The Great White's Ways
© Discover written by Glen Martin
RODNEY ORR was having a good day. By noon on that breezy Saturday in September nine years ago, the Santa Rosa, California, electrician was spearfishing 50 miles up the coast from San Francisco and had already taken his limit of abalone, so he decided to go for black snapper and ling. He kicked away from his fiberglass paddleboard and took a deep breath when suddenly he felt as if a boat had run over him. "I was ready to turn and make a dive, then the lights went out," Orr recalls. "All I heard was a big crunch, kind of like a garage door closing."
For a second or two he was enveloped in darkness, in water blackened with blood. Then it cleared and a glint of sunlight revealed rows of white teeth. As they pierced an eyelid and cheekbone on the left side of his face and ripped across his nose, he felt other teeth buried in his neck. Orr realized his entire head was in the grip of a shark. Then he saw the sea flashing below. "The shark had me up out of the water," he says. "And the sea was kind of flying by."
Orr flailed at the great white with his speargun in one hand and beat against the creature's teeth with his other hand, but the shark held his skull in a chillingly impassive grip as it thrashed him from side to side. Ten seconds after the attack began, it ended. "All of a sudden, I just popped out of the shark's mouth," says Orr. "He just let me go. When he went down I saw part of his head, and it was wider than my shoulders." Orr swam back to his paddleboard, a trail of blood marking the 60 or 70 feet the shark had carried him, and then paddled for shore as he tried to keep from passing out. He was picked up by a helicopter summoned by a passing highway patrolman, and by 10 P.M. he was home with nearly 80 stitches mapping the grisly encounter. Today, at age 58, Orr jokes that his scars blend with the weathering of his face. "The way the wrinkles went, that's the way the scars went," he says. "So I lucked out."
Why Orr survived--as do most human shark-attack victims--is one of the mysteries surrounding the great white shark, among the least understood of Earth's creatures. Even the size of great white populations--now a protected species in South Africa, Australia, and parts of the United States--is unknown. Scientists have seen as many as 18 sharks at one hunting ground off the California coast but won't hazard a guess about how many more there might be. "The problem is that we only see sharks when they make active attacks on prey," says ichthyologist Peter Klimley of the University of California at Davis.
The popular view of great whites--which most scientists refer to simply as whites--is at odds with the little that is known about them. Far from being the mindless killing machines of Jaws fame, they seem to observe social customs and rituals and appear to be particular about what they eat. They grow to 20 feet and more and can reach a weight of 5,000 pounds. Unlike most fish, they are born live, hatching inside the mother and emerging into the world five-and-a-half-feet long. But even basic information such as how and where the white shark mates remains unknown.
Scientists are struggling to paint a better picture. For the first time, marine biologists, using a sophisticated computer-tracking system linked to ultrasonic transmitters planted in the hide of the shark, are able to follow its underwater movements round-the-clock as it cruises a favorite hunting ground off the California coast. Scientists hope that another instrument, placed in the gut of the fish, will reveal where and when a shark eats--and how humans can avoid being on the menu. Study of the great white shark has broader implications, too. The white is an apex predator at the top of the food chain, so a change in white shark numbers is likely to ripple throughout the oceanic ecosystem. To cite just one example: sharks eat seals and seals eat salmon. Therefore, a drop in shark populations, leading to an increase in seals, could show up in a depletion of salmon fisheries.
The laboratory for this new research is located 23 miles from Santa Cruz, California, off the tiny island of Afro Nuevo. The spot is convenient because each fall, great whites swarm to this rocky outcrop, presenting biologists with an unparalleled opportunity. Nearby waters, with waves of 10 to 15 feet, are perhaps best known for surfing. But the sere and barren island--in a coastal area discovered by Spanish explorers in 1603--is also a prime breeding ground for the northern elephant seal, one of the world's largest pinnipeds. With a sloping shelf that eases the access from water to land, the island is a breeding ground from December to March for some 8,000 northern elephant seals. For marine mammal enthusiasts, Ano Nuevo Island is an extravagant spectacle, with huge seal beachmasters fighting for control of female harems. For mature great whites, it's dinner.
"An elephant seal rookery like Ano Nuevo is a supermarket for whites," says Burney Le Boeuf, a University of California at Santa Cruz behavioral ecologist and a leading expert on pinnipeds. "It's stationary, it's open 24 hours a day, and it's full of things they like to eat." Le Boeuf reasoned that to further his understanding of pinnipeds he needed a clearer picture of their relationship to their main adversary. So in 1996 he teamed up with Klimley in hopes of penetrating the secret life of the great white.
Klimley had previously videotaped more than 100 attacks on elephant seals, sea lions, and harbor seals at the Farallon Islands, a group of rocky islets west of San Francisco. The images, some of which should be R-rated for violence, show seals being torn apart. A few are attacked with such enthusiasm that they are decapitated outright. But Klimley also observed that a great white would take a tentative bite of an unfamiliar object, such as a buoy or surfboard, and then spit it out.
At Ano Nuevo, Klimley and Le Boeuf observed more examples of such unexpected table manners. The great whites gingerly bit a fake plywood seal. "More often than not, they tended to initially mouth prey candidates delicately rather than just munch down," says Le Boeuf. "They're very particular about what they bite into. I have an intuitive sense that they have a soft mouth, like bird dogs. They get a tremendous amount of information from their mouths."
Klimley theorizes that the jaws and teeth of a white are an exquisite tensiometer. He suspects a white can tell the relative fat content of an animal by first mouthing it gently; if the tensile resistance associated with blubber is revealed, the shark goes for a full-strength bite. If not, it will back off to save its energy for a more nutritious meal. "That's probably why most humans who are bitten are seldom killed," says Klimley. A human has too much muscle and not enough fat for a great white. The same calculation, he argues, may factor into the white's rejection of other potential prey. "We sometimes find sea otters floating dead with white teeth fragments stuck in their flesh," says Klimley. "Unlike other marine mammals, sea otters rely on dense pelts rather than blubber to conserve warmth. From a white's perspective, the lack of fat makes them an undesirable meal. So after a shark mouths an otter, it tends to spit it out."
Great whites might favor fat because they burn prodigious amounts of calories. In the early 1980s the late Frank Carey, an ichthyologist at the Woods Hole Oceanographic Institution, put a temperature probe in the muscle of a great white and found that the shark's body temperature was higher than the surrounding water. A few years later John McCosker, an ichthyologist at the California Academy of Sciences, induced a great white to swallow a temperature probe buried in a slab of seal blubber and confirmed Carey's startling discovery: like only a few other fish--porbeagles and mako sharks and tuna--the great white is warm-blooded. "They seem quite adept at regulating their body temperatures," says Klimley. "So far, the maximum differential we've found has been 15 degrees [Celsius] above the temperature of the surrounding water. That's pretty impressive."
Maintaining a warm core temperature allows great whites to cruise on extended hunts, make numerous and concerted dashes at prey, and bite elephant seals to death in furious combat. But warm-bloodedness could place great energy demands on an animal that lives in cold environs. So for great whites, fat, which contains nine calories per gram compared with four for protein and carbohydrates, is the good life. "To a white, elephant seals are the PowerBars of the sea," says Klimley.
© Discover written by Glen Martin