Every year, wild salmon travel hundreds of miles upstream. They fight fierce river currents, leap over rocks and small waterfalls, and die by the thousands of starvation, disease, and exposure to cold. Even if they surmount these obstacles, the fish risk becoming dinner for hungry predators like bears, birds, and humans. Guided by a keen sense of smell, the survivors travel to their original hatching grounds, where they breed, spawn, and quickly die...