There is rarely any warning. A surfer or swimmer is paddling along with no idea what is about to happen. Sometimes their first indication that something is wrong is a look of terror in the eyes of a nearby friend. More often, the first sign is a sudden, massive impact as an oncoming shark propels itself into the victim.

Sharks strike terror into the hearts of people around the world like no other creatures. Their fearsome appearance makes them seem like something straight out of a nightmare -- but are sharks really man-eating monsters with a taste for human flesh? Let’s find out.

Which Species of Shark Will Attack?
The three most aggressive and dangerous shark species are great white, tiger and bull sharks. These species are the most deadly for several reasons. They are widespread. They are large enough that humans can look like prey to them. They are so powerful that the initial bite can cause fatal damage. And, they are at the top of the food chain, which means they're not instinctively afraid of anything. Sand tigers, hammerheads, and makos are also responsible for some attacks, while a third of shark attacks are made by lesser known species, such as black tips, nurse sharks and various reef sharks. Overall, the bull shark may be the most dangerous species because of its aggressive attack patterns and its preferred habitat - shallow coastal waters.

Statistically, there are between 30 and 50 unprovoked shark attacks reported worldwide each year, with five to ten of them proving fatal. Florida has the most attacks in the United States, with numbers since 1990 ranging from 10 to 37 per year. The United States tops the list for attacks worldwide.

The vast majority of attacks occur within a few hundred yards of shore, simply because that's where most people enter the ocean. The number of attacks worldwide and in the U.S. have been increasing in recent years for a similar reason -- more people are taking coastal vacations and participating in ocean activities. There is no indication that sharks are actually becoming more aggressive. But why, exactly, do they attack?

Avoiding Shark Attacks Following these don’ts is a do in preventing shark attacks. Don't swim at dawn or dusk -- sharks are actively feeding at these times. And, visibility in the water is lower, which can lead to mistaken identity bites. Don't swim in murky water -- again, poor visibility is an issue. Don't swim with open cuts -- even a small amount of blood in the water can attract sharks from miles away. Don’t hang around sandbars, sea mounts, and drop-offs -- marine wildlife tends to congregate at these areas, including many fish that are a shark's natural prey. The sharks aren't usually far behind. Don't wear contrasting colors -- high-contrast or brightly-colored swimsuits seem to confuse sharks. Don't wear shiny jewelry -- the sun reflecting off of a watch or necklace can draw a shark's attention. Don't swim when a shark's natural prey is present in large numbers. Don't thrash around -- smooth, steady swimming strokes should be used. Frantic paddling and splashing looks like a wounded fish to a shark. The swimming patterns of dogs can also draw sharks. Don't think you're safe just because the water is shallow -- shark attacks can occur in less than three feet of water. Don't swim when there are sharks in the water.

Why Sharks Attack
A shark's diet consists of other sea creatures -- mainly fish, sea turtles, whales, sea lions and seals. Humans are not on the menu. In fact, humans don't provide enough high-fat meat for sharks, which need a lot of energy to power their large, muscular bodies. If sharks aren't interested in eating humans, why do they attack us? The first clue comes in the pattern that most shark attacks take. In the majority of recorded attacks, the shark bites the victim, hangs on for a few seconds (possibly dragging the victim through the water or under the surface), and then lets go. It is very rare for a shark to make repeated attacks and actually feed on a human victim. The shark is simply mistaking a human for something it usually eats. Once the shark gets a taste, it realizes that this isn't its usual food, and it lets go.

Quick Fact Between 75 and 100 shark attacks are reported every year, and fewer than 20 are fatal. Statistically, this is in extremely low number. To put it in perspective, more people are killed by pigs every year than by sharks.

The shark's confusion is easier to understand once we start to look at things from the shark's point of view. Many attack victims are surfers or people riding boogie boards. A shark swimming below sees a roughly oval shape with arms and legs dangling off, paddling along. This bears a close resemblance to a sea lion (the main prey of great white sharks) or a sea turtle (a common food for tiger sharks).

Attacks have also frequently occurred when humans were spear fishing in ocean waters. Sharks are attracted to the signs given off by dying fish -- the smell of blood in the water and the electrical impulses given off as the fish struggles. Sharks detect these 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. Once a shark arrives on the scene, it may become agitated and aggressive in the presence of so much food. A hungry, excited shark can easily mistake a human for its usual prey.

There are cases in which sharks seem to attack out of aggression, rather than hunger. Very little is known about shark behavior, but it is believed that some species, including great whites, display dominance behavior over other sharks. This behavior can take the form of "punching" with the snout, or bites that don't do much damage to the tough skin of a shark. Unfortunately, when a shark makes a dominance display toward a human, these "gentle" bites can still cause horrendous damage.

Jaws of Death Sharks have a very unique jaw structure, which makes their mouths especially effective weapons. In most animals, the lower jaw moves freely but the upper jaw is firmly attached to the skull. In sharks, the upper jaw rests below the skull, but can be detached when the shark attacks its prey. This lets the shark thrust its entire mouth forward to grab onto its prey. Jaw mobility varies among different species, but all modern sharks have this ability to some degree.

When Sharks Attack
Just as campers need to be aware of bears and other creatures, people who swim and surf in the ocean need to be aware that dangerous wild animals may be present. Educating yourself about the risk factors for shark attacks can help you greatly reduce the chances of becoming a victim. The best tip is to be alert and always swim, dive, or surf with a buddy. Some attacks can't be prevented, but having someone nearby to call for help can save your life. If the worst does happen and you find yourself being attacked by a shark, what should you do? If possible, fight back. Despite their ferocity, sharks tend to be wimps. They don't like prey that can cause them harm. Punching, kicking, stabbing and even head-butting are all ways attack victims have fought off sharks. The eyes are particularly sensitive. This kind of response seems to help the shark realize that whatever it just bit isn't its usual prey.

Try This!
Using this Web site: http://www.flmnh.ufl.edu/fish/sharks/isaf/graphs.htm, create a bar graph illustrating the number of fatal and non-fatal shark attacks in the world from 1996 to 2006. Next, create a bar graph illustrating the total number of attacks (fatal AND non-fatal) in these U.S. states from 1996 to 2006: California, Florida, Georgia, Hawaii, North Carolina, Oregon and South Carolina. Which state had the most attacks. Use the information on this Web site to find out what percentage of attacks, world wide, happened in Florida and California.