[Federal Register Volume 68, Number 152 (Thursday, August 7, 2003)]
[Proposed Rules]
[Pages 46989-47009]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 03-20087]


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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 ([email protected]) 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.

References Cited

    Adams, S.B., C.A. Frissell, and B.E. Rieman. 2000. Movements of 
nonnative brook trout in relation to stream channel slope. Transactions 
of the American Fisheries Society 129:623-638.
    Adams, S.B., C.A. Frissell, and B.E. Rieman. 2002. Changes in 
distribution of nonnative brook trout in an Idaho drainage over two 
decades. Transactions of the American Fisheries Society 131:561-568.
    Allendorf, F.W., and R.F. Leary. 1988. Conservation and 
distribution of genetic variation in a polytypic species, the cutthroat 
trout. Conservation Biology 2:170-184.
    Allendorf, F.W., R.F. Leary, P. Spruell, and J.K. Wenberg. 2001. 
The problems with hybrids: setting conservation guidelines. Trends in 
Ecology and Evolution 16:613-622.
    Allendorf, F.W., R.F. Leary, N.P. Hitt, K.L. Knudsen, L.L. 
Lundquist, and P. Spruell. 2003. Intercrosses and the U.S. Endangered 
Species Act: should hybridized populations be included as westslope 
cutthroat trout? Unpublished manuscript, from the Division of 
Biological Sciences, University of Montana, Missoula, submitted to the 
U.S. Fish and Wildlife Service, Bozeman, Montana. 23p.
    Arnold, M.L. 1997. Natural hybridization and evolution. Oxford 
University Press, New York.
    Avise, J.C., and N.C. Saunders. 1984. Hybridization and 
introgression among species of sunfish (Lepomis): analysis by 
mitochondrial DNA and allozyme markers. Genetics 108:237-255.
    Baker, J., P. Bentzen, and P. Moran. 2002. Molecular markers 
distinguish coastal cutthroat trout from coastal rainbow trout/
steelhead and their hybrids. Transactions of the American Fisheries 
Society 131:404-417.
    Bartholomew, J.L., and P.W. Reno. 2002. Review: the history and 
dissemination of whirling disease. Pages 3-24 in J.L. Bartholomew and 
J.C. Wilson, editors. Whirling disease: reviews and current topics. 
American Fisheries Society, Symposium 29, Bethesda, Maryland.
    Bartholomew, J.L., and J.C. Wilson, editors. 2002. Whirling 
disease: reviews and current topics. American Fisheries Society, 
Symposium 29, Bethesda, Maryland.
    Bartley, D.M., and G.A.E. Gall. 1991. Genetic identification of 
native cutthroat trout (Oncorhynchus clarki) and introgressive 
hybridization with introduced rainbow trout (O. mykiss) in streams 
associated with the Alvord Basin, Oregon and Nevada. Copeia 1991:854-
859.
    Behnke, R.J. 1992. Native trout of western North America. American 
Fisheries Society Monograph 6.
    Behnke, R.J. 2002. Trout and salmon of North America. Simon and 
Schuster, New York. 359p.
    Bernatchez, L., H. Glemet, C.C. Wilson, and R.G. Danzmann. 1995. 
Introgression and fixation of Arctic char (Salvelinus alpinus) 
mitochondrial genome in an allopatric population of brook trout 
(Salvelinus fontinalis). Canadian Journal of Fisheries and Aquatic 
Sciences 52:179-185.
    Bertorelle, G., and L. Excoffier. 1998. Inferring admixture 
proportions from molecular data. Molecular Biology and Evolution 
15:1298-1311.
    Bond, C.E. 1996. Biology of Fishes (2nd edition). Saunders College 
Publishing, Orlando, Florida. 750p.
    Busack, C.A., and G.A.E. Gall. 1981. Introgressive hybridization in 
populations of Paiute cutthroat trout (Salmo clarki seleniris). 
Canadian Journal of Fisheries and Aquatic Sciences 38:939-951.
    Campton, D.E. 1987. Natural hybridization and introgression in 
fishes: methods of detection and genetic interpretations. Pages 161-192 
in N. Ryman and F. Utter, editors. Population Genetics and Fishery 
Management. University of Washington Press, Seattle.
    Campton, D.E. 1990. Application of biochemical and molecular 
genetic markers to analysis of hybridization. Pages 241-263 in D.H. 
Whitmore, editor. Electrophoretic and isoelectric focusing techniques 
in fisheries management. CRC Press, Boca Raton, Florida.
    Campton, D.E., and F.M. Utter. 1985. Natural hybridization between 
steelhead trout (Salmo gairdneri) and coastal cutthroat trout (Salmo 
clarki clarki) in two Puget Sound streams. Canadian Journal of 
Fisheries and Aquatic Sciences 42:110-119.
    Carmichael, G.J., J.N. Hanson, M.E. Schmidt, and D.C. Morizot. 
1993. Introgression among Apache, cutthroat, and rainbow trout in 
Arizona. Transactions of the American Fisheries Society 122:121-130.
    Caro, T.M., and M.K. Laurenson. 1994. Ecological and genetic 
factors in conservation: a cautionary tale. Science 263:485-496.
    Childs, M.R., A.A. Echelle, and T.E. Dowling. 1996. Development of 
the hybrid swarm between Pecos pupfish (Cyprinodontidae: Cyprinodon 
pecosensis) and sheepshead minnow (Cyprinodon variegatus): a 
perspective from allozymes and mtDNA. Evolution 50:2014-2022.
    DeMarais, B.D., T.E. Dowling, M.E. Douglas, W.L. Minkley, and P.C. 
Marsh. 1992. Origin of Gila seminuda (Teleostei: Cyprinidae) through 
introgressive hybridization: implications for evolution and 
conservation. Proceedings of the National Academy of Science (USA) 
89:2747-2751.
    DeWitt, J.W., Jr. 1954. A survey of the coastal cutthroat trout, 
Salmo clarki clarki Richardson, in California. California Fish and Game 
40: 329-335.
    Dowling, T.E., and C.L. Secor. 1997. The role of hybridization in 
the evolutionary diversification of animals. Annual Reviews in Ecology 
and Systematics 28:593-619.
    Dowling, T.E., and M.R. Childs. 1992. Impact of hybridization on a 
threatened trout of the southwestern United States. Conservation 
Biology 6:355-364.
    Downing, D.C., T.E. McMahon, B.L. Kerans, and E.R. Vincent. 2002. 
Relation of spawning and rearing life history of rainbow trout and 
susceptibility to Myxobolus cerebralis infection in the Madison River, 
Montana. Journal of Aquatic Animal Health 14:191-203.
    Echelle, A.A., and A.F. Echelle. 1997. Genetic introgression of 
endemic taxa by non-natives: a case study with Leon Springs pupfish and 
sheepshead minnow. Conservation Biology 11:153-161.
    Epifanio, J.M., and D.P. Philipp. 1997. Sources of misclassifying 
genealogical origins in mixed hybrid populations. Journal of Heredity 
88:62-65.
    Ferguson, M.M., R.G. Danzmann, and F.W. Allendorf. 1985. Absence of 
developmental incompatibility in

[[Page 47008]]

hybrids between rainbow trout and two subspecies of cutthroat trout. 
Biochemical Genetics 23:557-570.
    Ferris, S.D., R.D. Sage, C.M. Huang, J.T. Nielsen, U. Ritte, and 
A.C. Wilson. 1983. Flow of mitochondrial DNA across a species boundary. 
Proceedings of the National Academy of Science (USA) 80:2290-2294.
    Forbes, S.H., and F.W. Allendorf. 1991a. Associations between 
mitochondrial and nuclear genotypes in cutthroat trout hybrid swarms. 
Evolution 45: 1332-1349.
    Forbes, S.H., and F.W. Allendorf. 1991b. Mitochondrial genotypes 
have no detectable effects on meristic traits in cutthroat trout hybrid 
swarms. Evolution 45: 1350-1359.
    Fuller, R. 2002. Letter dated November 4, 2002 from Ross Fuller, 
Chief, Fish Management Division, Washington Department of Fish and 
Wildlife. 7p. (plus 5 attachments).
    Gerber, A.S., C.A. Tibbets, and T.E. Dowling. 2001. The role of 
introgressive hybridization in the evolution of the Gila robusta 
complex (Teleostei: Cyprinidae). Evolution 55:2028-2039.
    Glemet, H., P. Blier, and L. Bernatchez. 1998. Geographical extent 
of Arctic char (Salvelinus alpinus) mtDNA introgression in brook char 
populations (S. fontinalis) from eastern Quebec, Canada. Molecular 
Ecology 7:1655-1662.
    Granath, W.O., and M.A. Gilbert. 2002. The role of Tubifex tubifex 
(Annelida: Oligochaeta: Tubificidae) in the transmission of Myxobolus 
cerebralis (Myxozoa: Myxosporea: Myxobolidae). Pages 79-85 in J.L. 
Bartholomew and J.C. Wilson, editors. Whirling disease: reviews and 
current topics. American Fisheries Society, Symposium 29, Bethesda, 
Maryland.
    Griffith, J.S. 1988. Review of competition between cutthroat trout 
and other salmonids. American Fisheries Society Symposium 4. 4:134-140.
    Hagener, M.J. 2002. Letter dated November 4, 2002 from M. Jeff 
Hagener, Director, Montana Fish, Wildlife and Parks Department. 7p. 
(plus 74 attachments).
    Hartman, G.F., and C.A. Gill. 1968. Distributions of juvenile 
steelhead and cutthroat trout (Salmo gairdneri and S. clarki clarki) 
within streams in southwestern British Columbia. Journal of the 
Fisheries Research Board of Canada 25: 33-48.
    Hedrick, P.W. 1995. Gene flow and genetic restoration: the Florida 
panther as a case study. Conservation Biology 9:996-1007.
    Hitt, N.P. 2002. Hybridization between westslope cutthroat trout 
(Oncorhynchus clarki lewisi) and rainbow trout (O. mykiss): 
distribution and limiting factors. Master of Science thesis. University 
of Montana, Missoula. 80p.
    Hitt, N.P., and C.A. Frissell. 2001. Umbrella species in habitat 
conservation planning: a case study from the interior Columbia basin. 
Unpublished manuscript. 17p.
    Howell, P., and P. Spruell. 2003. Information regarding the origin 
and genetic characteristics of westslope cutthroat trout in Oregon and 
central Washington. Preliminary report. 18p.
    Hubbs, C. 1955. Hybridization between fish species in nature. 
Systematic Zoology 4:1-20.
    Johnston, E.P. 2003. Letter dated February 12, 2003 from Eric 
Johnston, U.S. Forest Service. 1p. (plus 1 attachment).
    Kanda, N., R.F. Leary, P. Spruell, and F.W. Allendorf. 2002. 
Molecular genetic markers identifying hybridization between the 
Colorado River--greenback cutthroat trout complex and Yellowstone 
cutthroat trout or rainbow trout. Transactions of the American 
Fisheries Society 131:312-319.
    Kerans, B.L., and A.V. Zale. 2002. The ecology of Myxobolus 
cerebralis. Pages 145-166 in J.L. Bartholomew and J.C. Wilson, editors. 
Whirling disease: reviews and current topics. American Fisheries 
Society, Symposium 29, Bethesda, Maryland.
    Kruse, C.G., W.A. Hubert, and F.J. Rahel. 2001. An assessment of 
headwater isolation as a conservation strategy for cutthroat trout in 
the Absaroka Mountain of Wyoming. Northwest Science 75(1):1-11.
    Leary, R.F., F.W. Allendorf, S.R. Phelps, and K.L. Knudsen. 1984. 
Introgression between westslope cutthroat and rainbow trout in the 
Clark Fork River drainage, Montana. Proceedings of the Montana Academy 
of Sciences 43:1-18.
    Leary, R.F., F.W. Allendorf, and G.K. Sage. 1995. Hybridization and 
introgression between introduced and native fish. American Fisheries 
Society Symposium 15:91-101.
    Leary, R.F., W.R. Gould, and G.K. Sage. 1996. Success of 
basibranchial teeth in indicating pure populations of rainbow trout and 
failure to indicate pure populations of westslope cutthroat trout. 
North American Journal of Fisheries Management 16:210-213.
    Leary, R.F., F.W. Allendorf, and N. Kanda. 1997. Lack of genetic 
divergence between westslope cutthroat trout from the Columbia and 
Missouri River drainages. Wild Trout and Salmon Genetics Laboratory 
Report 97/1. University of Montana, Missoula. 25p.
    Loudenslager, E.J., and R. Kitchen. 1979. Genetic similarity of two 
forms of cutthroat trout, Salmo clarki, in Wyoming. Copeia 1979:673-
674.
    MacConnell, E., and E.R. Vincent. 2002. The effects of Myxobolus 
cerebralis on the salmonid host. Pages 95-107 in J.L. Bartholomew and 
J.C. Wilson, editors. Whirling disease: reviews and current topics. 
American Fisheries Society, Symposium 29, Bethesda, Maryland.
    Marnell, L.F., R.J. Behnke, and F.W. Allendorf. 1987. Genetic 
identification of cutthroat trout, Salmo clarki, in Glacier National 
Park. Canadian Journal of Fisheries and Aquatic Sciences 44: 1830-1839.
    McAllister, K.A. 2002. Letter dated November 1, 2002, from Kathleen 
McAllister, Deputy Regional Forester, U.S. Forest Service. 2p. (plus 11 
attachments).
    Meagher, S., and T.E. Dowling. 1991. Hybridization between the 
cyprinid fishes Luxilus albeolus, L. cornutus, and L. cerasinus, with 
comments on the hybrid origin of L. albeolus. Copeia 1991:979-991.
    Miller, R.R. 1950. Notes on the cutthroat and rainbow trouts with 
the description of a new species from the Gila River, New Mexico. 
Occasional Papers of the Museum of Zoology, University of Michigan, No. 
429. 43p.
    Moore, V. 2002. Letter dated October 31, 2002 from Virgil Moore, 
Chief, Bureau of Fisheries, Idaho Fish and Game Department. 6p. (plus 
15 attachments).
    Moore, V. 2003. Letter dated February 10, 2003 from Virgil Moore, 
Chief, Bureau of Fisheries, Idaho Fish and Game Department. 2p. (plus 3 
attachments).
    Moyle, P.B., and J.J. Cech, Jr. 1996. Fishes: an introduction to 
ichthyology (3rd ed.). Prentice Hall, Upper Saddle River, New Jersey. 
590p.
    Northwest Environmental Defense Center. 2002. Letter dated November 
4, 2002 from the Northwest Environmental Defense Center, Portland, 
Oregon. 6p. (plus 5 attachments).
    Nowak, R.M., and N.E. Federoff. 1998. Validity of the red wolf: 
response to Roy et al. Conservation Biology 12:722-725.
    O'Brien, S.J., and E. Mayr. 1991. Bureaucratic mischief: 
recognizing endangered species and subspecies. Science 251:1187-1188.
    Redenbach, Z., and E.B. Taylor. 2002. Evidence for historical 
introgression along a contact zone between two species of char (Pisces: 
Salmonidae) in northwestern North America. Evolution 56:1021-1035.
    Rhymer, J.M., and D. Simberloff. 1996. Extinction by hybridization 
and

[[Page 47009]]

introgression. Annual Review of Ecology and Systematics 27:83-109.
    Rieman, B.E., and J.B. Dunham. 2000. Metapopulations and salmonids: 
a synthesis of life history patterns and empirical observations. 
Ecology of Freshwater Fish 9:51-64.
    Rieseberg, L.H. 1997. Hybrid origins of plant species. Annual 
Reviews in Ecology and Systematics 28:359-389.
    Rubidge, E., P. Corbett, and E.B. Taylor. 2001. A molecular 
analysis of hybridization between native westslope cutthroat trout and 
introduced rainbow trout in southeastern British Columbia, Canada. 
Journal of Fish Biology 59 (Supplement A):42-54.
    Shepard, B.B., B.E. May, and W. Urie. 2003. Status of westslope 
cutthroat trout (Oncorhynchus clarki lewisi) in the United States: 
2002. Report of the westslope cutthroat interagency conservation team. 
88p. Available at http://www.fwp.state.mt.us/wildthings/westslope/content.asp. In addition, the data files analyzed as part of the 
preparation of this report may be obtained at http://www.streamnet.org/online-data/OutSideDataSets.html.
    Spruell, P., K.L. Pilgrim, B.A. Greene, C. Habicht, K.L. Knudsen, 
K.R. Lindner, J.B. Olsen, G.K. Sage, J.E. Seeb, and F.W. Allendorf. 
1999. Inheritance of nuclear DNA markers in gynogenetic haploid pink 
salmon. Journal of Heredity 90:289-296.
    Spruell, P., M.L. Bartron, N. Kanda, and F.W. Allendorf. 2001. 
Detection of hybrids between bull trout (Salvelinus confluentus) and 
brook trout (S. fontinalis) using PCR primers complementary to 
interspersed nuclear elements. Copeia 2001:1093-1099.
    Trotter, P.C., B. McMillan, N. Gayeski, P. Spruell, and R. Berkley. 
1999. Genetic and phenotypic catalog of native resident trout of the 
interior Columbia River basin: FY 1998 report on populations of the 
upper Yakima basin. Annual Report to Bonneville Power Administration, 
Portland, Oregon. 51p.
    Trotter, P.C., B. McMillan, N. Gayeski, P. Spruell, and M.K. Cook. 
2001. Genetic and phenotypic catalog of native resident trout of the 
interior Columbia River basin: FY 2001 report on populations in the 
Wenatchee, Entiat, Lake Chelan, and Methow River drainages. Northwest 
Power Planning Council, Bonneville Power Administration. 48p.
    Unterwegner, T. 2002. Letter dated November 1, 2002 from Tim 
Unterwegner, District Fish Biologist, Oregon Department of Fish and 
Wildlife. 9p.
    U.S. Fish and Wildlife Service. 1999. Status review for westslope 
cutthroat trout in the United States. Regions 1 and 6. Available at our 
web site http://mountain-prairie.fws.gov/endspp/fish/wct/.
    Utah Division of Wildlife Resources. 2000. Genetic considerations 
associated with cutthroat trout management. A position paper prepared 
by the fish and wildlife agencies of seven western States. Utah 
Division of Wildlife Resources Publication Number 00-26. Salt Lake 
City. 9p. Available at http://wildlife.utah.gov/pdf/cuttpos.pdf.
    Verspoor, E., and J. Hammar. 1991. Introgressive hybridization in 
fishes: the biochemical evidence. Journal of Fish Biology 39 (Suppl. 
A):309-334.
    Vincent, E.R. 2002. Relative susceptibility of various salmonids to 
whirling disease with emphasis on rainbow and cutthroat trout. Pages 
109-115 in J.L. Bartholomew and J.C. Wilson, editors. Whirling disease: 
reviews and current topics. American Fisheries Society, Symposium 29, 
Bethesda, Maryland.
    Weigel, D.E., J.T. Peterson, and P. Spruell. 2002. A model using 
phenotypic characteristics to detect introgressive hybridization in 
wild westslope cutthroat trout and rainbow trout. Transactions of the 
American Fisheries Society 131:389-403.
    Weigel, D.E., J.T. Peterson, and P. Spruell. 2003. Introgressive 
hybridization between native cutthroat trout and introduced rainbow 
trout. Ecological Applications 13(1):38-50.
    Wilson, C., and L. Bernatchez. 1998. The ghost of hybrids past: 
fixation of arctic charr (Salvelinus alpinus) mitochondrial DNA in an 
introgressed population of lake trout (S. namaycush). Molecular Ecology 
7:127-132.
    Young, W.P., C.O. Ostberg, P. Keim, and G.H. Thorgaard. 2001. 
Genetic characterization of hybridization and introgression between 
anadromous rainbow trout (Oncorhynchus mykiss irideus) and coastal 
cutthroat trout (O. clarki clarki). Molecular Ecology 10:921-930.

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