Sharks come silently, without warning. There are three ways they strike: the hit-and-run, the bump-and-bite and the sneak attack. The hit-and-run is the most common. The shark may see the sole of a swimmer's foot, think it's a fish and take a bite before realizing this isn't its usual prey. It swims away, leaving the bleeding victim in need of stitches. The bump-and-bite is far more serious. Last year Chuck Anderson was training for a triathlon off Gulf Shores, Ala., when he was bumped by a bull shark, testing whether he was preyworthy. It decided that he was and then repeatedly attacked Anderson. He lost an arm.

Then there's the sneak attack. The shark is in the right place to find its prey, it is the right time to feed, and the target is the right size. At sunset on July 6 off Pensacola, Fla., Jessie Arbogast, 8, apparently fit the needs of a bull shark. Dusk is one of the shark's feeding periods; the boy was in the shallow water where the bull prowls; and splashing about, Jessie may have seemed to be a large fish. The shark pounced. The ensuing attack and the boy's struggle to survive have stirred an inchoate fascination — part fancy, part dread — with nature's sleekest predator.

Suddenly reports of shark attacks — or what people thought were shark attacks — began to come in from all around the U.S. On July 15 a surfer was apparently bitten on the leg a few miles from the site of Jessie's attack. The next day another surfer was attacked off San Diego. Then a lifeguard on Long Island, N.Y., was bitten by what some thought was a thresher shark. Last Wednesday a 12-ft. tiger shark chased spear fishers in Hawaii. News crews stood on the sand to interview experts, who declared over and over that sharks killed only 10 people worldwide in 2000. But don't swim at dusk or dawn; avoid murky water and steep drop-offs; shed all jewelry. And do swimsuits in yellow — "yum-yum yellow" — attract sharks? No one was sure. Sharks don't give interviews.

Shark attacks have been on the rise in recent years. But for all the terror they stir, the numbers remain minuscule. Worldwide, there were 79 unprovoked attacks last year, compared with 58 in 1999 and 54 the year before. Two-thirds were in U.S. waters. The higher numbers may reflect more surfers, boogie-boarders and open-water swimmers — more people splashing around, hence more attacks. Volusia County, Fla., holds the state record for attacks because its long coastline and many beaches are increasingly packed with bathers from the booming cities of central Florida.

Humans are much more dangerous to sharks, which tend to end up in soup or medicine. Fishing nets tangle and drown about 100 million sharks each year. In California there is only one shark attack for every 1 million surfing days, according to the Surfrider Foundation. You are 30 times as likely to be killed by lightning. Poorly wired Christmas trees claim more victims than sharks, according to Australian researchers. And dogs — man's best friends — bite many thousands more people than sharks do.

But these are terrestrial and mundane risks. Sharks lurk in the vast, mysterious ocean, an element that still stirs mythic fear. Science is shedding light on why sharks behave the way they do. Researchers are tracking sharks via satellites and coming closer to understanding why they attack humans. The three large sharks that account for most attacks on people — the great whites, the tigers and the bull sharks — have been studied extensively. We now know that great white sharks keep their blood warmer than the surrounding water, that tiger sharks do not return to the site of an attack to prey again, and that bull sharks have the highest levels of testosterone measured in any creature, land or sea. Each has a different diet, a different behavior pattern and a different mode of attack.

Scientists ultimately hope to de-mythologize sharks, to erase their images as rogue man-eaters like the great white shark that figures in Jaws, the Peter Benchley novel turned Steven Spielberg movie classic. Benchley, who says he is now "a full-time ocean conservationist," told Time last week, "I couldn't write Jaws today." After 25 years of research, the demonization of sharks doesn't hold, he says. "It used to be believed that great white sharks did target humans; now we know that except in the rarest of instances, great white shark attacks are mistakes." Dr. Robert Lea, a marine biologist working for the state of California, goes further: "I used to call them shark attacks — now I call them incidents. It is not a case of sharks preying on humans. It is just humans sharing a spot in the ocean with sharks — at the wrong time."

Sharks are one of nature's ultimate designs, tested over 400 million years — confident, sleek and lethal (see graphic). Studies show some sharks can measure changes in electric currents as tiny as five-billionths of a volt. They use this ability to hunt for prey hidden under the sand and to navigate according to the earth's magnetic field. "They are like some high-tech AWACs thing, with all their sensors," says Sean Van Sommeran, executive director of the Pelagic Shark Research Foundation in Santa Cruz, Calif. When they do attack a human, the weight of evidence now suggests,they have mistaken a person for a seal or some other prey, and most often will spit out human flesh after the first bite. The problem is, of course, that the one bite comes from jaws that are up to 3 ft. across and lined with hundreds of knives.

THE GREAT WHITE
Scott Yerby never saw the great white shark before it attacked him as he surfed off Clam Beach near Eureka, Calif. "This thing jumped me — it had enough force to lift me right out of the water. It was on my leg, I could see my femur, there was blood in the water — I knew then it was pretty serious," says Yerby, who was 29 at the time of the August 1997 attack. He hit the shark on the nose (the prescribed last-ditch defense, along with ripping at its gills), managed to get back on his board, and with his surfing buddy, paddled back to shore. By the time an ambulance got him to the hospital, doctors said, he had lost almost half the blood in his body and was close to death. As he recovered from his wounds in the hospital, many of Yerby's visitors asked him if he intended to go out and hunt down the shark that attacked him. "I said I had no reason to — he was in his element," says Yerby.

The great white is perfectly adapted to its element. Sometimes growing to more than 20 ft. long and up to 4,000 lbs., it keeps its body temperature 5šF to 10šF higher than that of the surrounding water by recycling heat from its swimming muscles. This allows great whites to hunt in cooler seas. "It seems to make them more vigorous," says Van Sommeran. The sharks are voracious eaters of seals when they patrol the Red Triangle — a 100-mile strip of California coast from Bodega Bay to Santa Cruz. They have enormous livers to store energy, and can go for months without eating. Nobody has seen great whites mate, but some biologists theorize that after fattening up off the coast, they head into the deep to procreate.