Highly recognisable and most commonly encountered skate which, although improving, is still showing decline overall.

In brief

• The most commonly encountered skate in Northern Irish waters.
• Distinctive large spines.
• Historically overexploited through commercial fishing.
• Population decline may be slowing or stabilising but levels are still well below historic abundances.

Species description: The thornback skate is probably one of the commonest skate encountered by divers. Like all skate it has a flattened body with broad, wing-like pectoral fins. The body is kite-shaped with a long, thorny tail. The back is covered in numerous thorny spines. In sexually mature fish some of the spines are thickened with button-like bases (known as bucklers). These are particularly well developed on the tail and back of sexually mature females. The colour varies from light brown to grey with darker blotches and numerous small darker spots and yellow patches. Sometimes the yellow patches are surrounded by small dark spots. The underside is creamy-white with a greyish margin. Adult fish can grow to 1 m in length although most are less than 85 cm.

Similar species: Other skate do have spiny thorns, especially on their tails however only the thornback has large spines with button-like bases (bucklers).

How to see this species: The thornback skate is usually found on sediment type seabeds such as mud, sand or gravel at depths between 10-60 m. Juvenile fish feed on small crustaceans, particularly amphipods and bottom-living shrimps, Adults feed on crabs, shrimps and small fish.

Current status: Least Concern, however populations are thought to be in decline. Populations in the Irish Sea have been estimated to have undergone an approximately 45% decline in abundance between 1988–1997. They may now be stabilising but are well below historic levels, and more data are required to confirm this.

Why is this species a priority in Northern Ireland?

• Criterion 1: Internationally listed species.
• Criterion 2: Decline based on available data and expert judgement.

Threats: This species has historically been overexploited through commercial fishing, and although decline is thought to be slowing and some populations may be stabilising numbers are still well below former levels.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Investigate and monitor local population trends.
• Use data to inform fisheries management and conservation measures.
• Ensure adequate protection from bottom fishing in some areas to allow population and habitat recovery.

Conservation:

• Currently listed as Least Concern on Irish Red List, but Near Threatened in a European and Global context.
• On OSPAR list of Threatened and/or Declining Species and Habitats.

Distribution Map from NBN: Raja clavata at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Raja clavata at iNaturalist World Species Observations database.

WoRMS: Raja clavata at World Register of Marine Species. Accepted name: Raja clavata Linnaeus, 1758. AphiaID: 105883.

Classification: Biota; Animalia; Chordata; Vertebrata; Gnathostomata; Chondrichthyes; Elasmobranchii; Neoselachii; Batoidea; Rajiformes; Rajidae; Raja