Salmon use built-in magnetic compasses in their noses to navigate thousands of miles back to their birthplace.

Salmon migration is one of nature's most precise navigational feats, relying on a process called magnetoreception. Research published in journals like 'Current Biology' indicates that salmon possess microscopic crystals of magnetite in their snouts. These crystals are linked to the nervous system and allow the fish to detect the intensity and inclination of Earth's magnetic field.During a process known as 'magnetic imprinting,' juvenile salmon (smolts) record the magnetic coordinates of their home river before heading to sea. This biological record acts as a permanent reference point for their adult return. A study by Oregon State University researchers confirmed that salmon use these magnetic cues to navigate across thousands of miles of featureless ocean water where visual landmarks are absent.The magnetic field of Earth varies predictably across the globe, providing a grid-like map that the salmon can interpret. By comparing the local magnetic field to their imprinted memory, they can determine their position relative to their destination. This allows them to maintain a consistent heading even during storms or at night.While magnetism handles the long-distance navigation, salmon switch to their sense of smell once they reach the coastal area. They can detect chemical 'scents' of their home stream at concentrations as low as one part per billion. This dual-system approach ensures they find the specific gravel bed where they hatched to begin the next generation.