There is good and bad news for surfers regarding the great white shark (Carcharodon carcharias). The bad news, according to shark scientists, and contrary to popular opinion, is that great whites are sharp sighted, curious animals, prone to taking "taste tests" of unfamiliar objects that catch their eye.
The good news is they generally don't like to eat people.
"In the 20th century, there were 108 authenticated, unprovoked shark attacks along the Pacific Coast of the United States," said Ralph Collier, president of the Shark Research Committee in Canoga Park, California, and author of Shark Attacks of the Twentieth Century.
Of those, eight attacks were fatal. "When you consider the number of people in the water during that hundred year period, you realize deadly strikes are very rare," said Collier.
Films like Jaws propagate the image of great whites as mindless hunters prowling dark, coastal waters for hapless swimmers—an animal whipped to frenzy by the scent of human blood. Yet not only do most people survive their encounters, many suffer only moderate injuries. Swimmers dragged underwater by great whites are sometimes left with puncture marks, but the animals often don't inflict more severe wounds.
A great white shark can reach 20 feet (6 meters) in length and weigh up to 5,000 pounds (2,270 kilograms); survivors' explanations of their escapes amplify misconceptions about the nature of this beast.
The most common myth is that great whites, with their poor vision, attack divers and surfers in wet suits, mistaking them for pinnipeds (seals and sea lions), their main prey. In this scenario, once the animal realizes its mistake, it releases the victim and swims away.
"Completely false," said R. Aidan Martin, director of ReefQuest Centre for Shark Research in Vancouver, Canada. A shark's behavior while hunting a pinniped differs markedly from its demeanor as it approaches people—suggesting that the animal does not confuse surfers for seals.
"I spent five years in South Africa and observed over 1,000 predatory attacks on sea lions by great whites," said Martin. "The sharks would rocket to the surface and pulverize their prey with incredible force."
By comparison, sharks usually approach people with what he calls "leisurely or undramatic behavior."
On August 15, 1987, Craig Rogers, a landscape contractor then living in Santa Cruz, California, paddled out to go surfing at a nearby break. It was 7:30 a.m., Rogers was sitting up on his board, legs dangling over each side, searching the horizon for the next set of waves. Abruptly, he noticed his board stopped bobbing in the water.
"I looked down and my eyes filled with a sight of instantaneous horror," said Rogers. A great white shark was biting his board just in front of his left hand; the head was almost three feet (one meter) across. "I could have touched its eye with my elbow."
The shark had surfaced so quietly, Rogers hadn't heard a thing. He flung up his hands, accidentally grazing two of his fingers along the shark's teeth. "I yelled in terror and slid off the board to the opposite side," Rogers explained in a written report made just after the attack.
He was bleeding when he entered the water.
Submerging to his shoulder, he watched the shark gently release his board and sink like a submarine, disappearing beneath him. Later analyses of the puncture marks on his board suggest the shark was 17 feet (5 meters) in length.
"It is typical for a great white to swim up to someone at a relaxed pace, take a bite, then swim off," said Collier. This contrasts with the torpedo-like attacks on the seal, suggesting that the shark's goal is not predation.
Teeth Like Hands
"Great whites are curious and investigative animals," said Martin. "That's what most people don't realize. When great whites bite something unfamiliar to them, whether a person or a crab pot, they're looking for tactile evidence about what it is."
A great white uses its teeth the way humans use their hands. In a living shark, every tooth has ten to fifteen degrees of flex. When the animal opens its mouth, the tooth bed is pulled back, "causing their teeth to splay out like a cat's whiskers," said Martin.
"Combine that with the flexibility of each tooth, and you realize a great white can use its jaws like a pair of forceps. They're very adept at grabbing things that snag their curiosity."
Great whites are also sharp sighted, further evidence that they do not mistake humans for other prey. Scientists believe that sharks see as well below the surface as humans do above it. And they see in color.
"I've seen these sharks swim 70 feet (21 meters) to the surface to investigate a piece of debris no bigger than the palm of my hand," said Martin. They are also known to take bites of buoys, paddle boards, brightly colored kayaks, zodiac boats, and other man-made objects floating in the ocean.
"Everyone wants to think sharks just search out seals, but they bite a lot of things that don't resemble any of their known prey," said A. Peter Klimley, an expert in marine animal behavior at the University of California, Davis, and author of the Secret Lives of Sharks and co-author of Great White Sharks: The Biology of Carcharodon carcharias. "They don't tear these things to pieces. They take a bite, feel them over, then move on."
The Taste Test
If sharks bite to figure out the nature of various objects, then why do they usually spit out people rather than adding them to the menu?
"They spit us out because we're too bony," said Martin.
Great whites have extremely slow digestive tracts; if they eat something less than optimal, it slows down their digestive tract for days, prohibiting them from eating other things. "That makes them selective about what they eat," said Klimley.
The insulation that keeps seals warm is pure fat, which provides twice the calories of muscle. That makes them a favorite of great whites. A high fat diet is mandatory for the great white to maintain its body temperature and keep its brain warm in cold water.
Still, sharks do attack people along U.S. coasts and around the world, even if the nature and number of encounters belie expectations.
There are steps society can take to reduce the number of incidents.
Cities often use beaches as burial grounds for marine mammals that wash up dead—like beached whales. "There is a possibility that when those animals are buried, some of the decaying material washes out to sea and attracts sharks," said Collier.
A healthy avoidance of pinniped colonies is another way to minimize human fatalities. A more subtle point is to steer clear of river mouths dumping spawning fish into the sea. Fish runs attract pinnipeds, which attract great whites. They feast on both seals and salmon, also a favorite shark snack.
"What we need to remember is that if great whites really liked to eat people, there would be a lot more fatalities," said Collier. "And I wouldn't interview so many survivors."