Pacific salmon are tough and persistent fish. They begin life as energy-rich eggs maturing in the gravel of a western river, as far as hundreds of miles upstream of the Pacific Ocean. After months in the gravel, the young salmon hatch and begin a grueling journey downstream. They careen over dams and through power turbines, navigate polluted and silty waters, avoid predators attacking from the water and air. The lucky survivors hit salt water and spend the next several years eating, growing, and avoiding their natural enemies in the open ocean. Then, at the trigger of some ancestral signal, they head back home, enduring a gauntlet of nets and traps set for them by commercial fishermen.