As the largest fish in the world, whale sharks rely on their size to dissuade predators. Reaching up to 60 feet in length and weighing more than 20 tons upon maturity, adult whale sharks are only preyed upon by orcas and humans.
Unlike the adults, young whale sharks are often less than 2 feet long, and have been found in the stomachs of blue marlins and blue sharks. However, the young sharks grow quickly, which is likely a protective adaptation. Nevertheless, young whale sharks have a tough existence, and scientists suspect that as few as 1 in 10 survives to adulthood.
Boaters have reported a few instances in which whale sharks have butted or rammed their vessels. Because this likely occurs as a response to the perceived threat, this may be another anti-predator behavior. However, whale sharks are widely considered harmless to humans, and divers frequently swim with them in the open ocean.
Whale sharks are filter feeders who reach their large size by eating a diet of plankton, shrimp and other small aquatic creatures. They are able to feed more effectively than their relatives the basking and megamouth sharks, which are also large species that consume tiny creatures, by virtue of their powerful suction mechanism.