A large westerly species of crustacean, in Northern Ireland known only from the Rathlin Island area and one other site on the north coast. It is vulnerable to fishing activities, and populations in Northern Ireland and western Scotland have been declining.

In brief

• Found on the western end of Rathlin Island, Shamrock Pinnacle, and off Kinbane Head
• Subtidal rock faces, rocky seabed, and sometimes on open terrain
• Can be seen the year round
• A priority species on account of its scarcity and decline
• Main threats come from fishing; the species has a poor recovery rate after exploitation.

Species description: A large crustacean, capable of growing to 600mm in length, but more commonly to 400-500mm. It has antennae that are longer than its body, and it is heavily built, with body armour bearing large spines; the claws are small and hook-like. Its tail is formed of a cluster of broad plates. Colour is orange, with whitish or yellow edging to legs and claws, but brown, purple and sandy-coloured morphs have also been found. The species can be gregarious where the population density allows, and whilst they are mostly crawlers around the seabed, they can also swim. They feed on echinoderms, small snails and bivalves, shrimp larvae and worms.

Life cycle: Females moult from July to September prior to mating, whilst the moulting period of the males is less defined, probably focusing more on the winter. Sexual maturity begins when the carapace (upper shell) is 76-77mm in females, 82-83mm in males, and sexes are separate. Egg-bearing females migrate to deeper water whilst the eggs are developing, and then return for mating, fertilisation of eggs and release. The eggs then develop into planktonic larvae which develop for about five months before settling on the seabed as young crawfish.

Similar species: Homarus gammarus — the lobster is the only species likely to cause confusion. However Palinurus is basically orange coloured, lacks the heavy claws, and is much spinier. It is also more likely than the lobster to be seen wandering over the open seabed.

How to see this species: Palinurus has a primarily western distribution and in Northern Ireland can be found at a number of sites around the western third of Rathlin Island, Shamrock Pinnacle, and near Kinbane head on the north coast. Elsewhere in Ireland it has been recorded on Tory Island, in Donegal Bay, Achill Island, and a number of locations in County Mayo, and generally around south-west Ireland. In Britain it is found around western Scotland although it is becoming scarcer there, and on the Pembrokeshire and Cornish coasts. Key areas to search are open exposed rock faces, rocky seabeds and locations with holes and crevices, although they may also be found in open terrain. They can be found throughout the year, but subject to migration of egg-bearing females (see above).

Current status: In Northern Ireland, known only from three sites off the north coast. It has no legal protection, but is covered by fisheries regulations administered by Fisheries Division of DARD(NI).

Why is this species a priority in Northern Ireland? The species is scarce and declining. It is a UK priority species. It is known that other populations, for example those in western Scotland are also declining.

Threats: The likely cause of the declines is fisheries, particularly with respect to tangle net fishing. Research has demonstrated that the species is sensitive to extraction, and shows a poor rate of recovery.

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

iNaturalist: Palinurus elephas at iNaturalist World Species Observations database.

WoRMS: Palinurus elephas at World Register of Marine Species. Accepted name: Palinurus elephas (Fabricius, 1787). AphiaID: 107703.

Classification: Biota; Animalia; Arthropoda; Crustacea; Multicrustacea; Malacostraca; Eumalacostraca; Eucarida; Decapoda; Pleocyemata; Achelata; Palinuridae; Palinurus