i
ii

“Among these fishermen one occasionally hears more or less protracted

discussions as to whether the fish are trout or steelheads, whether they belong to

the same species as the larger steelheads which enter the river, whether they

differ from the smaller stream trout, whether they differ from the steelheads of

other rivers, what is a steelhead anyway...” (Snyder 1925, p. 50).

This document is available to the public through:

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22161
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EXECUTIVE SUMMARY

In February 1994, the National Marine Fisheries Service (NMFS) received a petition

seeking protection under the Endangered Species Act (ESA) for 178 populations of steelhead

(anadromous Oncorhynchus mykiss) in Washington, Idaho, Oregon, and California. At the

time, NMFS was conducting a status review of coastal steelhead populations (O. m. irideus)

in Washington, Oregon, and California. In response to the broader petition, NMFS expanded

the ongoing status review to include inland steelhead (O. m. gairdneri) occurring east of the

Cascade Mountains in Washington, Idaho, and Oregon. This report summarizes biological

and environmental information considered by the Biological Review Team (BRT) that

conducted the West Coast Steelhead Status Review.

The ESA allows listing of “distinct population segments” of vertebrates as well as

named species and subspecies. The policy of the NMFS on this issue for anadromous Pacific

salmonids is that a population will be considered “distinct” for purposes of the ESA if it

represents an evolutionarily significant unit (ESU) of the species as a whole. To be

considered an ESU, a population or group of populations must 1) be substantially

reproductively isolated from other populations, and 2) contribute substantially to the

ecological or genetic diversity of the biological species. Once an ESU is identified, a variety

of factors related to population abundance are considered in determining whether a listing is

warranted.

West Coast Steelhead ESUs

After considering available information on steelhead genetics, phylogeny and life

history, freshwater ichthyogeography, and environmental features that may affect steelhead,

the BRT identified 15 ESUs—12 for coastal steelhead and 3 for the inland form. The BRT

reviewed population abundance data and other risk factors for these steelhead ESUs and

concluded that five (Central California Coast, South-Central California Coast, Southern

California, Central Valley, and Upper Columbia River) are presently in danger of extinction,

five (Lower Columbia River, Oregon Coast, Klamath Mountains Province, Northern

California, and Snake River Basin) are likely to become endangered in the foreseeable future,

and four steelhead ESUs (Puget Sound, Olympic Peninsula, Southwest Washington, and

Upper Willamette River) are not presently in significant danger of becoming extinct or

endangered, although some individual stocks within these ESUs may be at risk. The BRT

concluded that the remaining steelhead ESU (Middle Columbia River) is not presently in

danger of extinction but was unable to reach a conclusion as to its risk of becoming

endangered in the foreseeable future.

The BRT concluded that, in general, the ESUs described below include resident

O. mykiss in cases where they have the opportunity to interbreed with anadromous fish.

Resident populations above long-standing natural barriers, and those that have resulted from

the introduction of non-native rainbow trout, would not be considered part of the ESUs.

Resident populations that inhabit areas upstream from human-caused migration barriers (e.g.,
viii

Grand Coulee Dam, the Hells Canyon Dam complex, and numerous smaller barriers in

California) may contain genetic resources similar to those of anadromous fish in the ESU, but

little information is available on these fish or the role they might play in conserving natural

populations of steelhead. The status, with respect to steelhead ESUs, of resident fish

upstream from human-caused migration barriers must be evaluated on a case-by-case basis as

more information becomes available.

Coastal Steelhead ESUs

1) Puget Sound—This 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. This ESU is primarily composed of winter

steelhead but includes several populations of summer steelhead. The steelhead in this ESU

generally smolt at age 2 years, whereas most steelhead in British Columbia smolt at age 3.

Steelhead from this area are genetically distinct from those in other areas of Washington,

both chromosomally and electrophoretically. Habitat in the Puget Sound region is dominated

by glacial effects, including extensive alluvial floodplains, and the fjord-like structure of

Puget Sound itself may promote distinctive steelhead migration patterns. Recent population

trends within the Puget Sound ESU are predominantly downward; however, trends in the two

largest stocks (Skagit and Snohomish Rivers) have been upward. The BRT was concerned

about the large proportion of hatchery steelhead in Puget Sound and their origination

primarily from a single stock; however, most hatchery fish appear to have advanced run

timing and to be harvested prior to spawning, thus limiting their interactions with naturally

spawning steelhead. Another concern of the BRT was the lack of information on the

abundance and status of summer steelhead in this ESU.

2) Olympic Peninsula—This 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 on the Washington coast. The Olympic Peninsula ESU is primarily composed

of winter steelhead but includes several populations of summer steelhead in the larger rivers.

Olympic Peninsula steelhead are genetically distinct from other steelhead ESUs; this

isolation is also supported by zoogeographic patterns of other species of fish and amphibians,

indicating a faunal shift in the vicinity of the Chehalis River Basin. Population trends within

this ESU are generally upward, with some stocks declining. As was the case with the Puget

Sound ESU, there is very little information regarding the abundance and status of summer

steelhead in this region, and there is also uncertainty regarding the degree of interaction

between hatchery and natural stocks.

3) Southwest Washington—This 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 primarily composed of winter steelhead but

includes summer steelhead in the Humptulips and Chehalis River Basins. Genetic data show

differentiation between steelhead of this ESU and those of adjacent regions. The ecological

connectivity of the region occupied by the Southwest Washington ESU is demonstrated by

similarities in riverine and estuarine ichthyofauna and current-driven sediment transfer from

the Columbia River to Grays Harbor and Willapa Bay. Most population trends within this
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ESU have been declining in the recent past. There is very little information regarding the

abundance and status of summer steelhead in this region, and there is also uncertainty

regarding the degree of interaction between hatchery and natural stocks.

4) Lower Columbia River—This 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 (see ESU 13-Middle Columbia River ESU). This ESU is

composed of both winter and summer steelhead. Genetic data show distinction between

steelhead of this ESU and adjacent regions, with a particularly strong difference between

coastal and inland steelhead in the vicinity of the Cascade Crest. The majority of stocks for

which we have data within this ESU have been declining in the recent past, but some have

been increasing strongly. However, the strongest upward trends are either non-native stocks

(Lower Willamette River and Clackamas River summer steelhead) or stocks that are

recovering from major habitat disruption and are still at low abundance (mainstem and North

Fork Toutle River). The data series for most stocks is quite short, so the preponderance of

downward trends may reflect the general coastwide decline in steelhead in recent years.

5) Upper Willamette River—This ESU occupies the Willamette River and its

tributaries upstream from Willamette Falls. The native steelhead of this basin are

late-migrating winter steelhead, entering fresh water primarily in March and April. This

unusual run timing appears to be an adaptation for ascending Willamette Falls, which

function as an isolating mechanism for upper Willamette River steelhead. Early migrating

winter steelhead and summer steelhead have been introduced to the Upper Willamette River

Basin; however, these non-native populations are not components of this ESU. Native winter

steelhead within this ESU have been declining on average since 1971 and have exhibited

large fluctuations in abundance. The main production of native (late-run) winter steelhead is

in the North Fork Santiam River, where estimates of hatchery proportion in natural spawning

range from 14% to 54%.

6) Oregon Coast—This 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). Native Oregon Coast steelhead are primarily winter

steelhead; native summer steelhead occur only in the Siletz and Umpqua River Basins.

Recent genetic data for steelhead in this ESU 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 (O. tshawytscha) and coho (O. kisutch)

salmon, from streams south of Cape Blanco tend to be south-migrating rather than

north-migrating. Most steelhead populations within this ESU have been declining in the

recent past, with increasing trends restricted to the southernmost portion (south of Siuslaw

Bay). There is widespread production of hatchery steelhead within this ESU, largely based

on out-of-basin stocks, and approximately half of the streams (including the majority of those

with upward trends) are estimated to have more than 50% hatchery fish in natural spawning

escapements. Given the substantial contribution of hatchery fish to natural spawning
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throughout the ESU and the generally declining or slightly increasing trends, it is likely that

natural stocks are not replacing themselves throughout the ESU.

7) Klamath Mountains Province—This ESU occupies river basins from the Elk

River in Oregon to the Klamath and Trinity Rivers in California, inclusive. This ESU

includes both winter and summer steelhead. Steelhead from this region are genetically

distinct from populations to the north and south. The “half-pounder” life history is reported

only from this region. The Klamath Mountains Province is a unique geographical area with

unusual geology and plant communities. While absolute abundance of steelhead within the

ESU remains fairly high, since about 1970 trends in abundance have been downward in most

steelhead populations for which we have data, and a number of populations are considered by

various agencies and groups to be at some risk of extinction. Declines in summer steelhead

populations are of particular concern. This ESU was previously studied under a separate

status review that was completed in December 1994 (Busby et al. 1994).

8) Northern California—This ESU occupies river basins from Redwood Creek in

Humboldt County, California south to the Gualala River, inclusive, and includes winter and

summer steelhead. Allozyme and mitochondrial DNA data indicate genetic discontinuities

between steelhead of this region and those to the north and south. Freshwater fish species

assemblages in this region are derived from the Sacramento River Basin, whereas streams to

the north include fishes representative of the Klamath-Rogue ichthyofaunal province.

Population abundances are very low relative to historical estimates, and recent trends are

downward in stocks for which we have data, except for two small summer steelhead stocks.

Summer steelhead abundance is very low. Risk factors identified for this ESU include

freshwater habitat deterioration due to sedimentation and flooding related to land

management practices and introduced Sacramento squawfish as a predator in the Eel River.

For certain rivers (particularly the Mad River), the BRT is concerned about the influence of

hatchery stocks, both in terms of genetic introgression and potential ecological interactions

between introduced stocks and native stocks.

9) Central California Coast—This 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. Mitochondrial DNA and allozyme data indicate genetic differences between

the steelhead from this region and those from adjacent areas. Environmental features

(e.g., precipitation patterns, vegetation, and soils) show a transition in this region from the

northern redwood forest ecosystem to the more xeric southern chaparral and coastal scrub

ecosystems. Steelhead populations within the major streams occupied by this ESU appear to

be greatly reduced from historical levels; for example, steelhead abundance in the Russian

River has been reduced roughly sevenfold since the mid-1960s, but abundance in smaller

streams appears to be stable at low levels. The primary risk factor for this ESU is

deteriorated habitat due to sedimentation and flooding related to land management practices.

Uncertainty regarding the genetic heritage of the natural populations in tributaries to San

Francisco and San Pablo Bays makes it difficult to determine which of these populations

should be considered part of the ESU.
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10) South-Central California Coast—This 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 do not

provide a clear picture of population structure. The climate in this region is drier and warmer

than it is to the north, resulting in chaparral and coastal scrub vegetation and stream mouths

that are closed seasonally by sand berms. In addition to vegetation transitions, the northern

end of this region is the southern limit of the distribution of coho salmon. 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. Total abundance of steelhead in this

ESU is extremely low and declining. Risk factors for this ESU are habitat deterioration due

to sedimentation and flooding related to land management practices and potential genetic

interaction with hatchery rainbow trout.

11) Southern California—This ESU occupies rivers from the Santa Maria River to

the southern extent of the species range. Steelhead occur at least as far south as Malibu

Creek, Los Angeles County, and may have historically occurred as far south as the

U.S.-Mexico border. Genetic data show large differences between steelhead populations

within this ESU as well as between these and populations to the north. 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. This affects steelhead migration patterns, as well as the ability to residualize

and survive elevated water temperatures. Steelhead have already been extirpated from much

of their historical range in this region. The BRT had a strong concern about the widespread

degradation, destruction, and blockage of freshwater habitats within the region, and the

potential results of continuing habitat destruction and water allocation problems. There was

also concern about the genetic effects of widespread stocking of rainbow trout.

12) Central Valley—This 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 National Fish Hatchery 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. Steelhead have already been extirpated from most of their historical range in this

region. Habitat concerns in this ESU focus on the widespread degradation, destruction, and

blockage of freshwater habitats within the region, and the potential results of continuing

habitat destruction and water allocation problems. The BRT also had a strong concern about

the pervasive opportunity for genetic introgression from hatchery stocks within the ESU, and

a strong concern for potential ecological interactions between introduced stocks and native

stocks.
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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. This ESU

includes the only populations of winter inland steelhead in the United States, in the Klickitat

River and Fifteenmile Creek. Some uncertainty exists about the exact boundary between

coastal and inland steelhead, and the western margin of this ESU reflects currently available

genetic data. There is good genetic and meristic evidence to separate this ESU from

steelhead of the Snake River Basin. The boundary upstream of the Yakima River is based on

limited genetic information and environmental differences including physiographic regions,

climate, topography, and vegetation. All BRT members felt special concern for the status of

this ESU, particularly Yakima River and winter steelhead stocks. Total steelhead abundance

in the ESU appears to have been increasing recently, but the majority of natural stocks for

which we have data within this ESU have been declining, including those in the John Day

River, which is the largest producer of wild, natural steelhead. There is widespread

production of hatchery steelhead within this ESU, but it is largely based on within-basin

stocks. Habitat degradation due to grazing and water diversions has been documented

throughout the range of the ESU.

14) Upper Columbia River—This ESU occupies the Columbia River Basin

upstream from the Yakima River. All upper Columbia River steelhead are summer

steelhead. The streams of this region that are utilized by steelhead primarily drain the

northern Cascade Mountains of Washington State. Streamflow is supplied by snowmelt,

groundwater, and glacial runoff, often resulting in extremely cold water temperatures that

retard the growth and maturation of steelhead juveniles, causing some of the oldest smolt

ages reported for steelhead and residualization of juvenile steelhead that fail to smolt. All

anadromous fish in this region were affected by the Grand Coulee Fish Maintenance Project

(1939 through 1943), wherein anadromous fish returning to spawn in the upper Columbia

River were trapped at Rock Island Dam, downstream of the Wenatchee River. Some of these

fish were then released to spawn in river basins above Rock Island Dam, while others were

spawned in hatcheries and the offspring were released into various upper Columbia River

tributaries; in both cases, no attempt was made to return these fish to their natal streams,

resulting in an undetermined level of stock mixing within the upper Columbia River fish.

While total abundance of populations within this ESU has been relatively stable or

increasing, this appears to be true only because of major hatchery supplementation programs.

Estimates of the proportion of hatchery fish in spawning escapement are 65% (Wenatchee

River) and 81% (Methow and Okanogan Rivers). The major concern for this ESU is the

clear failure of natural stocks to replace themselves. The BRT also had a strong concern

about problems of genetic homogenization due to hatchery supplementation within the ESU.

There was also concern about the apparent high harvest rates on steelhead smolts in rainbow

trout fisheries and the degradation of freshwater habitats within the region, especially the

effects of grazing, irrigation diversions, and hydroelectric dams.
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15) Snake River Basin—This ESU occupies the Snake River Basin of southeast

Washington, northeast Oregon, and Idaho. This region is ecologically complex and supports

a diversity of steelhead populations; however, genetic and meristic data suggest that these

populations are more similar to each other than they are to steelhead populations occurring

outside of the Snake River Basin. Snake River Basin steelhead spawning areas are well

isolated from other populations and include the highest elevations for spawning (up to

2,000 m) as well as the longest migration distance from the ocean (up to 1,500 km). Snake

River steelhead are often classified into two groups, A- and B-run, based on migration

timing, ocean age, and adult size. While total (hatchery + natural) run size for Snake River

steelhead has increased since the mid-1970s, the increase has resulted from increased

production of hatchery fish, and there has been a severe recent decline in natural run size.

The majority of natural stocks for which we have data within this ESU have been declining.

Parr densities in natural production areas have been substantially below estimated capacity in

recent years. Downward trends and low parr densities indicate a particularly severe problem

for B-run steelhead, the loss of which would substantially reduce life history diversity within

this ESU. The BRT had a strong concern about the pervasive opportunity for genetic

introgression from hatchery stocks within the ESU. There was also concern about the

degradation of freshwater habitats within the region, especially the effects of grazing,

irrigation diversions, and hydroelectric dams.
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AKNOWLEDGMENTS

This document represents the combined efforts of dozens of people who submitted

information on steelhead directly to NMFS; attended Biological and Technical Committee

meetings in Washington, Idaho, Oregon, and California; and answered seemingly endless

questions from the authors and biological review team (BRT) members on the telephone.

The authors particularly wish to acknowledge Stevan Phelps and Steve Leider of the

Washington Department of Fish and Wildlife for generous sharing of newly emerging

genetic data, and Jennifer Nielsen of Hopkins Marine Laboratory for sharing her DNA

studies in progress. We also wish to thank those that reviewed drafts of this and related

documents.

Significant contributions in the compilation and analyses of data were made by

Kathleen Neely, Ted Parker, and David Teel, all from NMFS Northwest Fisheries Science

Center (NWFSC). The biological review team for this status review included Peggy Busby,

Dr. Stephen Grabowski, Dr. Robert Iwamoto, Dr. Conrad Mahnken, Gene Matthews,

Dr. Michael Schiewe, Dr. Thomas Wainwright, Dr. Robin Waples, and Dr. John Williams,

from NMFS NWFSC; Greg Bryant and Craig Wingert from NMFS Southwest Region

(SWR); and Dr. Reg Reisenbichler from the National Biological Service (NBS), Seattle.
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INTRODUCTION

The U.S. Endangered Species Act (ESA) is intended to conserve threatened and

endangered species in their native habitats. Under the ESA, vertebrate populations are

considered “species” if they are “distinct.” According to National Marine Fisheries Service

(NMFS) policy, a salmon population or group of populations is considered “distinct” and

hence a “species” under the ESA if it represents an evolutionarily significant unit (ESU) of

the biological species.

The NMFS has received three petitions to list populations of steelhead (anadromous

Oncorhynchus mykiss) as threatened or endangered “species” under the ESA. The ESA

stipulates that, if a petition is found to present substantial information that a listing may be

warranted, NMFS must conduct a status review and issue a determination on its findings

within 1 year. On 6 May 1992, NMFS was petitioned by the Oregon Natural Resources

Council and 10 co-petitioners to list Oregon’s Illinois River winter steelhead (ONRC et al.

1992). NMFS concluded that Illinois River winter steelhead by themselves did not constitute

an ESA “species” (Busby et al. 1993, NMFS 1993a). At the same time, however, NMFS

initiated a status review of coastal steelhead populations to identify the ESU that includes

Illinois River winter steelhead. This status review has been completed and resulted in the

identification of a Klamath Mountains Province ESU that includes steelhead from the Illinois

River (Busby et al. 1994); NMFS has proposed listing this ESU as threatened (NMFS 1995).

Washington Trout (1993) petitioned NMFS on 21 September 1993 for ESA listing of

Washington’s Deer Creek summer steelhead. As was the case with Illinois River winter

steelhead, NMFS determined that Deer Creek summer steelhead did not by themselves

constitute an ESU (NMFS 1994b).

On 16 February 1994, Oregon Natural Resources Council and 15 co-petitioners asked

NMFS to list all steelhead in Washington, Idaho, Oregon, and California as threatened or

endangered under the ESA (ONRC et al. 1994). The petitioners identified 178 stocks of

steelhead of special concern and included information on stock origin, stock status, and

factors affecting their abundance.

Scope and Intent of the Present Document

This document addresses the ONRC et al. (1994) petition and presents environmental

and biological information concerning steelhead populations in Washington, Idaho, Oregon,

and California (Fig. 1). These will be collectively referred to in this document as west coast

steelhead. The Klamath Mountains Province ESU of southwest Oregon and northwest

California has been reviewed in detail elsewhere (Busby et al. 1994) and, therefore, will only

be summarized in the present document.

Because the ESA stipulates that listing determinations should be made on the basis of

the best scientific information available, NMFS formed a team of scientists with diverse
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backgrounds in salmon biology to conduct this status review. This Biological Review Team

(BRT) discussed and evaluated scientific information contained in an extensive public record

developed for west coast steelhead. This document reports conclusions reached by the BRT

for west coast steelhead. These conclusions are subject to revision should important new

information arise in the future.

Key Questions in ESA Evaluations

In determining whether a listing under the ESA is warranted, two key questions must

be addressed:

1) Is the entity in question a “species” as defined by the ESA?

2) If so, is the “species” threatened or endangered?

These two questions are addressed in separate sections of this report. If it is determined that

a listing(s) is warranted, then NMFS is required by law (1973 ESA Sec. 4(a)(1)) to identify

one or more of the following factors responsible for the species’ threatened or endangered

status: 1) destruction or modification of habitat; 2) overutilization by humans; 3) disease or

predation; 4) inadequacy of existing regulatory mechanisms; or 5) other natural or human

factors. This status review does not formally address factors for decline, except insofar as

they provide information about the degree of risk faced by the species in the future. A

separate document (NMFS in press a) identifies factors for decline of west coast steelhead.

The “Species” Question

As amended in 1978, the ESA allows listing of “distinct population segments” of

vertebrates as well as named species and subspecies. However, the ESA provides no specific

guidance for determining what constitutes a distinct population, and the resulting ambiguity

has led to the use of a variety of approaches for considering vertebrate populations. To

clarify the issue for Pacific salmon, NMFS published a policy describing how the agency will

apply the definition of “species” in the ESA to anadromous salmonid species, including

sea-run cutthroat trout and steelhead (NMFS 1991). A more detailed discussion of this topic

appeared in the NMFS “Definition of Species” paper (Waples 1991b). The NMFS policy

stipulates that a salmon population (or group of populations) will be considered “distinct” for

purposes of the ESA if it represents an evolutionarily significant unit (ESU) of the biological

species. An ESU is defined as a population that 1) is substantially reproductively isolated

from conspecific populations and 2) represents an important component of the evolutionary

legacy of the species.

The term “evolutionary legacy” is used in the sense of “inheritance”—that is,

something received from the past and carried forward into the future. Specifically, the

evolutionary legacy of a species is the genetic variability that is a product of past

evolutionary events and that represents the reservoir upon which future evolutionary potential

depends. Conservation of these genetic resources should help to ensure that the dynamic

process of evolution will not be unduly constrained in the future.
4

The NMFS policy identifies a number of types of evidence that should be considered

in the species determination. For each of the two criteria (reproductive isolation and

evolutionary legacy), the NMFS policy advocates a holistic approach that considers all types

of available information as well as their strengths and limitations. Isolation does not have to

be absolute, but it must be strong enough to permit evolutionarily important differences to

accrue in different population units. Important types of information to consider include

natural rates of straying and recolonization, evaluations of the efficacy of natural barriers, and

measurements of genetic differences between populations. Data from protein electrophoresis

or DNA analyses can be particularly useful for this criterion because they reflect levels of

gene flow that have occurred over evolutionary time scales.

The key question with respect to the second criterion is, If the population became

extinct, would this represent a significant loss to the ecological or genetic diversity of the

species? Again, a variety of types of information should be considered. Phenotypic and life

history traits such as size, fecundity, migration patterns, and age and time of spawning may

reflect local adaptations of evolutionary importance, but interpretation of these traits is

complicated by their sensitivity to environmental conditions. Data from protein

electrophoresis or DNA analyses provide valuable insight into the process of genetic

differentiation among populations but little direct information regarding the extent of

adaptive genetic differences. Habitat differences suggest the possibility for local adaptations

but do not prove that such adaptations exist.

The “Extinction Risk” Question

The ESA (section 3) defines the term “endangered species” as “any species which is

in danger of extinction throughout all or a significant portion of its range.” The term

“threatened species” is defined as “any species which is likely to become an endangered

species within the foreseeable future throughout all or a significant portion of its range.”

NMFS considers a variety of information in evaluating the level of risk faced by an ESU.

Important considerations include 1) absolute numbers of fish and their spatial and temporal

distribution; 2) current abundance in relation to historical abundance and carrying capacity of

the habitat; 3) trends in abundance, based on indices such as dam or redd counts or on

estimates of recruit-to-spawner ratios; 4) natural and human-influenced factors that cause

variability in survival and abundance; 5) possible threats to genetic integrity (e.g., selective

fisheries and interactions between hatchery and natural fish); and 6) recent events (e.g., a

drought or a change in management) that have predictable short-term consequences for

abundance of the ESU. Additional risk factors, such as disease prevalence or changes in life

history traits, may also be considered in evaluating risk to populations.

According to the ESA, the determination of whether a species is threatened or

endangered should be made on the basis of the best scientific information available regarding

its current status, after taking into consideration conservation measures that are proposed or

are in place. In this review, we do not evaluate likely or possible effects of conservation

measures. Therefore, we do not make recommendations as to whether identified ESUs

should be listed as threatened or endangered species, because that determination requires

evaluation of factors not considered by us. Rather, we have drawn scientific conclusions
5

about the risk of extinction faced by identified ESUs under the assumption that present

conditions will continue (recognizing, of course, that natural demographic and environmental

variability is an inherent feature of “present conditions”). Conservation measures will be

taken into account by the NMFS Northwest and Southwest Regional Offices in making

listing recommendations (see NMFS in press b for a discussion of conservation measures for

west coast steelhead).

Artificial Propagation

NMFS policy (Hard et al. 1992, NMFS 1993b) stipulates that in determining

1) whether a population is distinct for purposes of the ESA, and 2) whether an ESA species is

threatened or endangered, attention should focus on “natural” fish, which are defined as the

progeny of naturally spawning fish (Waples 1991b). This approach directs attention to fish

that spend their entire life cycle in natural habitat and is consistent with the mandate of the

ESA to conserve threatened and endangered species in their native ecosystems. Implicit in

this approach is the recognition that fish hatcheries are not a substitute for natural

ecosystems.

Nevertheless, artificial propagation is important to consider in ESA evaluations of

anadromous Pacific salmonids for several reasons. First, although natural fish are the focus

of ESU determinations, possible effects of artificial propagation on natural populations must

also be evaluated. For example, stock transfers might change the genetic or life history

characteristics of a natural population in such a way that the population might seem either

less or more distinctive than it was historically. Artificial propagation can also alter life

history characteristics such as smolt age and migration and spawn timing. Second, artificial

propagation poses a number of risks to natural populations that may affect their risk of

extinction or endangerment. These risks are discussed below in the “Assessment of

Extinction Risk” section. In contrast to most other types of risk for salmon populations,

those arising from artificial propagation are often not reflected in traditional indices of

population abundance. For example, to the extent that habitat degradation, overharvest, or

hydropower development have contributed to a population’s decline, these factors will

already be reflected in population abundance data and accounted for in the risk analysis. The

same is not true of artificial propagation. Hatchery production may mask declines in natural

populations that will be missed if only raw population abundance data are considered.

Therefore, a true assessment of the viability of natural populations cannot be attained without

information about the contribution of naturally spawning hatchery fish. Furthermore, even if

such data are available, they will not in themselves provide direct information about possibly

deleterious effects of fish culture. Such an evaluation requires consideration of the genetic

and demographic risks of artificial propagation for natural populations. The sections on

artificial propagation in this report are intended to address these concerns.

Finally, if any natural populations are listed under the ESA, then it will be necessary

to determine the ESA status of all associated hatchery populations. This latter determination

would be made following a proposed listing and is not considered further in this document.
6

Summary of the West Coast Steelhead Petition

The petition of February 1994 was filed by Oregon Natural Resources Council,

California Sport Fishing Protection Alliance, Coast Range Association, Fish in Northwest

Streams, Greater Ecosystem Alliance, National Wildlife Federation, Oregon Wildlife

Federation, Pilchuck Audubon Society, Quilcene Ancient Forest Coalition, Rivers Council of

Washington, Save the West, Siskiyou Audubon Society, Siskiyou Regional Educational

Project, Trout Unlimited of Oregon, University of Oregon Survival Center, and Western

Ancient Forest Campaign. The petition called upon the Secretary of Commerce to list

“anadromous steelhead trout (Oncorhynchus mykiss)” in Washington, Idaho, Oregon, and

California according to one of four alternatives presented: 1) all steelhead, 2) summer and

winter “races,” 3) each steelhead ESU, or 4) each of 178 individual stocks described in the

petition.

Petitioners’ “Definition of Species and Application to Steelhead Trout”

The petitioners focus on the anadromous form of O. mykiss, stating that “the common

fish culture practice of keeping separate brood stock for steelhead and resident rainbow trout

during captive breeding is the most obvious empirical proof for a genetic basis of anadromy”

(ONRC et al. 1994, p. 7). Among anadromous steelhead, homing is seen as an effective

mechanism for developing “distinct fish stocks” and “maintaining their genetic integrity”

(ONRC et al. 1994, p. 7).

Summer steelhead—The petition states that summer steelhead are reproductively

isolated from other steelhead temporally by migration and spawn timing and spatially

through spawning “in small tributaries generally not used by winter run steelhead” (ONRC

et al. 1994, p. 8). The petition states that “summer steelhead are evolutionarily significant

because of time of migration, state of gonadal maturity at migration, and location of

spawning” (ONRC et al. 1994, p. 8).

A- and B-run steelhead—The petition states that B-run summer steelhead from the

Clearwater and Salmon Rivers, Idaho differ from A-run steelhead based on “greater body

size at a given ocean age,” ... “late run timing, older average ocean age, and long river

migration,” and, therefore are evolutionarily significant (ONRC et al. 1994, p. 8).

Half-pounders—The petition states that the half-pounder life history1

 of steelhead

from the Rogue, Klamath, Mad, and Eel Rivers is evolutionarily significant.

1

 The half-pounder (Snyder 1925) is a life-history trait of steelhead that is found only in the

Rogue, Klamath, Mad, and Eel Rivers of southern Oregon and northern California. Following smoltification, half-pounders spend only 2-4 months in the ocean, then return to fresh

water. They overwinter in fresh water and emigrate to salt water again the following spring.

This is often termed a false spawning migration, as few half-pounders are sexually mature.
7

Southern steelhead—The petition states that southern steelhead1 comprise an ESU

based on the following: 1) “they are the southernmost distribution of native steelhead in

North America,” 2) they utilize seasonally warm rivers and streams that frequently have

dewatered reaches, 3) they occupy habitat that is different from that north of San Francisco,

4) they have lower smolt age and older ocean age, and 5) ”southern steelhead may breed as

metapopulations that allow for recolonization of streams after prolonged drought” (ONRC

et al. 1994, p. 9).

INFORMATION RELATING TO THE SPECIES QUESTION

In this section, we summarize biological and environmental information that is

relevant to determining the nature and extent of west coast steelhead ESUs. Again, in this

document, west coast steelhead refers to steelhead in the states of Washington, Idaho,

Oregon, and California. We considered information on steelhead from other locations, such

as Alaska and British Columbia, in addressing the species question. However, they are not

included in the phrase west coast steelhead and, when discussed in this document, they are

specifically mentioned.

Groupings of Oncorhynchus mykiss

The biological species Oncorhynchus mykiss is phylogenetically and ecologically

complex. The diversity of morphology and life history within this presently recognized

species has led to many classification schemes, including that of David Starr Jordan that

included “32 full species, which are presently referable to the diversity within rainbow and

cutthroat trout [O. clarki]” (Behnke 1992, p. 6). The volumes of work on this species have

resulted in the recognition of several groups within the species and the development of

terminology unique to O. mykiss. As these terms will be used extensively in this document,

they are introduced here.

Phylogenetic Groups

Two major genetic groups of O. mykiss are presently recognized in North America:

the inland and coastal groups, generally separated in the Fraser and Columbia River Basins

in the vicinity of the Cascade crest (Huzyk and Tsuyuki 1974, Allendorf 1975, Utter and

Allendorf 1977, Okazaki 1984, Parkinson 1984, Schreck et al. 1986, Reisenbichler et al.

1992). Both inland and coastal steelhead occur in British Columbia, Washington, and

Oregon; Idaho has only inland steelhead; California is thought to have only coastal steelhead.

These genetic groups apply to both anadromous and nonanadromous forms of O. mykiss; that

2

 A precise definition for southern steelhead does not exist. As described in the petition,

these are steelhead from the southern limit of the species range to as far north as San Luis

Obispo County or Monterey County, or south of San Francisco Bay.
8

is, rainbow (redband) trout east of the Cascades are genetically more similar to steelhead

from east of the Cascades than they are to rainbow trout west of the Cascades. Behnke

(1992) has proposed that the two forms should be considered subspecies and suggested the

names O. mykiss irideus and O. m. gairdneri for the coastal and inland forms, respectively.

Other subgroups of the species O. mykiss that may be involved in a discussion of west coast

steelhead are the redband trout of the upper Klamath and upper Sacramento River Basins

(O. m. newberrii and O. m. stonei, Behnke 1992), see Table 1.

Life History Variations

Oncorhynchus mykiss is considered by many to have the greatest diversity of life

history patterns of any Pacific salmonid species (Shapovalov and Taft 1954, Barnhart 1986),

including varying degrees of anadromy, differences in reproductive biology, and plasticity of

life history between generations.

Reproductive ecotypes—Within the range of west coast steelhead, spawning

migrations occur throughout the year, with seasonal peaks of activity. In a given river basin

there may be one or more peaks in migration activity; since these runs are usually named for

the season in which the peak occurs, some rivers may have runs known as winter, spring,

summer, or fall steelhead. For example, large rivers, such as the Columbia, Rogue, and

Klamath Rivers, have migrating adult steelhead at all times of the year. Through time, the

names of seasonal runs have generally been simplified, especially in the Pacific Northwest3

,

to two: winter and summer steelhead. There are local variations in the names used to

identify the seasonal runs of steelhead; in northern California, some biologists have retained

the use of the terms spring and fall steelhead to describe what others would call summer

steelhead.

Biologically, steelhead can be divided into two basic reproductive ecotypes, based on

the state of sexual maturity at the time of river entry and duration of spawning migration

(Burgner et al. 1992). The stream-maturing type (commonly known as fall steelhead in

Alaska, summer steelhead in the Pacific Northwest and northern California) enters fresh

water in a sexually immature condition and requires several months to mature and spawn.

The ocean-maturing type (spring steelhead in Alaska, winter steelhead elsewhere) enters

fresh water with well-developed gonads and spawns shortly thereafter. This document

generally uses the terms summer steelhead to refer to the stream-maturing type and winter

steelhead to refer to the ocean-maturing type.

In the Pacific Northwest, steelhead that enter fresh water between May and October

are considered summer steelhead, and steelhead that enter fresh water between November

and April are considered winter steelhead. Variations in migration timing exist between

populations, although there is considerable overlap. Some river basins have both summer

and winter steelhead; others have only one type. It appears that the summer, or

stream-maturing, steelhead occur where habitat is not fully utilized by winter steelhead;

summer steelhead usually spawn farther upstream than winter steelhead (Withler 1966,

3

 The Pacific Northwest includes the states of Washington, Idaho, and Oregon.
9
10

Roelofs 1983, Behnke 1992). In rivers where the two types co-occur, they are often

separated by a seasonal hydrologic barrier, such as a waterfall. Coastal streams are

dominated by winter steelhead, whereas inland steelhead of the Columbia River Basin are

almost exclusively summer steelhead. Winter steelhead may have been excluded from inland

areas of the Columbia River Basin by Celilo Falls, or by the great migration distance from

the ocean. The Sacramento-San Joaquin River Basin historically may have had multiple runs

of steelhead that probably included both ocean-maturing and stream-maturing stocks (CDFG

1995, McEwan and Jackson 1996, McEwan4

). Currently, the steelhead of this region are

referred to as winter steelhead by the California Department of Fish and Game (CDFG);

however, some biologists call them fall steelhead (Cramer et. al 1995). It is thought that

hatchery practices and modifications in the hydrology of the basin caused by large-scale

water diversions may have altered the migration timing of steelhead in this basin (McEwan

footnote 4).

A- and B-run steelhead—Inland steelhead of the Columbia River Basin, especially

the Snake River Subbasin, are commonly referred to as either A-run or B-run. These

designations are based on the observation of a bimodal migration of adult steelhead at

Bonneville Dam (Columbia River river kilometer (RKm) 235) and differences in age (1-

versus 2-ocean) and adult size observed among Snake River steelhead. Adult A-run

steelhead enter fresh water from June to August; as defined, the A-run passes Bonneville

Dam before 25 August (CBFWA 1990, IDFG 1994). Adult B-run steelhead enter fresh water

from late August to October, passing Bonneville Dam after 25 August (CBFWA 1990, IDFG

1994). Above Bonneville Dam (e.g., at Lower Granite Dam on the Snake River, 695 km

from the mouth of the Columbia River), run-timing separation is not observed, and the

groups are separated based on ocean age and body size (IDFG 1994). A-run steelhead are

defined as predominately age-1-ocean, while B-run steelhead are defined as age-2-ocean

(IDFG 1994). Adult B-run steelhead are also thought to be on average 75-100 mm larger

than A-run steelhead of the same age; this is attributed to their longer average residence in

salt water (Bjornn 1978, CBFWA 1990, CRFMP TAC, 1991). It is unclear, however, if the

life history and body size differences observed upstream have been correlated back to the

groups forming the bimodal migration observed at Bonneville Dam. Furthermore, the

relationship between patterns observed at the dams and the distribution of adults in spawning

areas throughout the Snake River Basin is not well understood. A-run steelhead are believed

to occur throughout the steelhead-bearing streams of the Snake River Basin; additionally,

inland Columbia River steelhead outside of the Snake River Basin are also considered A-run

(IDFG 1994). B-run steelhead are thought to be produced only in the Clearwater, Middle

Fork Salmon, and South Fork Salmon Rivers (IDFG 1994).

Half-pounders—The half-pounder (terminology of Snyder 1925) is an immature

steelhead that returns to fresh water after only 2 to 4 months in the ocean, generally

overwinters in fresh water, then outmigrates again the following spring. Half-pounders are

generally less than 400 mm (Kesner and Barnhart 1972, Everest 1973). Half-pounders are

only reported from the Rogue, Klamath, Mad, and Eel Rivers of southern Oregon and

4

 D. McEwan, California Department of Fish and Game, Inland Fisheries Division, 1416 9th

Street, Sacramento, CA 95814. Pers. commun., May 1995.
11

northern California (Snyder 1925, Kesner and Barnhart 1972, Everest 1973, Barnhart 1986);

however, it has been suggested that as mature steelhead, these fish may only spawn in the

Rogue and Klamath River Basins (Cramer et al. 1995). Various explanations for this unusual

life history have been proposed, but there is still no consensus as to what, if any, advantage

this life history affords to the steelhead of these rivers.

Rainbow and redband trout—As mentioned earlier, the species O. mykiss exhibits

varying degrees of anadromy. Nonanadromous forms of the species are usually called

rainbow trout; however, nonanadromous O. mykiss of the inland type are often called

Columbia River redband trout. Another form occurs in the upper Sacramento River and is

called Sacramento redband trout. Although the anadromous and nonanadromous forms have

long been taxonomically classified within the same species, the exact relationship between

the forms in any given area is not well understood. In coastal populations, it is unusual for

the two forms to co-occur; they are usually separated by a migration barrier, be it natural or

manmade. In inland populations, co-occurrence of the two forms appears to be more

frequent. Where the two forms co-occur, “it is possible that offspring of resident fish may

migrate to the sea, and offspring of steelhead may remain in streams as resident fish”

(Burgner et al. 1992, p. 6; see also Shapovalov and Taft 1954, p. 18). Mullan et al. (1992,

p. K-427) found evidence that in very cold streams, juvenile steelhead had difficulty attaining

“mean threshold size for smoltification” and concluded that “Most fish here [Methow River,

Washington] that do not emigrate downstream early in life are thermally-fated to a resident

life history regardless of whether they were the progeny of anadromous or resident parents.”

Additionally, Shapovalov and Taft (1954) reported evidence of O. mykiss maturing in fresh

water and spawning prior to their first ocean migration; this life history variation has also

been found in cutthroat trout (O. clarki) and some male chinook salmon (O. tshawytscha).

Environmental Features

West coast steelhead are presently distributed across 15 degrees of latitude, from

approximately 49°N at the U.S.-Canada border south to 34°N at the mouth of Malibu Creek,

California. In some years steelhead may be found as far south as the Santa Margarita River

in San Diego County. Climate and geological features vary greatly across this area, resulting

in a variety of landforms and diverse patterns of vegetation, weather, soils, and water quality

parameters that affect the distribution and ecology of plant and animal species, including fish.

West Coast Ichthyogeography

Geological events—Western North America, part of the Pacific Ring of Fire, is a

geologically active region that experiences large-scale volcanic, tectonic, and glacial events.

These events affect landforms, soil types, and, therefore, drainage patterns. Headwater

transfer and stream capture events have provided dispersal opportunities for several species

of freshwater fish in various drainages; Minckley et al. (1986) summarized several examples

of these events in Oregon and California streams.
12

Landforms and aquatic species distribution in the Pacific Northwest were greatly

affected by glaciation and flooding that occurred during the Wisconsin glacial age between

70,000 and 10,000 years ago (Porter 1983, Allen et al. 1986, Briggs 1986). In the late

Wisconsin glacial age, the Cordilleran ice sheet covered parts of present-day British

Columbia, Alberta, Washington, Idaho, and Montana. Although the Cordilleran ice sheet

extended only to the Puget Sound region, it affected sea level and climatic conditions much

farther south (Porter 1983). Thus, much of present-day patterns of landform and

zoogeography in western North America evolved in the last 10,000 years.

Ecoregions—Omernik (1987) delineated 13 ecoregions within the freshwater

distribution of west coast steelhead based on soils, land use, land surface form, and potential

natural vegetation (Table 2). The ecoregions occupied by west coast steelhead can be

grouped by climatic regions.

The north coastal region includes rivers and streams draining the Coast Ranges of

Washington, Oregon, and northern California. Climate in this area is under maritime

influence and, therefore, includes abundant precipitation (primarily in the form of rain),

summer fog, and moderate temperatures (Jackson 1993). Vegetation in this region is

dominated by conifers, Sitka spruce (Picea sitchensis) in the north and coast redwood

(Sequoia sempervirens) in the south (Donley et al. 1979, Jackson 1993).

In the south coastal region, south of Point Piedras Blancas, coastal rivers and streams

drain directly from the South Coast Range, and from the Transverse and Peninsular Ranges

of southern California to the coastal plain. This area is much drier than the north coastal

strip. Vegetation is dominated by chaparral, coastal scrub, and grassland (Donley et al.

1979).

The western lowlands include the Puget Lowland in Washington and the Willamette

Valley in Oregon. These areas include the rain shadows of the Coast and Olympic Mountain

Ranges and the foothills of the taller Cascade Range; they receive a moderate amount of

precipitation compared to regions east and west of them. Vegetation within these valleys is

primarily grassland, with oak woodlands occurring in the foothills and coniferous forest

dominant at higher elevations.

The Central Valley of California is positioned between the Coast Range and the

Cascade and Sierra Nevada Ranges. It is warmer and drier than the western lowlands.

Native vegetation in the Central Valley was bunchgrass prairie (Donley et al. 1979). The

intermountain valleys of the western lowlands and Central Valley of California are now

productive agricultural areas.

The rivers and streams of the Columbia Basin ecoregion (Omernik 1987) are in the

rain shadow of the Cascade Mountain Range. The vegetation in this zone includes pine,

juniper, and sagebrush. Streamflow is provided by snowmelt and springs. Many rivers in

this region experience extreme ranges in water temperature.

The northern Rockies zone includes the high elevation Clearwater and Salmon River

Basins of arid north-central Idaho. The region is dominated geologically by the Idaho
13
14

Batholith, which is composed of highly erosive granitic soils (see Matthews and Waples

1991 for a discussion on the effects on water quality and productivity).

Ichthyogeographical classification—Several authors have published

ichthyogeographical studies for western North America (e.g., Snyder 1907, Moyle 1976,

McPhail and Lindsey 1986, Swift et al. 1993). Within the range of west coast steelhead, five

major freshwater ichthyogeographic regions have been described (Snyder 1907, Moyle 1976,

McPhail and Lindsey 1986): Chehalis, Columbia, Klamath, Sacramento-San Joaquin, and

South Coastal Drainages. Although anadromy provides steelhead with distribution

opportunities not available to freshwater species, it is instructive to consider the distribution

of freshwater species for evidence of potential mechanisms of reproductive isolation between

steelhead populations, and for evidence of environmental parameters that address the

question of ecological diversity of the species.

Marine and estuarine ichthyogeography—Along the U.S. Pacific Coast, there are

two points where marine fish distribution and abundance markedly change: Cape Mendocino

(Allen and Smith 1988) and Point Conception (Briggs 1974); both are in California.

Environmental conditions that differ north and south of these points (e.g., ocean currents,

upwelling, temperature, productivity) may affect anadromous fish as well as marine species.

Monaco et al. (1992) grouped west coast U.S. estuaries that have similar species

assemblages. Their findings were largely consistent with ichthyofaunal distribution changes

in the vicinity of Cape Mendocino and Point Conception. Monaco et al. (1992) also

identified an assemblage within the inland estuaries of Puget Sound and Hood Canal in

Washington (Fjord Group). Other estuary groupings are less clear geographically and seem

to depend more on estuarine characteristics rather than on location.

Hydrology

Streamflow patterns show several geographic trends. Month of peak flow is delayed

with decreasing latitude, shifting from December in Washington and northern Oregon to

January from the Alsea River, Oregon south to Point Arena, California, to February from

Point Arena south to Big Sur, and to March in southern California (Hydrosphere 1993). In

northern Washington there are often two peaks in streamflow, the larger December peak

caused by precipitation (often a rain-on-snow event) and a smaller peak in spring caused by

snowmelt. Rivers in Oregon and California usually have one peak streamflow month

(Hydrosphere 1993). Additionally, northern streams have greater discharge per watershed

area, longer periods of peak flow, and more consistent base flow than southern streams.

Many coastal streams from southern Oregon to southern California experience seasonal

intermittent flows, including physical isolation from the ocean through formation of sand

berms. When a sand berm forms, through a combination of low streamflow and ocean

transport of sand, it functions as a dam, creating a lagoon in the lower stream reach. In

periods of drought, these closures may persist for extended periods of time—even years

(Snider 1983, Titus et al. in press). This affects access to salt water by juvenile steelhead and

access to freshwater spawning areas by adult steelhead.
15

Steelhead Life History and Ecology

Oncorhynchus mykiss exhibit perhaps the most complex suite of life history traits of

any species of Pacific salmonid. They can be anadromous or freshwater resident (and under

some circumstances, apparently yield offspring of the opposite form). Resident forms are

usually called rainbow, or redband, trout. Those that are anadromous can spend up to 7 years

in fresh water prior to smoltification, and then spend up to 3 years in salt water prior to first

spawning. The half-pounder life history type in southern Oregon and northern California

spends only 2 to 4 months in salt water after smoltification, then returns to fresh water and

outmigrates to sea again the following spring without spawning. Another life history

variation is the ability of this species to spawn more than once (iteroparity), whereas all other

species of Oncorhynchus, except O. clarki, spawn once and then die (semelparity).

Migration and Spawn Timing

The most widespread run type of steelhead is the winter (ocean-maturing) steelhead.

Winter steelhead occur in essentially all coastal rivers of Washington, Oregon, and

California, south to Malibu Creek. Summer (stream-maturing) steelhead, including spring

and fall steelhead in southern Oregon and northern California, are less common; for example,

on the Oregon coast only the Rogue, Umpqua, and Siletz Rivers have natural populations of

summer steelhead. Inland steelhead of the Columbia River Basin, however, are essentially

all stream-maturing steelhead; as discussed earlier, these inland steelhead are referred to in

terms of A-run and B-run.

Available information for natural populations of steelhead (Table 3) reveals

considerable overlap in migration and spawn timing between populations of the same run

type. Moreover, there is a high degree of overlap in spawn timing between populations

regardless of run type. California steelhead generally spawn earlier than those in areas to the

north; both summer and winter steelhead in California generally begin spawning in

December, whereas most populations in Washington begin spawning in February or March.

Relatively little information on spawn timing is available for Oregon and Idaho steelhead

populations. Among inland steelhead, Columbia River populations from tributaries upstream

of the Yakima River spawn later than most downstream populations.

Ageing

Steelhead exhibit great variation in smolt age and ocean age both within and between

populations, but there are some trends.

Smolt age—Smolt age discussed here is based on scale and otolith data from adult

steelhead. The emphasis on adult steelhead is based on the assumption that fish surviving to

spawning age are expressing the successful and adaptive life history strategy for steelhead in

a given geographical location. Steelhead from British Columbia and Alaska most frequently

smolt after 3 years in fresh water (Withler 1966, Narver 1969, Sanders 1985). In most other

populations for which there are data, the modal smolt age is 2 years (Table 4). Hatchery

conditions usually allow steelhead to smolt in 1 year; this difference is often used by
16
17
18
19
20
21
22
23
24
25
26

biologists to distinguish hatchery and wild steelhead. There appears to be an increase in the

frequency of naturally produced 1-year-old smolts in the southern portion of the steelhead

range (Table 4). Withler (1966) suggested that there may be a latitudinal cline in steelhead

smolt age; however, Titus et al. (in press) found no statistical evidence for a latitudinal cline

in steelhead smolt age from California to British Columbia.

Ocean age—North American steelhead most commonly spend 2 years (2-ocean) in

the ocean before entering fresh water to spawn (Table 5). Populations in Oregon and

California have higher frequencies of age-1-ocean steelhead than populations to the north,

but age-2-ocean steelhead generally remains dominant. Withler (1966) and Titus et al. (in

press) found that ocean age at spawning (and mean adult length) increased with increasing

latitude.

Total age—For most steelhead populations, total age at maturity can be estimated by

adding the smolt age and saltwater age. However, summer steelhead (especially in the

Columbia River Basin) enter fresh water up to a year prior to spawning, and that year is

generally not accounted for in the saltwater age designation; for example, a 2-ocean steelhead

from the Yakima River may actually have 3 years between smolting and spawning. Table 6

shows the most common life history patterns expressed by North American steelhead from

several river basins. Most steelhead in Alaska and British Columbia are 3/2 (smolt age/ocean

age) and have a total age of 5 years at first spawning. For coastal steelhead in Washington,

Oregon, and northern California, the modal total age at maturity is 4 years (2/2). Central and

southern California steelhead appear to spend less time in the ocean, and they are dominated

by 3-year-old (2/1) spawners. Complete life history data for southern California steelhead

are lacking; however, it appears that it is common for these fish to smolt in 1 year (CDFG

1995). If they only have one ocean year, as neighboring populations to the north do, then

adults may be spawning as 2-year-olds (1/1) in this region.

Determining total age at maturity for inland steelhead of the Columbia River Basin is

complicated by variations in reporting methods. Generally, these fish spend a year in fresh

water prior to spawning and this is not included in the age designation. Therefore, by adding

1 year after freshwater entry (indicated here as +1), most Columbia River inland steelhead are

4 years old at maturity (2/1+1). An exception is the Klickitat River; if these steelhead also

spend a year in fresh water before spawning, they are dominated by 5-year-old spawners

(2/2+1). Most of the available age data for Snake River steelhead are based on length

frequency; smolt age is often assumed or not reported. The data that are available from

scales show a high degree of variability in age structure, from 4-year-old spawners (2/1+1) in

the Clearwater River (Whitt 1954) to 7 year-old spawners (3/3+1) in the South Fork Salmon

River (BPA 1992).

Repeat Spawning

As noted above, most species of Oncorhynchus die after spawning, whereas O. mykiss

may spawn more than once. The frequency of multiple spawnings is variable both within

and among populations (Table 7). For North American steelhead populations north of

Oregon, repeat spawning is relatively uncommon, and more than two spawning migrations is
27
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30
31
32
33
34
35

rare. In Oregon and California, the frequency of two spawning migrations is higher, but

more than two spawning migrations is still unusual. The largest number of spawning

migrations for which we found data was five, from the Siuslaw River, Oregon (Bali 1959).

Iteroparous steelhead are predominately female.

Resident Fish

Although we have defined steelhead as anadromous O. mykiss, there are areas where

the separation between rainbow or redband trout and steelhead is obscured. In areas where

anthropogenic barriers have isolated populations of O. mykiss, these landlocked populations

could conceivably residualize5 and, therefore, continue to exist in the nonanadromous form.

Similarly, the mouths of some rivers in Oregon and California close seasonally, forming

lagoons (during droughts, these rivers may remain closed for extended periods of time—even

years). Again, landlocked O. mykiss in these systems could residualize. In some inland

populations, growth rate can cause O. mykiss to residualize (Mullan et al. 1992); this

apparently involves both fish that grow too quickly and those that grow too slowly.

Steelhead Genetics

Previous Studies of Population Genetic Structure

Protein electrophoresis—Allendorf (1975) first distinguished two major groups of

O. mykiss in Washington, Oregon, and Idaho, separated geographically by the Cascade Crest;

he termed these groups inland and coastal. These two groups have large and consistent

differences in allele frequency that apply to both anadromous and resident forms.

Subsequent studies have supported this finding (Utter and Allendorf 1977, Okazaki 1984,

Schreck et al. 1986, Reisenbichler et al. 1992), and similar differences have been identified

between O. mykiss from the interior and coastal regions of British Columbia (Huzyk and

Tsuyuki 1974, Parkinson 1984).

Several genetic studies since the mid-1970s have used protein electrophoresis to

examine population structure in coastal or inland O. mykiss. Allozyme studies of coastal

Oregon steelhead have been reported by Hatch (1990) and Reisenbichler et al. (1992). Hatch

(1990) surveyed 13 protein-coding loci in steelhead from 12 hatcheries and 26 coastal rivers

or tributaries in Oregon. He found evidence for a north-south cline in allele frequencies in 5

of the 13 enzyme systems analyzed, but only in river basins larger than 350 km2

. Hatch also

reported that “the area south of the Coos River was marked by sharp transition in four

enzymes...” (p. 17) and that “the pattern of several alleles ending their detectable Oregon

5

 Residual O. mykiss are those that have an anadromous lineage but are themelves

nonanadromous; the term was first proposed by Ricker (1938) in describing life-history

variations in O. nerka. The change in life history may be the result of a physical or

physiological barrier to migration (e.g., a dam, or slow growth that precludes smoltification).
36

presence just north of Cape Blanco suggests that there is a less than average amount of

straying between the populations north and south of this feature” (p. 33).

Reisenbichler et al. (1992) examined 10 polymorphic gene loci in steelhead from 37

natural and hatchery populations in the Pacific Northwest, including 24 from the Oregon

coast and two in northern California (Trinity River summer-run and Mad River Hatchery

winter-run). They did not discuss clines in allele frequencies; instead, they found evidence

for genetic differentiation between some clusters of populations. For example, steelhead

north of the Umpqua River formed a separate cluster from steelhead in southern Oregon. The

Trinity River sample was genetically similar to most of the Rogue River samples, but

steelhead from the Mad River Hatchery were genetically distinct from other hatchery and

natural populations in California and Oregon.

As part of previous ESA status reviews, NMFS biologists analyzed genetic variability

at 39 polymorphic gene loci in 20 samples of coastal steelhead from the Nehalem River in

northern Oregon to the Eel River in northern California (Busby et al. 1993, 1994). These

studies found evidence for three genetic groups of populations in the area sampled: Oregon

coast north of Cape Blanco (3 samples), Cape Blanco to the Klamath River Basin, inclusive

(13 samples), and south of the Klamath River Basin (4 samples). Little geographic pattern

was evident for samples from the area between Cape Blanco and the Klamath River.

Redwood Creek, the first major stream south of the Klamath River, appears to be in a

transitional zone; the sample from this stream is similar to the southern group but also has

some genetic affinity with samples from the Klamath River and areas to the north. The sharp

transition in allele frequencies for steelhead populations in this area is apparent in Figure 4 of

Busby et al. (1994).

Berg and Gall (1988) examined genetic variability at 24 polymorphic loci in 31

California populations “known to have been inhabited by anadromous rainbow trout prior to

the major water projects of the twentieth century” (p. 123). Twenty-three of their samples

were from the upper Sacramento River Basin, three were from the upper Klamath River

Basin, and the remaining five were from coastal streams from Eel River to San Diego

County. Sample sizes averaged about 30 fish per population and ranged from a high of 57 to

a low of 7. Berg and Gall (1988) found relatively high levels of genetic variability but no

clear geographic patterns in the genetic relationships among populations.

Reisenbichler and Phelps (1989) found variation at 19 gene loci in steelhead from 9

drainages in northwestern Washington (primarily the Olympic Peninsula). However, they

found genetic differences between drainages to be much smaller than had been reported by

Parkinson (1984) for steelhead populations from adjacent drainages in British Columbia.

Reisenbichler and Phelps (1989) and Reisenbichler et al. (1992) suggested that since both

Washington and Oregon had far more extensive hatchery steelhead programs in the 1970s

and early 1980s than did British Columbia, the relative homogeneity among populations in

these states may be due to introgression of hatchery fish into naturally spawning populations.

Furthermore, during that period, hatcheries in both Oregon and Washington predominately

used steelhead that had originated from one or two within-state sources (the Alsea River

stock in Oregon and the Chambers Creek and Skamania stocks in Washington). However,
37

Hatch (1990) pointed out that the geographic area covered by the Reisenbichler and Phelps

(1989) study (natural populations collected primarily from a 70 km stretch of coastline)

might be too small to allow a direct comparison with the British Columbia study.

As part of a comprehensive effort to inventory wild stocks of anadromous salmonids,

the Washington Department of Fish and Wildlife (WDFW) recently published a report of the

first year of genetic analyses for steelhead populations. Phelps et al. (1994) reported new

data for 56 variable gene loci for 12 natural and 8 hatchery populations, primarily in Puget

Sound and the lower Columbia River. Furthermore, WDFW data for additional samples

allowed the investigators to conduct analyses on 30 different populations. With few

exceptions, usually involving hatchery stocks, Phelps et al. found statistically significant

differences between all pairs of populations. This contrasts with results of Reisenbichler and

Phelps (1989), who generally failed to find significant differences between populations on

the Washington coast.

Phelps et al. (1994) used several different methods to examine population structure.

One consistent result was a high degree of genetic similarity among samples from winter-run

steelhead hatcheries, including those from Puget Sound (Skykomish River, Chambers Creek,

Tokul Creek), Olympic Peninsula (Bogachiel River), and the Columbia River (Skamania,

Beaver Creek). Relationships among the remaining Puget Sound samples were less clear.

For example, the summer-run sample from Deer Creek showed affinities to winter-run fish

from the North Fork Stillaguamish River (to which Deer Creek is a tributary), to summer-run

fish from the Skykomish River Hatchery, or to no populations in particular, depending on the

analysis.

Phelps et al. (1994) also considered data for 14 samples of steelhead from the

Columbia River in their study. Summer-run samples from the Wind and Washougal Rivers

in the lower Columbia River were outliers in the analyses. The Wind River sample contained

an allele at a frequency of 15% that was not found in steelhead in any other sample analyzed

by Phelps et al. (1994), and this presumably is responsible for the distinctiveness of the Wind

River sample. As expected, Phelps et al. (1994) found that inland steelhead were genetically

distinct from the samples of coastal steelhead examined. The inland group was represented

primarily by six samples from the Klickitat River, with additional samples from Big White

Salmon River, Satus Creek in the Yakima River Basin, and Wells Hatchery in the middle

Columbia River. The relationships among these samples are difficult to determine from the

results presented by Phelps et al. because the patterns of genetic affinity differed among the

various analyses they used.

Phelps et al. (1994) examined their genetic data for evidence of the effects of hatchery

fish on natural populations. The presence, in most cases, of statistically significant

differences between the hatchery and natural samples of steelhead suggests that at least some

native population structure remains. In addition, Phelps et al. found eight loci that had alleles

at relatively uniform frequencies among the winter-run hatchery steelhead populations that

could be used as indicators of the degree of introgression into natural populations. Based on

this analysis, they concluded that the Cedar River, Deer Creek, North Fork Skykomish, North

Fork Stillaguamish River, Wind River, Washougal River, and Big White Salmon River
38

populations had limited amounts of hatchery introgression and that the Green River,

Skykomish River main stem, Tolt River, Raging River, and Pilchuck River had moderate to

large amounts of hatchery introgression. Because the “marker” alleles only occurred at

frequencies of a few percent even in the hatchery steelhead stocks, these conclusions should

be regarded as tentative.

Phelps et al. (1994) also found large genetic distances (about three times as large as

the distance between inland and coastal steelhead) between four widely used rainbow trout

hatchery stocks from Washington and all steelhead populations examined. They concluded

that there has been little, if any, permanent genetic effect on the sampled steelhead

populations from the widespread stocking of rainbow trout over the past century. Campton

and Johnston (1985) found a different result for some O. mykiss populations in the Yakima

River Basin, where they found evidence for introgression of non-native rainbow trout into

wild populations. However, the affected populations were believed to be nonanadromous,

and Campton and Johnston (1985) found no evidence for introgression of hatchery rainbow

trout (or steelhead from Skamania Hatchery) into natural steelhead populations in the

Yakima River.

Leider et al. (1995) reported preliminary results for an additional 55 samples of

steelhead and wild resident rainbow trout from Washington. These samples considerably

extended the geographic coverage in the WDFW data set for the Olympic Peninsula and

southwest Washington coast. The most important result of the new samples is that they

revealed considerably more geographic coherence to the population genetic structure of

coastal steelhead in Washington than had been evident in previous studies. In the analyses of

Leider et al. (1995), the patterns of genetic affinity among populations differed somewhat

depending on the distance metric used, and some samples were outliers with no clear affinity

to any group. In general, however, samples from the following geographic areas tended to be

more similar to one another than they were to samples from other areas: north Puget Sound

(including the Stillaguamish River and drainages to the north), south Puget Sound, Olympic

Peninsula, southwest Washington, and lower Columbia River (Kalama, Wind, and

Washougal Rivers). Notable genetic outliers included the Nooksack River and the Tahuya

River. The genetic relationships among these geographic areas do not appear to be well

resolved because the pattern of affinities differed substantially among analyses.

Inland O. mykiss were represented by 48 samples in the Leider et al. (1995) study.

Analyses based on Nei’s (1978) and Cavalli-Sforza and Edward’s (1967) distances both

found consistent differences between samples from the Yakima and Klickitat River Basins,

and both analyses also showed that samples from Wells Hatchery were outliers within the

inland group. No samples from natural populations in the upper Columbia River were

included in the Leider et al. (1995) study. Leider et al. acknowledged some uncertainty in

identifying the boundary between inland and coastal forms, but on the basis of genetic data

tentatively placed it between the Wind and Big White Salmon Rivers.

Several other genetic studies have included steelhead from the Columbia River Basin.

Reisenbichler et al. (1992) focussed on steelhead from coastal streams but also included 10

samples from the Columbia River Basin. Within their study, they found the greatest degree
39

of genetic differentiation between the inland and coastal forms. Within the inland group, four

samples from the Snake River and three from the Deschutes River formed separate genetic

clusters. The three samples Reisenbichler et al. (1992) examined from the upper Willamette

River formed the most distinctive subgroup within the coastal group.

The study of Schreck et al. (1986), which examined life history and morphological

features as well as biochemical genetics, included the greatest number and geographic range

of steelhead samples from the Columbia River of any study to date. Again, they found the

largest differences between steelhead from east and west of the Cascades. Coastal forms

from west of the Cascades could be further partitioned into a subgroup from the upper

Willamette River, a subgroup from the lower Columbia River, and a subgroup containing

samples from both the lower Columbia and Willamette Rivers. East of the Cascades,

Schreck et al. also found evidence for differentiation among populations but only a weak

geographic pattern to the observed structure.

Hershberger and Dole (1987) examined samples from nine populations of inland

steelhead from tributaries of the Columbia River between Rock Island and Chief Joseph

Dams. They found 20 polymorphic gene loci but relatively little genetic differentiation

among populations from the Wenatchee, Methow, Entiat, and Okanogan Rivers. In contrast,

they found relatively large allele frequency differences between these samples and a sample

of coastal steelhead from the Skamania River.

Currens and Schreck (1993) examined genetic and meristic variation in adult

steelhead used for broodstock in the Umatilla River and in samples from 13 populations of

O. mykiss in the Umatilla River Basin. They found significant allele frequency differences

among populations but no strong geographic patterns. Results suggested that steelhead from

one population (McKay Creek) were the offspring of native and introduced rainbow trout.

Currens and Schreck (1993) did not compare genetic data for the Umatilla River samples to

data for other populations in the Columbia River Basin, but they did cite unpublished

meristic data that distinguished Snake River steelhead from those in the middle and upper

Columbia River.

Milner and Teel (1985) examined steelhead from 13 localities in the Snake River and

found three major genetic clusters: one including four Salmon River samples, another

including three samples from the Lochsa and Selway Rivers in the Clearwater River Basin,

and a third including Dworshak National Fish Hatchery (NFH), several samples from the

lower Clearwater River, and one sample each from the Grande Ronde and Imnaha River

Basins.

Waples et al. (1993) summarized genetic data based on 50 polymorphic gene loci for

2 years of samples of steelhead from the Snake River. Results included the following: 1)

The two samples from Dworshak NFH were the most distinctive genetically and have

substantial allele frequency differences compared to all other natural and hatchery samples.

2) Natural samples from the Clearwater River differed somewhat from those from other

drainages, and there was weaker evidence for differentiation between steelhead from the

Grande Ronde, Imnaha, and Tucannon Rivers (Salmon River populations were not included
40

in the experimental design). 3) In general, differences between temporal samples from the

same stream were smaller than differences between geographic populations.

The steelhead population in Dworshak NFH is derived from native fish from the

North Fork Clearwater River that were brought into the hatchery in 1969 when Dworshak

Dam blocked access to their native habitat. To evaluate whether the distinctive genetic

characteristics of Dworshak NFH steelhead might be the result of genetic changes in the

hatchery (for example, spawn timing has been shifted in the hatchery, and there may have

been selection for large fish, at least in the early years of the program), we examined genetic

profiles for a limited number of gene loci scored in samples from the hatchery dating back to

1972 (Milner 1977 and Teel6). These data show some variation over time but do not show a

trend toward greater divergence from natural populations in more recent samples.

Broodstock data7

 , which show that over 1,000 adults were spawned at the hatchery each year

since 1969, also fail to provide evidence for a population bottleneck that might have caused

substantial allele frequency changes due to drift. In the future, we hope to compare genetic

profiles of Dworshak NFH fish with populations of resident O. mykiss in the North Fork

Clearwater River, provided that native populations that have been largely unaffected by

releases of hatchery rainbow trout into Dworshak Reservoir can be identified.

DNA—In recent years, genetic methods that analyze DNA variation directly have

seen increasing use in salmonid studies, and we are aware of two studies of mitochondrial

DNA (mtDNA) that assess population structure in steelhead. In a study that remains

unpublished, Buroker8

 examined restriction-fragment-length polymorphisms in mtDNA from

120 individuals from 23 major river systems from Alaska to California. He found no

evidence for strong geographic structuring of populations, as most of the common clonal

types were widely dispersed. However, Buroker also found that steelhead from southern

Oregon were highly diverse in mtDNA. In the 120 fish analyzed, 18 different mtDNA clonal

types were observed. These clones were clustered into four lineages, all of which overlap in

southern Oregon. The 12 fish examined from the Rogue River had 6 of the 18 mtDNA

clonal types observed in the study.

In another study, Nielsen (1994; see also Nielsen et al. 1994) sequenced part of the

D-loop section of mtDNA in 37 samples of steelhead and rainbow trout in California and

found that a different mtDNA clonal type was the most common in each of three geographic

regions: north coast (Humboldt Bay to Gualala Point), central coast (Russian River to Point

Sur), and south coast (San Simeon Point to Santa Monica Bay). These regions were defined

through a combination of genetic and ecological (primarily ocean upwelling and plankton

6

 D. Teel, unpubl. data. National Marine Fisheries Service, Northwest Fisheries Science

Center, 2725 Montlake Boulevard East, Seattle, WA 98112-2097.

7

 R. Roseburg, USFWS, P.O. Box 18, Ahsahka, ID 83520. Pers. commun., November 1994.

8

 N. Buroker, 21617 88th Ave. West, Edmonds, WA 98026. Pers. commun., March 1993.
41

distribution) information (Nielsen9). Nielsen also found significant differences between the

regions in allele frequencies at a nuclear DNA microsatellite locus.

Neeley (1995) performed some additional statistical analyses on Nielsen’s data and

some new mtDNA data collected specifically for the status review (Cramer et al. 1995).

Neeley used principal components analysis to summarize variation at all 13 mtDNA alleles

reported by Nielsen. The first two principal components together explained 70% of the total

variation, and Neeley compared scores for each population on these two principal

components to a ranked indicator of their latitude. Simple and multiple regression analyses

suggested a partitioning of the populations into three groups based on latitude, with the

boundary between the northern and central groups occurring just north of the Russian River,

and the boundary for the central and southern groups occurring just south of the San Lorenzo

River. Additional variation exists in the mtDNA data that is not explained by the first two

principal components or the three-group partition, but no clear geographic patterns to this

variation could be detected.

Chromosomal studies—Chromosomal karyotypes in steelhead and rainbow trout

have also been extensively studied (see review in Thorgaard 1983). In a survey of steelhead

from Alaska to central California, Thorgaard (1983) found that although chromosome

numbers ranging from 58 to 64 were observed, a 58-chromosome karyotype was the most

common in most samples. In contrast to results for studies of morphological and allozyme

characters, Thorgaard did not find chromosomal differences between interior and coastal

O. mykiss populations. All interior/redband trout populations had predominately 58

chromosomes, as did most coastal rainbow trout and steelhead populations.

The exceptions to the 58-chromosome pattern, however, provide insight into

population genetic structuring in O. mykiss. Two geographic regions were characterized by

steelhead with 59 or 60 chromosomes: the Puget Sound/Strait of Georgia region and the

Rogue River/northern California region. However, the karyotypes of fish from these two

regions were different; northern fish with 59 or 60 chromosomes had a different number of

subtelocentric and acrocentric chromosomes than did southern fish (Thorgaard 1977).

Farther south, winter steelhead in the Mad and Gualala Rivers from northern California and

resident trout from the San Luis Rey River in southern California had 61-64 chromosomes

(Thorgaard 1983).

Although Thorgaard’s (1983) study showed that an unusual 60-chromosome

karyotype exists in the Puget Sound region, sampling in that study was limited to a very few

populations. Ostberg and Thorgaard (1994) examined additional populations in the area and

found the 60-chromosome karyotype in presumed native steelhead from the Nooksack,

Cedar, and Stillaguamish Rivers.

9

 J. Nielsen, Hopkins Marine Laboratory, Ocean View Boulevard, Pacific Grove, CA 93950.

Pers. commun., November-December 1994, and January 1995.
42

Comparison of Steelhead and Rainbow Trout

Allendorf (1975) found that the genetic distinction between coastal and inland

O. mykiss applies to both life history forms; that is, rainbow trout east of the Cascades are

genetically more similar to steelhead from east of the Cascades than they are to rainbow trout

west of the Cascades. Many recent studies of O. mykiss have focussed on either rainbow

trout or steelhead and thus provide no direct information about the relationship between the

forms on a finer geographic scale. However, Leider et al. (1995) included several new

samples of rainbow trout from the Elwha and Cedar Rivers in their study of steelhead

populations in Washington and found that their results “support the hypothesis that the two

forms were not reproductively isolated from each other.” Leider et al. also concluded that,

based on preliminary analysis of data collected previously for the Yakima and Big White

Salmon Rivers (Pearsons et al. 1994, Phelps et al. 1990), wild resident rainbow trout in those

streams would be indistinguishable from steelhead. In addition, some protein electrophoretic

studies that have reported data only for rainbow trout probably also included samples of

steelhead (K. Currens10). For example, in the John Day River, an Oregon tributary of the

Columbia River, genetic differences between O. mykiss from the North and South Forks were

larger than differences between presumed steelhead and rainbow trout in the South Fork

(Currens et al. 1987). In the Deschutes River, another Oregon tributary of the Columbia

River, Currens et al. (1990) found much larger genetic differences between O. mykiss from

above and below a barrier falls, but relatively modest differences between presumed

steelhead and rainbow trout from below the falls.

In a study of mtDNA in O. mykiss, Wilson et al. (1985) compared 19 steelhead from 4

locations in British Columbia with 19 rainbow trout from British Columbia, Alberta, and

California. No genetic differences were detected between steelhead and rainbow trout from

one British Columbia location (the lower Fraser River), but steelhead from the other three

populations showed a greater genetic affinity to each other than to rainbow trout from any of

the populations sampled. However, this result is difficult to interpret because of the small

sample sizes and the fact that there were only two localities at which both steelhead and

rainbow trout were collected. Furthermore, Buroker (footnote 8) found that the mtDNA

marker Wilson et al. (1985) used to distinguish rainbow trout was the most common type

found in his study of North American steelhead.

Gall et al. (1990) examined allozyme variation in resident O. mykiss from the San

Leandro Creek watershed, which drains into the east side of the San Francisco Bay. These

fish are believed to be descended from steelhead, which have not had access to this area since

the construction of Chabot Reservoir in 1875. Gall et al. (1990) found that samples from two

creeks upstream of the reservoir are genetically more similar to coastal O. mykiss than they

are to inland forms or to hatchery rainbow trout. Nielsen (footnote 9) compared mtDNA

haplotypes in southern steelhead with those in several California populations of resident O.

mykiss and in several stocks of hatchery rainbow trout that have been stocked in coastal

10 K. Currens, Oregon Cooperative Fishery Research Unit, Oregon State University,

Corvallis, OR 97331. Pers. commun., May 1994.
43

California streams. She found that some resident populations resemble nearby anadromous

populations in their mtDNA profiles, but others show evidence of introgression from

hatchery rainbow trout.

Run Timing

Differentiation based on timing of upstream migration in steelhead has also been

investigated by genetic methods. Allendorf (1975) and Utter and Allendorf (1977) found that

summer and winter steelhead of a particular coastal stream tended to resemble one another

genetically more than they resembled populations of adjacent drainages with similar run

timing. Later allozyme studies have supported these conclusions in a variety of geographical

areas (Chilcote et al. 1980, Schreck et al. 1986, Reisenbichler and Phelps 1989), including

the Rogue River (Reisenbichler et al. 1992). However, in each of these more recent studies,

the summer-run stocks have had some extent of hatchery introgression and therefore may not

represent the indigenous population. Furthermore, in at least some cases, interpretation of

the results may be complicated by difficulties in determining run timing of the fish sampled.

Thorgaard (1983) analyzed chromosomal variability in winter- and summer-run

steelhead from two rivers that had little history of hatchery introductions: the Quinault River

in Washington and the Rogue River in Oregon. Chromosome number differed between the

two river systems but was similar in summer and winter steelhead within each river system.

New Studies

For this status review, two types of new studies were undertaken by NMFS to

enhance our understanding of population genetic structure in west coast steelhead. First, new

samples from Idaho and California were collected for allozyme analysis. Second, recent data

collected by NMFS and WDFW were combined into a single data set to facilitate

comparisons among individual studies (Appendix A).

In 1994, the U.S. Fish and Wildlife Service (USFWS) and Idaho Department of Fish

and Game (IDFG) collected samples of steelhead from a number of natural populations in the

Clearwater and Salmon River Basins in an attempt to determine whether releases of hatchery

fish had affected the genetic structure of natural populations. Genetic analysis of these

samples performed by NMFS (Waples 1995) indicated that none of the populations in the

lower Clearwater River show evidence of substantial genetic introgression by steelhead from

Dworshak NFH, in spite of widespread outplanting in the area. The samples from the

Salmon River provided little clear insight into population structure. Two factors may have

contributed to this latter result: 1) Some of the Salmon River samples were small (about 25

fish), thus limiting power to detect population structure, and 2) the populations sampled were

among those believed most likely to have shown the effects of artificial propagation, so they

may not be a good indication of native population structure.

In order to obtain a more complete picture of genetic structure of steelhead in

California, NMFS worked with the California Department of Fish and Game to identify

natural populations of O. mykiss that could be sampled without placing local populations at
44

undue risk. Through these efforts, 10 samples (generally of 40-60 juvenile fish per sample)

were collected and analyzed by NMFS for allozyme variation. Tissue samples from these

collections are also being provided to J. Nielsen for use in her continuing studies of DNA

variation in California O. mykiss. In addition, we analyzed four samples of steelhead from

southern Oregon and northern California that were collected (but not analyzed) in 1992 as

part of the status review for Illinois River winter steelhead. Important results from these new

allozyme analyses can be summarized as follows.

1) The California samples show levels of population differentiation that are

unprecedented for the species. At one locus (FBALD-3*; Fig. 2), a sample from the Klamath

River was fixed for one allele and a sample from Gaviota Creek (near Santa Barbara) was

fixed for another allele. A fixed allelic difference between populations is a rare occurrence

for any Pacific salmon species, being generally encountered, if at all, only between

populations at extreme ends of a geographic range. Previously, Busby et al. (1994) found a

sharp transition in allelic frequencies at FBALD-3* in populations south of the Klamath River

drainage, but their study did not include samples from south of the Eel River.

2) More detail about population structure of California steelhead can be obtained by

examining Figures 3 and 4, which are different ways of summarizing patterns of genetic

relationships based on Nei’s (1978) unbiased genetic distance values between each pair of

populations. Figure 3 is a dendrogram constructed using the unweighted pair-group method

analysis (UPGMA) with arithmetic averaging, and Figure 4 is a different representation of

the same data using multidimensional scaling (MDS). Multidimensional scaling plots allow

one to view in two or three dimensions the pattern of relationships among populations; in

contrast, a dendrogram is essentially a one-dimensional representation of the data. In

general, two-dimensional MDS plots result in less distortion of the relationships among

populations than do dendrograms, and three-dimensional plots have less distortion than

two-dimensional plots. However, complex three-dimensional analyses are often difficult to

represent in two-dimensional figures, so two-dimensional MDS plots are sometimes

preferred for data sets that involve a large number of samples.

The new samples from the Chetco River and the Trinity River Hatchery and Cole

Rivers Hatchery (Rogue River) cluster with samples previously analyzed from the Klamath

Mountains Province, but the sample from Iron Gate Hatchery (Klamath River) is somewhat

of an outlier. A new sample from the Middle Fork of the Eel River showed an affinity to the

Mad River/Eel River/Redwood Creek group identified by Busby et al. (1994). The other new

California samples were all quite different from any samples of coastal or inland steelhead

previously examined. The sample from Coleman NFH and those from Mill and Deer Creeks

(the two natural populations in the Sacramento River Basin believed to contain the most

likely remnants of native steelhead) form a small, coherent group that is quite distinct from

all other California steelhead. The remaining California samples (from Ten Mile River in

Mendocino County to Gaviota Creek and Arroyo Hondo in Santa Barbara County) formed a

cluster that diverged from the other samples at a genetic distance (Nei’s D ≈ 0.03) higher

than that previously found between coastal and inland races of steelhead (e.g., Busby et al.

1993).
45
46
47
48

In spite of the large interpopulational genetic differences, the pattern of population

structure south of the Eel River is not entirely clear from the allozyme data. The MDS plot

(Fig. 4) shows the magnitude of the diversity but also illustrates the difficulty in drawing

inferences about geographic population structure. For example, the two samples from Santa

Barbara County are genetically quite divergent but are not similar to each other. In the

allozyme analysis, we found only modest genetic differences between the samples from Ten

Mile River and Lagunitas Creek (a tributary of Tomales Bay), both of which are north of San

Francisco, but we also found that these samples were more similar to the sample from Whale

Rock Hatchery (near San Luis Obispo) than they were to the geographically closer samples

from the San Francisco-Monterey area (Scott Creek, Carmel River, and San Lorenzo River).

3) Our allozyme analysis is consistent with Nielsen’s (1994) mtDNA study in finding

a high degree of interpopulational differentiation within California. The allozyme data also

support Nielsen’s finding of large genetic differences among samples from southern

California. One notable difference in the two analyses is that, whereas Nielsen found

substantial differences in the frequencies of some mtDNA alleles between samples from

Mendocino and Marin Counties, we did not (as evidenced by the relative similarity between

the Ten Mile River and Lagunitas Creek allozyme samples).

4) To examine possible explanations for the distinctive genetic characteristics of the

samples from the Sacramento River, we performed another analysis that included data for

five rainbow trout samples provided by WDFW, including the four that Phelps et al. (1994)

used in their comparisons with Washington state steelhead. This new analysis (Figs. 5 and 6)

showed that steelhead from the Sacramento River are genetically more similar to these

rainbow trout populations than they are to coastal steelhead populations from California.

This could be the result of integration of rainbow trout into the steelhead broodstock at

Coleman NFH and subsequent effects of Coleman NFH strays or outplants on natural

populations in the Sacramento River; the difficulty of distinguishing between

nonanadromous and anadromous O. mykiss during broodstock collection in the upper

Sacramento River has been described by several authors (e.g., Hallock et al. 1961, Behnke

1992, Cramer et al. 1995). On the other hand, this genetic similarity could simply reflect

ancestral relationships, since the origins of most of the present-day rainbow trout stocks can

be traced to collections of anadromous and nonanadromous O. mykiss from the McCloud

River in the Sacramento River Basin made early in the century (Behnke 1992).

To facilitate direct comparisons among recent collections by WDFW (whose samples

are all from within Washington state) and NMFS (whose new data are primarily from the

Snake River, Oregon, and California), the two agencies collaborated to integrate their genetic

data for steelhead into a single data set. Lead scientists for this collaboration were Stevan

Phelps from WDFW and Paul Aebersold from NMFS. Extensive inter-laboratory

communication that included exchange of recipes and procedures and detailed review of

photographic records indicated a high degree of consistency in data for the two agencies.

To reduce the number of samples in the analysis, collections from different years

within locations were combined to form single pooled samples for each location. This

combined data set includes information for samples from 100 natural populations of
49
50
51

steelhead and rainbow trout and 3 steelhead hatcheries. To account for some differences

between laboratories in the suite of gene loci examined, the number of polymorphic gene loci

used in this combined data set (42) was slightly less than the full complement used by either

NMFS or WDFW in their individual analyses. Therefore, those individual studies provide

more detailed information about genetic relationships within particular geographic areas.

Nevertheless, the combined data set provides the broadest geographic coverage to date for a

data set that takes advantage of significant advances in recent years in the number of genetic

markers for O. mykiss. Results of analyses of this data set are shown in Figures 7 and 8.

These figures show clearly the major difference between coastal and inland forms.

The position of one of the Klickitat River samples, #94 (Bowman Creek), which is not

clearly aligned with either the inland or coastal groups in Figure 8, may reflect the genetic

influence of hatchery coastal rainbow trout overlaid upon a native inland steelhead

population (Phelps11). Within the inland group, samples from the middle Columbia River

form a separate subgroup from those in the Snake River, with one Yakima River Basin

sample (Toppenish Creek) being an outlier. No recent genetic data are available for

populations in Columbia River tributaries upstream from the Yakima River. Dworshak NFH

was included in these figures to provide an indication of the relative distinctiveness of this

population.

Within the coastal group, the geographic differences among Washington populations

detected by Leider et al. (1995) are modest in comparison to the overall pattern of diversity

from Puget Sound to southern California. However, there are a number of coastal steelhead

samples from Washington that do not show a strong genetic affinity to any other populations.

The most notable outliers in the combined analysis were samples from the Upper Chehalis,

Washougal, Nooksack, and Tahuya Rivers. With the benefit of this combined data set, it is

apparent that populations south of Cape Blanco are genetically distinct from all northern

populations. Previous analyses that considered steelhead from the Klamath Mountains

Province (Busby et al. 1993, 1994) did not include samples from Washington, so this was the

first time a direct comparison of the two groups has been possible.

The relative magnitude of genetic diversity among steelhead populations from

California is readily apparent from these figures. In the dendrogram, California samples

from south of the Eel River form a genetically diverse cluster that joins the other west coast

steelhead populations external to the inland-coastal break in Washington and Oregon.

Although California steelhead, including those in the Sacramento River, are more similar

genetically to other coastal steelhead populations than they are to inland steelhead from the

Columbia River Basin (see Fig. 8), the genetic diversity within the coastal steelhead lineage

is considerable.

11 S. Phelps, Washington Department of Fish and Wildlife, Olympia, WA. Pers. commun.,

November 1994.
52
53
54

Synthesis and Discussion

The old and new genetic data from allozyme, DNA, and chromosomal studies can be

synthesized and summarized as follows:

1) All studies that have addressed the question have found large genetic differences

between coastal and inland forms (both anadromous and nonanadromous) of O. mykiss. In

the Columbia River Basin, the boundary between the two forms occurs at approximately the

Cascade Crest. However, available data are not sufficient to determine with certainty

whether there is a transitional (perhaps intergrade) zone between the forms or whether they

remain discrete. If the two forms are discrete even in this area of closest contact, the exact

boundaries are unclear.

2) Genetic data do not support the hypothesis that winter- and summer-run steelhead

are separate monophyletic units, as appears to be the case with inland and coastal forms.

Rather, steelhead with different run timing in the same geographic area may be genetically

more similar than either is to fish from another area with a similar run timing. This result,

however, does not mean that there cannot be genetic differences between summer and winter

steelhead in any given drainage.

3) The inland steelhead lineage is represented only by populations in the Columbia

and Fraser River Basins. Within the inland group, consistent differences are found between

populations from the Snake and Columbia Rivers, and there is also evidence for a modest

level of population differentiation between major drainages within each of these two rivers.

Steelhead from Dworshak NFH are genetically the most distinctive population within the

inland lineage.

4) Within the geographic area covered by this status review, coastal steelhead occur in

a diverse array of populations. A large group showing consistent geographic structure but

relatively modest genetic differences between populations includes most samples from Puget

Sound, coastal Washington, and the lower Columbia River. The few recent samples from

coastal Oregon north of Cape Blanco show some differences from this larger group, and

populations from the Klamath Mountains Province are genetically different from those to the

north or south. South of the Klamath River, large differences are found between coastal

populations, both for allozymes and DNA markers, but the geographic structure to the

variation is not fully resolved. Samples from the Sacramento River are quite distinct from all

other coastal and inland populations that have been sampled but show some affinity to

hatchery rainbow trout.

Any of several factors might explain the much higher diversity among coastal

steelhead populations in California than in Washington. First, it is possible that diversity

among populations in Washington was greater historically but has been eroded by human

influence. There is a long history of widespread releases of a few hatchery stocks in

Washington (see Reisenbichler and Phelps 1989). Phelps et al. (1994) found evidence for

substantial effects of hatchery stocks on several winter steelhead populations. The

occurrence of a number of quite distinct natural populations of coastal steelhead (e.g., upper
55

Chehalis, Washougal, Wind, Nooksack, and Tahuya Rivers) might be explained if they

represent remnants of more complex population structure that occurred historically.

Two factors, either individually or in combination, likely contributed to the high level

of genetic variation in California steelhead. First, environmental conditions in most streams

in central and southern California are extreme for anadromous salmonids, with low flows and

summer water temperatures that may reach or exceed typical thermal limits for O. mykiss.

These environmental conditions may promote strong local adaptations and inhibit gene flow

among populations. In addition, sand berms at the mouth of streams may completely block

migration of juveniles or adults in some years, and it is likely that this phenomenon fosters

flexible life history patterns, a greater importance of resident fish, and increased opportunities

for isolation. Second, it is possible that these factors, which historically would be likely to

promote isolation and differentiation, have been intensified by human-mediated events of the

past century. Major water projects in California have reduced stream flows and increased the

frequency and duration of stream blockages. South of San Francisco Bay, a high proportion

of native steelhead populations are declining or already extinct (Titus et al. in press),

indicating reduced opportunities for genetic contact between populations. In addition,

declines in abundance in the populations that do remain facilitate more rapid differentiation

among populations due to genetic drift.

Discussion and Conclusions on ESU Determinations

Based on a review of the biology and ecology of west coast steelhead, the Biological

Review Team (BRT) identified 15 ESUs, 12 of which include coastal forms and 3 of which

include inland forms (Fig. 9, Appendix B). Genetic data (from protein electrophoresis, DNA

markers, and chromosomal analysis) were the primary evidence considered for the

reproductive isolation criterion, supplemented by inferences about barriers to migration

created by natural geographic features. A number of factors were considered to be important

in evaluations of ecological/genetic diversity, with data for migration and spawn timing, life

history, ichthyogeography, hydrology, and other environmental features of the habitat being

particularly informative. In the following summaries, we describe only those factors that

were valuable in making individual ESU determinations.

Each of the ESUs includes multiple spawning populations of O. mykiss, and most

ESUs also extend over a considerable geographic area. This result is consistent with NMFS’

species definition paper, which states that, in general, “ESUs should correspond to more

comprehensive units unless there is clear evidence that evolutionarily important differences

exist between smaller population segments” (Waples 1991b, p. 20). However, considerable

diversity in genetic or life history traits or habitat features may exist within a single complex

ESU, and the descriptions below briefly summarize some of the notable types of diversity

within each ESU. This diversity is considered in the next section in evaluating risk to the

ESU as a whole.
56
57

Evolutionary Significance of Phylogenetic and Life History Forms

In defining ESUs for west coast steelhead, it is necessary to consider the significance

of the various phylogenetic and life history forms that have been described (see page 7). Of

these, only the coastal or inland groups are considered monophyletic, the others apparently

being adaptive expressions of the life history plasticity that is characteristic of O. mykiss.

Genetic analyses show large and consistent differentiation between coastal and inland

steelhead. Also, these groups have not been found to co-occur in nature, although some

degree of overlap in the Columbia River Basin in the vicinity of the Cascade Crest cannot be

ruled out.

Unlike the coastal/inland groups, summer and winter steelhead co-occur in several

river basins, primarily within the range of the coastal steelhead group. The few genetic

analyses that have considered this issue indicate that summer and winter steelhead from the

same river basin are more genetically similar to each other than to the same run type in

another river basin. This indicates that all summer steelhead, for example, are not descended

and distributed from one ancestral source and, therefore, are not a monophyletic unit.

Genetic assessments within and between river basins have not specifically been

conducted on A- and B-run steelhead. One reason for this is that most genetic analyses in the

Snake River Basin have been conducted on juvenile steelhead, while the characteristics of Aand B-run are manifested in the adults. We do know that there is geographic structure to the

genetic data that does not appear to strictly follow the distribution of the A- and B-runs

within the Columbia and Snake River Basins.

Half-pounders are only reported in the literature from a small geographic region in

southern Oregon and northern California. However, genetic data do not show a particularly

strong affinity among rivers having half-pounders; rather, the affinities are geographic,

including streams both with and without half-pounders. Additionally, winter steelhead

broodstock for Cole Rivers Hatchery on the Rogue River in Oregon were initially selected

for fish without evidence of the half-pounder life history, yet there is evidence that among

winter steelhead subsequently returning to the hatchery, approximately 30% underwent a

half-pounder migration (Evenson12), suggesting that this is not strictly a genetic trait.

Resident fish—Few detailed studies have been done on the relationship between

resident and anadromous O. mykiss in the same location. Genetic studies generally show that

the two forms from the same area are more similar to each other than either is to the same

form from a different geographic area. Thus, rainbow trout and steelhead from the same area

may share a common gene pool, at least over evolutionary time periods. It is also generally

believed (although definitive information on this topic is scarce) that progeny of

nonanadromous O. mykiss can be anadromous, and that anadromous O. mykiss can produce

nonanadromous progeny. It was the consensus of fishery biologists we consulted throughout

12 M. Evenson, District Fish Biologist, Oregon Department of Fish and Wildlife, 1495 East

Gregory Road, Central Point, OR 97502. Pers. commun., January 1993 and May 1994.
58

the region that resident fish should generally be considered part of the steelhead ESUs. On

the other hand, there is also evidence for substantial genetic divergence between resident and

anadromous fish in areas where resident populations have been isolated by long-standing

natural barriers. In addition, hatchery rainbow trout derived from a few mixed strains have

been widely planted throughout the range of west coast steelhead, and resident populations

established as a result of such transplants would not be native to the area.

Based on these considerations, the BRT concluded that, in general, the ESUs

described below include resident O. mykiss in cases where they have the opportunity to

interbreed with anadromous fish. Geographic areas in which the role of resident fish may be

particularly important include southern California and the upper Columbia River; in both of

these areas, extreme environmental conditions may promote increased flexibility in life

history strategies for native populations of O. mykiss. Resident populations above longstanding natural barriers, and those that have resulted from the introduction of non-native

rainbow trout, would not be considered part of the ESUs. Resident populations that inhabit

areas upstream from human-caused migration barriers (e.g., Grand Coulee Dam, the Hells

Canyon Dam complex, and numerous smaller barriers in California) may contain genetic

resources similar to those of anadromous fish in the ESU, but little information is available

on these fish or the role they might play in conserving natural populations of steelhead. The

status with respect to steelhead ESUs of resident fish upstream from human-caused migration

barriers must be evaluated on a case-by-case basis as more information becomes available.

Coastal Steelhead ESUs

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.
59

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
60

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
61

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
62

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
63

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.
64

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
65

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
66

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).
67

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.
68

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 Environment13 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

13 B. Shepherd, Fisheries Section Head, B.C. Ministry of the Environment, 3547 Skaha Lake

Road, Penticton, B.C., Canada V2AZK2. Pers. commun., November 1994.
69

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
70

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,
71

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.
72

Artificial Propagation

The remainder of this section is intended to provide a summary of the nature and

scope of artificial propagation activities for west coast steelhead.

Artificial propagation of O. mykiss began in the 1870s in the San Francisco Bay area

(Behnke 1992). These fish were presumably rainbow trout. From 1877 to 1888, egg taking

stations were established on the lower McCloud River (upper Sacramento River Basin) for

propagation of redband trout and coastal steelhead, with no apparent effort to separate the

two forms (Behnke 1992). From that time, O. mykiss has been widely propagated, and stocks

have been transported literally around the globe. Behnke (1992, p. 174) stated that “the

overwhelming majority of brood stocks of rainbow trout maintained around the world

originated mainly from various mixtures of coastal steelhead.” Therefore, in evaluating

artificial propagation of steelhead, it is also important to consider the propagation of rainbow

trout.

The popularity of O. mykiss as a cultured species makes it infeasible to discuss each

propagation facility on the west coast in this document. Behnke (1992, p. 174) noted that,

“in California alone, 169 hatcheries and egg-taking stations drew on diverse populations of

rainbow trout from 1870 to 1960.” A list of major steelhead propagation facilities currently

in operation is provided in Appendix C. Annual hatchery production of steelhead on the west

coast of North America increased from about 3 million juvenile steelhead in 1960 to over 30

million in 1985 (Light 1989). The majority of hatchery produced steelhead are from the

Pacific Northwest states of Idaho, Washington, and Oregon (Table 8, Appendix D),

predominately in the Columbia River Basin (Light 1989).

Below we summarize some of the major artificial propagation programs for west

coast steelhead.

Grand Coulee Fish Maintenance Project

In 1939, the construction of Grand Coulee Dam on the Columbia River (RKm 956)

blocked over 1,800 km of river from access by anadromous fish (Mullan et al. 1992). In an

effort to preserve fish runs affected by Grand Coulee Dam, all anadromous fish migrating

upstream were trapped at Rock Island Dam (RKm 729) from 1939 through 1943 and either

released to spawn in tributaries between Rock Island and Grand Coulee Dams or spawned in

hatcheries and the offspring released in that area (Peven 1990, Mullan et al. 1992, Chapman

et al. 1994). Through this process, stocks of all anadromous salmonids, including steelhead,

which historically were native to several separate subbasins above Rock Island Dam, were

randomly redistributed among tributaries in the Rock Island-Grand Coulee reach. Exactly

how this has affected stock composition of steelhead is unknown.

Widespread Steelhead Broodstocks

Several steelhead broodstocks have been widely used in steelhead propagation.

These broodstocks have had the greatest potential to affect native steelhead populations due
73
74

to their broad distribution and extensive incorporation into various steelhead propagation

programs throughout the west coast.

Chambers Creek winter steelhead—This stock of winter steelhead comes from

Chambers Creek, Tacoma, Washington and was first cultured in the 1920s (Crawford 1979).

Chambers Creek steelhead have been introduced throughout western Washington, including

the Puget Sound region, and in tributaries of the lower Columbia River. As much as 90% of

steelhead harvested from some western Washington streams can be attributed to Chambers

Creek winter steelhead, through artificial and established natural production (Crawford 1979,

WDF et al. 1993). Concerns over genetic introgression into native stocks by Chambers

Creek steelhead led to attempts to establish native brood stocks in Washington (Crawford

1979); however, the Chambers Creek steelhead stock is still considered essential to most of

Washington winter steelhead hatchery operations (Huew et al. 1990, WDF et al. 1993).

Skamania summer steelhead—Skamania summer steelhead were developed from

Washougal and Klickitat River summer steelhead in the late 1950s at the Skamania Hatchery,

Washington (Crawford 1979). This stock has been widely used in Washington, Idaho,

Oregon, California, Indiana, Rhode Island, and North Carolina (Crawford 1979, CDFG

1994). In many cases, Skamania stock have been introduced where summer steelhead did

not naturally exist, to provide recreational angling opportunities, for example, the Willamette

River. Additionally, Skamania stock have been introduced in river basins having endemic

summer steelhead populations, such as the Stillaguamish and Columbia River tributaries.

Alsea River winter steelhead—This stock is originally from the Alsea River,

Oregon and has been cultured since the 1930s (ODFW 1986). Historically introduced into

most coastal Oregon streams since the 1980s, Alsea stock have primarily been used on the

central Oregon coast (Salmon River south to Coquille River) and occasionally in the lower

Columbia River Basin (ODFW 1986, CBFWA 1990).

Big Creek and Cowlitz River winter steelhead—These two stocks dominate the

production of hatchery winter steelhead in the lower Columbia River Basin—the Big Creek

stock on the Oregon side, and the Cowlitz stock on the Washington side (CBFWA 1990).

The Big Creek stock was developed in the 1960s from the earliest maturing steelhead native

to Big Creek (Howell et al. 1985). The initial source for the Cowlitz Hatchery stock was a

1:1 mix of Chambers Creek and native Cowlitz River fish (Crawford 1979). The Big Creek

and Cowlitz Hatcheries produce about 700,000 and 650,000 smolts per year, respectively,

which are released into most major river basins tributary to the Columbia River below

Bonneville Dam (Howell et al. 1985). Cowlitz stock steelhead eggs have been used in

hatchery programs of other states, including California (Howell et al. 1985, CDFG 1994).

Big Creek winter steelhead have established naturally reproducing populations in the upper

Willamette River Basin (Howell et al. 1985).

Eel River winter steelhead—Eggs collected from Eel River winter steelhead were

used in establishing several CDFG steelhead hatchery programs, for example. Mad River and

Nimbus Hatcheries, until steelhead returns to these hatcheries supplied sufficient eggs for the
75

hatcheries’ production goals without such supplementation (CDFG 1994,1995; Will14). Eel

River winter steelhead eggs are collected at an egg-taking station located at Cape Horn Dam,

northeast of Ukiah, California. This facility, originally named Snow Mountain Station, was

established by Snow Mountain Light and Power Company in 1907; since the 1960s the egg

taking station has been operated by the California Department of Fish and Game under the

name Van Arsdale Fisheries Station15. Incorporation of Eel River steelhead into hatchery

programs generally occurred prior to 1975; most eggs collected since then have been reared

off-site, usually at Mad River Hatchery, then returned to the Eel River (CDFG 1994, Will

footnote 14).

Wells Hatchery summer steelhead—Summer steelhead from the Wells Hatchery

are the primary stock used in the Columbia River Basin above Rock Island Dam (Chapman

et al. 1994). The stock was developed in the early 1960s from naturally spawning

populations intercepted at fish passage facilities above Priest Rapids Dam (see page 72,

Grand Coulee Fish Maintenance Project). Since 1970, the Wells stock has been distributed

in the Columbia River Basin from the Big White Salmon River upstream to the Grand Ronde

River in the Snake River Basin, and the Similkameen River, a tributary of the Okanogan

River (Howell et al. 1985). About 1 million Wells summer steelhead are released annually

(Howell et al. 1985).

Lyons Ferry summer steelhead—Lyons Ferry Hatchery was constructed in the early

1980s to provide summer steelhead for streams in southeast Washington, including both the

Snake and Walla Walla River Basins (Delarm and Smith 1990d). The Lyons Ferry stock was

derived from eggs obtained from ODFW’s Wallowa Hatchery on the Grande Ronde River,

augmented with occasional transfers of Wells Hatchery stock (Delarm and Smith 1990d).

About 1 million fish per year are produced at the Lyons Ferry Hatchery (Delarm and Smith

1990d).

Dworshak summer steelhead—This stock was developed from native B-run North

Fork Clearwater River summer steelhead in 1969 (Howell et al. 1985). As many as 3 million

fish are released from Dworshak NFH every year, mostly into the Clearwater River Basin,

although limited introductions have occurred in the Salmon and Snake Rivers as well

(Howell et al. 1985).

Summary of Artificial Propagation by ESU

In general, hatchery stocks of steelhead have been widely introduced throughout the

west coast of the United States, so that today there are few native steelhead stocks that have

not had some influence from hatchery operations (Crawford 1979, Howell et al 1985, Light

14 B. Will, Manager, Rowdy Creek Fish Hatchery, P.O. Box 328, Smith River, CA 95567.

Pers. commun., May 1995.

15 In the present document, we will use the contemporary name, Van Arsdale Fisheries

Station, when referring to this propagation facility.
76

1989, Cramer et al 1995, ODFW 1994a-c). In this section, we present a brief overview of the

artificial propagation activities within the geographic ranges of the 15 west coast steelhead

ESUs.

1) Puget Sound—Artificial propagation of steelhead in the range of the Puget Sound

ESU is pronounced (Fig. 10). About 1,500,000 winter steelhead and 400,000 summer

steelhead, mostly smolts, are released annually into river basins in this area (WDF et al.

1993, WDFW 1994a). Hatchery programs in the Puget Sound region largely rely on

Chambers Creek winter steelhead and Skamania-stock summer steelhead (Crawford 1979,

Huew et al. 1990). The abundance of hatchery winter steelhead in Puget Sound results in a

target harvest rate of 90% (WDF et al. 1993). Most Skamania-stock summer steelhead are

introduced into streams not previously utilized by summer steelhead, although this stock is

also routinely planted in streams containing indigenous Puget Sound summer steelhead, such

as the Skagit, Stillaguamish, and Snohomish River systems (Crawford 1979). The Nisqually

River is the only major river in Puget Sound not receiving hatchery winter steelhead (WDF

et al. 1993); however, this river is planted with about 24,000 Skamania-stock summer

steelhead per year (WDFW 1994a).

2) Olympic Peninsula—The hatchery effort for steelhead on the Olympic Peninsula

is pronounced, but not to the extent found in Puget Sound, especially for summer steelhead

(Fig. 10). About 40,000 summer steelhead, primarily Skamania stock, are released annually

on the Olympic Peninsula, all in the Quillayute River Basin (Crawford 1979, WDF et al.

1993). However, these fish are known to stray into many nearby river systems when

returning to fresh water as adults (WDF et al. 1993). About 840,000 winter steelhead,

primarily from a stock designated as “Bogachiel/Chambers Creek,” are planted annually in

this area (WDF et al. 1993, WDFW 1994a).

Recently, wild steelhead have been incorporated into the hatchery stocks being

planted into a few streams in this area. However, based on the early spawn timing necessary

for compatibility with hatchery spawning protocols (WDF et al. 1993), most of these wild

fish would likely have a significant hatchery ancestry themselves. Hatchery fish derived

from native winter steelhead populations are released into the Quinault River and other

streams occupied by this ESU. However, because of the influence of nonindigenous stocks

that are also planted in the Quinault River Basin, the naturally spawning winter steelhead are

thought to be of mixed origin (WDF et al. 1993).

3) Southwest Washington—Southwest Washington winter steelhead hatchery stocks

were originally derived from the Chambers Creek stock (Puget Sound origin) (Fig. 11), but

recent hatchery efforts in southwest Washington streams have emphasized using stocks of

local origin (WDF et al. 1993). Dominant winter steelhead hatchery stocks used in Columbia

River tributaries occupied by this ESU are Beaver Creek Hatchery (Elochoman River/

Chambers Creek origin) in Washington, and Gnat and Big Creek steelhead stocks in Oregon

(Howell et al. 1985, ODFW 1993, WDF et al. 1993). Hatchery programs for summer

steelhead in this region use the Skamania stock, and the majority of all summer steelhead

returning to rivers in this ESU are Skamania hatchery fish (WDF et al. 1993).
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4) Lower Columbia River—More than 2 million winter steelhead and over 1 million

summer steelhead smolts are released each year within the basins occupied by the Lower

Columbia River ESU (Fig. 11). The primary winter steelhead stocks used in hatchery

programs in the Lower Columbia River are from Eagle Creek and Gnat Creek Hatcheries in

Oregon, and Beaver Creek (Elochoman River/Chambers Creek origin) and the Cowlitz River

in Washington (Howell et al. 1985). Chambers Creek winter steelhead from Puget Sound are

also an important component of Lower Columbia River hatchery management (Howell et al.

1985). In some cases, the influence of hatchery steelhead is pronounced: Cowlitz River

“wild” winter steelhead are almost all the progeny of feral Cowlitz Hatchery steelhead (WDF

et al. 1993). Skamania-stock summer steelhead are used extensively in both Washington and

Oregon tributaries of the Lower Columbia River (Howell et al. 1985, ODFW 1994c, WDF et

al. 1993).

5) Upper Willamette River—Over 175,000 winter steelhead are released annually

into the region occupied by this ESU (Howell et al. 1985, ODFW 1994c) (Fig. 12). Most of

these are from hatchery stocks derived from native winter steelhead from the Santiam River

system. However, substantial numbers of Gnat Creek (i.e., Big Creek-stock) winter steelhead

from the lower Columbia River are also introduced into the area every year (Howell et al.

1985, ODFW 1994c). The latter transplants have succeeded in establishing naturally

reproducing populations of Big Creek-stock steelhead in the Upper Willamette River Basin

(Howell et al. 1985). Summer steelhead are not native to the upper Willamette River, but

Skamania-stock summer steelhead are planted in this area (Howell et al. 1985, ODFW

1994c). Natural production of summer steelhead appears to be low (2.5% of total run in

1981), and the population is largely maintained by releases of hatchery fish (Howell et al.

1985).

6) Oregon Coast—Over 1,300,000 winter steelhead and more than 350,000 summer

steelhead are targeted for release in 1995 into Oregon coastal streams north of Cape Blanco

(ODFW 1994b). As is the case in several other steelhead ESUs, few Oregon coastal hatchery

stocks are native to the rivers receiving them (ODFW 1994a,c) (Fig. 12). However, releases

of specific hatchery steelhead stocks along the Oregon coast generally occur only within

certain geographic areas. For example, the Nehalem River hatchery stock is not planted in

streams south of the Nehalem River; Cedar Creek hatchery steelhead are released from the

Miami River south to the Little Nestucca River; Alsea Hatchery steelhead are released from

the Salmon River south to the Smith River (Umpqua River Basin); the Umpqua River is

planted only with its own stocks; and Coos/Coquille stock are used in rivers south of Coos

Bay to Cape Blanco (ODFW 1994b). Nonetheless, the overall impact of hatchery steelhead

on the Oregon coast is significant. For instance, of 19 Oregon coastal rivers examined for

hatchery influence, all but 2, the Coquille and North Umpqua Rivers, receive hatchery fish

that are “genetically dissimilar to wild fish” (ODFW 1994a). Furthermore, it is estimated

that 54% of the total number of winter steelhead spawning in these rivers are of hatchery

origin (ODFW 1994a). All summer steelhead in this ESU, apart from those in the Siletz and

Umpqua River Basins, are introduced from the Siletz River. Within the Siletz River, about

90% of the naturally spawning summer steelhead are of hatchery origin (ODFW 1994a).

North Umpqua River summer steelhead is the only stock of hatchery steelhead on the Oregon

Coast considered by ODFW to be genetically similar to the native steelhead from the area in

which it is released. This hatchery stock is derived from the native North Umpqua fish, and
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little attempt has been made to alter the stock’s life history characteristics (e.g., migration and

spawn timing) (ODFW 1994a).

7) Klamath Mountains Province—Total production of hatchery steelhead in the

rivers occupied by this ESU is about 1,500,000 fish per year, of which about 320,000 are

winter steelhead and the remainder are summer or fall steelhead (Busby et al. 1994) (Fig. 13).

Steelhead released into the Chetco and Rogue River Basins are derived primarily from local

stocks; however, prior to 1970 Alsea Hatchery steelhead were released into the Chetco River

(ODFW 1986). Although hatchery production in the Klamath River Basin relies primarily on

broodstock returns to the hatcheries, the Iron Gate or Trinity Hatcheries in the Klamath River

system received transfers of stock from the Cowlitz and Washougal Hatcheries, as well as

transfers from the Sacramento, Willamette, Mad, and Eel River Basins prior to 1973 (Busby

et al. 1994). In general, the rivers in this area are planted with hatchery fish derived primarily

from native stocks (e.g., Chetco, Rogue, and Klamath Rivers), or apparently are not stocked

at all (e.g., Pistol, Winchuck, and Illinois Rivers) (ODFW 1994c).

8) Northern California—The primary steelhead hatchery within the range of this

ESU is Mad River Hatchery, established in 1971 by CDFG for fisheries enhancement

(McEwan and Jackson 1996). The Mad River Hatchery winter steelhead stock was founded

with steelhead eggs from the Eel River (Van Arsdale Fisheries Station, see page 74) and the

San Lorenzo River (Cramer et al. 1995; Will footnote 14). Returns of steelhead to Mad

River Hatchery were sufficient to supply the hatchery’s production needs by 1974 (Cramer et

al. 1995). Van Arsdale Fisheries Station continues to transfer Eel River steelhead eggs to

Mad River Hatchery for rearing and subsequent release into the Eel River (CDFG 1994).

The migration and spawn timings of hatchery stocks in northern California have been

truncated since hatchery operations began (Cramer et al. 1995). In addition, both Mad River

Hatchery and Van Arsdale Fisheries Station release unsmolted steelhead (CDFG 1994),

which have been shown to survive poorly to spawning age (Cramer et al. 1995).

Introduced Skamania-stock summer steelhead appear to be reproducing naturally in

the Mad River (Cramer et al. 1995). An average of 96,000 juvenile steelhead of Van Arsdale

Fisheries Station and Mad River Hatchery stock origins have been released annually into the

Eel River Basin since 1970 (CDFG 1994). Approximately 233,000 juvenile steelhead of

various stock origins are released annually into Mad River (CDFG 1994). All other basins in

this area together receive about 75,000 steelhead per year (Cramer et al. 1995), for a total

annual hatchery release of at least 404,000 steelhead within the range of the Northern

California ESU (Fig. 13).

9) Central California Coast—Warm Springs Hatchery on the Russian River is

currently the only major steelhead facility within the region occupied by this ESU; however,

release records show that a substantial number of steelhead from Mad River Hatchery are

released in this area (CDFG 1994) (Fig. 14). In the early part of the century, steelhead from

the Scott Creek Hatchery, themselves a mix of various steelhead stocks from Oregon and

Washington, were widely introduced throughout the smaller river basins in this area (Bryant

1994). Although few out-of-basin stocks have been transferred into Warm Springs Hatchery,

Mad River Hatchery and Eel River steelhead have been introduced directly into the Russian
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River as recently as 1991, and many river and creek basins in this area periodically receive

Mad River Hatchery steelhead (CDFG 1994). Since 1971, the Russian River has received

about 140,000 fish per year of various stocks (CDFG 1994, Cramer et al. 1995). Release

records for hatchery steelhead in other basins occupied by the Central California Coast ESU

are incomplete and are not reported here.

10) South-Central California Coast—Artificial propagation efforts for steelhead

have not been extensive in this region (Fig. 14). For example, since 1971, about 16,000 Mad

River Hatchery winter steelhead have been planted into the Carmel River and San Luis

Obispo Creek (CDFG 1994).

11) Southern California—Compared to many other areas, the hatchery effort in

southern California has not been extensive (Fig. 14). Between 1910 and 1940, sporadic

introductions of steelhead into various streams within rivers occupied by this ESU were made

with small lots of more northerly stocks, primarily from Scott Creek, Central California ESU

(Bryant 1994). No records were found pertaining to hatchery activity in this region between

1940 and 1970. Since the early 1970s, steelhead from state hatcheries have been periodically

released in this area, but not on a large scale. For example, about 50,000 Mad River

Hatchery steelhead have been planted in southern California streams in the last 20 years,

mainly in the Ventura River and Arroyo Seco Creek (CDFG 1994).

12) Central Valley—There appear to be no steelhead-bearing rivers in the

Sacramento River Basin that have not received releases of multiple hatchery stocks (CDFG

1994, Cramer et al. 1995) (Fig. 15). Major steelhead production facilities within the Central

Valley of California include: Coleman NFH, Feather River Hatchery, Mokelumne River

Fish Installation, and Nimbus Hatchery. Each of these facilities has utilized steelhead stocks

originating from within the basin as well as out-of-basin stocks; stock transfers between the

Central Valley steelhead facilities have historically been commonplace (CDFG 1994).

Nimbus Hatchery, located on the American River (tributary to the Sacramento River),

was founded with Eel River winter steelhead from Van Arsdale Fisheries Station and

returning American River steelhead; Mad and Russian River stocks, as well as Sacramento

River stocks, have been mixed into the Nimbus Hatchery population over time (CDFG 1994,

Cramer et al. 1995). To mitigate the loss of steelhead in the Mokelumne River (San Joaquin

River Basin) following completion of Comanche Dam in 1963, Nimbus stock, as well as fish

from Coleman NFH and Feather River Hatchery, have been introduced to the Mokelumne

River (CDFG 1994, Cramer et al. 1995, McEwan and Jackson 1996). Further mixing of

steelhead stocks in the Sacramento River Basin may result from straying by hatchery stocks

within the basin, which has been observed to be as high as 24-35% in some cases (Hallock

1989, Cramer et al. 1995). Since 1983, about 2,800,000 juvenile steelhead have been

released annually into the Sacramento River Basin (CDFG 1994, Cramer et al. 1995,

McEwan and Jackson 1996).

Attempts to establish a summer steelhead fishery in the Central Valley began in the

late 1960s and continued intermittently into the 1980s using Skamania-stock (see page 74)

summer steelhead (CDFG 1994). Despite successful returns of summer steelhead to Nimbus
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Hatchery, this program appears to have been discontinued; the last record of Skamania-stock

releases from Nimbus hatchery occurred in fiscal year 1980-81 (CDFG 1994). Recent CDFG

documents and communications (e.g., CDFG 1995, McEwan and Jackson 1996) on

steelhead do not mention summer steelhead in the Central Valley.

13) Middle Columbia River—Over 2 million hatchery summer steelhead are

released into the rivers occupied by this ESU every year (Howell et al. 1985, CBFWA 1990,

Delarm and Smith 1990c,d) (Fig. 16). Hatchery steelhead in the Deschutes River are derived

from native stock, as is the current hatchery stock used in the Umatilla River, although both

systems received small plants of out-of-basin stocks many years ago (Howell et al. 1985).

However, strays from several Columbia River Basin hatcheries are common in the Umatilla

and Deschutes Rivers, where they can amount to 20% of the steelhead handled at Warm

Springs Hatchery (Howell et al. 1985). Various stocks have been, or are being, introduced

into other rivers in this region, with the Yakima River alone receiving Skamania, Wallowa,

Wells, and Lyons Ferry steelhead stocks from other ESUs (Howell et al. 1985, ODFW

1994c, WDFW 1994a). The John Day River in this ESU is not planted with steelhead

(Howell et al. 1985). In the Yakima River Basin, Satus Creek is reserved as a genetic refuge

for native steelhead and is not planted (Howell et al. 1985).

14) Upper Columbia River—Over 1,500,000 summer steelhead are released into

this ESU annually (Howell et al. 1985, CBFWA 1990, Delarm and Smith 1990d, Chapman et

al. 1994, WDFW 1994a) (Fig. 16). Beginning in the early 1940s, the wild stocks of

steelhead in this ESU were thoroughly mixed as a result of the Grand Coulee Fish

Maintenance Project, enacted to salvage fish runs blocked by the construction of Grand

Coulee Dam (Fish and Hanavan 1948, Mullan et al. 1992). All steelhead, including those

destined for Canadian streams, were collected at Rock Island Dam and distributed to streams

in this region. In addition, some of the mixture of returning adults were used to establish the

hatchery stocks used in this region (Fish and Hanavan 1948, Mullan et al. 1992). As a result,

the stocks in this ESU have essentially been homogenized since that time. The progeny of

hatchery broodstock collected at a few locations in the upper Columbia River continue to be

released throughout the region (Chapman et al. 1994).

15) Snake River Basin—Artificial propagation of steelhead within the rivers

occupied by the Snake River Basin ESU produces annual releases in excess of 10 million

smolts (Howell et al. 1985, CBFWA 1990, Delarm and Smith 1990a-d, ODFW 1994c,

WDFW 1994a) (Fig. 17). Hatcheries in this area are operated by the states of Washington,

Idaho, and Oregon, as well as the U.S. Fish and Wildlife Service. Most of the stocks used in

these hatcheries are from within the ESU; however, there has been substantial mixing of

these stocks among facilities. Several propagation facilities are operated to mitigate two

series of dams on the Snake River.

The Lower Snake River Compensation Plan (LSRCP) was developed to mitigate

fishery losses due to four dams on the lower Snake River (Ice Harbor, Lower Monumental,

Little Goose, and Lower Granite Dams). The LSRCP steelhead facilities include Dworshak

and Hagerman NFHs, and Clearwater, Sawtooth, and Magic Valley Hatcheries.
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The Hells Canyon Complex forms the second series of dams (Hells Canyon, Oxbow,

and Brownlee Dams); these block anadromous fish passage to the upper Snake River Basin.

Steelhead mitigation facilities for the Hells Canyon Complex include Oxbow, Pahsimeroi,

and Niagara Springs Steelhead Hatcheries. One goal of the Hells Canyon Complex

mitigation was to relocate part of the upper Snake River steelhead run to the Salmon River.

To accomplish this, steelhead broodstock are collected at Hells Canyon Dam, spawned at

Oxbow Hatchery, and the fertilized eggs are transferred to rearing facilities, such as Niagara

Springs Steelhead Hatchery (Hutchison 1993). These steelhead are subsequently released as

smolts at various locations within the Salmon River Basin, primarily near Sawtooth and

Pahsimeroi Hatcheries (Hutchison 1993, Kiefer16). These activities resulted in the

development of the “Pahsimeroi stock,” which was originally composed of indigenous

Salmon River Basin steelhead combined with upper Snake River steelhead. This Pahsimeroi

stock was also used to start the steelhead program at Sawtooth Hatchery. In recent years,

wild steelhead have been passed above Pahsimeroi and Sawtooth Hatcheries, and only

hatchery-origin fish have been used for broodstock.

Within the Snake River Basin, Dworshak NFH and Clearwater Hatchery appear to be

the only facilities that have not incorporated out-of-basin steelhead into their broodstock.

ASSESSMENT OF EXTINCTION RISK

Background

As outlined in the Introduction above, NMFS considers a variety of information in

evaluating the level of risk facing an ESU. Aspects of several of these risk considerations are

common to all west coast steelhead ESUs. These are discussed in general below; more

specific discussion of factors for each of the 14 ESUs under consideration here can be found

in the following sections. The status of the Klamath Mountains Province ESU (ESU 7), has

already been considered (Busby et al. 1994), and is referred to here only for comparison.

Absolute Numbers

The absolute number of individuals in a population is important in assessing two

aspects of extinction risk. First, for small populations that are stable or increasing,

population size can be an indicator of whether the population can sustain itself into the future

in the face of environmental fluctuations and small-population stochasticity; this aspect is

related to the concept of minimum viable populations (MVP) (Gilpin and Soulé 1986,

Thompson 1991). Second, for a declining population, the present abundance is an indicator

of the expected time until the population reaches critically low numbers; this aspect is related

to the concept of “driven extinction” (Caughley 1994).

16 S. Kiefer, Fisheries Staff Biologist, Idaho Department of Fish and Game, 600 South

Walnut, Box 25, Boise, ID 83707-0025. Pers. commun., June 1995.
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In addition to total numbers, the spatial and temporal distribution of adults is

important in assessing risk to an ESU. Spatial distribution is important both at the scale of

river basins within an ESU and at the scale of spawning areas within basins

(“metapopulation” structure). Temporal distribution is important both among years, as an

indicator of the relative health of different brood-year lineages, and within seasons, as an

indicator of the relative abundance of different life history types or runs.

Traditionally, assessment of salmonid populations has focused on the number of

harvestable or reproductive adults, and these measures comprise most of the data available

for Pacific salmon and steelhead. In assessing the future status of a population, the number

of reproductive adults is the most important measure of abundance, and we focussed on

measures of the number of adults escaping to spawn in natural habitat. However, total run

size (spawning escapement + harvest) is also important because it indicates potential

spawning in the absence of harvest. Data on other life history stages (e.g., freshwater smolt

production) can be used as supplemental indicators of abundance.

Because the ESA (and NMFS policy) mandates that we focus on viability of natural

populations, we attempted to distinguish natural fish from hatchery produced fish in this

review. All statistics were based on data that indicated the total number or density of adults

spawning in natural habitat (i.e., “naturally spawning fish”). The total of all naturally

spawning fish (i.e., “total escapement”) is divided into two components (Fig. 18): “Hatchery

produced” fish which are reared as juveniles in a hatchery but return as adults to spawn

naturally; and “natural” fish which are progeny of naturally spawning fish.

Historical Abundance and Carrying Capacity

The relationship of current abundance and habitat capacity to that which existed

historically is an important consideration in evaluating risk. Knowledge of historical

population conditions provides a perspective of the conditions under which present stocks

evolved, as well as the basis for establishing long-term trends in populations. Comparison of

present and past habitat capacity can also indicate long-term population trends and problems

of population fragmentation. The relationship of present abundance to present carrying

capacity is important for understanding the health of populations, but the fact that a

population is near its current capacity does not in itself mean that it is healthy. For a

population that is near capacity, there may be limits to the effectiveness of short-term

management actions in increasing abundance. For such a population, competition and other

interactions between hatchery and natural fish may also be important considerations because

the addition of hatchery fish may further increase population density in a limited habitat.

For steelhead, quantitative abundance estimates are rarely available for periods before

the 1950s. The main exceptions are long-term counts at dams in the Columbia River Basin

and northern California that extend back to the 1930s or 1940s. Quantitative assessments of

habitat are quite rare, although rough estimates of carrying capacity are frequently made for

setting management goals. From the evidence available, it is clear that production of natural

steelhead is now substantially below historical levels for all ESUs considered here, although
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this decline in natural production has been offset to a variable extent by increasing hatchery

production in many areas.

Although no analysis of the proportion of total habitat lost due to blockages has been

attempted by us, there have been significant blockages of freshwater habitat in every ESU.

Freshwater and estuarine habitats are also degraded throughout the entire region considered

here, although the severity of degradation varies among ESUs and is described in the

individual ESU summaries below.

Trends in Abundance

Short- and long-term trends in abundance are a primary indicator of risk in salmonid

populations. Trends may be calculated from a variety of quantitative data, including dam or

weir counts, stream surveys, and catch data. These data sources and methods are discussed

in more detail below, under Approach to Risk Assessment. Regular sampling has not been

conducted for many steelhead populations, and data series are quite short for most of those

populations with sampling data. Where data series were lacking, we inferred general trends

by comparing historical and recent abundance estimates, or by considering trends in habitat

quantity or condition.

The important role of artificial propagation (in the form of hatcheries) for Pacific

salmon and steelhead requires careful consideration in ESA evaluations. Artificial

propagation has implications both for evaluating production trends and for evaluating the

genetic integrity of populations. Waples (1991b) and Hard et al. (1992) discussed the role of

artificial propagation in ESU determinations and emphasized the need to focus on natural

production in a threatened or endangered status determination. To address this need, and

because of the ESA’s emphasis on ecosystem conservation, our analysis focused on naturally

reproducing steelhead. A fundamental question in ESA risk assessments is whether natural

production is sufficient to maintain the population without the continued infusion of

artificially produced fish. A full answer to this question is difficult without extensive studies

of relative production and interactions between hatchery and natural fish. When such

information is lacking, the presence of hatchery fish in natural populations leads to

substantial uncertainty in evaluating the status of a natural population.

One method of approaching this issue is to calculate the natural cohort replacement

ratio, defined as the number of naturally spawning adults that are naturally produced in one

generation divided by the number of naturally spawning adults (regardless of parentage) in

the previous generation. Because data for steelhead are rarely sufficient for this calculation,

we did not attempt to estimate this ratio in this report. However, the ratio can be

approximated from the average population trend if the degree of hatchery contribution to

natural spawning can be estimated (Busby et al. 1994, Appendix B). Where such estimates

were available, the presence of hatchery fish among natural spawners was taken into

consideration in evaluating the sustainability of natural production for individual populations

within the ESUs identified.

Recent coastwide trends in steelhead abundance provided a larger perspective for this

review. Between the 1890s and the 1960s, total U.S. commercial catch of steelhead declined
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sevenfold, but this may reflect restrictions on the fishery more than declines in abundance.

Rough estimates of total coastwide steelhead run size made in 1972 and 1987 were similar

(Sheppard 1972, Light 1987). By all accounts, however, there has been significant

replacement of natural production with hatchery fish. Throughout British Columbia,

Washington, and Oregon, both natural and hatchery steelhead stocks have exhibited recent

decreases in survival, which may be due at least in part to climate and ocean production

(Cooper and Johnson 1992).

Factors Causing Variability

Variations in the freshwater and marine environments is thought to be a primary

factor driving fluctuations in salmonid run size and escapement (Pearcy 1992, Beamish and

Bouillon 1993, Lawson 1993). Changes in ocean condition are discussed below under

Recent Events Affecting Extinction Risk. Habitat degradation and harvest have probably

made stocks less resilient to poor climate conditions, but these effects are not easily

quantifiable.

Threats to Genetic Integrity

In addition to its effect on natural replacement rates, artificial propagation can have a

substantial impact on the genetic integrity of natural salmon and steelhead populations. This

can occur in several ways. First, stock transfers that result in interbreeding of hatchery and

natural fish can lead to loss of fitness in local populations and loss of diversity among

populations. The latter is important to maintaining long-term viability of an ESU because

genetic diversity among salmonid populations helps to buffer overall productivity against

periodic or unpredictable changes in the environment (Riggs 1990, Fagen and Smoker 1989).

Ricker (1972) and Taylor (1991) summarized some of the evidence for local adaptations in

Pacific salmonids that may be at risk from stock transfers.

Second, because a successful salmon or steelhead hatchery dramatically changes the

mortality profile of a population, some level of genetic change relative to the wild population

is inevitable even in hatcheries that use local broodstock (Waples 1991a). These changes are

unlikely to be beneficial to naturally reproducing fish.

Third, even if naturally spawning hatchery fish leave few or no surviving offspring,

they still can have ecological and indirect genetic effects on natural populations. On the

spawning grounds, hatchery fish may interfere with natural production by competing with

natural fish for territory or mates and, if they are successful in spawning with natural fish,

may divert production from more productive natural X natural crosses. The presence of large

numbers of hatchery juveniles or adults may also alter the selective regime faced by natural

fish.

For smaller steelhead stocks (either natural or hatchery), small-population effects

(inbreeding, genetic drift) can also be important concerns for genetic integrity. Inbreeding

and genetic drift are well understood at the theoretical level, and researchers have found

evidence of inbreeding depression in various fish species (Allendorf and Ryman 1987).

Other studies have shown that hatchery practices commonly used with anadromous Pacific
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salmonids have the potential to affect genetic integrity (e.g., Simon et al. 1986, Withler 1988,

Waples and Teel 1990). However, we are not aware of empirical evidence for inbreeding

depression or loss of genetic variability in any natural or hatchery populations of Pacific

salmon or steelhead.

One type of genetic change in hatchery populations—advancement of run timing—is

particularly relevant to west coast steelhead because it is a commonly used management

strategy, particularly in Washington state. The logic behind this strategy is that displacing

the run timing of hatchery fish from that of natural populations will reduce the possibility for

genetic interactions between hatchery and natural fish and will allow for selective harvest of

hatchery fish. For coastal steelhead in Washington, WDFW has provided information

indicating substantial separation in peak run timing between hatchery and natural winter

steelhead, and this pattern may occur in other coastal areas as well. However, run timing

separation is seldom complete, and WDFW has found genetic evidence for substantial

hatchery introgression in several winter steelhead populations (Phelps et al. 1994; see

discussion under Steelhead Genetics, page 37). This issue is discussed further below under

Approach to Risk Assessment (see page 103).

Recent Events Affecting Extinction Risk

A variety of factors, both natural and human-induced, affect the degree of risk facing

salmonid populations. Because of time lags between these events and their effects, as well as

variability within populations, recent changes in any of these factors may affect current risk

without any apparent change in available population statistics. Thus, consideration of these

effects must go beyond examination of recent abundance and trends. Unfortunately,

forecasting future effects is rarely straightforward and usually involves qualitative

evaluations based on informed professional judgement. Events affecting populations may

include natural changes in the environment or human-induced changes, either beneficial or

detrimental. Possible future effects of recent or proposed conservation measures have not

been taken into account in this analysis, but we have considered documented changes in the

natural environment. A key question regarding the role of recent events is, given our

uncertainty regarding the future, how we evaluate the risk that a population may not persist.

Most Pacific salmonid stocks south of British Columbia have been affected by

changes in ocean production that occurred during the 1970s (Pearcy 1992, Lawson 1993).

Cooper and Johnson (1992) described a widespread decline in both natural and hatchery

steelhead production since 1985, extending from British Columbia through Oregon. They

attributed this decline largely to ocean factors but did not identify specific effects. However,

climate conditions are known to have changed recently in the Pacific Northwest and much of

the Pacific coast has also been experiencing drought conditions in recent years, which may

have depressed freshwater production. We do not know whether these climate conditions

represent a long-term shift in conditions which will continue affecting stocks into the future,

or whether they indicate short-term environmental fluctuations which may be reversed in the

near future.
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Other Risk Factors

Other risk factors typically considered for salmonid populations include disease

prevalence, predation, and changes in life history characteristics such as spawning age or

size. We have not found evidence that any of these factors are widespread throughout any

steelhead ESU. Various diseases have been reported as problems in some hatcheries, but we

have found no reports of substantial disease problems in natural steelhead populations.

Bacterial kidney disease, Ceratomyxa shasta, and infectious hematopoietic necrosis

are reported to be problems within steelhead hatcheries in northern California (Foott et al.

1994). Chapman et al. (1994) reported several diseases in Columbia River Basin steelhead

hatcheries. Predation by marine mammals or introduced freshwater fishes is important for

individual populations, as noted in the ESU summaries below.

Approach to Risk Assessment

Previous Assessments

In considering the status of ESUs, we evaluated both qualitative and quantitative

information. Qualitative evaluations included aspects of several of the risk considerations

outlined above, as well as recent, published assessments by agencies or conservation groups

of the status of west coast steelhead stocks (Nehlsen et al. 1991; Higgins et al. 1992;

Nickelson et al. 1992; WDF et al. 1993; USFS 1993a,b; Titus et al. in press). These

evaluations are summarized in Appendix E.

Nehlsen et al. (1991) considered salmonid stocks throughout Washington, Idaho,

Oregon, and California and enumerated all stocks that they found to be extinct or at risk of

extinction. Stocks that did not appear in their summary were excluded either because they

were not at risk of extinction or there was insufficient information to classify them. They

classified stocks as extinct (X), possibly extinct (A+), at high risk of extinction (A), at

moderate risk of extinction (B), or of special concern (C). They considered it likely that

stocks at high risk of extinction have reached the threshold for classification as endangered

under the ESA. Stocks were placed in this category if they had declined from historic levels

and were continuing to decline, or if they had spawning escapements less than 200. Stocks

were classified as at moderate risk of extinction if they had declined from historic levels but

appeared to be stable at a level above 200 spawners. They believed that stocks in this

category had reached the threshold for classification as threatened under the ESA. They

classified a stock as of special concern if a relatively minor disturbance could threaten it, if

insufficient data were available for it, or if it were influenced by large releases of hatchery

fish or possessed some unique character. For steelhead, they classified 98 stocks as follows:

23 extinct, 1 possibly extinct, 27 high risk, 17 moderate risk, and 30 special concern (Table

9).
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Higgins et al. (1992) used the same classification scheme as Nehlsen et al. (1991) but

provided a more detailed review of some northern California salmonid stocks. In this review,

their evaluation is relevant only to the northern California ESU.

Nickelson et al. (1992) rated coastal Oregon (excluding Columbia River Basin)

salmon and steelhead stocks on the basis of their status over the past 20 years. They used the

following classifications: depressed (spawning habitat underseeded, declining trends, or

recent escapements below long-term average), healthy (spawning habitat fully seeded and

stable or increasing trends), or of special concern (300 or fewer spawners or a problem with

hatchery interbreeding). They classified 27 steelhead populations in coastal Oregon as

follows: 21 depressed, 1 special concern, and 5 healthy.

WDF et al. (1993) categorized all salmon and steelhead stocks in Washington on the

basis of stock origin (native, non-native, mixed, or unknown), production type (wild,

composite, or unknown) and status (healthy, depressed, critical, or unknown). Status

categories were defined as follows: healthy, “experiencing production levels consistent with

its available habitat and within the natural variations in survival for the stock;” depressed,

“production is below expected levels ... but above the level where permanent damage to the

stock is likely;” and critical, “experiencing production levels that are so low that permanent

damage to the stock is likely or has already occurred.” Of the 141 steelhead stocks

identified, 36 were classified as healthy, 1 as critical, 44 as depressed, and 60 as unknown.

Most of those classified as unknown are small stocks without large fisheries.

USFS (1993a,b) provided verbal descriptions of the status of steelhead stocks on

Forest Service lands and noted their agreement or disagreement with status designations in

other reviews. In Appendix E, we have grouped their comments into status categories based

on key phrases used in their descriptions: stable or healthy (S); unknown (U); depressed,

declining, low, or moderate risk of extinction (D); critical, high risk of extinction, or severely

depressed (C); extinct (X); and not present (N).

Titus et al. (in press) provided a detailed review of steelhead populations south of San

Francisco Bay, classifying them by categories based on presence or absence of the species

and general trends in abundance. They used special symbols to categorize population status,

as follows: steelhead present, no discernable change from historical levels (X); production

reduced from historical levels, or likely so (<); current presence or absence unknown (?);

extinct (E).

We encountered several problems in applying results of these studies to ESA

evaluations, with a major problem being that the definition of “stock” or “population” varied

considerably in scale among studies, and sometimes among regions within a study.

Identified units range in size from large river basins (e.g., “Sacramento River” in Nehlsen et

al. 1991), to minor coastal streams and tributaries (Titus et al. in press).

A second problem was the definition of categories used to classify stock status. Only

Nehlsen et al. (1991) and Higgins et al. (1992) used categories intended to relate to ESA

“threatened” or “endangered” status, and they applied their own interpretations of these terms
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to individual stocks, not to ESUs as defined here. Nickelson et al. (1992) and WDF et al.

(1993) used general terms describing the status of stocks that could not be directly related to

the considerations important in ESA evaluations. For example, the WDF et al. (1993)

definition of healthy could conceivably include a stock at substantial extinction risk due to

loss of habitat, hatchery fish interactions, or environmental variation (although this does not

appear to be the case for any steelhead stocks).

A third problem is the selection of stocks or populations to include in the review.

Nehlsen et al. (1991) and Higgins et al. (1992) did not evaluate (or even identify) stocks not

perceived to be at risk, so it is difficult to determine the proportion of stocks they considered

to be at risk in any given area. For steelhead, WDF et al. (1993) included only stocks

considered to be substantially wild and included data only for the wild component for

streams that have both hatchery and natural fish escaping to spawn (Johnson17), giving an

incomplete evaluation of steelhead utilizing natural habitat.

Data Evaluations

Quantitative evaluations of data included comparisons of current and historical

abundance of steelhead and calculation of recent trends in escapement and the proportion of

natural spawning attributable to hatchery fish. Historical abundance information for these

ESUs is largely anecdotal. Time series data are available for many populations, but data

extent and quality varied among ESUs. We compiled and analyzed this information to

provide several summary statistics of natural spawning abundance, including (where

available) recent total spawning run size and escapement, percent annual change in total

escapement, recent naturally produced spawning run size and escapement, and average

percentage of natural spawners that were of hatchery origin.

Although this evaluation used the best data available, it should be recognized that

there are a number of limitations to these data, and not all summary statistics were available

for all populations. For example, spawner abundance was generally not measured directly;

rather, it often had to be estimated from catch (which itself may not always have been

measured accurately) or from limited survey data. In many cases, there were also limited

data to separate hatchery production from natural production.

Data types—Quantitative assessments were based on historical and recent run-size

estimates and time series of freshwater spawner and juvenile survey data, harvest rate

estimates, and counts of adults migrating past dams. We considered this information

separately for each ESU. Because of the disparity of data sources and quality for the

different ESUs, data sources and analyses are described separately for each ESU.

Information on stock abundance was compiled from a variety of state, federal, and tribal

agency records. We believe these records to be complete in terms of existing long-term adult

abundance information for steelhead in the region covered. Principal data sources were

17 T. Johnson, Washington Department of Fish and Wildlife, 283236 Hwy. 101, Port

Townsend, WA 98368. Pers. commun., March 1995.
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angler catch estimates, dam or weir counts, and stream surveys. None of these sources

provided a complete measure of adult spawner abundance for any of the streams; specific

problems are discussed below for each data type.

Sport harvest information was the main abundance data available for most Oregon

coastal populations. In 1952, Oregon instituted a punchcard system to record all salmon and

steelhead caught by species. There are a variety of problems in interpreting abundance trends

from sport harvest data; these are discussed in detail in the Oregon Coast ESU section below.

Counts of adult steelhead at dams and weirs are available from several river basins

along the coast. These counts are probably the most accurate estimates available of total

spawning run abundance, but often represent only small portions of the total population in

each river basin. As with angler catches, these counts typically represent a combination of

hatchery produced and natural fish, and thus are not a direct index of natural population

trends.

Stream surveys for steelhead spawning abundance have been conducted by various

agencies within most of the ESUs considered here. The methods and time spans of the

surveys vary considerably among regions, so it is difficult to assess their general reliability as

population indices. However, for most streams where these surveys were conducted, they are

the best local indication we have of population trends.

Computed statistics—To represent current run size or escapement where recent data

were available, we computed the geometric mean of the most recent 5 years reported (or

fewer years if data series is shorter than 5 years). We tried to use only estimates that reflect

the total abundance for an entire river basin or tributary, avoiding index counts or dam counts

that represent only a small portion of available habitat. For Oregon angler catch data for

coastal streams, catch was expanded to total run size and escapement (run size minus catch)

using the methods and harvest rate estimates of Kenaston (1989). For the inland streams, we

had no estimates of harvest rate to do this expansion. To avoid some local bias problems in

areas with few anglers, catch data were used only for streams with an average catch greater

than 100 steelhead per year. Where time-series data were not available, we relied on recent

estimates from state agency reports; time periods included in such estimates varied

considerably.

Where adequate data were available, trends in total escapement (or run size if

escapement data were not available) were calculated for all data sets with more than 5 years

of data, based on total escapement or an escapement index (such as fish per mile from a

stream survey). As an indication of overall steelhead population trends in individual streams,

we calculated average (over the available data series) percent annual change in adult spawner

indices within each river basin. Trends were calculated as the slope (a) of the regression of

ln(abundance) against years, corresponding to the biological model N(t) = b·eat, where b is

abundance at time t=0. Slopes significantly different from zero (P<0.05) were noted. The

regressions provided direct estimates of mean instantaneous rates of population change (a);

these values were subsequently converted to percent annual change, calculated as 100·(ea - 1).
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No attempt was made to account for the influence of hatchery produced fish on these

estimates, so the estimated trends include any supplementation effect of hatchery fish.

Percentages of hatchery fish in spawning escapements were computed from 5-year

geometric means of hatchery and natural escapement data where estimates of both were

available. In most cases, however, we had to rely on recent estimates from state agencies.

The time span and methods used in such estimates were often not reported, so the reliability

of many of these estimates is unknown. For many Washington winter steelhead populations,

we were able to calculate this percentage from WDFW steelhead inventory tables (WDFW

1994b) which provided estimates of both natural (late-run) and hatchery (early-run) spawner

abundance. In Oregon, the main source for hatchery percentage estimates was the ODFW

1992 Wild Fish Management Policy report (Chilcote et al. 1992). Many of the estimates in

that report were based on scale analysis of fish sampled from angler catches, and thus

probably overestimate the proportion of hatchery fish actually spawning because the sport

fishery selects for a higher proportion of hatchery fish in many areas. ODFW (1995a,b) has

provided improved estimates for several stocks, which we used where available.

Run timing—An issue that may play a significant role in determining the nature and

extent of interactions between hatchery and wild steelhead is separation of run timing. It is

common for hatchery stocks of steelhead to return and spawn several weeks or months earlier

than the natural populations they were derived from. This can occur either through selection

for early returning adults in broodstock collection, or through faster growth and higher

survival in the hatchery of progeny from early spawning fish. Earlier spawning for hatchery

steelhead has at least two advantages from a fishery management perspective. First, the

longer growth period makes it easier to produce hatchery fish that smolt in 1 year. Second,

separation of spawn timing for natural and hatchery fish provides an opportunity to maximize

harvest of hatchery fish while minimizing impacts on natural populations. Because winter

steelhead generally spawn later than summer steelhead, winter steelhead provide the greatest

opportunity for advancement of run and spawn timing in the hatchery.

State agencies in Washington and Oregon have adopted somewhat different

approaches to the issue of run timing in hatchery steelhead. The Washington Department of

Fisheries and Wildlife has intentionally developed early spawning hatchery stocks of winter

steelhead for planting into coastal and lower Columbia River drainages. The early run timing

is meant to accomplish two major objectives: provide an opportunity for high harvest rates

on early returning hatchery fish without undue risk to wild fish, and minimize opportunities

for interbreeding between naturally spawning hatchery fish and wild fish.

In contrast, the Oregon Department of Fish and Wildlife has not vigorously promoted

altered run timing in their hatchery steelhead stocks. Although steelhead from Oregon

coastal hatcheries commonly return and spawn somewhat earlier than their natural

counterparts, the timing difference is not generally as great as in Washington. It should be

noted, however, that WDFW generally uses only a few regional donor stocks (Chambers

Creek and Skamania throughout Western Washington; Elochoman, Cowlitz and Skamania in

the Lower Columbia River; Wells in the Upper Columbia River), so that stock transfers from

a few regional hatcheries provide advanced-run stock to a multitude of rivers. On the other
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hand, ODFW, although relying on some regional donor stocks, also maintains many

individual hatchery populations that are indigenous to the river into which they are planted

(e.g., North Umpqua, Chetco, Deschutes, Clackamas Rivers). Therefore, advanced-run fish

have not been distributed throughout the Oregon state hatchery system as extensively as have

those in Washington.

In reviewing the status of individual ESUs of west coast steelhead, we considered the

risks posed by artificial propagation to be important, particularly in combination with other

risk factors indicating declines in abundance. Information submitted to the ESA

Administrative Record for West Coast Steelhead indicates that, in general, the current

WDFW policy to encourage run and spawn time separation between hatchery and natural

winter steelhead and to maintain very high (80-90%) harvest rates on hatchery steelhead has

resulted in less overlap on the natural spawning grounds than is the case for winter steelhead

in Oregon. This factor was a consideration in the BRT’s conclusions that some of the ESUs

for coastal steelhead in Washington state are not at risk of extinction or endangerment (see

below). However, BRT conclusions on this issue should be regarded as preliminary because

information about the degree of interactions that actually occur between hatchery and natural

fish is still incomplete.

Furthermore, although the WDFW strategy may be effective in reducing opportunities

for direct interactions between hatchery and natural steelhead adults, those genetic and

ecological interactions that do occur may be more deleterious to the natural population. A

considerable body of evidence indicates that run and spawn timing in salmonids can have a

strong genetic component, and it is not likely that substantially altered spawn timing would

be advantageous to the natural population in the long term. In the short term, juvenile

progeny of early spawning hatchery fish that do survive will be larger and may outcompete

their natural counterparts. In addition, high harvest rates focused on hatchery fish may

eliminate early natural spawners, resulting in a selective shift in natural run timing.

Analysis of Biological Information

Coastal Steelhead ESUs

1) Puget Sound—Previous assessments of steelhead within the range of this ESU

have identified several stocks as being at risk or of concern. Nehlsen et al. (1991) identified

nine stocks as at some degree of risk or concern (Table 9). WDF et al. (1993) considered 53

stocks within the ESU, of which 31 were considered to be of native origin and predominantly

natural production. Their assessment of these 31 stocks was 11 healthy, 3 depressed, 1

critical, and 16 unknown. Their assessment of the remaining (not native/natural) stocks was

3 healthy, 11 depressed, and 8 unknown (Appendix E).

No estimates of historical (pre-1960s) abundance specific to the Puget Sound ESU are

available. Total run size for Puget Sound in the early 1980s can be calculated from estimates

in Light (1987) as approximately 100,000 winter steelhead and 20,000 summer steelhead.

Light provided no estimate of hatchery proportions specific to Puget Sound streams, but for
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Puget Sound and coastal Washington combined, he estimated that 70% of steelhead in ocean

runs were of hatchery origin. The percentage in escapement to spawning grounds would be

substantially lower due to differential harvest and hatchery rack returns.

Recent 5-year average natural escapements for streams with adequate data range from

less than 100 to 7,200, with corresponding total run sizes of 550-19,800 (Table 10). Total

recent run size for major stocks in this ESU was greater than 45,000, with total natural

escapement of about 22,000. The geographic distribution of escapement is illustrated in

Figure 19.

There are substantial habitat blockages by dams in the Skagit and Elwha River

Basins, and minor blockages, for example, impassable culverts, throughout the region. The

Washington State salmon and steelhead stock inventory (SASSI) (WDF et al. 1993)

appendices note habitat problems, including flooding, unstable soils, and poor land

management practices, for most stocks in this region. In general, habitat has been degraded

from its pristine condition, and this trend is likely to continue with further population growth

and resultant urbanization in the Puget Sound region. Because of their limited distribution in

upper tributaries, summer steelhead appear to be at more risk from habitat degradation than

are winter steelhead.

Of the 21 independent stocks for which we had adequate adult escapement

information to compute trends (Appendix E), 17 have been declining and 4 increasing during

the available data series, with a range from 18% annual decline (Lake Washington winter

steelhead) to 7% annual increase (Skykomish River winter steelhead). Eleven of these trends

(9 negative, 2 positive) were significantly different from zero. Note that these trends are for

the late run wild component of winter steelhead populations; no adult trend data are available

for summer steelhead. In addition, most of these trends are based on relatively short data

series and may be influenced by recent climate conditions. The two basins producing the

largest numbers of steelhead (Skagit and Snohomish Rivers) both have overall upward

trends. Trends for individual river basins are summarized in Table 10 and Figure 20.

Hatchery fish are widespread, spawn naturally throughout the Puget Sound region,

and are largely derived from a single stock (Chambers Creek). The proportion of spawning

escapement comprised of hatchery fish ranged from less than 1% (Nisqually River) to 51%

(Morse Creek). In general, hatchery proportions are higher in Hood Canal and the Strait of

Juan de Fuca than in Puget Sound proper (Table 10). Most hatchery fish in this region

originated from stocks indigenous to the ESU, but they are generally not native to their local

river basins. WDFW has provided information supporting substantial temporal separation

between hatchery and natural winter steelhead in this region. Given the lack of strong trends

in abundance for the major stocks and the apparent limited contribution of hatchery fish to

production of the late-run winter stocks, most winter steelhead stocks in the Puget Sound

ESU appear to be naturally self-sustaining at this time. However, there are clearly isolated

problems with sustainability of some steelhead runs in this ESU, notably with Deer Creek

summer steelhead (although juvenile abundance for this stock increased in 1994) and with

Lake Washington winter steelhead. Summer steelhead stocks within this ESU are all small,

occupy limited habitat, and in most cases are subject to introgression by hatchery fish. While
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there are few data to assess the status of these summer runs, there is cause for concern

regarding their sustainability.

At present, the major threat to genetic integrity for Puget Sound steelhead comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section.

2) Olympic Peninsula—Previous assessments of stocks within this ESU have not

identified any stocks as being at risk or of special concern. Nehlsen et al. (1991) identified

no stocks as at risk (Table 9). WDF et al. (1993) considered 31 stocks within the ESU, of

which 23 were considered to be of native origin and predominantly natural production. The

status of these 23 stocks was assessed as 11 healthy and 12 unknown, while the status of the

eight remaining (not native/natural) stocks was two healthy and six unknown (Appendix E).

No estimates of historical (pre-1960s) abundance specific to the Olympic Peninsula

ESU are available. Total run size for the major stocks in the Olympic Peninsula ESU during

the early 1980s was calculated from estimates in Light (1987) as approximately 60,000

winter steelhead. Light provided no estimate of hatchery proportion in these streams, but for

Puget Sound and coastal Washington together, he estimated that 70% of steelhead were of

hatchery origin. Recent 5-year average natural escapements for streams with adequate data

range from 250 to 6,900, with corresponding total run sizes of 450-19,700 (Table 11,

Appendix E). Total recent (1989-93 average) run size for major streams in this ESU was

approximately 54,000, with a natural escapement of 20,000 fish. The geographic distribution

of this escapement is illustrated in Figure 19.

No major habitat blockages are known for these streams, but minor blockages (such

as impassable culverts) are likely throughout the region. SASSI appendices (WDF et al.

1993) note freshwater habitat problems largely relating to poor land management practices,

and recent poor ocean productivity affecting most stocks in this region. Clearcut logging has

been extensive throughout most watersheds in this area, with the exception of the upper

reaches of the larger rivers that drain Olympic National Park. Because of their limited

distribution in upper tributaries, summer steelhead appear to be at more risk from habitat

degradation than winter steelhead.

Of the 12 independent stocks for which we had adequate adult escapement

information to compute trends (Appendix E), 7 have been declining and 5 increasing during

the available data series, with a range from 8% annual decline to 14% annual increase. Three

of the downward trends were significantly different from zero, but three of the four river

basins producing the largest numbers of natural fish have upward trends in basinwide total

numbers (Table 11, Fig. 20). Note that these trends are all for winter steelhead populations;

no adult trend data are available for summer steelhead.

Hatchery fish are widespread and escaping to spawn naturally throughout the region,

with hatchery production largely derived from a few parent stocks. Estimated proportions of

hatchery fish in natural spawning habitat range from 16% (Quillayute River) to 44%

(Quinault River). However, the two largest producers of natural fish (Quillayute and Queets
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Rivers) had the lowest proportions. WDFW has provided information supporting substantial

temporal separation between hatchery and natural winter steelhead in this region. Given the

lack of strong trends in abundance and the apparent limited contribution of hatchery fish to

production of the late-run winter stocks, most winter steelhead stocks in the Olympic

Peninsula ESU appear to be naturally sustaining at this time. However, there are clearly

isolated problems with sustainability of some winter steelhead runs in this ESU, notably the

Pysht/Independents stock, which has a small population with a strongly declining trend over

the available data series (even though it has been exceeding harvest management goals

recently), and the Quinault River stock, which has a declining trend and substantial hatchery

contribution to natural spawning.

At present, the major threat to genetic integrity for Olympic Peninsula steelhead

comes from past and present hatchery practices. Risk factors relating to these hatchery

practices were discussed previously in the Background section.

3) Southwest Washington—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified three

stock groups as at risk or of concern: moderate risk for small Columbia River tributaries and

special concern for the Grays and Elochoman Rivers (Table 9). WDF et al. (1993)

considered 22 stocks within the ESU, of which 19 were considered to be of native origin and

predominantly natural production. The status of these 19 stocks was 6 healthy, 6 depressed,

and 7 unknown. The status of the remaining three stocks (not native/natural or unknown

origin) was one healthy, one depressed, and one unknown. Most healthy stocks were in

tributaries to Grays Harbor, and most depressed stocks were in lower Columbia River

tributaries (Appendix E).

No estimates of historical (pre-1960s) abundance specific to this ESU are available.

Recent 5-year average natural escapements in individual tributaries with adequate data range

from 150 to 2,300, with the Chehalis River and its tributaries representing the bulk of

production (Appendix E). Total recent (5-year average) natural escapement for major

streams in this ESU was approximately 13,000 (Table 12). The geographic distribution of

escapement is illustrated in Figure 19.

No major habitat blockages are known for these streams, but minor blockages (such

as impassable culverts) are likely throughout the region. Habitat problems for most stocks in

this ESU are similar to those in adjacent coastal ESUs. Clearcut logging has been extensive

throughout most watersheds in this area. Because of their limited distribution in upper

tributaries, summer steelhead appear to be at more risk from habitat degradation than are

winter steelhead.

All but one (Wynoochee River) of the 12 independent stocks for which we had

adequate adult escapement information to compute trends (Appendix E) have been declining

during the available data series, with a range from 7% annual decline to 0.4% annual

increase. Six of the downward trends were significantly different from zero. However, most

of the data series used for trend calculations were short, beginning in the mid-1980s; thus, the

trends may largely reflect the effects of recent climate conditions.
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For Washington streams, these trends are for the late run wild component of winter

steelhead populations; Oregon data included all stock components. Most of the Oregon

trends are based on angler catch data, and so may not reflect trends in underlying population

abundance (see discussion for the Oregon Coast ESU). In general, stock condition appears to

be healthier in southwest Washington than in the lower Columbia River Basin (Appendix E).

Trends for individual river basins are summarized in Table 12 and Figure 20.

Hatchery fish, largely from parent stocks outside the ESU, are widespread and

escaping to spawn naturally throughout the region. This could substantially change the

genetic composition of the resource despite management efforts to minimize introgression of

the hatchery gene pool into natural populations. Estimates of proportion of hatchery fish on

natural spawning grounds range from 9% in the Chehalis River, the largest producer of

steelhead in the ESU, to 82% in the Clatskanie River. WDFW has provided information

supporting substantial temporal separation between hatchery and natural winter steelhead in

this region. However, some Washington stocks (notably lower Columbia River tributaries—

Table 12) appear to have received substantial hatchery contributions to their wild spawning

components, and Nehlsen et al. (1991) identified two stocks in this ESU as of special concern

due to hatchery influence (Table 9).

The preponderance of negative trends in abundance, the contribution of non-native

hatchery fish to production, and the poor condition of stocks in lower Columbia River

tributaries are causes for concern for the future of this ESU.

Again the major present threat to genetic integrity for steelhead in this ESU comes

from past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section.

4) Lower Columbia River—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified 19

stocks as at risk or of concern (Table 9). WDF et al. (1993) considered 23 stocks within the

ESU, of which 19 were considered to be of native origin and predominantly natural

production. The status of these 19 stocks was 2 healthy, 10 depressed, and 7 unknown. All

four of the remaining (not native/natural or unknown origin) stocks were classified as

depressed.

No estimates of historical (pre-1960s) abundance specific to this ESU are available.

Total run size for the major stocks in the lower Columbia River (below Bonneville Dam,

including the upper Willamette ESU) for the early 1980s can be calculated from the estimates

of Light (1987) as approximately 150,000 winter steelhead and 80,000 summer steelhead.

Light estimated that 75% of the total run (summer and winter steelhead combined) was of

hatchery origin. Recent 5-year average natural escapements for streams with adequate data

range from less than 100 to 1,100 (Table 13, Appendix E). Total recent (5-year average) run

size for major streams in this ESU was greater than 16,000, but this total includes only the

few basins for which estimates are available. The geographic distribution of escapement is

illustrated in Figure 19.
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Significant habitat blockages resulted from dams on the Sandy River, and

minor blockages (such as impassable culverts) are likely throughout the region. Habitat

problems for most stocks in this ESU are similar to those in adjacent coastal ESUs. Clearcut

logging has been extensive throughout most watersheds in this area, and urbanization is a

substantial concern in the Portland and Vancouver areas. Because of their limited

distribution in upper tributaries, summer steelhead appear to be at more risk from habitat

degradation than are winter steelhead.

Of the 18 stocks for which we had adequate adult escapement information to compute

trends (Appendix E), 11 have been declining and 7 increasing during the available data

series, with a range from 24% annual decline to 48% annual increase. Eight of these trends

(five negative, three positive) were significantly different from zero. Most of the data series

for this ESU are short, beginning only in the late 1970s to the mid-1980s; thus they may be

heavily influenced by short-term climate effects. Some of the Washington trends (notably

those for the Cowlitz and Kalama River Basins) have been influenced (positively or

negatively) by the 1980 eruption of Mount St. Helens; we have not attempted to correct for

this here. For Washington streams, these trends are for the late run wild component of winter

steelhead populations; Oregon data included all stock components. Most of the Oregon

trends are based on angler catch, and so they may not reflect trends in underlying population

abundance—see discussion under the Oregon Coast ESU. Trends for individual river basins

are summarized in Table 13 and Figure 20.

Hatchery fish are widespread and escaping to spawn naturally throughout the region.

Most of the hatchery stocks used originated primarily from stocks within the ESU, but many

are not native to local river basins. WDFW has provided information supporting substantial

temporal separation between hatchery and natural winter steelhead in this region; however,

some Washington stocks (notably Kalama River winter and summer steelhead—Appendix E)

appear to have substantial hatchery contribution to wild spawning, and Nehlsen et al. (1991)

identified several stocks in this ESU as of special concern due to hatchery influence

(Table 9). ODFW estimates of hatchery composition indicate a range from about 30%

(Sandy River and Tanner Creek winter steelhead) to 80% (Hood River summer steelhead)

hatchery fish in spawning escapements. Estimates for Hood River winter steelhead range

from 0% (ODFW 1995b) to greater than 40% (ODFW 1995a). Given the relatively low

natural run sizes to individual streams, the preponderance of negative trends in abundance,

and the apparent substantial contribution of hatchery fish to production, the BRT had

substantial concern that the majority of natural steelhead populations in this ESU (both

winter and summer) may not be self-sustaining.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed under Background above.

5) Upper Willamette River—The only previous assessment of risk to stocks within

this ESU is that of Nehlsen et al. (1991), who identified one stock (Calapooia River) as of

special concern (Table 9).
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No estimates of historical (pre-1960s) abundance specific to this ESU are available.

Total recent 5-year average run size for this ESU can be estimated from counts at Willamette

Falls for the years 1989-93. Dam counts indicate that the late-run (native) winter steelhead

average run size was approximately 4,200, while early-run winter and summer steelhead

averaged 1,900 and 9,700, respectively (Table 14, Fig. 21, Appendix E). Only the late-run

winter steelhead are included in this ESU; other runs are mentioned because of their possible

ecological interactions with the native stock. Adequate angler catch data were available to

derive approximate average winter steelhead escapement for three tributaries: Mollala River,

2,300 (predominantly non-native); North Fork Santiam River, 2,000; South Fork Santiam

River, 550.

Substantial habitat blockages resulted from Detroit, Big Cliff and Green Peter Dams

on the Santiam River, and flood control dams on the mainstem Willamette. Other blockages

such as smaller dams or impassable culverts are likely throughout the region. Habitat

problems for most stocks in this ESU are similar to those in adjacent coastal ESUs. Clearcut

logging has been common throughout most watersheds in this area, and there is extensive

urbanization in the Willamette Valley. Bottom et al. (1985) identified specific factors

affecting salmon habitat in various areas of Oregon, including streamflow and temperature

problems, riparian habitat losses, and instream habitat problems. Within the Willamette

Valley, they noted that temperatures and streamflows reach critical levels for salmonids in

places where there are significant water withdrawals or removal of streamside vegetation,

that loss of riparian vegetation results from agricultural practices and rural and urban

development, that bank erosion is severe in several areas of the basin, and that splash dams,

debris removal and stream channelization have caused long-term damage to salmonid

habitats.

Total basin run size or escapement estimates exhibit declines for both total winter and

late winter steelhead, while summer steelhead estimates exhibit an increase (Table 14,

Fig. 22). However, all of these basinwide estimates have exhibited large fluctuations

(Fig. 23). Of the three tributary winter steelhead stocks for which we had adequate adult

escapement information to compute trends, two have been declining and one increasing over

the available data series, with a range from 4.9% annual decline to 2.4% annual increase.

None of these trends were significantly different from zero (Table 14, Appendix E). Note

that two of these trends, those from the North and South Forks of the Santiam River, are

based on angler catch, and so may not reflect trends in underlying population abundance—

see discussion for the Oregon Coast ESU.

Hatchery fish are widespread throughout the region. Both summer steelhead and

early-run winter steelhead have been introduced to the basin and escape to spawn naturally in

substantial numbers. Indigenous late-run winter steelhead are also produced in the Santiam

River Basin. Estimates of hatchery composition for winter steelhead escapements are

available only for the North Fork Santiam River and the Mollala River. These estimates are

variable, ranging from 14% (ODFW 1995b) to 54% (ODFW 1995a) on the North Fork

Santiam River alone. There is probably some temporal and spatial separation in spawning

between the early and late winter stocks. While we have little information on the actual

contribution of hatchery fish to natural production, given the generally low numbers of fish

escaping to tributaries and the general declines in winter steelhead abundance in the basin,
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the BRT had substantial concern that the majority of natural winter steelhead populations in

this ESU may not be self-sustaining. All summer steelhead within the range of this ESU are

introduced from outside the area, so are not considered as contributing to natural production

of the ESU. Natural reproduction by these introduced summer steelhead may be quite

limited.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. While there is some separation in run timing between

hatchery and wild winter steelhead, there appears to be sufficient overlap in spawn timing for

some genetic introgression from nonlocal hatchery stocks to occur. An additional effect of

hatchery production may be directional selection within the natural stocks resulting both

from competition with hatchery fish (both winter and summer) and selective fishing pressure

that eliminates individuals with early run timing from the natural stocks. Other risk factors

relating to hatchery practices were discussed previously in the Background section.

6) Oregon Coast—Previous assessments within this ESU have identified several

stocks as being at risk or of special concern. Nehlsen et al. (1991) identified 12 stocks as

extinct, at risk, or of special concern (Table 9). Most of the stocks of special concern were

classified as such due to hatchery practices. ODFW (Nickelson et al. 1992) considered 21

stocks within the ESU, of which 3, North Umpqua River summer and winter steelhead and

Coquille River winter steelhead, were identified as healthy, 17 as depressed, and 1

(Necanicum River) of special concern.

No estimates of historical (pre-1960s) abundance specific to this ESU are available,

except for counts at Winchester Dam on the North Umpqua River which began in 1946, and

angler catch records which began in 1953. Early angler catch summaries did not distinguish

summer and winter steelhead and were not corrected for nonreporting bias, so these have not

been relied on in this review. Estimated total run size for the major stocks on the Oregon

Coast (including areas south of Cape Blanco) for the early 1980s were given by Light (1987)

as approximately 255,000 winter steelhead and 75,000 summer steelhead. Light estimated

that 69% of winter and 61% of summer steelhead were of hatchery origin, resulting in

naturally produced run sizes of 79,000 winter and 29,000 summer steelhead.

Recent 5-year average total (natural and hatchery) run sizes for streams with adequate

data range from 250 to 15,000, corresponding to escapements from 200 to 12,000 (Table 15,

Appendix E). Total recent (5-year average) run size for major streams in this ESU was

approximately 129,000 (111,000 winter, 18,000 summer), with a total escapement of 96,000

(82,000 winter, 14,000 summer). These totals do not include all streams in the ESU, so they

underestimate total ESU run size and escapements. The geographic distribution of

escapement is illustrated in Figure 21. Run size and escapement estimates are also based

primarily on expansions of angler catch using assumed harvest rates (Kenaston 1989), so

they should be viewed as rough approximations.

Regarding freshwater habitat, several minor blockages from dams are documented,

and other blockages such as impassable culverts are likely throughout the region. Bottom et

al. (1985) identified specific factors affecting salmon habitat in various areas of Oregon,
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including streamflow and temperature problems, riparian habitat losses, and instream habitat

problems. They noted that along the Oregon Coast summer temperatures and streamflow

reach critical levels for salmonids in areas where there are significant water withdrawals or

removal of streamside vegetation had occurred. They reported notable temperature problems

in Tillamook Bay tributaries and the Alsea, Siletz, Siuslaw, and Umpqua Rivers. Bottom

et al. (1995) also found that loss of riparian vegetation has resulted from agricultural and

forestry practices, and that splash dams, debris removal, and stream channelization had

caused long-term damage to salmonid habitats.

Sport harvest information was the main abundance data available for most Oregon

coastal populations. In 1952, Oregon instituted a punchcard system to record all salmon and

steelhead caught by species. However, methods of estimating and reporting catch changed in

1970, and division of catch statistics among tributaries changed substantially in 1977, so

earlier data are not directly comparable to those since 1977. Our analyses for Oregon river

basins focussed on data collected since those changes (ODFW 1980, 1992, 1993), although

trends from longer-term data have been included for comparison in some basins (Appendix

E).

Interpreting population abundance from angler catch data presents several problems.

First, numbers of fish caught do not directly represent abundance, which must be estimated

by applying assumptions about fishing effort and effectiveness. Fishing effort is largely

determined by socioeconomic factors, including fishery regulations. Fishing effectiveness is

a function of both the skill of the anglers and environmental conditions which affect behavior

of both fish and anglers. Both effort and effectiveness may exhibit long-term trends and

interannual fluctuations that can obscure the relationship between catch and abundance.

Second, estimates of catch may not be accurate. In Oregon, catch is estimated from

returns of punchcards and estimates are corrected for nonreporting bias. While catch

estimates are generated separately for each stream basin, the bias correction is calculated

statewide and may not be accurate for any particular stream due to local variations in the

tendency to return punchcards.

Third, when fishing effort varies across a river basin, catch may reflect only local

abundance rather than the total basin population. However, statewide salmon and steelhead

fishing effort, as indexed by number of punchcards issued, has been relatively constant since

the late 1970s, indicating that angler catch may accurately reflect trends in abundance over

large geographic areas. ODFW (1995b) provided evidence that the relationship of angler

catch to spawner abundance is weak in some basins, although there is generally a positive

correlation. Additionally, fishing effort has been increasingly focused on hatchery fish in

recent years, with wild catch and release regulations imposed in many Oregon coastal

streams in January 1992 (ODFW 1995b). Thus, recent trends may reflect hatchery

production more than natural production throughout the Oregon coast. Trend estimates

reported here include angler catch data through 1992 (Table 15, Appendix E). To test for

bias due to wild catch and release regulations, we also calculated trends excluding the 1991

and 1992 run years. While the resulting estimates were often different for individual basins,
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both upward and downward changes were apparent, and overall patterns were similar to those

obtained by using the full data set.

The following analysis was made with the assumption that catch trends reflect trends

in overall population abundance. We recognize the many problems with this assumption and

that the results may not precisely represent trends in the total population in a river basin.

However, angler catch is the only information available for most of these populations, and

we believe that changes in catch still provide a useful indication of trends in total population

abundance. Where alternate trend data were available, we used those data instead of angler

catch.

Adequate adult escapement information was available to compute trends for 42

independent stocks within this ESU. Of these, 36 stocks exhibited declines and 6 exhibited

increases during the available data series. Trends ranged from a 12% annual decline in Drift

Creek on the Siletz River to a 16% annual increase in North Fork Coquille River. Twenty of

these trends were significantly different from zero with 18 decreasing and 2 increasing

(Appendix E). Upward trends were found only in the southernmost portion of the ESU

(Fig. 22), from Siuslaw Bay south. In contrast, longer term trends in angler catch, using data

from the early 1950s to the present, generally were increasing. This may reflect longer term

stability of populations, or may be an artifact of long-term increases in statewide fishing

effort coupled with the differences in bias correction of catch summaries before and after

1970.

Hatchery fish are widespread and escape to spawn naturally throughout the region.

Most hatchery stocks used in this region originated from stocks indigenous to the ESU, but

many are not native to local river basins. ODFW estimates of hatchery composition for

recent winter steelhead escapements were high in many streams, ranging from 10% in the

North Umpqua River to greater than 80% in Drift Creek on the Alsea River and in Tenmile

Creek south of Umpqua Bay. For summer steelhead, hatchery composition (where reported)

ranged from 38% in the South Umpqua River to 90% in the Siletz River. Several summer

steelhead stocks have been introduced to rivers with no native summer runs.

Overall, approximately half of the stocks in this ESU for which we have information

have hatchery composition in excess of 50%. Few stocks in the region are documented to

have escapements above 1,000 fish and no significant decline (Appendix E); most of those

that do are in the southern portion of the ESU and have high hatchery influence. While we

have little information on the actual contribution of hatchery fish to natural production, given

the substantial presence of hatchery fish in the few stocks that are relatively abundant and

stable or increasing, the BRT had substantial concern that the majority of natural steelhead

populations in this ESU may not be self-sustaining.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section.
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7) Klamath Mountains Province—This ESU has been evaluated previously (Busby

et al. 1994), and is not discussed here.

8) Northern California—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified three

stocks as at risk of extinction: summer steelhead in Redwood Creek, Mad River, and Eel

River (Table 9). Higgins et al. (1992) provided a more detailed analysis of some of these

stocks and identified 11 summer steelhead stocks as at risk or of concern. They did not

evaluate winter steelhead stocks because of insufficient information. The USFS (1993b)

identified most stocks on Forest Service lands in this region as either depressed or critical,

with only the Little Van Duzen River winter steelhead stock identified as stable (Appendix

E).

Estimates of historical (pre-1960s) abundance specific to this ESU were available

(Table 16) from dam counts in the upper Eel River (Cape Horn Dam—annual average of

4,400 adult steelhead in the 1930s; McEwan and Jackson 1996), the South Fork Eel River

(Benbow Dam—annual average of 19,000 adult steelhead in the 1940s; McEwan and

Jackson 1996), and the Mad River (Sweasey Dam—annual average of 3,800 adult steelhead

in the 1940s; Murphy and Shapovalov 1951, CDFG 1994). In the mid-1960s, CDFG (1965,

table S-3) estimates steelhead spawning populations for many rivers in this ESU totaled

198,000 (Table 17). Estimated total run size for the major stocks in California (entire state)

for the early 1980s was given by Light (1987) as approximately 275,000. Of these, 22%

were of hatchery origin, resulting in a naturally produced run size of 215,000 steelhead.

Roughly half of this production was thought to be in the Klamath River Basin (including the

Trinity River), so the total natural production for all ESUs south of Punta Gorda was

probably on the order of 100,000 adults. The only current run-size estimates for this area are

counts at Cape Horn Dam on the Eel River where an average of 115 total and 30 wild adults

were reported (McEwan and Jackson 1996). Summer steelhead snorkel survey data are

available for a few tributaries, but they provide no total abundance estimate. Statewide adult

summer steelhead abundance is estimated at about 2,000 adults (McEwan and Jackson 1996).

Note that estimate apparently refers only to early-summer steelhead entering the rivers in

May, June, and July, not including the more numerous “fall-run” steelhead. While we have

no overall recent abundance estimate for this ESU (Table 18, Fig. 24), the substantial

declines in run size from historic levels at major dams in the region (Table 16) indicate a

probable overall decline in abundance from historical levels.

Two substantial habitat blockages are documented: Mathews Dam on the Mad River

and Scott Dam on the Eel River (McEwan and Jackson 1996), and other minor blockages

(such as impassable culverts) are likely throughout the region. Habitat throughout the north

coast of California was severely impacted by catastrophic flooding in 1964. Damage from

this flood was probably exacerbated by poor land use practices prior to the event (McEwan

and Jackson 1996). Forest practices have also contributed to incremental degradation of

stream habitats (Higgins et al. 1992, McEwan and Jackson 1996). Excessive sedimentation

and unstable spawning gravels are cited as major habitat problems in this region (CDFG

1991, Higgins et al. 1992). Other habitat problems similar to those cited for the Oregon

Coast ESU probably also occur in this region. A high abundance of non-native Sacramento

squawfish (Ptychocheilus grandis) has been reported recently in the Eel River Basin (Brown
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and Moyle 1991, Moyle and Yoshiyama 1992), which would suggest increased risk of

predation for juvenile steelhead.

Adequate adult escapement information was available to compute trends for seven

stocks within this ESU (Table 18, Fig. 25). Of these, five data series exhibit declines and

two exhibit increases during the available data series, with a range from 5.8% annual decline

to 3.5% annual increase. Three of the declining trends were significantly different from zero

(Appendix E). For one long data set (Eel River, Cape Horn Dam counts), a separate trend for

the last 21 years (1971-91) was calculated for comparison: while the full-series trend showed

significant decline, the recent data showed a lesser, nonsignificant decline, suggesting that

the major stock decline occurred prior to 1970.

Hatchery fish are widespread and escaping to spawn naturally throughout the region.

According to McEwan and Jackson (1996, p. 37), “despite the large number of hatchery

smolts released, steelhead runs in north coast drainages are comprised mostly of naturally

produced fish.” We have little information on the actual contribution of hatchery fish to

natural spawning, and little information on present total run sizes for this ESU. However,

given the preponderance of significant negative trends in the available data, there is concern

that steelhead populations in this ESU may not be self-sustaining.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section. Within this ESU, we have no information

regarding spatial or temporal separation of spawning hatchery and natural fish, but there is

probably sufficient overlap for some genetic introgression to occur.

9) Central California Coast—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified two

stock groups as at high risk of extinction: Napa River and San Francisco Bay Tributaries

(Table 9). Titus et al. (in press) provided a more detailed analysis of stocks south of San

Francisco Bay and identified numerous stocks that were declining.

Only two estimates of historical (pre-1960s) abundance specific to this ESU are

available: the first reported an average of about 500 adults in Waddell Creek in the 1930s

and early 1940s (Shapovalov and Taft 1954), and the second estimated 20,000 steelhead in

the San Lorenzo River before 1965 (Johnson 1964) (Table 19). In the mid-1960s, CDFG

(1965, table S-3) estimated 94,000 steelhead spawning in many rivers of this ESU (Table 17).

We have comparable recent estimates for only the Russian and San Lorenzo Rivers, which

contain the two largest stocks in the ESU. Recent total abundance in these two rivers is

estimated to be less than 15% of their abundance 30 years ago (Table 17). Additional recent

estimates are available for several other streams (Table 20, Fig. 26), but we have no recent

estimates for total run size for this ESU.
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McEwan and Jackson (1996) noted that steelhead in most streams tributary to San

Francisco and San Pablo Bays have been extirpated, although small “fair to good” runs of

steelhead reportedly occur in coastal Marin County tributaries (Cox18, Smith19).

Two substantial habitat blockages are documented: Coyote and Warm Springs Dams

in the Russian River Basin (McEwan and Jackson 1996), and other minor blockages (smaller

dams, impassable culverts, etc.) are likely throughout the region Titus et al. (in press)

reported blockages on 12 of 46 tributaries in the southern portion of this ESU, and he noted

fish passage problems in most other tributaries. Streams in this region probably suffer from a

variety of habitat factors, including urbanization and poor land management practices in both

forestry and agriculture.

Habitat throughout the north coast of California, including portions occupied by this

ESU, was severely impacted by catastrophic flooding in 1964. Damage from this flood was

probably exacerbated by poor land use practices prior to the event (McEwan and Jackson

1996). Forest practices have also contributed to incremental degradation of stream habitats

(McEwan and Jackson 1996). Dewatering due to irrigation and urban water diversions is

also a problem. Titus et al. (in press) documented some of these problems for specific

tributaries in the southern portion of this ESU. Other habitat problems similar to those cited

for the Oregon Coast ESU probably also occur in this region.

Adequate adult escapement information was not available to compute trends for any

stocks within this ESU (Table 20, Fig. 27). However, general trends can be inferred from the

comparison of 1960s and 1990s abundance estimates provided above, and these indicate

substantial rates of decline in the two largest steelhead stocks (Russian and San Lorenzo

Rivers).

Presently, the principal hatchery production in this ESU is from Warm Springs

Hatchery on the Russian River and the Monterey Bay Salmon and Trout Project located at

Big Creek Hatchery off Scott Creek and at other facilities. There are other small private and

cooperative programs producing steelhead within the range of this ESU. Most of the

hatchery stocks used in this region originated from stocks indigenous to the ESU, but many

are not native to their local river basins (Bryant 1994).

We have little information on the actual contribution of hatchery fish to natural

spawning, and little information on present total run sizes or trends for this ESU. However,

given the substantial negative trends in the stocks for which we do have data, it is likely that

the majority of natural production in this ESU is not self-sustaining. It appears that most of

the recent declines in steelhead abundance within this ESU have occurred in the larger river

18 B. Cox, California Department of Fish and Game, Region 3, P.O. Box 47, Yountville, CA

94599. Pers. commun., September 1994.

19 J. Smith , Department of Biological Sciences, San Jose State University, San Jose, CA

95192. Pers. commun., September 1994.
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systems, while populations in many smaller streams are relatively healthy and probably have

not experienced significant recent changes in abundance (Cox footnote 18, Smith footnote

19).

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. General risk factors relating to hatchery practices were

discussed previously in the Background section. Within this ESU, we have little information

regarding present hatchery production and no information regarding spatial or temporal

separation of spawning hatchery and natural fish. However, there is probably sufficient

overlap in spawning for some genetic introgression to occur. Habitat fragmentation and

population declines resulting in small, isolated populations also pose genetic risk from

inbreeding, loss of rare alleles, and genetic drift.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We have received insufficient information regarding resident trout in this region to

reasonably evaluate their status or their interactions with anadromous steelhead.

10) South-Central California Coast—Previous assessments within this ESU have

identified several stocks as being at risk or of special concern. Nehlsen et al. (1991)

identified five stocks as at risk (Table 9). Titus et al. (in press) provided a more detailed

analysis of stocks south of San Francisco Bay and identified numerous stocks that were

declining (Appendix E).

Historical estimates of steelhead abundance are available for a few streams in this

region (Table 21). The California Advisory Committee on Salmon and Steelhead (CACSS

1988) cited an estimate of 20,000 steelhead in the Carmel River in 1928. In the mid-1960s,

CDFG (1965, table S-3) estimated 27,750 steelhead spawning in many rivers of this ESU

(Table 17). However, comparisons with recent estimates for these rivers show a substantial

decline during the past 30 years. In contrast to the CDFG (1965) estimates, McEwan and

Jackson (1996) reported runs ranging from 1,000 to 2,000 in the Pajaro River in the early

1960s, and Snider (1983) estimated escapement of about 3,200 steelhead for the Carmel

River for the 1964-75 period.

While we have no recent estimates of total run size for this ESU, recent run-size

estimates are available for five streams (Table 22, Fig. 26). The total of these estimates is

less than 500, compared with a total of 4,750 for the same streams in 1965, which indicates a

substantial decline for the entire ESU from 1965 levels.

Minor habitat blockages (smaller dams, impassable culverts, etc.) are likely

throughout the region. Titus et al (in press) reported blockages on 28 of 66 tributaries in this

ESU, and some passage impairments on most other tributaries. Streams in this region

probably suffer from a variety of habitat factors similar to those affecting neighboring ESUs.

Forest practices have contributed to incremental degradation of stream habitats (McEwan and

Jackson 1996), and dewatering due to irrigation and urban water diversions is also a problem.
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Titus et al. (in press) have documented some of these problems for specific tributaries in the

southern portion of this ESU.

Adequate adult escapement information was available to compute a trend for only one

stock within this ESU: Carmel River above San Clemente Dam (Table 22, Fig. 27). These

data show a significant decline of 22% per year from 1963 to 1993, with a recent 5-year

average count of only 16 adult steelhead at the dam. However, general trends for the region

can be inferred by comparing the 1960s and 1990s abundance estimates provided above.

Presently, there is little hatchery production within this ESU. There are small private

and cooperative programs producing steelhead within this ESU, as well as one captive

broodstock program intended to conserve the Carmel River steelhead strain (McEwan and

Jackson 1996). Most hatchery stocks used in this region originated from stocks indigenous

to the ESU, but many are not native to their local river basins (Bryant 1994). We have little

information on the actual contribution of hatchery fish to natural spawning, and little

information on present total run sizes or trends for this ESU. However, given the substantial

reductions from historical abundance and the recent negative trends in the stocks for which

we do have data, it is likely that the majority of natural production in this ESU is not

self-sustaining.

Past and present hatchery practices probably pose some risk to steelhead in this ESU

as discussed previously in the Background section. Habitat fragmentation and population

declines resulting in small, isolated populations also pose genetic risk from inbreeding, loss

of rare alleles, and genetic drift.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We have received insufficient information regarding resident trout in this region to

reasonably evaluate their status or their interactions with anadromous steelhead.

11) Southern California—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified

11 stocks as extinct and 4 as at high risk (Table 9). Titus et al. (in press) provided a more

detailed analysis of these stocks and identified stocks within 14 drainages in this ESU as

extinct, at risk, or of concern. They identified only two stocks, those in Arroyo Sequit and

Topanga Creek, as showing no significant change in production from historical levels.

Historically, steelhead may have occurred naturally as far south as Baja California.

Estimates of historical (pre-1960s) abundance are available for several rivers in this ESU

(Table 23): Santa Ynez River, before 1950, 20,000-30,000; Ventura River, pre-1960,

4,000-6,000; Santa Clara River, pre-1960, 7,000-9,000; Malibu Creek, pre-1960, 1,000. In

the mid-1960s, CDFG (1965, table S-3) estimated steelhead spawning populations for

smaller tributaries in San Luis Obispo County as 20,000, but they provided no estimates for

streams farther south.
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The present total run sizes for 6 streams in this ESU were summarized by Titus et al.

(in press); all were less than 200 adults (Table 24, Fig. 26). Titus et al. (in press) concluded

that populations have been extirpated from all streams south of Ventura County, with the

exception of Malibu Creek in Los Angeles County. However, steelhead are still occasionally

reported in streams where stocks were identified by these authors as extirpated.

Titus et al. (in press) cited extensive loss of steelhead habitat due to water

development, including impassable dams and dewatering of portions of rivers. They also

reported that of 32 tributaries in this region, 21 have blockages due to dams, and 29 have

impaired mainstem passage. Habitat problems in this ESU relate primarily to water

development resulting in inadequate flows, flow fluctuations, blockages, and entrainment

into diversions (McEwan and Jackson 1996, Titus et al. in press). Other problems related to

land use practices and urbanization also certainly contribute to stock conditions.

No time series of data are available within this ESU from which to estimate

population trends, but Titus et al. (in press) summarized information for steelhead

populations based on historical and recent survey information. Of the populations south of

San Francisco Bay (including part of the Central California Coast ESU) for which past and

recent information was available, they concluded that 20% had no discernible change, 45%

had declined, and 35% were extinct. Percentages for the counties comprising this ESU are

given in Table 25 and show a very high percentage of declining and extinct populations.

There is no current hatchery production of steelhead within this ESU. The small run

sizes and almost universal declines in these populations strongly suggest that natural

production is not self-sustaining.

The influence of hatchery practices on this ESU is not well documented. Common

risk factors relating to hatchery practices were discussed previously in the Background

section. In some populations, there may be genetic introgression from past steelhead plants

and from planting of rainbow trout (Nielsen footnote 9). Habitat fragmentation and

population declines have also resulted in small, isolated populations that may face genetic

risk from inbreeding, loss of rare alleles, and genetic drift.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We do not have sufficient information regarding resident trout in this region to

reasonably evaluate their status or their interactions with anadromous steelhead.

12) Central Valley—Only Nehlsen et al. (1991) have provided a status assessment

for stocks within this ESU; they identified one stock (Sacramento River) as at high risk

(Table 9). However, this stock represents all the known populations of steelhead within the

ESU.

Historical abundance estimates are available for some stocks within this ESU

(Table 26), but no overall estimates are available prior to 1961, when Hallock et al. (1961)

estimated a total run size of 40,000 steelhead in the Sacramento River, including
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San Francisco Bay. In the mid-1960s, CDFG (1965, table S-3) estimated steelhead spawning

populations for the rivers in this ESU, totaling almost 27,000 fish (Table 17).

We have limited data on recent abundance for this ESU (Table 27, Fig. 28), but its

present total run size based on dam counts, hatchery returns, and past spawning surveys is

probably less than 10,000 fish. Both natural and hatchery runs have declined since the

1960s. Counts at Red Bluff Diversion Dam averaged 1,400 fish over the last 5 years,

compared with runs in excess of 10,000 fish in the late 1960s. Recent run-size estimates for

the hatchery produced American River stock average less than 1,000 fish, compared to

12,000-19,000 in the early 1970s (McEwan and Jackson 1996).

Historically, steelhead occurred naturally throughout the Sacramento and San Joaquin

River Basins; however, stocks have been extirpated from large areas of the Sacramento River

Basin and possibly from the entire San Joaquin River Basin. The California Advisory

Committee on Salmon and Steelhead (CACSS 1988) reported a reduction in Central Valley

steelhead habitat from 6,000 miles historically to 300 miles at present. Reynolds et al. (1993,

p. III-1) reported that 95% of salmonid habitat in California’s Central Valley has been lost,

largely due to mining and water development activities. They also noted (p. IV-8) that

declines in Central Valley steelhead stocks are “due mostly to water development, inadequate

instream flows, rapid flow fluctuations, high summer water temperatures in streams

immediately below reservoirs, diversion dams which block access, and entrainment of

juveniles into unscreened or poorly screened diversions.” Thus, overall habitat problems in

this ESU relate primarily to water development resulting in inadequate flows, flow

fluctuations, blockages, and entrainment into diversions (McEwan and Jackson 1996). Other

problems related to land use practices (agriculture and forestry) and urbanization have also

certainly contributed to stock declines.

Adequate adult escapement information was available to compute a trend for only one

stock within this ESU: the Sacramento River population above Red Bluff Diversion Dam

(Table 27, Fig. 29). This data series showed a significant decline of 9% per year from 1966

to 1992 (Table 27, Appendix E). McEwan and Jackson (1996) cite substantial declines in

hatchery returns within the basin as well. Most indigenous natural production of steelhead in

this ESU occurs in upper Sacramento River tributaries (Antelope, Deer, and Mill Creeks)

below Red Bluff Diversion Dam. Fish passing over that dam are primarily of hatchery origin

(70-90%). The American, Feather, and Yuba Rivers, and possibly the upper Sacramento and

Mokelumne Rivers, also have naturally spawning populations (CDFG 1995), but these

populations have had substantial hatchery influence and their ancestry is not clearly known.

The Yuba River had an estimated run size of 2,000 in 1984, and though recent run sizes are

unknown the population appears to be stable and supports a fishery (McEwan and Jackson

1996). However, the status of native, natural fish in this stock is unknown: the stock has

been influenced by Feather River Hatchery fish, and biologists familiar with the stock report

that the Yuba River supports almost no natural production of steelhead (Hallock 1989).

Nevertheless, CDFG (1995) asserted that “a substantial portion of the returning adults are

progeny of naturally spawning adults from the Yuba River.” This stock currently receives no

hatchery steelhead plants and is managed as a naturally sustained population (CDFG 1995,

McEwan and Jackson 1996).
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There are reports of a small remnant steelhead run in the Stanislaus River, steelhead

were observed in the Tuolumne River in 1983, and large rainbow trout (possibly steelhead)

have been observed at Merced River Hatchery recently (McEwan and Jackson 1996). Wild

stocks in Mill, Deer, and Antelope Creeks and other upper Sacramento tributaries may be

native or mostly native, but these populations are nearly extirpated. Given the widespread

recent declines in abundance and the large proportion of hatchery production in the basin as a

whole, natural production in this ESU is unlikely to be self-sustaining.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Common risk factors relating to hatchery practices were

discussed previously in the Background section. We have little information regarding spatial

or temporal separation of spawning hatchery and natural fish within this ESU, but there is

probably sufficient overlap for some genetic introgression to occur. There is also a

substantial problem with straying of hatchery fish within this ESU (Hallock 1989). Habitat

fragmentation and population declines resulting in small, isolated populations also pose

genetic risk from inbreeding, loss of rare alleles, and genetic drift.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We do not have sufficient information regarding resident trout in this region to

reasonably evaluate their status or their interactions with anadromous steelhead.

Inland Steelhead ESUs

13) Middle Columbia River—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified six

stocks as at risk or of concern (Table 9). WDF et al. (1993) considered six stocks within the

ESU, four of which were considered to be of native origin and predominantly natural

production. They considered the status of these four stocks as one depressed and three

unknown. The remaining two stocks were considered depressed.

Estimates of historical (pre-1960s) abundance specific to this ESU are available for

the Yakima River, with an estimated run size of 100,000 (WDF et al. 1993, Appendix 3). If

we assume that other basins had comparable run sizes for their drainage areas, the total

historical run size for this ESU might have been in excess of 300,000. Total run sizes for the

major stocks in the Columbia River above Bonneville Dam, including stocks in the Upper

Columbia River and Snake River Basin ESUs and parts of the Southwest Washington and

Lower Columbia River ESUs, were estimated by Light (1987) as approximately 4,000 winter

steelhead and 210,000 summer steelhead in the early 1980s. Based on dam counts for this

period, the Middle Columbia River ESU represented the majority of this total run estimate,

so the run returning to this ESU was probably somewhat below 200,000 at that time. Light

estimated that the total run (summer and winter steelhead combined) was of 80% hatchery

origin. We have estimated run sizes for this ESU by subtracting adult steelhead counts at

Lower Granite and Priest Rapids Dams from those at Bonneville Dam for the period 1975-93

(Fig. 30). The most recent 5-year average run size was 142,000, with a naturally produced
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component of 39,000. These data indicate approximately 74% hatchery fish in the total run

to this ESU.

We have recent escapement or run size estimates for only the following five basins in

this ESU (Table 28, Fig. 31). 1) For the main Deschutes River (counted at Sherars Falls),

total recent 5-year average run size was approximately 11,000, with a natural escapement of

3,000. Hatchery escapement to spawning grounds, calculated by subtracting Pelton Ladder

and other hatchery returns from the counts at Sherars Falls has averaged about 4,000 adults

over the last five brood years (BPA 1992). 2) For Warm Springs River steelhead passing

above Warm Springs NFH, escapement has averaged 150 adults over the last 5 years. 3) In

the Umatilla River, escapement counted at Three Mile Dam has averaged 1,700 adults over

the last 5 years. 4) In the Yakima River, total escapement has averaged 1,300 adults, with a

natural escapement of 1,200 adults over the last 5 years. 5) ODFW (1995a) suggested that

five subbasins of the John Day River each have runs in excess of 1,000, so the total run size

for the John Day River is probably in excess of 5,000 fish.

The only substantial habitat blockage at present in this ESU is at Pelton Dam on the

Deschutes River, but minor blockages from smaller dams, impassable culverts, etc., are likely

throughout the region. Several dams in the John Day River Basin previously blocked habitat,

but they have since been modified with ladders (CBFWA 1990); however, there is a

possibility that local native stocks were extirpated before these ladders were built.

Bottom et al. (1985) noted that high summer and low winter temperatures are limiting

factors for salmonids in many streams in this region. They noted that flows below

recommended levels occur in the Umatilla and John Day Rivers, that extreme temperature

conditions exist in the lower John Day River, and that water withdrawals and overgrazing

have seriously reduced summer flows in the principal summer steelhead spawning and

rearing tributaries of the Deschutes River. There is little or no late summer flow in sections

of the lower Umatilla and Walla Walla Rivers. Riparian vegetation is heavily impacted by

overgrazing and other agricultural practices, timber harvest, road building, and

channelization. Of stream segments inventoried within this ESU, riparian restoration is

needed for between 37% and 84% of the river bank in various basins. Instream habitat is also

affected by these same factors, as well as by past gold dredging and severe sedimentation due

to poor land management practices.

Stock trend data are available for various basins from dam counts, spawner surveys,

and angler catch. Because the relationship of angler catch to natural stock abundance is

unclear in this region and alternate data were available for most basins, we have not relied on

angler catch data in our evaluations of this ESU; trends in angler catch are included in

Appendix E for comparison. For these evaluations, spawner survey data for individual

tributaries have been aggregated by subbasin to avoid frequent zero counts and to provide

more representative regional trends.

Of the 14 independent stock indices for which we could compute trends (Appendix

E), 10 have been declining and 4 increasing during the available data series, with a range

from 20% annual decline to 14% annual increase (Table 28, Fig. 32). Eight of these trends
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were significantly different from zero, with seven negative and one positive (Appendix E).

Of the major basins, the Yakima, Umatilla, and Deschutes Rivers show upward trends

overall, although all trends in the Deschutes River tributaries are downward and the Yakima

River is recovering from a period of extremely low abundance in the early 1980s. The John

Day River probably represents the largest native, natural spawning stock in the region, and

combined spawner surveys for this basin have been declining at a rate of about 15% per year

since 1985. However, estimates of total run size for the ESU based on differences in counts

at dams (Fig. 30) show an overall increase in steelhead abundance, with a relatively stable

naturally produced component. It is likely that recent trends in most basins have been

negatively affected by recent drought in the region.

Hatchery fish are widespread and escaping to spawn naturally throughout the region.

Hatchery production in this region is derived primarily from within-basin stocks. Recent

estimates of the proportion of natural spawners that are of hatchery origin (Table 28,

Appendix E) range from low in the Yakima, Walla Walla, and John Day Rivers, to moderate

in the Umatilla and Deschutes Rivers. However, we have little information on the actual

contribution of hatchery production to natural spawning. The relatively low natural run sizes

in individual streams for which we have estimates, the preponderance of negative trends in

abundance, and the widespread presence of hatchery fish lead to concern that some natural

steelhead populations in this ESU may not be self-sustaining. There is particular concern that

Yakima River steelhead and winter steelhead stocks in the Klickitat River and Fifteenmile

Creek may be at risk.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We have insufficient information regarding resident trout in this region to reasonably

evaluate their status or their interactions with anadromous steelhead.

14) Upper Columbia River—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified six

stocks as at risk or of concern (Table 9). WDF et al. (1993) assessed three stocks within the

ESU, of which all were considered to be of mixed origin, wild production, and depressed.

WDF et al. considered only the wild component of mixed stocks in reaching their

conclusions.

Estimates of historical (pre-1960s) abundance specific to this ESU are available from

fish counts at dams. Counts at Rock Island Dam from 1933 to 1959 averaged 2,600-3,700,

suggesting a pre-fishery run size in excess of 5,000 adults for tributaries above Rock Island

Dam (Chapman et al. 1994). However, runs may already have been depressed by lower

Columbia River fisheries at this time. The following recent 5-year (1989-93) average natural

escapement estimates are available: 800 steelhead in the Wenatchee River and 450 steelhead

in the Methow and Okanogan Rivers (Table 29, Fig. 31). Recent average total escapement
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estimates for these stocks were 2,500 and 2,400, respectively. Average total run size at Priest

Rapids Dam for the same period was approximately 9,600 adult steelhead.

Substantial habitat blockages occurred with the construction of Chief Joseph and

Grand Coulee Dams, as well as smaller dams on tributary rivers. Habitat problems for this

ESU are largely related to irrigation diversions and hydroelectric dams, as well as degraded

riparian and instream habitat from urbanization and livestock grazing.

Trends in total (natural and hatchery) adult escapement are available for the

Wenatchee River (2.6% annual increase, 1962-93) and the Methow and Okanogan Rivers

combined (12% annual decline, 1982-93) (Table 29, Figs. 32 & 33). These two stocks

represent most of the escapement to natural spawning habitat within the range of the ESU,

although the Entiat River also has a small spawning run (WDF et al. 1993).

Hatchery fish are widespread and escaping to spawn naturally throughout the region.

The hatchery stock used in this region originated from stocks indigenous to the ESU during

the Grand Coulee Fish Maintenance Project, but represents a blend of fish from all basins

within the ESU and from areas above Grand Coulee Dam. Spawning escapement is strongly

dominated by hatchery production, with estimates of recent contributions averaging 65% in

the Wenatchee River and 81% in the Methow and Okanogan Rivers. WDFW estimated adult

replacement ratios of only 0.3:1.0 in the Wenatchee River and 0.25:1.0 in the Entiat River

and concluded that both these stocks and the Methow/Okanogan stock are not self-sustaining

without substantial hatchery supplementation. WDF et al. (1993) suggested that the original

Okanogan stock may be extinct, “except perhaps for resident morphs (rainbow trout) in

Salmon and Omak creeks.” This ESU might not exist today if there were not hatchery

production based on indigenous stocks.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices. Risk factors relating to hatchery practices were

discussed previously in the Background section. The stocks above Rock Island Dam are

largely driven by hatchery production. Although the major hatchery production in these

rivers has been derived from stocks indigenous to the ESU, there are distinct genetic risks

associated with hatchery supplementation.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We have received insufficient information regarding resident trout in this region to

reasonably evaluate their status or their interactions with anadromous steelhead.

15) Snake River Basin—Previous assessments within this ESU have identified

several stocks as being at risk or of special concern. Nehlsen et al. (1991) identified 13

stocks as at risk or of concern (Table 9). WDF et al. (1993) assessed three stocks within the

ESU, of which all were considered to be of mixed origin and composite production; all three

stocks were identified as depressed.
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No estimates of historical (pre-1960s) abundance specific to this ESU are available.

Light (1987) estimated that 80% of the total Columbia River Basin run above Bonneville

Dam (summer and winter steelhead combined) was of hatchery origin. All steelhead in the

Snake River Basin are summer steelhead and for management purposes are divided into

“A-run” and “B-run” fish. This division is based on several life history differences including

spawner size and run timing. Although there is little information for most stocks within this

ESU, there are recent run size or escapement estimates for several stocks (Table 30, Fig. 31).

Total recent 5-year average escapement above Lower Granite Dam was approximately

71,000, with a natural component of 9,400 (7,000 A-run and 2,400 B-run). Run-size

estimates are available for only a few tributaries within the ESU, all with small populations

(Table 30, Appendix E).

There have been several substantial habitat blockages in this ESU, the major ones

being the Hells Canyon Dam complex on the mainstem Snake River and Dworshak Dam on

the North Fork Clearwater River. Minor blockages (from smaller dams, impassable culverts,

etc.) are likely throughout the region. Bottom et al. (1985) noted that high summer and low

winter temperatures are limiting for salmonids in many streams in eastern Oregon. They

noted that flows below recommended levels occur in the Grande Ronde River, especially in

late fall through early spring, and that water withdrawals and low flows are severe in several

areas of that basin.

Riparian vegetation is heavily impacted by overgrazing and other agricultural

practices, timber harvest, road building and channelization. Prime steelhead spawning areas

have been degraded by overgrazing in several parts of the Grande Ronde Basin. Of

inventoried segments of streams in the Grande Ronde River Basin, restoration is needed for

between 38% (upper basin) and 59% (lower basin) of river bank. Instream habitat is also

affected by these same factors, as well as past gold dredging and severe sedimentation due to

poor land management practices. Although not as clearly documented, similar habitat

problems can be expected in other basins within this ESU. One of the most significant

habitat problems facing steelhead in this ESU is substantial modification of the migration

corridor by hydroelectric power development in the mainstem Snake and Columbia Rivers.

The aggregate trend in abundance for this ESU (indexed at Lower Granite Dam) has

been upward since 1975, although natural escapement has been declining during the same

period (Fig. 34). However, the aggregate trend has been downward (with wide fluctuations)

over the past 10 years, recently reaching levels below those observed at Ice Harbor Dam in

the early 1960s. Naturally produced escapement has declined sharply in the last 10 years.

Adult abundance trend information is available for several individual stocks from a variety of

sources, including spawner surveys, dam counts, and angler catch (Table 30, Fig. 32).

Because of the focus of angler catch on hatchery fish in this region and the availability of

other estimates, we have not used angler catch trends in our evaluations, although they are

included in Appendix E for comparison.

Of the 13 stock indices (excluding the Lower Granite Dam counts discussed above)

for which we had adequate information to compute trends, 9 have been declining and

4 increasing during the available data series, with a range from 30% annual decline to 4%
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annual increase. Four of the negative trends were significantly different from zero

(Appendix E). In addition to these adult abundance data, the focus of IDFG’s steelhead

monitoring program is juvenile (parr) surveys in wild or natural production areas. Most of

the individual juvenile data series available to us were too short to compute reliable trends,

but summaries presented by Leitzinger and Petrosky (in press) showed declines in average

parr density over the past 7 or 8 years for both A- and B-run steelhead in both wild and

natural production areas. From 1985 to 1993, estimates of mean percent of rated parr

carrying capacity for these surveys ranged from as low as 11.2% (wild-production B-run) to

62.1% (wild-production A-run). The Columbia River Fisheries Management Plan Technical

Advisory Committee found that A-run steelhead densities were closer to rated capacities than

were B-run steelhead, but noted that “percent carrying capacity indicates that all surveyed

areas are underseeded” (CRFMP TAC 1991, p. 6). It is likely that recent trends in most

basins have been negatively affected by recent drought in the region.

Hatchery fish are widespread and escape to spawn naturally throughout the region.

During the past 5 years, an average of 86% of adult steelhead passing Lower Granite Dam

were of hatchery origin. Only two hatchery composition estimates are available for

individual stocks: 0% for Joseph Creek (Grande Ronde River), and 57% for the Tucannon

River. We have little information on the actual contribution of hatchery production to natural

spawning, and on natural escapements for most stocks in this ESU. In general, there are wild

production areas with limited hatchery influence remaining in the Selway River, lower

Clearwater River, Middle and South Forks of the Salmon River, and the lower Salmon River

(Leitzinger and Petrosky in press). In other areas, such as the upper Salmon River, there

appears to be little or no natural production of locally native steelhead (IDFG 1995). Given

the relatively low natural run sizes to individual streams for which we have estimates, the

declines in natural returns at Lower Granite Dam, the declines in parr density estimates, and

the widespread presence of hatchery fish, we conclude that the majority of natural steelhead

populations in this ESU are probably not self-sustaining at this time.

The major present threat to genetic integrity for steelhead in this ESU comes from

past and present hatchery practices, discussed previously. Common risk factors relating to

hatchery practices were discussed previously in the Background section.

An additional concern in this ESU is the status of steelhead native to the North Fork

of the Clearwater River, now maintained at Dworshak NFH. While this hatchery population

is presently fairly large, it represents the only remaining gene pool for steelhead native to that

tributary. This population has not had access to its native habitat for 25 years.

In evaluating the status of this ESU, we have not accounted for abundance or trends

in populations of resident O. mykiss (rainbow trout), which may be a significant part of the

ESU. We have insufficient information regarding resident trout in this region to reasonably

evaluate their status or their interactions with anadromous steelhead.
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Conclusions

The BRT concluded that of the 14 ESUs reviewed here, 5 ESUs are presently in

danger of extinction: Central California Coast, South-Central California Coast, Southern

California, Central Valley, and Upper Columbia River. Four were classified as likely to

become endangered in the foreseeable future: Lower Columbia River, Oregon Coast,

Northern California, and Snake River Basin. The Puget Sound, Olympic Peninsula,

Southwest Washington, and Upper Willamette ESUs were classified as not presently likely to

become extinct or endangered. The BRT concluded that the remaining ESU (Middle

Columbia River) was not presently in danger of extinction, but BRT members failed to agree

on a conclusion regarding its likelihood of becoming endangered. A 15th ESU (Klamath

Mountains Province) was reviewed previously (Busby et al. 1994) and is discussed here only

for comparison.

Because of the requirements of the ESA, we have focused on factors contributing to

risk of extinction or endangerment, rather than on more positive indicators of population

“health.” We identified some risk factors that are of concern for natural populations in all

ESUs considered. Primary concerns for ESUs identified as either in danger of extinction or

likely to become so are outlined for each ESU.

The other ESUs (those not judged to be in danger nor likely to become so) are

generally distinguished by three characteristics. First, although population abundance in

these ESUs may be below historical levels, naturally reproducing steelhead still occupy most

of the historical range of the ESU in numbers that are sufficient to avoid most

small-population risk problems. Second, while trends in the past few years may be

downward, we did not find evidence that natural populations have failed to maintain

themselves over longer time spans. Third, hatchery production does not appear to pose a

major genetic risk to the natural populations in these ESUs, either because the level of

hatchery production is relatively low or because there is evidence of substantial reproductive

isolation between hatchery and natural populations.

Several factors relating to the status of steelhead populations were of substantial

concern in all ESUs. Population trends since the mid-1980s have been downward in almost

all ESUs. While this may reflect recent changes in regional climate patterns, it is unclear

whether climate change is the sole cause of declines. It is also unclear if or when climate

conditions may improve. Widespread degradation of both freshwater and estuarine habitats

within the region is a concern, as are the potential results of continuing habitat destruction.

The widespread production of hatchery fish raises concern for genetic integrity in most ESUs

and is also of concern in determining the sustainability of natural production. Although in

most cases available data are not sufficient to tell whether hatchery fish are having a strong

negative impact on naturally produced steelhead, competition with introduced stocks for

limited habitat could mask problems with the sustainability of natural stocks. Finally, many

of the conclusions for specific ESUs involve a substantial degree of uncertainty resulting

from lack of information on population abundance, trends, resident fish, and interactions

between hatchery and natural fish.
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Coastal Steelhead ESU Conclusions

1) Puget Sound—The BRT concluded that the Puget Sound steelhead ESU is neither

presently in danger of extinction nor likely to become endangered in the foreseeable future.

Despite this conclusion, the BRT has several concerns about the overall health of this ESU

and about the status of certain stocks within the ESU. Recent trends in stock abundance are

predominantly downward, although this may be largely due to recent climate conditions. Yet

trends in the two largest stocks (Skagit and Snohomish Rivers) have been upward.

The majority of steelhead produced within the Puget Sound region appear to be of

hatchery origin, but most hatchery fish are harvested, and estimates of hatchery fish escaping

to spawn naturally are all less than 15% of total natural escapement, except for the Tahuya

and Morse Creek/Independents stocks where the hatchery proportion is approximately 50%.

We are particularly concerned that the majority of hatchery production originates from a

single stock (Chambers Creek), which could increase genetic homogenization of the resource

despite management efforts to minimize introgression of the hatchery gene pool into natural

populations via separation of hatchery and natural run timing and high harvest rates focused

on hatchery runs.

The status of certain stocks within the ESU is also of concern, especially the

depressed status of most stocks in the Hood Canal area and the steep declines of Lake

Washington winter steelhead and Deer Creek summer steelhead.

These conclusions are tempered by two substantial uncertainties. First, there is very

little information regarding the abundance and status of summer steelhead in the Puget Sound

region. Although the numbers of summer steelhead have historically been small relative to

winter steelhead, they represent a substantially different life history strategy and loss of these

fish would diminish the ecological and genetic diversity of the entire ESU. Second, there is

uncertainty regarding the degree of interaction between hatchery and natural stocks.

Although WDFW’s conclusion that there is little overlap in spawning between natural and

hatchery stocks of winter steelhead throughout the ESU is generally supported by available

evidence, for many basins it is based largely on models and assumptions regarding run

timing rather than empirical data.

2) Olympic Peninsula—The BRT concluded that the Olympic Peninsula steelhead

ESU is neither presently in danger of extinction nor likely to become endangered in the

foreseeable future. Despite this conclusion, the BRT has several concerns about the overall

health of this ESU and about the status of certain stocks within it. The majority of recent

abundance trends are upward (including three of the four largest stocks), although trends in

several stocks are downward. These downward trends may be largely due to recent climate

conditions. There is widespread production of hatchery steelhead within this ESU, largely

derived from a few parent stocks, and this could increase genetic homogenization of the

resource despite management efforts to minimize introgression of the hatchery gene pool into

natural populations. Estimates of the proportion of hatchery fish on natural spawning

grounds range from 16% to 44%, with the two stocks with the largest abundance of natural

spawners (Queets and Quillayute) having the lowest hatchery proportions.
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These conclusions are tempered by substantial uncertainties. As for the Puget Sound

ESU, there is very little information regarding the abundance and status of summer steelhead

in this region and the degree of interaction between hatchery and natural stocks.

3) Southwest Washington—The BRT concluded that the Southwest Washington

steelhead ESU is neither presently in danger of extinction nor likely to become endangered in

the foreseeable future. The latter conclusion was not unanimous, and a minority concluded

that downward trends, coupled with introductions of hatchery fish from outside the ESU,

indicated likelihood of becoming endangered. Almost all stocks for which we have data

within this ESU have been declining in the recent past, although this may be largely due to

recent climate conditions. The BRT members had a strong concern about the pervasive

opportunity for genetic introgression from hatchery stocks within the ESU, and a great

concern for the status of summer steelhead in this ESU. There is widespread production of

hatchery steelhead within this ESU, largely from parent stocks outside the ESU. This

production could substantially change the genetic composition of the resource, despite

management efforts to minimize introgression of the hatchery gene pool into natural

populations. Estimates of the proportion of hatchery fish on natural spawning grounds range

from 9% in the Chehalis River, the largest producer of steelhead in the ESU, to 82% in the

Clatskanie River.

As for the Puget Sound and Olympic Peninsula ESUs, these conclusions are tempered

by substantial uncertainties regarding the abundance and status of summer steelhead in this

region, and the degree of interaction between hatchery and natural stocks.

4) Lower Columbia River—The BRT concluded that the Lower Columbia River

steelhead ESU is not presently in danger of extinction, but it is likely to become endangered

in the foreseeable future. The latter conclusion was not unanimous, and there were two

distinct minority opinions: one minority of the BRT concluded that there was little

likelihood that this ESU will become endangered, while another minority was uncertain

whether native steelhead still exist in this region. The majority of stocks for which we have

data within this ESU have been declining in the recent past, but some have been increasing

strongly. However, the strongest upward trends are those of either non-native stocks (Lower

Willamette River and Clackamas River summer steelhead) or stocks that are recovering from

major habitat disruption and are still at low abundance (mainstem and North Fork Toutle

River). The data series for most stocks are quite short, so the preponderance of downward

trends may reflect the general coastwide decline in steelhead in recent years. The BRT

members had strong concern about the pervasive opportunity for genetic introgression from

hatchery stocks within the ESU, and strong concern for the status of summer steelhead in this

ESU. There is widespread production of hatchery steelhead within this ESU, and several

stocks for which we have estimates of hatchery composition average more than 50% hatchery

fish in natural escapement. Concerns about hatchery influence are especially strong for

summer steelhead and Oregon winter steelhead stocks, where there appears to be substantial

overlap in spawning between hatchery and natural fish.

The major area of uncertainty in this evaluation is the degree of interaction between

hatchery and natural stocks within the ESU. WDFW’s conclusion that there is little overlap
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in spawning between natural and hatchery stocks of winter steelhead throughout the ESU is

generally supported by available evidence; however, with the exception of detailed studies of

the Kalama River winter stock, it is based largely on models and assumptions regarding run

timing rather than empirical data. There is apparently strong overlap in spawning between

hatchery and natural summer steelhead in Washington tributaries. We have no information

regarding potential spawning separation between hatchery and natural fish in Oregon

tributaries to the Lower Columbia River.

5) Upper Willamette—The BRT concluded that the Upper Willamette steelhead

ESU is neither presently in danger of extinction, nor likely to become endangered in the

foreseeable future. The latter conclusion was not unanimous, and a minority of the BRT

concluded that the small numbers and declining trend in the native stock, coupled with other

risk factors, indicate a likelihood of becoming endangered. While historical information

regarding this ESU is lacking, geographic range and historical abundance are believed to

have been relatively small compared to other ESUs, and current production probably

represents a larger proportion of historical production than is the case in other Columbia

River Basin ESUs.

Native winter steelhead within this ESU have been declining on average since 1971,

and have exhibited large fluctuations in abundance. The main production of native (late-run)

winter steelhead is in the North Fork Santiam River, where estimates of hatchery proportion

in natural spawning range from 14% to 54%. The BRT members had strong concern about

the pervasive opportunity for genetic introgression from hatchery stocks within the ESU, and

strong concern for potential ecological interactions between introduced stocks and native

stocks. There is widespread production of hatchery steelhead within the range of this ESU,

predominantly of non-native summer and early-run winter steelhead.

There are two major areas of uncertainty in this evaluation. First, the degree of

interaction between hatchery and natural stocks within the ESU is unknown. We have no

information regarding potential spawning separation between hatchery and natural fish.

Second, some of the trends for these populations are based on angler catch data, which may

not be a good indicator of actual trends in population (see discussion in the Background

section above).

6) Oregon Coast—The BRT concluded that the Oregon Coast steelhead ESU is not

presently in danger of extinction, but that it is likely to become endangered in the foreseeable

future. The latter conclusion was not unanimous, with a minority of the BRT concluding that

there is little likelihood that this ESU will become endangered. Most steelhead populations

within this ESU have been declining in the recent past (although this may be largely due to

recent climate conditions), with increasing trends restricted to the southernmost portion of the

ESU, south of Siuslaw Bay. The BRT members had strong concern about the pervasive

opportunity for genetic introgression from hatchery stocks within this ESU and strong

concern for potential ecological interactions between introduced stocks and native stocks.

There is widespread production of hatchery steelhead within this ESU, largely based on outof-basin stocks, and approximately half of the streams (including the majority of those with

upward trends) are estimated to have more than 50% hatchery fish in natural spawning
168

escapements. Given the substantial contribution of hatchery fish to natural spawning

throughout the ESU, and the generally declining or slightly increasing trends in abundance, it

is likely that natural stocks are not replacing themselves throughout the ESU.

There are two major areas of uncertainty in this evaluation. First, the degree of

interaction between hatchery and natural stocks within the ESU is unknown. We have no

information regarding potential spawning separation between hatchery and natural fish, nor

about the spawning success of hatchery produced fish. Second, the majority of trends for

these populations are based on angler catch data, which may not be a good indicator of actual

trends in population abundance.

7) Klamath Mountains Province—The BRT has previously concluded that this ESU

is not presently in danger of extinction, but that it is likely to become endangered in the

foreseeable future (Busby et al. 1994). Although historical trends in overall abundance

within the ESU are not clearly known, there has been substantial replacement of natural fish

with hatchery produced fish. While absolute abundance remains fairly high, since about

1970 trends in abundance have been downward in most steelhead populations for which we

have data within the ESU, and a number of populations are considered by various agencies

and groups to be at some risk of extinction. Declines in summer steelhead populations are of

particular concern. Most natural populations of steelhead within the area experience a

substantial infusion of naturally spawning hatchery fish each year. After accounting for the

contribution of these hatchery fish, we were unable to identify any steelhead populations that

are naturally self-sustaining.

8) Northern California—The BRT concluded that the Northern California steelhead

ESU is not presently in danger of extinction, but that it is likely to become endangered in the

foreseeable future. Population abundances are very low relative to historical estimates

(1930s dam counts), and recent trends are downward in stocks for which we have data,

except for two small summer steelhead stocks. Summer steelhead abundance is very low.

There is particular concern regarding sedimentation and channel restructuring due to floods,

apparently resulting in part from poor land management practices. The abundance of

introduced Sacramento squawfish as a predator in the Eel River is also of concern. For

certain rivers (particularly the Mad River), the BRT is concerned about the influence of

hatchery stocks, both in terms of genetic introgression and of potential ecological interactions

between introduced stocks and native stocks.

There are two major areas of uncertainty in this evaluation. First, we lack information

on steelhead run sizes throughout the ESU. Our conclusions were based largely on evidence

of habitat degradation and the few dam counts and survey index estimates of stock trends in

the region. Second, the genetic heritage of the natural winter steelhead population in the Mad

River is uncertain.

9) Central California Coast—The BRT concluded that the Central California Coast

steelhead ESU is presently in danger of extinction. The southernmost portion of the ESU

(south of Scott and Waddell Creeks, including one of two major rivers within the ESU) and

the portion within San Francisco and San Pablo Bays, appears to be at extreme risk. In the
169

northern coastal portion of the ESU, steelhead abundance in the Russian River has been

reduced roughly sevenfold since the mid-1960s, but abundance in smaller streams appears to

be stable at low levels. There is particular concern about sedimentation and channel

restructuring due to floods, apparently resulting in part from poor land management practices.

There are two major areas of uncertainty in this evaluation. First, due to the lack of

information on steelhead run sizes throughout the ESU, our conclusions were based largely

on evidence of habitat degradation and the few estimates of abundance and stock trends in

the region. Second, the genetic heritage of the natural populations in tributaries to San

Francisco and San Pablo Bays is uncertain, making it difficult to determine which of these

populations should be considered part of the ESU.

10) South-Central California Coast—The BRT concluded that the South-Central

California Coast steelhead ESU is presently in danger of extinction. Total abundance is

extremely low, and most stocks for which we have data in the ESU show recent downward

trends. There is particular concern about sedimentation and channel restructuring due to

floods, which apparently result in part from poor land management practices. There is also

concern about the genetic effects of widespread stocking of rainbow trout.

The major area of uncertainty in this evaluation is the lack of information on

steelhead run sizes throughout the ESU. Our conclusions were based largely on evidence of

habitat degradation and the few estimates of abundance and stock trends in the region.

11) Southern California—The BRT concluded that the Southern California

steelhead ESU is presently in danger of extinction. Steelhead have already been extirpated

from much of their historical range in this region. The BRT members had strong concern

about the widespread degradation, destruction, and blockage of freshwater habitats within the

region, and the potential results of continuing habitat destruction and water allocation

problems. There is also concern about the genetic effects of widespread stocking of rainbow

trout.

There are two major areas of uncertainty in this evaluation. First, accurate run size

and trend estimates are lacking for natural steelhead stocks in this ESU. Second, the

relationship between resident and anadromous forms of the biological species is unclear.

12) Central Valley—The BRT concluded that the Central Valley steelhead ESU is

presently in danger of extinction. Steelhead have already been extirpated from most of their

historical range in this region. Habitat concerns in this ESU focus on the widespread

degradation, destruction, and blockage of freshwater habitats within the region, and the

potential results of continuing habitat destruction and water allocation problems. The BRT

members also had strong concerns about the pervasive opportunity for genetic introgression

from hatchery stocks within the ESU and about potential ecological interactions between

introduced stocks and native stocks. There is widespread production of hatchery steelhead

within this ESU.

There are two major areas of uncertainty in this evaluation. First, there is a total lack

of recent run-size estimates for natural steelhead stocks in this ESU. Second, there is a
170

substantial question regarding the genetic heritage of remaining natural populations, making

it difficult to determine which populations should be considered part of the ESU.

Inland Steelhead ESU Conclusions

13) Middle Columbia—The BRT concluded that the Middle Columbia steelhead

ESU is not presently in danger of extinction, but reached no conclusion regarding its

likelihood of becoming endangered in the foreseeable future. All BRT members felt special

concern for the status of this ESU and concluded that NMFS should carefully evaluate

conservation measures affecting this ESU and continue monitoring its status. There is

particular concern about Yakima River stocks and winter steelhead stocks. Winter steelhead

are reported within this ESU only in the Klickitat River and Fifteenmile Creek; we have no

abundance information for winter steelhead in the Klickitat River, but they have been

declining in abundance in Fifteenmile Creek.

Total steelhead abundance in the ESU appears to have been increasing recently, but

the majority of natural stocks for which we have data within this ESU have been declining,

including those in the John Day River, which is the largest producer of wild, natural

steelhead. The BRT members expressed strong concern about the pervasive opportunity for

genetic introgression from hatchery stocks within the ESU. There is widespread production

of hatchery steelhead within this ESU, but it is largely based on within-basin stocks.

Estimated proportion of hatchery fish on spawning grounds ranges from low, in the Yakima,

Walla Walla, and John Day Rivers to moderate in the Umatilla and Deschutes Rivers.

Habitat degradation due to grazing and water diversions has been documented throughout the

ESU.

There are three major areas of uncertainty in this evaluation. First, run-size estimates

are lacking for most populations. Second, the degree of interaction between hatchery and

natural stocks within the ESU is uncertain; we have little information regarding potential

spawning separation between hatchery and natural fish. Third, the relationship between

anadromous and resident forms of O. mykiss is unclear; we have little information regarding

abundance of resident fish or their interactions with anadromous fish, but resident forms may

play an important role in some areas of this ESU.

14) Upper Columbia—The BRT concluded that the Upper Columbia steelhead ESU

is presently in danger of extinction. While total abundance of populations within this ESU

has been relatively stable or increasing, this appears to be occurring only because of major

hatchery supplementation programs. Estimates of the proportion of hatchery fish in

spawning escapement are 65% (Wenatchee River) and 81% (Methow and Okanogan Rivers).

The major concern for this ESU is the clear failure of natural stocks to replace themselves.

The BRT members are also strongly concerned about problems of genetic homogenization

due to hatchery supplementation within the ESU and about the apparent high harvest rates on

steelhead smolts in rainbow trout fisheries and the degradation of freshwater habitats within

the region, especially the effects of grazing, irrigation diversions, and hydroelectric dams.
171

There are two major areas of uncertainty in this evaluation. First, the relationship

between resident and anadromous forms of the biological species is unclear, both in terms of

native rainbow trout in the streams presently supporting steelhead and in terms of potential

residualized (footnote 5) steelhead above Grand Coulee Dam. Second, there is uncertainty

regarding the genetic heritage of naturally spawning fish within the ESU.

15) Snake River Basin—The BRT concluded that the Snake River Basin steelhead

ESU is not presently in danger of extinction, but it is likely to become endangered in the

foreseeable future. The latter conclusion was not unanimous, and a minority of the BRT

concluded that there was little likelihood that this ESU will become endangered. While total

(hatchery + natural) run size has increased since the mid-1970s, there has been a severe

recent decline in natural run size. The majority of natural stocks for which we have data

within this ESU have been declining. Parr densities in natural production areas have been

substantially below estimated capacity in recent years. Downward trends and low parr

densities indicate a particularly severe problem for B-run steelhead, the loss of which would

substantially reduce life history diversity within this ESU.

The BRT has a strong concern about the pervasive opportunity for genetic

introgression from hatchery stocks within the ESU. There is widespread production of

hatchery steelhead within this ESU. The total Snake River steelhead run at Lower Granite

Dam is estimated to average 86% hatchery fish in recent years. Estimates of proportion of

hatchery fish in spawning escapement for Snake River tributaries range from 0% in Joseph

Creek to above 80% in the upper Salmon River (IDFG 1995). The BRT members also were

concerned about the degradation of freshwater habitats within the region, especially the

effects of grazing, irrigation diversions, and hydroelectric dams.

There are three major areas of uncertainty in this evaluation. First, there is a lack of

run-size estimates for most populations. Second, the degree of interaction between hatchery

and natural stocks within the ESU is unknown. We have little information regarding

interactions between hatchery and natural fish. Third, the relationship between anadromous

and resident forms of O. mykiss is unclear; we have little information regarding abundance of

resident fish or their interactions with anadromous fish.
172
173

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196
197

Appendix A

Appendix A-1 - Samples of Oncorhynchus mykiss used in Genetic Analyses

Appendix A-2 - Mapped locations of the Samples of O. mykiss used in Genetic Analyses
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199
200
201
202
203
204
205
206
207
208
209

Appendix B

Petitioned Steelhead Populations Listed by Evolutionarily Significant Unit
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211
212
213
214
215
216
217

Appendix C

Steelhead Artificial Propagation Facilities
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219
220
221
222
223

Appendix D

Releases of Hatchery Steelhead
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225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241

Appendix E

Steelhead Abundance Data
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243
244
245
246
247
248
249
250
251
252
253
254
255

Appendix F

Glossary
256
257

Glossary

ageing

Ageing and backcalculated length at age are based on counts and measurements of

annual rings on scales or otoliths (a calcareous “earstone” found in the internal ear of fishes).

The typically anadromous life history of steelhead and their ability to undergo multiple

spawning migrations complicate the matter of reporting the age of fish of this species.

Numerous authors have developed notation styles for this purpose. Original citations should

be consulted for in-depth descriptions (e.g., Shapovalov and Taft 1954). Freshwater age is

generally separated from saltwater age by either a slash (/) or period (.); for example, a fish

which smolted after 2 years in fresh water and was caught after 3 years in the ocean could be

represented by 2/3 or 2.3.

allele

An allele is an alternate form of a gene (the basic unit of heredity passed from parent

to offspring). By convention, the “100 allele” is the most common allele in a population and

is the reference for the electrophoretic mobility of other alleles of the same gene. Other

genetic terms used in this document include allozymes (alternate forms of an enzyme

produced by different alleles and often detected by protein electrophoresis); gene locus (pl.

loci; the site on a chromosome where a gene is, found); genetic distance (D) (a quantitative

measure of genetic differences between a pair of samples); and introgression. (introduction

of genes from one population or species into another). See also DNA and electrophoresis.

artificial propagation

See hatchery.

Cape Blanco

A geographic feature on the Oregon coast at 43°50’N.

Cape Mendocino

A geographic feature on the California coast at 40°25’N.
258

coastal steelhead

Anadromous Oncorhynchus mykiss that occur in rivers from Alaska to California,

including tributaries to the Fraser and Columbia Rivers largely west of the Cascade Crest.

Coastal steelhead are genetically distinct from inland steelhead that occur in the Fraser and

Columbia River Basins largely east of the Cascade Crest. Behnke (1992) has proposed

subspecies status for these two forms and applies the taxonomic name O. m. irideus to

coastal steelhead. The resident form is commonly called rainbow trout.

DNA (deoxyribonucleic acid)

DNA is a complex molecule that carries an organism’s heritable information. The two

types of DNA commonly used to examine genetic variation are mitochondrial DNA

(mtDNA), a circular molecule that is maternally inherited, and nuclear DNA, which is

organized into a set of chromosomes. See also allele and electrophoresis.

electrophoresis

Electrophoresis refers to the movement of charged particles in an electric field. It has

proven to be a very useful analytical tool for biochemical characters because molecules can

be separated on the basis of differences in size or net charge. Protein electrophoresis, which

measures differences in the amino acid composition of proteins from different individuals,

has been used for over three decades to study natural populations, including all species of

anadromous Pacific salmonids. Because the amino acid sequence of proteins is coded for by

DNA, data provided by protein electrophoresis provide insight into levels of genetic

variability within populations and the extent of genetic differentiation between them. Utter et

al. (1987) provide a review of the technique using examples from Pacific salmon, and the

laboratory manual of Aebersold et al. (1987) provides detailed descriptions of analytical

procedures. Genetic techniques that focus directly on variation in DNA also routinely use

electrophoresis to separate fragments formed by cutting DNA with special enzymes

(restriction endonucleases).

Other genetic terms used in this document include allele (an alternate form of a gene);

allozymes (alternate forms of an enzyme produced by different alleles and often detected by

protein electrophoresis); chromosome (a thread-like structure containing many genes);

dendrogram (a branching diagram, sometimes resembling a tree, that provides one way of

visualizing similarities between different groups or samples); gene (the basic unit of heredity

passed from parent to offspring); gene locus (pl. loci; the site on a chromosome where a

gene is found); genetic distance (a quantitative measure of genetic differences between a pair

of samples); introgression (introduction of genes from one population or species into

another); and karyotype (the number, size, and morphology of the chromosome

complement).
259

ESA

The U.S. Endangered Species Act.

ESU

Evolutionarily significant unit; a “distinct” population of Pacific salmon, and hence a

species, under the Endangered Species Act.

escapement

The number of fish that survive to reach the spawning grounds or hatcheries. The

escapement plus the number of fish removed by harvest form the total run size.

half-pounder

A life history trait of steelhead exhibited in the Rogue, Klamath, Mad, and Eel Rivers

of southern Oregon and northern California. Following smoltification, half-pounders spend

only 2-4 months in the ocean, then return to fresh water. They overwinter in fresh water and

emigrate to salt water again the following spring. This is often termed a false spawning

migration, as few half-pounders are sexually mature.

hatchery

Salmon hatcheries use artificial procedures to spawn adults and raise the resulting

progeny in fresh water for release into the natural environment, either directly from the

hatchery or by transfer into another area. In some cases, fertilized eggs are outplanted

(usually in “hatch-boxes”), but it is more common to release fry (young juveniles) or smolts

(Juveniles that are physiologically prepared to undergo the migration into salt water).

The broodstock of some hatcheries is based on the adults that return to the hatchery

each year; others rely on fish or eggs from other hatcheries, or capture adults in the wild each

year.

inland steelhead

Anadromous Oncorhynchus mykiss that occur in the Fraser and Columbia River

Basins largely east of the Cascade Crest. Inland steelhead are genetically distinct from

coastal steelhead that occur in rivers from Alaska to California, including tributaries to the

Fraser and Columbia Rivers largely west of the Cascade Crest. Behnke (1992) has proposed

subspecies status for these two forms and applies the taxonomic name 0. m. gairdneri to

inland steelhead. The resident form is commonly called redband trout.
260

monophyletic

Relating to, descended from, or derived from one stock or source. See polyphyletic.

multidimensional scaling

A nonmetric ordination technique used to visualize genetic relationships among

populations in two or three dimensions.

ocean-maturing

Steelhead that enter fresh water with well-developed gonads and spawn shortly

thereafter; commonly referred to as winter steelhead. See stream-maturing.

phenotype

The phenotype is the appearance, or other observable characteristic, of an organism

resulting from the interaction of the genotype and the environment.

polymorphic

Having more than one form (e.g., polymorphic gene loci have more than one allele).

polyphyletic

Relating to or characterized by development from more than one ancestral type. See

monophyletic.

punchcard

A card (alternatively called a tag or stamp) used by steelhead and salmon anglers to

record catch information; it is returned to the management agency after the fishing season.
261

redd counts

Most salmonids deposit their eggs in nests called redds, which are dug in the

streambed substrate by the female. Most redds occur in predictable areas and are easily

identified by an experienced observer by their shape, size, and color (lighter than surrounding

areas because silt has been cleaned away).

Spawning surveys utilize counts of redds and fish carcasses to estimate spawner

escapement and identify habitat being used by spawning fish. Annual surveys can be used to

compare the relative magnitude of spawning activity between years.

river kilometer (RKm)

Distance, in kilometers, from the mouth of the indicated river. Usually used to

identify the location of a physical feature, such as a confluence, dam, or waterfall.

smolt

verb- The physiological process that prepares a juvenile anadromous fish to survive

the transition from fresh water to salt water.

noun- A juvenile anadromous fish which has smelted.

steelhead

The anadromous form of the species Oncorhynchus mykiss. Anadromous fish spend

their early life history in fresh water, then migrate to salt water, where they may spend up to

several years before returning to fresh water to spawn. Rainbow trout is the nonanadromous

form of Oncorhynchus mykiss.

stream-maturing

Steelhead that enter fresh water in a sexually immature condition and require several

months in fresh water to mature and spawn, commonly referred to as summer steelhead. See

ocean-maturing.