The Coral Island: Robert Ballantyne

Three teenage boys, the sole survivors of a shipwreck, find themselves marooned on a deserted island in the South Pacific. With little more than a telescope and a broken knife, the youths must find food and shelter and learn to survive. But though the coral island is a tropical paradise, full of natural beauty and exotic fruits and wildlife, dangers and adventures abound: sharks, pirates, and even bloodthirsty cannibals!