Another great white approaches the boat but doesn't come close enough to be tagged, and Kock decides to check the inshore waters. We approach a beach where dozens of people are swimming. Kock spots a huge silhouette below the surface and steers the boat closer. "She's almost 15 feet long and weighs more than 4,000 pounds," Kock cries with excitement. It's the second-largest great white shark she has seen this year.
I stare, barely able to absorb the animal's immensity. Kock follows the shark, but it pulls away. After trying for an hour to tag the beast, Kock gives up. It's the one that got away.
Despite scientists' years of research on great white shark biology (see sidebar), they still have lots to learn about behavior—and migratory patterns. In 2003, Wildlife Conservation Society researchers attached an electronic tag to a shark named Nicole off the coast of South Africa. The tag was programmed to record the shark's position for 99 days before detaching. When the tag surfaced off the coast of Western Australia—roughly 6,800 miles away—it was the first record of a great white shark migrating between oceans. Nicole was apparently on a round-trip journey, because in August 2004, researchers spotted her distinctive dorsal fin back in South African waters.
A recent study of California's great white sharks found similar patterns. Some sharks make annual journeys to the Hawaiian Islands and back to the same beaches where they were tagged. Oddly, though, even more of them swim to a spot about halfway to Hawaii, a shark hot spot previously unknown to researchers. Stanford marine biologist Salvador Jorgensen calls it "the white shark café." He isn't sure whether sharks gather there to eat, to mate or for some other reason entirely.
Another surprise to come out of recent tagging studies is that great whites from California and Hawaii do not mingle with those from South Africa and Australia. No one knows why. This could pose a problem for conservation efforts: if one population shrinks, it cannot be replenished from the other side of the ocean.
Great white sharks' numbers have plummeted; along the U.S. Atlantic coast, for instance, the population has declined by more than 75 percent in the past two decades. The main culprits are commercial net and long-line fishing, which inadvertently snare sharks; fin hunters, who sell their hauls for shark fin soup; and the illegal international trade in great white jaws and teeth. "I've seen the bodies of great whites with their jaws cut out," says Mike Rutzen, who runs a shark-diving business in South Africa. "A jaw with all its teeth can fetch $25,000 on the black market in the U.S., and a single tooth can cost $500." Shark fin sells for $300 or more per pound. Hunters usually cut off the dorsal and pectoral fins and toss the body back in the water. Unable to swim, the shark can't pass oxygen-rich water through its gills and drowns.
South Africa was the first country to ban commercial hunting of great white sharks, in 1991, followed by Namibia, Australia, the United States, Malta and New Zealand. The great white was listed as "vulnerable" by the United Nations in 2000, and in 2004 the Convention on International Trade in Endangered Species (CITES) outlawed most international trade in its jaws, teeth, fins or meat. California and Florida have placed a total ban on killing the species, frustrating sports fishermen. Not that the great white should be regarded as much of a trophy. "The great white is one of the easiest of fishes to catch," says Rutzen. The sharks will follow bait right up to a boat.
Alison Kock says great white sharks are drawn toward land during the summer when other fish arrive with the warm currents. She shows me a photograph of a beach where I have gone swimming in Cape Town. A 16-foot female great white lies next to Kock's boat, disturbingly close to children playing in the shallows. The researchers never chum near swimmers, but find sharks with the help of spotters on coastal mountains who scan the waters with binoculars. (The spotters' primary job is to alert lifeguards when a shark is near.) "It's very rare for great whites to attack humans as prey," Kock says. "Imagine the hundreds of thousands of swimmers here each summer, and then count the number of attacks. Over the past few years you can count them on one hand."
Three years ago, about 20 yards from the Cape Town shoreline, Tyna Webb, 77, was taking her morning swim, as she had done for 17 years. "From the beach I saw the fin, then the whole shark coming out of the water," a witness to the attack later reported. All that was found was Webb's red bathing cap. A few years earlier, only three of four South African spear-fishermen who went underwater together resurfaced. Compagno examined the missing diver's wet suit when it was recovered. "The tear marks indicated it was a great white shark that had somehow cut him out of the suit and devoured him," Compagno says.
There have been 236 great white shark attacks on humans recorded since 1876. About one-third have taken place in California waters. This past April, triathlete David Martin was killed by a great white north of San Diego. One attack that particularly haunts me happened in Australia in 1993. Newlyweds John and Deborah Ford were scuba diving at a seal rock 400 miles north of Sydney. They were decompressing a few yards below the surface when John saw a 16-foot great white heading toward his wife. He pushed her out of the way, and the shark swallowed him.