Grey seals spend most of their time at sea but come onshore to breed. From September to December are the key breeding months and they are legally protected in the UK during this period. Cows will come ashore and join a jealously guarded harem. Soon after they have given birth to their single pup they will be ready for mating again. The gestation period is about nine months and the implanting of the egg is delayed for about three months. This ensures that a cow will not give birth before the following autumn.

A cow will vigorously defend the area around her own pup with bard teeth, hoots and threatening lunges, repelling all intruders, even other pups. Her pup will suckle on her rich milk every five hours for three weeks. At this time the pup will lose its creamy-white baby coat and become pale grey. And by two months it is ready to go to sea.