After spawning, the female salmon expends much of her remaining energy to cover the newly deposited eggs under a layer of gravel for protection. After nearly 30 days living in the spaces between the gravel, salmon eggs are at a point when they are ready to hatch. You can make out their eyes within the egg casing.
Upon hatching, the young salmon have a yolk sac which is essentually their nutrient/food source for the next 30 days. At this point in their life stage, they are called alevin. They grow in the protection of the stream gravel, but are still at risk of big storm events which may scour the stream too much. The yolk sac is slowly absorbed over that time and the young salmon begin to look more like a small fish.
It is not until the yolk sac is completed absorbed that the young fish wriggle up from the gravel and emerge into the open water of the stream. It is here they hide in the shadows while seeking new sources of food. They will continue on their life path to the ocean and return in 2-5 years, perhaps to the very location from where they started.