North Cascades

Salmon and Their Life Cycle

The life of the salmon is a cycle.

The length of each stage of this cycle varies with each species of salmon.

Salmon begin their lives as reddish, pea-sized eggs in the gravel of a fresh water creek, river, or stream. It is in this same stream that their parents were born. Many eggs share the same nest or redd.

Salmon eggs stay in the redd for one to four months. The tiny, newly hatched fish, known as alevins, remain in the gravel layer for several weeks. During this stage they are nutritionally dependent on the yolk sac that is attached to their bellies. Once the yolk sac is absorbed, the alevins enter the fry stage.

In the fry stage, salmon eat zooplankton until they grow large enough to eat crustaceans and insects. Fry will feed in the area of the redd for up to several years. Fry grow into fingerlings.

Fingerlings are four to five inches long. They eat snails, worms, freshwater shrimp, amphibian larvae, fish eggs, and young fish.

Fingerlings of pink and chum salmon species, as soon as they move from the fry stage, will migrate downstream to coastal estuaries, where the fresh water meets the ocean. Fingerlings of other species remain in fresh water for two months to three years before migrating to the estuary.

Once the fingerlings reach the estuary they are called smolt. These small fish spend time in the estuary while their bodies undergo changes to help them adjust to salt water living.

For the next two to five years the salmon will swim hundreds of miles in the Pacific Ocean in search of food and trying to stay out of the mouths of predators.

Mature salmon return to the same estuary they visited as a smolt. The mature salmon will be guided by the chemical blueprint smell of the water of its natal stream and find its way back home.

In the estuary, the salmon's habits change; it will no longer feed, but will derive energy from stored fats The appearance of the fish changes as well; the males change radically. Turning from silvery to various shades and combinations of red, green, and brown, the male salmon develops a hooked jaw and, in some cases, a humped back. The female's changes are more subtle, usually involving only a slight change in color and pattern.

The female constructs several redds. The adults may guard the redds once they have finished spawning, but, eventually, their exhausted bodies will wash downstream. The carcasses of the adult fish feed scavengers. The nutrients of their decaying bodies feed stream organisms which will, in turn, feed the young salmon.

A female salmon will lay several thousand eggs. Less than 1 percent of those eggs will survive to become spawning adults.