When the time comes, the salmon migrate back to the streams where they were born. Guided largely by smell, they return home to coastal or inland rivers, swimming across thousands of kilometres of ocean.

As they prepare for spawning, salmon become brightly coloured and their bodies become distorted. They battle their way upstream until they arrive at a familiar stretch of riverbed. The males battle for the right to fertilize the females, and the females batter their bodies as they dig holes (or redds), in the river bottom in which to lay their eggs. When the salmon are spent, their carcasses lie rotting along the riverbanks. They provide food for scavenging birds and mammals and cycle nutrients back into the ecosystem. In time, the eggs hatch and a new generation of salmon begins the cycle again.