IN the ocean, sharks are the top predators (捕食者), not the prey (猎物). But the fearsome fish face a powerful enemy in humans, who have made their numbers much smaller by commercial fishing. Enter Madison Stewart, a 20-year-old Australian who’s been swimming with sharks since she was 12. She’s made it her life’s mission to protect them, raise awareness (意识) about their importance to the ocean’s ecosystem (生态系统), and stop the fishing and illegal finning (取鲨鱼鳍) that endanger them. Her inspiring story is the subject of the Smithsonian Channel documentary Shark Girl.