Chinook salmon are often classified into three different groupings or “runs” – spring, summer or fall based on when they enter fresh water. Spring Chinook salmon migrating to Idaho tend to enter the Columbia River from March through May, summer Chinook Salmon enter the Columbia June through July, and fall Chinook Salmon enter August through November.
In Idaho, most spring and summer Chinook salmon spawn from late August through September. Fall Chinook salmon tend to spawn from late October through early December. When spawning, the female will dig a hole in the gravel to lay her eggs. This hole is referred to as a “redd” and the female will lay anywhere from 4,000 to 15,000 eggs depending on her size. While the female lays her eggs, a male will simultaneously fertilize them with milt. When done spawning, the female will cover up the hole with gravel to help insure the eggs are protected from predators. When spawning is complete, both the male and female die.
The eggs hatch in the spring and the juvenile fish will live the next year in fresh water before migrating to the ocean. The exception is fall Chinook salmon that only live a months or two in fresh water before beginning their migration to the ocean. Chinook salmon from Idaho tend to spend one to five years in the ocean before returning to fresh water to spawn, with two years being the most common. Chinook salmon, like other salmon species, have the ability to find their way back to the same stream and often the exact same place to spawn that their parents spawned.
Young salmon eat both aquatic and terrestrial insects when in fresh water. They turn to a diet of fish once they reach salt water. Adults retuning to spawn do not eat once they enter fresh water; they live off their fat reserves.