I was asked last week in one of the blog comments if selkies appear in Mermaid and Other Water Spirit Tales From Around the World. The answer is, yes, they do, but not to a great extent. They appear in about five pages of the 800+ page book. As I edited the book, I was inundated with mermaid lore from Scotland and Ireland where selkies also capture the imagination. I chose to concentrate on the mermaid tales although selkies get a solid appearance in one article I included by R. J. Arnott. Scottish, Irish and English lore dominates the collection so selkies had to take a back seat under the "other" category, especially where outright mermaid tales were abundant.
On a related note, I have a Swan Maidens collection in the works with a late 2012 release date at this time. Most selkie tales are closely related to Swan Maiden tales so a section devoted to them is planned for that volume.
Here's an excerpt R. J. Arnott's article on "Scottish Mermaids" which appears in the book:
A still closer relationship, however, than is generally recognised, subsists between the seals and the semi-human denizens of the ocean. In Orkney and Shetland “selkie” is the popular name for the seal; and those of the larger species are often called “selkie-folk,” because they are supposed to have the power of turning into men and women. According to one statement, the original “selkie-folk” were fallen angels, who were condemned to this condition because of some fault, not serious enough to necessitate their consignment to the infernal regions. According to another version, they were human beings who, as a punishment for some wrong committed, were condemned to assume the form of the seal and to live in the sea, being only allowed to revert to their human character at certain periods and conditions of the tide, when they were on dry land. When they have doffed their sealskins, these “selkie-folk,” of both sexes, are said to be particularly striking for their beauty of feature and fairness of form, and sad havoc have they been known to play with the affections of the sons and daughters of the coast. It is believed to this day in some parts of the islands of the north that a certain horny growth on the palms of the hands and the soles of the feet denotes descent from one of the “selkie-folk,” this being the result of an attempt to cut away the webbed membrane appearing between the fingers and toes of the original offspring. There is, by the way, a beautiful legend that when a young and fair maiden is lost at sea she is not drowned, but taken captive by the “selkie-folk,” and becomes the bride of one of them. One curious characteristic about these creatures is that they are never known to appear alone (as is almost invariably the case with the mermaid), but always in groups, basking in the sunshine or gambolling about on some sea-surrounded skerry, with their sealskins lying beside them on the rock. The moment the alarm is given of the approach of anyone, they make a dash for their furry garments, and donning them, are immediately seals again, and plunge into the sea and make off.