Shima Maru by James Holding

Vetuka of the Shark Clan, anging Melanesian fishermen and ,diver is approached by his nephew Likuva and Japanese friend Michiko to find the wreck of the WW II-era Japanese warship Shima Maru, which was carrying 50,000 gold yen. They find the ship and make plans to retrieve the gold, but Vetuka discovers they have something far more nefarious in mind.