The life cycle of the wild salmon begins with the female salmon digging out a shallow redd, or nest, in the gravel on the river bottom. In this nest she lays her orange, pea-sized eggs. After the eggs are fertilized by the male, the female covers the eggs with small to pebble sized gravel. The gravel covering allows water to flow around the eggs and keep them healthy.
Photo courtesy of the Corps of Engineers, Portland District
Redds are fragile and can easily be destroyed by people or animals crossing the shallow river or by dirt being washed or knocked into the water and smothering the eggs. Horseback riders, fishermen, loggers, livestock, wild animals, or just the casual hiker can all accidentally destroy salmon redds without even realizing it.
Salmon eggs need cool, clean water to survive. Trees and plants along the side of the river provide shade which keeps the water temperature cool enough for the salmon eggs. The trees and plants along the river also help prevent soil erosion which will sometimes smother the eggs.
The eggs that are laid in the fall hatch the next spring. The small larval fish, about one inch in length, are called alevin and still have a yolk sac attached. The yolk sac contains protein, sugar, minerals, and vitamins. The alevin live on this "lunch bag" for a month or so before emerging from the gravel and beginning to hunt food for themselves. When the alevin completely absorb their yolk sacs, they leave the gravel and become fry. Alevin that leave the gravel before their yolk sac is completely absorbed are commonly called button-up fry.
Illustration courtesy of Cory Ench
Salmon face danger throughout their entire lives, from eggs to spawning adults. Gulls, dippers, sculpins, and trout all feed upon salmon eggs and young alevin.