The grey seal (Halichoerus grypus, meaning "hooked-nosed sea pig") is found on both shores of the North Atlantic Ocean. It is a large seal of the family Phocidae or "true seals". It is the only species classified in the genus Halichoerus. Its name is spelled gray seal in the US; it is also known as Atlantic grey seal and the horsehead seal.
It is a large seal, with bulls reaching 2.5–3.3 m (8.2–11 ft) long and weighing 170–310 kg (370–680 lb); the cows are much smaller, typically 1.6–2.0 m (5.2–6.6 ft) long and 100–190 kg (220–420 lb) in weight. Individuals from the western Atlantic are often much larger, males reaching 400 kg (880 lb) and females weighing up to 250 kg (550 lb). It is distinguished from the harbor seal by its straight head profile, nostrils set well apart, and fewer spots on its body. Bull Greys have larger noses and a less curved profile than common seal bulls. Males are generally darker than females, with lighter patches and often scarring around the neck. Females are silver grey to brown with dark patches.
Ecology and distribution 
In Great Britain and Ireland, the grey seal breeds in several colonies on and around the coasts. Notably large colonies are at Donna Nook (Lincolnshire), the Farne Islands off the Northumberland Coast (about 6,000 animals), Orkney and North Rona off the north coast of Scotland, Lambay Island off the coast of Dublin and Ramsey Island off the coast of Pembrokeshire. In the German Bight, colonies exist off the islands Sylt and Amrum and on Heligoland.
In the Western North Atlantic, the grey seal is typically found in large numbers in the coastal waters of Canada and south to about New Jersey in the United States. In Canada, it is typically seen in areas such as the Gulf of St. Lawrence, Newfoundland, the Maritimes, and Quebec. The largest colony in the world is at Sable Island, NS. In the United States it's found year round off the coast of New England, in particular Maine and Massachusetts, and slightly less frequently in the Middle Atlantic States. Its natural range extends south to Virginia.
In recent years, the number of grey seals has been on the rise in the west and in Canada there have been calls for a seal cull.
During the winter months grey seals can be seen hauled out on rocks, islands, and shoals not far from shore, occasionally coming ashore to rest. In the spring recently weaned pups and yearlings occasionally strand on beaches after becoming separated from their group.
The grey seal feeds on a wide variety of fish, mostly benthic or demersal species, taken at depths down to 70 m (230 ft) or more. Sand eels (Ammodytes spp) are important in its diet in many localities. Cod and other gadids, flatfish, herring and skates are also important locally. However, it is clear that the grey seal will eat whatever is available, including octopus and lobsters. The average daily food requirement is estimated to be 5 kg (11 lb), though the seal does not feed every day and it fasts during the breeding season.
The pups are born in autumn (September to November) in the eastern Atlantic and in winter (January to February) in the west, with a dense, soft silky white fur; at first small, they rapidly fatten up on their mothers' extremely fat-rich milk. Within a month or so they shed the pup fur, grow dense waterproof adult fur, and leave for the sea to learn to fish for themselves. In recent years, the number of grey seals has been on the rise in the west and in Canada there have been calls for a seal cull.
In the United States grey seal numbers are increasing rapidly. Up until 1962, Maine and Massachusetts had bounties on seals so that only a few isolated colonies of grey seals remained in Maine. Then in 1972 Congress passed the Marine Mammal Protection Act that prevented harming or harassing seals, and grey seal populations rebounded. For example there is a large breeding colony near Cape Cod, Massachusetts, where pups rebounded from a handful in 1980 to more than 2,000 in 2008. By 2009, thousands of grey seals there had taken up residence on or near popular swimming beaches when Great White Sharks started hunting them close to shore. Also grey seals are seen increasingly in New York and New Jersey waters, and it's expected that they will establish colonies further south.
In the UK seals are protected under the Conservation of Seals Act 1970, however it does not apply to Northern Ireland. In the UK there have also been calls for a cull from some fishermen, claiming that stocks have declined due to the seals.
The population in the Baltic Sea has increased about 8% per year between 1990 and the mid-2000s with the numbers becoming stagnant since 2005. As of 2011 hunting grey seals is legal in Sweden and Finland with 50% of the quota being used. Other anthropogenic causes of death include the drowning in fishing gear.
There are two recognized subspecies of this seal:
- Halichoerus grypus grypus (North Atlantic), synonymously known as H. g. atlantica
- Halichoerus grypus macrorhynchus (Baltic Sea), synonymously known as H. g. balticus
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 as separate subspecies.
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