5 myths about sharks

A rash of shark attacks this summer, including eight in North Carolina alone, has put the giant fish in the spotlight - not that the great white or hammerhead needed the publicity. Pop culture, medicine and the media have long been fascinated with sharks, shrouding them in misinformation and mythology. But with a creature this majestic, the reality is just as interesting.

1. Sharks pose a serious threat to humans.

Shark attacks often mean a media feeding frenzy: Coverage includes shots of bloody victims, pictures of great whites with gaping jaws and illogical descriptions such as "shark-infested waters." (Sharks live in the oceans. They are not an infestation.) After an attack in North Carolina this summer, audio of a 911 call from a distressed bystander saying, "It looks like her entire hand is gone" was all over the Internet.

With such treatment, no wonder sharks are one of the most feared animals in the world. But shark attacks are actually quite rare. There are almost 400 shark species, and only about a dozen have ever committed documented attacks on humans. According to the International Shark Attack File at the Florida Museum of Natural History, only 70 attacks occurred on average each year in the past decade, with a handful per year proving fatal. Recorded attacks have risen significantly since the 1960s - by 200 percent - though that's mostly attributable to an increase in people swimming in the sea for leisure and to better gathering of data.

The risk of a shark attack while you're in the water is infinitesimally small: about 11.5 million to 1. Humans are more likely to have deadly encounters with lions, which kill about 100 of us yearly, crocodiles (around 1,000) or snakes (close to 50,000). You're 10 times more likely to be bitten by another human in New York City than you are by a shark anywhere on the planet.

The threat, in fact, is the other way around: The World Wildlife Fund estimates that people slaughter about 100 million sharks per year. They're caught commercially for their liver oil, meat and fins, or they die because of sport fishing, drum lines (aquatic traps from which sharks usually don't emerge alive) and beach protection netting. These animals take several years to mature and often produce few young; many species face extinction.

2. Sharks have to keep swimming.

It's been repeated by sources both authoritative (textbooks) and slightly less so (Ripley's Believe It or Not!): Sharks must move constantly in order to breathe, or they die.

But for most species, that's not true. Sharks employ two methods to breathe. Ram ventilation entails swimming constantly, which forces water over the gills. Buccal pumping uses muscles in the mouth to pull liquid over the gills. Fish in this latter group, including angel and nurse sharks, don't need perpetual motion and can rest on the seafloor. Many shark species can use both techniques. About 20 species can't, though even they won't necessarily die if they stop swimming. Researchers have discovered that some of these animals can remain relatively stationary: In 1972, Caribbean reef sharks were observed at rest in a Mexican cave.

3. Sharks don't get cancer.

William Lane's 1992 bestseller, "Sharks Don't Get Cancer: How Shark Cartilage Could Save Your Life," helped popularize the mythical notion of sharks' invincibility. The book seemed at least partially grounded in reality: Research from the previous decade suggested that inserting shark cartilage into certain animals inhibited the growth of blood vessels that nourish tumors, and that sharks had lower incidences of cancer than humans did. Lane's book acknowledged that sharks occasionally get cancer, just not often. But it was the misleading title that resonated.

It's been known since 1908 that sharks get cancer; that was when the first incidence of a malignant growth was discovered in a specimen. More recently, a comprehensive 2004 study found 42 carcinomas in Chondrichthyes species, the class of cartilaginous fish that encompasses sharks, skates and rays. To date, cancer has been documented in 23 species of sharks.

No scientific evidence shows that cartilage extracts from these animals can prevent us from getting cancer or cure it, as Lane argued. In 2005, the National Center for Complementary and Alternative Medicine gave a brand of cartilage called BeneFin to patients who had advanced bowel or breast cancer. There were no positive effects.

Yet Lane made handsome profits through his company, LaneLabs, selling shark cartilage extracts to ease rheumatoid arthritis, psoriasis and diabetic retinopathy, an eye condition. The global market for such products was thought to have exceeded $30 million by 1995. In 1999, the Food and Drug Administration sued LaneLabs to prevent the company from marketing shark cartilage as an effective cancer treatment. Lane later agreed to pay a $1 million settlement.

4. Aerial patrols keep people safe from sharks.

A string of shark sightings and attacks in the past few years has prompted a number of Australian states to increase aerial patrols, manned aircraft that monitor recreational waters for sharks. But after decades of operation along the coast there, there's little evidence to suggest that this has any practical benefit in keeping swimmers safe.

Airplanes or helicopters have to survey a vast area in just a few hours. Some species, including the great white, are ambush hunters and come up to the surface only when they strike. Others lie deeper in the ocean; if the water is murky or the skies not clear, they can be almost undetectable.

A smarter way to ensure beach goers' safety is a "shark barrier," currently used in parts of Australia and Hong Kong. These thin mesh nets - which aren't harmful to wildlife and shouldn't be confused with shark nets - form an underwater fence from seabed to surface around beaches and keep predators out.

5. A shark attack is a case of "mistaken identity."

After an attack, media outlets often quote experts who say the shark mistook the human for something else; authorities including the National Oceanic and Atmospheric Administration reiterate that attacks on people are "usually a case of mistaken identity." But plenty of evidence suggests that shark attacks on humans, though rare, are intentional. Sometimes simple curiosity prompts a bite. A shark might also attack humans if they're in its territory or if it sees them as competition for food.

Some species have highly refined senses, and these remarkable hunters know exactly what kind of animal they are pursuing. These species will prey upon people. The tiger shark, nicknamed the "dustbin of the seas," will eat practically anything - remains of horses, dogs, license plates, tires and people have been found in their stomachs. Bull sharks have been implicated in many human fatalities. And the oceanic whitetip, which oceanographer Jacques Cousteau described as "the most dangerous of all sharks," has been known to target shipwreck and plane-crash survivors.