Mako: the jaws of death (1976)

A man accidentally learns that he has a mystical connection with sharks, and is given a strange medallion by a shaman. Becoming more and more alienated from normal society, he develops an ability to communicate with sharks telepathically, setting out to destroy anybody who harms sharks. People enter into his strange world to exploit his weird passion, and he uses the animals to gain revenge on anybody who double crosses him.