In the frigid Atlantic waters off Nova Scotia’s east coast, two orcas—a mother and her calf—swim freely within a long bay. They dive up to eighteen metres to the ocean floor, where rock crabs, sea stars, and mussels live and slimy eelgrass sways with the current. They sense nearby fish; they hear each other’s clicks and pulses. They swim openly within the bay, the only barrier being an eight-inch mesh fence made of Dyneema—“the world’s strongest…