Invasive hybridization between native and introduced species is widespread, especially in fishes, yet its effects on fitness-related traits across environments remain poorly understood. We combined individual genetic admixture estimates with capture–recapture data to quantify how hybridization between native Westslope Cutthroat Trout (Oncorhynchus lewisi) and invasive Rainbow Trout (Oncorhynchus mykiss) influences survival. We measured individual survival of 5186 trout across three populations in contrasting environments. Non-native admixture significantly affected survival in two populations, with positive effects during summer and negative effects during winter. Prior research has shown hybridization increases with stream temperature; however, survival patterns did not follow this trend. In a warmer stream, native trout in all size-classes had ≥20% higher annual survival than hybrids, whereas in a cooler stream, juvenile native trout had ≥20% lower survival than hybrids. These findings indicate that hybridization effects on survival are complex and vary among populations, environments, and size-classes. Landscape patterns of hybridization may therefore not reflect local survival (or fitness) outcomes, emphasizing that measures fitness-related traits across populations and environments could elucidate the eco-evolutionary consequences of invasive hybridization.

Genetic rescue, specifically translocation to facilitate gene flow among populations and reduce the effects of inbreeding, is an increasingly used approach in conservation. However, this approach comes with trade-offs, wherein gene flow may reduce fitness when populations have adaptive differentiation (i.e., outbreeding depression). A better understanding of the interaction between isolation, inbreeding, and adaptive divergence in key traits, such as life history traits, will help to inform genetic rescue efforts. Stream-dwelling salmonids, such as the westslope cutthroat trout (Oncorhynchus lewisi; WCT), are well-suited for examining these trade-offs because they are increasingly isolated by habitat degradation, exhibit substantial variation in life history traits among populations, and include many species of conservation concern. However, few genomic studies have examined the potential trade-offs in inbreeding versus outbreeding depression in salmonids. We used > 150,000 SNPs to examine genomic variation and inbreeding coefficients in 565 individuals across 25 WCT populations that differed in their isolation status and demographic histories. Analyses of runs of homozygosity revealed that several isolated WCT populations had "flatlined" having extremely low genetic variation and high inbreeding coefficients. Additionally, we conducted genome scans to identify potential outlier loci that could explain life history differences among 10 isolated populations. Genome scans identified one candidate genomic region that influenced maximum length and age-1 to age-2 growth. However, the limited number of candidate loci suggests that the life history traits examined may be driven by many genes of small effect or phenotypic plasticity. Although adaptive differentiation should be considered, the high inbreeding coefficients in several populations suggest that genetic rescue may benefit the most genetically depauperate WCT populations.

Amphibians have suffered widespread declines caused by many interacting factors whose effects are often difficult to isolate. We used complementary analyses to decouple effects of methylmercury (MeHg) and amphibian chytrid fungus (Bd) on survival of Columbia Spotted Frogs ( Rana luteiventris ) during a 5-year capture-mark-recapture study. We also evaluated whether effects on apparent survival were mediated through physiological responses (corticosterone, CORT). While Bd was unrelated to frog survival, geometric mean MeHg bioaccumulation in our population (164 ng/g) reduced survival by ~20%. Baseline CORT was negatively associated, and stress-induced CORT was positively associated with higher MeHg, suggesting that MeHg dysregulated glucocorticoid physiology. Survival was positively associated with higher baseline CORT, whereas survival was negatively associated with higher stress-induced CORT. Our results provide rare evidence linking CORT and long-term survival of wild vertebrates and that environmentally relevant concentrations of MeHg can influence survival of free-ranging amphibians, and these effects may be mediated by CORT.

Body condition of animals is often assumed to reflect advantages in survival or reproduction, but body condition indices may not reflect body composition, or condition may be unrelated to fitness-associated traits. The relationship between body condition indices and composition has rarely been quantified in amphibians, and body condition has not previously been related to growth in adult amphibians. We used laboratory (quantitative magnetic resonance) and field methods to evaluate the relationship between body composition and the four common body condition indices for wildlife studies (body mass index, Fulton’s index, scaled mass index, and residual index) in two frog and one salamander species in Montana, USA. We then assessed the relationship between body condition and summertime somatic growth during a 3-yr mark-recapture study of one of our study species (Columbia spotted frogs, Rana luteiventris ). Correlation of body condition indices with fat and lean mass differed across species, sexes, and whether components were represented as percentages or were scaled based on size. Scaled mass index, residual index, and Fulton’s index were most often well correlated ( r > 0.6) with scaled body components, but Fulton’s index was strongly correlated with body length. Scaled mass and residual indices predicted scaled fat relatively well and were uncorrelated with body length. Heavier condition predicted higher growth rates of Columbia spotted frogs, regardless of the index used. Frogs of heavy body condition (90 th percentile residual index) grew 0.04 and 0.05 mm/day greater than frogs of light condition (10 th percentile) for average length males and females, respectively. Frogs of short body length (10 th percentile) grew 0.11 and 0.19 mm/day more than long (90 th percentile) males and females, respectively. By examining the relationship between body condition indices and body composition and revealing a link between condition and future growth, our results provide an empirical basis for choosing the most appropriate condition index, as well as a potential link to fitness-related traits.

Protected areas are considered a critical antidote to global biodiversity loss. Yet, protected areas have not effectively preserved freshwater biodiversity compared to other taxonomic groups, in part because they are not designed or managed with freshwater ecosystems in mind. Additionally, historical and current human activities have degraded freshwater biodiversity, and climate driven transformation constrains the ability of protected areas to preserve freshwater biodiversity into the future. Management intervention is an important tool to ensure protected areas support current and future ecological, socio-cultural, and economic values surrounding freshwater biodiversity. Yet applying interventions is challenging because many protected areas limit human manipulation and control. The Resist-Accept-Direct (RAD) framework is a tool for weighing management approaches in an expanded decision space. As such, the RAD framework may help identify the most appropriate approaches to address ecological transformation while balancing the mandates and values of a given protected area. In this paper, we review federally protected areas of the United States and their varied ability to support freshwater biodiversity. We then recast past management approaches through a RAD lens, examining how they resist, accept, or direct freshwater biodiversity loss in these protected areas. This illustrates how elements of the RAD framework are already being applied and provides a foundation for managers to more formally resist, accept, or direct freshwater biodiversity loss in protected areas moving forward. We conclude with considerations for applying the RAD framework at the intersection of freshwater biodiversity and protected areas to benefit values of current and future generations.

Climate change is a primary threat to biodiversity, but for many species, we still lack information required to assess their relative vulnerability to changes. Climate change vulnerability assessment (CCVA) is a widely used technique to rank relative vulnerability to climate change based on species characteristics, such as their distributions, habitat associations, environmental tolerances, and life-history traits. However, for species that we expect are vulnerable to climate change yet are understudied, like many amphibians, we often lack information required to construct CCVAs using existing methods. We used the CCVA framework to construct trait-based models based on life history theory, using empirical evidence of traits and distributions that reflected sensitivity of amphibians to environmental perturbation. We performed CCVAs for amphibians in 7 states in the north-central USA, focusing on 31 aquatic-breeding species listed as species of greatest conservation need by at least 1 state. Because detailed information on habitat requirements is unavailable for most amphibian species, we used species distributions and information on traits expected to influence vulnerability to a drying climate (e.g., clutch size and habitat breadth). We scored species vulnerability based on changes projected for mid-century (2040-2069) from 2 climate models representing "least-dry" and "most-dry" scenarios for the region. Species characteristics useful for discriminating vulnerability in our models included small range size, small clutch size, inflexible diel activity patterns, and smaller habitat breadth. When projected climate scenarios included a mix of drier and wetter conditions in the future, the exposure of a species to drying conditions was most important to relative rankings. When the scenario was universally drier, species characteristics were more important to relative rankings. Using information typically available even for understudied species and a range of climate projections, our results highlight the potential of using life history traits as indicators of relative climate vulnerability. The commonalities we identified provide a framework that can be used to assess other understudied species threatened by climate change. 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Increasing temperatures and climate-driven disturbances like wildfire are a growing threat to many species, including cold-water specialists. Montane areas and cold streams are often considered climate refugia that buffer communities against change. However, climate refugia are often species-specific, and despite growing awareness that life histories and habitat requirements shape responses to change, small or non-game species are often under-represented in monitoring and planning programs. A recent study in Montana, USA, revealed much larger warming-related declines in occupancy for small, non-game slimy sculpin (Cottus cognatus) between 1993 and 1995 and 2011-2013 than for two socially valued salmonid fishes that shape regional conservation efforts. To broaden insight into climate change vulnerabilities of headwater stream communities, we analyzed data for Rocky Mountain tailed frogs (Ascaphus montanus) that were collected during those same electrofishing surveys for fishes from 241 stream reaches. Tailed frogs occupy small, cold streams and have several life-history traits that make them sensitive to environmental change. We used a Bayesian framework to estimate occupancy, colonization, and extinction dynamics relative to forest canopy, estimated stream temperature, and wildfire effects. Tailed frog occupancy decreased by 19 % from 1993 to 1995 to 2011-2013. Changes in occupancy were linked with increased extinction and reduced colonization where there were fire-driven reductions in canopy cover, and reduced colonization of stream reaches that warmed on average 0.8 degrees C during the study. Our results highlight extensive extirpations for oft-overlooked species and emphasize the importance of including species with diverse habitat requirements and life histories in conservation planning.

ObjectiveHybridization with nonnative Rainbow Trout Oncorhynchus mykiss is a primary threat to the persistence of Westslope Cutthroat Trout O. clarkii lewisi. Managers concerned with conserving migratory populations of Westslope Cutthroat Trout in the presence of Rainbow Trout often face the predicament of tolerating the spread of hybridization, intentionally isolating Westslope Cutthroat Trout populations, or suppressing Rainbow Trout source populations.MethodsSelective passage of migratory Westslope Cutthroat Trout above existing barriers is a management approach with the potential to limit hybridization, while minimizing the population impacts of barriers in populations with preexisting low levels of hybridization. We took a before-after-control-impact approach to evaluate a phenotype-based selective passage management program for migratory Westslope Cutthroat Trout in the Jocko River, Montana.ResultOf the 364 genotyped individuals selectively passed upstream of a barrier, 82% had a proportion of Rainbow Trout admixture < 0.01 and 98% had < 0.10. Over 14 years (2005-2019), there was no significant increase in hybridization at sites (n = 12) upstream of the barrier, but metrics increased within some of our control (no barrier, n = 8) sites. This increase was greatest at a site just downstream from the barrier, suggesting that blocked fish might have spawned opportunistically in this adjacent tributary.ConclusionWe demonstrate that phenotypic traits were useful in implementing a selective Westslope Cutthroat Trout passage program that allowed managers to promote the migratory life history without increasing nonnative admixture in this watershed.

The spread of aquatic invasive species typically occurs through a combination of natural and human mediated dispersal. For many aquatic invasive species, natural dispersal is limited to aquatic corridors connecting habitat. In contrast, human transport may facilitate more distant dispersal and transport among disconnected waterbodies. Genetic information can serve as a powerful tool to track invasion histories and identify both the sources and mechanisms of invasive species dispersal. We used genetic information to understand invasion history and dynamics of expanding northern pike invasion in the Columbia River basin. Results indicate that the initial introduction of northern pike into the Pend Oreille River (in eastern Washington State) resulted from human transport of fish, not dispersal from established populations upstream. Subsequent reproduction and natural dispersal from the Pend Oreille River resulted in downstream expansion of northern pike into Lake Roosevelt, a reservoir within the mainstem Columbia River. These results highlight the need for a holistic approach to suppression of invasive species. Immediate efforts must address the biological mechanisms of natural dispersal. Sustained suppression and eradication must take a broad approach that includes coordination between management agencies, as well as policy and public outreach aimed at prevention of repeated human transport events. The genetic database created from this study has already been used to eliminate potential source populations for new northern pike invasions in Washington State outside the Columbia River basin. This highlights the utility of genetic monitoring for both immediate and long-term applications to managing aquatic species invasions.

Amphibian populations are sensitive to environmental temperatures and moisture, which vary with local weather conditions and may reach new norms and extremes as contemporary climate change progresses. Using long-term (11–16 years) mark-recapture data from 10 populations of the Columbia spotted frog (Rana luteiventris) from across its U.S. range, we addressed hypotheses about how demographic relationships to weather depend upon a population’s position along climate gradients. We estimated the effect of seasonal weather on annual survival probability and recruitment rates both within populations and across the species’ range from subalpine forests to semi-arid deserts. We calculated population-specific weather variables that captured seasonal temperature and precipitation between summer sampling events, both for periods when frogs were active (spring to fall) and inactive (winter). Across all populations, we marked 15,885 adult frogs, with 33% of frogs recaptured at least once. Population demography varied with seasonal weather across the species’ range. Annual adult survival probability and recruitment rates of each population were influenced by a unique set of seasonal temperature and precipitation variables, particularly in winter and spring. Hence, adult survival varied with local conditions but, when analyzed across all populations, was predictable along a species-environment response curve associated with the timing of snowmelt and spring moisture. In contrast, recruitment rates for each population peaked at different values along an environmental gradient associated with the amount of snow during winter, and fall temperature and moisture levels, suggesting that recruitment may be responding to local conditions independently within each population. These findings highlight that sampling across the environmental (i.e., elevational and meteorological) gradients within a species range is necessary to predict species-level responses to regional climate change. This study also provides evidence of the importance of winter conditions on the demography of temperate amphibians, conditions that are already responding to climate change. Finally, this study further emphasizes that local context and spatiotemporal scale of inquiry remain paramount to understanding and potentially managing for climate effects on populations of amphibian species with broad geographic ranges.

Temperature is a critical driver of ectotherm life-history strategies, whereby a warmer environment is associated with increased growth, reduced longevity and accelerated senescence. Increasing evidence indicates that thermal adaptation may underlie such life-history shifts in wild populations. Single nucleotide polymorphisms (SNPs) and copy number variants (CNVs) can help uncover the molecular mechanisms of temperature-driven variation in growth, longevity and senescence. However, our understanding of these mechanisms is still limited, which reduces our ability to predict the response of non-model ectotherms to global temperature change. In this study, we examined the potential role of thermal adaptation in clinal shifts of life-history traits (i.e. life span, senescence rate and recruitment) in the Columbia spotted frog Rana luteiventris along a broad temperature gradient in the western United States. We took advantage of extensive capture-recapture datasets of 20,033 marked individuals from eight populations surveyed annually for 14-18 years to examine how mean annual temperature and precipitation influenced demographic parameters (i.e. adult survival, life span, senescence rate, recruitment and population growth). After showing that temperature was the main climatic predictor influencing demography, we used RAD-seq data (50,829 SNPs and 6,599 putative CNVs) generated for 352 individuals from 31 breeding sites to identify the genomic signatures of thermal adaptation. Our results showed that temperature was negatively associated with annual adult survival and reproductive life span and positively associated with senescence rate. By contrast, recruitment increased with temperature, promoting the long-term viability of most populations. These temperature-dependent demographic changes were associated with strong genomic signatures of thermal adaptation. We identified 148 SNP candidates associated with temperature including three SNPs located within protein-coding genes regulating resistance to cold and hypoxia, immunity and reproduction in ranids. We also identified 39 CNV candidates (including within 38 transposable elements) for which normalized read depth was associated with temperature. Our study indicates that both SNPs and structural variants are associated with temperature and could eventually be found to play a functional role in clinal shifts in senescence rate and life-history strategies in R. luteiventris. These results highlight the potential role of different sources of molecular variation in the response of ectotherms to environmental temperature variation in the context of global warming.

Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 populations (77 species) of nonavian reptiles and amphibians. We test hypotheses of how thermoregulatory mode, environmental temperature, protective phenotypes, and pace of life history contribute to demographic aging. Controlling for phylogeny and body size, ectotherms display a higher diversity of aging rates compared with endotherms and include phylogenetically widespread evidence of negligible aging. Protective phenotypes and life-history strategies further explain macroevolutionary patterns of aging. Analyzing ectothermic tetrapods in a comparative context enhances our understanding of the evolution of aging.

Variation in temperature is known to influence mortality patterns in ectotherms. Even though a few experimental studies on model organisms have reported a positive relationship between temperature and actuarial senescence (i.e., the increase in mortality risk with age), how variation in climate influences the senescence rate across the range of a species is still poorly understood in free-ranging animals. We filled this knowledge gap by investigating the relationships linking senescence rate, adult lifespan, and climatic conditions using long-term capture-recapture data from multiple amphibian populations. We considered two pairs of related anuran species from the Ranidae (Rana luteiventris and Rana temporaria) and Bufonidae (Anaxyrus boreas and Bufo bufo) families, which diverged more than 100 Mya and are broadly distributed in North America and Europe. Senescence rates were positively associated with mean annual temperature in all species. In addition, lifespan was negatively correlated with mean annual temperature in all species except A. boreas In both R. luteiventris and A. boreas, mean annual precipitation and human environmental footprint both had negligible effects on senescence rates or lifespans. Overall, our findings demonstrate the critical influence of thermal conditions on mortality patterns across anuran species from temperate regions. In the current context of further global temperature increases predicted by Intergovernmental Panel on Climate Change scenarios, a widespread acceleration of aging in amphibians is expected to occur in the decades to come, which might threaten even more seriously the viability of populations and exacerbate global decline.

Human-mediated hybridization threatens many native species, but the effects of introgressive hybridization on life-history expression are rarely quantified, especially in vertebrates. We quantified the effects of non-native rainbow trout admixture on important life-history traits including growth and partial migration behavior in three populations of westslope cutthroat trout over five years. Rainbow trout admixture was associated with increased summer growth rates in all populations and decreased spring growth rates in two populations with cooler spring temperatures. These results indicate that non-native admixture may increase growth under warmer conditions, but cutthroat trout have higher growth rates during cooler periods. Non-native admixture consistently increased expression of migratory behavior, suggesting that there is a genomic basis for life-history differences between these species. Our results show that effects of interspecific hybridization on fitness traits can be the product of genotype-by-environment interactions even when there are minor differences in environmental optima between hybridizing species. These results also indicate that while environmentally mediated traits like growth may play a role in population-level consequences of admixture, strong genetic influences on migratory life-history differences between these species likely explains the continued spread of non-native hybridization at the landscape-level, despite selection against hybrids at the population-level.

Climate warming is expected to have substantial impacts on native trout across the Rocky Mountains, but there is little understanding of how these changes affect future distributions of co-occurring native fishes within population strongholds. We used mixed-effects logistic regression to investigate the role of abiotic (e.g., temperature) and biotic factors (bull trout presence, Salvelinus confluentus) on distributions of westslope cutthroat trout (Oncorhynchus clarkii lewisi; WCT) in the North Fork Flathead River, USA and Canada. The probability of WCT presence increased with stream temperature and decreased with channel gradient and bull trout presence, yet the effect of bull trout was reduced with increasing pool densities. Combining this model with spatially explicit stream temperature projections, we predict a 29% increase in suitable habitat under high emissions through 2075, with gains at mid-elevation sites predicted to exceed bull trout thermal tolerances and high-elevation sites expected to become more thermally suitable for WCT. Our study illustrates the importance of considering abiotic and biotic drivers to assess species response to climate change, helping to guide local-scale climate adaptation and management.

Small waterbodies are numerically dominant in many landscapes and provide several important ecosystem services, but automated measurement of waterbodies smaller than a standard Landsat pixel (0.09 ha) remains challenging. To further evaluate sub‐Landsat pixel techniques for estimating inundation extent of small waterbodies (basin area: 0.06–1.79 ha), we used a partial spectral unmixing method with matched filtering applied to September 1985–2018 Landsat 5 and eight imagery from southern Arizona, USA. We estimated trends in modeled surface water area each September and evaluated the ability of several common drought indices to explain variation in mean water area. Our methods accurately classified waterbodies as dry or inundated (Landsat 5: 91.3%; Landsat 8: 98.9%) and modeled and digitized surface water areas were strongly correlated ( R 2 = 0.70–0.92; bias = −0.024 to −0.015 ha). Estimated surface water area was best explained by the 3‐month seasonal standardized precipitation index (SPI03; July‒September). We found a wide range of estimated relationships between drought indices (e.g. SPI vs. Palmer Drought Severity Index) and estimated water area, even for different durations of the same drought index (e.g. SPI01 vs. SPI12). Mean waterbody surface area decreased by ~14% from September 1985 to September 2018, which matches declines in local annual precipitation and regional trends of reduced inundation extent of larger waterbodies. These results emphasize the importance of understanding local systems when relying on drought indices to infer variation in past or future surface water dynamics. Several challenges remain before widespread application of sub‐pixel methods is feasible, but our results provide further evidence that partial spectral unmixing with matched filtering provides reliable measures of inundation extent of small waterbodies.

Human activities that fragment fish habitat have isolated inland salmonid populations. This isolation is associated with loss of migratory life histories and declines in population density and abundance. Isolated populations exhibiting only resident life histories may be more likely to persist if individuals can increase lifetime reproductive success by maturing at smaller sizes or earlier ages. Therefore, accurate estimates of age and size at maturity across resident salmonid populations would improve estimates of population viability. Commonly used methods for assessing maturity such as dissection, endoscopy and hormone analysis are invasive and may disturb vulnerable populations. Ultrasound imaging is a non-invasive method that has been used to measure reproductive status across fish taxa. However, little research has assessed the accuracy of ultrasound for determining maturation status of small-bodied fish, or reproductive potential early in a species’ reproductive cycle. To address these knowledge gaps, we tested whether ultrasound imaging could be used to identify maturing female Westslope Cutthroat Trout ( Oncorhynchus clarkii lewisi ). Our methods were accurate at identifying maturing females reared in a hatchery setting up to eight months prior to spawning, with error rates ≤ 4.0%; accuracy was greater for larger fish. We also imaged fish in a field setting to examine variation in the size of maturing females among six wild, resident populations of Westslope Cutthroat Trout in western Montana. The median size of maturing females varied significantly across populations. We observed oocyte development in females as small as 109 mm, which is smaller than previously documented for this species. Methods tested in this study will allow researchers and managers to collect information on reproductive status of small-bodied salmonids without disrupting fish during the breeding season. This information can help elucidate life history traits that promote persistence of isolated salmonid populations.

Introduced species can alter the dynamics of food webs, species interactions, populations, and communities and can reduce a system's recreational value. Several reports have documented the establishment of Redside Shiners Richardsonius balteatus in mountain lakes, resulting in declines in sizes and abundance of salmonid species. An illegal bait bucket release introduced Redside Shiners into Green Canyon Lake, Montana, USA, in the 1980s. Recently, local anglers began complaining of decreases in size and catch rates of Westslope Cutthroat Trout (WCT) Oncorhynchus clarkii lewisi. Our first objective was to understand the diet overlap between Redside Shiners and WCT in Green Canyon Lake. Based on delta N-15 and delta C-13 isotopic signatures and diet contents, we found little evidence that WCT were substantially preying upon Redside Shiners. We found moderate diet overlap between WCT and Redside Shiners, with both species predominately feeding on Diptera. For our second objective, we developed a population model to assess potential options for eradicating Redside Shiners. We observed Redside Shiners up to 7 years of age and with a maximum TL of 159 mm, high annual survival (50%), and mature females at age 2. We used an age-structured model to evaluate two hypothetical suppression actions: piscicide application and stocking of Rainbow Trout O. mykiss. Four consecutive piscicide treatments had a 20% probability of eradicating Redside Shiners, increasing to a 100% eradication probability after seven treatments. Bioenergetic simulations indicated that an individual Rainbow Trout (500 g) would consume 1,759 g of Redside Shiners annually. Incorporating this predation mortality and a compensatory response (50% increase in age-1 survival), we estimated that maintained abundances of up to 700 Rainbow Trout would not cause a decline in the Redside Shiner population. Our results suggest that eradication of an introduced prey fish like the Redside Shiner would be difficult and that effective removal will require dedicated effort and resources by managers.

Riverine fishes are sensitive to human-induced changes to their ecosystems and have experienced substantial declines in the past century. The presence and operation of dams modifies natural flow regimes thereby disrupting cues that signal migration and negatively influencing habitats critical to riverine fishes. Blue Suckers (Cycleptus elongatus) make large annual movements, require large and unfragmented reaches of river, and may be sensitive to modifications of cues that initiate migration. We assessed the influence of individual and abiotic factors on home ranges and movements of 62 transmittered Blue Suckers from 2006-2014 in the Missouri River upstream of Fort Peck Reservoir in Montana. Populations in this area are disjunct from those downstream and are influenced by upstream dam regulation. Blue Suckers used large expanses of river with overall home ranges similar to 88 river kilometers, but these home ranges were about two times smaller than reported elsewhere. Increasing discharge and water temperature were associated with movement rate and movement probability and cued spawning movements of Blue Suckers. Movement rates increased with discharge to peak and decreased thereafter. Surprisingly, movement rate and probability were highest at the lowest water temperatures we observed (similar to 1-58 degrees C) unlike previous studies in other systems when peak movement occurred at >= 10 degrees C. Blue Suckers aggregated and showed interannual fidelity to several locations during spawning. Aggregation and fidelity suggest that optimal spawning areas, which exist in tributaries, may be limited within our study area. Our results support evidence that riverine fishes require natural trends in discharge and water temperature, including occasional flood pulses and connectivity among seasonal habitats. The Upper Missouri River retains pseudonatural discharge and temperature regimes that elicit responses of Blue Sucker to environmental cues, but other rivers may not. Preserving or restoring these features, and entire riverscapes, would maintain natural environmental cues and habitats required by riverine fishes to complete their life histories.

A broader understanding of how landscape resistance influences climate change vulnerability for many species is needed, as is an understanding of how barriers to dispersal may impact vulnerability. Freshwater biodiversity is at particular risk, but previous studies have focused on popular cold‐water fishes (e.g., salmon, trout, and char) with relatively large body sizes and mobility. Those fishes may be able to track habitat change more adeptly than less mobile species. Smaller, less mobile fishes are rarely represented in studies demonstrating effects of climate change, but depending on their thermal tolerance, they may be particularly vulnerable to environmental change. By revisiting 280 sites over a 20 year interval throughout a warming riverscape, we described changes in occupancy (i.e., site extirpation and colonization probabilities) and assessed the environmental conditions associated with those changes for four fishes spanning a range of body sizes, thermal and habitat preferences. Two larger‐bodied trout species exhibited small changes in site occupancy, with bull trout experiencing a 9.2% (95% CI = 8.3%–10.1%) reduction, mostly in warmer stream reaches, and westslope cutthroat trout experiencing a nonsignificant 1% increase. The small‐bodied cool water slimy sculpin was originally distributed broadly throughout the network and experienced a 48.0% (95% CI = 42.0%–54.0%) reduction in site occupancy with declines common in warmer stream reaches and areas subject to wildfire disturbances. The small‐bodied comparatively warmer water longnose dace primarily occupied larger streams and increased its occurrence in the lower portions of connected tributaries during the study period. Distribution shifts for sculpin and dace were significantly constrained by barriers, which included anthropogenic water diversions, natural step‐pools and cascades in steeper upstream reaches. Our results suggest that aquatic communities exhibit a range of responses to climate change, and that improving passage and fluvial connectivity will be important climate adaptation tactics for conserving aquatic biodiversity.