Juan Duval

A schooner disappears at sea without a trace. Years later, evidence of possible survivors prompts the mother of the schooner's mate Jose to hire a tuna boat to investigate. They discover the lad living happily on a South Seas island, and, when he refuses to leave with them, they abduct him. However, Jose gets revenge by leading the ship into the lair of a mysterious giant manta ray. (imdb)

A ship disappears without trace. What happened to the crew? Years later there's news of possible survivors and soon a rescue team is setting sail. Eventually they discover a young man living on a remote island and they ask him to leave with them. He refuses, so they abduct him. But he gets his revenge and guides them into the lair of the devil of the deep...