There are mysteries associated with the ability of salmon to return home to spawn after years of migration over huge distances. Adult salmon lay their eggs in gravelly river beds, where fast water flows. Within days, these mature females die. After two or three years their relatively small offspring swim downstream to find the plentiful food supply of the ocean. Sometimes this journey covers thousands of kilometres. When the time comes to spawn, however, the salmon still remembers how to get back to the rapidly flowing shallow water where their eggs must be laid and fertilized.
How do salmon find their way back home? They often travel day and night, swimming upstream against swift currents, and up waterfalls that may be more than three metres high. Salmon runs along the Yukon River, for example, may involve a journey of some three thousand kilometres.
There are many theories about how salmon know their way home. Everything from the position of the sun to electrical charges generated by ocean currents has been suggested. Many feel their sense of smell guides them. Others suggest that they have an ability to memorize cues from the Earth’s magnetic field. Whatever the mechanism, the path is imprinted in the genes and passed on through the generations.
So next time you are daunted by a trip, think of the salmon and press on.
