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The grey seal (Halichoerus grypus) is the largest of the two seal species in the UK. Grey seals are among the rarest seals in the world: the UK population represents about 40% of the world population and 95% of the EU population. The current UK population is estimated at 107,000 to 171,000 seals, of which over 90% breed in Scotland. Furthermore, between the early 1960s and the early 1990s, grey seal pup production progressively increased.

Globally, there are three reproductively-isolated stocks of grey seal: a west Atlantic (northern North American) stock; a Baltic stock; and an East Atlantic stock. The latter extends from Iceland and northern Norway southwards to northern France, with the majority breeding around Great Britain and Ireland.

Size and lifespan

There are significant size differences between adult males and females: males can grow to 2.6 metres long and weigh 350 kg whereas females reach up to two metres in length and weigh around 200 kg. pup length 90-105cm at birth, adult, pup weight 11-20kg at birth. Fully grown males also have thick rolls of flesh around the neck and chest areas and a concave ‘Roman’ nose. Life span is in the region of 35 to 40 years.

Lifecycle

Grey seals are gregarious and may be found in groups out of the water. In the water they are typically solitary and can sometimes be seen ‘bottling’ – hanging vertically in the water with just the head visible above the surface. They can be vocal, often uttering a mournful, moaning cry. They are tolerant of human activity and may be seen in harbours in some numbers.

Grey seals feed on a wide variety of fish species found in inshore water and may on occasions take seabirds from the surface of the water. Their diet mainly consists of fish, but they will also eat squid, octopus and crustaceans. The average daily food requirement is estimated to be 5 kilograms, though they do not feed every day.

Neither lactating females nor dominant males feed during the breeding season, females usually for about 3 weeks and males sometimes for up to 6 weeks. Sub-dominant males may continue to feed since they remain at the periphery of the colonies. They may also take seabirds from the surface of the water and are generally opportunistic feeders. Grey seals are known to dive regularly to about 30-70m while feeding.

They come ashore in autumn to form breeding colonies on rocky shores, beaches, in caves, occasionally on sandbanks, and on small largely uninhabited islands. In such locations they may spread some distance from the shore and ascend to considerable heights.

Grey seals are polygynous with males competing actively with one another for the chance to mate with several females. This competition usually consists of vocalisations and physical posturing, but may sometimes break into physical contact.

The pups, born between September and December depending upon the colony, are restricted to rocky beaches of the foreshore above the high water mark for the first 3-4 weeks of their lives while they moult their initial yellowish-white, fluffy coat.

Females usually choose a remote and inaccessible site on land to pup. However this is not always the case. The mother usually remains in close attendance. Pups weigh about 15 kilograms at birth and are born with a dense, soft white coat. They will gain about 2 kilograms of weight a day due to the high fat content of their mother’s milk. Females will suckle their pup for approximately 3-4 weeks during which time the pup will shed its pup fur and start to develop the dense adult waterproof fur.

Towards the end of the period spent nursing her pup, the mother mates with one or more males and then after her pup is weaned she leaves it to fend for itself. Mating takes place on land, on ice or in the water. Generally the males enter the rookeries at about the time when the females start to pup and try to gain sole access to groups of females.

The successful males are able to mate with 2-10 females. The pup stays at the rookery until it has fully moulted, living off its blubber reserves, and eventually goes to sea to start feeding, usually about 1-4 weeks after it was weaned. Pups generally disperse in many different directions from the rookery and are known to wander widely, distances over 1,000km not uncommon.