Feeding And Diet
All sharks are carnivorous, meaning that they only eat other animals. The range of prey eaten by sharks is extremely broad, from snails to sea urchins, crabs, fish, rays, other sharks, seals, and birds. Some sharks eat carrion (animals that are already dead), but most only eat live prey. Sharks eat relatively little for their size, compared to mammals, because they do not use energy to maintain a high body temperature. Sharks eat the equivalent of 1-10% of their body weight per week, usually in one or two meals. Between meals they digest their food, and they do not eat again until they have finished digesting their previous meal.
Sharks that eat prey with hard shells, such as bullhead sharks, have flat crushing teeth. Bullheads eat a variety of prey, including barnacles, crabs, sea stars, and snails, which they crush with their rear teeth. The two largest sharks, whale sharks and basking sharks, eat nothing larger than 1-2 in (2-5 cm) long. These whales filter their tiny prey (called krill) from the water using their gills as giant strainers. The whales swim through the water with their mouth open, and small crustaceans in the water get caught in mesh-like extensions of the gills. Once caught, the krill are funneled back to the whale's throat and swallowed.
Species such as white sharks, makos, tiger sharks, and hammerheads attack and eat large fish, other sharks, and marine mammals such as seals. The feeding biology of the white shark has been well studied. This shark often approaches its prey from below and behind, so it is less visible to its victim. It approaches slowly to within a few meters, then rushes the final distance. If the prey is too large to be taken in one bite, the shark will bite hard once, and then retreat as the prey bleeds. When the prey is weakened, the shark again approaches for the kill.