In September 1997, the U. S. Fish and Wildlife Service received a formal petition to list the Great Basin redband trout as threatened or endangered throughout its range in southeastern Oregon, northeastern California, and northwestern Nevada.  After a review of all available scientific and commercial information, we found that listing this species was not warranted (U.S. Fish and Wildlife Service 2000). Currently, we consider the Great Basin redband trout a species of concern and are continuing to monitor its status.

Background

Native rainbow trout east of the Cascades are commonly called “redband trout” (Oncorhynchus mykiss ssp.).  Redband trout are a primitive form of rainbow trout and are an evolutionary intermediate between ancestral “cutthroat”-like species and coastal rainbow trout. Redband trout are described as inland populations of O. mykiss, with few morphological and meristic characters distinguishing them from coastal rainbow trout.  Although there is no consensus on the classification of redband trout east of the Cascades, there is some agreement that at least two broad groups exist in Oregon: the Interior Columbia Basin redband trout and the Oregon Great Basin redband trout. In addition, redband trout in the upper Klamath Basin (e.g., Sprague and Williamson Rivers) represent a third evolutionary group within Oregon. Refer to the map above for their broad geographic locations within the state of Oregon.

Historical Status and Current Trends

The potential range of all forms of redband trout included freshwaters west of the Rocky Mountains, extending from northern California to northern British Columbia, Canada. Despite their broad distribution, local extirpations (extinct locally but exists elsewhere) and important declines have occurred. Redband trout have more limited distribution and fewer strongholds than historically. Degradation and fragmentation of habitat, and the introduction of non-native species are primary factors that influenced the status and distribution of redband trout.

Habitat

Redband trout evolved in a variety of habitats from montane forests to high desert stream environments that are characterized by unpredictable and intermittent flows, high summer water temperatures, high alkalinity, drought, and fire. As a result, redband trout have historically been subject to naturally high levels of population fluctuation, and evolved traits that allow them to survive in conditions inhospitable to other types of trout.

Populations of redband trout in the Oregon Great Basin have been isolated for thousands of years and therefore evolved distinct genetic lineages (ancestries).

Like other species of trout, redband trout abundance has been strongly correlated with riparian cover components, including undercut banks, large woody debris, and overhanging vegetation. Good redband trout habitat is associated with higher gradient channels, often in riffles or with substrates dominated by boulders, cobbles, and pocket water. Redband trout also occupy lower gradient streams. Pools, which provide important holding and rearing habitat, resting places, over-wintering areas, and refuges from floods, drought, and extreme temperatures for juvenile and adult salmonids, should be available, and requirements for spawning include loose gravelly substrates to provide for oxygenation of eggs and embryos in redds in streams.

Life History

Three life history patterns have been identified for redband trout (excluding the anadromous form known as steelhead): (1) stream resident, (2) fluvial (migrate between larger and smaller streams), and (3) lake resident adfluvial (migrate between the lake and stream system). Stream resident (fluvial) populations of redband trout spend their entire life cycles in flowing waters and spawn in the headwaters of the streams they inhabit. The abilities of individuals to express all these life histories is often tied to climatic cycles, with fluvial life histories expressed during wet cycles and reversing to resident life history during dry cycles. Spawning is often in the spring (March to June), though they may reproduce at most any time of the year except summer. In the fall, redband migrate to over-wintering areas within their streams. They eat mainly streamside and benthic (bottom dwelling) macroinvertebrates in smaller stream habitat but also consume other fish when they occupy larger streams, rivers or lakes.

Adfluvial populations consist of trout that spend most of their life cycles in lakes and reservoirs, before returning to stream headwaters and tributaries within their native basin to spawn. When lacustrine habitats such as lakes and marshes are available and migratory corridors connect it with surrounding streams, adfluvial populations of redband trout flourish. This adfluvial form is much larger and more fecund than the fluvial form. Adfluvial juveniles typically migrate downstream after one to three years to mature in lakes.

Conservation Measures

Redband trout conservation and restoration is necessary to ensure the long-term persistence of self-sustaining populations across the species’ native range. Maintenance of multiple inter-connected populations of redband trout across the diverse habitats of their native range and preservation of the diversity of their life history strategies (fluvial and adfluvial forms) will be important.

Conserving and restoring healthy populations of non-anadromous redband trout may also be critical to the persistence or restoration of some steelhead stocks. Although the relationship between the two forms is not well understood there is evidence that some progeny of non-anadromous forms migrate to sea and some progeny of steelhead remain in freshwater. Steelhead confined above barriers adopt a non-anadromous life history appropriate to the habitats available. It has been reported that steelhead progeny in very cold streams can residualize and adopt a non-anadromous life history and that these fish retained the ability to produce anadromous offspring. If sympatric redband trout have the potential to rebuild steelhead populations, that has application for the recovery of unique populations of steelhead eliminated by human-caused barriers.

References and Links

Behnke, R.J.  1992.  Native Trout of Western North America. American Fisheries Society.  Monograph 6.  Bethesda, Md.   275 pp.

Thurow, R.F. B.E. Rieman, D.C. Lee, P.J. Howell and R.D. Perkinson.  2007.  Distribution and Status of Redband Trout in the Interior Columbia River Basin and Portions of the Klamath River and Great Basins.  Pp. 28-46 in Redband Trout: Resilience and Challenge in a Changing Landscape (R.K. Schroeder and J.D. Hall, eds)  Oregon Chapter, American Fisheries Society. 

US Fish and Wildlife Service.  2000.  Endangered and Threatened Wildlife and Plants; 12-Month Finding for a Petition To List the Great Basin Redband Trout as Threatened or Endangered.  Federal Register 54:14932-14936.