Fish Migration Highways

Rivers serve as corridors for species that move between fresh and salt water, and salmon navigate them with startling precision. At sea they steer by Earth's magnetic field, then switch to olfactory memory in rivers, literally smelling their way home to the stream where they hatched.

The European eel makes an even stranger journey. Born in the Sargasso Sea, juveniles drift to European rivers and live there for 15 to 30 years. When ready to breed, they cross the entire Atlantic to spawn and die.