Shark Facts: Attack Stats, Record Swims, More
for National Geographic News
|June 13, 2005|
The United States averages just 16 shark attacks each year and slightly
less than one shark-attack fatality every two years. Meanwhile, in the
coastal U.S. states alone, lightning strikes and kills more than 41
people each year.
Which just goes to show that sharks enjoy a reputation that is arguably more fearsome than their bite. Read on for more surprising shark facts compiled by National Geographic News:
Each year there are about 50 to 70 confirmed shark attacks and 5 to 15 shark-attack fatalities around the world. The numbers have risen over the past several decades but not because sharks are more aggressive: Humans have simply taken to coastal waters in increasing numbers.
Over 375 shark species have been identified, but only about a dozen are considered particularly dangerous. Three species are responsible for most human attacks: great white (Carcharodon carcharias), tiger (Galeocerdo cuvier), and bull (Carcharhinus leucas) sharks.
While sharks kill fewer than 20 people a year, their own numbers suffer greatly at human hands. Between 20 and 100 million sharks die each year due to fishing activity, according to data from the Florida Museum of Natural History's International Shark Attack File. The organization estimates that some shark populations have plummeted 30 to 50 percent.
The shortfin mako (Isurus oxyrinchus) is often recognized as the world's speediest shark. It has been clocked at speeds of up to 20 miles an hour (32 kilometers an hour) and can probably swim even faster than that. Makos are fast enough to catch even the fleetest fish, such as tuna and swordfish.
The largest shark is the whale shark (Rhincodon typus), which can grow to 60 feet (20 meters) long. The gentle giant eats tiny plankton.
Among the smallest shark species is the deepwater dogfish shark (Etmopterus perryi). A habitué of the Caribbean, the dogfish measures a less-than-intimidating 8 inches (20 centimeters) in length.
Sharks are known as eating machines. But because many species are cold-blooded, some sharks eat only about 2 percent of their body weight each day. That's a bit less than humans typically eat.
While scientists still have much to learn about shark migration, researchers do know that some species get around. Blue sharks (Prionace glauca), for example, roam the North Atlantic on journeys of 1,200 to 1,700 nautical miles (2,220 to 3,145 kilometers). After one record-breaking blue was tagged off New York, it swam 3,740 nautical miles (6,919 kilometers) to Brazil.
Some sharks must swim constantly to "breathe" oxygen from water passing through their gills. Other species can achieve this while stationary.
Sharks do not sleep. Rather, they experience alternating periods of activity and rest.
Sharks are among Earth's most ancient animals. The fossil record dates ancestors of modern sharks to as far back as 400 million years ago. Shark species have changed relatively little during that time span and are sometimes called living fossils.
Sharks can replace lost teeth in as little as 24 hours and may use thousands of teeth over the course of a lifetime. Ancient teeth are the source of most known shark fossils. (Shark skeletons, which are composed of cartilage, decompose quickly.)
Sharks are diverse reproducers, and their mating has been observed only on rare occasions. Some species are egg-laying (oviparous), while others bear live young (viviparous). Adult sharks do not care for their newborn pups, which are born or hatched as smaller, juvenile versions of their parents.
Two shark species can survive long periods in fresh water: the bull shark and the speartooth shark (Glyphis glyphis). Both species can engage in river journeys of epic scale. Bull sharks, for example, have been caught 1,700 miles (2,800 kilometers) up the Mississippi River and 2,100 miles (3,480 kilometers) up the Amazon. Neither species, however, lives in landlocked fresh water without ocean access.
A major cause of shark mortality is "finning," a process in which fishers kill sharks solely to remove their fins. Fins can sell for U.S. $400 per kilogram (U.S. $880 per pound) or more.
Known in China as yu chi or "fish wings," shark fins are used to make the traditional delicacy shark-fin soup. The culturally celebrated but controversial soup is found widely in Asia and will even be on the menu at Hong Kong Disneyland when the park opens in September.
Sharks are apex predators, and as such, they affect the entire ocean food chain from their position at the top. Because of their dominant role, sharks have long life spans and don't reach sexual maturity until they are 12 to 20 years old. Even then, sharks have low reproductive rates. Such predator populations, once diminished, have a hard time bouncing back.
As elasmobranches, sharks have skeletons made not of bone but of cartilage, tissue similar to that found in human noses and ears. Cartilaginous skeletons are lighter than bone and help sharks to remain neutrally buoyant (able to float without sinking or rising).
The media can have a voracious appetite for "shark bites man" stories. The summer of 2001, for example, saw an explosion of shark-attack hype and was even heralded on the cover of Time magazine as the "Summer of the Shark." Yet 2001 was statistically average: The year saw 76 shark attacks and 5 fatalities worldwide, compared to 85 attacks and 12 fatalities in 2000.
Thirty years ago the blockbuster Jaws brought the terror of shark attack to movie theaters. The record-breaking film, directed by Steven Spielberg and based on a best-selling novel by Peter Benchley, grossed nearly 130 million dollars (U.S.) in the United States alone. The movie arguably made sharks public enemy number one.
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