Ocean Migration By the age of two years, most salmon species have switched to a marine environment. The mature adult has developed strong jaws, sharp teeth and hard, protective scales. The gills that pumped in salts from the river water now pump them out, regulating the biochemical balance of their bodies (osmoregulation). Ocean-going salmon begin to eat small fish such as anchovies, herring, shrimp and squid. They also begin travelling, moving to faraway ocean feeding grounds, up to 3,200 kilometres away. Some salmon species remain in the ocean only for a year, while some feed and grow for up to five or six years, travelling many thousand kilometres.

Upstream Run About 10% of salmon smolts that enter the sea return to seek their home stream, survivors of ocean perils, such as tuna, swordfish, pollock, killer whales and adverse climate conditions. At the mouths of their river systems, their bodies begin a reverse transformation. Skin thickens, scales are absorbed and bodies become more compressed. The more defined markings and colours of the stream replace the silvery sheen of the ocean. Males begin to develop a hooked jaw, or kype, and in some cases, a humped back. Sexual organs ripen, and feeding halts entirely. The fish wait for heavy rains to raise the water levels, and when they arrive, the upstream spawning run begins. The fish travel mostly in mornings and evenings, resting in pools in mid-afternoon. Most travel single file. Smaller species, with less ability to fight heavy currents and overcome obstacles, spawn close to the ocean. Larger salmon, such as sockeye and Chinook, may travel more than 1,600 kilometres upstream, pushing against rapid water, leaping over waterfalls, climbing fish ladders. Predators, both human and animal, line the route. Fish that succeed in reaching their spawning grounds are often torn and battered. But the courting process begins, sometimes with a few one-year-old male jacks (or Atlantic salmon grilse) competing for mates, and a new generation of salmon is underway.