1) Puget Sound--This coastal steelhead ESU occupies river basins of the Strait of Juan de Fuca, Puget Sound, and Hood Canal, Washington. Included are river basins as far west as the Elwha River and as far north as the Nooksack River.
No recent genetic comparisons have been made of steelhead populations from Washington and British Columbia, but samples from the Nooksack River differ from other Puget Sound populations, and this may reflect a genetic transition zone or discontinuity in northern Puget Sound. In life history traits, there appears to be a sharp transition between steelhead populations from Washington, which smolt primarily at age 2, and those in British Columbia, which most commonly smolt at age 3. This pattern holds for comparisons across the Strait of Juan de Fuca as well as for comparisons of Puget Sound and Strait of Georgia populations. At the present time, therefore, evidence suggests that the northern boundary for this ESU coincides approximately with the U.S.-Canada border.
Recent genetic data provided by WDFW show that samples from the Puget Sound area generally form a coherent group, distinct from populations elsewhere in Washington. There is also evidence for some genetic differentiation between populations from northern and southern Puget Sound, but the BRT did not consider that ecological or life history differences were sufficient to warrant subdividing this ESU. Chromosomal studies show that steelhead from the Puget Sound area have a distinctive karyotype not found in other regions.
The Puget Sound region is in the rain shadow of the Olympic Mountains and therefore is drier than the Olympic Peninsula; most of the Puget Sound region averages less than 160 cm of precipitation annually, while most areas of the Olympic Peninsula exceed 240 cm (Jackson 1993). Climate and river hydrology change west of the Elwha River (see Weitkamp et al. 1995). The rivers in Puget Sound generally have high relief in the headwaters and extensive alluvial floodplains in the lowlands. Geology and topography are dominated by the effects of the Cordilleran Ice Sheet as evidenced by glacial deposits and the regional geomorphology.
Puget Sound's fjord-like structure may affect steelhead migration patterns; for example, some populations of coho and chinook salmon, at least historically, remained within Puget Sound and did not migrate to the Pacific Ocean itself (Wright 1968, Williams et al. 1975, Healey 1980). Even when Puget Sound steelhead migrate to the high seas, they may spend considerable time as juveniles or adults in the protected marine environment of Puget Sound, a feature not readily accessible to steelhead from other ESUs.
Most of the life history information for this ESU is from winter-run fish. Apart from the difference with Canadian populations noted above, life history attributes of steelhead within this ESU (migration and spawn timing, smolt age, ocean age, and total age at first spawning) appear to be similar to those of other west coast steelhead. Ocean age for Puget Sound summer steelhead varies among populations; for example, summer steelhead in Deer Creek (North Fork Stillaguamish River Basin) are predominately age-1-ocean, while those in the Tolt River (Snoqualmie River Basin) are most commonly age-3-ocean (WDF et al. 1993).
The Puget Sound ESU includes two stocks that have attracted considerable public attention recently: Deer Creek summer steelhead (North Fork Stillaguamish River Basin) and Lake Washington winter steelhead. Deer Creek summer steelhead were petitioned for listing under the ESA (Washington Trout 1993), but NMFS determined that this population did not by itself represent an ESU (NMFS 1994b). Adult Lake Washington winter steelhead have experienced a high rate of predation by California sea lions (Zalophus californianus) below the fish ladder at Hiram M. Chittenden Locks (also known as the Ballard Locks), the artificial outlet of Lake Washington. Deer Creek summer steelhead and Lake Washington winter steelhead were 2 of the 178 stocks identified in the west coast steelhead petition (ONRC et al. 1994).
This ESU is primarily composed of winter steelhead but includes several stocks of summer steelhead, usually in subbasins of large river systems and above seasonal hydrologic barriers. Nonanadromous O. mykiss co-occur with the anadromous form in the Puget Sound region; however, the relationship between these forms in this geographic area is unclear.
2) Olympic Peninsula--This coastal steelhead ESU occupies river basins of the Olympic Peninsula, Washington west of the Elwha River and south to, but not including, the rivers that flow into Grays Harbor.
Genetic data collected by WDFW support the hypothesis that, as a group, steelhead populations from the Olympic Peninsula are substantially isolated from those in other regions of western Washington. The Olympic Peninsula ESU is further characterized by habitat, climatic, and zoogeographical differences between it and adjacent ESUs. The Olympic Peninsula includes coastal basins that receive more precipitation than any other area in the range of west coast steelhead. Topography on the Olympic Peninsula is characterized by much greater relief than that to the south; the Olympic Mountains range from 1,200 to 2,400 m above sea level. This affects precipitation quantity and river-basin hydrography. The result is "copious amounts of rain and over 100 inches of snow during the winter months" as well as substantial summer precipitation (Jackson 1993, p. 50-51). One manifestation of the ecological difference between Puget Sound and the Olympic Peninsula is the shift in vegetation zone, respectively, from western hemlock (Tsuga heterophylla) to Sitka spruce (Picea sitchensis) (Frenkel 1993).
Zoogeographic patterns also support ecological separation of the Olympic Peninsula from adjacent areas. According to McPhail and Lindsey (1986, p. 631), west of the Cascades pygmy whitefish (Prosopium coulteri) and longnose sucker (Catostomus catostomus) are only known from previously glaciated areas to the north of the Chehalis River. The distribution of several amphibian species also appears to change at the Chehalis River Basin (Stebbins 1966, Cook 1984, Leonard et al. 1993).
Limited life history information is available for Olympic Peninsula steelhead, and the information that does exist is primarily from winter-run fish. As with the Puget Sound ESU, known life history attributes of Olympic Peninsula steelhead are similar to those of other west coast steelhead, the notable exception being the difference between U.S. and Canadian populations in age at smolting.
The Olympic Peninsula ESU is primarily composed of winter steelhead but includes several stocks of summer steelhead in the larger rivers. Nonanadromous O. mykiss co-occur with the anadromous form in Olympic Peninsula rivers; however, the relationship between these forms in this geographic area is unclear.
3) Southwest Washington--This coastal steelhead ESU occupies the tributaries to Grays Harbor, Willapa Bay, and the Columbia River below the Cowlitz River in Washington and below the Willamette River in Oregon.
This ESU is delineated primarily by genetics and habitat features. Recent genetic data (Leider et al. 1995) show consistent differences between steelhead populations from the southwest Washington coast and those from coastal areas to the north, as well as those from Columbia River drainages east of the Cowlitz River. However, existing data do not clearly define the genetic relationship between steelhead from the southwest Washington coast and those from Columbia River tributaries below the Cowlitz River.
The geographic location of this ESU corresponds to the Chehalis and Columbia River glacial refugia during the Wisconsin Glaciation. Although there are morphological differences between populations of fish species common to the Chehalis and Columbia Rivers, both share a common Columbia River ichthyofauna (McPhail and Lindsey 1986). The two river basins are physically separated at present, but transport of sediments of Columbia River origin to both Grays Harbor and Willapa Bay (Landry and Hickey 1989) provides an ecological link. Furthermore, Monaco et al. (1992) found similarities in the estuarine ichthyofauna of Grays Harbor, Willapa Bay, and the Columbia River.
This ESU is primarily composed of winter steelhead but includes summer steelhead in the Humptulips and Chehalis River Basins. Nonanadromous O. mykiss co-occur with the anadromous form in southwest Washington rivers; however, the relationship between these forms in this geographic area is unclear. Life history attributes for steelhead within this ESU appear to be similar to those of other west coast steelhead.
4) Lower Columbia River--This coastal steelhead ESU occupies tributaries to the Columbia River between the Cowlitz and Wind Rivers in Washington and the Willamette and Hood Rivers in Oregon, inclusive. Excluded are steelhead in the upper Willamette River Basin above Willamette Falls (see ESU 5-Upper Willamette River), and steelhead from the Little and Big White Salmon Rivers, Washington, which are in the Middle Columbia River ESU.
This ESU is delineated primarily by genetics and habitat features. Steelhead populations in this ESU are of the coastal genetic group (Schreck et al. 1986, Reisenbichler et al. 1992, Chapman et al. 1994), and a number of genetic studies have shown that they are part of a different ancestral lineage than inland steelhead from the Columbia River Basin. Genetic data also show steelhead from this ESU to be distinct from steelhead from the upper Willamette River and from coastal streams in Oregon and Washington. Recent genetic data from WDFW also show clear differences between samples from the Wind, Washougal, and Big White Salmon Rivers and those from the coast of southwest Washington.
Steelhead-bearing rivers within this geographical region drain the Cascade Mountains from Mount Ranier to Mount Hood, including the Toutle River that was greatly impacted by the eruptions of Mount St. Helens in the 1980s.
Much consideration has been given to the interface between coastal and inland steelhead, both in the current review and in other studies. The boundary presented here represents the best understanding of steelhead genetics, biology, and ecology to date and is consistent with the findings of WDFW and Oregon Department of Fish and Wildlife (ODFW). Clearly, additional genetic analysis of steelhead in this region is desirable.
This ESU is composed of winter steelhead and summer steelhead. Nonanadromous O. mykiss co-occur with the anadromous form in Lower Columbia River tributaries; however, the relationship between these forms in this geographic area is unclear. Life history attributes for steelhead within this ESU appear to be similar to those of other west coast steelhead.
5) Upper Willamette River--This coastal steelhead ESU occupies the Willamette River, and its tributaries, upstream from Willamette Falls.
Steelhead from the upper Willamette River are genetically distinct from those in the lower river. Reproductive isolation from lower river populations may have been facilitated by Willamette Falls (RKm 77), which is known to be a migration barrier to some anadromous salmonids. For example, winter steelhead and spring chinook salmon occurred historically above the falls, but summer steelhead, fall chinook salmon, and coho salmon did not.
The native steelhead of this basin are late-migrating winter steelhead, entering fresh water primarily in March and April (Howell et al. 1985), whereas most other populations of west coast winter steelhead enter fresh water beginning in November or December. As early as 1885, fish ladders were constructed at Willamette Falls to aid the passage of anadromous fish; the ladders have been modified and rebuilt, most recently in 1971, as technology has improved (Bennett 1987, PGE 1994). These fishways facilitated successful introduction of Skamania stock summer steelhead and early migrating Big Creek stock winter steelhead to the upper basin. Another effort to expand steelhead production in the upper Willamette River was the stocking of native steelhead in tributaries not historically utilized by that species. Native steelhead primarily used tributaries on the east side of the basin, with cutthroat trout predominating in streams draining the west side of the basin.
The Willamette River Basin is zoogeographically complex. In addition to the obvious connection with the Columbia River, the Willamette River Basin has historically had connections with coastal basins through stream capture and headwater transfer events (Minckley et al. 1986).
The relationship between anadromous and nonanadromous O. mykiss in this geographic area is unclear. Nonanadromous O. mykiss are known to occupy the Upper Willamette River Basin; however, most of these nonanadromous populations occur above natural and manmade barriers (Kostow 1995). Historically, spawning by Upper Willamette River steelhead was concentrated in the North and Middle Santiam River Basins (Fulton 1970). These areas are now largely blocked to fish passage by dams, and steelhead spawning is now distributed throughout more of the Upper Willamette River Basin than in the past (Fulton 1970). Due to introductions of non-native steelhead stocks and transplantation of native stocks within the basin, it is difficult to formulate a clear picture of the present distribution of native Upper Willamette River Basin steelhead, and their relationship to nonanadromous and possibly residualized (footnote 5) O. mykiss within the basin.
6) Oregon Coast--This coastal steelhead ESU occupies river basins on the Oregon coast north of Cape Blanco; excluded are rivers and streams that are tributaries of the Columbia River (see ESU 3-Southwest Washington).
Recent genetic data from steelhead in this ESU are limited, but they show a level of differentiation from populations from Washington, the Columbia River Basin, and coastal areas south of Cape Blanco. Ocean migration patterns also suggest a distinction between steelhead populations north and south of Cape Blanco. Steelhead, as well as chinook and coho salmon, from streams south of Cape Blanco tend to be south-migrating rather than north-migrating (Everest 1973, Nicholas and Hankin 1988, Pearcy et al. 1990, Pearcy 1992).
We have little information on migration and spawn timing of natural steelhead populations within this ESU. Age structure appears to be similar to other west coast steelhead, dominated by 4-year-old spawners. Iteroparity is more common among Oregon coast steelhead than populations to the north.
The Oregon Coast ESU primarily contains winter steelhead. There are only two native stocks of summer steelhead in this ESU; one occurs in the Siletz River above a waterfall that is a barrier to winter steelhead, and the other occurs in the Umpqua River Basin. Summer steelhead from the Siletz River have been used in attempts by ODFW to establish fisheries in other basins with little success, primarily due to susceptibility to Ceratomyxa shasta. Alsea River winter steelhead have been widely used for steelhead broodstock in coastal rivers.
Populations of nonanadromous O. mykiss (rainbow trout) are relatively uncommon on the Oregon coast, as compared with other areas, occurring primarily above migration barriers and in the Umpqua River Basin (Kostow 1995). The lack of life history diversity within the Oregon Coast ESU may reflect habitat availability in this region. Summer steelhead appear to occupy habitat not fully utilized by the winter steelhead (i.e., above seasonal barriers or in very long rivers where distance may serve as a migration barrier to ocean-maturing winter steelhead). Rainbow trout appear to occur primarily in habitat that is unavailable to steelhead, but it also occurs in rivers where temperature regimes or artificial barriers interfere with the smoltification process, therefore facilitating nonanadromy. Most rivers on the Oregon coast are comparatively short, draining the Coast Range, and their accessible steelhead habitat may be fully utilized by winter steelhead. The Umpqua River, which supports winter steelhead, summer steelhead, and rainbow trout is the longest river in this region; it is the only river within the range of the Oregon Coast ESU that arises in the Cascade Mountains and penetrates the Coast Range. Migration distance and thermal regimes may prevent full utilization of habitat by winter steelhead, allowing summer steelhead and rainbow trout to occur in the Umpqua River Basin.
7) Klamath Mountains Province--This coastal steelhead ESU occupies river basins from the Elk River in Oregon to the Klamath and Trinity Rivers in California, inclusive.
This ESU has been more fully described by Busby et al. (1994). The location of this ESU is dominated by a prominent geological feature known as the Klamath Mountains Province; this region includes diverse and unique floral communities. Similarities in ichthyofauna between the Rogue and Klamath Rivers have been described by Snyder (1907) and Moyle (1976). Protein electrophoretic analyses of coastal steelhead have indicated genetic discontinuities between the steelhead of this region and those to the north and south (Hatch 1990; Busby et al. 1993, 1994). Chromosomal studies have also identified a distinctive karyotype that has only been reported from populations within this ESU. Steelhead within this ESU include both winter and summer steelhead as well as the unusual half-pounder life history. Nonanadromous O. mykiss may co-occur with the anadromous form; however, the relationship between the two forms in this geographic area is unclear.
Among the remaining questions regarding this ESU is the relationship between O. mykiss below and above Klamath Falls, Oregon. Behnke (1992) has proposed that the two groups are in different subspecies, and that the upper group, a redband trout (O. m. newberrii), utilized anadromy until blocked by the Copco dams in the early 1900s. However, Moyle (1976) stated that Klamath Falls was the upstream barrier to anadromous fish prior to construction of the dams.
8) Northern California--This coastal steelhead ESU occupies river basins from Redwood Creek in Humboldt County, California to the Gualala River, inclusive.
The geographic boundaries of this ESU coincide closely with the northern California region of steelhead populations identified by Nielsen (1994) on the basis of genetic and biogeographic data. Allozyme data indicate a discontinuity between steelhead populations of this region and those to the north, and mitochondrial DNA data suggest a genetic transition in the area between Point Arena and San Francisco Bay. Thorgaard (1983) found unusually high numbers of chromosomes in steelhead from south of the Klamath River. Freshwater fishes in this geographic area are derived from the Sacramento River Basin (Snyder 1907, Moyle 1976), whereas streams to the north include fishes derived from the Klamath-Rogue ichthyofaunal province.
Precipitation is generally higher in this geographic area than in regions to the south, averaging 100 to 200 cm of rainfall annually (Donley et al. 1979). This area includes the extreme southern end of the contiguous portion of the Coast Range Ecoregion (Omernik 1987).
There are life history similarities between steelhead of the Northern California ESU and those of the Klamath Mountains Province ESU. Steelhead within this ESU include winter and summer steelhead, including what is presently considered to be the southernmost population of summer steelhead, in the Middle Fork Eel River. Half-pounder juveniles occur in this geographic area, specifically in the Mad and Eel Rivers; indeed, Snyder (1925) first described the half-pounder from the Eel River. However, Cramer et al. (1995) suggest that adults with the half-pounder juvenile life history may not spawn south of the Klamath River Basin. As with the Rogue and Klamath Rivers, some of the larger rivers in this area have migrating steelhead year-round, and seasonal runs have been named. Nonanadromous O. mykiss may co-occur with the anadromous form; however, the relationship between these forms in this geographic area is unclear.
9) Central California Coast--This coastal steelhead ESU occupies river basins from the Russian River to Soquel Creek, Santa Cruz County (inclusive), and the drainages of San Francisco and San Pablo Bays; excluded is the Sacramento-San Joaquin River Basin of the Central Valley of California.
Analysis of mtDNA data suggests that genetic transitions occur just north of the Russian River and just north of Monterey. Allozyme data show large genetic differences between steelhead populations from the Eel and Mad Rivers and those to the south.
Environmental characteristics differ between the central California coast and areas to the north and south. Landforms in this area are characterized by very erosive soils. The coastal climate is relatively moist and cool throughout the year, but inland regions (e.g., upper Russian River Basin) are warmer and drier. Annual precipitation is markedly less and month of peak flow is later for streams south of Point Arena than those to the north. Minimum winter water temperatures are higher in this area than in streams to the north. The central California coast area includes the southern limit of the redwood forest, and within this area there is a transition to the more xeric vegetation of the south coast and interior.
Only winter steelhead are found in this ESU and those to the south. Migration and spawn timing are similar to adjacent steelhead populations. We have little other life history information for steelhead in this ESU. The relationship between anadromous and nonanadromous O. mykiss, including possibly residualized (footnote 5) fish upstream from dams, is unclear.
10) South-Central California Coast--This coastal steelhead ESU occupies rivers from the Pajaro River, Santa Cruz County to (but not including) the Santa Maria River.
Mitochondrial DNA data provide evidence for a genetic transition in the vicinity of Monterey Bay. Both mtDNA and allozyme data show large genetic differences between populations in this area, but the data do not provide a clear picture of population structure.
Most rivers of this region drain the Santa Lucia Range, the southernmost unit of the California Coast Ranges. The climate is drier and warmer than in the north, which is reflected in the vegetational change from coniferous forest to chaparral and coastal scrub. Another biological transition at the north of this area is the southern limit of the distribution of coho salmon (O. kisutch). The mouths of many rivers and streams in this area are seasonally closed by sand berms that form during periods of low flow in the summer. The southern boundary of this ESU is near Point Conception, a well-recognized transition area for the distribution and abundance of marine flora and fauna.
Only winter steelhead are found in this ESU. Migration and spawn timing are similar to adjacent steelhead populations. We have little other life history information for steelhead in this ESU. The relationship between anadromous and nonanadromous O. mykiss, including possibly residualized (footnote 5) fish upstream from dams, is unclear but likely to be important.
11) Southern California--This coastal steelhead ESU occupies rivers from the Santa Maria River to the southern extent of the species range. Historically, O. mykiss occurred at least as far south as Rio del Presidio in Mexico (Behnke 1992, Burgner et al. 1992). Spawning populations of steelhead did not occur that far south but may have extended to the Santo Domingo River in Mexico (Barnhart 1986); however, some reports state that steelhead may not have existed south of the U.S.-Mexico border (Behnke 1992, Burgner et al. 1992). The present southernmost stream used by steelhead for spawning is generally thought to be Malibu Creek, California (Behnke 1992, Burgner et al. 1992); however, in years of substantial rainfall, spawning steelhead can be found as far south as the Santa Margarita River, San Diego County (Barnhart 1986, Higgins 1991).
Genetic data show large differences between steelhead populations within this ESU as well as between these and populations to the north. Steelhead populations between the Santa Ynez River and Malibu Creek show a predominance of a mitochondrial DNA type (ST8) that is rare in populations to the north. Allozyme data indicate that two samples from Santa Barbara County are genetically among the most distinctive of any natural populations of coastal steelhead yet examined.
Migration and life history patterns of southern California steelhead depend more strongly on rainfall and streamflow than is the case for steelhead populations farther north (Moore 1980, Titus et al. in press). Average rainfall is substantially lower and more variable in southern California than in regions to the north, resulting in increased duration of sand berms across the mouths of streams and rivers and, in some cases, complete dewatering of the lower reaches of these streams from late spring through fall. Environmental conditions in marginal habitats may be extreme (e.g., elevated water temperatures, droughts, floods, and fires) and presumably impose selective pressures on steelhead populations. Their utilization of southern California streams and rivers with elevated temperatures (in some cases much higher than the preferred range for steelhead) suggests that steelhead within this ESU are able to withstand higher temperatures than populations to the north. The relatively warm and productive waters of the Ventura River have resulted in more rapid growth of juvenile steelhead than occurs in more northerly populations (Moore 1980, Titus et al. in press, McEwan and Jackson 1996). However, we have relatively little life history information for steelhead from this ESU. Additionally, the relationship between anadromous and nonanadromous O. mykiss, including possibly residualized (footnote 5) fish upstream from dams, is unclear.
12) Central Valley--This steelhead ESU occupies the Sacramento and San Joaquin Rivers and their tributaries.
Recent allozyme data show that samples of steelhead from Deer and Mill Creeks and Coleman NFH on the Sacramento River are well differentiated from all other samples of steelhead from 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 anadromous fish. The distance from the ocean to spawning streams can exceed 300 km, providing unique potential for reproductive isolation among steelhead in California. The Central Valley is much drier than the coastal regions to the west, receiving on average only 10-50 cm of rainfall per year. The valley is characterized by alluvial soils, and native vegetation was dominated by prairie grasses prior to agricultural development.
Currently, all steelhead in the Central Valley are considered winter steelhead by the California Department of Fish and Game (CDFG), although "three distinct runs," including summer steelhead, may have occurred there as recently as 1947 (CDFG 1995, McEwan and Jackson 1996). Steelhead within this ESU have the longest freshwater migration of any population of winter steelhead. There is essentially a single 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 (McEwan and Jackson 1996).
There are two recognized taxonomic forms of native O. mykiss within the Sacramento River Basin: coastal steelhead/rainbow trout (O. m. irideus, Behnke 1992) and Sacramento redband trout (O. m. stonei, Behnke 1992). Sacramento redband trout from the McCloud River are presently on the Fish and Wildlife Service's Candidate List, category 1, for proposed listing under the ESA. How the coastal and Sacramento redband forms of O. mykiss interacted in the Sacramento River prior to construction of Shasta Dam in the 1940s, which blocked anadromous fish passage, is not clear. In describing the McCloud River egg-taking station (1879-1888), Behnke (1992) said that coastal steelhead and resident redband trout were spawned together. Therefore, it appears the two forms historically co-occurred at spawning time but may have maintained reproductive isolation. In addition to the relationship between coastal steelhead and Sacramento redband forms, the relationship between anadromous and nonanadromous forms of coastal O. mykiss, including possible residualized (footnote 5) fish upstream from dams, is unclear.
Inland Steelhead ESUs
13) Middle Columbia River--This ESU occupies the Columbia River Basin from above the Wind River in Washington and the Hood River in Oregon upstream to include the Yakima River, Washington. Steelhead of the Snake River Basin are not included.
Genetic differences between inland and coastal steelhead are well established, although some uncertainty remains about the exact geographic boundaries of the two forms in the Columbia River (see discussion above for ESU 4-Lower Columbia River). Electrophoretic and meristic data show consistent differences between steelhead from the middle Columbia River and the Snake River Basin. No recent genetic data exist for natural steelhead populations in the upper Columbia River, but recent WDFW data show that the Wells Hatchery stock from the upper Columbia River does not have a close genetic affinity to sampled populations from the middle Columbia River.
All steelhead in the Columbia River Basin upstream from The Dalles Dam are summer-run, inland steelhead (Schreck et al. 1986, Reisenbichler et al. 1992, Chapman et al. 1994). Steelhead in Fifteenmile Creek, Oregon are genetically allied with inland O. mykiss, but are winter-run. Winter steelhead are also found in the Klickitat and White Salmon Rivers, Washington.
Franklin and Dyrness (1973) place the Yakima River Basin in the Columbia Basin Physiographic Province (along with the Deschutes, John Day, Walla Walla, and lower Snake River Basins); rivers upstream from the Yakima River are in other physiographic provinces. Geology within this province is dominated by the Columbia River basalt formation, formed from lava deposition in the miocene epoch, which is overlain by plio-Pleistocene deposits of glaciolacustrine origin (Franklin and Dyrness 1973). This intermontane region includes some of the driest areas of the Pacific Northwest, generally receiving less than 40 cm of precipitation annually (Jackson 1993). Indeed, Deschutes River steelhead are occasionally referred to by anglers as "the desert steelhead." Vegetation in this region is of the shrub-steppe province, reflecting the xeric climate and harsh temperature extremes.
Life history information for steelhead of this region indicates that most middle Columbia River steelhead smolt at 2 years and spend 1 to 2 years in salt water prior to re-entering fresh water, where they may remain up to a year prior to spawning (Howell et al. 1985, BPA 1992). Within this ESU, the Klickitat River is unusual in that it produces both summer and winter steelhead, and the summer steelhead are dominated by age-2-ocean steelhead, whereas most other rivers in this region produce about equal numbers of both age-1- and 2-ocean steelhead. Nonanadromous O. mykiss (Columbia River redband trout) co-occur with the anadromous form within this ESU; information suggests that the two forms may not be reproductively isolated, except where barriers are involved. Questions remain regarding the degree of reproductive interaction between the forms, as well as the frequency of residualization of steelhead within this ESU, both below and above migration barriers. Some populations of Columbia River redband trout are presently on the Fish and Wildlife Service's Candidate List, category 2, for proposed listing under the ESA.
The BRT considered different scenarios for the composition of the Middle Columbia River ESU with respect to the downstream and upstream boundaries. Life history information for Klickitat River steelhead is more similar to Lower Columbia River steelhead than to other populations within the Middle Columbia River ESU; additionally, Schreck et al. (1986) placed Klickitat River steelhead in the coastal steelhead group based on genetic, morphometric, meristic and life history characteristics. However, recent genetic analyses (Phelps et al. 1994, Leider et al. 1995) suggest a closer affinity for Klickitat River steelhead with the inland steelhead group. Similarly, there was much consideration of whether Yakima River steelhead are within the Middle or Upper Columbia River ESU. The conclusion that Yakima River steelhead are part of the Middle Columbia River ESU was based on life history and habitat characteristics, as well as genetic evidence of some affinity between steelhead of the Yakima and Klickitat River Basins (Phelps et al. 1994).
14) Upper Columbia River--This inland steelhead ESU occupies the Columbia River Basin upstream from the Yakima River.
The rivers in this area primarily drain the east slope of the northern Cascade Mountains and include the Wenatchee, Entiat, Methow, and Okanogan River Basins. Some of these upper Columbia River subbasins, including the Okanogan River and the upper Columbia River proper, extend into British Columbia. The status of steelhead in British Columbia is, therefore, applicable to this ESU. The general consensus from discussions at the Pacific Salmon Biological and Technical Meeting on steelhead, Lewiston, Idaho (18 October 1994) and with the B.C. Ministry of the Environment (footnote 13) is that steelhead never occurred in large numbers in British Columbia in the upper Columbia River Basin. Therefore, it is considered that this ESU includes only U.S. populations.
The geographic area occupied by this ESU forms part of the larger Columbia Basin Ecoregion (Omernik 1987). The Wenatchee and Entiat Rivers are in the Northern Cascades Physiographic Province and the Okanogan and Methow Rivers are in the Okanogan Highlands Physiographic Province (Franklin and Dyrness 1973). The geology of these provinces is somewhat similar and very complex, having developed from marine invasions (beginning in the Paleozoic Era and continuing to the Cretaceous Period), volcanic deposits (Pleistocene Epoch), and glaciation (late Pleistocene) (Franklin and Dyrness 1973). Franklin and Dyrness (1973, p. 17) described the North Cascades as "a topographically mature area of great relief." The river valleys are deeply dissected and maintain low gradients except for the extreme headwaters (Franklin and Dyrness 1973).
Climate in this area includes extremes in temperatures and precipitation; most precipitation falls in the mountains as snow (Mullan et al. 1992). Streamflow in this area is provided by melting snowpack, groundwater, and runoff from alpine glaciers (Mullan et al. 1992). Mullan et al. (1992, p. iv) described this area as a harsh environment for fish and stated that it "should not be confused with the more studied, benign, coastal streams of the Pacific Northwest."
Life history characteristics for Upper Columbia River Basin steelhead are similar to those of other inland steelhead ESUs; however, some of the oldest smolt ages for steelhead, up to 7 years, are reported from this ESU. This may be associated with the cold stream temperatures discussed by Mullan et al. (1992), who stated (p. v) that the cold water in some of the streams of this area may cause some fish to be "thermally-fated to a resident (rainbow trout) life history regardless of whether they were the progeny of anadromous or resident parents." The relationship between anadromous and nonanadromous O. mykiss in this geographic area is unclear. Based on limited data available from adult fish, smolt age in this ESU is dominated by 2-year-olds. Again based on limited data, steelhead from the Wenatchee and Entiat Rivers return to fresh water after 1 year in salt water, whereas Methow River steelhead are primarily age-2-ocean (Howell et al. 1985). As with other inland steelhead, these remain in fresh water up to a year prior to spawning.
15) Snake River Basin--This inland steelhead ESU occupies the Snake River Basin of southeast Washington, northeast Oregon, and Idaho.
Most Snake River tributaries supporting steelhead populations are well isolated from steelhead streams outside of the Snake River Basin. Recent genetic data from NMFS and WDFW show that samples from the Snake River are more similar genetically to other Snake River samples than they are to samples from outside the Snake River, and meristic data support this finding. Ecologically, steelhead spawning habitat in the Snake River is distinctive in having large areas of open, low-relief streams at high elevation. In many Snake River tributaries, spawning occurs at a higher elevation (up to 2,000 m) than is found for steelhead in any other geographic region. Snake River Basin steelhead also migrate farther from the ocean (up to 1,500 km) than most (perhaps all) other steelhead populations in the world.
The Snake River flows through terrain that is warmer and drier on an annual basis than the upper Columbia River Basin or other drainages farther north. Geologically, the landforms are older and much more eroded than most other steelhead habitat. The eastern portion of the basin flows out of the granitic geological unit known as the Idaho Batholith; the western Snake River Basin drains sedimentary and volcanic soils of the Blue Mountains complex (Rosenfeld 1993). Collectively, the environmental factors of the Snake River Basin result in a river that is warmer and more turbid, with higher pH and alkalinity, than most others in the species' range.
Snake River Basin steelhead are summer steelhead, as are most inland steelhead, and comprise two groups, A- and B-run, based on migration timing, ocean-age, and adult size (see page 10 for more information). Snake River Basin steelhead enter fresh water from June to October and spawn during the following spring from March to May. A-run steelhead are thought to be predominately age-1-ocean, while B-run steelhead are thought to be age-2-ocean (IDFG 1994). Snake River Basin steelhead usually smolt as 2- or 3-year-olds (Whitt 1954, BPA 1992, Hassemer 1992).
The steelhead population from Dworshak NFH is the most divergent single population of inland steelhead based on genetic traits determined by protein electrophoresis. Additionally, steelhead returning to Dworshak NFH are considered to have a distinctive appearance, and are the one steelhead population that is consistently referred to as B-run. We considered the possibility that Dworshak NFH steelhead should be in their own ESU. However, we have little specific information about characteristics of this population's native habitat in the North Fork Clearwater River, which is currently unavailable to anadromous fish because Dworshak Dam has no fish passage facilities. At present, the Dworshak NFH population is considered to be part of the Snake River ESU.
Nonanadromous O. mykiss (Columbia River redband trout) may co-occur with the anadromous form within this ESU, but the relationship between anadromous and nonanadromous forms of inland O. mykiss, including possibly residualized (footnote 5) fish upstream from dams, is unclear. Some populations of Columbia River redband trout are presently on the Fish and Wildlife Service's Candidate List, category 2, for proposed listing under the ESA.
Relationship of Steelhead ESUs to State Conservation Management Units
Both Washington and Oregon have recently completed a preliminary inventory of conservation management units for steelhead populations (Leider et al. 1994, 1995; Kostow 1995). Washington Department of Fish and Wildlife's Genetic Conservation Management Units (GCMUs) for steelhead are intended to be comparable to ESUs and consider many of the same factors (genetics, environment, life history), while ODFW's Gene Conservation Groups (GCGs) are based primarily on genetics. In contrast to ESUs, which may transcend political boundaries, both GCMUs and GCGs consider only populations within their respective state boundaries. Neither Idaho nor California has identified conservation units for steelhead.
For the most part, the ESUs identified here for steelhead are congruent with the conservation units identified by the states. The Oregon coastal and upper Willamette River ESUs as proposed here are identical in geographic coverage to GCGs identified by ODFW, and the Oregon part of the Lower Columbia River and Southwest Washington ESUs are similar to one of Oregon's GCGs. The Klamath Mountains Province ESU includes two GCGs that ODFW has delineated on the Oregon coast south of Cape Blanco. In the Columbia River Basin, ODFW places the coastal/inland break between the Hood River (coastal) and Mosier Creek (inland), which is downstream of Fifteenmile Creek. We are proposing the same location for our coastal/inland break, yet recognize that this could be modified. Other boundaries of ODFW's GCGs for inland steelhead are consistent with the ESUs we have described.
WDFW initially proposed seven GCMUs of steelhead in Washington state (Leider et al. 1994), and later revised the number to nine (Leider et al. 1995). Whereas the earlier determination considered life history and habitat characteristics as well as genetics, the two new GCMUs were identified entirely on the basis of new genetic information. WDFW has emphasized that all GCMU designations should be considered provisional and subject to revision as warranted by new information. In their revised formulation, WDFW recognizes two GCMUs (North Puget Sound and South Puget Sound) within the geographic area occupied by the Puget Sound ESU. WDFW also has split the geographic area occupied by the Middle Columbia River ESU into two GCMUs, Mid-Columbia and Yakima River. The remaining five GCMUs in the revised WDFW scheme are consistent with steelhead ESUs 2, 3, 4, 14, and 15.
Relationship of Steelhead ESUs to Boundaries for Coho Salmon ESUs
In its coastwide status review for coho salmon, NMFS identified 6 ESUs in Washington, Oregon, and California (NMFS 1994a), whereas 15 ESUs have been identified for west coast steelhead. The additional nine steelhead ESUs are largely from areas not currently, or in some cases historically, inhabited by coho salmon (upper Columbia and Snake Rivers, upper Willamette River, Central Valley of California, and southern California). The six coho salmon ESUs are very similar in geographic coverage to six of the proposed ESUs for steelhead (Puget Sound, Olympic Peninsula, Southwest Washington, Lower Columbia River, Oregon Coast, Klamath Mountains Province, and Northern California ESUs). Principal differences are that the Puget Sound ESU for steelhead does not include Canadian populations, whereas the coho salmon ESU does; genetic data supported the separation of the Southwest Washington and Lower Columbia River steelhead ESUs, whereas genetic data for coho salmon indicated that these areas form one ESU for that species; the southern boundary for the Klamath Mountains Province ESU for steelhead is at the Klamath River, whereas the boundary for the comparable ESU for coho salmon is further south, at Punta Gorda; and the southernmost ESU for coho salmon includes rivers occupied by the Northern California and Central California Coast steelhead ESUs.