Is it possible that the turtle has been living for hundreds of years and that she already had relationships with other people?
shareThe turtle was a bit of a siren, eh?
She smashed his raft a couple times and obviously didn't want him to leave, then appeared as a beautiful woman and convinced him to cast away the last of his dry, dead wood, to forever stay on the island.
Possibly, given that the meaning of the ending was supposed to depict the fact that the turtle turned into the woman simply for the length of time the man wanted companionship, before going back to its life as the turtle.
shareWhen I watched this movie recently, my first impression was that the woman/turtle was a female supernatural being, such as a guardian angel or deity, whose purpose was to comfort and aid people who became marooned.
Also, maybe the reason why she obstructed his attempts to leave the island was because she knew he wouldn't make it to a friendly ship or inhabited land.