Federal Register: August 7, 2003 (Volume 68, Number 152)
DOCID: FR Doc 03-20087
DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
CFR Citation: 50 CFR Part 17
NOTICE: PROPOSED RULES
ACTION: Endangered and threatened species:
DOCUMENT ACTION: Notice of petition finding.
Endangered and Threatened Wildlife and Plants: Reconsidered Finding for an Amended Petition To List the Westslope Cutthroat Trout as Threatened Throughout Its Range
DATES: The finding announced in this document was made on August 1, 2003.
We, the Fish and Wildlife Service (Service), announce our reconsidered 12month 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 scientificallybased 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.
Findings on petitions, etc.—; Westslope cutthroat trout,
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,
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 12month 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 12month 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 MadisonGallatin 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 WashingtonBritish 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 (MountainPrairie Region), which had been assigned primary
responsibility for the WCT petition, prevented our staff from working on a 90day 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 90day 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 lifehistory forms. Finally,
plaintiffs claimed that we failed to account for the threat of whirling disease and other important factors, and
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 selfsustaining 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 scientificallybased 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 presentday 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 scientificallybased 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 temperatezone 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,
firstgeneration 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
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
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 wellestablished differences in the number of scales in the lateralline 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 mid1960s 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 finespotted 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 casebycase 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, lifehistory, or ecological adaptations of the indigenous population or species within a particular geographic area. Consequently, the Service plans to carefully evaluate the longterm conservation implications for each taxon separately on a casebycase 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.
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
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 nonWCT 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 lifehistory 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 scientificallybased 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, taxonomicallyrecognized 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
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 lifehistory 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 casebycase 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 lowfrequency 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, orin the absence of morphological datawe 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
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
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 populationlevel 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 fragmentlength polymorphisms'' (AFLPs) and
``paired interspersed nuclear elements'' (PINES; Weigel et al. 2002) do
not. Also, a minimum of four or five codominantlyexpressed, 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 = (N
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 ``hybridlooking'' 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
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 presentday 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
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 presentday status of WCT. In turn, the morerecent 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 presentday 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 hatcheryproduced 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
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, peerreview 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 presentday rangewide 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, BullwhackerDog, 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 laboratorybased 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 introgress
FOR FURTHER INFORMATION CONTACT
Lynn R. Kaeding, by e-mail (Lynn_
Kaeding@fws.gov) or telephone (4065820717).