How Shark Attacks Work

By: Ed Grabianowski
Shark Image Gallery To a shark, a surfer paddling on a surfboard can look a lot like its typical prey. See our collection of shark pictures.

Sharks strike terror into the heart­s of people around the world like no other creatures. Their fearsome appearance, large size, and hostile, alien environment combine­ to make them seem like something straight out of a nightmare. The sudden violence of a shark attack is truly a terrifying experience for the victim -- but are sharks really man-eating monsters with a taste for human flesh?

In this article, we'll find out why sharks attack, what an attack is like, and what kinds of sharks attack people most often. We'll also look at some ways to avoid shark attacks.


Why Sharks Attack

Ninety percent or more of shark incidents are mistakes. They assume that we're something that we are not.- Gary Adkison, diver ("Sharkbite! Surviving the Great White")

Although shark attacks can seem vicious and brutal, it's important to remember that sharks aren't evil creatures constantly on the lookout for humans to attack. They are animals obeying their instincts, like all other animals. As predators at the top of the ocean food chain, sharks are designed to hunt and eat large amounts of meat. A shark's diet consists of other sea creatures -- mainly fish, sea turtles, whales and 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.

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).


Shark Sensory System

A nurse shark photographed off the coast of Australia
Photo courtesy Carl Roessler

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.


Sometimes, the cause of a shark attack is simple to determine -- the shark is responding to human aggression. Nurse sharks, for example, are generally placid fish that lie still along the bottom of the ocean floor. For some reason, this makes some divers think that it's a good idea to pull their tails. Irritated nurse sharks have taught several divers to keep their hands to themselves. For this reason, shark attack statistics are divided between provoked and unprovoked attacks.

Anatomy of a Shark Attack

A great white shark tried to make a meal out of Kenny Doudt and his surfboard.
Photo courtesy Carl Roessler

The thing about a shark is, he's got lifeless eyes. Black eyes. Like a doll's eyes. When he comes at ya, he doesn't even seem to be livin'. 'Til he bites ya, and those black eyes roll over white and then..." - Quint, "Jaws"

There is rar­ely any warning. The 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 the oncoming shark propels itself into the victim. Great whites are known to attack sea lions with such force that they leap completely out of the water with the prey held in their jaws. In the book "Shark Attacks," pregnant lifeguard Dawn Schaumann recounts her attack, which happened about 100 yards off the coast of Florida in 1993: "A shark hit me so hard it felt like a huge truck," she said. "My first thought was: my time has come."


Surfer Kenny Doudt was attacked by a great white shark off the coast of Oregon in­ 1979. He describes the attack in his book, "Surfing With the Great White Shark": "I heard a muffled roar as the shark's massive jaws clamped across my back, pressing the board to my chest...The shark pulled me two feet under water, but couldn't hold me under due to the buoyancy of the surfboard...I felt tremendous pressure on my chest and heard ribs snapping and the crunching of the underside of the board."

The attack started out as if the shark was feeding normally -- great whites attack sea lions from below, taking a single massive bite and dragging the prey below the surface. They then allow the disabled prey to float in the water and bleed to death, returning to finish their meal a few minutes later. In Doudt's case, the shark was unable to accomplish its initial bite because of the surfboard, but kept trying for about 20 seconds. "I felt totally helpless, as my entire body was lifted high above the water, then slammed back down beneath the surface," he recalls.

In the next section we'll look at shark attack patterns.


Shark Attack Patterns

Survivors of the USS Indianapolis en route to a hospital following their rescue
Photo courtesy US Navy, National Archives

Eventually the shark let go of Doudt and he never saw it again. Although he feared a subsequent attack as he paddled for the shore, the shark swam off and did n­ot make a second strike. The shark probably realized that a surfer and surfboard would not make a good meal. Great whites are actually very picky about what they eat -- refusing to bite things that were not their usual prey, such as floating sheep carcasses, after an initial taste.

However, there are many species of sharks, and not every shark follows the same pattern. Circumstances can also change the pattern of attack. Shark attacks in deep sea water are usually not hit-and-run attacks. In these cases, where the victims are often the survivors of sinking ships or plane crashes, sharks circle the scene. They will then bump into victims on the outskirts of the group, or those that are already wounded, before making bite attacks.


One of the most famous shark attacks is that of the USS Indianapolis, sunk by Japanese torpedoes in the Pacific Ocean in 1945. It took several days for rescuers to reach the ship, because the mission had been so top secret that no one reported the ship missing. By the time Navy rescue craft arrived, only 317 men were still alive out of the almost 1,000 that survived the initial sinking. Tiger sharks were responsible for most of the deaths.

­­The bull shark is also noted for its atypi­cal attack behavior. It gets its name in part due to its tendency to attack persistently, hitting a target, circling, hitting again, and repeating. A 14-year-old girl who was recently involved in a fatal shark attack off of Florida's panhandle was hit by a bull shark that did not let go of her leg even when a rescuer reached the scene. It continued circling and attacking, even making a run at another rescuer.

We'll look at the damage a shark attack can cause in the next section.


Shark Attack Damage

The shark had inflicted a half-pie-shaped wound that went from just below my armpit to the middle of my left side...Dr. Starr quit counting the stitches taken when he reached five hundred. - Ken Doudt

An attacking shark can deal massive damage to a human. In some cases, the initial bite is powerful enough to sever a limb completely. The surgeon who operated on a teenaged surfer in Australia described the loss of the surfer's leg as "guillotine-like." Sharks can generate more than 40,000 pounds of pressure per square inch, measured at the tip of a tooth -- large specimens might be capable of even more crushing jaw power.


If the shark doesn't bite off a limb, it generally takes a large chunk of flesh, tearing away muscle and bone. A bite on the torso can result in cracked ribs and other broken bones in addition to massive rips in the skin. In some cases, this can leave internal organs exposed and damaged. Spear fisher Rodney Fox was opened from shoulder to hip by a great white in 1963 near Adelaide, Australia. He survived, though it took 462 stitches and four hours of surgery to repair him.

However, shark attack victims don't usually die from sudden traumatic damage. They usually bleed to death. It can take several minutes to get a victim to shore, and even more time for emergency personnel to arrive. The difference between life and death is usually having someone at the scene who knows how to stem the blood loss, and every second counts. In the case of a boy who was attacked in 2005 off Cape San Blas, Florida, a doctor and a nurse vacationing on the beach put pressure on an artery in his leg, which helped him to survive.

Oddly enough, one of the potential dangers of swimming in the ocean can also help shark attack victims survive. When someone is attacked in cold water, their body temperature can drop dangerously low. This drop in temperature slows down the body's functions, including blood loss. This can keep victims alive for extended periods.

Once the victim has received emergency care, there is another danger -- infection. Shark mouths and ocean water aren't exactly clean. A shark bite inevitably leaves harmful bacteria in the wound, which can be as deadly as the bite itself. Fortunately, modern antibiotics help protect shark victims from these infections.

We'll find out what the most dangerous sharks in the world are in the next section.


Dangerous Waters

It has been suggested that the greatest danger from sharks occurs in warm tropical seas, [however] there are records of sharks attacking people in the distinctly chilly seas of high latitudes, such as the fisherman at Wick, northernmost Scotland...who was bitten on the arm. - Rodney Steel, "Sharks of the World"

We've already mentioned the three most aggressive and dangerous shark species: 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.
  • They are at the top of the food chain, which means they're not instinctively afraid of anything.

However, other shark species aren't completely innocent. 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 were 64 confirmed unprovoked shark attacks reported worldwide in 2019, with two of them proving fatal. Florida had 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. [ref]

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. increase 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.

Government protection of aquatic mammals has led to thriving populations of seals, sea lions, and sea otters off the west coast of the U.S. All of these animals are prey for great white sharks. As a result, coastal areas near San Francisco -- particularly places that are obviously inhabited by large ocean mammal populations -- have increased numbers of great white sharks. There hasn't been a spike in great white attacks in these areas because for the most part people know better than to go swimming with sea lions when they know great whites are around.

Although shark attacks do tend to be clustered in certain areas, sharks travel great distances and frequently break out of their range. Great whites in particular have no problem with cold water -- they can be found as far north as Oregon on the west coast and New England coastal waters in the east. Bull sharks are noted for their ability to tolerate fresh water, and they have been found swimming in rivers thousands of miles from the ocean. However, they generally prefer a tropical climate.


Avoiding Shark Attacks

Danger: Forbidden - Sign Ahead.
Photo courtesy Tom Raycove, RQCSR

How to Avoid Shark Attacks

It is not very often that a shark enters a well populated beach area to select a victim from among a group of people. On the other hand, quite often the victim is the person suddenly left alone and farther out from shore than others in the water.

- David H. Baldridge, "Shark Attack"


Every summer, media coverage brings a lot of attention to shark attacks. One result of all this attention is that we tend to perceive the threat as greater than it really is. The same thing happens with airplane crashes. Statistically, driving a car is far deadlier than flying. However, plane crashes are relatively infrequent and horribly catastrophic. They end up all over the news, and the images stay in our minds for a long time. As a result, we tend to overestimate the dangers of flying.

When news stories and scientists do offer real statistics, these are sometimes misleading. For example, it is often reported that you are more likely to be struck by lightning than to be attacked by a shark. This statistic is based on the number of incidents each year. However, anyone can be struck by lightning when there's a storm going through. Your chance of being attacked by a shark is zero if you live in Kansas and don't take a vacation on the coast. If you surf every day off the coast of Florida, the odds of a shark attacking you are much higher.

This isn't to say that anyone who goes into the water should be terrified of sharks, but 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.

Here are some general guidelines:

  • Don't swim at dawn or dusk -- sharks are actively feeding at these times. Visibility in the water is lower, which can lead to mistaken identity bites.
  • Don't swim in murky water -- again, the poor visibility increases the chances of a shark mistaking you for prey.
  • Don't swim with open cuts -- even a small amount of blood in the water can attract sharks from miles away. Some experts recommend that menstruating women also avoid swimming in the ocean.
  • Avoid 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. Even contrasting tan lines are speculated to lead to mistaken identity bites.
  • 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 -- if you are swimming near marine mammals or other shark prey species, and you see them react with sudden alarm and flee the area, follow their example.
  • 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. While shark activity tends to be greater a few hundred yards from shore, stay alert even if you're in thigh-deep water.
  • Don't leave shark bait in the water -- large amounts of bait fish or animal blood will attract hungry sharks. If you're fishing while standing in the ocean, keep your bait out of the water until you use it, and don't stay in one place too long.
  • Don't swim when there are sharks in the water -- this is the most obvious way to avoid sharks. If you know they're present, stay out of the water.

These tips are not foolproof. There are plenty of instances where sharks attacked in defiance of all shark attack patterns. 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.


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More Great Links

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  • Best, Joel. More Damned Lies and Statistics. University of California Press, 2004. 0520238303.
  • "Boy stable after 2nd Florida shark attack." CNN, June 26, 2005.
  • Burgess, George. How, When, & Where Sharks Attack. International Shark Attack File.
  • Clickable Shark. Nova Online: World of Sharks.
  • Doudt, Kenny. Surfing with the Great White Shark. Shark Bite, 1992. 0-9633342-7-1.
  • Fitzgerald, Patrick J. Shark Attacks. Grolier, 2000. 0-516-23318-1.
  • Gibson, Andrea. Sharks. St. Martin's, 2002. 0-312-30607-5.
  • Handwerk, Brian. "Great Whites May Be Taking the Rap for Bull Shark Attacks." National Geographic News, August 2, 2002.
  • ISAF Statistics for the Worldwide Locations with the Highest Shark Attack Activity Since 1990.
  • Klimley, A. Peter, Ph.D. The Secret Life of Sharks. Simon & Schuster, 2003. 0-7432-4170-3.
  • MacCormick, Alex. Shark Attacks. St. Martin's, 1998. 0-312-96618-0.
  • Steel, Rodney. Sharks of the World. Facts On File, 1998. 0-8160-5212-3.
  • Strong, Mike. Shark! The truth behind the terror. Capstone Curriculum, 2003. 0-7368-9547-7.
  • Find A Fish: Bull Shark. Australian Museum Fish Site. Links