South Hams, Devon: These are monstrous animals, growing to 3 metres and reaching 40mph, and I was lucky enough to see a pack in hunting mode It is a perfect autumn day for a clifftop walk: sea and sky blend into a veil of baby blue, and the water is calm and dazzling. A motorboat unzips the ocean as we squint out over the bay. My companion points to a dark line snaking along in the water. It seems to intensify for a moment, then erupts in a silver commotion. Through binoculars I can make out the frantic leaping of a shoal of eel-like fish. “Garfish,” he says. “Now just watch.”