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We describe the historical and current distributions and genetic status of westslope cutthroat trout Oncorhynchus clarkii lewisii (WCT) throughout its range in the western United States using data and expert opinion provided by fish managers. Westslope cutthroat trout historically occupied 90,800 km and currently occupy 54,600 km; however, these are probably underestimates due to the large-scale (1:100,000) mapping we used. Genetic analyses found no evidence of genetic introgression in 768 samples (58% of samples tested), but the numbers of individuals tested 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 national parks (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 interconnected metapopulations occupied much more stream length (34,820 km, or 88%). While conservation populations were distributed throughout the historical range (occupying 67 of 70 historically occupied basins), they were much denser at the core than at the fringes. From the information provided we determined that conserving isolated populations (for their genetic integrity and isolation from nonnative competitors and disease) and metapopulations (for their diverse life histories and resistance to demographic extinction) is reasonable. We conclude that while the distribution of WCT has declined dramatically from historical levels, as a subspecies WCT are not currently at imminent risk of extinction because (1) they are still widely distributed, especially in areas protected by stringent land use restrictions; (2) many populations are isolated by physical barriers from invasion by nonnative fish and disease; and (3) the active conservation of many populations is occurring.

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We sampled 19 isolated headwater populations of westslope cutthroat trout Oncorhynchus clarki lewisi in Montana to provide estimates of fecundity, longevity, sex ratio, and age at sexual maturity. Fecundity was estimated for 31 fish collected from two streams in the upper Missouri River drainage. Females smaller than 149 mm fork length (FL) were generally immature and their fecundities could not be estimated. Mean fecundities (SD) were 227 eggs (41.1) for 150-174-mm fish, 346 eggs (85.6) for 175-199-mm fish, and 459 eggs (150.8) for 200-mm and larger fish. A linear regression model (two stream samples combined) to predict fecundity (£) from fork length was developed (E = -494.9 -I-4.4-FL; r 2 = 0.51. P < 0.001) for westslope cutthroat trout in the upper Missouri River drainage. Regression slopes of fecundity against fish length differed significantly (P < 0.01) between these and some of the previously studied populations. Steeper slopes were associated with lacustrine-adfluvial populations. The average sex ratio was 1.3 males per female across all sampled streams. Males began to mature sexually at age 2 and all were mature by age 4. Some females (27%) were sexually mature at age 3 and most of them (93%) were mature by age 5. Length was a better predictor of sexual maturity than age. Males matured at 110-160 mm and females at 150-180 mm FL. The maximum estimated age was 8 years based on otoliths from 475 fish collected from our 19 study streams and 14 additional streams.

Hybridization between invasive and native species, a significant threat to worldwide biodiversity, is predicted to increase due to climate-induced expansions of invasive species. Long-term research and monitoring are crucial for understanding the ecological and evolutionary processes that modulate the effects of invasive species. Using a large, multidecade genetics dataset (N = 582 sites, 12,878 individuals) with high-resolution climate predictions and extensive stocking records, we evaluate the spatiotemporal dynamics of hybridization between native cutthroat trout and invasive rainbow trout, the world's most widely introduced invasive fish, across the Northern Rocky Mountains of the United States. Historical effects of stocking and contemporary patterns of climatic variation were strongly related to the spread of hybridization across space and time. The probability of occurrence, extent of, and temporal changes in hybridization increased at sites in close proximity to historical stocking locations with greater rainbow trout propagule pressure, warmer water temperatures, and lower spring precipitation. Although locations with warmer water temperatures were more prone to hybridization, cold sites were not protected from invasion; 58% of hybridized sites had cold mean summer water temperatures (<11°C). Despite cessation of stocking over 40 years ago, hybridization increased over time at half (50%) of the locations with long-term data, the vast majority of which (74%) were initially nonhybridized, emphasizing the chronic, negative impacts of human-mediated hybridization. These results show that effects of climate change on biodiversity must be analyzed in the context of historical human impacts that set ecological and evolutionary trajectories.

Mean densities of bull trout estimated from electrofishing in the Flathead and the Toboggan, MacKenzie and Wigwam drainages of British Columbia 3 2 19 Mean densities of age 0, age I, age II, age III, all bull trout and age I and older bull trout in pools, runs, riffles and pocketwater of the upper Flathead River basin (1979-1981) .... 33 20 Flow pattern or habitat units used by juvenile bull trout and Dolly Varden in streams of Maitana, British Columbia and Alaska. 3 3 21 Cover used by juvenile bull trout and Dolly Varden in streams of Alaska, Montana, and British Columbia 3 5 22 Depth and velocity used by juvenile bull trout in the Flathead and general depth and velocity measures of juvaiile bull trout in streams of British Columbia, adopted from Griffith 1979. .. vi i 36 LIST OF TABLES (Cont.) TABLE P^E 23 Substrate asscx:iated with juvenile bull trout in British Columbia and the Flathead 3 7 24 Percent of age I, II, III, and IV bull trout emigrating from tributary streams 3 9 25 Number of days trapping occurred, number of juvenile bull trout passed downstream through traps, and number of trapped juvenile bull trout per trap day by month from North Fork tributaries during 1976 to 1980 and Middle Fork tributaries during 1981.. . 39 26 Characteristics of bull trout spawning, including time of year, size of spawner, sex ratio and fecundity observed in river drainages of Montana, Idaho and British Coluik^ia 4 6 27 Characteristics of bull trout redds including redd size (disturbed area) , depth of egg deposition, water depth, velocity and streambed conposition observed in river drainages of Montana, Idaho and British Columbia 48 4 5 X LIST OF APPENDICES APPENDIX PAGE A Summary of results for downstream trapping of juvenile westslope cutthroat and bull trout in upper Flathead River tributaries from 1976 to 1981 ai B Sumnary of tag return information illustrating movement of westslope cutthroat and bull trout in the upper Flathead River Basin b l C Age-growth information for westslope cutthroat and bull trout in the upper Flathead River drainage ci xi

Despite the widespread use of redd counts to monitor trends in salmonid populations, few studies have evaluated the uncertainties in observed counts. We assessed the variability in redd counts for migratory bull trout Salvelinus confluentus among experienced observers in Lion and Goat creeks, which are tributaries to the Swan River, Montana. We documented substantially lower observer variability in bull trout redd counts than did previous studies. Observer counts ranged from 78% to 107% of our best estimates of true redd numbers in Lion Creek and from 90% to 130% of our best estimates in Goat Creek. Observers made both errors of omission and errors of false identification, and we modeled this combination by use of a binomial probability of detection and a Poisson count distribution of false identifications. Redd detection probabilities were high (mean ¼ 83%) and exhibited no significant variation among observers (SD ¼ 8%). We applied this error structure to annual redd counts in the Swan River basin to correct for observer error and thus derived more accurate estimates of redd numbers and associated confidence intervals. Our results indicate that bias in redd counts can be reduced if experienced observers are used to conduct annual redd counts. Future studies should assess both sources of observer error to increase the validity of using redd counts for inferring true redd numbers in different basins. This information will help fisheries biologists to more precisely monitor population trends, identify recovery and extinction thresholds for conservation and recovery programs, ascertain and predict how management actions influence distribution and abundance, and examine effects of recovery and restoration activities.

Westslope cutthroat trout Oncorhynchus clarki lewisi now occupy less than 5% of the subspecies' historical range within the upper Missouri River drainage in Montana. We assessed the risk of extinction for 144 known populations inhabiting streams within federally managed lands in the upper Missouri River basin using a Bayesian viability assessment procedure that estimates probability of persistence based on subjective evaluation of population survival and reproductive rates as influenced by environmental conditions. We first customized this model using estimates of demographic parameters from the literature and field data. Each population was classified into one of three risk groups based on their Bayesian probability of persistence over 100 years (p100). Most (71 %) of the 144 populations had a very high predicted risk of extinction (p100 ≤ 50%), 19% exhibited a high risk (50% < p100 ≤ 80%), and 10% had a moderate risk (80 < p100 ≤ 95%). Higher average predictions of p100 were consistently associated with populations inhabiting watersheds with lower levels of management activities. Analysis of variance and a matrix of information divergence measures indicated that livestock grazing, mineral development, angling, and the presence of nonnative fish had the greatest association with both estimated population parameters and persistence probabilities. Of 26 major subbasins within the upper Missouri River drainage, 16 support at least one known westslope cutthroat trout population on federal lands, and 14 of these 16 support at least one population with an estimated p100 value of 0.5 or greater. Results of our analysis have led to action by citizens of Montana, prompting state and federal managers to develop a conservation and restoration program for this subspecies in the upper Missouri River basin.