The grey seal (Halichoerus grypus), or gray seal in the United States, is a large seal of the family Phocidae, which are commonly referred to as "true seals" or "earless seals". The only species classified in the genus Halichoerus, it is found on both shores of the North Atlantic Ocean. In Latin, Halichoerus grypus means "hook-nosed sea pig". It is also known as the horsehead seal, owing to its large head.
The grey seal is large and heavy, with individuals from the eastern Atlantic being long and weighing , while individuals from the western Atlantic are up to long, and can reach a weight of as much as . It is found widely across the northern Atlantic, ranging from the US to Russia, and occasionally as far south as Portugal. It can be divided into two subspecies: the Baltic grey seal (Halichoerus grypus grypus), found in the Baltic Sea, and the Atlantic grey seal (Halichoerus grypus atlantica), found everywhere else. The largest populations are in Canada and the UK.
Grey seals have a varied diet, feeding mostly on fish, and occasionally on invertebrates such as octopuses and lobsters. Their main predators are orcas, and they are also prey to sharks. The pups main predator is often eagles and gulls.
Taxonomy There are two recognized subspecies: Image Subspecies Distribution Halichoerus grypus grypus Baltic Sea Halichoerus grypus atlantica western North Atlantic stock (eastern Canada and the northeastern United States), the eastern North Atlantic stock (British Isles, Iceland, Norway, Denmark, the Faroe Islands, and Russia)
The type specimen of H. g. grypus (Zoological Museum of Copenhagen specimen ZMUC M11-1525, caught in 1788 off the island of Amager, Danish part of the Baltic Sea) was believed lost for many years, but was rediscovered in 2016, and a DNA test showed it belonged to a Baltic Sea specimen rather than from Greenland, as had previously been assumed (because it was first described in Otto Fabricius' book on the animals in Greenland: Fauna Groenlandica). The name H. g. grypus was therefore transferred to the Baltic subspecies (replacing H. g. macrorhynchus), and the name H. g. atlantica resurrected for the Atlantic subspecies.
Molecular studies have indicated that the eastern and western Atlantic populations have been genetically distinct for at least one million years, and could potentially be considered separate subspecies.
In 2022, overlap in the range of the two subspecies was recorded for the first time. This brings the possibility that hybridisation may occur. As of 2026, no hybrids have been reported.
Description
The grey seal is large and heavy: In the eastern Atlantic, males are typically long and weigh ; the females are much smaller, typically long and in weight. Individuals from the western Atlantic are often much larger, with males averaging up to and reaching a weight of as much as and females averaging up to and sometimes weighing up to . Record-sized bull grey seals can reach about in length. A common average weight in Great Britain was found to be about for males and for females whereas in Nova Scotia, Canada, adult males averaged and adult females averaged .
Colours and patterns are highly variable. Males tend to have a light pattern on a dark background, while females tend to have the opposite — a dark pattern on a light background, often with a noticeably light belly. The neck and chest of males tend to be wrinkled and scarred, while females are smoother. Males have an especially wide muzzle. Males have a large, visible opening on the lower abdomen, while females have no obvious openings. Juveniles are often a solid colour, and can be difficult or impossible to sex. About 1 in 400 seal pups are melanistic, where they have a solid black coat.
Differences from other seals
Grey seals lack external ear flaps (as with their fellow earless seals), and characteristically have large snouts, often referred to as a "Roman nose".
The Harbour seal occurs across the entire range of the grey seal, and they can be difficult to tell apart. Compared to the harbour seal, the grey seal has a longer, more sloped snout, a flatter head, and eyes which are set farther apart. The nostrils of the harbour seal form a "V" shape, appearing to meet at the bottom, while the nostrils of the grey seal are more parallel. The grey seal has fewer, larger spots than the harbour seal. Grey seals are often larger than harbour seals, and are about 3 times heavier.
Wintering hooded seals can be confused with grey seals as they are about the same size and somewhat share a large-nosed look. They can be distinguished by the fact that the hooded seal has a paler base colour and usually evidences a stronger spotting.
Distribution and habitat
The grey seal is resident to 18 countries: Belgium, Canada, Denmark (including Faroe Islands), Estonia, Finland, France, Germany, Iceland, Ireland, Latvia, Lithuania, the Netherlands, Norway, Poland, Russia, Sweden, the United Kingdom, and the United States of America. It is also an occasional vagrant in Greenland and Portugal. The global population was estimated to be about 632,000 in 2016.
In the UK, the most ecologically significant breeding grounds, classified as Special Areas of Conservation (SACs) Grade A/B, are as follows (percentage of annual UK pup production in parentheses): Monach Islands, Outer Hebrides (20%); Faray and Holm of Faray, Orkney (9%); North Rona, Outer Hebrides (5%); Isle of May, Fife (4.5%); Treshnish Isles, Inner Hebrides (3%); Berwickshire and North Northumberland Coast (2.5%); and Pembrokeshire Marine (2%).
Some of the more touristically significant breeding grounds in the UK which aren't SACs include: Blakeney Point and Horsey Beach in Norfolk, various locations in Cornwall, and Donna Nook in Lincolnshire. Large numbers of grey seals have recently commenced a recolonisation of the tidal section of the River Thames in London; a survey conducted by the ZSL in 2024 found that around 3,000 grey seals were living in the area. In Ireland, the 5 largest colonies are in order: Inishkea Islands, County Mayo; various islands in Connemara, County Galway; various islands in County Donegal; Blasket Islands, County Kerry; and Saltee Islands, County Wexford.
In the German Bight, colonies exist off the islands Sylt, Amrum and on Heligoland.
In Iceland, the largest colony is in Breiðafjörður, with 62% of Iceland's pups being born there. Other large colonies can be found on Iceland's northwest coast, in Strandir and Skagafjörður, and the south coast, in Öræfi and Surtsey.
In Canada, the grey seal is typically found in large numbers in the coastal waters of the Maritime Provinces. It is typically seen in areas such as the Gulf of St. Lawrence, Newfoundland, Prince Edward Island, and Quebec. The largest colony in the world is on Sable Island, Nova Scotia, with an estimated 76,600 pups born in 2021.
In the US, it is found year-round off the coast of New England, in particular Maine and Massachusetts. There are colonies all along the northern Atlantic coast as far south as New Jersey, and occasional sightings have been reported as far as North Carolina. Archaeological evidence confirms grey seals in southern New England with remains found on Block Island, Martha's Vineyard, and near the mouth of the Quinnipiac River in New Haven, Connecticut, and there is a report by Farley Mowat of historic breeding colonies as far south as Cape Hatteras, North Carolina. Its range is expanding south, with a growing population in North Carolina.
+ Local population numbers of grey seal Region Pups born annually Year Canada (total) 98,200 2021 Canada, Sable Island 76,600 2021 UK (total) 57,000 2012 UK, Scotland 50,000 2012 Canada, Gulf of St Lawrence 16,900 2021 Europe (total, excluding UK) 10,700 n/a UK, Northeast England 4,900 2012 Baltic Sea 4,700 2007 United States 2,600 2008 Ireland 2,100 2012 Norway 1,300 2008 Iceland 1,550 2022 Russia 800 1994 Wadden Sea 600 2014 Total 168,850 n/a
Behaviour
Grey seals spend most of their time at sea. They can be seen hauled out on rocks, islands, and shoals not far from shore, occasionally coming ashore to rest. The Baltic subspecies most frequently hauls out at night, beginning right after sunset. This may be related to the behaviour of its main prey species, Atlantic herring, which forms large schools during the day and disperses at night.
Reproduction
Breeding colonies are known as rookeries, and are generally on beaches and remote islands, although in the Baltic and the Gulf of St Lawrence grey seals have been known to occasionally breed on sea ice. Females generally return to the exact location where they were born to give birth, but they sometimes venture to different rookeries.
Females reach sexual maturity at 3–5 years old, while males reach maturity at 6 years. Males, known as bulls, form a territory on the beach, and can mate with more than 6 females, known as cows, a year. Mating can take place on land or in water. The females are pregnant for about 11 and a half months, and give birth to a single pup at the same time each year. Pups weigh at birth, and have dense, soft, silky white fur.
The time of year that pups are born varies depending on the location, landing somewhere between September and March. The earliest pups are born in Ireland and Southwest UK in September. The time at which pups are born along the UK becomes progressively later in a counterclockwise manner; pups are born on the Isles of Scilly and Cornwall in September, in Scotland and the Farne Islands in December, and on the southeast coast in January. In Canada, pups are born in January, and in the Baltic, pupping is in February or March.
All parental care is provided by the female. Males do not provide parental care, but they defend females against other males for mating. During lactation, the pups rapidly fatten up on their mothers' extremely fat-rich milk, quadrupling their body weight in 18 days. The milk can consist of up to 60% fat. After lactation, at about 18–21 days old, they shed their pup fur and grow dense waterproof adult fur, and enter a post-weaning fast for 21 days. After their fast, they leave for the sea to learn to fish for themselves. The pups are precocial, with mothers returning to the sea to forage once pups are weaned. The mother doesn't eat at all while raising their pup, and can lose up to 40% of their weight each breeding season.
Seal pup first-year survival rates are estimated to vary from 80 to 85% to below 50% depending on location and conditions. Starvation due to difficulties in learning to feed appears to be the main cause of pup death.
Male grey seals engage in aggressive sexual behaviour, which can lead to severe injuries and even death for the female. Sometimes they will also target females from other seal species. In the North Sea, multiple cases were recorded of pregnant harbour seals dying as a result of forced copulation with male grey seals.
Communication
While it was once thought that marine mammals communicate vocally, research conducted by researchers at Monash University shows that grey seals can clap their flippers underwater as a form of communication. This may be used to deter a predator from attacking or to attract a mate. The head researcher, Dr. Burville, had been diving for 17 years in an attempt to capture this behaviour on camera. He stated: "The discovery of 'clapping seals' might not seem that surprising, after all, they're famous for clapping in zoos and aquaria, but where zoo animals are often trained to clap for our entertainment -- these grey seals are doing it in the wild of their own accord."
Ecology
Diet