October used to be a good month for sharks in La Paz. When the waters cooled, hammerhead sharks arrived in this part of the Mexican state of Baja California in droves. In the late ’70s, marine biologists discovered massive swirling schools of hammerheads around a nearby undersea mountain called El Bajo — so many that they could simply hold their breath, dive down a few dozen feet, pick one at random, and affix an electronic tag on it with a stick.
At the time, perhaps because of their odd-shaped head, the iconic sharks were feared as maneaters. The seamount eventually became a magnet for scientists and photographers alike. The images of hundreds of schooling hammerheads, with their instantly recognizable oblong heads, became an emblem of the ocean’s bounty and one of the greatest wonders of the natural world.
In October 2011, when I arrived in La Paz, the colder water was still attracting recreational divers, fishermen and a new generation of shark scientists. Taylor Chapple, one of the shark world’s rising stars, wandered into the historic town square looking every bit the surfer gringo: shorts, button-down shirt and an ornamental stone fish hanging from his neck. Between his long, blondish hair and broad shoulders, he could have been just another tourist looking for waves.
But Chapple had come to northwest Mexico hoping to prove a longstanding scientific theory: that hammerheads and perhaps other sharks navigate through a powerful magnetic sense. To prove the reality of the ancient sense, he had conceived a truly novel experiment.
He would catch a shark, attach a magnetic transmitter to its head and release it to the wild. Then, as the shark trolled the waters, Chapple would alter the magnetic current by remote control. If the animal sensed magnetism, Chapple’s device would direct the shark like a remote-controlled toy car.
