Sea turtles often sun themselves on the black sand beaches. I believe Ryan's reptile friend is a rare/endangered Hawksbill Turtle, since those are known to nest at this particular beach. You can find sea turtles at many locations around the island.
I was surprised by how hard, clean, and translucent the shell of this turtle was (also true of the half-dozen nearby turtles not in the photo). Turtles seem unconcerned by people, or sometimes curious and friendly in the water. Don't worry -- the turtles we saw were sunning themselves, not nesting.