The Atlantic Grey Seal, Halichoerus grypus, is one of the world's rarer mammals. In 1954 R. M. Lockley estimated its total population as 33,500 and there is no reason to suppose there has since been an increase. About 20,000 of these seals live in colonies around the coasts of the British Isles, all on the north and west, except for one colony which inhabits the Fame Islands, a National Trust nature reserve off the Northumberland coast.