A roker’s tail

Found on the beach: all that’s left of a thornback ray (Raja clavata) - its distinctive tail.

The thornback ray, or ‘roker’ as it is often called in the UK, is a familiar and charismatic resident of British coastal waters, including the shores around Brighton. Its name comes from the distinctive thorn-like spines that stud its back and tail - these are actually modified skin teeth, giving the ray a rough, almost armored appearance. With its broad, diamond-shaped body and short snout, the thornback ray glides over sandy and muddy seabeds, its mottled brown-grey upper surface dappled with yellowish patches and dark spots, blending perfectly with the sea floor.

Unlike most true rays, thornback rays are technically skates, and they lay eggs rather than giving birth to live young. Each spring and summer, females deposit tough, rectangular egg cases - known to beachcombers as ‘mermaid’s purses’ - in sheltered areas on the seabed (see also A catshark that is a dogfish.) Inside each case, a single embryo develops, feeding on a yolk sac for four to five months before hatching as a miniature ray, already equipped with the beginnings of its signature thorns. Juveniles spend their early months in shallow nursery grounds, gradually venturing into deeper waters as they grow. Males reach maturity at around seven years old, females at about nine, and some individuals may live for over two decades.

Thornback rays are opportunistic predators, feeding on a variety of crustaceans and small fish. Juveniles prefer shrimps and small crabs, while adults tackle larger crustaceans and fish, using their powerful jaws to crush shells. The thornback’s rough skin and formidable thorns provide some defense against predators, and these features become more pronounced with age, especially in females, who develop a line of large thorns along their backs.

There is often confusion between skates and rays, but the differences are subtle yet significant. Skates like the thornback lay eggs, while most true rays bear live young. Skates have stockier tails without venomous spines and tend to have more pronounced dorsal fins, whereas rays often have slender, whip-like tails and, in some species, venomous stings. In the UK, the term ‘ray’ is often used for both, adding to the muddle, especially at fishmongers where ‘skate wings’ are a common offering.

Around Brighton, the thornback ray is a familiar catch for anglers and is sometimes landed by commercial fisheries. Conservation groups in Sussex have launched campaigns to monitor ray populations and promote sustainable fishing practices, though the thornback ray is currently listed as Least Concern on the IUCN Red List.

Other rays share these waters, including the undulate ray with its wavy markings, the blonde ray, and the once-abundant but now critically endangered common skate. The fate of these species is intertwined with that of the thornback, as they are often caught together in mixed fisheries. The challenge is compounded by the difficulty in identifying species once they are skinned and sold as generic ‘skate’ wings. See Wikipedia for more on the roker!