I am a research fisheries biologist with the U.S. Geological Survey’s Northern Rocky Mountain Science Center and an adjunct faculty in the Ecology Department at Montana State University in Bozeman, MT.
Research interests:
I am an applied biologist with goals of providing robust information to inform the management and conservation of aquatic ecosystems. My specific research focuses on improving our understanding of how natural and anthropogenic disturbances influence aquatic ecosystems, the interactions between native and non-native species, and how the life-history patterns and template of aquatic systems will be altered under anticipated changes in global and regional climates. Within this framework my research program consists of a combination of field studies and analytical studies to advance conservation and management and at the same time develop new paradigms in aquatic ecology. My research is built upon a premise of strong collaboration and interaction to facilitate effective research.
Mendenhall Project Title: Forecasting the Effects of Climate Change on the Interactions of Native and Nonnative Salmonids.
Education and Certifications
Ph.D. Aquatic Ecology. Utah State University
B.S. Biology. University of Utah
B.A. Economics. Bates College
Science and Products
Assessing the Vulnerability of Native Trout in the Northern Rockies: Linking Science and Management for Climate Adaptation
Integrated Ecohydrological Science in the Northern Rocky Mountains — the variability of water availability and the effects on ecosystems
Predicting Climate-Induced Expansions of Invasive Fish in the Pacific Northwest: Implications for Climate Adaptation of Native Salmon and Trout
Understanding Climate Impacts on Native and Invasive Fish for Conservation, Management, and Economic Goals in the Northern Rockies
Western Waters Invasive Species and Disease Research Program
Evaluating the reintroduction potential and limiting factors associated with anadromous fish reintroductions in the Upper Lewis River, WA
Food web and Pyramid Lake fishery evaluation
Forecasting the effects of climate change on the interactions of native and non-native salmonids
Improving our understanding of forest-road effects on substrate in headwater streams of the Southwest Crown of the Continent
Developing stream temperature networks for the Greater Yellowstone to aid in managing aquatic resources under a changing climate
Evaluating the linkages between regional climate patterns, local climate data, and native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) and non-native brook trout (Salvelinus fontinalis) growth, survival, and life-history expressions.
Modeling species response to environmental change: development of integrated, scalable Bayesian models of population persistence
Cutthroat trout mark-recapture and growth data from western Montana and western Wyoming 2011-2016
Juvenile Smallmouth Bass Sampling from the Yellowstone River, Montana 2016-2019
Environmental DNA data, fish abundance data, and stream habitat data from northwest Montana and northeast Washington and southern British Columbia, Canada
Yellowstone Cutthroat Trout and Brown Trout capture-recapture and diet data from Duck Creek, MT in summer and fall (2013-2016)
Shrinking body size and climate warming: Many freshwater salmonids do not follow the rule
Redd superimposition mediates the accuracy, precision, and significance of redd counts for cutthroat trout
Using continuous surveys to evaluate precision and bias of inferences from design-based reach-scale sampling of stream habitat
Socioeconomic resilience to climatic extremes in a freshwater fishery
Stream size, temperature, and density explain body sizes of freshwater salmonids across a range of climate conditions
Climate change and expanding invasive species drive widespread declines of native trout in the northern Rocky Mountains, USA
Evaluation of remote site incubators to incubate wild- and hatchery-origin Westslope Cutthroat Trout embryos
It’s complicated…environmental DNA as a predictor of trout and char abundance in streams
Detecting population declines via monitoring the effective number of breeders (Nb)
Appendix C: Patterns of bull trout Salvelinus confluentus demography, life history and abundance in the North Fork Lewis River — 2019 Annual Report
Climate-induced expansions of invasive species in the Pacific Northwest, North America: A synthesis of observations and projections
New insights into the ecology of adfluvial Bull Trout and the population response to the Endangered Species Act in the North Fork Lewis River, Washington
Science and Products
- Science
Assessing the Vulnerability of Native Trout in the Northern Rockies: Linking Science and Management for Climate Adaptation
Trout are one of the most culturally, economically, and ecologically important groups of freshwater fishes in the Rocky Mountain region. However, human impacts and climate change are significantly altering freshwater ecosystems that support native trout species. Despite their broad importance, many of the region’s trout populations are threatened and some require immediate conservation efforts toIntegrated Ecohydrological Science in the Northern Rocky Mountains — the variability of water availability and the effects on ecosystems
Our primary goal is to better understand and characterize how stream environments and the ecosystems they support are influenced by climate change and drought in the Northern Rocky Mountains.Predicting Climate-Induced Expansions of Invasive Fish in the Pacific Northwest: Implications for Climate Adaptation of Native Salmon and Trout
The headwaters of the Columbia River Basin in the Northern Rocky Mountains region is widely recognized as a stronghold for native fish, containing some of the last remaining connected cold-water habitats for species such as the threatened bull trout and native westslope cutthroat trout. However, as temperatures rise, non-native invasive fish species could be poised to prosper in the region as condUnderstanding Climate Impacts on Native and Invasive Fish for Conservation, Management, and Economic Goals in the Northern Rockies
As the origin of three major basins that drain the Columbia, Missouri, and Saskatchewan rivers, Montana is the hydrologic apex for North America. The Northern Rocky Mountain region is home to some of the last remaining interconnected habitats for many native fishes, including the threatened bull trout and native westslope cutthroat trout. The Northern Rockies are also experiencing rapidly changingWestern Waters Invasive Species and Disease Research Program
Researchers at the Northern Rocky Mountain Science Center's Western Waters Invasive Species and Disease Research Program work extensively with federal, state, tribal, regional, and local partners to deliver science to improve early detection and prevention of invasive species and disease; understand complex interactions that promote invasive species and disease, and their impacts (and associated...Evaluating the reintroduction potential and limiting factors associated with anadromous fish reintroductions in the Upper Lewis River, WA
Hydropower facilities on the Lewis River, WA eliminated historic runs of anadromous species to the headwaters of the Lewis River. As anadromous reintroductions are considered and implemented, there remains considerable uncertainty in the viability of reintroductions in reservoir and tributary systems where large populations of non-native species persist and where spawning and rearing habitat may...Food web and Pyramid Lake fishery evaluation
Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) is an important cultural and economic resource to the Pyramid Lake Paiute Tribe and a Threatened species under the Endangered Species Act. Here we are integrating the food web information with field estimates of Lahontan cutthroat vital rate and growth information to guide future management and recovery efforts within Pyramid Lake and the...Forecasting the effects of climate change on the interactions of native and non-native salmonids
Changes in temperature and precipitation patterns under global climate change are expected to expand the range of suitable habitat for non-natives within stream networks, resulting in significant increases in the distribution and abundance of non-natives. However, our understanding of how landscape attributes can affect local thermal and hydrologic patterns suggests that changes in global climate...Improving our understanding of forest-road effects on substrate in headwater streams of the Southwest Crown of the Continent
In 2010, Congress established ten decade-long Collaborative Forest Landscape Restoration Program projects to carry out fuel reduction and ecological restoration treatments on public lands across the country. The Southwest Crown of the Continent was selected as one of the locations under this initiative, given the importance of this region to the economic vitality of local communities and the...Developing stream temperature networks for the Greater Yellowstone to aid in managing aquatic resources under a changing climate
The topographic diversity and extensive area of protected public land within the Greater Yellowstone demonstrate the importance of this region as a natural resource reserve. Understanding the effects of anticipated changes in climate on aquatic resources and means for managing these resources will ultimately require accurate linkages between empirical data and regional climatic patterns. This...Evaluating the linkages between regional climate patterns, local climate data, and native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) and non-native brook trout (Salvelinus fontinalis) growth, survival, and life-history expressions.
Beyond large-scale climate models, it is becoming increasingly important to quantify how regional climate patterns link with in situ stream temperatures and hydrologic regimes and concomitantly, fish behavior, growth, and survival. Here, we are using comprehensive mark-recapture techniques to evaluate how changing climatic conditions are likely to influence native westslope cutthroat trout and non...Modeling species response to environmental change: development of integrated, scalable Bayesian models of population persistence
Estimating species response to environmental change is a key challenge for ecologists and a core mission of the USGS. Effective forecasting of species response requires models that are detailed enough to capture critical processes and at the same time general enough to allow broad application. This tradeoff is difficult to reconcile with most existing methods. We propose to extend and combine exis - Data
Cutthroat trout mark-recapture and growth data from western Montana and western Wyoming 2011-2016
Data include a mark-recapture dataset of cutthroat trout. Data indicate date of marking and recapture, size at marking, growth, basin data were collected, year data were collected, and unique identification tags.Juvenile Smallmouth Bass Sampling from the Yellowstone River, Montana 2016-2019
Field data of age-0 smallmouth bass (Micropterus dolomieu) estimated age, lengths and weights, distribution from field sampling, and results from environmental DNA surveys from the Yellowstone River in Montana. Data were used in conjunction with existing stream temperature data from USGS gages to evaluate if temperature is related to age-0 size at the onset of winter.Environmental DNA data, fish abundance data, and stream habitat data from northwest Montana and northeast Washington and southern British Columbia, Canada
Field estimates of the abundance of two trout species (bull trout and westslope cutthroat trout) in Montana and rainbow trout in Washington and British Columbia were collected in concert with environmental DNA samples (eDNA) to evaluate if eDNA copy numbers correlated with abundance of trout. In addition, stream habitat data including channel units (pools, riffles), substrate, large woody debris,Yellowstone Cutthroat Trout and Brown Trout capture-recapture and diet data from Duck Creek, MT in summer and fall (2013-2016)
We collected lengths and weights and diets of Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) and brown trout (Salmo trutta) above (Yellowstone cutthroat trout allopatry) and below (Yellowstone cutthroat trout sympatry with brown trout) a natural barrier in Duck Creek, Montana. - Publications
Filter Total Items: 49
Shrinking body size and climate warming: Many freshwater salmonids do not follow the rule
Declining body size is believed to be a universal response to climate warming and has been documented in numerous studies of marine and anadromous fishes. The Salmonidae are a family of coldwater fishes considered to be among the most sensitive species to climate warming; however, whether the shrinking body size response holds true for freshwater salmonids has yet to be examined at a broad spatialAuthorsMary Solakas, Zachary S. Feiner, Robert Al-Chokhachy, Phaedra E. Budy, Tyrell DeWeber, Jouko Sarvala, Greg G. Sass, Scott A. Tolentino, Timothy E. Walsworth, Olaf P. JensenRedd superimposition mediates the accuracy, precision, and significance of redd counts for cutthroat trout
Redd counts are commonly applied to estimate spawning population size for salmonids and allow for broad spatial and temporal coverage in monitoring efforts. However, the utility of redd counts may be compromised by observation error, particularly with respect to superimposition, where later arriving spawners construct redds overlapping existing redds. Here, we provide a mechanistic evaluation of tAuthorsJeffrey R. Baldock, Robert Al-Chokhachy, Timothy E. Walsworth, Annika W. WaltersUsing continuous surveys to evaluate precision and bias of inferences from design-based reach-scale sampling of stream habitat
Accurately estimating stream characteristics is essential for managing and restoring populations and aquatic ecosystems. Reach-based sampling designs have been used extensively to collect fisheries related data; however, few studies have examined the effectiveness of reach-based sampling designs for stream habitat assessments. Here, we used continuous habitat surveys to census stream attributes inAuthorsChristopher L. Clark, Robert Al-Chokhachy, Kai RossSocioeconomic resilience to climatic extremes in a freshwater fishery
Heterogeneity is a central feature of ecosystem resilience, but how this translates to socioeconomic resilience depends on people’s ability to track shifting resources in space and time. Here, we quantify how climatic extremes have influenced how people (fishers) track economically valuable ecosystem services (fishing opportunities) across a range of spatial scales in rivers of the northern RockyAuthorsTimothy Joseph Cline, Clint C. Muhlfeld, Ryan P. Kovach, Robert Al-Chokhachy, David Schmetterling, Diane Whited, Abigail LynchStream size, temperature, and density explain body sizes of freshwater salmonids across a range of climate conditions
Climate change and anthropogenic activities are altering the body sizes of fishes, yet our understanding of factors influencing body size for many taxa remains incomplete. We evaluated the relationships between climate, environmental, and landscape attributes and the body size of different taxa of freshwater trout (Salmonidae) in the USA. Hierarchical spatial modeling across a gradient of habitatsAuthorsRobert K. Al-Chokhachy, Benjamin Letcher, Clint C. Muhlfeld, Jason Dunham, Timothy Joseph Cline, Nathaniel P. Hitt, James Roberts, David SchmetterlingClimate change and expanding invasive species drive widespread declines of native trout in the northern Rocky Mountains, USA
Climate change and invasive species are major threats to native biodiversity, but few empirical studies have examined their combined effects at large spatial and temporal scales. Using 21,917 surveys collected over 30 years, we quantified the impacts of climate change on the past and future distributions of five interacting native and invasive trout species throughout the northern Rocky Mountains,AuthorsDonovan A. Bell, Ryan P. Kovach, Clint C. Muhlfeld, Robert Al-Chokhachy, Timothy Joseph Cline, Diane C. Whited, David Schmetterling, Paul M Lukacs, Andrew R. WhiteleyEvaluation of remote site incubators to incubate wild- and hatchery-origin Westslope Cutthroat Trout embryos
Fish managers must weigh trade-offs among cost, speed, efficiency, and ecological adaptation when deciding how to translocate native salmonids to either establish or genetically augment populations. Remote site incubators (RSIs) appear to be a reasonable strategy, but large-scale evaluations of this method have been limited. We used 129 RSIs to incubate >35,700 eyed embryos of Westslope CutthroatAuthorsBradley B. Shepard, Patrick Clancey, Lee M. Nelson, Carter Kruse, Robert K. Al-Chokhachy, Daniel Drinan, Alexander V. ZaleIt’s complicated…environmental DNA as a predictor of trout and char abundance in streams
The potential to provide inferences about fish abundance from environmental (e)DNA samples has generated great interest. However, the accuracy of these abundance estimates is often low and variable across species and space. A plausible refinement is the use of common aquatic habitat monitoring data to account for attributes that influence eDNA dynamics. We therefore evaluated the relationships betAuthorsAdam J. Sepulveda, Robert Al-Chokhachy, Matthew Laramie, Kyle Crapster, Ladd Knotek, Brian T. Miller, Alexander V. Zale, David PilliodDetecting population declines via monitoring the effective number of breeders (Nb)
Estimating the effective population size and effective number of breeders per year (Nb) can facilitate early detection of population declines. We used computer simulations to quantify bias and precision of the one-sample LDNe estimator of Nb in age-structured populations using a range of published species life history types, sample sizes, and DNA markers. Nb estimates were biased by ~5%–10% when uAuthorsGordon Luikart, Tiago Antao, Brian K. Hand, Clint C. Muhlfeld, Matthew C. Boyer, Ted Corsart, Brian Trethewey, Robert K. Al-Chokhachy, Robin S. WaplesAppendix C: Patterns of bull trout Salvelinus confluentus demography, life history and abundance in the North Fork Lewis River — 2019 Annual Report
No abstract available.AuthorsRobert K. Al-Chokhachy, Jeremiah DoyleClimate-induced expansions of invasive species in the Pacific Northwest, North America: A synthesis of observations and projections
Climate change may facilitate the expansion of non-native invasive species (NIS) in aquatic and terrestrial systems. However, empirical evidence remains scarce and poorly synthesized at scales necessary for effective management. We conducted a literature synthesis to assess the state of research on the observed and predicted effects of climate change on a suite of 398 aquatic and terrestrial NIS nAuthorsJennifer Gervais, Ryan P. Kovach, Adam J. Sepulveda, Robert K. Al-Chokhachy, J. Joseph Giersch, Clint C. MuhlfeldNew insights into the ecology of adfluvial Bull Trout and the population response to the Endangered Species Act in the North Fork Lewis River, Washington
Like many other salmonids, Bull Trout Salvelinus confluentus migratory life-history expressions are becoming increasingly rare. A critical step in effectively refining management and conservation strategies is a robust assessment of the effectiveness of such strategies and key biological information used in monitoring and recovery planning. To address this need, we integrated a variety of methodAuthorsRobert K. Al-Chokhachy, Jeremiah Doyle, James Lampierth