A salmon river in autumn is a magical place, for this is where you’re most likely to see these muscular fish living up to their scientific name Salmo salar – salire means ‘to jump’ in Latin. The secret to their dramatic leaps lies in the standing wave at the base of each waterfall, which helps lift the salmon into the air, enabling them to save precious energy.
Conserving resources is vital, because adult salmon do not feed in fresh water, and some individuals may linger in a river for up to 14 months before heading to the shallow, gravelly upper reaches where they spawn. During that time, they spend long periods quiescent in deep pools and under banks. They only travel upriver in response to increases in flow, especially in autumn at the ‘tail’ of a spate, just after the peak flow has passed.
This urgent journey homeward against the current is the final stage of a long and arduous migration. It began when the fish, triggered by the earliest stages of sexual maturation, left their marine feeding grounds in Arctic waters. Here the salmon fed voraciously on mid-water crustaceans and small fish for between one and four years.
We know from tagging studies that salmon may dive as deep as 300m in search of prey, but their return migration to our coastal waters seems to be undertaken near the surface of the sea. This may facilitate the use of celestial navigational cues, though they could also use magnetic ones. Once in coastal waters, the imprinted smell and taste of the home river takes over and guides them to the very area where their heroic lives began.