In 1994, the National Marine Fisheries Service (NMFS) received a petition (PRO-salmon 1994) requesting the listing of four populations of chinook salmon (Oncorhynchus tshawytscha) in Puget Sound as threatened or endangered species under the federal Endangered Species Act (ESA). In response to this petition and the more general concerns for the status of Pacific salmon throughout the region, NMFS announced that it would initiate ESA status reviews for all species and populations of anadromous salmonids in the states of Washington, Idaho, Oregon, and California. Subsequently, NMFS received a petition (ONRC and Nawa 1995) to list all chinook salmon south of British Columbia under the ESA.
The ESA allows the 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.
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." According to the ESA, the determination as to 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.
For the purposes of this review, the BRT did not evaluate likely or possible effects of conservation measures and therefore did not make recommendations as to whether identified ESUs should be listed as threatened or endangered species. The BRT did, however, draw scientific conclusions about the risk of extinction faced by ESUs under the assumption that present conditions will continue.
With respect to the 11 newly-identified ESUs, the BRT concluded that two (Sacramento
River Spring Run and Upper Columbia River Spring Run) are at risk of extinction, primarily due
to seriously depressed abundance. Five ESUs (Central Valley Fall Run, Southern Oregon and
California Coast, Puget Sound, Lower Columbia River, and Upper Willamette River) are at risk
of becoming endangered, due to a variety of factors. Only four ESUs (Upper Klamath and
Trinity Rivers, Oregon Coast, Washington Coast, and Middle Columbia River Spring Run) are
not at risk of extinction or endangerment.
Historically, the winter run was abundant and comprised populations in the McCloud, Pit,
Little Sacramento, and Calaveras Rivers. Presently, the ESU has been reduced to a single
spawning population confined to the mainstem Sacramento River below Keswick Dam. Since
counting began in 1967, the population has been declining at an average rate of 18% per year, or
roughly 50% per generation. This ESU is currently listed as endangered under the California
Endangered Species Act and was listed as threatened in 1989 and reclassified as endangered in
1994 under the U.S. Endangered Species Act.
2) Central Valley Spring-Run ESU
Spring-run chinook salmon were once the predominant run in the Central Valley. Dam
construction and habitat degradation has eliminated spring-run populations from the entire San
Joaquin River Basin and from many tributaries to the Sacramento River Basin. Abundance has
declined dramatically from historical levels, and much of the present day production is from
artificial propagation. There are only a few naturally-spawning populations remaining and these
all have relatively low abundances (<1000). Furthermore, there is concern that the hatchery
propagated spring-run fish have been inadvertently hybridized with fall-run fish. Hatchery
release practices result in high levels of straying and an increased potential for hatchery strays
spawning with native fish. The majority of the BRT concluded that this ESU was at risk of
extinction in the foreseeable future.
Total abundance in this ESU is relatively high, perhaps near historical levels. However,
the status of populations in the San Joaquin River Basin are extremely depressed. Spawning and
rearing habitat quality throughout the ESU are severely impacted by agricultural and municipal
water use activities. Returns to the hatcheries account for 20% of the spawning escapement, and
hatchery strays spawning in the wild may account for an further 30% of the spawning
escapement. The exchange of stocks between Central Valley hatcheries may have resulted in
considerable loss of among-population genetic diversity. Furthermore, naturally-spawning
populations that are least influenced by hatchery strays are experiencing generally negative trends
in abundance. Finally, relatively high ocean and freshwater harvest rates may threaten the
sustainability of naturally spawning populations. The majority of the BRT felt that this ESU is
likely to become at risk of extinction in the foreseeable future.
Populations in this ESU have generally experienced declines in abundance from historical
levels, with the exception of populations in the Rogue River. Spring-run populations outside of
the Rogue River have undergone severe declines. There is an almost complete lack of data for
coastal rivers south of the Klamath River, and many rivers which historically sustained large
populations of fall-run chinook salmon contain severely reduced populations or their populations
have been extirpated. The BRT unanimously concluded that this ESU was likely to become at
risk of extinction in the foreseeable future.
Fall-run populations in this ESU are at relatively high abundances, near historical levels,
and trends are generally stable. Hatchery production contributes significantly to total
escapement. In contrast, spring-run abundance is at only 10% of historical levels, and much of
the present production is hatchery-derived. Dam construction eliminated much of the historical
spring-run spawning and rearing habitat and was responsible, in part, for the extirpation of at
least seven spring-run populations. Due to the disparity in risk status between spring and fall
runs, the BRT had considerable difficulty in evaluating the status of this ESU. The majority of
the BRT concluded that this ESU, as a whole, was not presently at significant risk of extinction,
but there was substantial concern for the status of spring-run populations.
Total abundance in this ESU is relatively high. Long-term trends for populations are
generally upward, although a number of populations are experiencing severe short-term trends in
abundance. Spring-run populations are generally in better condition in this ESU than in other
coastal ESUs. Hatchery production appears to be a relatively minor component of total
escapement. The BRT unanimously concluded that chinook salmon in this ESU are not in
danger of extinction nor are they likely to become so in the foreseeable future.
Long-term trends for most populations in this ESU have been upward; however, several
smaller populations are experiencing sharply downward trends. Fall-run populations are
predominant and tended to be at a lower risk than spring or summer runs. Hatchery production is
significant in the southern portion of this ESU, whereas the majority of the populations in the
northern portion of the ESU have minimal hatchery influence. The BRT unanimously concluded
that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so
in the foreseeable future.
Total abundance in the ESU is relatively high; however, much of this production is
hatchery-derived. Both long- and short-term trends in abundance are predominantly downward,
and several populations are exhibiting severe short-term declines. Spring-run chinook salmon
populations throughout this ESU are all depressed. The BRT was concerned that the high level
of hatchery production is masking more severe underlying trends in abundance. In many areas,
spawning and rearing habitats were severely degraded and migratory access restricted or
eliminated. A majority of the BRT concluded that this ESU is likely to become endangered in
the foreseeable future.
Abundance in this ESU is relatively high; however, the majority of the fish appear to be
hatchery-produced. The chinook salmon fall run in the Lewis River appears to be the only
healthy naturally-produced population in this ESU. Long- and short-term trends in abundance
are mostly negative, some severely so. The numbers of naturally-spawning spring runs are very
low, in fact, the BRT was unable to identify any healthy native spring-run populations. The
pervasive influence of hatchery fish in almost every river in this ESU and the degradation of
freshwater habitat suggested that many naturally-spawning populations are not able to replace
themselves. The majority of the BRT concluded that this ESU is likely to become endangered in
the foreseeable future.
Total abundance in this ESU is relatively high (20,000-30,000 adults) and stable;
however, approximately 10% of escapement spawns naturally, and of the natural spawners more
than half are first-generation hatchery strays. The introduction of non-native fall-run chinook
salmon above Willamette Falls is viewed as a potential risk to the genetic integrity of this ESU.
Furthermore, exchanges of fish between hatcheries in this ESU has most likely lead to the
homogenization of populations within the ESU, although this ESU is still quite distinct from
adjacent ESUs. The majority of the historical spawning habitat is now inaccessible, and the
remaining habitat is quite limited and degraded. The majority of the BRT concluded that this
ESU is likely to become endangered in the foreseeable future.
Total abundance in the ESU has declined considerably from historical levels, but appears
to be relatively stable during recent years. Natural production accounts for most of the
escapement in the Yakima and Deschutes River Basins. Habitat degradation, especially due to
agricultural practices, affects most of the rivers in this ESU. The majority of the BRT concluded
that chinook salmon in this ESU are not in danger of extinction nor are they likely to become so
in the foreseeable future.
Total abundance in this ESU is quite high, although naturally spawning chinook salmon
in the Hanford Reach are responsible for the vast majority of the production. The BRT was
concerned about the recent decline in summer-run populations in this ESU, and the apparent
increase in the contribution of hatchery return to total escapement. It was unclear if, under
current conditions, the naturally spawning summer-run chinook salmon populations are self-
sustaining. In an earlier review, this ESU was determined to be neither at risk of extinction nor
likely to become so, and its status was not reviewed in detail here.
Recent total abundance in this ESU is quite low, and escapements from 1994-96 were the
lowest in 60 years. At least 6 populations of spring-run chinook salmon in the ESU have been
extirpated, and almost all remaining naturally-spawning populations have fewer than 100
spawners. Hydrosystem development has blocked access to much historical habitat and directly
impeded adult and smolt migrations. The majority of the BRT concluded that this ESU is
currently at risk of extinction.
Historically the Snake River component of this ESU was the predominant source of
production. Currently the five-year average for Snake River fall-run chinook salmon is about
500 adults (compared with 72,000 in the 1930s and 1940s). The abundance of naturally-
spawning fish in the Deschutes River has averaged about 6,000 fish (1990-96). There is some
uncertainty as to the origins of fish spawning in the lower Deschutes River, and their relationship
to fish in the upper Deschutes River (above Sherars Falls). Extirpated populations in the John
Day, Umatilla, and Walla Walla Rivers are believed to have belonged to this ESU. Hydrosystem
development blocks access to most of the historical spawning habitat in the Snake River portion
of this ESU, as well as affecting migration corridors. Snake River fall-run chinook salmon are
currently listed as a threatened species under the U.S. ESA. The BRT concluded that the newly
defined ESU (which includes the Deschutes River population) is likely to become in danger of
extinction in the foreseeable future.
Recent abundance of the naturally-spawning population for this ESU has averaged about 2,500 fish, compared to historical levels of approximately 1.5 million. Both long- and short-term trends are negative for all populations. A number of populations have been extirpated in this ESU, primarily due to dam construction. This ESU is presently listed as a threatened species under the U.S. ESA and was not reviewed further in this document.
The status review for west coast chinook salmon was conducted by a team of scientists
from the National Marine Fisheries Service (NMFS) and the U.S. Geological Survey (USGS).
The members of the biological review team (BRT) contributed a substantial amount of time and
effort to this process. The BRT included: Peggy Busby, Dr. Stewart Grant, Dr. Robert Iwamoto,
Dr. Robert Kope, Dr. Conrad Mahnken, Gene Matthews, Dr. James Myers, Philip Roni,
Dr. Michael Schiewe, David Teel, Dr. Thomas Wainwright, F. William Waknitz, Dr. Robin
Waples, and Dr. John Williams of NMFS Northwest Fisheries Science Center; Gregory Bryant
and Craig Wingert of NMFS Southwest Region; Dr. Peter Adams and Dr. Steve Lindley from
NMFS Southwest F.S.C. (Tiburon Laboratory); Alex Wertheimer of NMFS Alaska Fisheries
Science Center (Auke Bay Laboratory); and Dr. Reg Reisenbichler from the USGS Biological
Resource Division. Their review was dependent on information submitted directly to NMFS,
which was presented at one of the Biological and Technical Committee meetings, provided in
response to queries by NMFS or previously published in reports or the scientific literature. A
number of state, federal, and tribal agencies actively provided information and critical review
during the status review process. The authors wish to acknowledge in particular the efforts of
Lisa Seeb and Penny Crane of the Alaska Department of Fish and Game; Alan Baracco, Colleen
Harvey, Bill Loudermilk, Debra McKee, Mike Wallace, Dave McLeod, Larry Preston, and Wade
Sinnen from the California Department of Fish and Game; Kathryn Kostow and Jay Nicholas of
the Oregon Department of Fish and Wildlife; Susan Bishop, formerly of the Northwest Indian
Fisheries Commission; Duane Anderson and Gary Christofferson of StreamNet; Jim Craig and
Doug Olsen from U.S. Fish and Wildlife Service; Jerry Boberg and Al Olsen of the U.S. Forest
Service; and Anne Marshall, Carol Smith, Bill Tweit, and Bob Woodard of the Washington
Department of Fish and Wildlife.
The authors also wish to thank the external reviewers, Dr. T. Bjornn, Dr. D. Hankin, Dr. E. Taylor, and Dr. F. Utter, who provided considerable insight and clarity to the complex issues concerning chinook salmon. Additional thanks to Judith Larsen, Tod McCoy, Sue Joerger, Kathleen Jewett, and JoAnne Butzerin for their editorial and technical writing skills.