"Selkies (also known as silkies or selchies) are mythological creatures in Irish, Icelandic, and Scottish mythology that can transform themselves from seals to humans, where "selkie" is simply the Orcadian word for "seal". The legend apparently originated on the Orkney Islands. ... Selkies are able to transform to human form by shedding their seal skins and can revert to seal form by putting their selkie skin back on. Stories concerning selkies are generally romantic tragedies. Sometimes the human will not know that their lover is a selkie, and wakes to find them gone. Other times the human will hide the selkie's skin, thus preventing them from returning to seal form. A selkie can only make contact with one particular human for a short amount of time before they must return to the sea. They are not able to make contact with that human again for seven years, unless the human is to steal their selkie's skin and hide it or burn it. The Grey Selkie of Suleskerry is a ballad typical of the former, while The Secret of Roan Inish is a movie telling the latter tale.
Male selkies are very handsome in their human form, and have great seduction powers over human women. They typically seek those who are dissatisfied with their romantic life. This includes married women waiting for their fishermen husbands. If a woman wishes to make contact with a selkie male, she has to go to a beach and shed seven tears into the sea.
If a man steals a female selkie's skin, she is in his power, to an extent, and she is forced to become his wife. Female selkies are said to make excellent wives, but because their true home is the sea, they will often be seen gazing longingly to the ocean. If her skin is found she will immediately return to her home - sometimes, her selkie husband - in the sea.
Sometimes, a selkie maiden is taken as a wife by a human man and she has several children by him. In these stories, it is one of her children who discovers her sealskin (often unwitting of its significance) and she soon returns to the sea. The selkie woman avoids seeing her human husband again but is sometimes shown visiting her children and playing with them in the waves.
Seal changelings similar to the selkie exist in the folklore of many cultures. A corresponding creature existed in Swedish legend, and the Chinook Indians of North America have a similar tale of a boy who changes into a seal (see the children's story The Boy Who Lived With The Seals by Rafe Martin)."