Two weeks into his trip, while Buyle and the team dive and bait near a fish farm not far from Boucan Canot, he finds his sharks. When they arrive in the boat, the water beneath them is swarming with bull sharks. Big ones. After a few warm-up dives, Buyle clenches his speargun and heads in with Winram. As they approach a depth of 120 feet, a shark notices Buyle and diverts its path to him. Buyle takes aim and shoots. The speartip, which is as sharp as a nail and could pass through a human head from 20 feet away, bounces off the shark's cartilage, leaving the tagging unit flaccid on the seafloor. They have found Réunion's sharks, but they will have to return another day, better equipped, in order to place the transmitters.
In the 1940s and 1950s, researchers began tagging sharks in an effort to understand their migratory routes, population, and habits. Actual plastic tags eventually gave way to transmitters in the mid-1960s. The transmitters, once adhered to a shark, could trace depth, swimming speed, and location. With the proliferation of satellite and acoustic technologies in the past 10 years (GPS technology doesn’t work underwater), shark tagging provides researchers access to intricately detailed data on shark body temperature, feeding patterns, location, and behavior. The latest tagging technology is an acoustic-based system using cigar-size transmitters affixed to the shark's dorsal fin. The beacons send out a signal via 10 relay hubs. When the shark approaches within 500 meters, the hub recognizes the acoustic beacon like a fingerprint and sends an instant alert to a computer server, which updates a website and mobile app.
Today, from Western Australia to South Africa and Florida, thousands of sharks glide through the world's oceans, transmitting their every move to satellites. But the challenge for researchers hasn't been developing the technology but getting it onto the sharks in the first place. Tagging from boats can put the sharks at risk – wayward spears can kill them. Tagging from cages or with scuba doesn't work because the sharks become nervous and swim away or approach at the wrong angle. Free-divers, who are unobtrusive and can swim hundreds of feet below the surface without disturbing the sharks, make optimal shark taggers.
Buyle's first job tagging sharks was on the island of Malpelo, off the west coast of Colombia, in 2005. Researchers had speculated that hammerhead sharks in the area could be migrating as far south as the Galápagos Islands, some 1,400 miles away. If they were, Colombia could establish the whole region as a marine reserve, protecting the shark. But first they'd need to prove it. Over three trips, Buyle dove to depths of more than 200 feet and tagged 150 hammerheads. The data that came back was startling. Not only were the hammerheads migrating to waters around the Galápagos, and farther away, but they were doing so in packs of several hundred, swimming head to fin with one another like stealth fighters. As a result, in 2006, 3,300 square miles around Malpelo was named a Unesco World Heritage site.