Counties of Santa Barbara, Ventura and San Luis Obispo


Steelhead Information

Life History
Steelhead rainbow trout (Oncorhynchus mykiss) are the anadromous form of resident rainbow trout, spending part of their life in the ocean and part in freshwater. Anadromous means that the fish migrates as a juvenile from freshwater to the ocean, then returns to spawn in freshwater. Steelhead usually spend one to two years in the ocean before returning to spawn for the first time (Shapovalov and Taft 1954). Steelhead are unusual among the Pacific salmonids in that they do not necessarily die after spawning. Steelhead typically migrate upstream when streamflows rise during a storm event (Moyle 1976) and after the sandbar, present across the mouth of most southern and south-central California streams, is breached (Shapovalov and Taft 1954).

Depending on rainfall, upstream migration and spawning typically occur from January through April in most southern and south-central California streams (Shapovalov and Taft 1954, Moyle and Yoshiyama 1992, NMFS 1996), and can potentially occur through June in some southern systems like the Ventura River (NMFS 1996). Steelhead usually spawn in small streams with cool water and gravel substrate (Moyle 1976). The female selects a site where there is flow between gravel, digs a nest or pit, and then deposits her eggs while a male fertilizes them. Often more than one male will fertilize the eggs before the female covers the eggs with gravel creating a "redd" (Moyle 1976, 2002).

Young fish, called fry, emerge four to six weeks later (depending on water temperature, dissolved oxygen concentration, and substrate composition) and move to other parts of the stream to feed. Steelhead fry and juveniles feed on a variety of invertebrates including aquatic and terrestrial insects, amphipods, and snails (Moyle 2002). In California, juveniles generally spend one to three years in freshwater before migrating to the ocean usually between March and June (Shapovalov and Taft 1954) to complete their maturation. The time that steelhead spend in the ocean before returning to their natal streams is also quite variable, but usually is one to two years.

The average size of steelhead is about 10 inches, but they can range up to 45 inches in length and up to 40 pounds. They are silver in the ocean, then become darker and spotted with a reddish-pink stripe when they migrate upstream to spawn.

Resident forms of steelhead are called rainbow trout. These fish remain in freshwater all of their life and do not migrate to the ocean. In California, many streams support both resident and anadromous forms. Presence of resident rainbow trout populations tends to increase in the southern part of the North American range (Cramer et al 1995).

For additional information, check out Salmon Facts from the NMFS Northeast Fisheries Science Center.