Endangered and threatened species: Findings on petitions, etc.— Westslope cutthroat trout,

[Federal Register: August 7, 2003 (Volume 68, Number 152)]

[Proposed Rules]

[Page 46989-47009]

From the Federal Register Online via GPO Access [wais.access.gpo.gov]

[DOCID:fr07au03-14]

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.

SUMMARY: We, the Fish and Wildlife Service (Service), announce our reconsidered 12-month finding for an amended petition to list the westslope cutthroat trout (WCT) (Oncorhynchus clarki lewisi) as a threatened species throughout its range in the United States, pursuant to a Court order and the Endangered Species Act (Act) of 1973, as amended. After a thorough review of all available scientific and commercial information, we find that listing the WCT as either threatened or endangered is not warranted at this time. Also pursuant to the Court order, we assert our scientifically-based conclusion about the extent to which it is appropriate to include ``hybrid'' WCT populations and populations of unknown genetic characteristics in the taxonomic group that we considered for listing.

DATES: The finding announced in this document was made on August 1, 2003.

ADDRESSES: Data, information, comments, or questions regarding this document should be sent to the Chief, Branch of Native Fishes Management, U.S. Fish and Wildlife Service, Montana Fish and Wildlife Management Assistance Office, 4052 Bridger Canyon Road, Bozeman, Montana 59715. The complete administrative file for this finding is available for inspection, by appointment and during normal business hours, at the above address. The new petition finding, the status update report for WCT, the amended petition and its bibliography, our initial status review document and petition finding, related Federal Register notices, the Court Order and Judgement and Memorandum Opinion, and other pertinent information, may be obtained at our Internet Web site: http://mountain-prairie.fws.gov/endspp/fish/wct/.

FOR FURTHER INFORMATION CONTACT: Lynn R. Kaeding, by e-mail (Lynn_ Kaeding@fws.gov) or telephone (406-582-0717).

SUPPLEMENTARY INFORMATION:

Background

Section 4(b)(3)(B) of the Endangered Species Act of 1973 (Act), as amended (16 U.S.C. 1531 et seq.), requires that within 90 days of receipt of the petition, to the maximum extent practicable, we make a finding on whether a petition to list, delist, or reclassify a species presents substantial scientific or commercial information indicating that the requested action may be warranted. The term ``species'' includes any subspecies of fish or wildlife or plants,

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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

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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 (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

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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., =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

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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

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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

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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) (