There are only four types of sharks that are well known for attacks on human beings. These are the great white shark, the tiger shark, the bull shark and the oceanic whitetip. The great white is the most notorious of these, largely thanks to the movie "Jaws." Great white sharks are found in almost every coastal area of the world, and can weigh up to 5,000 lbs., with a typical weight about half that. In most attacks by great white sharks, the attack is broken off after the first bite by the shark. That first bite is called 'test-biting,' and sharks have been known to do this with a number of different objects to find out what they are. In others, the attacks are often headed off by the use of a buddy system, where a second diver can often get an injured companion out of the water before the shark can finish the attack, as the shark often waits for his prey to bleed out before finishing him off.
These four are the only kinds of sharks that have been recorded as a frequent offender. However, there are a handful of other species that are responsible for the occasional attack. These include the gray reef, blacktip reef, the hammerhead and the silky shark. For the most part, though, these sharks present little danger and the attacks often come in conditions of poor visibility where a human swimmer or diver can be mistaken for something else.
The majority of reported shark attacks happen in the United States. However, they can happen in any place that humans come in close contact with sharks, and this is a wide area. Great white sharks inhabit nearly all coastal areas across the globe. Tiger sharks are typically found in the coastal areas of more tropical areas, that draw human visitors for much the same tropical climate. The bull shark inhabits mostly shallow waters in the tropical and subtropical band across the globe, and is unique in its ability to live in freshwater areas as well as saltwater. Bull sharks have been known to travel inland up rivers, making them the most likely to come in contact with humans. The oceanic whitetip, on the other hand, is perhaps the most elusive of these sharks, and inhabits the open sea as its name suggests.
Documented shark attacks date back to the 1830s in the United States alone, and include individuals wading ashore from capsized boats and even a 15-year-old boy killed by a bull shark while swimming in Florida's Trout River. The most notorious episode of shark attacks in American history took place on the New Jersey shore between July 1 and July 12, 1916. Four people were killed and one was injured by an unidentified species of shark. Beaches that summer were overcrowded with New Jersey and New York residents trying to escape a heat wave and an epidemic of polio. It's important to note that the victims of these shark attacks were not solo swimmers or divers. The first attack claimed the life of a 25-year-old vacationer in the town of Beach Haven, New Jersey, with the second attack taking place approximately 50 miles north of the first. The last attacks took place even further north, at Matawan Creek, New Jersey. In each instance, the attack happened in view of others, and with one exception the victims died of blood loss from powerful bites after being dragged ashore by rescuers. The single survivor was a 14-year-old boy whose left leg was bitten; he was rescued and rushed to the hospital. These attacks inspired Peter Benchley to write "Jaws."
A number of different methods have been tried to drive sharks away from not only individual divers, but also away from the areas that people frequent. One method that seems to have met with a certain amount of success is the use of magnetic equipment. Since a shark uses an ability that allows to to sense the electric and magnetic fields disrupted by muscle tissue in the water, it has been found that sharks will often swim away from different kinds of magnets that are placed in the water as a perimeter. There have also been experiments in harnessing electricity to produce the same response in sharks. Some materials produce an electric current when submerged in salt water, and it is this electric current that turns the sharks away. This electromagnetic method of interrupting a shark's ability to sense disturbances is the theory behind the most successful finding to date--the Protective Oceanic Device, or POD. Small enough to be worn by a single diver, the drawback to the "Shark Shield" is that it protects only a single person, and does not have an effect that reaches across an entire beach.
Because there are no natural enemies of sharks, they have little reason to fear anything that the come in contact with in the water. As top of the food chain predators, they are naturally curious about anything that they run into that they aren't familiar with, and because they obviously have no hands to explore something with, the only way they can get a feel for the new object is to bite. While such a bite may not be intended to kill the target, sharks have incredibly powerful jaws which can make the bite deadly. Sharks do not attack a human with the express purpose of getting an easy meal. The digestive system of a shark works extremely slowly, and it is difficult for sharks to digest the high ratio of human bone that is contained within a person. (It is also not worth the effort to try to strip the flesh from the bones of a human--it is too time consuming and difficult to maneuver the prey with no way to hold it save with the mouth.)
Many shark attacks come when the person is swimming above the shark, and therefore visible only in shape. It's easy for a shark to mistake a diver clad in a wet suit for a seal. In addition, sharks use the sense of electricity from living muscle to find prey, and the shape of the field given off by a diver with fins is similar to that given by a seal. In the twenty-firsst century, reported shark attacks have been on the rise. However, many law enforcement agencies doubt the validity of such claims without outside witnesses, suspecting that claims of such an attack could be used to hide a murder.
