With a cat's normal aversion to water, it is surprising that it would enjoy being on a small boat, off shore with his owners, particularly hanging around the boat's edge where he could easily fall into the ocean. In this case, however, the cat's natural curiosity wins out as he has "discovered" dolphins alongside the boat, something he's never seen before. The cat is fascinated with the dolphins and they with it. They are just as curious and fascinated as the cat.

http://www.slothster.com/2352-Cat-On-Boat-Plays-With-Dolphins.html