Of Poseidon, Paperback

Galen, a Syrena prince, searches land for a girl he's heard can communicate with fish. It's while Emma is on vacation at the beach that she meets Galen. Although their connection is immediate and powerful, Galen's not fully convinced that Emma's the one he's been looking for. That is, until a deadly encounter with a shark proves that Emma and her Gift may be the only thing that can save his kingdom. He needs her help--no matter what the risk.
Of Poseidon is the start of The Syrena Legacy series by Anna Banks.