The Columbia River Basin provides habitat for six species of anadromous salmon: chinook, coho, chum, sockeye, pink, and steelhead. Anadromous salmon hatch in freshwater rivers and tributaries, where they grow for a year or two. They migrate to the ocean, where they mature. After two to five years there, they return to their place of origin to spawn and die.

Many factors affect salmon survival, and the fish face tough odds. Only about 1 to 2 percent of all salmon hatched will live to become adults. That is why female salmon carry as many as 5,000 eggs—it is nature’s way of dealing with a challenging lifecycle and naturally high mortality. In fact, the highest mortality occurs early in the salmon’s lifecycle, when eggs emerge from the gravel in rivers and streams.

For adults, ocean conditions are the overwhelming factor driving salmon returns. In the ocean, salmon can face a scarcity of food to grow and thrive. The salmon themselves are an essential part of the oceanic food chain—consumed by other fish, sharks, whales and birds. Long term and short term changes in climate, atmospheric pressure and water temperature create ocean conditions that are sometimes favorable to salmon survival and sometimes not.

Also, ocean harvest by the United States, China, Japan and other countries is believed to have a huge but relatively undocumented impact on salmon returns. Other important mortality factors include natural predators, such as cormorants, terns and sea lions. Dams, pollution and habitat destruction all take their toll. Plus, those adult salmon who do make it to the mouth of the Columbia to spawn the next generation face commercial, sport and tribal fishing that reduces their numbers by as high as 50%, depending on the season and species.

Factors that Impact Salmon

Salmon Life Cycle and Habitat 


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nwrpMany Factors Impact Salmon