Taken by the Sea.

Being shipwrecked is the last thing that Jonathan Plush expected when he signed up as crew on a small salvage ship. On the seventh day of drifting Jonathan spots someone swimming in the sea. The mysterious stranger reveals that he can control the ocean and transform into a seal. He offers to save Jonathan, but for a terrible price.
Warning: contains material too hot for minors: Sodomy, anal sex, and a twisted menage between a shipwrecked man and two shapeshifting seal-men.