Process — The life cycle of the salmon

The diagram depicts the six stages in the life cycle of the salmon, from egg to spawning adult.

Overall, the cycle is a closed one that spans several years and two very different habitats: salmon hatch in fresh water, mature in the open sea, and finally return to the river of their birth to breed, after which most of them die and the cycle begins again.

The cycle starts in autumn, when eggs are laid in the gravel beds of the upper river. The eggs hatch into small fry, which remain in fresh water for five to six months, feeding and growing. At roughly two years of age the young fish, now known as smolts, swim downstream and enter the sea.

The adult salmon then spend up to four years feeding and growing in the ocean, where they reach full size. When they are ready to breed, they undertake a remarkable return journey, swimming back up the very river in which they hatched and even leaping waterfalls on the way. In the final stage, the females spawn in the same gravel beds, and although the vast majority of adults die soon afterwards, the newly laid eggs ensure the cycle restarts.