Central Valley Steelhead (Oncorhynchus mykiss)

Steelhead in the Sierra Nevada


Steelhead The rivers and streams of the west slope of the Sierra Nevada once teemed with ocean migrating runs of trout, called steelhead. Currently, all California runs of steelhead are threatened with extinction, and are listed under the Endangered Species Act. During this century, over 23 indigenous, naturally reproducing stocks of steelhead are believed to have been extirpated, and many more are thought to be in decline in numerous coastal and inland streams in Washington, Oregon, Idaho, and California.

The Sacramento and San Joaquin Rivers offer the only migration route to the drainages of the Sierra Nevada and southern Cascade mountain ranges for these anadromous fish. Nevertheless, there has been relatively little research directed at steelhead in California's Central Valley, and efforts to restore Central Valley steelhead have been greatly hampered by lack of information. Today, steelhead populations are largely maintained by fish hatcheries which capture migrating adults and harvest their eggs, rear them in artifical holding tanks, and release them back into streams.

Primary threats to the survival of west coast steelhead include destruction and modification of habitat, primarily from forestry, agriculture including grazing; mining, urbanization, and introduction of diseases and predatory non-native fish into riverine habitat. Water diversions, dams, sedimentation, and pollutants are the primary source of loss of habitat and habitat quality. It is estimated that California has lost 91 percent of its wetlands. More than 95 percent of historical steelhead spawning habitat is no longer accessible, or degraded such that the water temperatures are too high. Over utilization, or recreational fishing, is a lesser threat that has contributed to the decline of steelhead. Disease, and predation from introduced non-native predators, are additional factors on the increase. Due to the cumulative nature of stressors there is greater potential for susceptibility to disease, loss of survivability, and mortality.

Along with these threats, the National Marine Fisheries Service (NMFS) also cited the inadequacy of existing regulatory mechanisms in its rationale for listing steelhead as a threatened species under the ESA. While rules and regulations may appear to be adequate on the books, the agency found that requirements to protect sensitive resources and habitat were rarely enforced.

In the case of private forestry, the California Department of Forestry and Fire Protection enforces the state's forest practice rules (CFPRs). Timber harvest activities have been documented to result in negative effects on streams and streamside zones, including the loss of riparian vegetation, sedimentation, and the loss of habitat complexity and connectivity. In spite of small modifications to the California Forest Practice Rules, after ten years little progress has been made to adequately address and mitigate the cumulative impacts of timber harvests upon salmonid habitat. In particular, Sierra Nevada streams receive almost no special protection on behalf of critically endangered and threatened salmonids during the review of timber harvest plans by agency personnel.

Egg mortality begins to occur at 56°F, and thermal stress has been reported at temperatures beginning at 66°F, and temperatures demonstrated to be lethal to adults have been reported at 70°F. Industry sponsored research studies in the Sierra Nevada have cynically been conducted in cold, spring-fed streams that fail to capture the true timber harvest impacts on temperature that results from reduced forest canopy shading. Sadly, our public regulatory agencies charged with protecting our trust resources continue to approve unsustainable levels of timber harvests in the Sierra Nevada, even routinely granting waivers from minimal stream buffer protections. Such practices greatly underscore the need to preserve quality aquatic habitat on publicly owned forest lands in the Sierra Nevada.

Habitat and Life History

O. mykiss exhibits one of the most complex suites of life history traits of any salmonid species. Individuals may exhibit anadromy (meaning they migrate as juveniles from fresh water to the ocean, and then return to spawn in fresh water) or freshwater residency (meaning they reside their entire life in fresh water). Resident forms are usually referred to as ‘‘rainbow’’ or ‘‘redband’’ trout, while anadromous life forms are termed ‘‘steelhead.’’ Steelhead trout are sea-going rainbow trout.

Steelhead often live in swift streams flowing out of the mountains. In California, peak spawning occurs from December through April in small streams and tributaries with cool, well-oxygenated water. The length of time it takes for eggs to hatch depends mostly on water temperature. Steelhead eggs hatch in about 30 days at 51°F. Very small fish live in shallow riffles and calm pools at the stream's edge. Older juvenile steelhead claim and defend positions in larger riffles, where food is delivered by the flowing water. They retreat to deep, cold pools to rest. The young fish stay in freshwater from one to three years before migrating to sea.

They are very agile, and can jump water falls up to 15 feet high. Although they do not get as large as chinook and coho salmon, they have the advantage of sometimes remaining alive after spawning. Unlike salmon, all of which do die after spawning, steelhead may spawn more than once.

The distance from the Pacific Ocean to spawning streams can exceed 300 km, providing unique potential for reproductive isolation among steelhead. The Central Valley is much drier than the coastal regions to the west, receiving on average of only 10 to 50 cm of rainfall annually. The valley is characterized by alluvial soils, and native vegetation was dominated by oak forests and prairie grasses prior to agricultural development. Steelhead within this ESU have the longest freshwater migration of any population of winter-run steelhead. There is essentially one continuous run of steelhead in the upper Sacramento River. River entry ranges from July through May, with peaks in September and February. Spawning begins in late December and can extend into April.

Steelhead spawn in practically every tributary of the upper Sacramento River, and appear to do so in numbers proportionate to a given tributary's runoff. That is, large streams such as Mill, Deer, and Battle creeks have the largest runs. Actual numbers of naturally spawning steelhead in these streams are generally unknown. However, an average of 1160 steelhead per year migrated into Mill Creek during a 10 year period from 1954 to 1963. Peak immigration upstream appears to be in the fall (September-October), while migration downstream peaks in the spring but can occur anytime.   


In 2005, in accordance with the requirements of the Endangered Species Act, the National Marine Fisheries Service (NMFS) and the National Oceanic and Atmospheric Administration (NOAA) issued a final rule designating critical habitat for seven evolutionary significant units of Pacific salmon and steelhead in California. To qualify as a distinct population segment, a Pacific salmon or steelhead population must be substantially reproductively isolated from other conspecific populations and represent an important component in the evolutionary legacy of the biological species. A population meeting these criteria is considered an Evolutionary Significant Unit or ESU.

Critical habitat is defined as 1) specific areas within the geographical area occupied by the species at the time of listing under the ESA, on which are found those physical or biological features that are essential to the conservation of the listed species and that may require special management considerations or protection, and 2) specific areas outside the geographical area occupied by the species at the time of listing that are essential for the conservation of a listed species.

Critical habitat designations were made for 2,308 steam miles for Central Valley steelhead, of which 8.6 percent occurs on Federal lands, and 88.3 percent occurs on private lands. Critical habitat designation has virtually no impact on private lands, unless there is a tie to federal activity, such as when a land owner must apply for a federal permit or license. Exclusions for designating occupied habitat were granted, due to "economic considerations," for the entire Nevada City, Sutter Creek, NF Cosumnes, Paynes Creek, and other watersheds. Counties with critical habitat designation include: Tehama, Butte, Glenn, Shasta, Yolo, Sacramento, Solano, Colusa, Yuba, Sutter, Placer, Calaveras, San Joaquin, Stanislaus, Tuolumne, Merced, Alameda and Contra Costa.

In Tehama County, $42.75 million in funding has been awarded for implementing Phase 1 of the Battle Creek Salmon and Steelhead Restoration Project. The project is one of the largest cold water anadromous fish restoration efforts in North America. The stream with its two branches, the North Fork and the South Fork, has been designated as a prime recovery site for spring and winter-run Central Valley Chinook (winter-run is an endangered species currently limited to the Sacramento River because of dams on the upper Sacramento, Pit and McCloud Rivers) and steelhead, because of its relatively clean water and cold temperature fed by numerous springs along its length. Current plans are now in place to remove one diversion dam, modify another, and install new fish screens and ladders that will hopefully ensure safe passage for the imperiled salmonids. Currently there are nine dam sites currently located in the Battle Creek watershed. When the project is completed ultimately five dams will be dismantled, including the dam at Coleman Fish Hatchery which now holds the fish back. After the dam is removed, anadromous fish will return to Battle Creek without impediment for the first time since 1942.


Central Valley steelhead was listed as threatened under the Endangered Species Act in 1998 and reaffirmed during review in 2005. Critical habitat designations for all listed Pacific salmonids occuring in California were also designated in 2005. The Federal Register documents can be accessed below, under Supporting Resources.

The National Marine Fisheries Service cited the ongoing aquatic and riparian restoration efforts funded in the Central Valley Project Improvement Act (CVPIA) and CALFED as justification for "threatened" status listing under the Endangered Species Act, rather than "endangered" as proposed for Central Valley steelhead. Restoration actions identified in these programs are largely directed at chinook salmon recovery, however, with comparatively little emphasis on specific actions needed to recover steelhead. To date, most plans have not even been implemented.

Scientific Research

Erman. N. 1996. Status of Aquatic Invertebrates. In Sierra Nevada Ecosystem Project: Final Report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildlife Resources. (290KB PDF)

Kondolf, G.M., R. Kattelmann, M. Embury, and D.C. Erman. 1996. Status of Riparian Habitat. In Sierra Nevada Ecosystem Project: Final Report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildlife Resources. (1.4 MB PDF)

Meek, M.H., Stephens, M.R., Tomalty, K.M., et al. 2014. Genetic considerations for sourcing steelhead reintroductions: Investigating possibilities for the San Joaquin River. San Francisco Estuary and Watershed Science 12(1) March 2014. (407 KB PDF)

Moyle, P. 1996. Potential Aquatic Diversity Management Areas. In Sierra Nevada Ecosystem Project: Final Report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildlife Resources. (240 KB PDF)

Moyle, P.B., R.N. Yoshiyama, and R.A. Knapp. 1996. Status of Fish and Fisheries. In Sierra Nevada Ecosystem Project: Final Report to Congress, vol. II, Assessments and scientific basis for management options. Davis: University of California, Centers for Water and Wildlife Resources. (373 KB PDF)

National Marine Fisheries Service. 2017. Genetic analysis of Oncorhynchus mykiss in the Upper Tuolumne and Merced Rivers to evaluate ancestry and adaptive genetic variation. (2.66 MB PDF)

Yoshiyama, R.N., E.R. Gerstung, F.W. Fisher, and P.B. Moyle. 1996. Historical and Present Distribution of Chinook Salmon in the Central Valley Drainage of California. 1996. In Sierra Nevada Ecosystem Project: Final Report to Congress, vol. III, Assessments, reports, and background information. Davis: University of California, Centers for Water and Wildlife Resources. (462 KB PDF)

Supporting Resources

Central Valley Steelhead Listed as Threatened Species in 1998 Federal Register Final Rule (URL)

Reaffirmation of Threatened Status for Central Valley Steelhead -- published in Federal Register in 2006 (URL)

Designation of Critical Habitat for California salmonids--Final Rule 2005 (URL)

2007 Federal Recovery Outline for the Evolutionarily Significant Units of Sacramento River Winter-run Chinook Salmon and Central Valley Spring-run Chinook Salmon and the Distinct Population Segment of California Central Valley Steelhead. Prepared by the National Marine Fisheries Service, Southwest Region, Sacramento Area Office (2.75 MB)

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