How Do Salmon Return to Where They Were Born?

Salmon spend most of their life in the ocean, but they return to the river where they were born when it's time to lay eggs. Salmon can remember the smell of the river they originally came from. Once they find it, they swim up it and spawn. Salmon hatch in rivers and live there for about three months, then do downstream to the ocean. In the fall of the fourth year they return to their native rivers. Scientists are not sure how salmon know which way to head in the middle of vast oceans. Some believe that salmon can tell direction from the position of the sun, or that they may determine their location by sensing the magnetic field of the earth. When salmon reach coastal waters, they rely on memory to detect the smell of their river of origin.