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By observing sharks repeatedly over the years, Klimley was able to solve the long-standing mystery of why hammerheads gather in schools. It's clearly not for protection, since nothing preys on what Klimley calls "the big tough guys of the ocean." It turns out that they gather, at least in part, for an elaborate mating ritual, in which large, dominant females fight their way to the center of the school. The males know which females are most desirable by their position in the pack.
Klimley also discovered what may be the reason the hammerheads school year after year at an undersea mountain known as Espiritu Santo, 15 miles east of the Baja Peninsula. The metal-rich seamount, he found, has a particularly strong magnetic field. So do bands of ancient congealed lava that radiate from the seamount like spokes from a wheel. The hammerheads, he believes, can detect this magnetism and use it for navigation. The seamount is essentially a depot: the hammerheads gather there before going out to their feeding grounds.
This idea hasn't yet been confirmed by other shark researchers, but they don't dismiss it either. They know that sharks are extremely sensitive to electromagnetic signals; a "sixth sense" lets them home in on faint electricity generated by another fish's movement, gill action or even heartbeat. Indeed, Holland's team in Hawaii routinely tricks baby hammerheads at Coconut Island into striking at electrodes dangling in the water. Adult sharks, apparently drawn by the same process, have been known to bite through undersea cables. Holland is planning to investigate what sorts of electric signal might repel rather than attract sharks--protecting not just hardware but people as well.
While any shark 6 ft. long or more is potentially dangerous to humans, some species are more aggressive than others. None is considered deadlier than the great white. This huge fish, which can exceed 20 ft. in length and 2 tons in weight, is relatively rare among sharks but is responsible for more recorded attacks than any other species. Most of those have occurred off California, in the so-called Red Triangle, which extends from Monterey Bay to San Francisco to the Farallon Islands, 30 miles offshore.
It was here, in the early 1980s, that Klimley first saw an attack by a great white, on a 400-lb. elephant seal. The shark rose almost entirely out of the water, with the massive seal in its jaws. "It was stunning," he recalls. "The shark ambushed the seal, then came back several times to take three or four bites out of it. I had never seen anything like it." Since then Klimley has analyzed more than 130 videotaped white-shark attacks. All seem to follow a pattern. The powerful first bite usually takes place underwater, and the first sign of an attack is often a blood slick on the surface. Within 20 min., a sea lion or seal pops to the surface with a big chunk taken out of it. Then the shark appears, seizes the carcass and finishes it off.
Where Jaws went astray was in portraying great whites as mindless eating machines. Ken Goldman, a shark researcher from the Virginia Institute of Marine Science, in Gloucester Point, has been studying great whites in the Farallons for the past seven years. Says he: "Their attacks are very controlled, as is their feeding behavior." Klimley agrees: "The white shark is a skillful and stealthy predator that eats with both ritual and purpose."