Understanding shark attack

Last year, 79 unprovoked shark attacks occurred worldwide, the highest number since detailed record-keeping began in 1958 and a continuation of the upswing in reported attacks over the past century. Ten of the attacks were fatal, according to the International Shark Attack File. While some of the increase can be attributed to better reporting facilitated by the Internet, much of the surge is a result of more people recreating in the ocean. The odds of being attacked by a shark remain small compared to dog bites, car crashes, and many other hazards, but people active in and on the ocean can minimize their risk by understanding the natural history of sharks and taking certain precautionary measures.

North America consistently leads the world in reported shark attacks. In 2000, 51 attacks took place in the United States and four in the Bahamas, representing nearly 70 percent of the global total. Other confirmed attacks, fatal and nonfatal, happened in Japan, New Caledonia, Tonga, Fiji, Papua New Guinea, the Galapagos Islands, Kiribati, Reunion, South Africa, Tanzania, and Australia. Three people died from attacks in Australia and two in Tanzania, while single deaths occurred in Japan, Fiji, New Caledonia, and Papua New Guinea. Each year, such statistics are compiled by scientists who maintain the International Shark Attack File (ISAF), housed at the Florida Museum of Natural History. They investigate and confirm reports of shark attacks from around the world, excluding any provoked attacks as well as interactions between humans and sharks in aquariums and other non-wild settings.

According to the scientists, last year’s tally continues the rise in attacks observed in recent decades. With 536 attacks reported between 1990 and 2000, the 1990s saw more shark encounters than any previous 10-year period. In 1988, for example, the ISAF recorded only 38 attacks, compared to the annual average during the 1990s of 54. But last year’s total even ranked high compared to the previous year’s 58 attacks. Not included in the 79 attacks during 2000 were four shark attacks of boats, four provoked attacks, two attacks characterized by the ISAF as “doubtful,” and one supported by too little evidence to allow categorization.

The upswing in attacks is a product of the rapidly increasing human population and popularity of ocean recreation, said George Burgess, director of the ISAF. Both of these factors mean that more people are spending more time in the ocean - resulting in more contact between humans and sharks.

“The number of shark-human interactions transpiring in a given year is directly correlated to the amount of human time spent in the sea,” said Burgess. “As the world population continues to upsurge and the time spent in aquatic recreation greatly rises, we might expect an annual increase in the number of attacks.”

No evidence exists to suggest that per-capita rates of attack on humans are rising, however, indicating that increasing numbers of sharks or aggression by the animals are not factors. In fact, many shark populations are rapidly dwindling because of overfishing, presumably reducing the odds for shark-human encounters in some places. But local conditions can substantially affect shark numbers and behavior and the likelihood of encounters, making it difficult to fully understand or predict long- or short-term trends in attacks.

Other factors also complicate the basic question of documenting of overall shark-attack trends. The International Shark Attack File was initiated in 1958 by the United States Navy as part of a research program aimed largely at developing an effective shark repellent. While that goal was never truly attained, the researchers did begin tracking shark attacks. However, due to funding woes, ISAF data-gathering has sometimes been inconsistent or nonexistent. For example, the data show an increase in total attacks each decade from 1900 to 2000, except for a dip during the 1970s and 80s. Yet the dip probably reflects the inactivity of the ISAF during those two decades rather than an actual drop in shark attacks.

Similarly, the ISAF numbers for other decades may reflect the data-gathering capabilities and efforts as much as the true numbers of attacks. Data for the early part of the century were collected retrospectively and probably underestimate due to limitations of searching through old news reports. Conversely, the rise of the Internet and e-mail over the past 10 years have dramatically increased people’s capabilities for reporting attacks around the globe. In addition, public interest in shark attacks and media coverage of these sensationalized events has increased, making it more likely that whatever shark attacks do occur will become known to scientists and included in the statistics. Together, these factors could help shape the apparent “surge” in worldwide shark attacks.

Availability of attack information also varies geographically. Such data are more difficult to obtain from developing nations where the scientific community is smaller and news reporting is less comprehensive. Moreover, in some cases reports of shark attacks are actively suppressed to prevent bad publicity. Because of these factors, numbers compiled by the ISAF probably continue to undercount the actual total number of attacks. Regardless, the ISAF does provide an unprecedented view of shark attacks worldwide.


In 2000, Florida retained its title as shark-attack hotbed of the United States. Thirty-four attacks occurred in the Sunshine State, including the only fatality in U.S. waters, in Pinellas County, Florida. Since 1990, the state had averaged some 17 attacks each year, leading some wags to suggest a new nickname: the Shark-bite State. Shark encounters also occurred last year in North Carolina, California, Alabama, Hawaii, Texas, Louisiana, Puerto Rico, and South Carolina.

Historically, along the entire east coast of North America, one attack has been reported from Newfoundland, at least twelve in the northeastern United States, more than two dozen in the middle Atlantic states, and more than 50 from North Carolina to Georgia. The cold waters of the West Coast are less hospitable to sharks. Only approximately 20 attacks are on record from Canada to Oregon. But with 100 total attacks on file, California has averaged some three attacks annually since 1990. Altogether, the ISAF estimates that 70 to 100 shark attacks typically occur worldwide each year, 5 to 15 of them fatal.

Scientists have identified three main types of shark attacks on humans: hit-and-run, bump-and-bite, and sneak attack. Hit-and-run attacks are the most frequent type - but also the least dangerous.

“These typically occur in the surf zone with swimmers and surfers the normal targets,” said Burgess. “The victim seldom sees its attacker, and the shark does not return after inflicting a single bite or slash wound.”

In these situations, scientists believe that the shark might mistake the person for its usual prey. In the restricted water visibility and turbulent conditions near shore, sharks often need to respond rapidly and reflexively as soon as they perceive possible food. Under those circumstances, the shark might act aggressively without knowing that it has encountered a person, rather than a fish or seal. A person’s splashing, apparel, and silvery jewelry that flashes like fish scales could also suggest “prey” to the shark. Usually the victim of a hit-and-run attack escapes with just a single slash or bite below the knee.

“We suspect that, upon biting, the shark quickly realizes that the human is a foreign object, or that it is too large, and immediately releases the victim and does not return,” said Burgess.

Bump-and-bite and sneak attacks are less common but more deadly. Victims tend to be swimmers or divers offshore, although shoreline attacks do occur. According to the ISAF, shark encounters during ship and plane disasters at sea typically involve bump-and-bite or sneak attacks. In a bump-and-bite attack, the shark first circles its victim and bumps him or her before actually attacking. In a sneak attack, the bite comes without notice. Unlike the hit-and-run, these attacks often involve repeated bites.

“Injuries incurred during this type of attack are usually quite severe, frequently resulting in death,” said Burgess. “We believe these types of attack are the result of feeding or antagonistic behaviors rather than being cases of mistaken identity.”Different species

The vast majority of sharks are too small to be a threat, however. In practical terms, nearly any shark more than six feet long might pose a danger. Yet 50% of shark species range from six inches to three and a half feet; eighty-two percent measure less than six and a half feet; and just four percent are truly large: 13 to 40 feet.

The major culprits in shark attacks are the tiger shark, the bull shark, and – of course – the great white shark. These species live nearly worldwide and, as part of their usual diet, devour sizable foods like sea turtles, marine mammals, and large fish. Also implicated in some bump-and-bite and sneak attacks are shortfin mako, oceanic whitetip, reef, Galapagos, and great hammerhead sharks.

While these species are some of the most commonly known, more than 350 different species of sharks populate the world’s oceans with a fossil lineage that extends back at least 450 million years. Although many species fit the classic image of a sleek, powerful eating machine, other sharks exist in a remarkable variety of forms, from sluggish bottom-dwellers to mammoths that loll at the ocean surface feeding harmlessly on microscopic plankton.

The thresher shark, for example, stuns fish with its long tail before eating them. Its oversized vertebrae render the tail a powerful weapon.

Another unusual species is the goblin shark, referred to by one expert as “the ugliest of living sharks.” Inhabiting continental shelves and outer slopes of the eastern and western Atlantic Ocean and the western Pacific Ocean, the creature features beady eyes, a flabby body, and a long hornlike snout. Below the snout dangles a gaping, curved, protruding jaw that looks like Homer Simpson’s mouth grafted onto a fish.

Wide-ranging but rare, the bizarre megamouth shark was not discovered until 1982. Even now, only approximately a dozen specimens have been found. Up to 17 feet long, this Muppet-mouthed shark swims the oceans’ mid-depths, feeding on small shrimp, copepods, and jellyfish.

Some of the shark species most likely to be encountered by sailors are also the largest: the whale shark and basking shark. Reputedly measuring as long as 60 feet, the whale shark is the world’s biggest fish. It swims near the surface of warm temperate and tropical seas, either near shore or in the open ocean, where it feeds on tiny algae and crustaceans. Its slightly smaller cousin, the basking shark, measuring up to 50 feet long, also filter-feeds at the surface, cruising at about two knots and filtering more than a thousand tons of water each hour. Both of these giants are docile and easily approached by boat, but divers should be careful of accidental injury – to themselves, not the sharks.Shark adaptations

Unlike most bony fishes, which reproduce by broadcasting large numbers of eggs and sperm into the water, sharks reproduce by internal fertilization. Depending on the species, they produce large, well-nourished eggs or give birth to live young that have developed in the mother’s uterus. The shark’s body is superbly adapted to its lifestyle, whether it’s a flat-bodied bottom-dwelling species or a hydrodynamically shaped torpedo built for long-distance, high-speed cruising. While some sharks spend their entire lives within a few square miles, others travel great distances. Individual blue sharks tagged near England have shown up off Brazil and New York. Others tagged near Long Island, N.Y., have been recaptured off Spain. For buoyancy, sharks are aided by their lightweight cartilaginous skeletons and oil-rich livers rather than the gas-filled swim-bladders employed by bony fishes. Scientists suspect that this difference in buoyancy systems might permit sharks to ascend and descend more readily; the buoyancy of the liver oil doesn’t vary much with depth, unlike the gases of swim bladders, which must be adjusted depending on depth. For lift and maneuverability, hammerhead sharks also gain from their wing-shaped heads.

For successful survival, sharks rely on a host of adaptations, including some remarkable sensory mechanisms. Along the animal’s body extends a row of tiny hairs, called the lateral line. Connected to the brain by thousands of nerves, the hairs apparently transmit information about swimming speed and direction and can sense vibrations of prey in the water. Sharks may also employ built-in “compasses” to detect the Earth’s magnetic field and to orient themselves during long migrations. Their abilities to sense chemicals in the water are unparalleled. By detecting minute quantities of blood or other molecules in the water, the shark can “smell” prey from great distances. Once it has approached within close range, the predator can pinpoint the exact location of its victim by sensing its electric field. This is accomplished with organs called ampullae of Lorenzini, consisting of jelly-filled canals in the head.

While feeding, many sharks frequent the ocean surface or shallow coastal waters, where they can reliably find marine mammals and other prey. Not surprisingly, most attacks on humans also occur here, often along beaches with steep drop-offs or behind sandbars. The sole shark-bite fatality in U.S. last year happened when a Florida man leaped off his dock and was mauled. Of shark encounters documented during 2000, nearly half involved swimmers or waders, and almost a third surfers or windsurfers. Only some 18 percent implicated divers or snorkelers.

People worried about being attacked by a shark can take at least a shred of comfort knowing that fatality rates along the U.S. East Coast have plummeted from 44 percent prior to 1950 to just 2 percent since then, primarily because of improvements in medical response and care. They can also gain comfort from the fact that many mundane and routine events pose much greater odds of injury or death.

“Many more people are injured and killed on land while driving to and from the beach than by sharks in the water,” said Burgess. “Shark attack trauma is also less common than such beach-related injuries as spinal damage, dehydration, jellyfish and stingray stings, and sunburn. Indeed, many more sutures are expended on seashell lacerations of the feet than on shark bites.”

If that’s not sufficiently reassuring in placing shark attacks in perspective, consider that in some years (1981, for example) more people have been bitten by hamsters in New York City (52) than by sharks in the entire country (12). And that, in the United States, the risk of being killed by a shark is 30 times less than the odds of death by lightning.

Pete Taylor is a freelance writer specializing in natural history. He lives in Portland, Maine, where he avoids sharks and hamsters as much as possible.

By Ocean Navigator