The main defenses for a whale shark are its thick skin and large size. Whale sharks are one of the largest fish in the sea, so this is usually enough of a deterrent. If they are attacked, their skin, which can be up to six inches thick, fends off attacks.
Whale sharks have many teeth like other sharks, but since they are filter feeders, the teeth are very small. When whale sharks are young, they are small and haven't yet developed thick skin, so they are easy prey for predators. Whale sharks grow quickly in order to minimize this vulnerability. Around humans, whale sharks are very gentle and have little protection from boats, propellers and human exploitation.