Idaho has three runs of chinook: called spring, summer and fall, based on the time of arrival in Idaho waters. NMFS has combined spring and summer chinook into one "species" called Snake River spring/summer chinook salmon. Fall chinook remains a separate "species." After arriving in the Clearwater, Salmon and Snake rivers, chinook salmon spawn in late summer or autumn, in sites that have the best combination of gravel and coarse sand, adequate depth, and good water flow to provide oxygen for eggs. Depending on water temperature, egg incubation varies from 80 to 140 days. The alevins, or sac-fry, spend the winter buried in the gravel, living on energy stored in the egg yolk which remains attached to their abdomen. Fully-formed fry swim up from gravel nests in early spring. The young salmon, called "smolts," migrate to the ocean after six months to a year. After one to four years in the ocean, the fish begin their journey upstream back to natal waters to spawn and start the cycle over again.
Credit: U.S. Fish and Wildlife Service |
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