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 typically migrate upstream when streamflows rise during a storm event (Moyle 1976) and after the sandbar, present across the mouth of most southern California streams, is breached (Shapovalov and Taft 1954).

Depending on rainfall, upstream migration and spawning typically occur from January through April in most southern California streams (Shapovalov 1944 as cited in ENTRIX 1995, Moyle and Yoshiyama 1992, NMFS 1996), and can potentially occur through June in 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 (called a "redd") and deposits eggs while a male fertilizes them. The eggs are then covered with gravel.

Young fish, called fry, emerge four to six weeks later and move to other parts of the stream to feed. 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.

Steelhead Trout in the Ventura River

The steelhead trout was once abundant and widespread in the coastal rivers and streams of southern California. Now, it is restricted to small populations mainly in the Santa Clara River, Ventura River, Santa Ynez River and Malibu Creek.

Historically, the Ventura River reportedly supported a substantial run of steelhead (an endangered fish) until the late 1940's when a prolonged drought and the construction of Matilija Dam apparently contributed to the decline of the species. Currently, steelhead can occur in the Ventura River below Robles Diversion Dam and portions of San Antonio Creek and its tributaries.

Listing Status of Steelhead

On August 17, 1997, steelhead were listed as "endangered" by the National Marine Fisheries Service (NMFS) under the Endangered Species Act (ESA) in the Evolutionarily Significant Unit (ESUs) from the Santa Maria River to Malibu Creek (NMFS 1997). On May 1, 2002, NMFS extended the range of listed Southern California steelhead to the U.S.-Mexico Border.