The grey seal is the larger of the two species of seal that breed around the coast of the British Isles. It is found across the North Atlantic Ocean and in the Baltic Sea. There are two centres of population in the North Atlantic; the largest is in Canada, the other lies mostly in Scottish coastal waters. Populations in all three major centres are increasing, although numbers are still relatively low in the Baltic.
Grey seals come ashore on remote islands and coastlines to give birth to their pups in the autumn, to moult in spring, and at other times of the year to haul out between trips to forage for food at sea. Female grey seals give birth to a single white-coated pup, which moults and is abandoned by its mother about 3 weeks later.
About 40% of the world population of grey seals can be found in Britain and over 90% of British grey seals breed in Scotland, the majority in the Hebrides and in Orkney. There are also breeding colonies in Shetland, on the North and East coasts of mainland Britain and in Southwest Britain. Although the number of pups born at colonies in the Hebrides has remained approximately constant since 1992, the total number of pups born throughout Britain has grown steadily since the 1960s, when records began.
Adult male grey seals may weigh up to 350 kg and grow to over 2.3 m in length. Females are smaller at a maximum of 250 kg in weight and 2 m in length. Grey seals are long-lived animals. Males will live for over 20 years and begin to breed from about age 10. Females often live for over 30 years and begin to breed at about age 5.
Grey seals feed mostly on fish that live on or close to the seabed. Their diet is largely composed of sandeels, whitefish (cod, haddock, whiting, ling), and flatfish (plaice, sole, flounder, dab), although this varies seasonally and from region to region. Food requirements depend on the size of the seal and oiliness of the prey but an average figure is 7 kg of cod or 4 kg of sandeels per day.
Common (harbour) seals
Common (or harbour) seals are found around the coasts of the North Atlantic and North Pacific from the subtropics to the Arctic. Common seals in Europe belong to a distinct sub-species which, in addition to the UK, is found mainly in Icelandic, Norwegian, Danish, German and Dutch waters. Britain holds approximately 40% of the world population of the European sub-species. Common seals are widespread around the West coast of Scotland and throughout the Hebrides and Northern Isles. On the East coast, their distribution is more restricted with particular concentrations in the Wash, Firth of Tay and the Moray Firth
Between 1996 and 2001, 34,625 common seals were counted in the whole of Britain, of which 30,196 (87%) were in Scotland and 4,245 (13%) were in England. The total British population cannot be estimated accurately because it is not possible to count all individuals in the population. Accounting for those animals that are not seen during surveys using a conversion factor leads to an estimate for the total British population of 50-60 thousand animals.
Common seals come ashore in sheltered waters typically on sandbanks and in estuaries but also in rocky areas. They give birth to their pups in June and July and moult in August. At other times of the year, common seals haul out on land regularly in a pattern that is often related to the tidal cycle. Common seal pups are born without a white coat and can swim almost immediately.
Adult common seals typically weigh about 80-100 kg. Males are slightly bigger than females. Like grey seals, common seals are long-lived with individuals living up to 20-30 years.
Common seals normally feed within 40-50 km around haul out sites. They take a wide variety of prey including sandeels, whitefish, herring and sprat, flatfish, octopus and squid. Diet varies seasonally and from region to region. Because of their smaller size, common seals eat less food than grey seals, perhaps 3-5 kg per day depending on the prey species.