Selkies are able to become human by shedding their seal skins, and can return to seal form by putting it 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. Examples of such stories are the ballad, The Great Silkie of Sule Skerry and the movie The Secret of Roan Inish.
In The Secret of Roan Inish, a fisherman steals the selkie's pelt while she is sunbathing. She is then forced to return to his house, as she cannot escape back into the sea, and becomes his wife and bears him children. The skin of the seal gives her power over men, but without it she is a mortal woman, trapped on land, slave to the whims of her husband. The life there slowly suffocates her and she spends much time splashing in the shallows of the ocean. Years later, one of the children sees the pelt and asks what it is. The wife immediately knows, drops what she is doing and retrieves the pelt from its hiding place, having long ago despaired of ever finding it. She does not hesitate; she rushes to the ocean to return to her former life as a seal.
The selkie legend is also told in Wales, but in a slightly different form. The selkies are humans who have returned to the sea. Dylan (Dylan Eil Don) the firstborn of Arianrhod, was variously a merman or sea spirit, who in some versions of the story escapes to the sea immediately after birth.
In the Faroe Islands there are two versions of the story of the Selkie or Seal Wife. A young farmer from the town of Mikladalur on Kalsoy island goes to the beach to watch the selkies dance. He hides the skin of a beautiful selkie maid, so she can't go back to sea, and forces her to marry him. He keeps her skin in a chest, and keeps the key with him both day and night. One day when out fishing, he discovers that he has forgotten to bring his key. When he returns home, the selkie wife has escaped back to sea, leaving their children behind. Later, when the farmer on a hunt kills both her selkie husband and two selkie sons, she promises to take revenge upon the men of Mikladalur. Some shall be drowned, some shall fall from cliffs and slopes, and this shall continue, until so many men have been lost that they will be able to link arms around the whole island of Kallsoy.
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 — a regional variant on the motif of the swan maiden, unusual in that the bride's animal form is usually a bird. Female selkies are said to make excellent wives, but because their true home is the sea, they will often be seen gazing longingly at the ocean. If she finds her skin again, she will immediately return to her true home, and sometimes to 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 usually avoids seeing her human husband again but is sometimes shown visiting her children and playing with them in the waves.
Selkies are not always faithless lovers. One tale tells of the fisherman Cagan who married a seal-woman. Against his wife's wishes he set sail dangerously late in the year, and was trapped battling a terrible storm, unable to return home. His wife shifted to her seal form and saved him, even though this meant she could never return to her human body and hence her happy home.
Some stories from Shetland have selkies luring islanders into the sea at midsummer, the lovelorn humans never returning to dry land.
Seal shapeshifters similar to the selkie exist in the folklore of many cultures. A corresponding creature existed in Swedish legend, and the Chinook people 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). Jane Yolen incorporated such a shapeshifters as a selkie into her picture book, Greyling.
Theories of origins
One folklorist theory of the origin of the belief is that the selkies were actually fur-clad Finns, traveling by kayak. Another is that shipwrecked Spaniards washed ashore and their jet black hair resembled seals. As the anthropologist A. Asbjorn Jon has recognized though, there is a strong body of lore that indicates that selkies "are said to be supernaturally formed from the souls of drowned people".