Amblyraja radiata (Donovan 1808), Thorny skate (Rajidae)

Author: Ronald Fricke, Germany

1. Description of the habitat/autecology of the species

The thorny skate Amblyraja radiata (synonym: Raja radiata) is a demersally living skate species occurring on soft bottoms (occasionally also hard bottoms) below 20 m depth, with a preference to water temperatures of 1-10°C. Amblyraja radiata apparently reproduces throughout the year; the species is oviparous and deposits its egg-case in algae and seagrass beds. Thorny skates feed on crustaceans, bony fish and polychaete worms (Fricke, 1987: 50; Froese & Pauly, 2005; Sulikowski et al., 2005). Maximum total length 10 cm, maximum total weight 4,25 kg.

2. Distribution (past and present)

Distributed in the western HELCOM area from Kattegat to Kiel Bay. Outside the HELCOM area, cold waters of North Sea and Western Atlantic.

3. Importance (sub-regional, Baltic-wide, global)

According to the definition in HELCOM (2007), this species is neither of global nor local importance in the HELCOM area. Swedish landings of Rajidae species amounts to less than one tonnes yearly in Kattegat but the tenfold in Skagerrak.

4. Status of threat/decline

In the HELCOM area, thorny skate is classified as endangered (EN) according to IUCN criteria, and as a HELCOM high priority species (HELCOM, 2007). Suggested as endangered (EN) by George (2003, personal communication 2004) and listed as threatened migrant (TM) in Germany. The species is not on the global IUCN red list and it is considereded abundant by the ICES WGEF (ICES 2006).

5. Threat/decline factors

Threatened by several factors: habitat loss due to effects of sand and gravel extraction, trawling, eutrophication of sand bottoms (since the species inhabits clean oxygenated sand bottoms where it can bury and breathe), and fisheries (as by-catch in demersal fisheries). It is rare in the HELCOM area but abundant in adjacent waters. It is sensitive to human activities, but not a keystone species.

6. Options for improvement

Amblyraja radiata could benefit from restrictions to benthic fisheries (trawl etc.), and a restrictive sand and gravel extraction. Hence, it would benefit from marine protected areas without fisheries pressure and sand/gravel extraction. As the threats for the species occur mainly outside the HELCOM area in the neighbouring OSPAR area, OSPAR could be requested to consider providing additional protection for this species.

7. References

Fricke R. 1987. Deutsche Meeresfische. Bestimmungsbuch. Hamburg (DJN), 219 pp.

Froese R. & Pauly, D. (eds) 2005. FishBase. Available in: www.fishbase.org, version (11/2005).

George M.R. 2003.  Die Ost- und Nordsee als Lebensraum für Haie, Rochen und Chimären. Meer und Museum, 17: 15-24. 

HELCOM 2007. HELCOM Red list of threatened and declining species of lampreys and fish of the Baltic Sea. Baltic Sea Environmental Proceedings, No. 109, 40 pp. Available in: http://www.helcom.fi/stc/files/Publications/Proceedings/bsep109.pdf

ICES. 2006. Report of the Working Group on Elasmobranch Fishes (WGEF), 14–21 June

2006, ICES Headquarters. ICES CM 2006/ACFM:31. 291 pp.

Sulikowski J.A., Kneebone J., Elzey S., Danley P.D., Howell W.H. & Tsang P.W.C. 2005. The reproductive cycle of the thorny skate (Amblyraja radiata) in the western Gulf of Maine. Fisheries Bulletin 103 (3): 536-543.