Salmonid Life History

Salmon and some species of trout have unique life histories that categorize them as "salmonids." Salmonids are characterized by having an anadromous life cycle, which means that they begin their life in freshwater, migrate to sea to live out their adult life before finally returning to freshwater to reproduce and begin the next generation. Each year a generation of salmonids returns to freshwater from the ocean to breed before dying. A new generation is born and, for months to years, the survival of these young fish depends on the quality of their natal freshwater stream habitat.

In California, San Mateo and Santa Cruz Counties currently make up the southern extent of the freshwater habitat range for coho salmon (Oncorhynchus kisutch) and provide habitat for steelhead trout (O. mykiss). The people who live in these counties are the stewards of the adult breeding and juvenile rearing grounds. Maintaining viable habitat conditions is imperative to salmonid spawning success and the survival of juveniles.

The following sections describe these species by following them through their life history and the associated habitat requirements.

Salmonid Life Cycle

Roll your mouse over each image to find out more about each life stage.

A New Generation is Born

The salmonid eggs incubate within their gravel nest (redd).

Hatchlings

Young salmonids (alevins) hatch from the eggs and remain in the redd until they are ready to feed.

Young salmon

Juvenile salmonids (fry) rear in freshwater. Depending upon the species, young salmonids may stay from a few months to three years before migrating to sea.

Smolts

As juveniles mature, they smolt (undergo physiological changes that prepare them to survive in saltwater). The estuarine environment provides an important place for juveniles to feed and grow prior to migrating to the ocean.

Ocean Life

Adult salmonids live and grow in the ocean for between one and three years depending on the species. At sea, adult salmonids are pelagic - occurring in the open sea - and prey mostly on other fishes. While in the ocean, adult salmonids stay fairly close to the coast within a few hundred kilometers of their spawning stream.

Return to Esuary

Estuaries are equally important as an environment for adult salmonids to undergo the physiological changes necessary to prepare them to survive in fresh water prior to migrating upstream to spawn.

Return to Streams

Adult salmonids return from the ocean one to three years after outmigration, and migrate upstream to their home stream to spawn.

Spawning

Spawning salmonids create a gravel nest (redd) on the stream bottom. After spawning, adult salmonids die (some steelhead live to spawn again), but the next generation will soon be born.

dynamic illustration of salmonid life cycle

Illustration by Ted Andersen.