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The Salmon Life Cycle

After returning from the ocean to their natal stream, male and female salmon pair up and defend spawning territories. Females dig depressions in the streambed with their tails. These depressions are generally dug in loose gravel where the eggs are laid and then buried.

Once hatched, the baby salmon, or alevin (Ale´-uh-vin), must remain in the gravel until they absorb their yolk sac.

When the sac is absorbed, the alevin emerge from the gravel and enter the fry stage. As a fry, the salmon begin feeding on live prey.

The salmon continue to feed and grow and eventually begin their journey downstream to the open ocean. Before juvenile salmon migrate toward the estuary, they begin a process known as smoltification. They undergo the majority of this process in estuaries (the area where salt water from the ocean mixes with the fresh water delivered from rivers). Here they adapt to a new life in salt water. Once juvenile salmon, now called "smolt", enter the Pacific Ocean, they are able to grow and mature quickly due to a rich diet of marine invertebrates and fish. Time spent in the ocean varies between different species and between individual fish, but is typically between 1-5 years. Once reaching maturity, salmon begin their migration back to the stream where they originally hatched. Scientists believe salmon are able to locate their natal streams through olfactory perception (sense of smell).

Once back in fresh water, salmon quit feeding and use their energy reserves to migrate upstream and spawn. At this time the salmon physically change. Their colors change from ocean silver to dark reds, greens, and black. They develop large hooked toothy snouts and some species even develop humped backs. These changes help the fish attract mates and defend territories on the spawning grounds.

To see larger images of the salmon life cycle, look at eggs, juveniles, and adults.