[Federal Register: August 7, 2003 (Volume 68, Number 152)]
[Proposed Rules]
[Page 46989-47009]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr07au03-14]
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DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
Endangered and Threatened Wildlife and Plants: Reconsidered
Finding for an Amended Petition To List the Westslope Cutthroat Trout
as Threatened Throughout Its Range
AGENCY: Fish and Wildlife Service, Interior.
ACTION: Notice of petition finding.
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SUMMARY: We, the Fish and Wildlife Service (Service), announce our
reconsidered 12-month finding for an amended petition to list the
westslope cutthroat trout (WCT) (Oncorhynchus clarki lewisi) as a
threatened species throughout its range in the United States, pursuant
to a Court order and the Endangered Species Act (Act) of 1973, as
amended. After a thorough review of all available scientific and
commercial information, we find that listing the WCT as either
threatened or endangered is not warranted at this time. Also pursuant
to the Court order, we assert our scientifically-based conclusion about
the extent to which it is appropriate to include ``hybrid'' WCT
populations and populations of unknown genetic characteristics in the
taxonomic group that we considered for listing.
DATES: The finding announced in this document was made on August 1,
2003.
ADDRESSES: Data, information, comments, or questions regarding this
document should be sent to the Chief, Branch of Native Fishes
Management, U.S. Fish and Wildlife Service, Montana Fish and Wildlife
Management Assistance Office, 4052 Bridger Canyon Road, Bozeman,
Montana 59715. The complete administrative file for this finding is
available for inspection, by appointment and during normal business
hours, at the above address. The new petition finding, the status
update report for WCT, the amended petition and its bibliography, our
initial status review document and petition finding, related Federal
Register notices, the Court Order and Judgement and Memorandum Opinion,
and other pertinent information, may be obtained at our Internet Web
site: http://mountain-prairie.fws.gov/endspp/fish/wct/.
FOR FURTHER INFORMATION CONTACT: Lynn R. Kaeding, by e-mail (Lynn_
Kaeding@fws.gov) or telephone (406-582-0717).
SUPPLEMENTARY INFORMATION:
Background
Section 4(b)(3)(B) of the Endangered Species Act of 1973 (Act), as
amended (16 U.S.C. 1531 et seq.), requires that within 90 days of
receipt of the petition, to the maximum extent practicable, we make a
finding on whether a petition to list, delist, or reclassify a species
presents substantial scientific or commercial information indicating
that the requested action may be warranted. The term ``species''
includes any subspecies of fish or wildlife or plants,
[[Page 46990]]
and any Distinct Population Segment (DPS) of any species of vertebrate
fish or wildlife that interbreeds when mature. If the petition contains
substantial information, the Act requires that we initiate a status
review for the species and publish a 12-month finding indicating that
the petitioned action is either: (a) Not warranted, (b) warranted, or
(c) warranted but precluded from immediate listing proposal by other
pending proposals of higher priority. A notice of such 12-month
findings is to be published promptly in the Federal Register.
On June 6, 1997, we received a petition to list the WCT
(Oncorhynchus clarki lewisi) as threatened throughout its range and
designate critical habitat for this subspecies of fish pursuant to the
Act. The petitioners were American Wildlands, Clearwater Biodiversity
Project, Idaho Watersheds Project, Montana Environmental Information
Center, the Pacific Rivers Council, Trout Unlimited's Madison-Gallatin
Chapter, and Mr. Bud Lilly.
The WCT is 1 of 14 subspecies of cutthroat trout native to interior
regions of western North America (Behnke 1992, 2002). Cutthroat trout
owe their common name to the distinctive red or orange slash mark that
occurs just below both sides of the lower jaw. Adult WCT typically
exhibit bright yellow, orange, and red colors, especially among males
during the spawning season. Characteristics of WCT that distinguish
this fish from the other subspecies of cutthroat trout include a
pattern of irregularly shaped spots on the body, with few spots below
the lateral line except near the tail; a unique number of chromosomes;
and other genetic and morphological traits that appear to reflect a
distinct evolutionary lineage (Behnke 1992).
Although its extent is not precisely known, the historic (i.e.,
native) range of WCT is considered the most geographically widespread
among the 14 subspecies of inland cutthroat trout (Behnke 1992). West
of the Continental Divide, the subspecies is believed to be native to
several major drainages of the Columbia River basin, including the
upper Kootenai River drainage from its headwaters in British Columbia,
through northwest Montana, and into northern Idaho; the Clark Fork
River drainage of Montana and Idaho downstream to the falls on the Pend
Oreille River near the Washington-British Columbia border; the Spokane
River above Spokane Falls and into Idaho's Coeur d'Alene and St. Joe
River drainages; and the Salmon and Clearwater River drainages of
Idaho's Snake River basin. The historic distribution of WCT also
includes disjunct areas draining the east slope of the Cascade
Mountains in Washington (Methow River and Lake Chelan drainages, and
perhaps the Wenatchee and Entiat River drainages), the John Day River
drainage in northeastern Oregon, and the headwaters of the Kootenai
River and several other disjunct regions in British Columbia. East of
the Continental Divide, the historic distribution of WCT is believed to
include the headwaters of the South Saskatchewan River drainage (United
States and Canada); the entire Missouri River drainage upstream from
Fort Benton, Montana, and extending into northwest Wyoming; and the
headwaters of the Judith, Milk, and Marias Rivers, which join the
Missouri River downstream from Fort Benton.
Previous Federal Actions
On July 2, 1997, we notified the petitioners that our Final Listing
Priority Guidance, published in the December 5, 1996, Federal Register
(61 FR 64425), designated the processing of new listing petitions as
being of lower priority than were the completion of emergency listings
and processing of pending proposed listings. A backlog of listing
actions, as well as personnel and budget restrictions in our Region 6
(Mountain-Prairie Region), which had been assigned primary
responsibility for the WCT petition, prevented our staff from working
on a 90-day finding for the petition.
On January 25, 1998, the petitioners submitted an amended petition
to list the WCT as threatened throughout its range and designate
critical habitat for the subspecies. The amended petition contained
additional new information in support of the requested action.
Consequently, we treated the amended petition as a new petition.
On June 10, 1998, we published a notice (63 FR 31691) of a 90-day
finding that the amended WCT petition provided substantial information
indicating that the requested action may be warranted and immediately
began a comprehensive status review for WCT. In the notice, we asked
for data, information, technical critiques, comments, and questions
relevant to the amended petition.
In response to that notice, we received information on WCT from
State fish and wildlife agencies, the U.S. Forest Service, National
Park Service, tribal governments, and private corporations, as well as
private citizens, organizations, and other entities. That information,
subsequently compiled in a comprehensive status review document (U.S.
Fish and Wildlife Service 1999), indicated that WCT then occurred in
about 4,275 tributaries or stream reaches that collectively encompassed
more than 37,015 kilometers (km) (23,000 miles [mi]) of stream habitat.
Those WCT were distributed among 12 major drainages and 62 component
watersheds in the Columbia, Missouri, and Saskatchewan River basins. In
addition, WCT were determined to naturally occur in 6 lakes totaling
about 72,843 hectares (ha) (180,000 acres [ac]) in Idaho and Washington
and in at least 20 lakes totaling 2,164 ha (5,347 ac) in Glacier
National Park in Montana. That status review also revealed that most of
the habitat for extant WCT was on lands administered by Federal
agencies, particularly the U.S. Forest Service. Moreover, most of the
strongholds for WCT were within roadless or wilderness areas or
national parks, all of which afforded considerable protection to WCT.
Finally, the status review indicated that there were numerous Federal
and State regulatory mechanisms that protected WCT and their habitats
throughout the subspecies' range.
On April 14, 2000, we published a notice (65 FR 20120) of our
finding that the WCT is not likely to become either a threatened or an
endangered species within the foreseeable future. We also found that,
although the abundance of the WCT subspecies had been reduced from
historic levels and its extant populations faced threats in several
areas of the historic range, the magnitude and imminence of those
threats were small when considered in the context of the overall status
and widespread distribution of the WCT subspecies. Therefore, we
concluded that listing the WCT as either a threatened or an endangered
species under the Act was not warranted at that time.
On October 23, 2000, plaintiffs filed, in the U.S. District Court
for the District of Columbia, a suit alleging four claims. They alleged
that our consideration of existing regulatory mechanisms was arbitrary.
Plaintiffs further claimed that our consideration of hybridization as a
threat to WCT was arbitrary because, while identifying hybridization as
a threat to WCT, we relied on a draft Intercross policy (61 FR 4710) to
include hybridized WCT in the WCT subspecies that we considered for
listing under the Act. Their third claim averred that we arbitrarily
considered the threats to WCT posed by the geographic isolation of some
WCT populations and the loss of some WCT life-history forms. Finally,
plaintiffs claimed that we failed to account for the threat of whirling
disease and other important factors, and
[[Page 46991]]
that our decision to not list the WCT as threatened was arbitrary and
capricious. In the subsequent oral argument before the Court,
plaintiffs conceded that their strongest argument, and the one from
which their other concerns stemmed, was that we included hybridized
fish in the WCT subspecies considered for listing under the Act, while
also recognizing hybridization as a threat to the subspecies. The
hybridization threat to WCT is posed by certain nonnative fishes that
management agencies and other entities stocked into streams and lakes
in many regions of the historic range of WCT, beginning more than 100
years ago. Subsequently, those nonnative fishes or their hybrid
descendants became self-sustaining populations and remain as such
today.
On March 31, 2002, the U.S. District Court for the District of
Columbia found that our listing determination for WCT did not reflect a
reasoned assessment of the Act's statutory listing factors on the basis
of the best available science. The Court remanded the listing decision
to us with the order that we reconsider whether to list the WCT as a
threatened species, and that in so doing we evaluate the threat of
hybridization as it bears on the Act's statutory listing factors.
Specifically, the Court ordered us to determine: (1) The current
distribution of WCT, taking into account the prevalence of
hybridization; (2) whether the WCT population (i.e., subspecies, as
used in the present document) is an endangered or a threatened species
because of hybridization; and (3) whether existing regulatory
mechanisms are adequate to address the threats posed by hybridizing,
nonnative fishes.
The Court also pointed out that the draft Intercross policy (61 FR
4710; February 7, 1996) in no way indicates what degree of
hybridization would threaten WCT, or that the existing levels of
hybridization do not presently threaten WCT. Furthermore, the Court
directed the Service to present a scientifically-based conclusion about
the extent to which it is appropriate to include hybrid WCT stocks
(i.e., populations, as used in the present document) and populations of
unknown genetic characteristics in the WCT subspecies considered for
listing.
On September 3, 2002, we announced (67 FR 56257) initiation of a
new status review for the WCT and solicited comments from all
interested parties regarding the present-day status of this fish. We
were particularly interested in receiving data, information, technical
critiques, and relevant comments that would help us to address the
issues that had been raised by the Court.
During the subsequent comment period, we received written requests
for an extension of that period from the fish and wildlife agencies of
the States of Washington, Oregon, Idaho, and Montana, as well as the
Kalispel Tribe of Indians and the Earthjustice Legal Foundation. In
their letters, those entities indicated that they were assembling or
awaiting important information relevant to the status of WCT and that
those entities wanted to make such information available to us for use
in the new status review. Accordingly, on December 18, 2002, we
announced (67 FR 77466) that the comment period was reopened until
February 15, 2003.
For the purposes of this listing determination, ``WCT subspecies''
refers explicitly to all populations of WCT within the international
boundaries of the United States, although populations of WCT also occur
in Canada. As part of this listing determination, the WCT subspecies
many be found to consist of DPSs, as described in a subsequent section
of this finding.
The Value of Hybrid Westslope Cutthroat Trout in Listing Determinations
As described in the preceding section, the U.S. District Court for
the District of Columbia ruled that the Service must provide a
scientifically-based conclusion about the extent to which it is
appropriate to include ``hybrid WCT stocks'' and ``stocks of unknown
genetic characteristics'' in the WCT subspecies considered for listing.
We herewith respond to the Court.
In the past, natural hybridization between congeneric or closely-
related species of fish was thought to be rare. However, during the
first half of the 20th Century, Professor Carl Hubbs and his associates
demonstrated that natural hybridization between morphologically
distinct species, particularly for temperate-zone freshwater fishes in
North America, was common in areas where the geographic ranges of those
species overlap (Hubbs 1955). Such natural hybridization may be
especially common among centrarchid (basses and sunfishes) and cyprinid
(minnows) fishes in the central United States (Avise and Saunders 1984;
Dowling and Secor 1997).
Many investigators have subsequently demonstrated that several
extant species of fish most likely originated from the interbreeding of
two or more ancestral or extant species (Meagher and Dowling 1991;
DeMarais et al. 1992; Gerber et al. 2001). Indeed, natural
hybridization between taxonomically distinct species has long been
recognized as an important evolutionary mechanism for the origin of new
species of plants (Rieseberg 1997). Conversely, natural hybridization
has only recently been recognized as an important evolutionary
mechanism for the origin of new species of animals (Dowling and Secor
1997). Natural hybridization is now acknowledged as an important
evolutionary mechanism that: (a) Creates new genotypic diversity, (b)
can lead to new, adaptive phenotypes, and (c) can yield new species
(Arnold 1997).
Hybridization also can result in the extinction of populations and
species (Rhymer and Simberloff 1996). Indeed, hybridization resulting
from anthropogenic factors is considered a threat to many species of
fish (Campton 1987; Verspoor and Hammar 1991; Leary et al. 1995; Childs
et al. 1996; Echelle and Echelle 1997). In particular, the extensive
stocking of rainbow trout (O. mykiss) outside their native geographic
range has resulted in appreciable hybridization with other species of
trout (Bartley and Gall 1991; Behnke 1992, 2002; Dowling and Childs
1992; Carmichael et al. 1993). This interbreeding also has occurred for
WCT where natural hybridization with introduced rainbow trout and
Yellowstone cutthroat trout (O. c. bouvieri; YCT) is considered a
threat to the WCT subspecies (see subsequent section, Hybridization
with Nonnative Fishes).
Hybridization also can result in the genetic introgression of genes
from one species into populations of another species if F1 (i.e., the
first filial generation) and F2 hybrids are fertile and can interbreed,
or backcross, with individuals of a parental species. For example,
first-generation hybrids between WCT and rainbow trout appear to be
fully fertile (Ferguson et al. 1985), and levels of genetic
introgression or ``admixture'' vary widely (<1 to 50
percent) among natural populations of WCT (e.g., Weigel et al. 2002).
In this context, admixture refers to the percentage of a population's
gene pool derived from rainbow trout genes (or alleles) versus WCT
trout genes. In these latter situations, the Service must determine
which populations represent WCT, and the genetic resources of WCT,
under the Act and which populations threaten the continued existence of
the WCT subspecies.
The purpose of the Act is to conserve threatened and endangered
``species'' and the ecosystems on which those species depend. The
definition of ``species'' under the Act includes any taxonomic species
or subspecies, and ``distinct population segments'' of vertebrate
species. The issue here for
[[Page 46992]]
this status review is not the definition of ``species'' under the Act,
but rather, the scientific criteria used by professional zoologists and
field biologists to taxonomically classify individuals, and populations
of interbreeding individuals, as members of a particular species or
subspecies.
The scientific criteria for describing and formally recognizing
taxonomic species of fish are based almost entirely on morphological
characters (Behnke 1992; Bond 1996; Moyle and Cech 1996). Indeed, the
scientific basis for distinguishing rainbow trout and cutthroat trout
(O. clarki) as distinct species are well-established differences in the
number of scales in the lateral-line series, spotting patterns on the
sides of the body, and the presence of: (a) Basibranchial teeth (i.e.,
teeth on a series of bones behind the tongue and between the gills) and
(b) a distinctive red or orange slash mark that occurs just below both
sides of the lower jaw in cutthroat trout but not in rainbow trout
(Miller 1950). Morphological differences, particularly external
spotting patterns, also distinguish subspecies of cutthroat trout
(Behnke 1992). These morphological differences among cutthroat trout
subspecies are consistent with their distinct, geographic distributions
(e.g., Yellowstone [River] vs. Lahontan [basin] cutthroat trout [O. c.
henshawi]). In addition, the common names of the various species of
trout clearly reflect their distinctive morphological appearances,
e.g., rainbow trout, redband trout (O. m. gairdneri), cutthroat trout,
and golden trout (O. m. aguabonita) (Behnke 2002).
The advent of molecular genetic techniques in the mid-1960s added
an additional set of biological characters that can be used to
distinguish species and subspecies of native trouts (Oncorhynchus spp.)
in the western United States. In most cases, the new molecular genetic
data simply confirmed the evolutionary distinctness of species and
subspecies that had already been described taxonomically on the basis
of morphology (Behnke 1992). One notable exception was the failure of
molecular genetic techniques to distinguish fine-spotted Snake River
cutthroat trout (O. c. subsp.) and YCT as two evolutionarily distinct
forms (Loudenslager and Kitchen 1979).
Although molecular genetic data have had little impact on the
taxonomic recognition of rainbow trout, cutthroat trout, and their
respective subspecies, molecular genetic markers are very sensitive
tools for detecting natural hybridization and small amounts of genetic
introgression. For example, Campton and Utter (1985) used allozymes
(proteins) to first document the incidence of natural hybridization
between naturally sympatric populations of coastal cutthroat trout (O.
c. clarki) and rainbow trout/steelhead (O. mykiss), although earlier
morphological descriptions had suggested such interbreeding was
occurring (DeWitt 1954; Hartman and Gill 1968). The sensitivity of the
molecular genetic data simply provided compelling evidence that
interbreeding was indeed occurring.
In general, molecular genetic methods are capable of detecting
extremely small amounts of genetic introgression (e.g., <1 percent)
undetectable by other methods (Weigel et al. 2002; see also Fig. 2 of
Kanda et al. 2002). For example, a large number of situations exist in
the scientific literature where the mitochondrial DNA (mtDNA) from one
species appears to have introgressed via hybridization into the nuclear
genetic background of a closely related species (e.g., Ferris et al.
1983; Bernatchez et al. 1995; Glemet et al. 1998; Wilson and Bernatchez
1998; Redenbach and Taylor 2002). This ability to detect very low
levels of introgression raises fundamental questions regarding the
criteria by which introgressed populations, and individuals in those
populations, should be included with, or excluded from, their parental
or morphological species. In the mtDNA situations cited above, the
scientific community considers the ``introgressed'' individuals to be
legitimate members of their morphological species despite the presence
of mtDNA from another species. Similarly, individuals of a particular
``species'' may possess nuclear genes from another taxon detectable
only by molecular genetic methods, yet those individuals may still
conform morphologically, behaviorally, and ecologically to the
scientific taxonomic description of the parental or native species
(e.g., Busack and Gall 1981; Weigel et al. 2002).
Previous Service positions regarding hybridization, based upon
interpretations in a series of opinions by the U.S. Department of the
Interior, Office of the Solicitor, generally precluded conservation
efforts under the authorities of the Act for progeny, or their
descendants, produced by matings between taxonomic species or
subspecies (O'Brien and Mayr 1991). However, advances in biological
understanding of natural hybridization (e.g., Arnold 1997) prompted
withdrawal of those opinions. The reasons for that action were
summarized in two sentences in the withdrawal memorandum (Memorandum
from Assistant Solicitor for Fish and Wildlife, U.S. Department of the
Interior, to Director, U.S. Fish and Wildlife Service, dated December
14, 1990): ``New scientific information concerning genetic
introgression has convinced us that the rigid standards set out in
those previous opinions should be revisited. In our view, the issue of
``hybrids'' is more properly a biological issue than a legal one.''
Our increasing understanding of the wide range of possible outcomes
resulting from exchanges of genetic material between taxonomically
distinct species, and between entities within taxonomic species that
also can be listed under the Act (i.e., subspecies, DPSs), requires the
Service to address these situations on a case-by-case basis. In some
cases, introgressive hybridization may be considered a natural
evolutionary process reflecting active speciation or simple gene
exchange between naturally sympatric species. In other cases,
hybridization may be threatening the continued existence of a taxon due
to anthropogenic factors or natural environmental events. In many
cases, introgressed populations may contain unique or appreciable
portions of the genetic resources of an imperiled or listed species.
For example, populations with genes from another taxon at very low
frequencies may still express important behavioral, life-history, or
ecological adaptations of the indigenous population or species within a
particular geographic area. Consequently, the Service plans to
carefully evaluate the long-term conservation implications for each
taxon separately on a case-by-case basis where introgressive
hybridization may have occurred. The Service shall perform these
evaluations objectively based on the best scientific and commercial
information available consistent with the intent and purpose of the
Act.
For example, the Service may recognize that small amounts of
genetic introgression do not disqualify individuals or populations from
``species membership'' or the Act's protections if those individuals or
populations conform to the scientific taxonomic description of that
species. A natural population of a particular species that possesses
genes from another taxon at low frequency, yet retains the
distinguishing morphological, behavioral, and ecological characters of
the native species, may remain very valuable to the overall
conservation and survival of that species.
[[Page 46993]]
The Service also recognizes special cases where all individuals of
a ``species'' are considered hybrids. For example, the Service
recognizes that deliberate hybridization may be necessary in extreme
cases to prevent extinction of the genetic resources associated with a
highly endangered species, as was the case for the Florida panther
(Felis concolor coryi) (Hedrick 1995). Similarly, the Service continues
to protect red wolves (Canis rufus) under the Act despite ongoing
controversies regarding their possible hybrid origin (Nowak and
Federoff 1998). In both of those cases, extending the Act's
jurisdictions and protections to ``hybrids'' may contribute to the
conservation of the genetic resources of those taxa, consistent with
the intent and purpose of the Act.
A potential dichotomy thus exists under the Act between: (a) The
need to protect the genetic resources of a species in which
introgression has occurred and (b) the need to minimize or eliminate
the threat of hybridization posed by another taxon. Implementing
actions under the Act that distinguish between these two alternatives
is difficult when imperiled species are involved because a large number
of populations may have experienced small amounts of genetic
introgression from another taxon. These decisions are further
complicated for WCT because the native geographic ranges of WCT and
rainbow (redband) trout overlap in portions of the Columbia River
drainage. For example, as noted by Howell and Spruell (2003), ``It is
apparent that WSCT [WCT] x RB [rainbow trout] hybridization can be
extensive in areas, such as the John Day [River] subbasin, where both
taxa are native and there have been little to no introductions of
hatchery RB.''
For the purpose of providing conservation guidelines, Allendorf et
al. (2001) have suggested that hybridization be categorized as either
anthropogenic or ``natural.'' They further suggest that ``hybrid''
populations or taxa resulting from natural causes would be eligible for
conservation protection, whereas genetically introgressed individuals
or populations resulting from anthropogenic causes would generally not
be protected unless ``hybrids'' were the last remaining genetic
representatives of a hybridized species (their ``Type 6''
hybridization). Such criteria may be useful for prioritizing management
options for populations or species that are not eligible for listing
under the Act. However, the issue for species under potential
jurisdiction of the Act is the extent to which hybridization poses a
threat to the continued existence of the ``species'' regardless of
whether the cause is anthropogenic or ``natural.'' Both natural
evolutionary processes, including catastrophic environmental events
(e.g., floods, earthquakes), and anthropogenic factors can lead to
secondary contact and hybridization between species. Also,
distinguishing between anthropogenic and natural causes of
hybridization, particularly for species with naturally overlapping
geographic ranges, may be extremely difficult (e.g., Campton and Utter
1985; Young et al. 2001; Baker et al. 2002). A complicating issue in
these determinations is the degree to which ``natural'' hybridization
may have compromised the identity of a distinct species prior to
anthropogenic influences (e.g., Weigel et al. 2002). The principal
issues here under the Act are the threats and potential outcomes of
hybridization, including other potential risks associated with the five
statutory listing factors (e.g., habitat loss, disease), and not
necessarily the mechanistic causes (natural or anthropogenic) of those
threats. In this context, the Act does not distinguish between natural
and ``manmade'' factors that may threaten the continued existence of a
species (section 4(a)(1)).
Several studies have demonstrated that natural populations, and
individual fish, conforming morphologically to the scientific taxonomic
description of WCT may contain genes derived from rainbow trout or YCT
as the result of a past hybridization event (Leary et al. 1984; Marnell
et al. 1987; Forbes and Allendorf 1991a, b; Leary et al. 1996; Weigel
al. 2002, 2003). For example, Leary et al. (1984) reported that an
introgressed population of WCT, with an estimated 20 percent of its
nuclear genes derived from rainbow trout, was indistinguishable
morphologically from nonintrogressed WCT populations. A subsequent
study revealed a strong, positive correlation between percent rainbow
trout genes in natural populations of WCT and the percent of
individuals without basibranchial teeth in those populations (Table 1
in Leary et al. 1996). Indeed, based on this latter study, the percent
of individuals without basibranchial teeth appears to be a fairly
accurate predictor of the percent rainbow trout genes in natural
populations where WCT are native. However, this correlation collapses
in nonintrogressed populations of WCT where up to 18 percent of the
individuals may not have any basibranchial teeth (Leary et al. 1996).
Weigel et al. (2002) recently conducted the most extensive study to
date comparing variation in morphological characters to levels of
genetic introgression in natural populations of WCT. In that study,
Weigel et al. (2002) compared variation in morphological characters to
nuclear DNA genotypes at 16 dominant marker loci (Spruell et al. 1999,
2001) in random samples of 20 trout from each of 100 sites in the
Clearwater and Lochsa River drainages in Idaho. In that study, the
presence of at least 1 rainbow trout DNA marker among the 20
individuals tested at a particular site was accepted as evidence that
genetic introgression had occurred in the native WCT population
inhabiting that site. According to the authors, their DNA methods and
sample sizes (n = 20) allowed them to achieve 95 percent confidence
(probability) of detecting genetic introgression in WCT populations
with as little as 1 percent rainbow (or redband) trout genes. However,
because those authors used ``dominant'' genetic markers, they could not
distinguish heterozygotes from homozygotes, thus precluding
calculations of allele frequencies and true estimation of admixture
proportions (i.e., percent rainbow trout genes) in each sample or
population evaluated.
Despite those limitations, three main results pertinent to this
status review can be gleaned from the paper by Weigel et al. (2002):
(1) The percent of fish at each sample site with at least 1 rainbow
trout marker was bimodally distributed among the 100 sample sites
examined (see Figure 2 in Weigel et al. 2002); approximately 62 percent
of the sites yielded population samples where zero to 30 percent of the
fish showed evidence of introgression, while approximately 36 percent
of the sample sites had 50 to 100 percent of the individuals showing
evidence of introgression. (2) Variation in the mean values of four
morphological characters among natural populations of WCT (i.e., the
presence or absence of red or orange slash marks, the number of
basibranchial teeth, the shape of individual spots on the body, and the
ratio of head length to total body length) was correlated with the
amount of rainbow trout genetic introgression in those populations. (3)
By employing a dichotomous morphology key, field observers attained 93
percent accuracy in morphologically detecting genetic introgression in
natural populations of WCT where 50 percent or more of the fish in
those populations had at least one rainbow trout DNA marker; however,
those same observers were unable to accurately distinguish WCT
populations with no DNA evidence of introgression from populations with
low
[[Page 46994]]
levels of introgression where less than 50 percent of the individuals
expressed at least one rainbow trout DNA marker. Given the statistical
power of the authors' methods and their use of dominant genetic
markers, we conclude that rainbow trout genes constituted less than 25
percent of the genes in those latter WCT populations where less than 50
percent of the individuals expressed a rainbow trout DNA marker.
In a recent unpublished report to the Service, Allendorf et al.
(2003) reviewed results from their laboratory regarding the threshold
levels of rainbow trout or YCT genetic introgression (i.e., threshold
percent genetic admixture) detectable by morphological criteria (see
also Leary et al. 1984; Marnell et al. 1987; Leary et al. 1996).
Allendorf et al. (2003) presented data indicating that introgressed
populations of WCT with less than 20 percent of their genes derived
from another taxon are morphologically indistinguishable from
nonintrogressed populations with zero percent genetic admixture. They
also presented data indicating that introgression exceeding 50 percent
non-WCT genes in natural populations of WCT would most likely be
detectable by morphological methods.
Therefore, based on the best scientific and commercial data
available, we conclude that natural populations of WCT may have a
genetic ancestry derived by as much as 20 percent from rainbow trout or
YCT when fish in those populations express a range of morphological
variation that conforms to the scientific taxonomic description of WCT.
In other words, a natural population of WCT with less than 20 percent
of its genes derived from rainbow trout or YCT is, most likely,
morphologically indistinguishable from nonintrogressed populations of
WCT with no hybrid ancestry.
As noted previously, on March 31, 2002, the U.S. District Court for
the District of Columbia found that our listing determination for WCT
did not reflect a reasoned assessment of the Act's statutory listing
factors on the basis of the best available science. The Court remanded
the listing decision to us with specific instructions to evaluate the
threat of hybridization as it bears on the Act's statutory listing
factors and the status of the WCT subspecies. The Court also ruled that
inclusion of introgressed populations or ``hybrid stock'' (Court's
term) as part of the WCT subspecies in our status review, based on the
visually based, professional opinions of field biologists familiar with
the subspecies, ``was arbitrary and capricious.'' During the Court
proceedings, we noted that the Act does not require ``100 percent
genetic purity'' and the plaintiffs agreed with this proposition,
noting that they were not insisting on genetic purity. The Court, in
effect, concurred. ``Genetic purity'' is not a condition for including
populations or individual fish with the WCT subspecies under the Act,
but the conditions for including potential ``hybrid stock'' with WCT
may not be arbitrary and capricious.
In reconciling the dichotomy between hybridization as a threat and
the potential inclusion of ``hybrid stock'' with WCT under the Act, one
must make a clear distinction between the action (hybridization) and
the outcome of that action (hybrid stock). Therefore, we must define
these terms more precisely. Consequently, in response to the Court
order and for the purpose of this new status review for WCT, we define
``hybridization'' as the direct interbreeding between two individuals
that conform morphologically to different species or subspecies,
including the interbreeding between individuals conforming
morphologically to WCT and individuals not conforming morphologically
to WCT. We further define ``hybrid stock'' (Court's term), or
introgressed population, as a group of potentially interbreeding
individuals with a genetic ancestry derived from two or more extant
species or subspecies. Under these definitions, ``hybridization'' may
represent a ``natural or manmade factor affecting the continued
existence'' of the WCT subspecies. Similarly, introgressed populations
composed of individuals not conforming morphologically to the
scientific taxonomic description of WCT may be a potential
hybridization threat to the continued existence of the WCT subspecies.
Conversely, in accordance with the above definition of
hybridization, we do not consider populations or individual fish
conforming morphologically to the scientific taxonomic description of
WCT to be a hybridization threat to the WCT subspecies. Although such
individuals may have genes from another taxon at low frequency, we are
not aware of any information to suggest that such individuals express
behavioral, ecological, or life-history characteristics differently
than do WCT native to the particular geographic area. Without such
changes, we expect the frequency of genes from the other taxon to
remain low in the population. Therefore, we do not consider such
populations as contributing to the threat of hybridization to the WCT
subspecies.
Therefore, in accordance with the Court's order, we provide our
scientifically-based conclusion about the extent to which it is
appropriate to include hybrid or genetically introgressed WCT
populations, and populations of unknown genetic characteristics, in the
WCT subspecies considered for listing. These criteria are specific to
this listing determination for WCT under the Act and may not be
applicable to other species or taxa.
To determine which natural populations we should consider as WCT
under the Act, we used the best scientific data available (as described
previously) to establish three principal criteria: (1) The population
under consideration must first exist within the recognized, native
geographic range of WCT (Behnke 1992; Shepard et al. 2003). The
population must then satisfy one of the following two additional
criteria to be considered WCT under the Act; (2) If all measured
individuals in the population have morphological characters that are
all within the scientific, taxonomically-recognized ranges of those
characters for the WCT subspecies, then the population shall be
considered WCT; or (3) if not all of the measured individuals have
morphological characters that are within the scientific, taxonomically-
recognized ranges of those characters for the WCT subspecies, then
additional evidence of reproductive discreteness between individuals
that conform morphologically to the WCT subspecies and individuals that
do not conform morphologically to the subspecies will be examined. If
the two forms are considered reproductively discrete (e.g., naturally
sympatric populations of native redband trout and WCT that may only
occasionally interbreed), then we shall consider the population under
consideration to be WCT under the Act. In making these latter
determinations, we will consider the following additional information:
(a) Whether rainbow (redband) trout are native to the geographic area
under consideration; (b) the percent of measured individuals that do
not conform morphologically to the taxonomic scientific description of
WCT, including their range of morphological variation (e.g., a single
anomalous individual reflecting a congenital abnormality would not
disqualify the population from inclusion); (c) the results of genetic
tests that would indicate reproductive discreteness between the two
forms; and (d) any other additional information that would assist with
these determinations (e.g., information on the locations and timing of
spawning for each of the two forms).
Hence, our principal criterion for including potentially
introgressed populations, and populations of unknown genetic
characteristics, with
[[Page 46995]]
the WCT subspecies under the Act is whether fish in those populations
conform morphologically to the scientific taxonomic description of the
WCT subspecies. As noted previously, natural populations conforming
morphologically to the scientific taxonomic description of WCT are
presumed to express the behavioral, ecological, and life-history
characteristics of WCT native to the geographic areas where those
populations occur.
The Service acknowledges that molecular genetic data also can be
very useful for guiding these decisions regarding inclusion or
exclusion of particular populations from the WCT subspecies under the
Act. For example, on the basis of data described previously in this
section, our general conclusion is that natural populations conforming
morphologically to the scientific taxonomic description of WCT may have
up to 20 percent of their genes derived from rainbow trout or YCT.
Consequently, for populations for which molecular genetic data may be
the only data available, populations with less than 20 percent
introgression will be considered WCT under the Act, whereas populations
with more than 20 percent introgression will generally be excluded from
the WCT subspecies. However, such decisions involving possible
inclusion or exclusion will need to consider other potentially
important characteristics of the populations, including the ecological
setting, geographic extent of the introgression across the population's
range, and whether rainbow (or redband) trout are naturally sympatric
with WCT in the particular region under consideration.
The Service shall evaluate natural populations for which no
morphological or genetic data exist on a case-by-case basis considering
their geographic relationship to natural populations for which such
data do exist and any other available information pertinent to those
evaluations (e.g., ecological setting, degree of geographic isolation,
and historical stocking records of nonnative trout species).
The species criteria described above are consistent with the best
scientific and commercial data available because they are based on: (a)
The criteria by which taxonomic species of fish are recognized
scientifically, and (b) the biological relationship between those
taxonomic criteria and levels of genetic introgression detected by
molecular genetic methods in natural populations of WCT. Those criteria
exclude from the WCT subspecies considered for listing genetically
introgressed populations and individual fish that do not conform
morphologically to the scientific taxonomic description of the
subspecies.
These criteria are further justified for this subspecies because:
(a) There are no generally applicable standards for the extent of
hybridization considered acceptable under the Act; (b) decisions
regarding status of WCT under the Act must be made for the entire
subspecies and its component populations (see Distinct Population
Segments section); (c) in most cases, the taxonomic classification of
extant WCT has been based on the pattern of spots on the fish's body
and the professional evaluations and experiences of fishery biologists
who examined the fish in the field (see also Marnell et al. 1987); and
(d) spotting pattern was chief among the morphological characteristics
diagnostic of the type specimens of WCT.
Our approach further acknowledges that a significant proportion of
the genetic resources associated with WCT throughout its native
geographic range may be represented by populations with low-frequency
genes from other taxa (e.g., rainbow trout) detectable only by
molecular genetic methods. Such populations, if they conform
morphologically to the scientific taxonomic description of WCT, are
considered part of the WCT subspecies under the Act. As noted
previously, individual fish or populations conforming to the scientific
taxonomic description of WCT shall not be considered a threat to the
continued existence of the subspecies.
Conversely, we will consider genetically introgressed populations
not classified as WCT as potential hybridization threats to the WCT
subspecies. By definition, these latter populations do not conform
morphologically to the scientific taxonomic description of WCT, or--in
the absence of morphological data--we would expect them to not conform
morphologically to WCT based on the level of introgression detected by
a molecular genetic test or other available information.
As a result, the Service must determine which natural populations
represent potential hybridization ``threats'' to the future existence
of the WCT subspecies and which populations represent potential genetic
resources of the subspecies itself. The criteria we use to make such
decisions must not only be consistent with previous Service rulings
dealing with ``hybrids'' under the Act, but decisions resulting from
those criteria also must be consistent with the intent and purpose of
the Act itself. The Service has concluded that, in such situations, the
intent and purpose of the Act is to be inclusionary, not exclusionary.
Consequently, any natural population conforming to the scientific
taxonomic description of WCT, as conditioned by the criteria stated
previously, will be considered WCT under the Act. The Service also has
concluded that alternative approaches would either be arbitrary and
capricious (e.g., =90 percent genetic ``purity'' required
for inclusion) or inconsistent with the intent and purpose of the Act
(e.g., 100 percent genetic ``purity'' required for inclusion). For
example, the best scientific and commercial data available indicate
that WCT populations with 1 percent to 20 percent of their genes
derived from another taxon are indistinguishable morphologically from
nonintrogressed populations of WCT. Hence, establishing a threshold of
``90 percent genetic purity'' would be arbitrary and capricious because
no scientific or commercial data exist to support that threshold based
on the morphological criteria by which species are described
taxonomically. In contrast, the ``80 percent genetic threshold''
described previously is based on the best scientific and commercial
data available, although, as we have described, that threshold is not
the principal criterion by which populations are included or excluded
from the WCT subspecies. Similarly, as noted previously, the
Solicitor's Office for Department of the Interior overturned
(withdrew)--in December 1990--the Service's old ``hybrid policy'' which
precluded federal protections to hybrid offspring or their descendants
under the Act (O'Brien and Mayr 1991). Moreover, the court in the
present WCT case ruled that ``100 percent genetic purity'' is not a
condition for including populations or individual fish with the WCT
subspecies under the Act.
Our criteria for including potentially introgressed populations of
WCT with the WCT subspecies considered for listing under the Act also
are consistent with a recent Position Paper developed by the fish and
wildlife agencies of the intermountain western States (Utah Division of
Wildlife Resources 2000). That document identifies, for all subspecies
of inland cutthroat trout, three tiers of natural populations for
prioritizing conservation and management options under the States' fish
and wildlife management authorities: (1) Core conservation populations
composed of =99 percent cutthroat trout genes; (2)
conservation populations that generally ``have less than 10 percent
introgression, but [in which] introgression may extend to a greater
amount depending upon
[[Page 46996]]
circumstances and the values and attributes to be preserved''; and (3)
cutthroat trout sport fish populations that, ``at a minimum, meet the
species (e.g., WCT) phenotypic expression defined by morphological and
meristic characters of cutthroat trout.'' Conservation populations of
cutthroat trout also include those believed to have uncommon, or
important, genetic, behavioral, or ecological characteristics relative
to other populations of the subspecies under consideration. Sport fish
populations are those that conform morphologically (and meristically)
to the scientific taxonomic description of the subspecies under
consideration but do not meet the additional criteria of
``conservation'' or ``core'' populations. Consequently, the Service's
criteria for including potentially introgressed populations of WCT with
the WCT subspecies considered for listing under the Act include the
first two tiers, as defined by the intermountain State fish and
wildlife agencies, as well as those sport fish populations in the third
tier for which morphological or genetic data are available. The
implicit premise of the Position Paper is that populations must
conform, ``at a minimum,'' to the morphological and meristic characters
of a particular cutthroat trout subspecies in order for those
populations to be included in a State's conservation and management
plan for that subspecies. Signatories to the Position Paper are the
Colorado Division of Wildlife, Idaho Department of Fish and Game,
Montana Department of Fish, Wildlife and Parks, Nevada Division of
Wildlife, New Mexico Game and Fish Department, Utah Division of
Wildlife Resources, and the Wyoming Game and Fish Department.
Molecular genetic methods for estimating percent introgression, or
genetic admixture proportions, in natural populations of WCT need to be
consistent to help guide the conservation decisions described here
under the Act. The continual development of new types of molecular
genetic markers for population-level evaluations complicates estimation
of genetic admixture proportions in introgressed populations (e.g.,
Weigel et al. 2002). The most accurate estimates are obtained with
codominant genetic markers in which heterozygotes and homozygotes at
single loci can be distinguished. Allozymes and alleles at
microsatellite nuclear DNA (nDNA) loci meet this ``codominance''
criterion. ``Amplified fragment-length polymorphisms'' (AFLPs) and
``paired interspersed nuclear elements'' (PINES; Weigel et al. 2002) do
not. Also, a minimum of four or five codominantly-expressed, diagnostic
loci are usually required to attain sufficient statistical power in
evaluations of introgressive hybridization (Fig. 2 in Campton 1990;
Figure 1 in Epifanio and Phillip 1997; Figure 2 in Kanda et al. 2002).
Under these conditions, percent introgression (P) in a population can
be calculated as P = (NA/2LN) x 100, where L = the number of
diagnostic, codominantly expressed loci that distinguish the two taxa
or species, N = the number of individual fish in a random sample of
individuals from the population, and NA = the number of
alleles from another taxon observed at the diagnostic loci in the
sample of individuals. This estimator is equally applicable to allozyme
and microsatellite nDNA markers and is identical to the statistic
proposed by the State fish and wildlife agencies (Utah Division of
Wildlife Resources 2000). Consequently, this estimator provides a
standardized approach for evaluating genetic introgression in natural
populations. Evaluations of introgression based on dominant markers
(Weigel et al. 2002) should computationally convert the observed data
(e.g., percent of individuals with one or more rainbow trout alleles)
into estimates of percent introgression on the basis of explicitly
stated assumptions (e.g., that a single, random-mating population was
sampled). If one or more codominantly expressed loci are not diagnostic
between species, then the statistical methods of least squares or
maximum likelihood can be used to estimate admixture proportions in
introgressed populations (Campton 1987; Bertorelle and Excoffier 1998).
Further support for the morphological and genetic criteria
developed by the Service and the State fish and wildlife agencies for
classifying natural populations as WCT comes from field observations of
the effects of natural and artificial selection in genetically
introgressed populations of other taxa. Gerber et al. (2001) note that
natural selection may act to retain the morphological phenotypes of
native species despite introgressive hybridization resulting from
secondary contact of a colonizing, congeneric species. Busack and Gall
(1981) note a similar outcome resulting from artificial selection
(i.e., selective removal of ``hybrid-looking'' individuals) for the
Paiute cutthroat trout (O. c. seleniris) phenotype within introgressed
populations of this latter subspecies. Those results suggest the lack
of a genetic correlation between morphological phenotypes (i.e., the
genes affecting those phenotypes) and molecular genetic markers used to
detect introgression in natural populations. In other words, molecular
genetic markers (e.g., microsatellite DNA alleles, DNA fingerprint
patterns) provide very sensitive methods for evaluating ancestral or
pedigree relationships among populations, species, or individuals
independent of the genes affecting morphology and other species-
specific characters.
We now perform our new status review for WCT based on the described
criteria for including potentially introgressed populations and
populations of unknown genetic characteristics with the WCT subspecies
considered for possible listing under the Act.
New Status Review
Background
In response to our September 3 and December 18, 2002, Federal
Register notices, we received comments and information on WCT from
several State fish and wildlife agencies, the U.S. Forest Service,
private citizens and organizations, and other entities. Among the
materials that we received, the most important was a status update
report for WCT, a comprehensive document (Shepard et al. 2003) prepared
by the fish and wildlife agencies of the States of Idaho, Montana,
Oregon and Washington, and the U.S. Forest Service.
The WCT status update report (Shepard et al. 2003) and the
comprehensive database that is the report's basis, presented to us the
best scientific and commercial information available that describes the
present-day rangewide status of WCT in the United States. To compile
that important information, 112 professional fishery biologists from 12
State, Federal, and Tribal agencies and private firms met at 9
workshops held across the range of WCT in fall 2002. Those fishery
biologists had a combined 1,818 years of professional experience, 63
percent of which involved work with WCT or other subspecies of
cutthroat trout. At the workshops, the biologists submitted essential
information on the WCT in their particular geographic areas of
professional responsibility or expertise, according to standardized
protocols. Presentation of information directly applicable to
addressing the issues raised by the Court, as well as other concerns
that we consider when making listing determinations under the Act, was
central to those protocols.
In conducting the new status review for WCT in the United States
described
[[Page 46997]]
in the present document, we considered our initial review (U.S. Fish
and Wildlife Service 1999) to be the foundational compendium of
information on the present-day status of WCT. In turn, the more-recent
WCT status update report (Shepard et al. 2003), as well as the other
materials that we received or otherwise obtained while conducting the
new review, clarified and improved our understanding of the present-day
status of WCT and also helped us to address the important issues that
had been raised by the Court. While describing our findings in the
present document, we will often compare the recently received
information for WCT to that found during our initial status review.
Findings of the New Status Review
Distinct Population Segments
The Service and the National Marine Fisheries Service have adopted
criteria (61 FR 4722; February 7, 1996) for designation of DPSs for
vertebrate organisms, such as WCT, under the Act. To constitute a DPS,
a population or group of populations must be: (1) Discrete (i.e.,
spatially, ecologically, or behaviorally separated from other
populations of the taxonomic group [i.e., taxon]); (2) significant
(e.g., ecologically unique for the taxon, extirpation would produce a
significant gap in the taxon's range, the only surviving native
population of the taxon, or substantial genetic divergence occurs
between the population and other populations of the taxon); and (3) the
population segment's conservation status must meet the Act's standards
for listing.
In our initial status review, we found no morphological,
physiological, or ecological data for WCT that indicated unique
adaptations of individual WCT populations or groups of populations that
inhabit discrete areas within the subspecies' historic range. Although
the disjunct WCT populations in Washington and Oregon, as well as the
populations in Montana's upper Missouri River basin, met the first
criterion for DPS designation (i.e., discreteness), scientific evidence
in support of the second criterion (significance) was absent or
insufficient to conclude that any of those populations represented a
DPS (U.S. Fish and Wildlife Service 1999).
Extant WCT show a remarkably large amount of genetic variation at
the molecular level, both within and among WCT populations across the
subspecies' historic range (Allendorf and Leary 1988; Leary et al.
1997). Leary et al. (1997) found that 65 percent of the total measured
genetic variation in the WCT genome is within WCT populations, 34
percent is among the populations themselves, and about 1 percent is
between the aggregates of populations in the Columbia and Missouri
River basins. Those authors also found that there can be genetic
differences among WCT populations that are separated by short
geographic distances. In the context of DPS designation, those
differences suggest reproductive isolation among populations that may
be indicative of ``discreteness.'' Nevertheless, because of the large
amount of genetic variation in the WCT subspecies, the occurrence of a
WCT population with molecular genetic characteristics that differ
statistically (with adequate sample sizes) from those of other WCT
populations is often sufficient to meet the discreteness criterion but
not sufficient to meet the significance criterion indicative of unique
morphological, behavioral, physiological, or ecological attributes.
Recently, the Northwest Environmental Defense Center (2002) argued
that the WCT populations in Oregon's John Day River drainage merited
listing as a DPS; however, the Northwest Environmental Defense Center
provided no supportive, empirical evidence for that contention and only
speculated as to why those populations may be significant in the
context of DPS designation. Congress has made clear that DPSs should be
used ``sparingly'' in the context of the Act (see Senate Report 151,
96th Congress, 1st Session). While conducting the new status review for
WCT, we found no compelling evidence for recognizing DPSs of WCT.
Instead, for purposes of the new status review, we recognize WCT as a
single taxon in the contiguous United States.
Disjunct Westslope Cutthroat Trout Populations in Washington
In addition to the historic range of WCT previously described (see
Background), Behnke (1992) speculated that the WCT is native to the
Wenatchee and Entiat River drainages in Washington. Because Behnke's
conclusion was largely speculative, we did not consider those two
drainages as being within the historic range of WCT in our initial
status review (U.S. Fish and Wildlife Service 1999). Similarly, those
drainages were not included in the WCT status update report (Shepard et
al. 2003) because the Washington Department of Fish and Wildlife did
not consider those drainages to be within the historic range of WCT.
Because of the extensive introductions of hatchery-produced WCT
(and the probable human transport and stocking of native WCT into
waters outside the subspecies' historic range) during the 20th Century,
WCT populations are more numerous and widely distributed in Washington
today than prior to European settlement (U.S. Fish and Wildlife Service
1999). Those populations now occur in over 493 streams and 311 lakes in
Washington (Fuller 2002). Similarly, some WCT populations have been
intentionally established in Oregon's John Day River drainage
(Unterwegner 2002). However, as was done during our initial status
review (U.S. Fish and Wildlife Service 1999), our decision whether or
not to recommend listing the WCT as a threatened or an endangered
species, as described in the present document, will be based entirely
on WCT that presently occur within the formally recognized historic
range of the subspecies (Behnke 1992), as modified by Shepard et al.
(2003) in their status update report.
Recent data from ongoing studies suggest that native WCT
populations do occur in the Yakima, Entiat, and Wenatchee River
drainages of Washington (Trotter et al. 1999, 2001; Howell and Spruell
2003). In assessing the origins of the cutthroat trout they collected
from selected streams in those drainages, Trotter et al. (1999, 2001)
assumed that the absence of a written stocking record for WCT,
particularly in the studied streams where those fish are now present,
was evidence that WCT are native to those areas. However, as pointed
out by Howell and Spruell (2003), who are presently conducting a
similar study of the WCT in those drainages as well as in Oregon's John
Day River drainage, the historic stocking records of management
agencies in Washington and Oregon are incomplete and have ``large
gaps.'' Moreover, as Trotter et al. (2001) indicate, during the 20th
century it was common for the representatives of many Federal, State,
and county agencies, and even private citizens, to stock hatchery-
produced fish. Those fish were often readily obtained from nearby fish
hatcheries, whose managers took advantage of the willingness of
citizens to haul hatchery fish to remote areas by whatever means.
Moreover, angler conservationists often moved fish from established
populations to nearby ostensibly fishless streams.
Howell and Spruell (2003) concluded that WCT in the Yakima,
Wenatchee, Entiat, and Methow River drainages of Washington are
probably native WCT because populations from each of those drainages
possessed some genetic characteristics (i.e., allozyme alleles) that
were absent from those of the Twin
[[Page 46998]]
Lakes WCT hatchery population maintained by the State of Washington.
However, as those authors point out, the Twin Lakes population is not
the only population of hatchery WCT that was stocked in Washington
during the past century. Moreover, random genetic drift, which has a
greater probability of occurring in small, isolated populations, could
have resulted in genetic differences among populations of introduced
WCT, and perhaps in the Twin Lakes hatchery population itself.
Howell and Spruell (2003) describe their study as a ``work in
progress.'' We agree and suggest that their caveat should be applied to
both the recent and ongoing investigations of WCT populations in
Washington. Extensive discussions of the available data and their
interpretations among members of the scientific community, as part of
the normal, peer-review process, will be required to determine whether
any of the putative, native WCT populations that Trotter et al. (1999,
2001) and Howell and Spruell (2003) have identified in Washington are
native to the streams from which the fish were collected. However since
these populations are putative, we did not include them as part of this
listing decision. Rather in our assessment we relied on those
populations that the best scientific data currently indicate are native
(as described by Behnke 1992 and Shepard et al. 2003).
Distribution of Westslope Cutthroat Trout and the Prevalence of
Hybridization
New, definitive information on both the probable historic and
present-day range-wide distributions of WCT was provided in the status
update report (Shepard et al. 2003). That information indicated WCT
historically occupied about 90,928 km (56,500 mi) of stream in the
United States and now occupy about 33,500 (59 percent) of those stream
miles. About 33,000 (58 percent) of the historically occupied stream
miles were in Montana, 19,000 (34 percent) in Idaho, 1,000 (2 percent)
in Oregon, 3,000 (5 percent) in Washington, and 161 km (100 mi) (<1
percent) in Wyoming (i.e., Yellowstone National Park). Shepard et al.
(2003) also concluded that several river drainages, including the Milk
Headwaters, Upper Milk, Willow, Bullwhacker-Dog, Box Elder, and the
Upper, Middle, and Lower Musselshell in the Missouri River basin, the
Hangman River watershed in the Spokane River drainage, and the North
John Day River drainage in Oregon, were outside the historic range of
WCT. On the basis of the less definitive information available prior to
the WCT status update report, preceding assessments (e.g., U.S. Fish
and Wildlife Service 1999) had treated the streams in those drainages,
except Hangman River, as historic WCT habitat. Today, WCT occupy over
28,968 km (18,000 mi) of stream in Idaho (95 percent of historic range
in Idaho), about 20,922 km (13,000 mi) in Montana (39 percent of
historic range in Montana), about 402 km (250 mi) in Oregon (21 percent
of historic range in Oregon), and about 3,219 km (2,000 mi) of stream
in Washington (66 percent of historic range in Washington). In our
initial status review (U.S. Fish and Wildlife Service 1999), we
reported that WCT occupied about 37,015 km (23,000 mi) of stream in the
United States.
Information provided in the WCT status update report (Table 9 of
Shepard et al. 2003) also indicated that laboratory-based genetic
testing has been performed on samples of WCT collected from locations
representative of about 6,100 (18 percent) of the occupied stream miles
and that nonintrogressed (i.e., showing no evidence of introgressive
hybridization) WCT are known to inhabit about 3,500 of those stream
miles (57 percent of tested stream miles; 10 percent of occupied
miles). An additional 1,669 km (1,037 mi) of stream contained a mixture
of individual WCT that were either nonintrogressed or introgressed.
Finally, based on the absence of nonnative, potentially hybridizing
fish species, we conclude WCT inhabiting an additional 14,645 km (9,100
mi) of stream, for which genetic testing of the WCT therein has not yet
been performed (Table 9 of Shepard et al. 2003), are most likely not
introgressed (see preceding section on the Value of Hybrid Westslope
Cutthroat Trout in Listing Determinations). Thus, nonintrogressed WCT
are known to inhabit 5,633 km (3,500 mi) of stream and probably inhabit
as many as 20,278 km (12,600 mi) of stream in which no potentially
hybridizing fishes occur. In our initial status review (U.S. Fish and
Wildlife Service 1999), we reported that: (1) WCT occupied about 37,015
km (23,000 mi) of stream; (2) data on the genetic characteristics of
WCT were limited and available mainly for Montana; and (3)
nonintrogressed WCT were known to occupy 4,237 km (2,633 mi) of stream.
The WCT status update report (Shepard et al. 2003) grouped most of
the WCT in the occupied miles of stream into 563 separate
``conservation'' populations. Those conservation populations
collectively occupied 39,349 km (24,450 mi) of stream or 72 percent of
the occupied habitat; WCT in the remaining 28 percent of occupied
habitat did not satisfy the criteria of ``conservation'' populations
and are thus being managed as ``sport fish'' populations, as described
previously (Utah Division of Wildlife Resources 2000). Individual
conservation populations ranged in geographic extent from small,
nonintrogressed, isolated populations (i.e., isolets) to large
metapopulations that included numerous populations and encompassed
hundreds of stream miles. According to Shepard et al. (2003), 457 (81.2
percent) of the 563 WCT conservation populations were isolets that were
often restricted to headwater areas and represented 11.5 percent of the
total occupied stream miles. Most of the occupied stream miles (88.5
percent) were habitat for WCT in metapopulations.
Finally, the status update report (Shepard et al. 2003) revealed
that 70 percent of the habitat occupied by extant WCT populations lies
on lands managed by Federal agencies, including lands designated as
national parks (2 percent of occupied habitat), wilderness areas (19
percent), or U.S. Forest Service roadless areas (40 percent). Although
we could not distinguish wilderness and roadless areas from other
Federal lands in our initial status review (U.S. Fish and Wildlife
Service 1999), we reported that most of the habitat for extant WCT
populations was on lands administered by Federal agencies, particularly
the U.S. Forest Service.
Occurrence of Westslope Cutthroat Trout Life-History Forms
Biologists commonly recognize three WCT life-history forms:
resident fish do not move long distances and spend their lives entirely
in their natal stream, where they themselves were produced; fluvial
fish spawn in small tributaries and their young migrate downstream to
larger rivers, where they grow and mature; and adfluvial fish spawn in
streams and their young migrate downstream (or upstream, in the case of
outlet-spawning populations) to mature in lakes. All three life-history
forms may occur in a single drainage and whether they represent
opportunistic behaviors, heritable (i.e., genetically-based) traits, or
a combination of these factors is unknown.
In our initial status review (U.S. Fish and Wildlife Service 1999),
we found that adfluvial WCT occur naturally in 6 lakes in Idaho and
Washington that total about 72,843 ha (180,000 ac) and at least 20
lakes that total 2,164 ha (5,347 ac) in Glacier National Park in
Montana. Most of those populations receive the high
[[Page 46999]]
level of protection afforded by Glacier National Park. We also reported
that about 37,015 km (23,000 mi) of stream were occupied by WCT, most
of which were of either the resident or fluvial life-history form. More
recently, the status update report (Shepard et al. 2003) indicated that
WCT populations that include resident and fluvial fish, both of which
live entirely in streams, presently occur in 53,913 km (33,500 mi) of
stream habitat. In preparing that report, the lake habitats occupied by
WCT were necessarily treated as stream habitat because of the
limitations of the hydrologic database used in the geographic
information systems-based analyses. Consequently, perhaps several
hundred of the stream miles that Shepard et al. (2003) reported as
occupied by WCT were actually lake habitats. The WCT in those lakes
have the adfluvial life history. In addition, the extensive WCT
conservation populations that function as metapopulations encompass
hundreds of stream miles and frequently exhibit all three life-history
forms. Nonetheless, WCT with the adfluvial life history probably
constitute the smallest proportion of the WCT subspecies today, and
this may have been true historically.
Analysis of Extant Threats to Westslope Cutthroat Trout
The Act identifies five factors of potential threats to a species:
(1) The present or threatened destruction, modification, or curtailment
of the species' habitat or range; (2) overutilization for commercial,
recreational, scientific, or educational purposes; (3) disease or
predation; (4) the inadequacy of existing regulatory mechanisms; and
(5) other natural or manmade factors affecting the species' continued
existence.
We examined each of these factors in the context of present-day
WCT. We also used the database of Shepard et al. (2003) to more closely
examine the effects of several specific threats (i.e., whirling
disease, nonnative predators, competition from nonnative brook trout
[Salvelinus fontinalis], and hybridization) to WCT in two categories of
extant populations: (1) Nonintrogressed and suspected nonintrogressed
WCT populations and (2) introgressed and suspected introgressed WCT
classified as ``conservation'' populations (Utah Division of Wildlife
Resources 2000). Collectively, those two categories exclude
introgressed ``sport fish'' populations and thus are a subset of the
populations we defined previously as WCT under the Act (see section on
The Value of Hybrid Westslope Cutthroat Trout in Listing
Determinations). We applied our analyses of threats to this more
restricted subset of WCT populations to take advantage of the States'
detailed database and to be conservative regarding the status and
viability of extant WCT populations. This approach also avoided
classification uncertainties associated with possible marginal
populations managed primarily as sport fisheries (i.e., populations
that may not explicitly meet our stated criteria of WCT under the Act
but for which detailed morphological or genetic analyses have not been
performed). Detailed geographic summaries of biological information
pertinent to each of the drainages within the historic range of WCT
were provided in our initial status review (U.S. Fish and Wildlife
Service 1999). Our evaluations of the five factors of potential threats
to the aforementioned subset of WCT populations are presented below.
(A) Present or Threatened Destruction, Modification, or Curtailment of
the Species' Habitat or Range
Our initial status review revealed that most of the habitat for
extant WCT populations lies on lands administered by Federal agencies,
particularly the U.S. Forest Service (U.S. Fish and Wildlife Service
1999). Moreover, most of the strongholds for WCT populations occurred
within roadless or wilderness areas or national parks, all of which
afforded considerable protection to WCT. More recently, the information
that we received during the two comment periods, in particular the
information provided in the status update report (Shepard et al. 2003),
entirely supported our earlier conclusions and clearly indicated that
WCT populations are widespread across the subspecies' historic range,
abundant in several regions, and that many of those populations receive
the appreciable protections afforded by roadless and wilderness areas
and national parks (see also Hagener 2002). The status update report
(Shepard et al. 2003) indicated that 70 percent of the habitat occupied
by extant WCT populations lies on lands managed by Federal agencies,
including lands designated as national parks (2 percent of occupied
habitat), wilderness (19 percent), or U.S. Forest Service roadless
areas (40 percent). In addition, the regulatory mechanisms in place to
prevent the destruction or adverse modification of WCT habitat on those
Federal lands and elsewhere are extensive (see subsequent section,
Regulatory Mechanisms Involving Land Management).
The best scientific and commercial information available to us
indicates that the WCT subspecies is not threatened by the present or
threatened destruction, modification, or curtailment of its habitat or
range.
(B) Overutilization for Commercial, Recreational, Scientific, or
Educational Purposes
Our initial status review revealed that each of the States and the
National Park Service greatly restricted the harvest of WCT and that in
many regions only catch-and-release angling was allowed (U.S. Fish and
Wildlife Service 1999). However, catch-and-release-only angling
regulations are not essential to protecting WCT from excessive harvest
by anglers. Instead, the angling regulations must not allow harvests
that cause adverse population depletion and thereby threaten population
survival. Our initial status review also revealed that, where there was
collection of WCT for educational or scientific purposes, such
collection was highly regulated and had a negligible effect on the WCT
subspecies.
The additional information that we received while conducting this
new status review confirmed our earlier conclusions. In Montana,
recreational fishing and scientific collecting are highly regulated and
have become increasingly restrictive. Enforcement of regulations
pertaining to native fishes is a priority, and regulations limit the
locations, dates, bag limits, and methods of fishing. In many WCT
waters in the Columbia River basin, and in all waters in the Missouri
River basin in Montana, fishing is restricted to catch-and-release
(Hagener 2002; Shepard et al. 2003). In Idaho, nearly all WCT
populations are managed with restrictive fishing regulations (Moore
2002). In Oregon, angling regulations in areas occupied by WCT are
designed to protect Endangered Species Act-listed Mid-Columbia
steelhead and Columbia Basin bull trout (Salvelinus confluentus). There
is little angling pressure in the John Day River drainage, particularly
in areas occupied by WCT (Unterwegner 2002). In Washington, the
sportfishing rules for 2003-2004 allow the daily harvest of 2 trout
longer than 20 centimeters (8 inches) from most streams, and 5 trout of
any size from lakes, with the exception that all wild cutthroat trout
caught from Lake Chelan and its tributaries, as well as from the Methow
River, must be released alive.
The best scientific and commercial information available to us
indicates that the WCT subspecies is not
[[Page 47000]]
threatened by overutilization for commercial, recreational, scientific,
or educational purposes.
(C) Disease or Predation
Threats from Disease--As part of both the initial and new status
reviews, we considered the threat that diseases may pose to WCT.
Perhaps the most important of the contemporary diseases is whirling
disease, which is caused by an exotic myxozoan parasite. That
microscopic parasite was introduced to the eastern United States from
Europe in the 1950s and has since been found in many western States.
Two separate host organisms are necessary for completion of the
parasite's life cycle, a salmonid (i.e., salmon, trout, and their close
relatives) fish and a specific aquatic oligochaete worm. Within the
range of WCT, whirling disease was first found in Idaho in 1987 and in
Montana in 1994 (Bartholomew and Reno 2002).
The WCT status update report (Shepard et al. 2003) concluded that
the threats to extant WCT populations from diseases in general were
greater for the extensive WCT metapopulations than for the smaller WCT
populations that occur as isolets. The key assumption made in reaching
that conclusion was that, because the ranges of individual
metapopulations were naturally much larger and encompassed habitats
more diverse than those of isolets, the probability that diseases may
be introduced and become established in WCT populations was greater for
metapopulations than isolets. As noted previously, we examined the
database of Shepard et al. (2003) to assess the disease risk to two
groups of extant WCT: (1) Nonintrogressed or suspected nonintrogressed
populations and (2) introgressed or suspected introgressed fish
classified as ``conservation'' populations. Results indicated that only
about 10 percent of the 1,944 stream miles occupied by nonintrogressed
and suspected nonintrogressed WCT populations occurring in isolets were
at moderately high or high risk of disease, whereas 69 percent of the
9,999 stream miles occupied by nonintrogressed WCT in the considerably
more-extensive metapopulations were considered to be at similar risk.
Similarly, introgressed or suspected introgressed WCT ``conservation''
populations occurring as isolets were at moderately high or high risk
of disease in about 20 percent of their 751 occupied stream miles,
whereas introgressed WCT in metapopulations were considered at similar
risk in 88 percent of their 11,775 occupied stream miles.
However, we believe that the procedures used by Shepard et al.
(2003) to assemble their database inevitably led to inflated estimates
of the proportions of stream miles in which the WCT are at moderately
high or high risk of disease. Moreover, as we will describe, the
available scientific information indicates whirling disease is not a
substantial threat to the majority of populations constituting the WCT
subspecies. Although the whirling disease parasite continues to spread
in many waters of the western United States (Bartholomew and Reno
2002), few outbreaks of whirling disease in resident fishes (mainly
rainbow trout) have occurred. Studies summarized by Downing et al.
(2002) indicated that presence of the whirling disease parasite does
not portend outbreaks of the disease in resident fishes. For example,
although 46 of 230 sites tested in Montana were positive for the
parasite, disease outbreaks were known to have occurred at only 6 of
those sites. Downing et al. (2002) provided evidence that the frequent
absence of manifest whirling disease in resident trout, despite
presence of the parasite, is due to complex interactions among the
timing and spatial locations of important host-fish life-history events
(e.g., spawning, fry emergence from stream gravels, and early-life
growth) and spatial and temporal variation in the occurrence of the
parasite itself. Only under specific conditions, which evidently occur
only in a small proportion of the locations where the parasite has been
found, are those interactions such that disease outbreaks occur in
resident fishes. The available scientific information specific to
whirling disease thus indicates considerable variation in the probable
disease threat among individual WCT populations and provides evidence
that the disease is not a significant threat to the majority of
populations constituting the WCT subspecies. The database procedures
used by Shepard et al. (2003) necessarily resulted in entire WCT
metapopulations being treated at the same level of risk from disease,
even though that risk applied only to specific populations within those
metapopulations. Thus, we conclude that the percent of stream miles in
which Shepard et al. (2003) reported that WCT are at moderately high or
high risk of disease is inflated to an extent that cannot be quantified
with the available data.
A broad suite of variables has been shown to influence the
incidence and intensity of infections of salmonid fishes by the
whirling disease parasite, including host-fish species and age,
parasite dose, and water temperature (Kerans and Zale 2002; MacConnell
and Vincent 2002). Among the salmonid fishes that have been examined
under controlled conditions, rainbow trout has been found to be the
most susceptible to whirling disease (Bartholomew and Wilson 2002).
Studies conducted on various salmonids by Vincent (2002) revealed that
WCT were moderately susceptible to whirling disease and had the lowest
susceptibility of the three cutthroat trout subspecies examined. We are
unaware of any studies of the susceptibility of the hybrids of rainbow
trout and WCT to whirling disease.
In addition, although the parasite's essential oligochaete host,
Tubifex tubifex, can be found in a wide variety of habitats and is
considered ubiquitous across the diversity of freshwater habitats used
by trout, T. tubifex has a much higher probability of occurring at
locations with abundant fine sediments in eutrophic (i.e., nutrient-
rich) lakes and streams (Granath and Gilbert 2002). The mountain
streams that WCT often inhabit are cold and have low biological
productivity, factors that make those streams much less suited to both
the whirling disease parasite and T. tubifex (Bartholomew and Wilson
2002).
Extensive research is being conducted to determine the distribution
of whirling disease, the susceptibility of WCT and other fishes to
whirling disease, infection rates, and possible control measures
(Bartholomew and Wilson 2002). Although no means have been found to
eliminate the whirling disease parasite from streams and lakes, the
States have established statutes, policies, and protocols that prevent
the human-caused spread of extant pathogens and the introduction of new
pathogens (e.g., Hagener 2002). Except for whirling disease, the fish
pathogens that occur in the natural habitats of WCT are mainly benign
in wild populations and cause death only when the fish are stressed by
severe environmental conditions.
On the basis of the best scientific and commercial information
available to us, we conclude that the WCT subspecies is not threatened
by whirling disease, although some specific populations may be at
higher risk.
Threats From Predation--The instances when predation by other
fishes may negatively affect extant WCT populations are few and limited
to a few large rivers, lakes and reservoirs (U.S. Fish and Wildlife
Service 1999; Hagener 2002). However, as reported in the initial status
review, predacious, nonnative fishes in Idaho's Coeur d'Alene Lake,
Montana's Flathead Lake, and other lakes have negatively affected
resident WCT. In those instances,
[[Page 47001]]
predation has reduced the abundance of WCT that have the adfluvial life
history.
We examined the database of Shepard et al. (2003) to assess the
extent that nonnative fishes, including recognized predacious species,
co-occur (i.e., are sympatric) with extant WCT for: (1) Nonintrogressed
or suspected nonintrogressed populations and (2) introgressed or
suspected introgressed ``conservation'' populations. Results indicated
that two predacious species, brown trout (Salmo trutta) and lake trout
(Salvelinus namaycush), each occur in only small proportions of the
habitat occupied by WCT, mainly WCT that occur in metapopulations.
However, for reasons related to the database and described previously
for whirling disease, those small proportions are inflated to an extent
that cannot be quantified using the available data. Brown trout occur
primarily in mainstem rivers and their major tributaries, whereas lake
trout occur almost exclusively in lakes. When one or the other species
occurred in the range of a WCT metapopulation, the procedures of
Shepard et al. (2003) necessarily resulted in the entire WCT
metapopulation being treated as sympatric with the nonnative species,
although the actual region of species overlap within that range may be
small.
The best scientific and commercial information available to us
indicates that the WCT subspecies is not threatened by predation from
brown trout, lake trout, or other predaceous, nonnative fishes.
However, where such predation does occur, it is mainly on WCT that have
either the fluvial or adfluvial life history. The remaining, nonnative
fishes sympatric with WCT will be discussed in subsequent sections of
this document.
(D) Inadequacy of Existing Regulatory Mechanisms
The Act requires us to examine the adequacy of existing regulatory
mechanisms with respect to those extant threats that place the species
in danger of becoming either threatened or endangered. Our initial
status review (U.S. Fish and Wildlife Service 1999) revealed that there
are numerous existing Federal and State regulatory mechanisms whose
purpose is to protect WCT and their habitats throughout the subspecies'
range. Neither our initial nor our new status review revealed
information to indicate that those mechanisms were not working or will
not work to protect the WCT subspecies.
Regulatory Mechanisms Involving Land Management--During our initial
status review (U.S. Fish and Wildlife Service 1999), we found numerous
laws and regulations that help to prevent the adverse effects of land-
management activities on WCT. More recently, Hagener (2002) reiterated
that Montana laws that benefit WCT include the Montana Stream
Protection Act, the Streamside Management Zone Law, the Montana Natural
Streambed and Land Preservation Act, and the Montana Pollutant
Discharge Elimination System. Federal laws that protect WCT and their
habitats in Montana and elsewhere include the CWA, Federal Land
Management Protection Act (FLMPA), and the National Environmental
Policy Act (NEPA). Much of the habitat of extant WCT is managed by
Federal agencies, including the U.S. Forest Service and the Bureau of
Land Management. Those Federal agencies have adopted the Inland Native
Fish Strategy (INFISH) that includes standards and guidelines that
protect watersheds. Furthermore, because the broad distribution of bull
trout--listed as a threatened species under the Act in 1999--
considerably overlaps the distribution of WCT, the WCT will benefit
from the Act's section 7 protective actions for bull trout in areas
where the two species coexist.
In addition, the U.S. Forest Service recently reported (McAllister
2002) that existing regulatory mechanisms that protect WCT habitat
include the Northwest Forest Plan; the Interim Strategies for managing
Anadromous Fish-producing Watersheds in Eastern Oregon and Washington,
Idaho, and Portions of California (i.e., PACFISH); INFISH; the
Wilderness Act; and the Upper Missouri (River) Memorandum of
Understanding and Land Use Strategy (in draft). In Idaho (Moore 2002),
regulatory mechanisms that protect WCT habitat include the Stream
Channel Protection Act, the Lake Protection Act, and the Forest
Practices Act. At the Federal level, protection is afforded by the CWA,
the National Forest Management Act, NEPA, Wild and Scenic Rivers
legislation, and the Wilderness Act. The St. Joe and Lochsa rivers are
protected by ``Wild and Scenic'' designation and nearly all of the
Middle Fork Salmon and Selway rivers and their watersheds are protected
by Wilderness Act designations. In addition, the range of WCT in Idaho
is almost entirely overlapped by that of one or more federally listed
fish species, namely, bull trout, Kootenai River white sturgeon
(Acipenser transmontanus), chinook salmon (O. tshawytscha), sockeye
salmon (O. nerka), or steelhead. Protective measures under the Act for
those listed fishes also benefit WCT.
During our initial status review, we found Federal regulations and
guidelines that protect WCT and their habitat in Oregon and Washington
included CWA, NEPA, FLPMA, INFISH, PACFISH, and National Forest
Management Plans (U.S. Fish and Wildlife Service 1999). More recently,
information received from Oregon (Unterwegner 2002) indicated that the
Oregon Plan for Salmon and Watersheds (ORS 541.405) mandates
restoration of watersheds and the recovery of fish and wildlife
populations therein to productive and sustainable levels in a manner
that provides substantial environmental, cultural, and economic
benefits; the Oregon Forest Practices Act (ORS 527.610) mandates the
protection, maintenance, and, where appropriate, improvement of
functions and values of streams, lakes, wetlands, and riparian
management areas; State fill and removal laws (ORS 196.800-990) require
that a permit be obtained before materials are moved and mitigation
measures be implemented if stream habitats will be negatively affected;
a water right must be obtained before any surface water is diverted
from a stream for beneficial use; and a Water Quality Management Plan
is being written that addresses nonpoint source water-quality issues in
the mainstem John Day River, identifies nonpoint source pollution, and
ensures that agricultural producers do not degrade water quality as
prescribed by the CWA. In Oregon, WCT inhabit a number of protected
areas, including the Strawberry and North Fork John Day Wilderness
Areas, and the Vinegar Hill-Indian Rock Scenic Areas.
In Washington, the Act's section 7 protections accorded to bull
trout and Pacific salmon also benefit WCT. The same holds true for
Oregon, where bull trout and mid-Columbia River steelhead are listed
fishes.
Hitt and Frissell (2001) used data from the Interior Columbia
(River) Basin Ecosystem Management Project (ICBEMP) to assess the
degree of spatial overlap between populations of bull trout and
populations of WCT that were both considered ``strong'' by the ICBEMP.
Those authors found that about 75 percent of the WCT populations did
not co-occur with bull trout. Accordingly, Hitt and Frissell (2001)
concluded that the bull trout may not be a good ``umbrella'' species,
i.e., a species whose protections accorded by the Act's section 7 also
would serve to protect WCT. However, our conclusion stated herein that
the Act's section 7 protections accorded bull trout and other listed
fish species also would benefit WCT is not based on the
[[Page 47002]]
assumption that all extant WCT populations co-occur with one or more of
those listed fishes. Rather, we believe that in those instances of co-
occurrence, the WCT will derive protections from the section 7
protections that are accorded the listed species.
Regulatory Mechanisms That Address Threats From Hybridizing,
Nonnative Fishes--Montana has a number of laws and regulatory
mechanisms that address threats posed by the unlawful stocking of
potentially hybridizing, nonnative fishes (Hagener 2002). These include
statutes, rules, and policies that restrict the capture, possession,
transportation, and stocking of live fish, including fishes that may
hybridize with WCT, as well as rigorous fish-health policies that
restrict the transport or stocking of live fish. The stocking of
private ponds also is closely regulated. Furthermore, although the
stocking of rivers and streams with a variety of nonnative fishes was
routine early in the 20th Century, it no longer occurs in Montana. In
1976, Montana adopted a policy that prohibits the stocking of hatchery
fish in rivers and streams. Consequently, unless done for government-
sponsored conservation purposes, no other trout or nonnative fish may
be stocked in rivers and streams inhabited by WCT.
In Idaho, regulatory mechanisms that protect extant WCT from
hybridization are in place (Moore 2002, 2003). The Idaho Department of
Fish and Game helped develop and has adopted the interstate position
paper on genetic considerations associated with cutthroat trout
management (Utah Division of Wildlife Resources 2000). Department of
Fish and Game management direction, as described in its Fisheries
Management Plan (a publicly reviewed, Commission-adopted document),
gives priority in management decisions to wild, native populations of
fish. The Department of Fish and Game has redirected almost all of its
hatchery rainbow trout program to the production of sterile, triploid
fish, and only triploid rainbow trout are now stocked in waters
connected to or near WCT habitat. In addition, the transport of live
fish to, within, and from Idaho is regulated by the Department of Fish
and Game and the Idaho Department of Agriculture. The Department of
Fish and Game regulates private ponds in the State and applies the same
criteria to private-pond stocking that it does to the stocking of
public waters, i.e., stocking of potentially hybridizing fishes that
may pose a hybridization threat to native cutthroat trout is
prohibited.
In Washington, the Department of Fish and Wildlife no longer stocks
resident rainbow trout in tributaries that contain native WCT
populations. In areas where stocking occurs in mainstem river reaches
(e.g., the Pend Oreille River), only sterile (i.e., triploid) rainbow
trout are stocked (Fuller 2002). In Oregon, the Department of Fish and
Wildlife exclusively manages all streams within the John Day River
drainage for wild fish production and none of those streams has been
stocked with hatchery fish since 1997 (Unterwegner 2002).
The best scientific and commercial information available to us
indicates that the WCT subspecies is not threatened by the inadequacy
of existing regulatory mechanisms related to the stocking of
potentially hybridizing, nonnative fishes. However, as described in a
subsequent section (see Hybridization with Nonnative Fishes),
hybridization with introduced, nonnative fishes that have become
established as self-sustaining populations does pose a threat to WCT.
As discussed in that subsequent section, there are no regulatory
mechanisms that would prevent hybridization from self-sustaining
populations of an introduced species. However, in some instances,
certain management actions may serve as preventative actions and there
also may be natural factors that limit the spread of hybridization in
the WCT subspecies.
(E) Other Natural or Manmade Factors Affecting the Species' Continued
Existence
Fragmentation and Isolation of Small Westslope Cutthroat Trout
Populations in Headwater Areas--Our initial status review (U.S. Fish
and Wildlife Service 1999) revealed that extant WCT populations are not
necessarily small or limited to headwater streams. Instead, that review
indicated that many river drainages had numerous, interconnected miles
of stream habitat occupied by WCT. Those areas included Montana's Clark
Fork River drainage (8,314 stream km [5,166 stream mi]) and Idaho's
Salmon River drainage (6,563 stream km [4,078 stream mi]). Furthermore,
our initial review revealed no evidence that the isolation of some WCT
populations had resulted in either deleterious inbreeding (see also
Caro and Laurenson 1994) or stochastic extirpations that threatened the
WCT subspecies.
Information provided in the WCT status update report (Shepard et
al. 2003) substantiated our earlier conclusions and indicated that,
although 457 (81.2 percent) of the 563 WCT conservation populations
were isolets that were often restricted to headwater areas, those
isolets represented only 11.5 percent of the total stream miles
occupied by WCT. Thus, the small WCT populations in headwater areas
were numerous but they occupied a small proportion of the total habitat
occupied by WCT. Most of the occupied stream miles (88.5 percent) were
habitat for WCT in metapopulations. Consequently, the best scientific
and commercial information available to us indicates that the WCT
subspecies is not threatened by the fragmentation and isolation of
small WCT populations in headwater areas.
Competition From Introduced Brook Trout--Brook trout, a nonnative
species that can adversely compete with WCT (e.g., Griffith 1988), have
been stocked in numerous areas throughout the range of WCT. We examined
the database of Shepard et al. (2003) to assess the extent that brook
trout co-occur (i.e., are sympatric) with extant WCT. Results indicated
that in the: (1) Combined nonintrogressed and suspected nonintrogressed
WCT populations and (2) the introgressed or suspected introgressed WCT
conservation populations, both of which occur as either isolets or
metapopulations, brook trout are sympatric with a substantial
proportion of those populations (41 to 90 percent of the collective
stream miles for each category). However, as was the case for
assessments of other threats made using this database, it was not
possible to determine the extent that brook trout are distributed
throughout the range of an individual WCT population, nor was it
possible to quantify the competitive effect of brook trout on the
abundance or viability of WCT. Nonetheless, it is evident from their
longstanding coexistence in some streams that complete competitive
exclusion of WCT by brook trout is not inevitable where the two fishes
co-occur. In addition, the database did not provide conspicuous
insights into how far upstream brook trout may eventually move in the
various drainages in which they now occur. Nonetheless, as we will
describe, the available scientific information indicates brook trout
are not a substantial threat to the majority of extant populations
constituting the WCT subspecies.
Adams et al. (2000) assessed the ability of brook trout to move
upstream in four headwater streams in a mountainous area of northern
Idaho. They concluded that the upstream movement of brook trout was
inhibited, but not precluded, by stream gradients up to 13 percent.
That study did not involve the experimental introduction of brook trout
into streams in which they were absent; instead, brook trout were
already established in the study
[[Page 47003]]
streams. The study design involved mechanical removal of brook trout in
certain stream reaches; the marking of brook trout in neighboring
reaches; and the subsequent assessment of movement of marked brook
trout into the stream reaches that had been mechanically depopulated.
Because they were already inhabited by brook trout, the four streams
examined by Adams et al. (2000) may have been among streams especially
conducive to colonization by brook trout. Thus, it is not possible to
extrapolate the results of Adams et al. (2000) to the broad array of
headwater streams in which WCT presently occur but brook trout do not,
even though brook trout occur in the downstream portions of those
drainages.
More recently, Adams et al. (2002) assessed historic changes in the
upstream limits of distribution of brook trout in 17 streams accessible
by the fish in the upper South Fork Salmon River drainage in central
Idaho. Brook trout already inhabited portions of 10 of the streams in
1971-1985. In 1996, their upstream-distribution limit remained
unchanged in 8 streams that historically contained brook trout and 5 of
6 streams that did not (i.e., one stream was invaded by brook trout).
In the remaining 4 streams, the distribution of brook trout had moved
upstream 1.9 to 3.1 km (1.2 to 1.9 mi). There was no detectable
increase in the upstream distribution of brook trout in 10 streams that
had no obvious physical barriers to such movement. The authors
concluded that upstream colonization by brook trout is not continuously
progressing throughout much of the drainage, and that the absence of
brook trout in streams with no apparent barriers to the upstream
movement of fish indicated that other factors were limiting the
upstream expansion of brook trout. Consequently, the best scientific
and commercial information available to us indicates that the WCT
subspecies is not threatened by competition from introduced brook
trout, although some populations may be at higher risk.
Risks Associated With Catastrophic, Natural Events--Our initial
status review found that the geographic isolation of some extant WCT
populations had not resulted in stochastic extirpations of such
populations (due, for example, to floods, landslides, or wildfires) to
a degree that threatened the WCT subspecies (U.S. Fish and Wildlife
Service 1999).
Information provided in the WCT status update report (Shepard et
al. 2003) ranked each of four measures of population viability that
could make WCT vulnerable to catastrophic, natural events or adverse
human effects on the aquatic environment: (1) Population productivity,
(2) temporal variability, (3) isolation, and (4) population size. That
analysis suggested that about 76 percent of the stream miles occupied
by WCT conservation populations considered isolets were at high risk
from catastrophic events because WCT would not be available to
naturally recolonize those habitats. In contrast, only a small ([sim]2
percent) proportion of the stream miles occupied by WCT conservation
populations considered metapopulations were at moderately high or high
risk from catastrophic or human events with respect to the four
measures of population viability. However, on the basis of empirical
information, Rieman and Dunham (2000) reported that none of the small
WCT populations they studied in the Coeur d'Alene River drainage were
extirpated by a large winter flood that was considered a once-in-100-
years event and affected more than 50 watersheds. Similarly, despite
large wildfires in 1996 and 2002 in Oregon's Indian Creek and Roberts
Creek drainages, respectively, WCT populations in those streams have
exhibited no immediate negative effects of the fires (Unterwegner
2002). The widespread geographic distribution of WCT across the
subspecies' range further mitigates potential negative effects
resulting from local population extinctions following future
catastrophic natural events, as no single event is likely to impact a
significant percent of the overall number of isolated populations.
Moreover, given the widespread efforts for the conservation of these
fish (see ``Evaluation of Ongoing Conservation Efforts,'' below), any
such local extirpation is likely to be followed by reintroduction
efforts if WCT were not available naturally to recolonize those
habitats.
Kruse et al. (2001) assessed the possible demographic and genetic
consequences of purposely isolating the populations of another
cutthroat trout, the YCT, in headwater streams in the Absaroka
Mountains, Wyoming. Such isolation may actually result, for example,
from intentional placement of a movement barrier to prevent nonnative
fishes downstream from invading upstream reaches. Kruse et al. (2001)
made estimates of population size for YCT in each of 23 streams, then
compared those estimates to minimum criteria that the authors
considered necessary to prevent population extirpation. Kruse et al.
(2001) acknowledged that their minimum-viability criteria had not been
confirmed for YCT and that there was debate among researchers regarding
the applicability of those criteria. Despite those limitations, 21 of
23 YCT populations met 2 of the 3 criteria, and the third criterion
(i.e., a population size of at least 500 fish) was met by 7 of the 23
populations. Nevertheless, the authors speculated that isolated YCT
populations are vulnerable to chance extinctions, although they also
pointed out that ``there has been little opportunity to observe the
real effects of small population size and isolation on native, extant
Yellowstone cutthroat trout populations.'' We believe those limitations
of knowledge also apply to WCT in isolated headwater streams across the
subspecies' range. Consequently, the best scientific and commercial
information available to us indicates that the WCT subspecies is not
threatened at the present time by risks associated with catastrophic,
natural events.
Threats to Any of the Three Westslope Cutthroat Trout Life-History
Forms--The three WCT life-history forms occur in numerous areas across
the subspecies' range. In our initial status review, we found that WCT
naturally occur in 6 lakes in Idaho and Washington that total about
72,843 ha (180,000 ac) and in least 20 lakes that total 2,164 ha (5,347
ac) in Glacier National Park, Montana (U.S. Fish and Wildlife Service
1999). All of those WCT in lakes are adfluvial (i.e., migratory)
populations and many of them receive the high level of protection
afforded by Glacier National Park. However, outside the park,
protections accorded WCT in most lakes are less rigorous (U.S. Fish and
Wildlife Service 1999). Today, WCT with the adfluvial life history
probably constitute the smallest proportion of the WCT subspecies, and
probably did so historically.
We also found (U.S. Fish and Wildlife Service 1999) that resident
(i.e., showing little movement) and fluvial (i.e., migratory) WCT
populations, which live entirely in streams, constitute the most common
WCT life-history forms and occur in about 4,275 tributaries or stream
reaches that collectively encompass more than 37,015 km (23,000 linear
mi) of stream habitat. Those WCT populations are distributed among 12
major drainages and 62 component watersheds in the Columbia, Missouri,
and Saskatchewan River basins, within the international boundaries of
the United States. As described in the preceding section Occurrence of
Westslope Cutthroat Trout Life-history Forms, the information recently
provided to us (Shepard et al. 2003) indicates even
[[Page 47004]]
greater abundance of WCT across the subspecies' range than we had
estimated during the initial status review. The available data do not
suggest the future loss of any of the three life-history forms
represented by WCT. Consequently, we conclude that the WCT subspecies
is not threatened by the loss of one or more of its life-history forms
throughout all or a significant portion of its historic range.
Hybridization With Nonnative Fishes--Hybridization with introduced,
nonnative fishes, particularly rainbow trout and their hybrid
descendants that have established self-sustaining populations, is
recognized as an appreciable threat to the WCT subspecies.
Hybridization requires that the nonnative species invade the WCT
habitat, the two species interbreed, and the resulting hybrids
themselves survive and reproduce. If the hybrids backcross with one or
both of the parental species, genetic introgression can occur.
Continual introgression can eventually lead to the loss of genetic
identity of one or both parent species, thus resulting in a ``hybrid
swarm'' consisting entirely of individual fish that each contain
genetic material from both of the parental species.
The WCT is known to interbreed with rainbow trout and YCT, both of
which were first stocked into many regions of the historic range of WCT
more than 100 years ago. Nonetheless, the limited data available at the
time of our initial status review revealed that numerous,
nonintrogressed WCT populations inhabited more than 4,184 km (2,600 mi)
of stream (U.S. Fish and Wildlife Service 1999). Moreover, in the
present document, we have concluded that nonintrogressed WCT are known
to inhabit 5,633 km (3,500 mi) of stream and probably inhabit as many
as 20,278 km (12,600 mi) of stream in which no potentially hybridizing
fishes occur. Clearly, not all nonintrogressed WCT populations have
been equally vulnerable to introgressive hybridization. In Idaho, WCT
in many populations are sympatric with potentially hybridizing, native
redband trout but remain nonintrogressed (Moore 2002). Thus, the
occurrence of potentially hybridizing fishes does not portend their
imminent hybridization with WCT.
The WCT status update report (Shepard et al. 2003) concluded that
the threats to extant WCT populations from introgressive hybridization
were greater for the extensive WCT metapopulations than for the smaller
WCT populations that occurred as isolets. As pointed out by Shepard et
al. (2003), the vulnerability to hybridization of WCT in
metapopulations stems from the key characteristic of the metapopulation
itself, i.e., the ability of its member fish to move (and interbreed)
among the various WCT populations that constitute the metapopulation.
It is assumed that potentially hybridizing fishes are similarly
unencumbered in their movements throughout the geographic area occupied
by the metapopulation and, accordingly, WCT metapopulations can
inevitably become completely introgressed as a hybrid swarm.
We examined the database of Shepard et al. (2003) to assess the
introgressive hybridization risk to extant WCT that consist of: (1)
Nonintrogressed or suspected nonintrogressed populations and (2)
introgressed or suspected introgressed ``conservation'' populations.
Results indicated that nonintrogressed and suspected nonintrogressed
WCT populations occurring as isolets were at moderately high or high
risk of introgression in about 16 percent of their 1,944 occupied
stream miles, whereas nonintrogressed populations occurring in
metapopulations were considered to be at similar risk in 89 percent of
their 9,999 occupied stream miles. Similarly, WCT in introgressed or
suspected introgressed conservation populations occurring as isolets
were at moderately high or high risk of introgression in about 38
percent of their 751 occupied stream miles, whereas introgressed
populations occurring in metapopulations were considered at similar
risk in 99 percent of their 11,775 occupied stream miles. The WCT in
introgressed or suspected introgressed populations inhabited a total
19,262 km (11,943 mi) of stream, 1,060 km (657 mi) less than reported
by Shepard et al. (2003). However, those authors also reported the 563
WCT ``conservation'' populations collectively occupied 39,349 km
(24,450 mi) of stream, nearly identical to the amount that we found
(i.e., 39,466 km or 24,469 mi) when the database was examined. The
reason for the small discrepancy (5.2 percent) in the total amounts of
habitat occupied by WCT in introgressed or suspected introgressed
populations is unknown but may be due to differences in the specific
database queries.
The hybridization risk to WCT is almost entirely from rainbow
trout, YCT, and the hybrid offspring and descendants of those fishes
that have established self-sustaining populations within the range of
extant WCT populations. We examined the database of Shepard et al.
(2003) to assess the extent that rainbow trout and ``other cutthroat
trout'' (primarily YCT) co-occur (i.e., are sympatric) with extant WCT
in: (1) Nonintrogressed or suspected nonintrogressed populations and
(2) introgressed or suspected introgressed ``conservation''
populations. Rainbow trout or YCT occur in 47 to 91 percent of the
stream miles occupied by WCT metapopulations but only 0 to 22 percent
of the stream miles occupied by WCT isolets.
In most cases today, it is not technologically possible to
eliminate the self-sustaining populations of potentially hybridizing,
nonnative fishes from entire drainages or even individual streams.
Consequently, perceived threats to extant WCT posed by nonnative fishes
in streams are sometimes met by installing barriers to the upstream
movement of the nonnative fishes into stream reaches occupied by WCT.
In a few cases, usually involving small streams that provide the
greatest opportunity for success, fish toxins may be used to completely
remove all fishes upstream from such barriers, after which WCT may be
stocked (e.g., Hagener 2002). In either case, because of technological,
budgetary, and other limitations, such actions are now being taken for
only a small proportion of WCT populations across the subspecies'
range.
Because self-sustaining populations of nonnative fishes pose the
greatest hybridization threat to WCT and few of those populations can
be eliminated or appreciably reduced, a key concern is for the extent
that introgressive hybridization may eventually pervade extant,
nonintrogressed or suspected nonintrogressed WCT populations,
particularly those that inhabit headwater streams in high-elevation
areas. Hitt (2002) reported that 55 percent of 40 WCT populations
examined in the Flathead River drainage in Montana showed evidence of
introgressive hybridization with rainbow trout, and that introgression
had progressed upstream in several tributaries during the past 2
decades. Additional evidence suggested that the upstream introgression
of rainbow trout genes would eventually be halted by diminished stream
size, as evidenced by the observation that rainbow trout usually
inhabit larger streams than cutthroat trout. However, Hitt (2002)
further speculated that the stream reaches upstream from those
potentially limiting locations would be too small to support viable WCT
populations.
In the Clearwater River drainage in Idaho, Weigel et al. (2003)
similarly found that WCT at 64 percent of the 80 sample sites showed
evidence of introgression with rainbow trout or native redband trout.
The incidence and intensity of that introgression was
[[Page 47005]]
negatively associated with stream elevation, which the authors believed
resulted from the interaction of low water temperatures or other
characteristics of the high-elevation hydrologic regimes and either the
physiological or habitat requirements of rainbow trout and their
hybrids with WCT. In a study conducted in the Kootenay (= Kootenai)
River, British Columbia, Rubidge et al. (2001) found that WCT
introgressive hybridization with rainbow trout had become more
widespread in the drainage since the mid-1980s, which the authors
attributed to the ongoing stocking of rainbow trout into Koocanusa
Reservoir in British Columbia.
In addition, many extant WCT populations occur upstream from
barriers that entirely prevent the upstream movements of nonnative
fishes, including those that may potentially hybridize with WCT. We
examined the database of Shepard et al. (2003) to determine the extent
that extant, nonintrogressed or suspected nonintrogressed WCT
populations occur upstream from such ``complete'' barriers. Results
indicated that 48 percent of the 1,944 stream miles inhabited by WCT in
isolets are protected by such barriers, whereas about 6 percent of the
9,999 stream miles inhabited by nonintrogressed WCT in metapopulations
are similarly protected. Thus, nonintrogressed or suspected
nonintrogressed WCT populations inhabiting 2,454 km (1,525 mi) of
stream are protected from introgressive hybridization by barriers to
the upstream movement of nonnative fishes.
The available empirical evidence and speculations by many fishery
scientists indicate that rainbow trout genes are expected to continue
moving upstream into many stream reaches presently inhabited by
nonintrogressed WCT, although, as we have discussed, there may be
limits to that upstream dispersal set by low stream temperatures or
other factors. However, the observation that numerous nonintrogressed
WCT populations persist today despite both the longstanding occurrence
(i.e., more than 100 years) of potentially hybridizing fishes in
regions downstream and the absence of obvious intervening barriers to
the upstream movement of those fish suggests that not all
nonintrogressed WCT populations have been and are equally vulnerable to
introgression. Behnke (1992, 2002) provides evidence that
phenotypically true, native cutthroat trout of several subspecies
persist in many essentially undisturbed, natural habitats because they
have fitness superior to that of nonnative fishes, including
potentially hybridizing species and their hybrid descendants. Thus, the
eventual extent that rainbow trout, or YCT, genes move upstream may be
stream-specific and unpredictable. Nonetheless, as noted previously
(see previous section, ``The Value of Hybrid Westslope Cutthroat Trout
in Listing Determinations''), small amounts of genetic introgression do
not disqualify individual WCT or their populations from species
membership under the Act. Finally, nonintrogressed or suspected
nonintrogressed populations of WCT inhabiting 2,454 km (1,525 mi) of
stream are considered secure from genetic introgression because those
populations occur upstream from barriers to the upstream movement of
nonnative fishes or their hybrid descendants. Therefore, the best
scientific and commercial information available to us indicates that
the WCT subspecies is not threatened by introgressive hybridization.
Evaluation of Ongoing Conservation Efforts
In the initial status review (U.S. Fish and Wildlife Service 1999),
we identified numerous, ongoing conservation efforts that benefitted
WCT and their habitats. For example, the U.S. Forest Service, State
fish and wildlife agencies, and National Park Service reported more
than 700 ongoing projects directed toward the protection and
restoration of WCT and their habitats.
Recent information indicates that these important conservation
efforts are ongoing and increasing in number. At the time of the
initial status review, the four State fish and wildlife agencies, the
U.S. Forest Service, and other entities were implementing WCT
conservation actions in a minimally coordinated manner. The State of
Montana had developed a formalized conservation program for WCT that
included a State-wide conservation agreement, a conservation strategy
with specific goals and objectives, a steering committee consisting of
representatives from various key agencies and other concerned entities,
and a technical oversight group. At that time, Idaho, Oregon, and
Washington also were implementing WCT conservation actions as an
integral part of their fisheries management programs. The U.S. Forest
Service also was protecting WCT habitat as specified under INFISH and
PACFISH, and had established a new professional position whose
incumbent focused entirely on inland cutthroat trout conservation in
the western United States.
More recently, the conservation efforts for WCT have been enhanced
by formalized coordination among the four State fish and wildlife
agencies, the U.S. Forest Service, and the Service. Beginning in June
2001, formal coordination meetings have been held under the leadership
of a representative of the Idaho Department of Fish and Game. A formal
coordination agreement is now being developed, consistent conservation
goals and objectives for WCT have been identified, and an emphasis on
consistency and continuity in WCT conservation among the agencies has
emerged. An indication of the important level of coordination that has
been achieved is provided by the recent WCT status update report
(Shepard et al. 2003), which was completed through a concerted effort
among the parties to the coordination agreement. To complete that
report, 112 biologists--working with 19 geographic information systems
and data-entry specialists--completed the task of updating the current
information on WCT in a timely and comprehensive manner.
In Idaho, hundreds of conservation efforts have been undertaken in
recent years to protect WCT and their habitats (Moore 2003). Those
efforts include initiation of a study to determine movement patterns of
WCT in the Middle Fork of the Salmon River basin (this study will be
expanded into the upper Salmon River basin), accelerated genetic
sampling of fishes in central and northern Idaho streams, addition of a
qualified geneticist to Department of Fish and Game staff, and
implementation of joint efforts with the U.S. Forest Service focused on
protection and enhancement of WCT habitat and populations. Montana
Fish, Wildlife and Parks continues to implement its conservation
agreement and plan. In Montana, more than 200 projects that directly
benefit WCT have now been completed, many of which were accomplished as
part of a Memorandum of Understanding and Conservation Agreement for
Westslope Cutthroat Trout in Montana, and numerous, additional projects
are ongoing (Hagener 2002). Included in the Montana Fish, Wildlife and
Parks efforts are removal of nonnative trout through both physical and
chemical means, installation of fish-passage barriers, and coordinated
efforts with U.S. Forest Service and other management authorities
focused on WCT habitat protection and enhancement.
Oregon and Washington fishery agencies are likewise planning and
implementing WCT conservation actions. In Oregon (Unterwegner 2002),
the Department of Fish and Wildlife is developing a Native Fish
Conservation
[[Page 47006]]
Policy in response to a Governor's Executive Order to review the
existing Wild Fish Management Policy. The Oregon Department of Fish and
Wildlife also has an active fish-screening program for irrigation
diversions in the John Day River drainage and elsewhere. That program
began in the 1950s and more than 300 fish screens are now in place and
operated during the annual irrigation season. The Oregon Department of
Fish and Wildlife also has accomplished several habitat-restoration
projects throughout the drainage, funded mainly by the Bonneville Power
Administration and Oregon Watershed Enhancement Board.
The U.S. Forest Service has a very active conservation program in
place for WCT. Between 1998 and 2002, the U.S. Forest Service, in
partnership with the States and others, implemented 324 projects that
benefit WCT. The total investment of funds for these projects was
approximately $9,665,000 (McAllister 2002). During the 2002 Fiscal
Year, the U.S. Forest Service accomplished 54 on-the-ground restoration
projects, inventories, evaluations, and public outreach efforts at a
cost of $1.6 million (Johnston 2003).
The conservation efforts presently being accomplished as part of
the routine management objectives of State and Federal agencies, and as
part of formal interagency agreements and plans, provide substantial
assurance that the WCT subspecies is being conserved. The best
information available to us indicates that numerous, ongoing
conservation efforts for WCT are being implemented across the
subspecies' range. These ongoing conservation efforts are commendable
and they contribute to the certainty that WCT can be conserved and
protected.
Listing Determinations Made Under the Act
In the context of the Act, the term ``threatened species'' means
any species (or subspecies or, for vertebrates, DPS) that is likely to
become an endangered species within the foreseeable future throughout
all or a significant portion of its range. The term ``endangered
species'' means any species that is in danger of extinction throughout
all or a significant portion of its range. The Act does not indicate
threshold levels of historic population size at which, as the
population of a species declines, listing as either ``threatened'' or
``endangered'' becomes warranted. Instead, the principal considerations
in the determination of whether or not a species warrants listing as a
threatened or an endangered species under the Act are the threats that
now confront the species and the probability that the species will
persist in ``the foreseeable future.'' The Act does not define the term
``foreseeable future.'' However, the WCT interagency conservation team,
the group that produced the WCT status update report, considered the
``foreseeable future'' to be 20 to 30 years (approximately 4 to 10 WCT
generations) beyond the present time (Shepard et al. 2003), a measure
that we believe is both reasonable and appropriate for the present
listing determination.
In our initial status review, we provided evidence from the
Missouri River basin that indicated a conspicuous decline in the WCT
subspecies occurred early in the 20th Century (U.S. Fish and Wildlife
Service 1999). We attributed that decline to rapid, abundant
colonization of mainstem rivers and their major tributaries by one or
more introduced nonnative fish species (e.g., brown trout, rainbow
trout, and brook trout) that had adverse effects on WCT. Our analysis
also showed that the rate of decline in the WCT subspecies is markedly
lower today than it was early in the 20th century. We believe that the
evidence from the Missouri River basin provided a model for the
historic decline of WCT that was applicable to WCT in many other
regions of the subspecies' historic range.
Conclusions
The information that we have summarized in this document,
particularly that obtained from the status update report (Shepard et
al. 2003), indicates even greater abundance of WCT across the
subspecies' range than we had estimated during the initial status
review (U.S. Fish and Wildlife Service 1999). Today, 563 extant WCT
``conservation'' populations collectively occupy 39,349 km (24,450 mi)
of stream in Idaho, Montana, Oregon, Washington, and Wyoming. Those WCT
populations are distributed among 12 major drainages and 62 component
watersheds in the Columbia, Missouri, and Saskatchewan River basins,
within the international boundaries of the United States. In our
initial status review (U.S. Fish and Wildlife Service 1999), we
reported that WCT occupied about 37,015 km (23,000 mi) of stream in the
United States. In addition, nonintrogressed WCT are now known to
inhabit 5,633 km (3,500 mi) of stream and probably inhabit as many as
20,278 km (12,600 mi) of stream in which no potentially hybridizing
fishes occur. In our initial status review (U.S. Fish and Wildlife
Service 1999), we reported that nonintrogressed WCT were known to
occupy 4,237 km (2,633 mi) of stream.
Although the WCT subspecies has been reduced from historic levels
and its extant populations face threats in several areas of the
historic range, we find that the magnitude and imminence of those
threats do not jeopardize the continued existence of the subspecies
within the foreseeable future. Many former threats to WCT, such as
those posed by excessive harvest by anglers or the widespread stocking
of nonnative fishes, are no longer factors that threaten the continued
existence of the WCT subspecies. The effects of other extant threats
are being effectively countered by the management actions of State and
Federal agencies, in conjunction with existing regulatory mechanisms.
Nonetheless, hybridization with nonnative rainbow trout or their hybrid
progeny and descendants, both of which have established self-sustaining
populations in many areas in the range of WCT, remains the greatest
threat to WCT. The available empirical evidence and speculations of
many fishery scientists indicate that introgression of rainbow trout
genes will continue to move upstream into many stream reaches presently
inhabited by WCT, although there may be limits to that upstream spread
set by environmental factors and the superior fitness of extant WCT
populations in their native habitats. The eventual extent that such
hybridization moves upstream may be stream-specific and impossible to
predict. Nonetheless, the criteria that we provided for inclusion of
individual fishes in the WCT subspecies, in response to the Court's
order, allow for the limited presence in WCT of genetic material from
other fish species, consistent with the intent and purpose of the Act.
The WCT subspecies is widely distributed and there are numerous,
robust WCT populations and aggregates of populations throughout the
subspecies' historic range. Moreover, numerous nonintrogressed WCT
populations are distributed in secure habitats throughout the
subspecies' historic range. In addition, despite the frequent
occurrence of introgressive hybridization, we find that numerous WCT
populations are nonintrogressed or nearly so, and thus retain
substantial portions of their genetic ancestry. We consider slightly
introgressed WCT populations, with low amounts of genetic introgression
detectable only by molecular genetic methods, to be a potentially
important and valued component of the overall WCT subspecies.
Finally, the numerous ongoing WCT conservation efforts clearly
demonstrate the broad interest in protecting WCT
[[Page 47007]]
held by State, Federal, local, and nongovernmental organizations and
other entities. Nonetheless, those ongoing conservation efforts, while
important, are not pivotal to our decision whether or not to list the
WCT as either a threatened or an endangered species under the Act. That
decision is based mainly on the present-day status of the WCT
subspecies, and the occurrence of the numerous extant laws and
regulations that work to prevent the adverse effects of land-management
and other activities on WCT, particularly on those lands administered
by Federal agencies.
On the basis of the best available scientific and commercial
information, which has been broadly discussed in this notice and
detailed in the documents contained in the Administrative Record for
this decision, we conclude that the WCT is not likely to become either
a threatened or an endangered species within the foreseeable future.
Therefore, listing of the WCT as a threatened or an endangered species
under the Act is not warranted at this time.
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Authors
The primary author of this document is Lynn R. Kaeding (see
ADDRESSES section).
Authority
The authority for this action is the Endangered Species Act (16
U.S.C. 1531 et seq.).
Dated: August 1, 2003.
Steve Williams,
Director, Fish and Wildlife Service.
[FR Doc. 03-20087 Filed 8-6-03; 8:45 am]
BILLING CODE 4310-55-P