For almost 15 years, Salvador Jorgensen from the Monterey Bay Aquarium has been studying great white sharks off the coast of California. He and his colleagues would lure the predators to their boats using bits of old carpet that they had cut in the shape of a seal. When the sharks approached, the team would shoot them with electronic tags that periodically emit ultrasonic signals. Underwater receivers, moored throughout Californian waters, detected these signals as the sharks swam by, allowing the team to track their whereabouts over time. In 2009, the team tagged 17 great whites, which spent months circling Southeast Farallon Island and picking off the local elephant seals. But this period of steady hunting ended on November 2 of that year, when two pods of killer whales (orcas) swam past the islands in the early afternoon. In the space of eight hours, all 17 great whites abruptly disappeared. They weren't dead; their tags were eventually detected in distant waters. They had just