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Status and Conservation of Westslope Cutthroat Troutwithin the Western United StatesBradley B. Shepard a , Bruce E. May b & Wendi Urie ba Montana Fish, Wildlife, and Parks; and Ecology Department , Montana State University ,1400 South 19th Avenue, Bozeman, Montana, 59718, USAb U.S. Forest Service , Bozeman, Montana, 59718, USAPublished online: 08 Jan 2011.

To cite this article: Bradley B. Shepard , Bruce E. May & Wendi Urie (2005) Status and Conservation of Westslope CutthroatTrout within the Western United States, North American Journal of Fisheries Management, 25:4, 1426-1440, DOI: 10.1577/M05-004.1

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North American Journal of Fisheries Management 25:1426–1440, 2005 [Article]q Copyright by the American Fisheries Society 2005DOI: 10.1577/M05-004.1

Status and Conservation of Westslope Cutthroat Trout withinthe Western United States

BRADLEY B. SHEPARD*Montana Fish, Wildlife, and Parks; and

Ecology Department, Montana State University,1400 South 19th Avenue, Bozeman, Montana 59718, USA

BRUCE E. MAY AND WENDI URIE

U.S. Forest Service, Bozeman, Montana 59718, USA

Abstract.—We describe the historical and current distributions and genetic status of westslopecutthroat trout Oncorhynchus clarkii lewisii (WCT) throughout its range in the western UnitedStates using data and expert opinion provided by fish managers. Westslope cutthroat trout histor-ically occupied 90,800 km and currently occupy 54,600 km; however, these are probably under-estimates due to the large-scale (1:100,000) mapping we used. Genetic analyses found no evidenceof genetic introgression in 768 samples (58% of samples tested), but the numbers of individualstested per sample were variable and sample sites were not randomly selected. Approximately 42%of the stream length occupied by WCT is protected by stringent land use restrictions in nationalparks (2%), wilderness areas (19%), and roadless areas (21%). A total of 563 WCT populations(39,355 km) are being managed as ‘‘conservation populations,’’ and while most (457, or 81%)conservation populations were relatively small, isolated populations, large and interconnectedmetapopulations occupied much more stream length (34,820 km, or 88%). While conservationpopulations were distributed throughout the historical range (occupying 67 of 70 historicallyoccupied basins), they were much denser at the core than at the fringes. From the informationprovided we determined that conserving isolated populations (for their genetic integrity and iso-lation from nonnative competitors and disease) and metapopulations (for their diverse life historiesand resistance to demographic extinction) is reasonable. We conclude that while the distributionof WCT has declined dramatically from historical levels, as a subspecies WCT are not currentlyat imminent risk of extinction because (1) they are still widely distributed, especially in areasprotected by stringent land use restrictions; (2) many populations are isolated by physical barriersfrom invasion by nonnative fish and disease; and (3) the active conservation of many populationsis occurring.

Westslope cutthroat trout Oncorhynchus clarkiilewisii (WCT) is the most widely distributed sub-species of cutthroat trout O. clarkii (Allendorf andLeary 1988; Behnke 1992). Declines in the abun-dance and distribution of WCT have been relatedto introductions of nonnative fishes, habitat chang-es, and overexploitation (Hanzel 1959; Liknes andGraham 1988; Behnke 1992; McIntyre and Rie-man 1995; Shepard et al. 1997; U.S. Fish andWildlife Service 1999), while genetic introgres-sion by nonnative fish has compromised manyWCT populations (Allendorf and Leary 1988).

The U.S. Fish and Wildlife Service (FWS) ad-ministers the U.S. Endangered Species Act (ESA)to conserve native fauna deemed at risk of ex-tinction. In 1997 the FWS received a formal pe-

* Corresponding author: bshepard@montana.edu

Received January 6, 2005; accepted May 23, 2005Published online November 3, 2005

tition to list WCT as ‘‘threatened throughout itsrange’’ under the ESA (U.S. Office of the FederalRegister 1998). After conducting a status reviewthe FWS concluded that a ‘‘threatened’’ listing was‘‘not warranted’’ for WCT because of the currentlywide distribution of this subspecies and ongoingconservation measures (U.S. Fish and WildlifeService 1999; U.S. Office of the Federal Register2000). Subsequently, a suit brought against theFWS argued there were numerous flaws in the ra-tionale the FWS used for their determination.While the Court rejected some of the plaintiffs’concerns, the Court found that FWS’s inclusion ofhybridized WCT in the taxon considered for list-ing, while at the same time considering hybrid-ization as a threat to WCT, was arbitrary and ca-pricious. The Court also suggested that the FWSfailed to adequately consider threats from disease,and remanded the ‘‘not warranted’’ listing decisionback to the FWS (U.S. Office of the Federal Reg-ister 2002a).

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1427WESTSLOPE CUTTHROAT TROUT IN THE WESTERN UNITED STATES

FIGURE 1.—Map delineating the distribution of westslope cutthroat trout throughout their range within the westernUnited States. Colored lines indicate genetic status; gray lines indicate historical range.

In 2002 a team of fisheries professionals wasconvened to conduct a consistent and comprehen-sive rangewide status assessment for WCT in theUSA. Team members believed that it was mutuallybeneficial to work together to compile existingknowledge, evaluate risks to WCT populations,and summarize current conservation efforts so thatthe FWS would have the best scientific informationto use in their listing determination (U.S. Officeof the Federal Register 2002b). Information wascompiled on historically occupied range, on cur-rent distribution and genetic status, and to assessrisks for WCT throughout their range (Shepard etal. 2003). This assessment provided consistent andcurrent information on WCT that helped the FWSreview their initial listing determination and reachanother ‘‘not warranted’’ listing conclusion (U.S.Office of the Federal Register 2003).

The objectives of this paper are to (1) betterdefine the historical distribution of WCT by bench-marking to a more specific, and defensible, timeperiod; (2) display the current distribution of WCT

and associated federal land designations that af-ford various levels of habitat protections for thissubspecies using a spatially explicit analysis; (3)define populations that fish managers are currentlyconserving, including the rationale fish managersused to define these populations; and (4) evaluatethe risks to these defined conservation populations.The goal of this review was to determine the cur-rent status of and conservation efforts for WCT,especially as they relate to U.S. implementation ofthe ESA.

Analysis Area

The analysis area included all of the probablehistorical range of WCT within the United States.We relied primarily on Behnke (1992) to delineatelikely historical range and then modified theseboundaries based on more recent survey data andinformation (Figure 1). This area includes (fromeast to west) the upper portions of the Missouri,Saskatchewan, Columbia, and Snake river basinsin Montana, Idaho, and Washington; the John Day

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1428 SHEPARD ET AL.

TABLE 1.—Genetic classes used for assessing genetic status of westslope cutthroat trout in the western United Statesduring 2002. Contaminating species include any introduced species or subspecies, excluding native species (inlandredband trout and steelhead [both variants of O. mykiss]), that could hybridize with westslope cutthroat trout.

Genetic status Abbreviated status

Genetically unaltered (,1% introgression); tested via electrophoresis or DNA Tested; unalteredIntrogressed $1% and #10%; tested via electrophoresis or DNA Tested; #10% introgressedIntrogressed .10% and #25%; tested via electrophoresis or DNA Tested; .10% to #25% introgressedIntrogressed .25%; tested via electrophoresis or DNA Tested; .25% introgressedSuspected unaltered with no record of stocking or contaminating species present Suspected unalteredPotentially hybridized with records of contaminating species being stocked or occurring

in streamPotentially altered

Hybridized and pure populations co-exist in stream (used only if reproductive isolationis suspected and testing completed)

Mixed stock; altered and unaltered

basin in Oregon; and the Methow and Lake Chelanbasins in Washington. We did not include the Ca-nadian portion of the WCT’s range.

Methods

We convened 112 fisheries professionals fromstate, federal, and tribal agencies as well as privateorganizations and consulting firms in nine regionalworkshops to compile information on WCT withintheir respective geographical areas of responsibil-ity and expertise. Twenty-one geographic infor-mation system (GIS) and data management spe-cialists also participated in these workshops to en-ter data and display the information for real-timedata editing. In a few cases, data editing took placefollowing the workshops through phone contactswith individual biologists. Historical and currentdistributions of WCT and current genetic samplingresults were entered into georeferenced databases(ARCVIEW version 3.2; ESRI 1999; MicrosoftAccess). A WCT interagency conservation team,consisting of state and federal agency represen-tatives, developed a standardized approach andprotocols that were consistently followed by allworkshop participants (see Shepard et al. 2003 fordetails).

We delineated the probable historical distribu-tion of WCT at the time of European expansioninto the western United States (circa 1800) bymodifying Behnke’s (1992) description of histor-ical range based on (1) the physical ability ofstream and river reaches (we use the term‘‘stream’’ to indicate both streams and rivers) tosupport WCT, (2) known geological barriers to up-stream invasion and lack of WCT above these bar-riers, (3) historical accounts, and (4) current sur-vey information. All streams identified on a 1:100,000-scale hydrography layer that were cur-rently occupied by WCT were delineated andclassified by genetic status (Table 1). We used 1:

100,000-scale hydrography because this was theonly scale for which hydrography coverage wasavailable over the entire analysis area. While lakeand reservoir habitats were not explicitly identifiedduring this assessment, linear distances throughany lake or reservoir that was bisected by anystream delineated on the 1:100,000-scale hydrog-raphy were included.

We recognized that there are issues related tomapping scale for which we did our assessment.Summaries based on this scale will underestimate‘‘true’’ field lengths of stream habitats due to scale-based error. There are several potential sources ofscale-based bias. First, map-derived stream lengthsunderestimate actual stream lengths. Firman andJacobs (2002) found that while hip-chained mea-surements of Oregon coastal streams were signif-icantly correlated to stream lengths computed us-ing MapTech Terrain Navigator software and 1:24,000-scale maps, map lengths needed to be mul-tiplied by about 1.14 to estimate measured streamlengths. Secondly, there are scale differences be-tween 1:100,000- and 1:24,000-scale hydrogra-phy. Two types of scale differences potentially ex-ist: differences in lengths of streams identified onboth of these two scales, and identification of morestreams on the 1:24,000 scale than on the 1:100,000 scale. We evaluated both these differencesby (1) comparing the lengths of 30 streams iden-tified on both scales from three different river ba-sins (10 per basin), and (2) calculating and com-paring the hydrographic density (kilogram ofstreams/ha) of both scales in two watersheds.

Genetic status determinations were based on ge-netic testing or likely sympatry with potentiallyhybridizing species (Table 1). Fish tissue samplescollected during 1,333 sampling events (repre-senting over 22,500 individual fish) were geneti-cally tested using either allozyme (n 5 1,129 sam-ples) or DNA (paired interspersed nuclear element

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1429WESTSLOPE CUTTHROAT TROUT IN THE WESTERN UNITED STATES

FIGURE 2.—Distribution of the number of samples tak-en for genetic analysis by the number of fish sampledclassed by level of introgression detected (,1% or$1%).

[PINE] sequence analysis; n 5 204) techniques.Most genetic sampling was not done randomly be-cause most samples were taken from fish that phe-notypically appeared to be WCT. Consequently,the available genetics information did not consti-tute a random sample taken from throughout theentire distribution of WCT.

Since the sample sizes for evaluating geneticstatus were variable, we evaluated the samples andfound that of the 785 that detected less than 1%introgression, 234 (30%) consisted of 25 fish ormore (Figure 2). Most genetic testing techniqueshave a 95% probability of detecting 1% intro-gression with a 25-fish sample, based on the num-ber of diagnostic alleles. Thus, we can confidently(95% CI) classify only 30% of samples where ge-netic testing found no evidence of introgression asnonintrogressed based on an introgression detec-tion level of 1%.

In some cases, particularly in larger streams, fishpopulations could comprise mixed stocks, a por-tion of stock made up of WCT that were not in-trogressed and another portion that contained in-dividuals with varying levels of introgression. Forthese cases the population was considered a‘‘mixed-stock’’ population, and a component ofthat population was considered to be nonintro-gressed WCT only if ancillary evidence was avail-able that indicated the WCT and any other poten-tially hybridizing nonnative species in the popu-lation were reproductively isolated, either tem-porally or spatially.

For much of the stream length analyzed no ge-netic sampling had been done, so we used the doc-umented presence or absence of potentially hy-

bridizing species to classify the likelihood of in-trogression. Where stocking records and field sur-veys indicated potentially hybridizing specieswere absent, WCT were classified as ‘‘suspectedunaltered,’’ while they were classified as ‘‘poten-tially altered’’ if any information suggested thatpotentially hybridizing species had ever been pre-sent. Lengths of stream occupied, by genetic sta-tus, were summarized and spatial distribution wasdisplayed.

Many populations of WCT receive additionalconservation management emphasis and thesewere identified as ‘‘conservation’’ populationsbased on the genetic, life history, or unique habitatadaptation values represented by each population(Utah Division of Wildlife Resources 2000). WhileWCT populations generally have important rec-reational fishery values, if they did not meet atleast one of the above conservation criterion, fishmanagers did not designate them as a conservationpopulation. Any stream segment that supportedWCT and met at least one of the above conser-vation criteria was designated by the fish managersas either an individual isolated conservation pop-ulation, or aggregated as part of a larger conser-vation metapopulation (Hanski and Gilpin 1991),depending upon the isolation or connectivity andlikely genetic exchange among spawning stocks.Where fish migration barriers were known to occurbetween stream segments that supported WCT, fishmanagers used these barriers to subdivide thesestream segments into separate, isolated popula-tions. We summarized information for designatedconservation populations based on the length ofstream occupied, number of populations, and geo-graphical distribution.

Potential risks to conservation populations wereidentified as risks that could occur in the ‘‘fore-seeable future,’’ which the WCT interagency con-servation team considered to be two to three de-cades. Risks were stratified into genetic, disease,and demographic and stochastic population riskcategories (Table 2). Genetic risk depended pri-marily on the distance from potential sources ofanthropogenic introgression (Allendorf et al.2001), and the presence of documented barriersbetween those sources and the conservation pop-ulation. Diseases of concern were those that couldcause severe and significant impacts to populationhealth and included, but were not limited to, whirl-ing disease, furunculosis, and infectious pancreaticnecrosis. Disease risk was either directly assessedor reviewed by fish health professionals from eachrespective state’s fish and wildlife agency. De-

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1430 SHEPARD ET AL.

TABLE 2.—Risks assigned to populations of westslope cutthroat trout (WCT) within the western United States des-ignated as conservation populations by risk category (abbreviations used through the rest of the article are givenparentheses). Genetic risk assumes hybridizing species includes any introduced species or subspecies, excluding nativespecies (inland redband trout and steelhead), that could hybridize with westslope cutthroat trout. Population risks arebroken into four subcategories (productivity, temporal variability, isolation, and size).

Risk Risk attribute

Genetic

Low Hybridizing species cannot interact with existing WCT population. Barrier provides complete blockage toupstream fish movement.

Med–low Hybridizing species are in same stream, drainage further than 10 km from WCT population, or both but not insame stream segment as WCT or within 10 km where a barrier currently exists (though that barrier may beat risk of failure).

Med–high Hybridizing species are in same stream, drainage within 10 km of WCT population and no barrier exists,or both; however, hybridizing species not yet found in same stream segment as WCT population.

High Hybridizing species are sympatric with WCT population in same stream segment.

Disease

Low Significant diseases and the pathogens that cause them have very limited opportunity to interact with existingWCT population. Significant disease and pathogens are not known to exist in stream or watershed associatedwith WCT population.

Med–low Significant diseases, pathogens, or both have been introduced, identified, or both in stream, drainage furtherthan 10 km from WCT population, or both but not in same stream segment as WCT or within 10 kmwhere existing barriers exist (though barriers may be at risk of failure).

Med–high Significant diseases, pathogens, or both have been introduced, identified, or both in same stream, drainagewithin 10 km of WCT population, or both, and no barriers exist between disease, pathogens, or both anddiseased fish species and WCT population.

High Significant disease, pathogens, or both and disease-carrying species are sympatric with WCT in samestream segment.

Population productivity (Pop prod)

Low Population is increasing or fluctuating around an equilibrium that fills available habitat that is near potential.No nonnative competing or predating species present. Represents high population productivity.

Med–low Population has been reduced from potential but is fluctuating around an equilibrium (population relativelystable and either habitat quality is less than potential or another factor—disease, competition, etc.—islimiting the population).

Med–high Population has been reduced and is declining (year-class failures are periodic; competition may be reducingsurvival; habitat limiting population).

High Population has been much reduced and has either been declining over a long time period or has beendeclining at a fast rate over a short time period (year-class failures are common; competition or habitatdramatically reducing survival). Represents low population productivity.

Population temporal variability (Pop var)

Low At least 75 km of connected habitats—good connectivityMed–low 25–75 km of connected habitatsMed–high 10–25 km of connected habitatsHigh ,10 km of connected habitats—poor connectivity

Population isolation (Pop iso)

Low Migratory forms must be present and migration corridors are open (connectivity maintained)—not isolated.Med–low Migratory forms are present, but connection with other migratory populations disrupted at a frequency that

allows only occasional spawning.Med–high Questionable whether migratory form exists within connected habitat; however, possible infrequent straying

of adults from other populations into area occupied by population.High Population is isolated from any other population segment, usually due to a barrier, but may be related to

lack of movement or distance to nearest population—isolated.

Population size (Pop size)

Low .2,000 adultsMed–low 500–2,000 adultsMed–high 50–500 adultsHigh ,50 adults

mographic and stochastic population risks wereranked using criteria established by Rieman et al.(1993). Both empirical evidence and professionaljudgment were used to rank these risks. We rated

risks to 539 of the 563 designated WCT conser-vation populations by both number of populationsand length of stream occupied. We were unable torate extinction risk for 24 conservation popula-

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1431WESTSLOPE CUTTHROAT TROUT IN THE WESTERN UNITED STATES

TABLE 3.—Criteria used to rate relative size of streamswithin the range of westslope cutthroat trout in the westernUnited States and number of streams that fell in each cat-egory.

Relativesize

Criteria for lengthof stream Number of streams

1 #5 km 9,9212 .5 and #10 km 5,1183 .10 and #15 km 1,6294 .15 and #25 km 1,0125 .25 and #40 km 4896 .40 km 202

TABLE 4.—Number and percentage (based on the 539 conservation populations that were evaluated) of designatedwestslope cutthroat trout conservation populations in the western United States that have had various types of conser-vation, restoration, and management actions applied as of 2002.

Conservation action Number Percentage

Angling regulations 298 55Bank stabilization 39 7Barrier construction 21 4Barrier removal 24 4Channel restoration 39 7Chemical removal of competing–hybridizing species 3 1Culvert replacement 50 9Diversion modification 18 3Fish ladder installation 11 2Fish screen installation 21 4Grade control 11 2Instream cover habitat 16 3Irrigation efficiency 9 2Physical removal of competing–hybridizing species 27 5Pool development 27 5Population restoration–expansion 23 4Public outreach (interpretive site) 31 6Riparian fencing 48 9Riparian restoration 53 10Spawning habitat enhancement 13 2Water lease–flow enhancement 9 2Watershed under protective management (wilderness or park) 54 10Woody debris addition 30 6

tions because one tribal government consideredthis information proprietary.

Habitat loss (which we define as loss of capacityto support WCT over a length of stream) is a keythreat to the continued persistence of many species(Diamond 1984; cited in Caughley 1994), and theFWS specifically addressed this threat in their sta-tus review (U.S. Fish and Wildlife Service 1999;U.S. Office of the Federal Register 2000). Whilethis assessment did not specifically evaluate hab-itat loss, we determined the spatial extent and dis-tribution of stream reaches that currently supportWCT and also have high levels of habitat protec-tion. This type of analysis is similar to gap-typeanalyses for vegetation (Caicco et al. 1995). Wedid this by overlaying a land management GISlayer that delineated National Parks, Forest Ser-

vice Wilderness Areas, Forest Service ‘‘roadless’’areas, and all federally managed lands onto hy-drography layers that delineated stream segmentscurrently occupied by WCT and stream segmentsoccupied by conservation populations. U.S. Bu-reau of Land Management (BLM) designated wil-derness and roadless area GIS maps were not read-ily available for our entire analysis area, so theseareas were not included. We used a GIS to computethe length of hydrography currently occupied byWCT and occupied by conservation populationswithin each of the above land management des-ignations.

We summarized the stream lengths occupied byeach genetic class and by designated conservationpopulations, stratified into isolates or metapopu-lations, by relative stream size based on 1:100,000-scale hydrography. Since we had no measurementsof stream width or other standardized stream sizemetric, we used the total length of each streamidentified on the 1:100,000-scale hydrography asan indicator of relative stream size (Table 3). Rel-ative stream sizes were ranked from smallest (1)to largest (6), the smallest ranks generally repre-senting short headwater tributaries and the largestranks representing rivers. We evaluated conser-vation efforts by determining whether varioustypes of conservation activities had been imple-mented for any part of each conservation popu-

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TABLE 5.—Length of stream or river (km) occupied by westslope cutthroat trout by genetic status and relative sizeof stream or river (1 5 smallest and 6 5 largest). Refer to Table 1 for more complete descriptions of genetic statuscodes and to Table 3 for relative sizes of streams or rivers.

Genetic status

Relative size

1 2 3 4 5 6 Total

Tested; unaltered 315 1,376 1,127 1,423 907 450 5,598Tested; .25% introgressed 25 207 228 303 219 498 1,480Tested; #25% to .10% introgressed 27 126 236 213 191 14 807Tested; #10% introgressed 84 434 341 459 601 66 1,985Suspected unaltered 3,281 5,696 2,590 1,374 1,022 842 14,805Potentially altered 5,561 7,683 3,852 4,088 2,907 4,110 28,201Mixed stock; altered and unaltered 27 138 144 217 209 950 1,686Total 9,320 15,660 8,517 8,078 6,056 6,931 54,561

TABLE 6.—Number and kilometers of designated westslope cutthroat trout conservation populations by rationale usedfor so designating populations and whether those populations consist of single isolated populations (isolates) or con-nected groups of subpopulations (metapopulations).

Rationale for designation

Isolates

Number Km

Metapopulations

Number Km

Total

Number Km

Core conservation population 254 2,457 34 1,927 288 4,384Unique life history 142 1,496 46 29,449 188 30,945Ecological adaptation 2 9 1 19 3 29Other 59 573 25 3,425 84 3,998Total 457 4,535 106 34,820 563 39,355(%) 81% 12% 19% 88%

lation (Table 4). We did not segregate these con-servation activities by stream length so could notreport the length of stream for which each of theseactivities was applied. Angling restrictions wereincluded as an appropriate conservation measure(Gresswell and Liss 1995).

Results

We found that the lengths of streams derivedfrom 1:100,000-scale hydrography were onlyabout 1% shorter than estimates of that samestream using 1:24,000-scale hydrography. How-ever, differences in the number of streams iden-tified on the two different scales were much moreof a problem as 35% higher stream densities werefound on the 1:24,000-scale hydrography than onthe 1:100,000-scale hydrography for some riverbasins.

We estimated that WCT historically occupied90,800 km and currently occupy 54,600 km (59%of historical) of lotic habitats within the westernUnited Statea (Figure 1). Genetic sampling (n 51,333 samples) of putative WCT found no evi-dence of genetic introgression in 768 samples(58%), indicating that WCT in about 5,600 km ofstream length were not introgressed (Table 5).Westslope cutthroat trout that were likely part ofa mixed-stock population with no evidence of in-

trogression occupied almost another 1,700 km(mostly in larger streams and rivers), and approx-imately 14,500 km of streams were occupied byWCT that were suspected to be (but not tested)genetically unaltered (Figure 1).

A total of 563 WCT populations, occupying39,355 km of stream length (72% of occupiedstream length), were being managed as conser-vation populations (Figure 3; Table 6). Conser-vation populations were spread throughout the his-torical range, occurring in 67 of the 70 river basinshistorically occupied by WCT, though more ofthese populations were concentrated near the corethan near its fringes (Figure 3). Individual con-servation populations occupied from 0.5 to over9,780 km of lotic habitats (median 5 8.6 km). Thedistribution of stream length occupied by conser-vation populations was skewed as most of the pop-ulations occupied less than 20 km. Most conser-vation populations were isolated; however, con-servation populations that were defined as meta-populations occupied much more stream length(Table 6). Most (60%, or 339) of the designatedconservation populations had at least one geneticsample that found no introgression, and we sus-pected that 172 (30%) WCT conservation popu-lations were not introgressed based on both geneticsampling and physical isolation. These 172 sus-

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1433WESTSLOPE CUTTHROAT TROUT IN THE WESTERN UNITED STATES

FIGURE 3.—Map showing the current distribution of westslope cutthroat trout vis-a-vis federal lands, designatedwilderness areas, roadless areas, and national parks. Colored lines indicate conservation populations; gray indicatespopulations not designated as conservation populations.

TABLE 7.—Length of stream or river (km) that was occupied by conservation populations of westslope cutthroat troutin the western United States by genetic status and relative size of stream or river (1 5 smallest and 6 5 largest). Referto Table 1 for more complete descriptions of genetic status codes and to Table 3 for relative sizes of streams and rivers.

Genetic status

Relative size

1 2 3 4 5 6 Total

Tested; unaltered 315 1,318 1,091 1,392 897 450 5,463Tested; .25% introgressed 2 21 12 53 22 110Tested; #25% to .10% introgressed 5 9 38 9 82 144Tested; #10% introgressed 73 345 277 399 526 66 1,685Suspected unaltered 3,056 5,230 2,413 1,244 975 820 13,738Potentially altered 2,995 4,978 2,307 2,294 1,824 2,618 17,016Mixed stock; altered and unaltered 23 138 139 207 193 499 1,199Total 6,468 12,039 6,278 5,599 4,518 4,453 39,355

pected genetically pure conservation populationsoccupied from 0.6 to 20.6 km of stream length(Table 7).

Of the nearly 54,600 km of stream length cur-rently occupied by WCT, 2% was in national parks,19% was in designated Forest Service wildernessareas, 21% was in Forest Service2designated

roadless areas (excluding wilderness areas), and30% was in other federally managed lands (Figure3). Designated wilderness areas and national parkssupported 1,000 km of the stream length occupiedby genetically tested WCT populations with noevidence of introgression (representing 1–2% ofall occupied length). Of the over 39,000 km ofD

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FIGURE 4.—Relative extinction risk (low to high) dueto six factors (vertical axes; see Table 2 for detaileddescriptions of each risk factor) by length of streamwithin designated westslope cutthroat trout conservationpopulations that were isolated (top panel) and connected(metapopulations; bottom panel).

stream length occupied by conservation popula-tions, 76% was located within federally adminis-tered lands, 49% was in roadless areas, 24% wasin designated wilderness areas, and 1.6% was innational parks.

In general, fish managers considered isolatedconservation populations to be at higher risk thanmetapopulations due to temporal variability, pop-ulation size, and isolation but at lower risk due togenetic introgression, disease, and population de-mographics (Figure 4). Some type of restorationactivity has occurred, or is currently occurring, insome portion of 435 of the 563 identified conser-vation populations (77%), and many conservationpopulations had more than one conservation ac-tivity occurring for at least part of its occupiedlength (Table 4). Since fish managers considerWCT a game fish over all their range within the

western Unites States, angling regulations applyto all WCT populations. Implementation of an-gling restrictions that were more stringent than thegeneral angling regulation was the most commonconservation action, affecting over half of the des-ignated conservation populations. These morestringent restrictions often consisted of catch-and-release fishing for WCT, but other restrictions suchas reductions in daily limits, size limits, and gearrestrictions were also included. Habitat restorationactivities—such as culvert replacement, channelrestoration, bank stabilization, and riparian fenc-ing—have each been implemented for 5–10% ofthe conservation populations. Projects to removepotential hybridizing or competing nonnative spe-cies, either by chemical or physical techniques,have occurred for over 5% of the conservationpopulations.

Discussion

The use of 1:100,000-scale hydrography for thisanalysis resulted in underestimate (downward) bi-ases for both historical and current WCT distri-butions. However, these biases should be consis-tent. We have found that some streams not shownon 1:100,000-scale hydrography but appearing on1:24,000-scale hydrography actually supportedWCT (in fact, we have also found WCT in streamsnot identified on 1:24,000-scale maps), but thesestreams were not included in our assessment.

Historical Distribution

The length of the streams that we estimated tobe within the WCT historical range in the westernUnited States was less than previous estimates(Hanzel 1959; Behnke 1979; Liknes and Graham1988; Behnke 1992; Van Eimeren 1996; Lee et al.1997; Shepard et al. 1997; Thurow et al. 1997;U.S. Fish and Wildlife Service 1999). There areseveral reasons for these differences. First, we de-fined the historical time period as the time of Eu-ropean expansion into the western United States(circa 1800), later than the time period defined bymost other authors. Secondly, we eliminatedstream reaches above barriers (geological falls orthermal) or where habitats were unsuitable (i.e.,extremely high channel gradient, intermittentstreamflow), and there was no evidence suggestingWCT ever occupied the reach. Most previous as-sessments lumped relatively large geographical ar-eas as being wholly within the historical range andassumed all reaches within these areas were his-torically occupied. We believe it is appropriate tobenchmark historical range occupancy to a specific

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time period and used a more contemporary timeperiod than some previous authors because we be-lieved it was important to have some level of doc-umentation for delineating historical range.

Current Distribution

We estimated that WCT currently occupy morestream length than earlier estimates for analogousareas. For example, Liknes and Graham (1988)estimated WCT occupied 6,900 km of lotic habi-tats in 1986 within Montana, Van Eimeren (1996)estimated 17,400 km were occupied in 1995, andwe estimated that WCT occupied 20,900 km in2002. Similar differences were also found amonglengths these authors estimated were occupied byWCT with no evidence of introgression. These dif-ferences could easily be attributed to additionalsampling that was done from 1986 (217 geneticsamples and 2,224 fish surveys) to 1995 (1,232and 6,586), and then to our summary in 2002(1,994 and 10,299), and to the more detailed as-sessment we conducted. In contrast, Lee et al.(1997) and Thurow et al. (1997) estimated thatWCT occupied 85% of their historical range in theupper and middle Columbia River basin using sub-watershed areas (mean 5 7,800 ha), a finding sim-ilar to ours for this basin (82%), though we usedstream length. We caution that while over half ofthe genetic samples found no evidence of intro-gression, only 30% of these samples had enoughindividuals sampled to detect 1% introgression atthe 95% level of confidence. Thus, we can onlysay that about 15% of all genetic samples had noevidence of introgression (,1%) with a high de-gree of confidence.

Westslope cutthroat trout currently occupy ahigher proportion of the core of their historicalrange and display sparser occupancy near rangefringe areas, particularly in the Missouri River sys-tem of Montana and disjunct habitats in Washing-ton and Oregon (Figure 1). Several studies, boththeoretical and empirical, have suggested a declinein the proportion of sites occupied and in popu-lation densities from the center to the fringe of aspecies range for many vertebrate species (e.g.,Brown 1984; Caughley et al. 1988; Lawton 1993).

Habitat Protection

Our finding that wilderness and roadless areasprovide important strongholds for WCT was sim-ilar to findings from other assessments (Liknes andGraham 1988; Marnell 1988; Rieman and Apper-son 1989; Thurow et al. 1997). Since we did notassess BLM wilderness or roadless areas in this

assessment because compatible GIS layers forBLM-administered lands were not readily avail-able, our estimates of the proportions of habitatcurrently occupied by WCT within lands managedas wilderness and roadless are underestimates.

Designation of Conservation Populations

We found that state, tribal, and national parkfish managers designated genetically pure, slightlyintrogressed, and genetically untested WCT asconservation populations (Utah Division of Wild-life Resources 2000). Fish managers generally didnot include WCT populations with introgressionlevels of 10% or higher as conservation popula-tions unless they made up part of a larger, inter-connected metapopulation that was designated toconserve migratory life history characteristics. Wefound that only 5% of conservation populationshad one or more stream reaches where introgres-sion higher than 10% was documented by genetictesting.

The decision to conserve hybridized fish is sub-ject to debate. However, we believe the inclusionof slightly hybridized fish may be prudent because(1) much of the genetic variation within WCT re-sults from unique alleles (often occurring at rel-atively high frequencies) found in only one or twolocal populations (Allendorf and Leary 1988; Tay-lor et al. 2003), and (2) several authors have sug-gested that conserving slightly introgressed pop-ulations was a reasonable strategy to ensure theconservation of local phenotypic, genotypic, andbehavioral variation but should be based on localconsiderations (Dowling and Childs 1992; Allen-dorf et al. 2001; Peacock and Kirchoff 2004).Dowling and Childs (1992) recommended that‘‘extreme care must be exercised when consideringelimination of any (genetically) contaminated pop-ulation lest the unique genetic identity of the nativetaxon be lost forever.’’ In contrast, others haverecommended that only genetically pure WCTshould be protected under ESA (Allendorf et al.2004). We do not believe that eradicating slightlyintrogressed populations is a reasonable or prudentconservation strategy.

Conservation Efforts

The potential vulnerability of WCT to both dis-placement (MacPhee 1966; Griffith 1972; Behnke1979; Liknes and Graham 1988; Griffith 1988;Shepard et al. 2002; Dunham et al. 2003) and hy-bridization (Allendorf and Leary 1988; Allendorfet al. 2001, 2004) by nonnative trout has causeda dilemma for fish managers charged with con-

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serving this subspecies. Metapopulation theory(Hanski and Gilpin 1991; Doak and Mills 1994;Hanski and Simberloff 1996) suggests that main-taining groups of connected local populations re-duces long-term risks of extinction, and many re-searchers and managers have called for universallyapplying this theory in the conservation of nativesalmonids (Rieman and McIntyre 1993; Bisson1995; Li et al. 1995; Reeves et al. 1995; Schlosserand Angermeier 1995; Independent ScientificGroup 1996; National Research Council 1996; Leeet al. 1997; Policansky and Magnuson 1998; Rie-man and Dunham 2000). However, maintaining orestablishing connectivity among local populationsof WCT may place these populations at high riskof invasion, and subsequent displacement or in-trogression, by nonnative trout (Allendorf andLeary 1988; Adams 1999; Allendorf et al. 2001;Adams et al. 2000; Adams et al. 2001; Rubidge etal. 2001; Dunham et al. 2003; Hitt et al. 2003;Weigel et al. 2003).

There were two types of conservation strategiesinherent in how fish managers designated WCTconservation populations. One strategy empha-sized conserving genetic integrity by isolatingWCT populations that have no evidence of geneticintrogression to prevent introgression. Isolatingnonintrogressed WCT populations also reduces therisks associated with competition by nonnative fishand diseases. Isolated conservation populationsaccounted for 168 (98%) of the 172 conservationpopulations with no evidence of introgression, andthe designation of 161 (94%) of these populationsas conservation populations was based on con-serving their genetic integrity. Of these 168 con-servation populations, 56 (33%) were genetically‘‘secured’’ by the presence of a fish migration bar-rier. Fish managers believed that while smaller,isolated WCT populations would be more suscep-tible to population-level risks due to isolation,small population size, and temporal variability,their isolation would make them less susceptibleto risks from genetic introgression and disease.The assumption made in rating population risks ashigh for these isolated conservation populationswas based on theoretical population dynamics,which assumes that groups of populations occu-pying relatively large connected habitats are at alower risk of extinction than smaller, isolated pop-ulations.

The other strategy emphasized maintaining con-nectivity among WCT populations by protectinglarge areas of continuous habitat, thus allowingWCT to express all life history traits, especially

migratory life histories. While metapopulationswere believed less vulnerable to population riskssuch as temporal variability, isolation, and smallpopulation size, their connectedness made themmore susceptible to risks from genetic introgres-sion, competition, and disease. Thus, the risks in-herent in these two different conservation strate-gies are dramatically different.

Some authors have indicated that cutthroat troutpopulations need to be supported by an effectivepopulation of 500 reproducing adults based on the50/500 ‘‘rule’’ (Franklin 1980; Soule 1980); thus,they have considered extinction risks to be highfor most isolated, small populations of cutthroattrout (Shepard et al. 1997; Kruse et al. 2001; Hild-erbrand and Kershner 2000). Harig and Fausch(2002) found that cutthroat trout translocationswere most successful when the drainage area wasat least 15 km2, which translates to inhabited hab-itat lengths of about 5 km. Hilderbrand and Kersh-ner (2000) estimated that cutthroat trout needed atleast 9 km of habitat at moderately high densitiesto persist under the 500 rule. Rieman and Dunham(2000) provided data that indicated small, isolatedpopulations of WCT might not be as prone to ex-tinction as other vertebrates, and even other sal-monids, based on their evaluation of the persis-tence of isolated headwater populations of WCTin the Coeur d’Alene basin of Idaho.

Since genetic introgression and nonnative com-petition threats may outweigh stochastic risks overthe short term for many extant WCT populations,we suggest that isolating the remaining nonintro-gressed WCT populations is a prudent, short-termconservation strategy (Novinger and Rahel 2003).Replicating and refounding existing isolated, non-introgressed WCT populations that have high ex-tinction risk due to stochastic or demographic pres-sures has been recognized as a viable conservationstrategy (e.g., Montana Fish, Wildlife, and Parks1999; Young and Harig 2001), and we recommendthis strategy, where feasible. Applying this con-servation management strategy implies that hu-mans must act as the dispersal agent, via conser-vation stocking, to refound WCT populations thatare lost from isolated habitats due to stochasticprocesses.

Evaluation of Workshop Approach

We suggest that the regional workshop approachused for simultaneously collecting both data andexpert opinion provided consistent informationacross the range of this subspecies; however, wehave several observations on why this worked and

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recommendations to improve this process. First,we believe that the consistent protocol that wasdeveloped and agreed upon prior to beginningworkshop sessions was an integral reason for thesuccess of this effort. Quality control and assur-ance was maintained by using a few facilitatorswho attended each workshop. Secondly, there wasa strong commitment by each management agencythat made attendance mandatory for their respec-tive staffs. Thirdly, having baseline data availableat each workshop in both electronic and hard copyformat—displayed both in databases and onmaps—allowed workshop participants to startfrom a common baseline. Fourthly, having dataentry and GIS technicians at each workshop toenter and edit the data in real time and then displaythe new data on a GIS was invaluable. However,we strongly recommend that all final editing becompleted at these workshops to avoid having torecontact individuals to verify or edit the infor-mation later.

We identified several weaknesses that weremodified for subsequent assessments. While over-all data quality was rated for each WCT popula-tion, we recommend rating data quality for eachestimated parameter (i.e., upper distributionbound, lower distribution bound, abundance, ge-netic status, barrier status, barrier location). Par-ticipants did not explicitly include estimates ofpopulation size, relative abundance, or streamwidth, so it was impossible to assess abundanceor density of remaining WCT populations. Partic-ipants attributed various conservation activitiesand human impacts to individual conservationpopulations, but not to specific stream segmentsoccupied by that conservation population. Whilethis generalization limited our ability to analyzethese types of data, we found from an earlier as-sessment for Yellowstone cutthroat trout O. c. bou-vieri that fish managers had difficulty directly link-ing human impacts to spatially explicit reachesbecause these data were usually not available. Wesuggest conservation activities might be linked tospecific reaches but are unsure whether human im-pacts could be determined with currently availableinformation.

Conclusions

Shepard et al. (2003) provided a baseline of in-formation that can be used to assess future con-servation progress and to prioritize and plan WCTconservation efforts. Updating this database withdata from well-designed field monitoring programswill serve as a barometer to monitor the status of

WCT over time. This monitoring should provideempirical evidence for testing and contrasting thesuccess of isolation versus connection conserva-tion strategies.

We found that WCT currently occupy significantportions of their historical range within the west-ern United States, that they are well distributedacross that range, and that fish managers are ac-tively conserving many remaining WCT popula-tions. Over 20% of the current length of streamsoccupied by WCT in the western United States arelocated within lands with very stringent land userestrictions that should adequately protect theseaquatic habitats. Fish managers are working to re-duce threats to WCT from genetic introgression,nonnative fish competition and predation, diseases,habitat loss, and angler harvest, while concurrentlytrying to maintain some WCT populations withmigratory life histories.

Fish migration barriers are being used to isolatesome WCT populations from threats of geneticintrogression, nonnative fish competition and pre-dation, and diseases. However, this strategy mayincrease potential extinction risks due to stochasticenvironmental and demographic processes. Fishmanagers are trying to address these risks by rep-licating some of these isolated populations, there-by having the potential to use these replicates torefound populations that go extinct. MaintainingWCT metapopulations in relatively large con-nected systems will likely increase risks of intro-gression, nonnative fish competition, and diseasefor some of these connected populations, but thiswill be a necessary trade-off in some systems inorder to maintain populations with migratory lifehistories and to reduce stochastic environmentaland demographic risks.

We conclude that while the distribution andabundance of WCT have declined dramaticallyfrom historical levels, as a subspecies WCT arenot currently at imminent risk of extinction be-cause (1) they are still widely distributed, espe-cially within lands that have stringent habitat pro-tection measures in place, (2) many populationsare isolated by physical barriers from invasion bynonnative fish and disease, and (3) the active con-servation of many populations is occurring. How-ever, this conclusion does not reduce the need forcontinued aggressive conservation of this subspe-cies throughout its range, and particularly for pop-ulations located at the fringes of its historicalrange.

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Acknowledgments

These data were collected for a WCT assessmentthat was originally developed and reported underthe oversight of the WCT Interagency Conserva-tion Team that, in addition to the primary authors,included: C. Corsi (Team Leader), K. McDonald,R. Snyder, T. Unterwegner, J. Uehara, and K.Walker. This team provided both information andeditorial oversight. We thank all the fisheries bi-ologists and data entry and geographical infor-mation technicians who provided information, en-tered data, and assisted with GIS applications. S.Carson provided support and applications for theGIS program ARCVIEW. Data were provided bythe states of Washington, Oregon, Idaho, and Mon-tana; Glacier and Yellowstone National Parks;Confederated Salish and Kootenia, Couer d’Alene,Nez Perce, Shoshone-Bannock, Kalispel, and Ko-otenai of Idaho tribes; the U.S. Forest Service,USDA; FWS; and BLM. Region 6 of the FWShelped fund the WCT assessment. Montana Fish,Wildlife, and Parks; a BLM Challenge Cost-Sharegrant; and the U.S. Forest Service supported themain authors’ efforts. S. Kalinowski, M. Camp-bell, S. Yundt, L. Kaeding, all members of theWCT Interagency Conservation Team, D. Schill,S. Riley, and an anonymous reveiwer reviewedearlier drafts of either the original report or thismanuscript and provided many helpful sugges-tions. Reference to trade names does not implyendorsement by the U.S. Government.

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