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[Federal Register: March 9, 1998 (Volume 63, Number 45)]
[Proposed Rules]
[Page 11481-11520]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr09mr98-31]
[[Page 11481]]
_______________________________________________________________________
Part II
Department of Commerce
_______________________________________________________________________
National Oceanic and Atmospheric Administration
_______________________________________________________________________
50 CFR Parts 222, 226, and 227
Endangered and Threatened Species: West Coast Chinook Salmon; Listing
Status Change; Proposed Rule
[[Page 11482]]
DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
50 CFR Parts 222, 226, and 227
[Docket No. 980225050-8050-01; I.D. 022398C]
RIN 0648-AK65
Endangered and Threatened Species: Proposed Endangered Status for
Two Chinook Salmon ESUs and Proposed Threatened Status for Five Chinook
Salmon ESUs; Proposed Redefinition, Threatened Status, and Revision of
Critical Habitat for One Chinook Salmon ESU; Proposed Designation of
Chinook Salmon Critical Habitat in California, Oregon, Washington,
Idaho
AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and
Atmospheric Administration (NOAA), Commerce.
ACTION: Proposed rule; proposed redefinition; proposed designation and
revision of critical habitat; request for comments.
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SUMMARY: NMFS completed a comprehensive status review of west coast
chinook salmon (Oncorhynchus tshawytscha, or O. tshawytscha)
populations in Washington, Oregon, Idaho, and California in response to
petitions filed to list chinook salmon under the Endangered Species Act
(ESA). Based on this review, NMFS identified a total of 15
Evolutionarily Significant Units (ESUs) of chinook salmon within this
range, including two Snake River ESUs already listed under the ESA, one
previously identified ESU (mid-Columbia River summer/fall run) for
which no listing was proposed, and one population (Sacramento River
winter run) that was listed as a ``distinct population segment'' prior
to the formulation of the NMFS ESU policy. With respect to the 12 ESUs
that are the subject of this proposed rule, NMFS has concluded that two
ESUs are at risk of extinction and five ESUs are at risk of becoming
endangered in the foreseeable future. NMFS also concluded that one
currently listed ESU should be redefined to include additional chinook
salmon populations and that this redefined ESU is at risk of becoming
endangered in the foreseeable future. NMFS also concluded that four
ESUs are not at risk of extinction nor at risk of becoming endangered
in the foreseeable future. Finally, NMFS also renamed the previously
identified Mid-Columbia River summer/fall-run ESU as the Upper Columbia
River summer/fall-run ESU.
NMFS is now issuing a proposed rule to list two ESUs as endangered,
five ESUs as threatened, and to redefine one currently listed ESU to
include additional chinook populations, under the ESA. The endangered
chinook salmon are located in California (Central Valley spring-run
ESU) and Washington (Upper Columbia River spring-run ESU). The
threatened chinook salmon are dispersed throughout California, Oregon,
and Washington. They include the California Central Valley fall-run
ESU, the Southern Oregon and California Coastal ESU, the Puget Sound
ESU, the Lower Columbia River ESU, and the Upper Willamette River ESU.
NMFS also proposes to redefine the Snake River fall-run chinook salmon
ESU to include fall chinook salmon populations in the Deschutes River,
and proposes to list this redefined ESU as a threatened species. This
proposal does not affect the current definition and threatened status
of the listed Snake River fall chinook salmon ESU.
In each ESU identified as threatened or endangered, only naturally
spawned, non-introduced chinook salmon are proposed for listing. Prior
to the final listing determinations, NMFS will examine the relationship
between hatchery and natural populations of chinook salmon in these
ESUs and assess whether any hatchery populations are essential for the
recovery of the natural populations and thus will be listed.
NMFS is proposing to designate critical habitat for the chinook
salmon ESUs newly proposed for listing within this notice, and for the
Snake River fall-run ESU, proposing to revise its existing critical
habitat. At this time, proposed critical habitat for these ESUs is the
species' current freshwater and estuarine range, certain marine areas,
and includes all waterways, substrate, and adjacent riparian zones
below longstanding, impassible, natural barriers.
NMFS is requesting public comments on the issues pertaining to this
proposed rule. NMFS is also requesting suggestions and comments on
integrated local/state/tribal/Federal conservation measures that will
achieve the purposes of the ESA to recover the health of chinook salmon
populations and the ecosystems upon which they depend. Should the
proposed listing be made final, NMFS will adopt protective regulations
and a recovery plan under the ESA.
DATES: Comments must be received by June 8, 1998. NMFS will announce
the dates and locations of public hearings in Washington, Oregon,
Idaho, and California in a forthcoming Federal Register notice.
Requests for additional public hearings must be received by April 23,
1998.
ADDRESSES: Comments on this proposed rule, requests for reference
materials, and requests for public hearings should be sent to Chief,
Protected Species Division, NMFS, 525 NE Oregon Street, Suite 500,
Portland, OR 97232-2737.
FOR FURTHER INFORMATION CONTACT: Garth Griffin, 503-231-2005, Craig
Wingert, 562-980-4021, or Joe Blum, 301-713-1401.
SUPPLEMENTARY INFORMATION:
Previous Federal ESA Actions Related to West Coast Chinook
West Coast chinook salmon have been the subject of many Federal ESA
actions. In November 1985, NMFS received a petition to list Sacramento
River winter-run chinook salmon from the American Fisheries Society
(AFS). NMFS determined that the petitioned action might be warranted
and announced it would conduct a review of the run's status (51 FR
5391, February 13, 1986). In its status review, NMFS determined that
Sacramento River winter-run chinook salmon was a ``species'' for the
purposes of the ESA, but based upon the conservation and restoration
efforts by California and other Federal resource agencies, declined to
list the winter-run chinook at that time (52 FR 6041, February 27,
1987). Subsequent low returns prompted NMFS to adopt an emergency rule
listing Sacramento River winter-run chinook salmon as a threatened
species under the ESA (54 FR 10260, August 4, 1989). NMFS then issued a
proposed rule to list Sacramento River winter-run chinook as a
threatened species under the ESA (55 FR 102260, March 20, 1990), and
also published a second emergency rule listing the winter-run chinook
as threatened to avoid any lapse in ESA protections while considering
the proposed rule (55 FR 12191, April 2, 1990). On November 5, 1990,
NMFS completed its listing determination for Sacramento River winter-
run chinook, and published a final rule listing the run as a threatened
species under the ESA (55 FR 46515).
In June 1991, AFS petitioned NMFS to reclassify the winter-run as
an endangered species. Based on the information submitted by AFS, and
after reviewing all other available data, NMFS determined that the
petitioned action may be warranted, and announced its intention to
review the status of the winter-run chinook (56 FR 58986, November 7,
1991), and then published a proposed rule to reclassify
[[Page 11483]]
winter-run chinook salmon as endangered under the ESA (57 FR 27416,
June 19, 1992). Critical habitat for Sacramento winter-run chinook
salmon was designated on June 16, 1993 (58 FR 33212). After several
extensions of the listing determination and the comment period, NMFS
finalized its proposed rule and re-classified the winter-run chinook as
an endangered species under the ESA (59 FR 440, January 4, 1994).
While NMFS was reviewing and reclassifying the status of Sacramento
River chinook, NMFS also received a petition from Oregon Trout and five
co-petitioners on June 7, 1990, to list Snake River spring/summer and
fall chinook salmon as threatened species under the ESA. On September
11, 1990, NMFS determined that the petition presented substantial
scientific information indicating that the proposed action may be
warranted, and initiated a status review (55 FR 37342). NMFS published
a proposed rule listing two Snake River chinook salmon runs as
threatened under the ESA on June 27, 1991 (56 FR 29542 and 56 FR
29547). NMFS finalized its rule listing these Snake River chinook
salmon runs as threatened species on April 22, 1992 (57 FR 14653).
Meanwhile, on June 3, 1993, American Rivers and 10 other
organizations petitioned NMFS to add Mid-Columbia River summer chinook
salmon to the list of endangered species. NMFS determined that this
petition presented substantial scientific information indicating that
the petitioned action may be warranted, and initiated a status review
(58 FR 46944, September 3, 1993). Subsequently, NMFS determined that
mid-Columbia River summer chinook salmon did not qualify as an ESU, and
therefore was not a ``distinct population segment'' under the ESA (59
FR 48855, September 23, 1994). However, NMFS determined that mid-
Columbia River summer chinook salmon were part of a larger ESU that
included all late-run (summer and fall) Columbia River chinook salmon
between McNary and Chief Joseph dams. NMFS also concluded that this ESU
did not warrant listing as a threatened or endangered species (59 FR
48855, September 23, 1994).
Immediately prior to that determination, NMFS determined that a
petition filed on March 14, 1994, by Professional Resources
Organization-Salmon (PRO-Salmon) to list various populations of chinook
salmon in Washington contained substantial scientific information
indicating that the petitioned action may be warranted (59 FR 46808,
September 12, 1994). NMFS then announced that it would commence a
coast-wide status review of all west coast chinook salmon (59 FR
46808). Shortly after initiating this comprehensive coast wide status
review for chinook and other salmon species, NMFS received a petition
from Oregon Natural Resource Council and Dr. Richard Nawa on February
1, 1995, to list chinook salmon throughout its range. NMFS determined
that this petition contained substantial scientific information
indicating that the petitioned action may be warranted, and reconfirmed
its intention to conduct a comprehensive coast wide status review of
west coast chinook salmon (60 FR 30263, June 8, 1995).
In the intervening period between the two most recent petitions to
list various populations of west coast chinook salmon, NMFS published
an emergency rule on August 18, 1994 (59 FR 42529) after determining
that the status of Snake River spring/summer-run and Snake River fall-
run chinook salmon warranted reclassification as endangered, based on
projected declines and low abundance levels of adult chinook salmon.
Because emergency rules under the ESA have a maximum duration of 240
days (see 16 U.S.C. 1533(b)(7) and 50 CFR Sec. 424.20(a)), NMFS
published a proposed rule reclassifying listed Snake River spring/
summer-run and Snake River fall-run chinook salmon ESUs as endangered
on December 28, 1994 (59 FR 66784). Since publishing that proposed
rule, a congressional moratorium on listing activities, a large ESA
listing determination backlog and other delays prevented NMFS from
completing its assessment of the proposed rule. During this period,
abundance of both stocks of Snake River chinook salmon has increased.
Based on these increases, along with improved management activities
affecting these chinook salmon, NMFS concluded that the risks facing
these chinook salmon ESUs are lower than they were at the time of the
proposed rule, and thus NMFS withdrew the proposed reclassification (63
FR 1807, January 12, 1998).
During the coast wide chinook salmon status review initiated in
September, 1994, NMFS assessed the best available scientific and
commercial data, including technical information from Pacific Salmon
Biological Technical Committees (PSBTCs) and interested parties in
Washington, Oregon, Idaho, and California. The PSBTCs consisted
primarily of scientists (from Federal, state, and local resource
agencies, Indian tribes, industries, universities, professional
societies, and public interest groups) possessing technical expertise
relevant to chinook salmon and their habitats.
A NMFS Biological Review Team, composed of scientists from NMFS'
Northwest and Southwest Fisheries Science Centers, NMFS' Northwest and
Southwest Regional Offices, as well as a representative of the National
Biological Service, completed a coast wide status review for chinook
salmon [Memorandum to W. Stelle and W. Hogarth from M. Schiewe,
December 18, 1997, Chinook Salmon Status Review Report]. The review
(summary follows) evaluates the status of 15 chinook salmon ESUs in the
four states. The complete results of NMFS' status review for chinook
salmon populations will be published in a forthcoming NOAA Technical
Memorandum (Myers et al., 1998).
Chinook Salmon Life History and Ecology
Chinook salmon (O. tshawytscha) are easily distinguished from other
Oncorhynchus species by their large size. Adults weighing over 120
pounds have been caught in North American waters. Chinook salmon are
very similar to coho salmon (O. kisutch) in appearance while at sea
(blue-green back with silver flanks), except for their large size,
small black spots on both lobes of the tail, and black pigment along
the base of the teeth. Chinook salmon are anadromous and semelparous.
This means that as adults, they migrate from a marine environment into
the fresh water streams and rivers of their birth (anadromous) where
they spawn and die (semelparous). Adult female chinook will prepare a
spawning bed, called a redd, in a stream area with suitable gravel
composition, water depth and velocity. Redds will vary widely in size
and in location within the stream or river. The adult female chinook
may deposit eggs in 4 to 5 ``nesting pockets'' within a single redd.
After laying eggs in a redd, adult chinook will guard the redd from 4
to 25 days before dying. Chinook salmon eggs will hatch, depending upon
water temperatures, between 90 to 150 days after deposition. Stream
flow, gravel quality, and silt load all significantly influence the
survival of developing chinook salmon eggs. Juvenile chinook may spend
from 3 months to 2 years in freshwater after emergence and before
migrating to estuarine areas as smolts, and then into the ocean to feed
and mature. Historically, chinook salmon ranged as far south as the
Ventura River, California, and their northern extent reaches the
Russian Far East.
Among chinook salmon, two distinct races have evolved. One race,
described
[[Page 11484]]
as a ``stream-type'' chinook, is found most commonly in headwater
streams. Stream-type chinook salmon have a longer freshwater residency,
and perform extensive offshore migrations before returning to their
natal streams in the spring or summer months. The second race is called
the ``ocean-type'' chinook, which is commonly found in coastal streams
in North America. Ocean-type chinook typically migrate to sea within
the first three months of emergence, but they may spend up to a year in
freshwater prior to emigration. They also spend their ocean life in
coastal waters. Ocean-type chinook salmon return to their natal streams
or rivers as spring, winter, fall, summer, and late-fall runs, but
summer and fall runs predominate (Healey, 1991). The difference between
these life history types is also physical, with both genetic and
morphological foundations.
Juvenile stream- and ocean-type chinook salmon have adapted to
different ecological niches. Ocean-type chinook salmon tend to utilize
estuaries and coastal areas more extensively for juvenile rearing. The
brackish water areas in estuaries also moderate physiological stress
during parr-smolt transition. The development of the ocean-type life
history strategy may have been a response to the limited carrying
capacity of smaller stream systems and glacially scoured, unproductive,
watersheds, or a means of avoiding the impact of seasonal floods in the
lower portion of many watersheds (Miller and Brannon, 1982).
Stream-type juveniles are much more dependent on freshwater stream
ecosystems because of their extended residence in these areas. A
stream-type life history may be adapted to those watersheds, or parts
of watersheds, that are more consistently productive and less
susceptible to dramatic changes in water flow, or which have
environmental conditions that would severely limit the success of
subyearling smolts (Miller and Brannon, 1982; Healey, 1991). At the
time of saltwater entry, stream-type (yearling) smolts are much larger,
averaging 73-134 mm depending on the river system, than their ocean-
type (subyearling) counterparts and are therefore able to move offshore
relatively quickly (Healey, 1991).
Coastwide, chinook salmon remain at sea for 1 to 6 years (more
commonly 2 to 4 years), with the exception of a small proportion of
yearling males (called jack salmon) which mature in freshwater or
return after 2 or 3 months in salt water (Rutter, 1904; Gilbert, 1912;
Rich, 1920; Mullan et al., 1992). Ocean- and stream-type chinook salmon
are recovered differentially in coastal and mid-ocean fisheries,
indicating divergent migratory routes (Healey, 1983 and 1991). Ocean-
type chinook salmon tend to migrate along the coast, while stream-type
chinook salmon are found far from the coast in the central North
Pacific (Healey 1983 and 1991; Myers et al., 1984). Differences in the
ocean distribution of specific stocks may be indicative of resource
partitioning and may be important to the success of the species as a
whole.
There is a significant genetic influence to the freshwater
component of the returning adult migratory process. A number of studies
show that chinook salmon return to their natal streams with a high
degree of fidelity (Rich and Holmes 1928; Quinn and Fresh, 1984;
McIssac and Quinn, 1988). Salmon may have evolved this trait as a
method of ensuring an adequate incubation and rearing habitat. It also
provides a mechanism for reproductive isolation and local adaptation.
Conversely, returning to a stream other than that of one's origin is
important in colonizing new areas and responding to unfavorable or
perturbed conditions at the natal stream (Quinn, 1993).
Chinook salmon stocks exhibit considerable variability in size and
age of maturation, and at least some portion of this variation is
genetically determined. The relationship between size and length of
migration may also reflect the earlier timing of river entry and the
cessation of feeding for chinook salmon stocks that migrate to the
upper reaches of river systems. Body size, which is correlated with
age, may be an important factor in migration and redd construction
success. Roni and Quinn (1995) reported that under high density
conditions on the spawning ground, natural selection may produce stocks
with exceptionally large-sized returning adults.
Early researchers recorded the existence of different temporal
``runs'' or modes in the migration of chinook salmon from the ocean to
freshwater. Freshwater entry and spawning timing are believed to be
related to local temperature and water flow regimes (Miller and
Brannon, 1982). Seasonal ``runs'' (ie., spring, summer, fall, or
winter) have been identified on the basis of when adult chinook salmon
enter freshwater to begin their spawning migration. However, distinct
runs also differ in the degree of maturation at the time of river
entry, the thermal regime and flow characteristics of their spawning
site, and their actual time of spawning. Egg deposition must occur at a
time to ensure that fry emerge during the following spring when the
river or estuary productivity is sufficient for juvenile survival and
growth.
Other Life History Traits
Pathogen resistance is another locally adapted trait. Chinook
salmon from the Columbia River drainage were less susceptible to
Ceratomyxa shasta, an endemic pathogen, than stocks from coastal rivers
where the disease is not known to occur (Zinn et al., 1977). Alaskan
and Columbia River stocks of chinook salmon exhibit different levels of
susceptibility to the infectious hematopoietic necrosis virus (IHNV)
(Wertheimer and Winton 1982). Variability in temperature tolerance
between populations is likely due to selection for local conditions;
however, there is little information on the genetic basis of this trait
(Levings, 1993).
Consideration as a ``Species'' Under the ESA
To qualify for listing as a threatened or endangered species, the
identified populations of chinook salmon must be considered ``species''
under the ESA. The ESA defines a ``species'' to include ``any
subspecies of fish or wildlife or plants, and any distinct population
segment of any species of vertebrate fish or wildlife which interbreeds
when mature.'' NMFS published a policy (56 FR 58612, November 20, 1991)
describing the agency's application of the ESA definition of
``species'' to anadromous Pacific salmonid species. NMFS' policy
provides that a Pacific salmonid population will be considered distinct
and, hence, a species under the ESA if it represents an ESU of the
biological species. A population must satisfy two criteria to be
considered an ESU, it must be reproductively isolated from other
conspecific population units, and it must represent an important
component in the evolutionary legacy of the biological species. The
first criterion, reproductive isolation, need not be absolute, but must
be strong enough to permit evolutionarily important differences to
accrue in different population units. The second criterion is met if
the population contributes substantially to the ecological and genetic
diversity of the species as a whole. Guidance on the application of
this policy is contained in a scientific paper ``Pacific Salmon
(Oncorhynchus spp.) and the Definition of `Species' under the
Endangered Species Act'' (Waples, 1991) and a NOAA Technical Memorandum
``Definition of `Species' Under the Endangered Species Act: Application
to Pacific Salmon'' (NMFS F/NWC-194) which are available upon request
(see ADDRESSES). The following sections
[[Page 11485]]
describe the genetic, ecological, and life history characteristics, as
well as human-induced genetic changes that NMFS assessed to determine
the number and geographic extent of chinook salmon ESUs.
Reproductive Isolation
Genetic data provide useful indirect information on reproductive
isolation because they integrate information about migration and gene
flow over evolutionarily important time frames.
Genetic information obtained from allozyme, DNA, and chromosomal
sampling indicate strong differentiation between chinook salmon ESUs,
and were largely consistent with those described in previous studies of
chinook salmon. Puget Sound populations of chinook salmon appear to
constitute a genetically distinct group, a conclusion that is
consistent with the results of Utter et al. (1989) and Marshall et al.
(1995). In NMFS' analyses, Washington coastal populations appeared to
form a genetically distinct group that was most similar to, but still
distinct from, Oregon coastal populations. The Washington coastal group
included the Hoko River population in the western part of the Strait of
Juan de Fuca. Chinook salmon in the Elwha River, which also drains into
the Strait of Juan de Fuca, were genetically intermediate between Puget
Sound and Washington coastal populations.
Chinook salmon populations in the Columbia and Snake Rivers appear
to be separated into two large genetic groups: those producing ocean-
type outmigrants and those producing stream-type outmigrants. The first
group includes populations in lower Columbia River tributaries, with
both spring-run and fall-run (``tule'') life histories. These ocean-
type populations exhibit a range of juvenile life history patterns that
appear to depend on local environmental conditions. The Willamette
River hatchery populations form a distinct subgroup within the lower
Columbia River group. Ocean-type chinook salmon populations east of the
Cascade Range Crest include both summer-and fall-run (``bright'')
populations, and are genetically distinct from lower Columbia River
ocean-type populations. Fall-run populations in the Snake River,
Deschutes River, and Marion Drain (Yakima River) form a distinct
subgroup.
The second major group of chinook salmon in the Columbia and Snake
River drainage consists of spring- or summer-run fish. Based on
analysis of genetic clusters, three relatively distinct subgroups
appeared within these stream-type populations. One subgroup includes
spring-run populations in the Klickitat, John Day, Deschutes, and
Yakima Rivers of the mid-Columbia River. A second subgroup includes
upper Columbia River spring-run chinook salmon in the Wenatchee and
Methow Rivers, but also includes spring-run fish in the Grande Ronde
River and Carson Hatchery. This is likely due to the releases of exotic
Carson hatchery stock in these basins, rather than to natural genetic
similarities. A third subgroup consists of Snake River spring- and
summer-run populations in the Imnaha and Salmon Rivers, as well as
those in the Rapid River and Lookingglass Hatcheries. The Klickitat
River spring-run population appears to be genetically intermediate
between upper and lower Columbia River groups.
All populations of chinook salmon south of the Columbia River
drainage appear to consist of ocean-type fish. Populations along the
north coast of Oregon form a genetically distinct group, consisting of
populations north of and including the Elk River, except for the Rock
Creek Hatchery spring-run population, which show greater genetic
affinity to southern Oregon coastal populations. A southern coastal
group includes populations south of the Elk River to and including
populations in the lower Klamath River in northern California. However,
Euchre Creek, which is located near the Rogue River and has been
planted extensively with Elk River stock, is more similar to
populations north of Cape Blanco. Upper Klamath River populations of
chinook salmon are genetically distinct from other northern California,
southern Oregon and California Central Valley populations.
Sacramento and San Joaquin River populations are genetically
distinct from northern California coastal and Klamath River
populations. Previous studies grouped populations in the Sacramento
River with those in the San Joaquin River (Utter et al., 1989; Bartley
and Gall, 1990; Bartley et al., 1992). However, Hedgecock et al.
(1995), Banks (1996), and Nielsen (1995 and 1997) surveyed DNA markers
and these results indicate that the winter, spring, fall, and late-fall
runs may be genetically distinct from one another.
Genetic Changes Due to Human Activities
The effects of artificial propagation and other human activities
such as harvest and habitat modification, can be relevant to ESA
listing determinations in two ways. First, such activities can
genetically change natural populations so much that they no longer
represent an evolutionarily significant component of the biological
species (Waples, 1991). For example, in 1991, NMFS concluded that, as a
result of massive and prolonged effects of artificial propagation,
harvest, and habitat degradation, the agency could not identify natural
populations of coho salmon (O. kisutch) in the lower Columbia River
that qualified for ESA listing consideration (56 FR 29553, June 27,
1991). Second, risks to the viability and genetic integrity of native
salmon populations posed by human activities may contribute to their
threatened or endangered status (Goodman, 1990; Hard et al., 1992). The
severity of these effects on natural populations depends both on the
nature of the effects (e.g., harvest rate, gear size, or type of
hatchery practice) and their magnitude (e.g., duration of a hatchery
program and number and life-history stage of hatchery fish involved).
For example, artificial propagation is a common practice to
supplement chinook salmon stocks for commercial and recreational
fisheries. However, in many areas, a significant portion of the
naturally spawning population consists of hatchery-produced chinook
salmon. In several of the chinook salmon ESUs, over 50 percent of the
naturally spawning fish are from hatcheries. Many of these hatchery-
produced fish are derived from a few stocks which may or may not have
originated from the geographic area where they are released. However,
in several of the ESUs analyzed, insufficient or uncertain information
exists regarding the interactions between hatchery and natural fish,
and the relative abundance of hatchery and natural stocks.
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 bases or
phenotypic expression of life history characteristics in 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 (e.g., Crawford, 1979, NRC 1996). Second, artificial
propagation poses a number of risks to natural populations that may
affect their risk of extinction or endangerment. Finally, if any
natural populations are listed under the ESA, then it will be necessary
to determine the ESA status of
[[Page 11486]]
all associated hatchery populations. This latter determination would be
made following a proposed listing and is not considered further in this
document.
The impacts of hatchery activities on specific ESUs is discussed in
the Status of Chinook Salmon ESUs and Summary of Factors Affecting the
Species sections.
Ecological and Genetic Diversity
Several types of physical and biological evidence were considered
in evaluating the contribution of chinook salmon from Washington,
Oregon, Idaho, and California to the ecological and genetic diversity
of the biological species throughout its range. Factors examined
included: (1) The physical environment--geology, soil type, air
temperature, precipitation, river flow patterns, water temperature, and
vegetation; (2) biogeography--marine, estuarine, and freshwater fish
distributions; and (3) life history traits--age at smolting, age at
spawning, river entry timing, and spawning timing. An analysis of the
physical environment and life history traits provides important insight
into the ecological and genetic diversity of the species and can
reflect unusual or distinctive adaptations that promote evolutionary
processes.
The predominant differentiation in chinook salmon life history
types is that between ocean- and stream-type chinook salmon. Ocean-type
populations typically migrate to the ocean in their first year of life
and spend most of their marine life in coastal waters, whereas stream-
type populations migrate to sea as yearlings and often make extensive
ocean migrations.
In some areas within the Columbia River Basin, stream- and ocean-
type chinook salmon stocks spawn in relatively close proximity to one
another but are separated by run timing. Stream-type chinook salmon
include spring-run populations in the Columbia River and its
tributaries east of the Cascade Crest, and spring- and summer-run fish
in the Snake River and its tributaries. Ocean-type chinook salmon
include fall-run chinook salmon in both the Columbia and Snake River
Basins, summer-run chinook salmon from the Columbia River, and spring-
run fish from the lower Columbia River. There are substantial genetic
differences between stream- and ocean-type chinook salmon in both the
Fraser and Columbia River Basins, and the genetic analyses show clearly
that the two life history forms represent two major evolutionary
lineages.
Adult run-time has also long been used to identify different
temporal ``races'' of chinook salmon. In cases where the run-time
differences correspond to differences between stream- and ocean-type
fish (e.g., in the Columbia and Fraser River Basins), relatively large
genetic differences (as well as ecological and life history
differences) can be found between the different runs. In most coastal
areas, however, life history and genetic differences between the runs
are relatively modest, relative to the larger differences used in
designating other ESUs. Although many populations have some fraction of
yearling migrants, all the coastal populations are part of the ocean
lineage, and spring- and fall-run fish are very similar in ocean
distribution.
Among basins supporting only ocean-type chinook salmon, the
Sacramento River system is somewhat unusual in that its large size and
ecological diversity historically allowed for substantial spatial as
well as temporal separation of different runs. Genetic and life history
data both suggest that considerable differentiation among the runs has
occurred in this basin. The Klamath River Basin, as well as chinook
salmon in Puget Sound, shares some features of coastal rivers but
historically also provided an opportunity for substantial spatial
separation of different temporal runs. As discussed below, the
diversity in run timing made identifying ESUs difficult in the Klamath
and Sacramento River Basins.
NMFS considers differences in life history traits as a possible
indicator of adaptation to different environmental regimes and resource
partitioning within those regimes. The relevance of the ecologic and
genetic basis for specific chinook salmon life-history traits as they
pertain to each ESU is discussed in the brief summary that follows.
ESU Determinations
The ESU determinations described here represent a synthesis of a
large amount of diverse information. In general, the proposed
geographic boundaries for each ESU (i.e., the watersheds within which
the members of the ESU are typically found) are supported by several
lines of evidence that show similar patterns. However, the diverse data
sets are not always entirely congruent (nor would they be expected to
be), and the proposed boundaries are not necessarily the only ones
possible. For example, in some cases (e.g., in the Middle Columbia
River near the Cascade Crest), environmental changes occur over a
transition zone rather than abruptly.
Based on the best available scientific and commercial information,
NMFS has identified 15 ESUs of chinook salmon from Washington, Oregon,
Idaho, and California, including 11 new ESUs, and one redefined ESU.
The 15 ESUs are briefly described and characterized below. Genetic data
(from studies of protein electrophoresis and DNA) were the primary
evidence considered for the reproductive isolation criterion,
supplemented by inferences about barriers to migration created by
natural geographic features and human-induced changes resulting from
artificial propagation and harvest. Factors considered to be most
informative in evaluating ecological and genetic diversity include data
pertaining to the physical environment, ocean conditions and upwelling,
vegetation, estuarine and freshwater fish distributions, river entry,
and spawning timing.
Most of the ESUs described below include multiple spawning
populations of chinook salmon, and most 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, 1991, p. 20). However, considerable
diversity in genetic or life history traits or habitat features exists
within most ESUs, and maintaining this diversity is critical to their
overall health. The descriptions below briefly summarize some of the
notable types of diversity within each ESU, and this diversity is
considered in the next section in evaluating risk to the ESUs as a
whole.
(1) Sacramento River Winter-Run ESU
This run was determined to be a distinct population segment by NMFS
in 1987, prior to development of the NMFS species policy. The NMFS
concluded that this run meets the criteria to be considered an ESU. It
includes chinook salmon entering the Sacramento River from November to
June and spawning from late-April to mid-August, with a peak from May
to June. No other chinook salmon populations have a similar life
history pattern. In general, winter-run chinook salmon exhibit an
ocean-type life-history strategy, with smolts emigrating to the ocean
after 5 to 9 months of freshwater residence (Johnson et al., 1992) and
remaining near the coasts of California and Oregon. Winter-run chinook
salmon also mature at a
[[Page 11487]]
relatively young age (2-3 years old). DNA analysis indicates
substantial genetic differences between winter-run and other chinook
salmon in the Sacramento River.
Historically, winter-run populations existed in the Upper
Sacramento, Pit, McCloud, and Calaveras Rivers. The spawning habitat
for these stocks was primarily located in the Sierra Nevada Ecoregion
(Omernik, 1987). Construction of dams on these rivers in the 1940s led
to the extirpation of populations in the San Joaquin River Basin and
displaced the Sacramento River population to areas below Shasta Dam.
(2) Central Valley Spring-Run ESU
Existing populations in this ESU spawn in the Sacramento River and
its tributaries. Historically, spring chinook salmon were the dominant
run in the Sacramento and San Joaquin River Basins (Clark, 1929), but
native populations in the San Joaquin River have apparently all been
extirpated (Campbell and Moyle, 1990). This ESU includes chinook salmon
entering the Sacramento River from March to July and spawning from late
August through early October, with a peak in September. Spring-run fish
in the Sacramento River exhibit an ocean-type life history, emigrating
as fry, subyearlings, and yearlings. Recoveries of hatchery chinook
salmon implanted with coded-wire-tags (CWT) are primarily from ocean
fisheries off the California and Oregon coast. There were minimal
differences in the ocean distribution of fall- and spring-run fish from
the Feather River Hatchery (as determined by CWT analysis); however,
due to hybridization that may have occurred in the hatchery between
these two runs, this similarity in ocean migration may not be
representative of wild runs.
Substantial ecological differences in the historical spawning
habitat for spring-run versus fall- and late-fall-run fish have been
recognized. Spring chinook salmon run timing was suited to gaining
access to the upper reaches of river systems (up to 1,500 m elevation)
prior to the onset of prohibitively high water temperatures and low
flows that inhibit access to these areas during the fall. Differences
in adult size, fecundity, and smolt size also occur between spring- and
fall/late fall-run chinook salmon in the Sacramento River.
No allozyme data are available for naturally spawning Sacramento
River spring chinook salmon. A sample from Feather River Hatchery
spring-run fish, which may have undergone substantial hybridization
with fall chinook salmon, shows modest (but statistically significant)
differences from fall-run hatchery populations. DNA data show moderate
genetic differences between the spring and fall/late-fall runs in the
Sacramento River; however, these data are difficult to interpret in the
context of this broad status review because comparable data are not
available for other geographic regions.
(3) Central Valley Fall/Late Fall-Run ESU
This ESU includes fall and late-fall chinook salmon spawning in the
Sacramento and San Joaquin Rivers and their tributaries. These
populations enter the Sacramento and San Joaquin Rivers from July
through April and spawn from October through February.
Both runs are ocean-type chinook salmon, emigrating predominantly
as fry and subyearlings and remaining off the California coast during
their ocean migration.
Sacramento/San Joaquin Basin chinook salmon are genetically and
physically distinguishable from all other coastal forms (Clark, 1929;
Synder, 1931). Ecologically, the Central Valley also differs in many
important ways from coastal areas. There were also a number of life-
history differences noted between Sacramento and San Joaquin River
Basin fall/late fall-run populations. In general, San Joaquin River
populations tend to mature at an earlier age and spawn later in the
year than Sacramento River populations. These differences could have
been phenotypic responses to the generally warmer temperature and lower
flow conditions found in the San Joaquin River Basin relative to the
Sacramento River Basin. There was no apparent difference in the
distribution of marine CWT recoveries from Sacramento and San Joaquin
River hatchery populations, nor were there genetic differences between
Sacramento and San Joaquin River fall/late fall-run populations (based
on DNA and allozyme analysis) of a similar magnitude to that used in
distinguishing other ESUs. This apparent lack of distinguishing life
history and genetic characteristics may be due, in part, to large scale
transfers of Sacramento River fall/late fall-run chinook salmon into
the San Joaquin River Basin.
(4) Southern Oregon and California Coastal ESU
This ESU includes all naturally spawned coastal spring and fall
chinook salmon spawning from Cape Blanco (inclusive of the Elk River)
to the southern extent of the current range for chinook salmon at Point
Bonita (the northern landmass marking the entrance to San Francisco
Bay). The Cape Blanco region is a major biogeographic boundary for
numerous species (e.g., steelhead and coho salmon). Chinook salmon
spawn in several small tributaries to San Francisco Bay, however it is
uncertain whether these small populations are part of this ESU, or
wanderers from Central Valley chinook salmon ESUs.
Chinook salmon from the Central Valley and Klamath River Basin
upstream from the Trinity River confluence are genetically and
ecologically distinguishable from those in this ESU. Chinook salmon in
this ESU exhibit an ocean-type life-history; ocean distribution (based
on marine CWT recoveries) is predominantly off of the California and
Oregon coasts. Life-history information on smaller populations,
especially in the southern portion of the ESU, is extremely limited.
Additionally, only anecdotal or incomplete information exists on
abundance of several spring-run populations including, the Chetco,
Winchuck, Smith, Mad, and Eel Rivers. Allozyme data indicate that this
ESU is genetically distinguishable from the Oregon Coast, Upper Klamath
and Trinity River, and Central Valley ESUs. This data also shows some
divergence between chinook populations north and south of the Klamath
River, but the available information is incomplete to describe chinook
salmon south of the Klamath River as a separate ESU. Life history
differences also exist between spring- and fall-run fish in this ESU,
but not to the same extent as is observed in larger inland basins.
Ecologically, the majority of the river systems in this ESU are
relatively small and heavily influenced by a maritime climate. Low
summer flows and high temperatures in many rivers result in seasonal
physical and thermal barrier bars that block movement by anadromous
fish. The Rogue River is the largest river basin in this ESU and
extends inland into the Sierra Nevada and Cascades Ecoregions.
(5) Upper Klamath and Trinity Rivers ESU
Included in this ESU are all Klamath River Basin populations from
the Trinity River and the Klamath River upstream from the confluence of
the Trinity River. These populations include both spring- and fall-run
fish that enter the Upper Klamath River Basin from March through July
and July through October and spawn from late August through September
and September through early January, respectively. Body morphology
[[Page 11488]]
(vertebral counts, lateral-line scale counts, and fin-ray counts) and
reproductive traits (egg size and number) for populations from the
Upper Klamath River differ from those of populations in the Sacramento
River Basin. Genetic analysis indicated that populations from the Upper
Klamath River Basin form a unique group that is quite distinctive
compared to neighboring ESUs. The Upper Klamath River crosses the
Coastal Range, Sierra Nevada, and Eastern Cascades Ecoregions, although
dams prevent access to the upper river headwaters of the Klamath River
in the Eastern Cascades Ecoregion.
Within the Upper Klamath River Basin, there are statistically
significant, but fairly modest, genetic differences between the fall
and spring runs. The majority of the spring- and fall-run fish emigrate
to the marine environment primarily as subyearlings. Recoveries of CWTs
indicate that both runs have a coastal distribution off of the
California and Oregon coasts. There was no apparent difference in the
marine distribution of CWT recoveries from fall-run (Iron Gate and
Trinity River Hatcheries) and spring-run populations (Trinity River
Hatchery).
NMFS was concerned that the only estimate of the genetic
relationship between spring and fall runs in this ESU is from a
comparison of hatchery stocks that may have undergone some
introgression during hatchery spawning operations, thus blurring the
distinguishable traits between spring- and fall-run chinook in this
ESU. NMFS acknowledges that the ESU determination should be revisited
if substantial new information from natural spring-run populations
becomes available.
(6) Oregon Coast ESU
This ESU contains coastal populations of spring- and fall-run
chinook salmon from the Elk River north to the mouth of the Columbia
River. These populations exhibit an ocean-type life-history and mature
at ages 3, 4, and 5. In contrast to the more southerly ocean
distribution pattern shown by populations from the lower Columbia River
and farther south, CWT recoveries from populations within this ESU are
predominantly from British Columbia and Alaska coastal fisheries. There
is a strong genetic separation between Oregon Coast ESU populations and
neighboring ESU populations. This ESU falls within the Coastal
Ecoregion and is characterized by a strong maritime influence, with
moderate temperatures, high precipitation levels, and easy migration
access.
(7) Washington Coast ESU
Coastal populations spawning north of the Columbia River and west
of the Elwha River are included in this ESU. These populations can be
distinguished from those in Puget Sound by their older age at maturity
and more northerly ocean distribution. Allozyme data also indicate
geographical differences between populations from this area and those
in Puget Sound, the Columbia River, and the Oregon coast ESUs.
Populations within this ESU are ocean-type chinook salmon and generally
mature at age 3, 4, and 5. Ocean distribution for these fish is more
northerly than that for the Puget Sound and Lower Columbia River ESUs.
The boundaries of this ESU lie within the Coastal Ecoregion, which is
strongly influenced by the marine environment: high precipitation,
moderate temperatures, and easy migration access.
(8) Puget Sound ESU
This ESU encompasses all naturally spawned spring, summer and fall
runs of chinook salmon in the Puget Sound region from the North Fork
Nooksack River to the Elwha River on the Olympic Peninsula, inclusive.
Chinook salmon in this area all exhibit an ocean-type life history.
Although some spring-run chinook salmon populations in the Puget Sound
ESU have a high proportion of yearling smolt emigrants, the proportion
varies substantially from year to year and appears to be
environmentally mediated rather than genetically determined. Puget
Sound stocks all tend to mature at ages 3 and 4 and exhibit similar,
coastally-oriented, ocean migration patterns. There are substantial
ocean distribution differences between Puget Sound and Washington coast
stocks, with CWT recoveries of Washington coastal chinook found in much
larger proportions from Alaskan waters. The marine distribution of
Elwha River chinook salmon most closely resembled other Puget Sound
stocks, rather than Washington coast stocks.
The NMFS concluded that, on the basis of substantial genetic
separation, the Puget Sound ESU does not include Canadian populations
of chinook salmon. Allozyme analysis of North Fork and South Fork
Nooksack River spring chinook salmon identified them as outliers, but
most closely allied with other Puget Sound samples. DNA analysis
identified a number of markers that appear to be restricted to either
the Puget Sound or Washington coastal stocks. Some allozyme markers
suggested an affinity of the Elwha River population with the Washington
coastal stocks, while others suggested an affinity with Puget Sound
stocks.
The boundaries of the Puget Sound ESU correspond generally with the
boundaries of the Puget Lowland Ecoregion. Despite being in the
rainshadow of the Olympic Mountains, the river systems in the western
portion of Puget Sound maintain high flow rates due to the melting
snowpack in the surrounding mountains. Temperatures tend to be
moderated by the marine environment. The Elwha River, which is in the
Coastal Ecoregion, is the only system in this ESU which lies outside
the Puget Sound Ecoregion. Furthermore, the boundary between the
Washington Coast and Puget Sound ESUs (which includes the Elwha River
in the Puget Sound ESU) corresponds with ESU boundaries for steelhead
and coho salmon. In life history and genetic attributes, the Elwha
River chinook salmon appear to be transitional between populations from
Puget Sound and the Washington Coast ESU.
(9) Lower Columbia River ESU
This ESU includes all naturally spawned chinook populations from
the mouth of the Columbia River to the crest of the Cascade Range,
excluding populations above Willamette Falls. Celilo Falls, which
corresponds to the edge of the drier Columbia Basin Ecosystem and
historically may have presented a migrational barrier to chinook salmon
at certain times of the year, is the eastern boundary for this ESU. Not
included in this ESU are ``stream-type'' spring chinook salmon found in
the Klickitat River (which are considered part of the Mid-Columbia
River spring-run ESU) or the introduced Carson spring-chinook salmon.
``Tule'' fall chinook salmon in the Wind and Little White Salmon Rivers
are included in this ESU, but not introduced ``upriver bright'' fall
chinook salmon populations in the Wind, White Salmon, and Klickitat
Rivers. Available information suggests that spring chinook salmon
presently in the Clackamas and Sandy Rivers are predominantly the
result of introductions from the Willamette River ESU and are thus
probably not representative of spring chinook salmon found
historically.
In addition to the geographic features mentioned above, genetic and
life-history data were important factors in defining this ESU.
Populations in this ESU are considered ocean type. Some spring-run
populations have a large proportion of yearling migrants, but this
trend may be biased by yearling hatchery releases. Subyearling migrants
were found to contribute to the
[[Page 11489]]
escapement. CWT recoveries for Lower Columbia River ESU populations
indicate a northerly migration route, but with little contribution to
the Alaskan fishery. Populations in this ESU also tend to mature at age
3 and 4, somewhat younger than populations from the coastal, upriver,
and Willamette ESUs. Ecologically, the Lower Columbia River ESU crosses
several ecoregions: Coastal, Willamette Valley, Cascades and East
Cascades.
(10) Upper Willamette River ESU
This ESU includes naturally spawned spring-run populations above
Willamette Falls. Fall chinook salmon above the Willamette Falls are
introduced and although they are naturally spawning, they are not
considered a population for purposes of defining this ESU. Historic,
naturally spawned populations in this ESU have an unusual life history
that shares features of both the stream and ocean types. Scale analysis
of returning fish indicate a predominantly yearling smolt life-history
and maturity at 4 years of age, but these data are primarily from
hatchery fish and may not accurately reflect patterns for the natural
fish. Young-of-year smolts have been found to contribute to the
returning 3 year-old year class. The ocean distribution is consistent
with an ocean-type life history, and CWT recoveries occur in
considerable numbers in the Alaskan and British Columbian coastal
fisheries. Intra-basin transfers have contributed to the homogenization
of Willamette River spring chinook salmon stocks; however, Willamette
River spring chinook salmon remain one of the most genetically
distinctive groups of chinook salmon in the Columbia River Basin.
The geography and ecology of the Willamette Valley is considerably
different from surrounding areas. Historically, the Willamette Falls
offered a narrow temporal window for upriver migration, which may have
promoted isolation from other Columbia River stocks.
(11) Mid-Columbia River Spring-Run ESU
Included in this ESU are stream-type chinook salmon spawning in the
Klickitat, Deschutes, John Day, and Yakima Rivers. Historically,
spring-run populations from the Hood, Walla Walla, and Umatilla Rivers
may have also belonged in this ESU, but these populations are now
considered extinct. Chinook salmon from this ESU emigrate to the ocean
as yearlings and apparently migrate far off-shore, as they do not
appear in appreciable numbers in any ocean fisheries. The majority of
adults spawn as 4-year-olds, with the exception of fish returning to
the upper tributaries of the Yakima River, which return predominantly
at age 5. Populations in this ESU are genetically distinguishable from
other stream-type chinook salmon in the Columbia and Snake Rivers.
Streams in this region drain desert areas east of the Cascades
(Columbia Basin Ecoregion) and are ecologically differentiated from the
colder, less productive, glacial streams of the upper Columbia River
spring-run ESU and from the generally higher elevation streams of the
Snake River.
(12) Upper-Columbia River Summer-and Fall-Run ESU
This ESU was first identified as the Mid-Columbia River summer/fall
chinook salmon ESU. Previously, Waknitz et al. (1995) and NMFS (1994)
identified an ESU that included all ocean-type chinook salmon spawning
in areas between McNary Dam and Chief Joseph Dam (59 FR 48855,
September 23, 1994). However, NMFS has now concluded that the
boundaries of this ESU do not extend downstream from the Snake River.
In particular, NMFS concluded that Deschutes River fall chinook salmon
are not part of this ESU. The ESU status of the Marion Drain population
from the Yakima River is still unresolved. NMFS also identified the
importance of obtaining more definitive genetic and life history
information for naturally spawning fall chinook salmon elsewhere in the
Yakima River drainage.
Chinook salmon from this ESU primarily emigrate to the ocean as
subyearlings but mature at an older age than ocean-type chinook salmon
in the Lower Columbia and Snake Rivers. Furthermore, a greater
proportion of CWT recoveries for this ESU occur in the Alaskan coastal
fishery than is the case for Snake River fish. The status review for
Snake River fall chinook salmon (Waples et al., 1991; NMFS, 1992) also
identified genetic and environmental differences between the Columbia
and Snake Rivers. Substantial life history and genetic differences
distinguish fish in this ESU from stream-type spring chinook salmon
from the mid- and upper-Columbia Rivers.
The ESU boundaries fall within part of the Columbia Basin
Ecoregion. The area is generally dry and relies on Cascade Range
snowmelt for peak spring flows. Historically, this ESU likely extended
farther upstream; spawning habitat was compressed down-river following
construction of Grand Coulee Dam.
(13) Upper Columbia River Spring-Run ESU
This ESU includes stream-type chinook salmon spawning above Rock
Island Dam--that is, those in the Wenatchee, Entiat, and Methow Rivers.
All chinook salmon in the Okanogan River are apparently ocean-type and
are considered part of the Upper Columbia River summer- and fall-run
ESU. These upper Columbia River populations exhibit classical stream-
type life-history strategies: yearling smolt emigration with only rare
CWT recoveries in coastal fisheries. These populations are genetically
and ecologically well separated from the summer- and fall-run
populations that exist in the lower parts of many of the same river
systems.
Rivers in this ESU drain the east slopes of the Cascade Range and
are fed primarily by snowmelt. The waters tend to be cooler and less
turbid than the Snake and Yakima Rivers to the south. Although these
fish appear to be closely related genetically to stream-type chinook
salmon in the Snake River, NMFS recognized substantial ecological
differences between the Snake and Columbia Rivers, particularly in the
upper tributaries favored by stream-type chinook salmon. Allozyme data
demonstrate even larger differences between spring chinook salmon
populations from the mid- and upper-Columbia River.
Artificial propagation programs have had a considerable influence
on this ESU. During the Grand Coulee Fish-Maintenance Project (GCFMP,
1939-1943), all spring chinook salmon reaching Rock Island Dam,
including those destined for areas above Grand Coulee Dam, were
collected and they or their progeny were dispersed into streams in this
ESU (Fish and Hanavan, 1948). Some ocean-type fish were undoubtedly
also incorporated into this program. Spring-run escapements to the
Wenatchee, Entiat, and Methow Rivers were severely depressed prior to
the GCFMP but increased considerably in subsequent years, suggesting
that the effects of the program may have been substantial.
Subsequently, widespread transplants of Carson stock spring chinook
salmon (derived from a mixture of Columbia River and Snake River
stream-type chinook salmon) have also contributed to erosion of the
genetic integrity of this ESU.
In spite of considerable homogenization, this ESU still represents
an important genetic resource, in part because it presumably contains
the last remnants of the gene pools for populations from the headwaters
of the Columbia River.
[[Page 11490]]
(14) Snake River Fall-Run ESU
This ESU, which includes ocean-type fish, was identified in an
earlier status review (Waples et al., 1991; NMFS, 1992). In that status
review and in a later review of mid-Columbia River summer chinook
salmon (Waknitz et al., 1995), the ESU status of populations from
Marion Drain and the Deschutes River was not resolved, so these issues
were considered in the current review.
Both populations show a greater genetic affinity to Snake River
fall chinook salmon than to other ocean-type Columbia River populations
such as the Upper Columbia River summer/fall-run ESU. After evaluation,
NMFS concluded that chinook salmon spawning in the Marion Drain could
not be assigned to any historic or current ESU with any certainty.
However, after further review, NMFS has concluded that the
Deschutes River chinook salmon population should be considered part of
the Snake River fall-run ESU. The Deschutes River historically
supported a population of fall chinook salmon, as evidenced by counts
of fish at Sherars Falls in the 1940s. Genetic and life history data
for the current population indicate a closer affinity to fall chinook
salmon in the Snake River than to those in the Columbia River.
Similarities were observed in the distribution of CWT ocean recoveries
for Snake River and Deschutes River fall-run chinook salmon; however,
information on Deschutes River fish was based on a limited number of
releases over a relatively short time frame. CWT recovery data indicate
that straying by non-native chinook salmon into the Deschutes River is
very low and does not appear to be disproportionately influenced by
Snake River fall-run chinook salmon (Hymer et al., 1992). Fall-run
chinook populations from the John Day, Umatilla, and Walla Walla Rivers
would also be included in this ESU, but are believed to have been
extirpated.
(15) Snake River Spring- and Summer-Run ESU
This ESU, which includes populations of spring- and summer-run
chinook salmon from the Snake River Basin (excluding the Clearwater
River), was identified in a previous status review (Matthews and
Waples, 1991; NMFS, 1992). These populations show modest genetic
differences, but substantial ecological differences, in comparison with
Mid- and Upper Columbia River spring- and summer-run chinook salmon
populations. Populations from this ESU emigrate to the ocean as
yearlings, mature at ages 4 and 5, and are rarely taken in ocean
fisheries. The majority of the spawning habitat occurs in the Northern
Rockies and Blue Mountains ecoregions.
Status of Chinook Salmon ESUs
The ESA 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.'' In previous status reviews (e.g., Weitkamp et al., 1995), NMFS
has identified a number of factors that should be considered in
evaluating the level of risk faced by an ESU, including: (1) Absolute
numbers of fish and their spatial and temporal distribution; (2)
current abundance in relation to historical abundance and current
carrying capacity of the habitat; (3) trends in abundance; (4) natural
and human-influenced factors that cause variability in survival and
abundance; (5) possible threats to genetic integrity (e.g., from strays
or outplants from hatchery programs); and (6) recent events (e.g., a
drought or changes in harvest management) that have predictable short-
term consequences for abundance of the ESU.
During the coastwide status review for chinook salmon, NMFS
evaluated both qualitative and quantitative information to determine
whether any proposed ESU is threatened or endangered according to the
ESA. The types of information used in these assessments are described
below, followed by a summary of results for each ESU.
Qualitative Evaluations
Qualitative assessments of the status of chinook salmon stocks have
been published by agencies or conservation groups (Nehlsen et al.,
1991; Higgins et al., 1992; Nickelson et al., 1992; WDF et al., 1993;
Huntington et al., 1996). 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. Nehlsen et al. (1991) classified stocks as extinct,
possibly extinct, at high risk of extinction, at moderate risk of
extinction, or of special concern. 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 had spawning escapements less than 200. Stocks were
classified as at moderate risk of extinction if they had declined from
historic levels but presently appear to be stable at a level above 200
spawners. They felt that stocks in this category had reached the
threshold for threatened under the ESA. They classified stocks as of
special concern if a relatively minor disturbance could threaten them,
insufficient data were available for them, they were influenced by
large releases of hatchery fish, or they possess some unique
characteristic.
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 Southern Oregon and California Coastal and
Upper Klamath and Trinity Rivers ESUs.
Nickelson et al. (1992) rated wild coastal (excluding Columbia
River Basin) Oregon salmon and steelhead stocks on the basis of their
status over the past 20 years, classifying stocks as ``healthy,''
``depressed,'' ``of special concern,'' or ``unknown''.
WDF et al. (1993) categorized all salmon and steelhead stocks in
Washington on the basis of stock origin, production type, and status
(``healthy,'' ``depressed,'' ``critical,'' or ``unknown'').
Huntington et al. (1996) surveyed the condition of healthy native
or wild stocks of anadromous salmonids in the Pacific Northwest and
California. Stocks were classified as healthy based upon abundance,
self-sustainability, and not having been previously identified as at
substantial risk of extinction. Healthy stocks were described at two
levels: ``adult abundance at least two-thirds as great as would be
found in the absence of human impacts'' (Level I); and ``adult
abundance between one-third and two-thirds as great as expected without
human impacts'' (Level II).
There are problems in applying results of these studies to ESA
evaluations. A major problem is 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. A second problem is
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 to individual
stocks, not to
[[Page 11491]]
ESUs as defined here. WDF et al. (1993) used general terms describing
status of stocks that cannot be directly related to the considerations
important in ESA evaluations. 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 discuss 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 chinook salmon, 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, giving an incomplete
evaluation of chinook salmon utilizing natural habitat.
Quantitative Evaluations
Quantitative evaluations of data included comparisons of current
and historical abundance of chinook salmon, calculation of recent
trends in escapement, and evaluation of 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. NMFS compiled and analyzed this information to provide
several summary statistics of natural spawning abundance, including
(where available) recent total spawning escapement, percent annual
change in total escapement (both long-term and most recent ten years),
recent naturally produced spawning escapement, and average percentage
of natural spawners that were of hatchery origin.
Although this evaluation used the best data available, 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.
Sport and commercial harvest impacts were compiled from a variety
of sources. In presenting this information, NMFS has tried to maintain
a clear distinction between harvest rates (usually calculated as catch
divided by catch plus escapement for a cohort or brood year) and
exploitation rates (age-specific rates of exploitation in individual
fisheries).
Stream surveys for chinook salmon 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 the general reliability of these
surveys as population indices. For most streams where these surveys are
conducted, they are the best local indication of population trends.
Dam counts provide quantitative estimates of run size, but in most
cases, these counts cannot be resolved to the individual population
level and are subject to errors stemming from fallback, run
classification, and unaccounted mortality. Run reconstructions
providing estimates of both adult spawning abundance and fishery
recruits are being prepared for many stream-type chinook salmon
populations in the Columbia River Basin (Beamsderfer et al., 1997 draft
report), but were not available in final form for this review.
As noted above, NMFS attempted to distinguish natural and hatchery
production in these evaluations. Doing this quantitatively would
require good estimates of the proportion of natural escapement that was
of hatchery origin, and knowledge of the effectiveness of spawning by
hatchery fish in natural environments. Unfortunately, this type of
information is rarely available, and for most ESUs NMFS is limited to
reporting whatever estimates of escapement of hatchery fish to natural
systems that were made available.
Computed Statistics
To represent current run size or escapement where recent data were
available, NMFS computed the geometric mean of the most recent five
years reported, while trying 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.
Recent average abundance is reported as the geometric mean of the
most recent 5 years of data. Where time-series data were not available,
NMFS relied on recent estimates from state agency reports; time periods
included in such estimates varied considerably.
Historic run size estimates from cannery pack data were made by
converting the largest number of cases of cans packed in a single
season to numbers of fish in the spawning run.
NMFS calculated recent trends from the most recent 10 years, using
data collected after 1984 for series having at least 7 observations
since 1984. No attempt was made to account for the influence of
hatchery-produced fish on these estimates, so the estimated trends
include the progeny of naturally spawning hatchery fish.
After evaluating patterns of abundance drawn on these quantitative
and qualitative assessments, and evaluating other risk factors for
chinook salmon from these ESUs, NMFS reached the following conclusions
summarized below.
(1) Sacramento River Winter-Run ESU
Presently listed as endangered under the California and Federal
Endangered Species Acts, this ESU has been extensively reviewed by NMFS
(NMFS 1987, 1989, 1990a,b, 1994b). That information is only summarized
and updated here.
Historically the winter run was abundant and comprised populations
in the McCloud, Pit, Little Sacramento, and Calaveras Rivers.
Construction of Shasta Dam in the 1940s eliminated access to all of the
historic spawning habitat for winter-run chinook salmon in the
Sacramento River Basin. Since then, the ESU has been reduced to a
single spawning population confined to the mainstem Sacramento River
below Keswick Dam (Reynolds et al., 1993).
The fact that this ESU is comprised of a single population with
very limited spawning and rearing habitat increases risk of extinction
due to local catastrophe or poor environmental conditions. There are no
other natural populations in the ESU to buffer it from natural
fluctuations.
Because the Sacramento River winter-run ESU is currently listed as
an endangered species, NMFS did not review its previous risk conclusion
here.
(2) Central Valley Spring-Run ESU
Native spring chinook salmon have been extirpated from all
tributaries in the San Joaquin River Basin, which represents a large
portion of the historic range and abundance of the ESU as a whole. The
only streams considered to have wild spring-run chinook salmon are Mill
and Deer Creeks, and possibly Butte Creek (tributaries to the
Sacramento River), and these are relatively small populations with
sharply declining trends. Demographic and genetic risks due to small
population sizes are thus considered to be high.
Habitat problems are the most important source of ongoing risk to
this ESU. Spring-run fish cannot access most of their historical
spawning and rearing habitat in the Sacramento and San Joaquin River
Basins (which is now above impassable dams), and current spawning is
restricted to the mainstem and a few river tributaries in the
Sacramento River. The remaining spawning habitat accessible to fish is
severely degraded. Collectively, these
[[Page 11492]]
habitat problems greatly reduce the resiliency of this ESU to respond
to additional stresses in the future. The general degradation of
conditions in the Sacramento River Basin (including elevated water
temperatures, agricultural and municipal diversions and returns,
restricted and regulated flows, entrainment of migrating fish into
unscreened or poorly screened diversions, and the poor quality and
quantity of remaining habitat) has severely impacted important juvenile
rearing habitat and migration corridors.
There appears to be serious concern for threats to genetic
integrity posed by hatchery programs in the Central Valley. Most of the
spring-run chinook salmon production in the Central Valley is of
hatchery origin, and naturally spawning populations may be
interbreeding with both fall/late fall- and spring-run hatchery fish.
This problem is exacerbated by the increasing production of spring
chinook salmon from the Feather River and Butte Creek Hatcheries,
especially in light of reports suggesting a high degree of mixing
between spring- and fall/late fall-run broodstock in the hatcheries. In
addition, hatchery strays are considered to be an increasing problem
due to the management practice of releasing a larger proportion of fish
off station (into the Sacramento River delta and San Francisco Bay).
The only previous assessment of risk to stocks in this ESU is that
of Nehlsen et al. (1991), who identified several stocks as being at
risk or of special concern. Four stocks were identified as extinct
(spring/summer-run chinook salmon in the American, McCloud, Pit, and
San Joaquin (including tributaries) Rivers) and two stocks (spring-run
chinook salmon in the Sacramento and Yuba Rivers) were identified as
being at a moderate risk of extinction.
As discussed above, habitat problems were considered to be the most
important source of ongoing risk to this ESU. However, NMFS is also
quite concerned about threats to genetic integrity posed by hatchery
programs in the Central Valley, as well as related harvest regimes that
may not be allowing recovery of this at-risk population. Based on this
risk, NMFS concluded that chinook salmon in this ESU are in danger of
extinction.
(3) Central Valley Fall/Late Fall-Run ESU
Although total population abundance in this ESU is relatively high,
perhaps near historic levels, NMFS identified several concerns
regarding its status. The abundance of natural fall chinook salmon in
the San Joaquin River Basin is low leading NMFS to conclude a large
proportion of the historic range of this ESU is severely degraded.
Habitat blockage is not as severe for fall/late fall-run chinook salmon
as it is for winter- and spring-run chinook salmon in this region
because most of fall/late fall-run spawning habitat was below dams
constructed in the region. However, there has been a severe degradation
of the remaining habitat, especially due to agricultural and municipal
water use activities in the Central Valley (which result in point and
non-point pollution, elevated water temperatures, diminished flows, and
smolt and adult entrainment into poorly screened or unscreened
diversions). Additionally, stray rates are high because many hatchery
fish are released off-station to avoid adverse river conditions,
resulting in a much larger proportion of hatchery chinook salmon
present in the natural spawning population.
A mitigating factor for the overall risk to the ESU is that a few
of the Sacramento and San Joaquin River Basin tributaries are showing
recent, short-term increases in abundance. However, the streams
supporting natural runs considered to be the least influenced by
hatchery fish have the lowest abundance and the most consistently
negative trends of all populations in the ESU. In general, high
hatchery production combined with infrequent monitoring of natural
production make assessing the sustainability of natural production
problematic, resulting in substantial uncertainty in assessing the
status of this ESU.
Other concerns facing chinook salmon in this ESU are the high ocean
and freshwater harvest rates in recent years, which may be higher than
is sustainable by natural populations given the productivity of the ESU
under present habitat conditions. The mixed stock ocean salmon off
California fisheries are managed to achieve spawning escapement goals
for two main indicator stocks: Sacramento River fall chinook and
Klamath River fall chinook. Harvest may be further constrained to meet
NMFS' ESA requirements for listed species, including Sacramento River
winter chinook, Central California Coastal and Southern Oregon/Northern
California coho, and Snake River fall chinook. Since 1993, the need to
address Indian fishing rights in the Klamath River Basin has required
significant reductions in the ocean harvest rate on Klamath River fall
chinook. As a result of the need to constrain ocean harvest rates on
Klamath River fall chinook, commercial fisheries have not been allowed
to harvest Central Valley stocks to the extent that would be permitted
by the management goal for Sacramento River fall chinook alone (122,000
to 180,000 adult hatchery and natural spawners). Spawning escapements
have been well above the goal range in recent years. A record number of
adults (324,000) returned in 1997. The harvest rate on Central Valley
stocks is indicated by the Central Valley Harvest Rate Index, which is
computed as the chinook harvest south of Point Arena divided by the sum
of the chinook harvest south of Point Arena and Central Valley adult
chinook spawning escapement of the same year. This harvest rate index
has averaged 0.73 over the past 10 years and declined somewhat in 1996
and 1997 to 0.64 and 0.66 respectively.
The only previous assessment of risk to stocks in this ESU is that
of Nehlsen et al. (1991), who identified two stocks (San Joaquin and
Cosumnes Rivers) as of special concern.
Even though total population abundance in this ESU is relatively
high, perhaps near historical levels, the abundance of natural fall
chinook salmon in the San Joaquin River Basin is low. Habitat problems
were considered to be the most important source of ongoing risk to this
ESU, although NMFS is extremely concerned about threats to genetic
integrity posed by hatchery and harvest programs related to fall/late
fall-run chinook salmon. Therefore, NMFS concluded that chinook salmon
in this ESU are not presently in danger of extinction but are likely to
become endangered in the foreseeable future.
(4) Southern Oregon and California Coastal ESU
This ESU contains chinook salmon from the Elk River, Oregon south
to the northern cape forming San Francisco Bay. Chinook salmon spawning
abundance in this ESU is highly variable among populations, with
populations in California and spring-run chinook salmon throughout the
ESU being of particular concern. There is a general pattern of downward
trends in abundance in most populations for which data are available,
with declines being especially pronounced in spring-run populations.
The extremely depressed status of almost all coastal populations south
of the Klamath River is an important source of risk to the ESU. NMFS
has a general concern that no current information is available for many
river systems in the southern portion of this ESU, which historically
maintained numerous large populations. Although these California
coastal
[[Page 11493]]
populations do not form a separate ESU, they represent a considerable
portion of genetic and ecological diversity within this ESU.
Habitat loss and/or degradation is widespread throughout the range
of the ESU. The California Advisory Committee on Salmon and Steelhead
Trout (CACSST) reported habitat blockages and fragmentation, logging
and agricultural activities, urbanization, and water withdrawals as the
most predominant problems for anadromous salmonids in California's
coastal basins (CACSST, 1988). They identified associated habitat
problems for each major river system in California. CDFG (1965, Vol.
III, Part B) reported that the most vital habitat factor for coastal
California streams was ``degradation due to improper logging followed
by massive siltation, log jams, etc.'' They cited road building as
another cause of siltation in some areas. They identified a variety of
specific critical habitat problems in individual basins, including
extremes of natural flows (Redwood Creek and Eel River), logging
practices (Mad, Eel, Mattole, Ten Mile, Noyo, Big, Navarro, Garcia, and
Gualala Rivers), and dams with no passage facilities (Eel, and Russian
Rivers), and water diversions (Eel and Russian Rivers). Such problems
also occur in Oregon streams within the ESU. The Rogue River Basin in
particular has been affected by mining activities and unscreened
irrigation diversions (Rivers, 1963) in addition to the problems
resulting from logging and dam construction. Kostow (1995) estimated
that one-third of spring chinook salmon spawning habitat in the Rogue
River was inaccessible following the construction of Lost Creek Dam
(River Kilometer (RKm) 253) in 1977. Recent major flood events
(February 1996 and January 1997) have probably affected habitat quality
and survival of juveniles within this ESU. Although NMFS has little
information on these floods specific to this ESU, effects are probably
similar to those discussed below for the Oregon and Washington Coastal
Region.
Artificial propagation programs in the Southern Oregon and Coastal
California ESU are less extensive than those in Klamath/Trinity or
Central Valley ESUs. The Rogue, Chetco and Eel River Basins and Redwood
Creek have received considerable releases, derived primarily from local
sources. Current hatchery contribution to overall abundance is
relatively low except for the Rogue River spring run. The hatchery-to-
total run ratio of Rogue River spring chinook salmon, as measured at
Gold Ray Dam (RKm 201), has exceeded 60% in some years (Kostow, 1995).
Previous assessments of stocks within this ESU have identified
several stocks as being at risk or of concern. Nehlsen et al. (1991)
identified seven stocks as at high extinction risk and seven stocks as
at moderate extinction risk. Higgins et al. (1992) provided a more
detailed analysis of some of these stocks, and identified nine chinook
salmon stocks as at risk or of concern. Four of these stocks agreed
with the Nehlsen et al. (1991) designations, while five fall chinook
salmon stocks were either reassessed from a moderate risk of extinction
to stocks of concern (Redwood Creek, Mad River, and Eel River) or were
additions to the Nehlsen et al. (1991) list as stocks of special
concern (Little and Bear Rivers). Fall chinook salmon in the Rogue
River represent the only relatively healthy population(s) NMFS could
identify in this ESU (Huntington et al., 1996).
There is a general pattern of downward trends in abundance in most
populations for which data are available, with declines being
especially pronounced in spring-run populations within this ESU. The
lack of population monitoring, particularly in the California portion
of the range, led to a high degree of uncertainty regarding the status
of these populations. NMFS concluded that the extremely depressed
status of almost all coastal populations south of the Klamath River is
an important source of risk to the ESU. Overall, NMFS concluded that
chinook salmon in this ESU are likely to become endangered in the
foreseeable future.
(5) Upper Klamath and Trinity Rivers ESU
The question of overall risk was difficult to evaluate because of
the large disparity in the status of spring- and fall-run populations
within the ESU. Spring-run chinook salmon were once the dominant run
type in the Klamath-Trinity River Basin. Most spring-run spawning and
rearing habitat was blocked by the construction of dams in the late
1800s and early 1900s in the Klamath River Basin, and in the 1960s in
the Trinity River Basin. As a result of these and other factors,
spring-run populations are at less than 10 percent of their historic
levels, and at least 7 spring-run populations that once existed in the
basin are now considered extinct. The remaining spring runs have
relatively small population sizes and are isolated in just a few areas
of the basin, resulting in genetic and demographic risks.
Fall-run chinook populations in this ESU are stable or increasing
slightly. Substantial numbers of fall-run chinook salmon spawn
naturally in many areas of the ESU. However, natural populations have
frequently failed to meet modest spawning escapement goals despite
active harvest management. In addition to habitat blockages, there
continues to be severe degradation of remaining habitat due to mining,
agricultural and forestry activities, and water storage and transfer.
Furthermore, hatchery production in the basin is substantial, with
considerable potential for interbreeding between natural and hatchery
fish. NMFS is concerned that hatchery fish spawning naturally may mask
declines in natural populations.
Previous assessments of stocks within this ESU have identified
several stocks as being at risk or of concern. Nehlsen et al. (1991)
identified seven stocks as extinct, two stocks (Klamath River spring
chinook salmon and Shasta River fall chinook salmon) as at high
extinction risk, and Scott River fall chinook salmon as of special
concern. Higgins et al. (1992) provided a more detailed analysis of
some of the stocks identified by Nehlsen et al. (1991), classifying
three chinook salmon stocks as at risk. Additionally, three chinook
salmon stocks were identified as of special concern. Of these, one
(Scott River fall run) agreed with Nehlsen et al. (1991), while two
were additions (Trinity River spring run and South Fork Trinity River
fall run).
In summary, the question of overall risk was difficult to evaluate
because of the large disparity in the status of spring- and fall-run
populations within the ESU. However, NMFS has concluded that, because
of the relative health of the fall-run populations, chinook salmon in
this ESU are not at significant risk of extinction, nor are they likely
to become endangered in the foreseeable future.
(6) Oregon Coast ESU
Production in this ESU is mostly dependent on naturally-spawning
fish, and spring-run chinook salmon in this ESU are in relatively
better condition than those in adjacent ESUs. Long-term trends in
abundance of chinook salmon within most populations in this ESU are
upward.
In spite of a generally positive outlook for this ESU, several
populations are exhibiting recent and severe (>9 percent per year)
short-term declines in abundance. In addition, there are several
hatchery programs and Salmon and Trout Enhancement Programs (STEP)
releasing chinook salmon throughout the ESU, and many of the fish
released are derived from a single stock (Trask River). Most
importantly, there is a lack of clear information on
[[Page 11494]]
the degree of straying of these hatchery fish into naturally-spawning
populations. There are also many populations within the ESU for which
there are no abundance data; thus NMFS is concerned about the uncertain
risk assessment given these data gaps. Finally, exploitation rates on
chinook salmon from this ESU have been high in the past, and the level
of harvest could be a significant source of risk if it continues at
historically high rates. Also, freshwater habitats are generally in
poor condition, with numerous problems such as low summer flows, high
temperatures, loss of riparian cover, and streambed changes.
Previous assessments of stocks within this ESU have identified
several as being at risk or of concern; however, the preponderance of
stocks have been identified as healthy. Nehlsen et al. (1991)
identified two stocks as at high extinction risk (South Umpqua River
and Coquille River spring-run), one stock as at moderate extinction
risk (Yachats River fall-run) and five stocks as of special concern. Of
the 44 stocks within this ESU considered by Nickelson et al. (1992), 26
were identified as healthy, 2 as depressed (South Umpqua River and
Coquille River spring chinook salmon), 7 as of special concern due to
hatchery strays, and 9 of unknown status (4 of which they suggested may
not be viable). Huntington et al. (1996) identified 18 stocks in their
survey: 6 healthy Level I and 12 healthy Level II stocks.
Abundance of this ESU is relatively high, and fish are well
distributed among numerous, relatively small river basins. Long-term
trends in abundance of chinook salmon within most populations in this
ESU are upward. NMFS has concluded that chinook salmon in this ESU are
neither presently in danger of extinction nor are they likely to become
endangered in the foreseeable future.
(7) Washington Coast ESU
Long-term trends in population abundance have been predominantly
upward for the medium and larger populations but are sharply downward
for several of the smaller populations. In general, abundance and trend
indicators are more favorable for stocks in the northern portion of the
ESU, and more favorable for fall-run populations than for spring- or
summer-run fish. This disparity was a source of concern regarding the
overall health of the ESU.
All basins are affected by habitat degradation, largely related to
forestry practices. Tributaries inside Olympic National Park are
generally in the best condition regarding habitat quality. Special
concern was expressed regarding the status of spring-run populations
throughout the ESU and fall-run populations in Willapa Bay and parts of
the Grays Harbor drainage.
Hatchery production is substantial in several basins within the
range of the ESU, and several populations are identified as being of
composite production. There is considerable potential for hatchery fish
to stray into natural populations, especially since some hatcheries are
apparently unable to effectively attract returning adults. Hatchery
influence is greatest in the southern part of the ESU region,
especially in Willapa Bay, where there have been numerous introductions
of stocks from outside of the ESU. Furthermore, the use of an exotic
spring-run stock at the Sol Duc Hatchery was cited as a cause of
concern.
Previous assessments of stocks within this ESU have identified
several as being at risk or of concern, but more stocks have been
identified as healthy than at risk. Nehlsen et al. (1991) identified
one stock as extinct (Pysht River fall run), one as possibly extinct
(Ozette River fall run), and one as at high risk of extinction
(Wynoochee River spring run), although there is some question whether
the Wynoochee River spring run ever existed (WDFW, 1997a). WDF et al.
(1993) considered the status of 18 native stocks, and concluded that 11
were healthy, 4 were depressed, and 3 were unknown. Huntington et al.
(1996) identified 12 stocks in their survey: 1 healthy Level I stock
(Quillayute/Bogachiel River fall run) and 11 healthy Level II stocks.
Recent abundance has been relatively high, although it is less than
estimated peak historical abundance in this region. Chinook salmon in
this ESU are distributed among a relatively large number of
populations, most of which are large enough to avoid serious genetic
and demographic risks associated with small populations. NMFS concluded
that chinook salmon in this ESU are not presently in danger of
extinction nor are they likely to become endangered in the foreseeable
future.
(8) Puget Sound ESU
Overall abundance of chinook salmon in this ESU has declined
substantially from historical levels, and many populations are small
enough that genetic and demographic risks are likely to be relatively
high. Both long- and short-term trends in abundance are predominantly
downward, and several populations are exhibiting severe short-term
declines. Spring chinook salmon populations throughout this ESU are all
depressed.
Habitat throughout the ESU has been blocked or degraded. In
general, upper tributaries have been impacted by forest practices and
lower tributaries and mainstem rivers have been impacted by agriculture
and/or urbanization. Diking for flood control, draining and filling of
freshwater and estuarine wetlands, and sedimentation due to forest
practices and urban development are cited as problems throughout the
ESU (WDF et al., 1993). Blockages by dams, water diversions, and shifts
in flow regime due to hydroelectric development and flood control
projects are major habitat problems in several basins. Bishop and
Morgan (1996) identified a variety of important habitat issues for
streams in the range of this ESU, including changes in flow regime (all
basins), sedimentation (all basins), high temperatures (Dungeness,
Elwha, Green/Duwamish, Skagit, Snohomish, and Stillaguamish Rivers),
streambed instability (most basins), estuarine loss (most basins), loss
of large woody debris (Elwha, Snohomish, and White Rivers), loss of
pool habitat (Nooksack, Snohomish, and Stillaguamish Rivers), and
blockage or passage problems associated with dams or other structures
(Cedar, Elwha, Green/Duwamish, Snohomish, and White Rivers). The Puget
Sound Salmon Stock Review Group (PFMC) provided an extensive review of
habitat conditions for several of the stocks in this ESU (PFMC, 1997a).
They concluded that reductions in habitat capacity and quality have
contributed to escapement problems for Puget Sound chinook salmon,
citing evidence of curtailment of tributary and mainstem habitat due to
dams, and losses of slough and side-channel habitat due to diking,
dredging, and hydromodification.
Nearly 2 billion fish have been released into Puget Sound
tributaries since the 1950s. The preponderance of hatchery production
throughout the ESU may mask trends in natural populations and makes it
difficult to determine whether they are self-sustaining. This
difficulty is compounded by the dearth of data pertaining to proportion
of naturally-spawning fish that are of hatchery origin. There has also
been widespread use of a limited number of hatchery stocks, resulting
in increased risk of loss of fitness and diversity among populations.
WDF et al. (1993) classified 11 out of 29 stocks in this ESU as being
sustained, in part, through artificial propagation. The vast majority
of these have been derived from local returning fall-run adults.
Returns to hatcheries have accounted for over half of the total
spawning escapement,
[[Page 11495]]
although the hatchery contribution to spawner escapement is probably
much higher than that, due to hatchery-derived strays on the spawning
grounds. In the Stillaguamish River, summer chinook have been
supplemented under a wild broodstock program for the last decade. In
some years, returns from this program have comprised up to 30-50% of
the natural spawners, suggesting that the unaided stock is not able to
maintain itself (NWIFC, 1997). Almost all of the releases into this ESU
have come from stocks within this ESU, with the majority of within ESU
transfers coming from the Green River Hatchery or hatchery broodstocks
that have been derived from Green River stock (Marshall et al., 1995).
The electrophoretic similarity between Green River fall-chinook salmon
and several other fall chinook salmon stocks in Puget Sound (Marshall
et al., 1995) suggests that there may have been a significant effect
from some hatchery transplants. Overall, the pervasive use of Green
River stock throughout much of the extensive hatchery network that
exists in this ESU may reduce the genetic diversity and fitness of
naturally spawning populations.
Harvest impacts on Puget Sound chinook salmon stocks are quite
high. Ocean exploitation rates on natural stocks averaged 56-59%; total
exploitation rates average 68-83% (1982-89 brood years) (Pacific Salmon
Commission (PSC), 1994). Total exploitation rates on some stocks have
exceeded 90% (PSC, 1994).
Previous assessments of stocks within this ESU have identified
several stocks as being at risk or of concern. Nehlsen et al. (1991)
identified four stocks as extinct, four stocks as possibly extinct, six
stocks as at high risk of extinction, one stock as a moderate risk
(White River spring run), and one stock (Puyallup River fall run) as of
special concern. WDF et al. (1993) considered 28 stocks within the ESU,
of which 13 were considered to be of native origin and predominantly
natural production. The status of these 13 stocks was: 2 healthy (Upper
Skagit River summer run and Upper Sauk River spring run), 5 depressed,
2 critical (South-Fork Nooksack River spring/summer run and Dungeness
River spring/summer run), and 4 unknown.
Overall abundance of chinook salmon in this ESU has declined
substantially from historical levels, and both long-and short-term
trends in abundance are predominantly downward. Several populations are
exhibiting severe short-term declines. Spring chinook salmon
populations throughout this ESU are all depressed. NMFS concluded that
chinook salmon in this ESU are not presently in danger of extinction,
but they are likely to become endangered in the foreseeable future.
(9) Lower Columbia River ESU
Apart from the relatively large and apparently healthy fall-run
population in the Lewis River, production in this ESU appears to be
predominantly hatchery-driven with few identifiable naturally spawned
populations.
All basins are affected (to varying degrees) by habitat
degradation. Major habitat problems are primarily related to blockages,
forest practices, urbanization in the Portland and Vancouver areas, and
agriculture in floodplains and low-gradient tributaries. Substantial
chinook salmon spawning habitat has been blocked (or passage
substantially impaired) in the Cowlitz (Mayfield Dam 1963, RKm 84),
Lewis (Merwin Dam 1931, RKm 31), Clackamas (North Fork Dam 1958, RKm
50), Hood (Powerdale Dam 1929, RKm 7), and Sandy (Marmot Dam 1912, RKm
48; Bull Run River dams early 1900s) Rivers (WDF et al., 1993; Kostow,
1995).
Hatchery programs to enhance chinook salmon fisheries abundance in
the lower Columbia River began in the 1870s, expanded rapidly, and have
continued throughout this century. Although the majority of the stocks
have come from within this ESU, over 200 million fish from outside the
ESU have been released since 1930. A particular concern at the present
time is the straying by Rogue River fall chinook salmon, which are
released into the lower Columbia River to augment harvest
opportunities. Available evidence indicates a pervasive influence of
hatchery fish on natural populations throughout this ESU, including
both spring-and fall-run populations (Howell et al., 1985; Marshall et
al., 1995). In addition, the exchange of eggs between hatcheries in
this ESU has led to the extensive genetic homogenization of hatchery
stocks (Utter et al., 1989). The large numbers of hatchery fish in this
ESU make it difficult to determine the proportion of naturally produced
fish. In spite of the heavy impact of hatcheries, genetic and life
history characteristics of populations in this ESU still differ from
those in other ESUs. The loss of fitness and diversity within the ESU
as an important concern.
Harvest rates on fall-run stocks are moderately high, with an
average total exploitation rate of 65 percent (1982-89 brood years)
(PSC, 1994). The average ocean exploitation rate for this period was 46
percent, while the freshwater harvest rate on the fall run has averaged
20 percent, ranging from 30 percent in 1991 to 2.4 percent in 1994.
Harvest rates are somewhat lower for spring run stocks, with estimates
for the Lewis River averaging 24 percent ocean and 50 percent total
exploitation rates in 1982-89 (PSC, 1994). In inriver fisheries,
approximately 15 percent of the lower river hatchery stock was
harvested, 29 percent of the lower river wild stock was harvested, and
58 percent of the Spring Creek hatchery stock was harvested, while the
average inriver exploitation rate on the stock as a whole was 29
percent during the 1991-1995 period (PFMC, 1996b).
Previous assessments of stocks within this ESU have identified
several stocks as being at risk or of concern. Nehlsen et al. (1991)
identified two stocks as extinct (Lewis River spring run and Wind River
fall run), four stocks as possibly extinct, and four stocks as at high
risk of extinction. WDF et al. (1993) considered 20 stocks within the
ESU, of which only 2 (Lewis River and East Fork Lewis River fall runs)
were considered to be of native origin, predominantly natural
production, and healthy. Huntington et al. (1996) identified one
healthy Level I stock in their survey (Lewis River fall run).
There have been at least six documented extinctions of populations
in this ESU, and it is possible that extirpation of other native
populations has occurred but has been masked by the presence of
naturally spawning hatchery fish. Long-and short-term trends in
abundance of individual populations are mostly negative, some severely
so. About half of the populations comprising this ESU are very small,
increasing the likelihood that risks due to genetic and demographic
drift processes in small populations will be important. NMFS concluded
that chinook salmon in this ESU are not presently in danger of
extinction but are likely to become endangered in the foreseeable
future.
(10) Upper Willamette River ESU
While the abundance of Willamette River spring chinook salmon has
been relatively stable over the long term, and there is evidence of
some natural production, it is apparent that at present production and
harvest levels the natural population is not replacing itself. With
natural production accounting for only \1/3\ of the natural spawning
escapement, it is questionable whether natural spawners would be
capable of replacing themselves even in the absence of fisheries. While
hatchery programs in the Willamette River Basin have maintained
broodlines that are
[[Page 11496]]
relatively free of genetic influences from outside the basin, they may
have homogenized the population structure within the ESU. The
introduction of fall-run chinook salmon into the basin and laddering of
Willamette Falls have increased the potential for genetic introgression
between wild spring-and hatchery fall-run chinook salmon, but there is
no direct evidence of hybridization (other than an overlap in spawning
times and spawning location) between these two runs. Prolonged
artificial propagation of the majority of the production from this ESU
may also have had deleterious effects on the ability of Willamette
River spring chinook salmon to reproduce successfully in the wild.
Habitat blockage and degradation are significant problems in this
ESU. Available habitat has been reduced by construction of dams in the
Santiam, McKenzie, and Middle Fork Willamette River Basins, and these
dams have probably adversely affected remaining production via thermal
effects. Agricultural development and urbanization are the main
activities that have adversely affected habitat throughout the basin
(Bottom et al., 1985, Kostow, 1995).
Another concern for this ESU is that commercial and recreational
harvests are high relative to the apparent productivity of natural
populations. The average total harvest mortality rate was estimated to
be 72 percent in 1982-89, with a corresponding ocean exploitation rate
of 24 percent (PSC, 1994). This estimate does not fully account for
escapement, and ODFW is in the process of revising harvest rate
estimates for this stock; revised estimates may average 57 percent
total harvest rate, with 16 percent ocean and 48 percent freshwater
components (Kostow,1995). The inriver recreational harvest rate
(Willamette River sport catch/estimated run size) for the period from
1991 through 1995 was 33 percent (data from PFMC, 1996b).
The only previous assessment of risk to stocks in this ESU is that
of Nehlsen et al. (1991), who identified the Willamette River spring-
run chinook salmon as of special concern. They noted vulnerability to
minor disturbances, insufficient information on population trend, and
the special character of this stock as causes for concern.
NMFS concluded that chinook salmon in this ESU are not presently in
danger of extinction but are likely to become endangered in the
foreseeable future. Total abundance has been relatively stable at
approximately 20,000 to 30,000 fish; however, recent natural escapement
is less than 5,000 fish and has been declining sharply. Furthermore, it
is estimated that about two-thirds of the natural spawners are first-
generation hatchery fish, suggesting that the natural population is
falling far short of replacing itself. Another concern for this ESU is
that commercial and recreational harvest are high relative to the
apparent productivity of natural populations.
(11) Middle Columbia River Spring-Run ESU
Total abundance of this ESU is low relative to the total basin
area, and 1994-96 escapements have been very low. Several historical
populations have been extirpated, and the few extant populations in
this ESU are not widely distributed geographically. In addition, there
are only two populations (John Day and Yakima Rivers) with substantial
run sizes. However, these major river basins are predominantly
comprised of naturally produced fish, and both of these exhibit long-
term increasing trends in abundance. Additionally, recent analyses done
as part of the PATH process indicates that productivity of natural
populations in the Deschutes and John Day Rivers has been more robust
than most other stream-type chinook salmon in the Columbia River
(Schaller et al., 1995).
Habitat problems are common in the range of this ESU. The only
large blockage of spawning area for spring chinook salmon is at the
Pelton/Round Butte dam complex on the Deschutes River, which probably
eliminated a natural population utilizing the upper Deschutes River
Basin (Kostow, 1995; Nehlsen, 1995). Spawning and rearing habitat are
affected by agriculture including water withdrawals, grazing, and
riparian vegetation management. Mainstem Columbia River hydroelectric
development has resulted in a major disruption of migration corridors
and affected flow regimes and estuarine habitat.
Hatchery production accounts for a substantial proportion of total
escapement to the region. However, screening procedures at the Warm
Springs River weir apparently minimize the potential for hatchery-wild
introgression in the Deschutes River basin. Although straying is less
of a problem with returning spring-run adults, the use of the
composite, out-of-ESU Carson Hatchery stock to reestablish the Umatilla
River spring run would be a cause for concern if fish from that program
stray out of the basin.
Stocks in this ESU experience very low ocean harvest rates and only
moderate instream harvest. Harvest rates have been declining recently
(PSC, 1996).
Previous assessments of stocks within this ESU have identified
several as being at risk or of concern. Nehlsen et al. (1991)
identified five stocks as extinct, one as possibly extinct (Klickitat
River spring chinook salmon), and one as of special concern (John Day
River spring chinook salmon). WDF et al. (1993) considered five stocks
within the ESU, of which three, all within the Yakima River Basin, were
considered to be of native origin and predominantly natural production
(Upper Yakima, Naches, and American Rivers). Despite increasing trends
in these three stocks, these stocks and the two remaining (not native/
natural) stocks were considered to be depressed on the basis of
chronically low escapement numbers (WDF et al., 1993).
Despite low abundances relative to estimated historical levels,
long-term trends in abundance have been relatively stable, with an
approximately even mix of upward and downward trends in populations.
NMFS concluded that chinook salmon in this ESU are not presently in
danger of extinction, nor is it likely to become endangered in the
foreseeable future.
(12) Upper Columbia River Summer- and Fall-Run ESU
The status of this ESU was recently reviewed by NMFS (Waknitz et
al., 1995). In the earlier review, this ESU was determined to be
neither at risk of extinction nor likely to become so. However, new
data shows the proportion of naturally spawning summer chinook salmon
of hatchery origin has been increasing rapidly in areas above Wells
Dam. There is corresponding concern about the possible genetic and/or
life-history consequences to the sustainability of natural populations
in that area from the shift in hatchery releases from subyearlings to
yearlings.
Nearly 38 million summer-run fish have been released from the Wells
Dam Hatchery since 1967. Efforts to establish the Wells Dam summer-run
broodstock removed a large proportion of the spawners (94 percent of
the run in 1969) destined for the Methow River and other upstream
tributaries (Mullan et al., 1992). Additionally, a number of fall-run
fish have been incorporated into the summer-run program, especially
during the 1980s (Marshall et al., 1995). Large numbers of fall chinook
salmon have been released into the mainstem Columbia River and into the
Yakima River. Although no hatcheries operate on the Yakima River,
releases of upriver bright fall-run chinook salmon into the
[[Page 11497]]
lower Yakima River (below Prosser Dam) are thought to have overwhelmed
local naturally spawning stocks (WDF et al., 1993; Marshall et al.,
1995). Fall chinook salmon also spawn in the mainstem Columbia River;
this occurs primarily in the Hanford Reach portion of the Columbia
River, with additional spawning sites in the tailrace areas of mainstem
dams. Upriver bright fall chinook salmon hatchery stocks represent a
composite of stocks intercepted at various dams. This stock has also
been released in large numbers by hatcheries on the mainstem Columbia
River. Although the upriver bright stocks incorporated representatives
from the mainstem spawning populations in the Hanford Reach and those
displaced by the construction of Grand Coulee Dam and other mainstem
dams, they have also incorporated individuals from the Snake River
fall-run ESU (Howell et al., 1985). The mixed genetic background of
upriver bright stocks may result in less accurate homing (McIssac and
Quinn 1988; Chapman et al., 1994). However, the naturally spawning
Hanford Reach fall-run population appears to stray at very low levels
(Hymer et al., 1992b).
Previous assessments of stocks within this ESU have identified
several as being at risk or of concern. Nehlsen et al. (1991)
identified six stocks as extinct, one as a moderate extinction risk
(Methow River summer chinook salmon), and one as of special concern
(Okanogan River summer chinook salmon). WDF et al. (1993) considered 10
stocks within the ESU, of which 3 were considered to be of native
origin and predominantly natural production. The status of these three
stocks was two healthy (Marion Drain and Hanford Reach fall-runs) and
one depressed (Okanogan River summer-run). Huntington et al. (1996)
identified one healthy Level I stock in their survey (Hanford Reach
fall run).
In an earlier review, NMFS concluded that this ESU was not in
danger of extinction, nor likely to become endangered in the
foreseeable future. None of the information reviewed in this assessment
provides a basis for NMFS to change this earlier conclusion. However,
if negative trends in this ESU continue, NMFS will reevaluate the
status of these chinook salmon.
(13) Upper Columbia River Spring-Run ESU
Access to a substantial portion of historical habitat was blocked
by Chief Joseph and Grand Coulee Dams. There are local habitat problems
related to irrigation diversions and hydroelectric development, as well
as degraded riparian and instream habitat from urbanization and
livestock grazing. Mainstem Columbia River hydroelectric development
has resulted in a major disruption of migration corridors and affected
flow regimes and estuarine habitat. Some populations in this ESU must
migrate through nine mainstem dams.
Artificial propagation efforts have had a significant impact on
spring-run populations in this ESU, either through hatchery-based
enhancement or the extensive trapping and transportation activities
associated with the GCFMP. Prior to the implementation of the GCFMP,
spring-run chinook salmon populations in the Wenatchee, Entiat, and
Methow Rivers were at severely depressed levels (Craig and Suomela,
1941). Therefore, it is probable that the majority of returning spring-
run adults trapped at Rock Island Dam for use in the GCFMP were
probably not native to these three rivers (Chapman et al., 1995). All
returning adults were either directly transported to river spawning
sites or spawned in one of the National Fish Hatcheries (NFHs) built
for the GCFMP.
In the years following the GCFMP, several stocks were transferred
to the NFHs in this area. Naturally spawning populations in tributaries
upstream of hatchery release sites have apparently undergone limited
introgression by hatchery stocks, based on CWT recoveries and genetic
analysis (Chapman et al. 1995). Artificial propagation efforts have
recently focused on supplementing naturally spawning populations in
this ESU (Bugert, 1998), although it should be emphasized that these
naturally spawning populations were founded by the same GCFMP
homogenized stock. Furthermore, the potential for hatchery-derived non-
native stocks to genetically impact naturally spawning populations
exists, especially given the recent low numbers of fish returning to
rivers in this ESU. Risks associated with interactions between wild and
hatchery chinook salmon are a concern, because there continues to be
substantial production of the composite, non-native Carson stock for
fishery enhancement and hydropower mitigation.
Harvest rates are low for this ESU, with very low ocean and
moderate instream harvest. Harvest rates have been declining recently
(ODFW and WDFW, 1995).
Previous assessments of stocks within this ESU have identified
several as being at risk or of concern. Nehlsen et al. (1991)
identified six stocks as extinct. Due to lack of information on chinook
salmon stocks that are presumed to be extinct, the relationship of
these stocks to existing ESUs is uncertain. They are listed here based
on geography and to give a complete presentation of the stocks
identified by Nehlsen et al. (1991). WDF et al. (1993) considered nine
stocks within the ESU, of which eight were considered to be of native
origin and predominantly natural production. The status of all nine
stocks was considered depressed. Populations in this ESU have
experienced record low returns for the last few years.
Recent total abundance of this ESU is quite low, and escapements in
1994-1996 were the lowest in at least 60 years. At least 6 populations
of spring chinook salmon in this ESU have become extinct, and almost
all remaining naturally-spawning populations have fewer than 100
spawners. In addition to extremely small population sizes, both recent
and long-term trends in abundance are downward, some extremely so. NMFS
concluded that chinook salmon in this ESU are in danger of extinction.
(14) Snake River Fall-Run ESU
Snake River fall-run chinook salmon are currently listed as a
threatened species under the ESA (57 FR 14653, April 22, 1992). As
discussed above, NMFS concluded that the Snake River fall-run ESU also
includes fall chinook salmon in the Deschutes River and, historically,
populations from the John Day, Umatilla, and Walla Walla Rivers that
have been extirpated in the twentieth century.
Almost all historical Snake River fall-run chinook salmon spawning
habitat in the Snake River Basin was blocked by the Hells Canyon Dam
complex; other habitat blockages have also occurred in Columbia River
tributaries. Hydroelectric development on the mainstem Columbia and
Snake Rivers continues to affect juvenile and adult migration.
Remaining habitat has been reduced by inundation in the mainstem Snake
and Columbia Rivers, and the ESU's range has also been affected by
agricultural water withdrawals, grazing, and vegetation management.
The continued straying by non-native hatchery fish into natural
production areas is an additional source of risk to the Snake River
chinook salmon.
Assessing extinction risk to the newly-configured ESU is difficult
because of the geographic discontinuity and the disparity in the status
of the two remaining populations. NMFS also notes considerable
uncertainty regarding the origins of fall chinook salmon in the lower
Deschutes River and their relationship to fish in the upper Deschutes
River. Historically, the
[[Page 11498]]
Snake River populations dominated production in this ESU; total
abundance is estimated to have been about 72,000 in the 1930s and
1940s, and it was probably substantially higher before that. Production
from the Deschutes River was presumably only a small fraction of
historic production in the ESU. In contrast, recent (1990-96) returns
of naturally spawning fish to the Deschutes River (about 6,000 adults
per year) have been much higher than in the Snake River (5-year mean
about 500 adults per year, including hatchery strays). The relatively
recent extirpation of fall-run chinook in the John Day, Umatilla and
Walla Walla Rivers is also a factor in assessing the risk to the
overall ESU.
Long term trends in abundance are mixed--slightly upward in the
Deschutes River and downward in the Snake River. Short-term trends in
both remaining populations are upward. After considering the addition
of the Deschutes River fall chinook populations to the listed Snake
River fall-run chinook salmon ESU, NMFS concluded that the ESU as a
whole is likely to become an endangered species within in the
foreseeable future throughout all or a significant portion of its
range, in spite of the relative health of the Deschutes River
population.
(15) Snake River Spring- and Summer-Run ESU
This ESU has been extensively reviewed by NMFS (Matthews and
Waples, 1991; NMFS, 1995b). The Snake River Spring and summer-run ESU
is listed as a threatened species and NMFS did not review its previous
risk conclusion here.
Summary of Factors Affecting the Species
Section 2(a) of the ESA states that various species of fish,
wildlife, and plants in the United States have been rendered extinct as
a consequence of economic growth and development untempered by adequate
concern for ecosystem conservation. Section 4(a)(1) of the ESA and the
listing regulations (50 CFR Part 424) set forth procedures for listing
species. NMFS must determine, through the regulatory process, if a
species is endangered or threatened based upon any one or a combination
of the following factors: (1) The present or threatened destruction,
modification, or curtailment of its habitat or range; (2)
overutilization for commercial, recreational, scientific, or education
purposes; (3) disease or predation; (4) inadequacy of existing
regulatory mechanisms; or (5) other natural or human-made factors
affecting its continued existence.
NMFS has prepared two supporting documents which address the
factors that have led to the decline of chinook salmon and other
salmonids. The first is entitled ``Factors for Decline: A Supplement to
the Notice of Determination for West Coast Steelhead'' (NMFS, 1996).
That report, available u |