Regularity: Regularly occurring
Type of Residency: Year-round
Global Range: Southern tributaries of the Kuskokwim River, Alaska, southward along the North American Pacific coast to Malibu Creek, California (formerly to the Otay River or, if subspecies NELSONI of the Rio Santo Domingo is not recognized, Baja California Norte). In California, summer runs occur south to the Eel River in northern California; see Moyle et al. (1989) for details for California.
Habitat Type: Freshwater
Comments: Most of the following pertains specifically to steelhead populations. Coastal rainbow trout occur in the ocean, in rivers and creeks, and in large inland lakes. Adults prefer waters with summer temperatures of 10-15 C, can survive for extended periods in waters up to 20 C and 27 C for short periods (Moyle et al. 1989). Juveniles remain in freshwater streams for 2-3 years (most often 2 years) before migrating to Pacific Ocean, where they spend 1-3 years (most often 2 years) before returning to natal stream to spawn (Spahr et al. 1991). Smaller, usually immature, individuals may enter streams in late summer and early fall after spending only a few months in the ocean; these fishes (called "half-pounders") return to the ocean in spring and migrate upstream again in summer or fall (Barnhart 1986). Migrating individuals require deep (at least 3 m) holding pools with cover; these are used during the period between upstream migration and spawning; optimally 4-5 undisturbed pools per river mile (Moyle et al. 1989). In winter, deep pools with low water velocity and extensive cover are important for shelter (Spahr et al. 1991).
Spawns in gravelly substrate in cool, clear, well-oxygenated streams (natal stream), in water flowing 23-155 cm/sec and 10-150 cm deep, usually at the tail of a pool or at the riffle at the head of a pool; favors areas with well-vegetated banks and abundant instream cover such as boulders, logs, and undercut banks. Can spawn in intermittent streams (juveniles move to perennial sections soon after hatching); this is common in Rogue River system, Oregon. Close to the ocean, spawners return to sea between spawning periods (Spahr et al. 1991).
Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.
Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Both anadromous and nonanadromous forms exist. Anadromous forms migrate between freshwater breeding and marine nonbreeding habitats; California breeders migrate to nonbreeding habitats as far away as Alaska (Moyle et al. 1989).
Comments: Eats aquatic insects, crustaceans, and zooplankton; also other fishes and fish eggs; may defend feeding area. Adult migrants seldom feed in freshwater.
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
10,000 to >1,000,000 individuals
Comments: Most populations in California are small (less than 100 individuals); in California, there were at least 25 isolated populations, many on the verge of extinction, in the 1980s (see Moyle et al. 1989 for details on individual populations).
Life History and Behavior
The following pertains specifically to steelhead populations. Summer-run steelhead enter freshwater between May and October and mature after spending several months in fresh water. In California, adult migrants of summer-run steelhead enter freshwater streams April-June (sometimes extending into July), during or shortly after final high spring flows (Moyle et al. 1989). Winter-run steelhead enter fresh water between November and April, with well-developed gonads. In drainages with both summer-run and winter-run steelhead, spawning may or may not be temporally or spatially segregated. Spawns from late December through April in northern California. Spawning tapers off by March in Oregon. Incubation lasts 3-4 weeks. Fry emerge from gravel 2-3 weeks later. Sexually mature at 2-5 years (Spahr et al. 1991), after spending generally 2 years in freshwater followed by usually 2 years in the ocean (length of time in each habitat may vary). May survive after spawning. In the Eel River, northern California, about 9% of the breeders are repeat spawners; this percentage may vary greatly (0-50%) in different locations (Stearley 1992). See Stearley (1992) for a discussion of the historical ecology and life history evolution of Pacific salmons and trouts (ONCORHYNCHUS).
National NatureServe Conservation Status
Rounded National Status Rank: N4 - Apparently Secure
NatureServe Conservation Status
Rounded Global Status Rank: T4 - Apparently Secure
Reasons: Still widespread and common, but with local declines and extirpations.
Global Short Term Trend: Decline of 10-30%
Comments: Many stocks have been extirpated (Nehlsen et al. 1991). Has declined considerably in most river systems over the past 30-40 years. In California, as of the late 1980s, had not recovered from declines related to the 1964 floods. On the Oregon coast, has declined in the Rogue and Siletz rivers. Populations in 3 northern Puget Sound (Washington) streams (Deer Creek, Tolt River, Nooksack River) appeared to be declining in the 1980s and early 1990s (Nehlsen et al. 1991).
Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: California populations were negatively affected by the 1964 floods, which filled in many holding pools. Moyle et al. (1989) listed the following as also contributing to the decline in California: poaching of fishes in summer holding pools, drought-related mortality of juveniles; harvest of migrating adults; habitat degradation (e.g., sedimentation of pools) resulting from poor watershed management (heavy grazing, poor logging practices); natural predation on the increasingly smaller and restricted populations; stress related to human activity in streams (rafting, swimming, gold dredging); possibly mortality in oceanic gillnet fishery; detrimental genetic and competitive effects of hatchery-raised fishes that are introduced in, but not native to, a given stream; and, locally, possibly the gillnet fishery of Native Americans (e.g., on the Klamath River). Threats to the Rogue and Siletz river populations on the Oregon coast reportedly include adverse ocean feeding conditions and predation by marine mammals, as well as habitat damage and water withdrawals in the Rogue River and hatchery fish interactions in the Siletz River (Nehlsen et al. 1991). Snake River native stocks are threatened by mainstem passage problems, inadequate water flows, and habitat degradation (Nehlsen et al. 1991). Dams cause problems for migrants via mortality in turbines, increased predation in impoundments and below dams, and loss of migratory motivation in the impoundments (Spahr et al. 1991). Stocks in northern Puget Sound streams are threatened by habitat damage and siltation from logging, overfishing, poaching, and interactions with hatchery fishes (Nehlsen et al. 1991).
Management Requirements: Hatchery stock is being used to maintain runs in many areas (Spahr et al. 1991). General management needs were listed by Moyle et al. (1989): better protection of summering areas from poachers; better watershed management to keep summer flows up and temperatures down; better regulation of adult harvest during migrations; better management of downstream areas to favor out-migrating juveniles; habitat improvement; restoration of extirpated populations; and protection of depleted populations from predation. See Roelefs (1983) for comprehensive management recommendations. See Nehlsen et al. (1991) for general protection and management recommendations for anadromous salmonids.
Biological Research Needs: Determine summer survival rates. Investigate ecology of juveniles.
Names and Taxonomy
Comments: Formerly included in Salmo gairdneri (Smith and Stearley 1989), but this taxon is closely related to Pacific salmon and is conspecific with Asiatic steelhead (Oncorhynchus mykiss mykiss).
Moyle et al. (1989) stated that "summer steelhead" (sometimes called spring-run steelhead) comprise a temporally and spatially isolated group that is genetically distinct from winter steelhead. However, NMFS (Federal Register, 16 March 1995) cited lack of evidence of consistent genetic differences among run-types within individual regions and concluded that all steelhead runs (i.e., those termed summer-, fall-, and winter-run) within the steelhead range between Cape Blanco (Oregon) and the Klamath River basin (inclusive) (Oregon and California) should be considered together as a single Evolutionarily Significant Unit (ESU) (a "species" under the Endangered Species Act).
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