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NATURAL HISTORY

SOUTHERN CALIFORNIA STEELHEAD TROUT } Oncorhynchus mykiss
FAMILY: Salmonidae

DESCRIPTION: Steelhead can reach up to 55 pounds in weight and 45 inches in length, though their average size in southern California is much smaller. They are usually dark-olive in color, shading to silvery-white on the underside with a heavily speckled body and a pink to red stripe running along their sides.

HABITAT: Southern steelhead can survive a wide range of temperature conditions, but require streams with adequate dissolved oxygen. Spawning habitat consists of gravel substrates free of excessive silt.

RANGE: Steelhead inhabit the Santa Maria River from San Luis Obispo County, California to the United States-Mexico border.

MIGRATION: Adult steelhead migrate from the ocean into freshwater streams to spawn between December and April.

BREEDING: Female steelhead dig a nest (or redd) in a stream area with suitable gravel composition, water depth, and velocity. Male fish battle for the right to spawn with females. Females may deposit eggs in four to five nests within a single redd.

LIFE CYCLE: Steelhead eggs hatch three to four weeks after being deposited. Juvenile steelhead typically spend one to two years rearing in freshwater before migrating to estuarine areas as smolts and then into the ocean to feed and mature. Steelhead can then remain at sea for up to three years before returning to freshwater to spawn.

FEEDING: Young trout fry feed mostly on zooplankton. Adult steelhead eat aquatic and terrestrial insects, mollusks, crustaceans, fish eggs, minnows, and other small fishes.

THREATS: Dams, water diversions, urban development, livestock grazing, and gravel mining threaten the species.

POPULATION TREND: An estimated 30,000 to 50,000 steelhead once spawned in southern California rivers, but the recent runs in four major river systems were made by fewer than 500 adults total. Steelhead could once be found in 46 watersheds in the region, but only remained in 17 to 20 drainages by 2002. Many of these creeks and rivers now sustain only the resident form of steelhead, rainbow trout. Anadromous steelhead currently occur in only four large river systems in southern California — the Santa Maria, Santa Ynez, Ventura, and Santa Clara rivers.

Photo by Alex Vejar, California Department of Fish and Game