I read a book last summer and I can't remember the name or author. Plot summary is something like this:

A crew is assembled to go out on a ship to film a "documentary" providing (fake) evidence that the existence of mermaids is possible. The crew includes a company of "professional mermaids" that will be used in the filming. Once they're on location, things start going wrong. People disappear, and the professional mermaids start getting killed while they're out practicing in the ocean. It ends with the ship being overrun by the actual, blood-thirsty mermaids, who devour the entire crew. The ship is left drifting in the ocean and is discovered, empty, some time later. No one ever finds out what happened.

I can even remember what the book looked like. Small, thin, blue. The title was short and probably just one word.

Anyone???