Waves by Howl Avery

A year after ending his engagement a mere two days before the wedding, Ezra has settled into his new life: documenting the local seal population, walking the beaches with his black lab, or having lunch with his one remaining friend. Life is simple, quiet, and predictable until the day Ezra befriends a man who walks right out of the sea.
Kai has been alone for a long time—a very, very long time. So much so, he can’t remember living as anything but a seal or caring about anyone human. Until one day, he meets someone amid the ocean who drives his urge to return to land again.