But scientists have learned that some species of sharks can go for days or weeks without feeding. During this time, the oil stored in their liver probably nourishes them. Scientists do not know why sharks sometimes attack people and at other times leave them alone. The American Elasmobranch Society studies shark attacks throughout the world. The society supports safety rules for people who swim in water where sharks may be nearby.
Blood attracts sharks.
Swim as smoothly as possible because thrashing movements might attract the shark. How people use sharks. Commercial fishing crews catch sharks mainly for their hides, fins, and flesh. Shark hide makes an especially luxurious leather after the scales have been removed. Chinese people often use dried shark fins to make a popular and expensive soup.