Salmon Life Cycle

Salmon begin their lives as tiny eggs in freshwater streams and rivers. Fertilized eggs lay in redds, or gravel beds dug out along the streambed, where the flow of water provides oxygen and removes excess sediment or waste products. The eggs will remain buried in the gravel until they are developed enough to emerge.

Eggs “hatch” into tiny salmon called alevins. Alevins have their egg yolk sac attached to their bellies. The yolk sac continues to provide nutrients as the alevins grow. For a few months, alevins rely on their yolk sac and cover from the surrounding gravel until they are large enough to swim away from the redd.

After alevins have fully absorbed their yolk sac, they become fry. Once fry have left their redd, they search for food and try to avoid being eaten. During this stage, fry may begin moving from freshwater to saltwater. Each species may spend a different amount of time developing before begining migration from freshwater to saltwater.

At some point, fry pick up environmental cues and begin their migration to the ocean. This migration requires fry to go through a physical change, allowing them to survive in the ocean’s saltwater. At this stage, the salmon are called smolts. They grow new scales, giving them a silvery color. This is the last time salmon will be in freshwater until they are ready to spawn

Now in saltwater, salmon continue to look for food. Adult salmon can stay in the ocean, depending on species, anywhere from 1-8 years. Much like their initial transition, salmon pick up new cues to return to the streams where they were born.

Once adult salmon have begun their migration back to freshwater, their bodies undergo more changes to prepare for spawning. Spawners adapt to freshwater, their coloring changes, and some grow humped backs or hooked jaws. The journey back to their natal streams is incredibly challenging, not only because of the changes they undergo but also because of the challenges they face returning upstream. Once salmon end their journey and leave fertilized eggs in new redds, they have completed their lifecycle and die shortly after.

The salmon carcasses then are distributed by the river’s current along the watershed to provide nutrients to other species and habitat. These dead salmon are particularly special to the surrounding environment because they release nutrients from the ocean.