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NOAA Technical Memorandum NMFS-NWFSC-22

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Status Review for Mid-Columbia River Summer Chinook Salmon

F. William Waknitz, Gene M. Matthews, Thomas Wainwright, and Gary A. Winans

National Marine Fisheries Service
Northwest Fisheries Science Center
Coastal Zone and Estuarine Studies Division
2725 Montlake Blvd. E.
Seattle WA 98112

July 1995

Ronald H. Brown, Secretary

National Oceanic and Atmospheric Administration
D. James Baker, Administrator

National Marine Fisheries Service
Rolland A. Schmitten, Assistant Administrator for Fisheries

Key Questions in ESA Evaluations
The "Species" Question
Hatchery Fish and Natural Fish
Thresholds for Threatened or Endangered Status
Summary of Petitioners' Claims
Reproductive Isolation
Geographic Isolation
Distinctive Life History and Body Size Characteristics
Evolutionary Significance
Population Trends
BRT Summary of Biological Information
Environmental Features
Life History Characteristics
Juvenile Life History Characters
Run and Spawn Timing
Age at Spawning, Sex Ratio, and Fecundity
Ocean Distribution
Juvenile Behavior
"June hogs"
Stock Histories
Grand Coulee Fish Maintenance Project, 1939-43
Artificial Propagation
Phenotypic Characteristics
Genetic Characteristics
Population Abundance and Threshold Evaluations
Historic Abundance Estimates and Trends
Present Abundance Estimates and Trends
Discussion and Conclusions
Reproductive Isolation
Genetic Characters
Phenotypic Characters
Life History Charactersv
Spawn and Run Timing
Evolutionary Significance
Phenotypic and Life History Traits
Genetic Data
Conclusion: Species Determination
Threshold Determination
Appendix: Protein Loci and Sample Information for Genetic Analyses

We have concluded that mid-Columbia River summer chinook salmon as petitioned are not a species or Evolutionarily Significant Unit (ESU) as defined by the U.S. Endangered Species Act (ESA). Rather, they are part of a larger ESU that includes all late-run (summer and fall), ocean-type chinook salmon from the mainstem Columbia River and its tributaries (excluding the Snake River) between Chief Joseph and McNary Dams. We have also concluded that at the present time this larger ESU is not likely to become endangered in the foreseeable future and does not warrant listing as a threatened or endangered species.


The Biological Status Review of mid-Columbia River summer chinook salmon was conducted by a team of scientists from the Northwest Fisheries Science Center of the National Marine Fisheries Service. This Biological Review Team relied upon the extensive public record developed pursuant to the petition. Team members included Peggy Busby, Dr. David Damkaer, Robert Emmett, Dr. Stephen Grabowski, Dr. Jeffrey Hard, Dr. Orlay Johnson, Dr. Conrad Mahnken, Gene Matthews, Dr. Michael Schiewe, Lowell Stuehrenberg, Dr. Thomas Wainwright, William Waknitz, Dr. Robin Waples, Laurie Weitkamp, Dr. John Williams, and Dr. Gary Winans. Bill Hevlin from the Northwest Regional Office of the National Marine Fisheries Service also contributed information and participated in discussions.



Chinook salmon (Oncorhynchus tshawytscha) are distributed from central California to northern Alaska on the North American coast and are native to the Columbia River Basin (Healey 1991). This species was once extremely abundant throughout most of the basin's large, complex river system (Chapman 1986) and has often been partitioned into three races (spring, summer, and fall) based upon timing of adult entry into fresh water. From the late 19th century until the present, a variety of factors have led to a reduction in many Columbia River chinook salmon populations (Nehlsen et al. 1991).

This situation prompted American Rivers, Northwest Environmental Defense Center, The Sierra Club, Northwest Resource Information Center, Friends of the Earth, Inland Empire Public Lands Council, Washington Wilderness Coalition, North Central Washington Audubon Society, Trout Unlimited, Washington Trout, and Federation of Fly Fishers (NEDC et al. 1993) to petition the National Marine Fisheries Service (NMFS) to list mid-Columbia River summer-run chinook salmon as a threatened or endangered species under the U.S. Endangered Species Act (ESA) of 1973 (U.S.C. 1531 et seq.).

Mid-Columbia was used by the petitioners to refer to the Columbia River Basin between Priest Rapids and Chief Joseph Dams.

This report summarizes a review of the biological status of mid-Columbia River summer-run chinook salmon. This review was conducted by the NMFS Northwest Fisheries Science Center.Biological Review Team (BRT). Because previous studies have consistently found genetic and life-history similarities between summer- and fall-run chinook salmon in the middle Columbia River above McNary Dam, the BRT also considered information for this larger group. In this review, both summer- and fall-run chinook salmon will be referred to as "late-run" chinook salmon or stocks. Fall-run chinook salmon in the Snake River were listed as threatened in 1992 (NMFS 1992).


Two key questions must be addressed in determining whether a listing under the ESA is warranted:

  1. Is the entity in question a "species" as defined by the ESA?
  2. If so, is the "species" threatened or endangered?

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 provided no specific guidance for determining what constitutes a distinct population, and the resulting ambiguity led to the use of a variety of criteria in listing decisions over the past decade. 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 description of this topic appeared in the NMFS "Definition of Species" paper (Waples 1991). 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 in the evolutionary legacy of the species (Waples 1991). Information that can be useful in determining the degree of reproductive isolation includes incidence of straying, rates of recolonization, degree of genetic differentiation, and physical or ecological barriers to migration. Insight into evolutionary significance can be provided by data on genetic and life-history characteristics, habitat differences, and the effects of stock transfers or supplementation efforts.

Hatchery Fish and Natural Fish

Because artificial propagation of Pacific salmonids has been widespread for many years, the influence of hatchery fish must be considered in most ESA status reviews. NMFS policy stipulates that in determining whether a population is distinct for purposes of the ESA, attention should focus on "natural" fish, which are defined as the progeny of naturally spawning fish (Waples 1991). 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 hatcheries are not a substitute for natural ecosystems.

The decision to focus on natural fish is based entirely on ecosystem considerations; the question of the relative merits of hatchery vs. natural fish is a separate issue. Fish are not automatically excluded from ESA consideration because some of their direct ancestors were reared in a hatchery. Conversely, identifying a group of fish as "natural" as defined here does not necessarily mean that they are part of a listed ESU. For a discussion of artificial propagation of Pacific salmon under the ESA, see Hard et al. (1992).

Thresholds for Threatened or Endangered Status

The ESA (sec. 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." Neither NMFS nor the U.S. Fish and Wildlife Service (USFWS), which share authority for administering the ESA, has an official policy regarding thresholds for considering ESA "species" as threatened or endangered. An information document on this topic published by NMFS suggests that conventional rules of thumb, analytical approaches, and simulations may all be useful in making this determination (Thompson 1991). There is considerable interest in incorporating the concepts of population viability analysis (PVA) into ESA threshold considerations for Pacific salmon. However, available PVA models generally require substantial life-history information that is not available for most Pacific salmon populations, so quantitative PVA is not practical at this time.

Therefore, NMFS considers a variety of information in evaluating the level of risk faced by an ESU. Important factors 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 spawner-recruit 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 naturally-produced fish); and 6) recent events (e.g., a drought, a change in management procedure, or improvements in mainstem passage) that have predictable short-term consequences for abundance of the ESU.

In evaluating these factors, the role of artificial propagation is an important issue. Because of the ESA's emphasis on conserving species in their native ecosystems, threshold determinations must focus on the status of natural fish, on the premise that an ESU is not healthy unless a viable population exists in the natural habitat.

Artificial production may have direct or indirect impacts on the status of a population through direct supplementation of numbers, by altering the genetic composition of the population, or through ecological interactions(competition, predation, disease transmission, etc.) between artificially-produced and natural fish. A mixture of artificially-produced and natural fish in a population also complicates assessment of the natural fish: abundance and viability of the natural stock is difficult to estimate unless artificially-produced fish are clearly marked, and abundance trends in the natural stock can be obscured by the infusion of artificially-produced fish and their progeny into the natural population.


This section summarizes declarations made in the petition by the Northwest Environmental Defense Center and others (NEDC et al. 1993) to support the designation of mid-Columbia River (MCR) summer-run chinook salmon as an ESU. Information regarding the assertions of the petitioners, as well as additional relevant information, is presented following this section. The petitioners' arguments and other relevant information are evaluated in the Discussion and Conclusions section of this review.

Reproductive Isolation

Geographic Isolation

Homing fidelity--The petitioners stated that MCR summer chinook salmon have a reduced likelihood of straying due to specificity of the homing instinct and the long migration to the spawning grounds (NEDC et al. 1993, p. 7).

Life history--The petitioners described MCR summer chinook salmon as reproductively isolated from Snake River summer chinook salmon by differences in migration, spawning, and rearing times, as well as by geographic separation. They noted that NMFS determined that the two summer chinook salmon stocks were reproductively isolated in 1992 (NEDC et al. 1993, p. 7-8).

Genetics--NEDC et al. (1993, p. 8) cited a protein electrophoretic study by Hershberger et al. (1988) to show that spring-run and summer-run chinook salmon in the MCR were separated into two genetic clusters. The petitioners stated that there is little available genetic information comparing summer and fall chinook salmon populations in the MCR (NEDC et al. 1993, p. 8), and that this lack of scientific data supports keeping these stocks separate.

The petitioners also claimed that fall chinook salmon in the MCR were historically considered "inferior" to summer chinook salmon (NEDC et al. 1993, p. 8). The Okanogan River was said to contain the only documented native stock of summer chinook salmon in the MCR (NEDC et al. 1993, p. 6). According to the petitioners, the legacy of the race of summer chinook salmon that migrated past the site of what is now Grand Coulee Dam was partially preserved by the Grand Coulee Fish Maintenance Project (NEDC et al. 1993, p. 2). .

Distinctive Life History and Body Size Characteristics

Time of peak spawning--The petitioners state that MCR summer chinook are distinct because peak spawning occurs during the last 2 weeks in October and continues through November (NEDC et al. 1993, p. 7 and 10).

Age and body size at spawning--The petitioners claimed that MCR summer chinook were referred to as "June hogs" because of their time of migration and size (NEDC et al. 1993, p. 1-2). They claimed that the age at spawning of MCR summer chinook ranges from 2 to 6 years, with 4- and 5-year-old fish making up nearly 80% of the spawning run (NEDC et al. 1993, p. 10). They also claimed that the size range for 4- and 5-year-old fish varied from 78 to 89 cm (NEDC et al. 1993, p. 10).

Smolt age--The petitioners stated that the largest number of MCR summer chinook juveniles emigrate seaward as subyearlings in mid-to-late summer (NEDC et al. 1993, p. 10).

Effects of hatchery fish--The petitioners stated that the Wells Hatchery has recently been contaminating the summer chinook salmon stock with fall chinook salmon, and that this intermixing has changed inriver migration times of chinook salmon in the MCR (NEDC et al. 1993, p. 7). However, they also assert that introgression of hatchery fish with natural MCR summer chinook has been slight in the MCR Basin, and they estimate that 65% of the summer chinook are "natural" (NEDC et al. 1993, p. 8).

Evolutionary Significance

Geographic location--The petitioners claim that summer chinook salmon spawn in two distinct areas: in tributaries of the Snake River and in tributaries of the MCR above Rock Island Dam (NEDC et al. 1993, p. 1-2). The petitioners stated that Methow, Okanogan, and Wenatchee River summer chinook salmon occupy unique ecosystems with often hostile conditions (NEDC et al. 1993, p. 9).

Spawning distribution--The petitioners stated that the original spawning distribution of MCR summer chinook included the Columbia River as far upstream as Lake Windemere in British Columbia (NEDC et al. 1993, p. 1), but that currently, MCR summer chinook salmon spawn only in the Wenatchee, Methow, and Okanogan Rivers (NEDC et al. 1993, p. 6).

Population Trends

Abundance--The petitioners cited early pioneers' stories of millions of salmon, mostly summer chinook, ascending Kettle Falls (NEDC et al. 1993, p. 5). They state that the abundance of Columbia River summer chinook salmon has been declining continuously since 1973, with an adult count over Bonneville Dam of 15,100 adults in 1992, the lowest count on record. Current numbers of MCR summer chinook were reported by the petitioners to be under 9,700 in the Wenatchee, Methow, and Okanogan Rivers (NEDC et al. 1993, p. 11). The population of summer chinook salmon in the Entiat River was said to be so small as to be considered extinct (NEDC et al. 1993, p. 12).

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