Apparently in the first edition of the book, the words "Moby-Dick" were hypenated on the cover, but not in the text. According to G. Thomas Tanselle:
The title of the book, as it appears on the title page (and divisional title page), contained the hyphen; but the name of whale, in its many appearances within the body of the book, was not hyphenated (except once as commented below). The title, of course, was "The Whale," but the subtitle "or, Moby Dick" appeared on the half-title page, and the name had no hyphen there, or anywhere else. The question whether the hyphen should be retained in the title is not an easy one. The numerous occurances of the unhyphenated "Moby Dick" within in the text would seem to offer conclusive evidence that the name of the whale was not hyphenated in the manuscript and that Melville did not intent it to be hyphenated; but that fact does not automatically answer the question about the title of the book. As the Historical Note explains, the title page and divisional title page were set at a late stage, since the title was altered from "The Whale" only after the American proof sheets had already been sent to the English publisher; if it could be shown that the hyphenation of titles was a common practice among American publishers at this time, one would have a conceivable explanation for the presence of the hyphenation of titles was a common practice among American publishers at this time, one would have a conceivable explanation ... However, one should hesitate to assume that the hyphenation of Moby-Dick resulted merely from carelessness of the part of a compositor...As this photo from a collection of 180 volumes of Moby-Dick shows, that convention has not been consistently applied:
Speculation re the origin of the word "Moby" is offered at The Life and Works of Herman Melville:
The name of Melville's most famous creation was suggested by an article by Jeremiah Reynolds, published in the New York Knickerbocker Magazine in May 1839. Mocha Dick: or The White Whale of the Pacific recounted the capture of a giant white sperm whale that had become infamous among whalers for its violent attacks on ships and their crews. The meaning of the name itself is quite simple: the whale was often sighted in the vicinity of the island of Mocha, and "Dick" was merely a generic name like "Jack" or "Tom" -- names of other deadly whales cited by Melville in Chapter 45 of Moby-Dick...Addendum 2015: A tip of the blogging hat to the author of this Smithsonian article for posting additional information on this matter. She affirms that "These days, most scholars simply refer to the book with a hyphen and the whale without."
Oh, and btw - the island of Mocha is here.
Top image (not the first edition) from Ghost in the Machine, via A London Salmagundi.