The undulate ray is medium sized member of the skate family that can grow up to 100 cm in length. This species is only very rarely observed in Northern Ireland waters, being more commonly associated with southern areas. The undulate ray is an offshore demersal species with a depth range of 50-200 m. It feeds on a wide range of sea-bed dwelling organisms.

In brief

• It prefers to dwell on the sea-bed, mainly in sandy substrate
• This species is at threat from being caught as bycatch in long-line and trawl fisheries and also targeted and recreational fisheries. Habitat destruction may also have negative effects for the inshore populations
• Occurrences of undulate rays are very rare in Northern Irish/Irish waters and they are listed as endangered on the IUCN (International Union for the Conservation of Nature) Red List

Species description: The undulate ray has broadly rounded pectoral fins and the front outline of the disc is undulating. It has a dorso-ventrally flattened body with eyes and spiracles at the top of the head. It has a pointed snout. The tail, which is slender, starts from rhomboid pectoral discs. The back is covered with prickles except on the hind parts of the disk and pelvic fins. The dorsal fins are well separated, usually with inter-dorsal spines. The colour on the back is yellowish brown with white spots and long wavy dark brown bands edged with light spots. Ventrally white like other rays except for a greyish end to the tail.

Life cycle: Juveniles are more common in shallower waters, progressing to deeper water as they mature. However research has shown that undulate ray juveniles can have a tendency to follow large objects, such as their mother. One of the main reasons this species is vulnerable is the late stage that it reaches sexual maturity. A study into Portuguese undulate ray populations showed that males reach sexual maturity between the age of 6-12 yrs (70-83 cm) and females reach sexual maturity between the age of 8-13 yrs (75-88 cm). This same study showed that reproduction occurred during the winter months; however studies in different regions have shown spawning in Spring and early Summer. It is thought that spawning could be related to water temperature, which accounts for the differing time of year. Eggs are oblong capsules with stiff pointed horns at the corners. They are deposited in sandy or muddy flats. Egg capsules are 7.2-9.0 cm long and 4.2-5.2 cm wide. The embryos feed purely on the yolk within the egg casing before hatching.

Similar species: There are many similar species from the Rajidae family. Some of the most common of these that are present in Northern Irish waters are the cuckoo ray, Leucoraja naevus, the spotted ray Raja montagui, and the thornback ray Raja clavata.

How to see this species: Undulate rays are very rarely seen in the waters around Northern Ireland. They are more commonly seen further to the south. In particular, Tralee Bay in SW Ireland (where all elasmobranch species have been protected) has had regular sightings of undulate rays over the years, making it a good place to see this rare species.

Current status: Endangered and declining. Data deficient. The severe lack of recorded landings of undulate ray in Northern Irish waters makes it difficult to categorise its status within Northern Ireland. Estimated population size and distribution within Northern Ireland is not possible with the current data available.

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:

• Due to their habitat type the undulate ray is vulnerable to being captured as by-catch by commercial fishing trawlers targeting other species. It is potentially vulnerable to exploitation because, as with most elasmobranchs, it matures relatively late and produces few young. As a result, immature individuals are vulnerable to fishing mortality before they are able to spawn.
• Given that this large-bodied species has a patchy distribution in inshore waters of the southern Celtic Sea; it is susceptible to localized over-exploitation, with some of these areas showing signs of depletion. In Tralee Bay, southwest Ireland, populations have declined by 60-80% since 1981 and it has been absent in English Channel surveys in recent years.
• Habitat destruction may also have negative effects for the inshore populations.

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:

• Anglers should employ a tag and release approach with all landings of undulate ray.
• Adequate areas should receive protection from harmful bottom fishing methods in order to allow for population and habitat recovery.

Conservation:

• Listed as Endangered on Irish Red List, and Near Threatened on European and Global Red List.
• In 2007, the undulate ray was included on the UK Biodiversity Action Plan (BAP) list. Though this does not provide any legal protection for the species in itself, it includes provisions to work towards European conservation legislation. Its proposed objectives include plans to stabilise populations in refuge areas and to facilitate the migration of animals from refuge populations to areas where they are scarce or extinct.
• In 2009 the undulate ray received full protection from the European Council in ICES areas VIa-b, VIIa-k, VIII and IX, meaning that it cannot be retained or landed if caught. As elasmobranchs have no swim bladder that can overinflate or rupture, they are more likely to survive capture and release than teleost fish. The mandatory release order is therefore likely to significantly reduce the level of fishing mortality.
• Removed from the Irish Specimen Fish Committee list due to fears over its conservation status.

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

iNaturalist: Raja undulata at iNaturalist World Species Observations database.

WoRMS: Raja undulata at World Register of Marine Species. Accepted name: Raja undulata Lacepède, 1802. AphiaID: 105891.

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