Halichoerus grypus
A big North Atlantic predator with an unflattering name and a habit scientists only recently uncovered.
The grey seal has one of the least flattering scientific names in zoology. Halichoerus grypus translates roughly as "hooked-nosed pig of the sea", and it refers to the long, straight, heavy snout that separates this animal from every other seal in the North Atlantic. In an adult bull the snout is genuinely enormous, wide across the bridge, with the nostrils set almost parallel. Field guides everywhere teach the same trick: look at the nostrils. In a harbor seal they meet at the bottom in a V. In a grey seal they stay apart, like two commas.
That head is not decoration. Bulls fight for breeding position on crowded beaches, rearing up and biting at each other's necks and shoulders, and the thick, scarred, heavily folded neck skin of an older male is armour built for exactly that. You can often read a bull's history from his scars.
Females look so different that beach-goers regularly report two kinds of seal in one colony. They are smaller, paler, more finely spotted, and their muzzle is shorter and less exaggerated. Both sexes share the same short, clawed foreflippers and the same shuffling, caterpillar-like movement on land, because true seals cannot rotate their hind flippers forward to walk the way sea lions do.
Grey seal pups are born on beaches, sandbars, rocky islands and sometimes ice, in white woolly coats that are useless in water. For about three weeks the pup does almost nothing except drink. Grey seal milk is extraordinarily rich, far fattier than cow's milk, and the pup puts on roughly 1.4 kilograms a day, tripling in weight while its mother eats nothing at all and burns her own blubber to make the milk.
Then she leaves. She mates again before she goes and returns to sea to feed, and the pup is on its own. It sheds the white lanugo, sits on the beach living off its new fat for another week or two, and eventually works out how to swim and hunt with nobody teaching it. A very large fraction of pups do not survive their first year.
Grey seal pups are also loud, and their calls sound uncomfortably like a human baby crying. That is not sentiment, it is signal. On a beach holding hundreds of pups, a returning mother has to find her own. Mothers recognise their pups by voice and by smell, and will refuse to feed another female's pup.
For years, harbour porpoises washed up on beaches around the southern North Sea with long, clean, spiral-shaped wounds. The injuries looked mechanical, and ship propellers and fishing gear were both blamed. The truth turned out to be stranger. Researchers swabbed the bite margins on mutilated porpoises and found grey seal DNA, and separately observed grey seals attacking porpoises directly.
A Dutch team then went back through photographs of 1,081 porpoises stranded between 2003 and 2013. Of the 271 carcasses fresh enough to assess properly, about a quarter carried bite and claw marks matching the pattern on the DNA-confirmed cases. The victims were mostly healthy, well-fed juveniles. The conclusion published in 2014 was blunt: grey seal predation is one of the leading causes of death for harbour porpoises in Dutch waters.
Later work in Scotland found that grey seals also kill and eat grey seal pups, which explains some of the same spiral wounds turning up on seals. None of this makes grey seals villains. It makes them a large, powerful, intelligent predator that had been quietly underestimated, and it is a good reminder that a species can be studied for a century and still be doing something nobody had noticed.
Britain passed the Grey Seals (Protection) Act in 1914, one of the earliest laws anywhere written to protect a wild mammal. The species has recovered strongly across most of its range since. UK pup production has climbed for decades and reached a record 79,122 pups in the 2022/2023 season. The Baltic population, cut down in the twentieth century first by hunting and then by pollutants that caused widespread infertility, has been climbing since the 1980s and stood at just under 49,000 in 2024.
Recovery brings conflict. Grey seals eat commercially valuable fish, damage nets, and take fish directly off gear, and fishing organisations across the North Atlantic argue about their impact on salmon and cod. SCOS estimated 452 harbour and grey seals killed as bycatch in UK fisheries in 2022, most of them young grey seals. Acoustic deterrents designed to keep porpoises out of nets may, awkwardly, be attracting seals to them instead.
Managing any of this means being able to say how many seals there are, and how many could be removed without harming the population. That is why the counting work matters so much, and why it is harder than it sounds.
Grey seals cannot be counted at sea. Instead, scientists count what stays put: pups on breeding colonies, photographed from aircraft across a whole season, and adults hauled out during the August moult. Neither number is the population. Pup counts have to be converted using estimates of survival, fecundity and the ratio of males to females, and moult counts have to be scaled up using telemetry data showing what fraction of seals is out of the water at any given moment.
Every one of those conversion factors carries uncertainty, which is why the British estimate is published as 157,829 with a range of 136,546 to 185,054 rather than as one tidy figure. SCOS 2025 was candid that the existing population model no longer fits the data well in some regions, partly because seals are moving between areas in ways the model does not account for, and recommended building a new one.
Newer tools are being tested. Drones work for small sites, satellite imagery is currently too coarse and too often blocked by cloud, and artificial intelligence counting is promising but not yet operational for aerial seal surveys. For now the most reliable method is still a crewed aircraft, a very good camera, and people looking carefully at photographs.
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