The Man Hunter.

Lady Jane Winston travels to the Ivory Coast of Africa to investigate George Castle, the manager of her family's rubber and ivory company, whom she suspects of embezzlement. On the voyage, Rin Tin Tin ("Rinty") leaps overboard near the African coast and befriends Jim Clayton, a beachcomber and former company employee. Together, the dog and Clayton rescue Lady Jane from a shark attack, prompting a partnership to expose Castle.