in the QSR 2023 or by expert judgement.
↓ key pressures and human activities reducing
↑ key pressures and human activities increasing
←→ no change in key pressures and human activities
? Change in pressure and human activities uncertain
Threat or impact[overall assessment
red – significant threat or impact;
green –no evidence of a significant threat or impact
Blue cells – ? insufficient information available
NA – not applicable
1 – direct data driven
2 – indirect data driven
3 – third party assessment, close-geographic match
4 – third party assessment, partial-geographic match
5 – expert judgement
The thornback ray was nominated for inclusion on the OSPAR List of Threatened and/or Declining Species and Habitats in 2006 and it has been included since 2008 (OSPAR Agreement 2008-6). The original evaluation against the Texel-Faial criteria listed sensitivity and decline in OSPAR Region II as the reasons for listing of this species. Although there were no population estimates for the species, the abundance and range had declined. Owing to its life-history traits, the species has a moderate biological productivity. Therefore, while the level of fishing pressure is moderate, the recovery from depletion is slow and the threats are still present.
The status of this species is based on ICES advice to fisheries managers for fishing opportunities. This advice has been integrated into an assessment for conservation purposes.
Geographical Range and Distribution
The thornback ray is distributed in continental shelf seas from Iceland to South Africa, including the Azores archipelago, the Mediterranean Sea and the Black Sea. Its distribution may also extend into western parts of the Baltic Sea. Thornback rays occur in/over a variety of benthic substrate types including mud, sand, shingle, gravel and rocky areas. The species occurs in OSPAR Regions II, III, IV and V, and in the southern limits of Region I.
Thornback rays are most abundant in coastal areas at c. 10–200m depth, being shallower in occurrence in cold temperate waters, and deeper in warmer waters. The species is nevertheless commonly recorded in waters up to 100m deep, and occasionally recorded to depths of at least 750m (ICES 2018). Outer estuaries and large shallow bays, particularly the Wash and the Thames Estuary in the UK, are important spring/summer spawning grounds, nurseries and feeding areas (e.g. Wheeler 1969, Ellis et al. 2005, Hunter et al. 2006, Wirtz et al. 2008).
ICES assesses and provides advice on fishing opportunities for seven stocks of thornback rays in the ICES Area, namely: (i) Subarea 4 and Divisions 3.a & 7.d (OSPAR Region II); (ii) Subarea 6, (iii) Divisions 7.afg, and (iv) Division 7.e (OSPAR Region III); (v) Subarea 8 and (vi) Division 9.a (OSPAR Region IV), and (vii) around the Azores archipelago (in OSPAR Region V).
Based on ICES advice, current indications are that the stocks of thornback ray are increasing within OSPAR Regions II and III, either stable (Subarea 8) or increasing (Division 9.a) within OSPAR Region IV (Subarea 8), while catch rates around the Azores archipelago (in OSPAR Region V) are stable at a low level.
There is considerable uncertainty around these stock size estimates and biomass indices in some areas, however, as can be seen in Figure 2 they do not provide precise population figures. Furthermore, the indications of increases in stock size are relatively recent (i.e. within the last 5-10 years). Therefore knowledge of thornback ray populations (i.e. species abundance) as a whole within individual OSPAR Regions remains somewhat inconclusive at present.
The thornback ray is a relatively fast-growing species, with higher fecundity than many elasmobranchs. A length range of 10–97 cm in total length (TL) for males and 10–105 cm TL for females, has been observed (McCully et al. 2012, Serra-Pereira et al 2011). Based on mark-recapture data, the maximum age is at least 17 years (Bird et al. 2020). In Region III, individuals reach maturity at age 6 and length 65–71 cm (Gallagher et al. 2005), whereas in Region IV females reach maturity at age 7.5 and 78.4 cm and males at 5.8 years and 67.6cm (Serra-Pereira et al 2011). Fecundity is estimated from 60–140 eggs per year (Holden 1975).
Threats and Impacts
The original rationale for including this species on the OSPAR List was because it had been depleted by fisheries in most of Region II, where the area of its distribution had contracted significantly. There were lesser declines in other parts of the OSPAR area. A general decrease in fishing effort is shown in the Northeast Atlantic from the beginning of the 21st century (e.g. Gascuel et al. 2016, Couce et al. 2020, ICES 2020c). However, bycatch is still a problem and measures for more effective bycatch mitigation still have to be developed.
Measures that address key pressures from human activities or conserve the species/habitat
For EU waters, fishing pressure on thornback ray is currently regulated through a Group-TAC which includes all skate and ray species except Raja undulata and those listed as prohibited. The Group-TAC was introduced in 1999 in the North Sea (Division 3.a and Subarea 4) and in 2009 in the eastern English Channel (Division 7.d) and other areas.
Studies on individual survivability in different fishing métiers show that thornback ray has a survivability of >50% in the pulse-trawl fishery (Schram and Molenaar 2018) and >90% in gill nets (Enever et al. 2009, Catchpole et al. 2017). Recent studies suggest variable at-vessel mortality and discard survival, depending on several factors (e.g. gear type, soaking time, fish size) (Ellis et al., 2018; Schram and Molenaar, 2018; Serra-Pereira and Figueiredo, 2019). It is possible that this bycaught small-bodied species may be less susceptible to fishing pressure than the large-bodied skates (e.g. Silva et al., 2012), though further studies on discard survival are required. Further studies on discard survival in particular in bottom trawls are nevertheless required.
Conclusion (including management considerations)
Based on ICES assessment, the biomass indices of thornback ray are increasing within parts of OSPAR Region II and Region III, either stable (ICES Subarea 8) or increasing (ICES Division 9.a) in OSPAR Region IV, while catch rates around the Azores archipelago (in OSPAR Region V) are stable at a low level. Based on this evidence the overall conclusion on the species’ status is positive and improving, although there is uncertainty (i.e. relatively wide confidence intervals) around some stock-related estimates. Furthermore, indications of increases in stock size are relatively recent (i.e. within the last 5-10 years), therefore the status of Thornback ray populations as a whole within individual OSPAR Regions is inconclusive at present.
The species’ sensitivity has not changed however, while further understanding of the life-cycle and population structure of this species is still required. Bycatch mortality is still a problem for this species and measures for more effective bycatch mitigation have to be developed. Understanding how to increase avoidance, gear selectivity, and thornback ray survival should be further investigated and measures to address these issues should be developed. In the coming years attention should be given to the species-specific differences in susceptibility to fishing pressure, and a species-specific approach to management could usefully be considered.
A substantial lack of knowledge remains on both the spawning and nursery areas for thornback rays (outside the Thames estuary and other UK coastal areas) and also on the population structure of this species. This limits the development of spatio-temporal management measures for the species. Tagging (electronic and conventional) programmes and DNA analyses focusing on thornback rays throughout their range should be considered. In addition, existing survey data could provide information on the locations of nursery grounds and other juvenile habitats, which should be further investigated to identify sites where there are large numbers of 0-groups (i.e. fish in their first year of life) and where these life-history stages are found on a regular basis (ICES 2019b).
Understanding how to increase avoidance, gear selectivity and thornback ray survival should be further researched and appropriate management measures should be developed accordingly.
The population size is not known and the information on life history and population structure is incomplete. The Working Group on Elasmobranch Fishes (WGEF) states that: “WGEF is still concerned about the possibility of misidentification of skates in some recent IBTS surveys, especially differentiation between R. clavata and starry ray Amblyraja radiata” (ICES 2019b). The effect of such misidentifications would be to underestimate Thornback ray abundance.
The assessment is based on ICES stock assessments (survey trends).
Bird, C., Burt, G.J., Hampton, N., McCully Phillips, S.R., Ellis, J.R. 2019. Fifty years of tagging skates (Rajidae): using mark recapture data to evaluate stock units. Journal of the Marine Biological Association of the United Kingdom 1–11. https://doi.org/10.1017/S0025315419000997
Catchpole, T., Wright, S., Bendall, V., Hetherington, S., Randall, P., Ross, E., Santos, A. R., Ellis, J., Depestele, J., and Neville, S. 2017. Ray Discard Survival: Enhancing evidence of the discard survival of ray species. CEFAS Report: 1-70.
Couce, E., Schratzberger, M., and Engelhard, G. H. 2020. Reconstructing three decades of total international trawling effort in the North Sea. Earth System Science Data, 12, 373–386. https://doi.org/10.5194/essd-12-373-2020.
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), p.113.
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(6): 1702-1719.
Enever, R., Catchpole, T. L., Ellis, J. R. and Grant, A. 2009. The survival of skates (Rajidae) caught by demersal trawlers fishing in UK waters. Fish Res 97: 72-76
Gallagher, M.J., Nolan, C.P. and Jeal, F. 2005. Age, growth and maturity of the commercial skates species from the Irish Sea. Journal of Northwest Atlantic Fishery Science, 35: 47-66.
Gascuel, D., Coll, M., Fox, C., Guénette, S., Guitton, J., Kenny, A., Leyla Knittweis, L., Nielsen, J. R., Piet, G., Raid, T., Travers-Trolet, M., and Shepard, S. 2016. Fishing impact and environmental status in European seas: a diagnosis from stock assessments and ecosystem indicators. Fish and Fisheries, 17: 31–55. https://doi.org/10.1111/faf.12090.
Holden, M.J. 1975. The fecundity of Raja clavata in British waters. Journal du Conseil International pourl'Exploration de la Mer. 36 (2), 110-118.
Hunter, E., Berry, F., Buckley, A. A., Stewart, C., and Metcalfe, J. D. 2006. Seasonal Migration of Thornback rays and Implications for Closure Management. Journal of Applied Ecology, 43: 710-720. https://doi.org/10.1111/j.1365-2664.2006.01194.x
ICES. 2018. Report of the Working Group on Elasmobranch Fishes (WGEF), 19–28 June 2018, Lisbon, Portugal. ICES CM 2018/ACOM:16. 1306 pp.
ICES. 2019a. Thornback ray (Raja clavata) in Subarea 4 and in divisions 3.a and 7.d (North Sea, Skagerrak, Kattegat, and eastern English Channel). In Report of the ICES Advisory Committee, 2019. ICES Advice 2019, rjc.27.3a47d, https://doi.org/10.17895/ices.advice.4836.
ICES 2019b. Working Group on Elasmobranch Fishes (WGEF). ICES Scientific Reports. 1:25. 964 pp. http://doi.org/10.17895/ices.pub.5594.
ICES. 2019c. Rays and skates (Rajidae), mainly thornback ray (Raja clavata) in subareas 10 and 12 (Azores grounds and north of Azores). In Report of the ICES Advisory Committee, 2019. ICES Advice 2019, raj.27.1012, https://doi.org/10.17895/ices.advice.4832.
ICES. 2020a. Thornback ray (Raja clavata) in divisions 7.a and 7.f–g (Irish Sea, Bristol Channel, Celtic Sea North). In Report of the ICES Advisory Committee, 2020. ICES Advice 2020, rjc.27.7afg. https://doi.org/10.17895/ices.advice.5785.
ICES. 2020b. Thornback ray (Raja clavata) in Subarea 6 (West of Scotland). In Report of the ICES Advisory Committee, 2020.
ICES Advice 2020, rjc.27.6. https://doi.org/10.17895/ices.advice.5789.
ICES. 2020c. Thornback ray (Raja clavata) in Subarea 8 (Bay of Biscay) (advice for 2021 and 2022). In Report of the ICES Advisory Committee, 2020. ICES Advice 2020, rjc.27.8. https://doi.org/10.17895/ices.advice.5786.
ICES. 2020d. Thornback ray (Raja clavata) in Division 9.a (Atlantic Iberian waters). In Report of the ICES Advisory Committee, 2020. ICES Advice 2020, rjc.27.9a. https://doi.org/10.17895/ices.advice.5788.
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.
Ryland, J. S., and Ajayi, T. O. 1984. Growth and population dynamics of three Raja species in Carmarthen Bay, British Isles. Journal du Conseil International pour l’Exploration de la Mer, 41: 111 –120.
Schram, E., and Molenaar, P. 2018. Discards survival probabilities of flatfish and rays in North Sea pulse-trawl fisheries. Wageningen Marine Research (University & Research Centre). Wageningen Marine Research report C037/18: 39 pp.
Serra-Pereira, B., Figueiredo, I., & Gordo, L. S. (2011). Maturation, fecundity, and spawning strategy of the thornback ray, Raja clavata: do reproductive characteristics vary regionally? Marine Biology, 158(10), 2187-2197.
Wheeler A. 1969. The fishes of the British Isles and North-West Europe. McMillan (ed) London, Melbourne, Toronto: I-XVII + 613 p.
Wirtz, P., Fricke, R., and Biscoito, M.J., 2008. The coastal fishes of Madeira Island—new records and an annotated check-list. Zootaxa, 1715(1), p.1.