Many shark attacks, while deadly, are mistakes. So why do sharks attack humans? And how can you avoid being mistaken for prey next time you're at the beach?
A shark swimming below the surface might see a roughly oval shape with arms and legs dangling off, paddling along. This bears a close resemblance to a sea turtle, a common food for tiger sharks.
Sharks detect blood and other signals with their ampullae of Lorenzini, a set of detectors under the skin on a shark's snout. The ampullae are electrically sensitive cells that connect to the skin's surface through small tubes. They can lead a shark to mistake a human for a seal.
Sharks usually eat sea turtles, seals, sea lions or whales, and there is no evidence that they have a natural appetite for humans. Most shark attacks on humans are mistakes -- the shark thinks it's attacking a sea creature. When it realizes it's not, it typically lets go and swims away. Unfortunately, by the time a shark realizes its mistake, the results can be lethal.
Contrary to their reputation in popular culture, great whites are actually very picky about what they eat -- refusing to bite things that are not their usual prey, such as floating sheep carcasses, after an initial taste.
While most shark attacks you hear about are hit-and-run -- a shark bites before realizing its mistake -- attacks at lower depths usually involve sharks circling the scene before moving in to attack.
The bull shark is noted for its atypical attack behavior. It gets its name because of its persistence when attacking, often biting its prey, circling, biting again and repeating.
Sharks can generate an astonishing 40,000 pounds per square inch in jaw power, measured at the tip of the tooth. Their powerful bite can sever a human limb completely.
Contrary to what most people think, most shark attack victims bleed to death, as it can take several minutes to bring a victim ashore and provide medical help. The difference between life and death is usually having someone at the scene who knows how to stop the blood loss.
Because of their unusual attacking habits and penchant for shallow coastal waters, bull sharks are considered the most dangerous. However, great white and tiger sharks are also among the most powerful and aggressive, residing at the top of the ocean food chain.
Florida has consistently had the most attacks in the United States in the last two decades, with numbers since 1990 ranging from 10 to 37 per year. The U.S. tops the list for attacks worldwide.