The hook-nosed sea pig is a master of the North Atlantic's rocky shores

Nature · Published 3 October 2026 · Updated 25 October 2026 Swipe more like this →

In short: Known as the horsehead seal, the grey seal is a formidable marine mammal that spends most of its life at sea. While they are rare globally, the United Kingdom hosts nearly all of the European population, relying on remote, undisturbed islands to raise their pups in vast, protected breeding colonies.

The grey seal, scientifically known as Halichoerus grypus, earns its name from the Latin for hook-nosed sea pig. As a member of the Phocidae family, or true seals, it lacks external ear flaps and possesses a distinctively sloped, Roman-nosed profile. These animals are sexually dimorphic; males are generally larger, featuring wrinkled, scarred necks and dark coats with lighter patterns, whereas females are smoother and typically display dark spots on a lighter background. They are often confused with harbour seals, but grey seals are significantly heavier and exhibit parallel nostrils rather than the V-shaped configuration seen in their smaller cousins.

These seals are distributed across the North Atlantic, with major populations residing in Canada and the UK. Genetic research suggests that the eastern and western Atlantic groups have remained separate lineages for at least a million years, leading some experts to propose they be classified as distinct subspecies. Within the UK, the species is a conservation priority. Since the late 1970s, the cessation of commercial hunting and large-scale control measures has allowed their numbers to rebound significantly. Today, they are protected through a network of Special Areas of Conservation, which safeguard critical breeding rookeries.

Breeding occurs in autumn, when seals congregate on rocky shores, beaches, and remote islands. The UK's largest colonies are concentrated in the Hebrides and Orkney, with the Monach Islands alone accounting for over 20% of annual pup production. These sites are chosen for their isolation and access to suitable terrain, such as grassy swards or sea caves. While the global population was estimated at approximately 632,000 in 2016, the UK remains a vital stronghold, holding roughly 40% of the world's grey seals and 95% of the European total, underscoring the nation's unique responsibility for their long-term survival.

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