To most of us sharks are the most dangerous fish in the sea and they attack humans. However, according to Dr. Clark, who has studied the behavior of sharks for 12 years, humans are not normally on the shark's menu. What do sharks feed on? Mainly fish and other small sea animals. Dr. Clark also found that sharks don't eat as much food as people think. For instance, a nine-foot shark only needs two pounds of food a day to keep healthy. But she says, sometimes sharks starve and at other times they fill themselves with what they have killed.