Undulate Ray

Fascinating facts about the Undulate Ray

• A single undulate ray can tip the scales at 22.13 lb (10.04 kg), nearly double the average 10 lb (4.5 kg) size, showing how much growth potential lies in a species that often stays hidden on the seafloor. This weight range hints at the hidden biomass these rays contribute to coastal ecosystems.
• From March through September, a female lays roughly 30 leathery “mermaid’s purses” each year, each measuring 72–90 mm long and 42–52 mm wide, turning the ocean floor into a seasonal egg-factory. The sheer number of eggs explains why stray eggcases sometimes litter beaches after storms.
• Both sexes wait almost a decade before joining the breeding crowd, females mature at about 9 years and males at 8, meaning each generation takes a long time to replace lost members. This slow turnover makes the species especially fragile under heavy fishing pressure.
• Scientists have counted up to 21–23 years as the maximum lifespan of this skate by reading growth rings in its vertebrae. Such longevity underscores how losing adult individuals can have lasting impacts on population health.
• Since 2009 EU law has forced fishers to release any caught undulate rays unharmed, a direct response to steep declines that have already wiped the species out of English Channel records. This legal safeguard illustrates how policy can step in when biology alone can’t keep a population afloat.

At a glance

About the Undulate Ray

The undulate ray, Raja undulata, glides over the soft, silty floors of the Mediterranean and eastern Atlantic with a disc that is triangular at the front and nearly circular at the rear, its dorsal surface a patchwork of light brown, citrine or grey hues broken by darker wavy bands and speckled white spots. Dermal denticles form protective spines, median spines scattered in adults, regular in juveniles, while males sport a single lateral row of spines on each side and alar spines on the pectoral disc, and females display three lateral rows. Its eyes sit atop a medium-sized head, feeding through a ventrally placed, slightly arched mouth that leads to five pairs of small gill slits, and a tail as long as the body bears two well-separated dorsal fins near its tip, each usually flanked by a spine. Weighing around 10 lb (4.5 kg) but capable of reaching 22.13 lb (10.04 kg) and 100 cm (39 in) in length, the ray prefers sandy or muddy bottoms at 50–200 m depth, though it can be found shallower, especially around the north-west of Ireland, the eastern English Channel, and the south coast of Portugal. Its diet is a opportunistic mix of small fish, crustaceans, molluscs and other macrobenthos, captured while the ray lies partially buried, waiting for prey to drift by. Remarkably, the species reproduces via leathery black eggcases, "mermaid's purses", that measure 72–90 mm by 42–52 mm and often wash ashore empty after storms, a silent testament to a life cycle that spans up to 21–23 years and reaches sexual maturity at nine years for females and eight for males. This slow-growing, late-maturing skate navigates a world where each eggcase is a fragile promise of the next generation, a promise increasingly jeopardized by human hands.

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