The pearl oysters of the Polynesian lagoons are raised in protective nets. They are particularly vulnerable during their first year, until their valves are thick enough to withstand the attacks of most of their predators. Octopuses and several fish species are indeed able to crush the young valves with their beak-shaped jaws and devour the molluscs. The most voracious predator is the ray which can squash 3-4 years old oyster shells with a diameter of 5.9in (15cm) and a thickness of 0.2in (5mm).