Klamath River Basin Research Articles

Recasting Klamath Dam Removal as Eco-Cultural Revitalization and Restorative Justice through Karuk Tribal Leadership

Moving from an era of dam building to dam removal brings additional perspectives to indigenous water governance and hydrosocial relations in the Klamath River Basin (US). This collaborative research initiative with the Karuk Tribe builds greater understanding of the sociocultural impacts of Klamath dam removal and river restoration through Karuk knowledge. Addressing a knowledge gap around the social dimensions of dam removal, we held focus groups and interviews with Karuk cultural practitioners, tribal leaders, and tribal youth in the six-month period leading up to demolition. Extending beyond a focus on infrastructure removal or single-species restoration, we consider how Indigenous environmental relations and cosmologies are embedded in dam removal and river restoration. Specifically, Karuk knowledge shifts the significance of dam removal by elucidating deeply interconnected ecological, cultural, and ceremonial relations that are co-constituted with the Klamath watershed, thereby recasting dam removal as a holistic eco-cultural revitalization initiative. This reconfigures dam removal goals to include improving community health and well-being, enhancing spiritual elements of river restoration, responding to colonial legacies, and engaging tribal youth. In the Klamath case, restorative justice becomes possible through Karuk participation in river restoration to facilitate the revitalization of reciprocal relations held between Karuk people and the Klamath River—including Karuk eco-cultural and ceremonial practices for restoring balance in the world.

Using mixed-method analytical historical ecology to map land use and land cover change for ecocultural restoration in the Klamath River Basin (Northern California)

Ecocultural restoration involves the reciprocal repair of ecosystems and revitalization of cultural practices to enhance their mutual resilience to natural and anthropogenic disturbances and climate change stressors. Resilient ecocultural systems are adapted to retain structure and function in the face of disturbances that remain within historical ranges of severity. To assist in ecocultural restoration and management, understanding how a system has historically responded to different types of disturbances is therefore invaluable in understanding how social-ecological resilience can be maintained in the face of future stressors and disturbances. However, records of disturbances and ecocultural responses can be limited for certain landscapes and human communities. In this methods paper, we demonstrate a mixed-method process for integrating oral history, field-based knowledge, archival information, and historical and contemporary aerial images to gain insight into the changes on the Klamath River in Northern California from the 1940s through 2020. We georegistered historical imagery, quantified changes between land cover classes, and contextualized these classifications with qualitative assessments of changes in larger surrounding areas. By synthesizing these data sources with field measurements, mining and other land survey maps, timber management plans, fire and flood histories, and interviews with members of the Karuk Tribe, we were able to reconstruct the land use and land cover change histories at five sites. We noted that recovery of canopy cover from fire and logging practices was faster than for flood, which was faster than recovery from mining, consistent with the relative severity of likely soil disturbance. By combining different sources of information with complementary strengths, we were able to provide managers with site-specific information on recovery from different types of disturbance. Though this approach was labor-intensive, with emerging tools for supervised classification of high-resolution imagery, mixed-method analytical historical ecology could be applied more broadly, supporting ecocultural restoration on a larger scale.

Challenges and Strategies for Knowledge Co-Production in Ecosystem and Natural Hazards Research

The grand environmental challenges society faces cannot be solved without knowledge contributions from communities that are touched by the outcomes and impacts of research. Recognizing and valuing these sources, a research method known as co-production of knowledge involves collaboration of interested parties and knowledge owners in activities ranging from identifying research needs to study design, data collection, interpretation, and evaluation. We present a novel approach to the administrative and financial support for knowledge co-production developed by Oregon Sea Grant and provide examples from two funded project teams. We summarize barriers to these approaches, discuss points of symmetry, and propose good practices. One project emphasized equitable alternative strategies for chronic and acute coastal hazard adaptation and mitigation. The other project looked beyond dam removal in the Klamath River Basin to generate place-based and generalizable understanding of, and equitable decisions around, water quality and socio-ecological systems undergoing change. Both projects provide high-level lessons regarding opportunities and challenges encountered in the engaged research process, highlighting flexibility and adaptability as two important considerations.

Co-production of models to evaluate conservation alternatives for a threatened fish in a rapidly changing landscape

Reintroductions are one means of managing species distributions, but the feasibility of such efforts is uncertain. Here we consider reintroduction for threatened bull trout (Salvelinus confluentus) that currently occupy a small fraction of historically occupied habitats in the upper Klamath River basin owing to climate warming and human modifications of ecosystems. We engaged stakeholders across multiple organizations to co-produce a decision support model that estimated the potential of reintroduction to establish new populations and persistence of donor populations. Stakeholders identified recipient and donor populations, strategy (e.g., artificial propagation, translocation), number of individuals, and life stage of bull trout. The most optimal decision for reintroduction was artificial propagation of 10,000 fry into Annie Creek. This strategy may have negative consequences on donor populations, with the exception of Sun Creek, which was resilient to simulated removal of bull trout. Donor populations and recipient streams identified as most feasible were generally consistent across all of these scenarios. During model development, however, an unexpected and intense wildfire affected half of the streams considered and may have dramatically impacted donor populations. With models in hand from the initial feasibility assessment, we adapted them to further evaluate the potential of supplementation following this massive disturbance. Overall, results of this study indicate the value of developing co-produced tools that can be rapidly adapted to evaluate the consequences of whole-system transformations in near-real-time assessments.

Lampreys in California (Lampetra spp. and Entosphenus spp.): Mitochondrial phylogenetic analysis reveals previously unrecognized lamprey diversity

AbstractObjectiveProtecting biodiversity is important for preserving ecosystem functions and services, and understanding the diversity present in a system is necessary for effective conservation. Lampreys display extensive diversity in morphology and life history strategy. The extent of this diversity and the underlying genetic patterns have not yet been fully characterized. Uncertainty about species boundaries and operational taxonomic units hinders lamprey management and conservation. Limited data have been collected on California lampreys (Lampetra spp. and Entosphenus spp.), but evidence suggests widespread population decline across the west coast of North America. Study objectives were to identify which nominal species are present at study sites across northern and central California, determine whether current taxonomic classifications accurately and sufficiently describe lamprey diversity in California, and characterize the biogeographic distribution of genetically distinct lamprey lineages across the study area.MethodsTo achieve these objectives, this study utilized DNA barcoding, phylogenetic analysis, and species delimitation analysis. Lamprey individuals (N = 87) from 19 sites in the Sacramento–San Joaquin River basin, San Francisco Bay, and Klamath River basin were sequenced for the mitochondrial cytochrome b (cyt b) gene, and the data were combined with publicly available lamprey cyt b sequences for analysis.ResultResults showed relatively deep phylogenetic divergence between Lampetra and Entosphenus. Distinct and genetically divergent lineages were observed within Lampetra, while distinct but genetically similar lineages were observed within Entosphenus. This study revealed novel Lampetra lineages in the Napa River and Alameda Creek, and results suggest that the biogeographic distribution of lamprey diversity may follow patterns observed in other native fishes. Species delimitation results indicated that at least seven separate candidate species of Lampetra can be found in California, suggesting that California holds more species‐level diversity than the expected three nominal Lampetra species known to occur in the state.ConclusionThese results highlight the underestimated diversity of lampreys in California and the need for further assessment of taxonomic classifications and operational taxonomic unit designations of California lampreys.

Enhancing Indigenous Food Sovereignty and Community Health Through the Karuk Agroecosystem Resilience Initiative: We Are Caring for It: xúus nu'éethti.

Indigenous communities in the United States experience some of the highest rates of food insecurity and diet-related diseases despite an abundance of food assistance programs and other public health interventions. New approaches that center Indigenous perspectives and solutions are emerging and urgently needed to better understand and address these challenges. This Practice Note shares lessons learned from ongoing collaboration between the Karuk Tribe and University of California, Berkeley researchers and other partners to assess and enhance food sovereignty among Tribes and Tribal communities in the Klamath River Basin. Through two participatory research and extension projects, we demonstrate the importance of centering Indigenous knowledge to strengthen research findings and identify more culturally appropriate solutions to community identified food access, health, and ecosystem challenges. Key findings suggest that approaches to food sovereignty and community health must emanate from the community, be approached holistically, reflect community values and priorities, and center Indigenous land stewardship.

Water and Endangered Fish in the Klamath River Basin: Do Upper Klamath Lake Surface Elevation and Water Quality Affect Adult Lost River and Shortnose Sucker Survival?

AbstractIn the western United States, water allocation decisions often incorporate the needs of endangered fish. In the Klamath River basin, an understanding of temporal variation in annual survival rates of Shortnose Suckers Chasmistes brevirostris and Lost River Suckers Deltistes luxatus and their relation to environmental drivers is critical to water management and sucker recovery. Extinction risk is high for these fish because most individuals in the populations are approaching their maximum life span and recruitment of new fish into the adult populations has never exceeded mortality losses in the past 22 years. We used a time series of mark–recapture data from the years 1999–2021 to analyze the relationship between lake level, water quality covariates, and survival of adult Shortnose Suckers and two spawning populations of Lost River Suckers in Upper Klamath Lake, Oregon. We compared competing model hypotheses in a maximum likelihood framework using Akaike's information criterion and then ran the top environmental covariates in a Bayesian framework to estimate how much of the variation in survival was explained by these covariates as compared to random variation. The complementary analyses found almost unequivocal support for our base model without environmental covariates. Estimated adult sucker survival was high across the time series and consistent with sucker life history (mean annual survival = 0.82–0.91). This suggests that adult suckers were generally robust to interannual variation in lake levels as well as consistently poor water quality within the years of our data set. Recovery time is limited, as a declining survival trend for adult suckers in recent years may be due to the onset of senescence. The successful recovery of suckers in Upper Klamath Lake may rely on shifting research from the causes of adult mortality and its relationship with lake surface elevation to the causes of poor recruitment into adult populations.

Population genomic analysis of the Speckled Dace species complex identifies three distinct lineages in California

AbstractObjectiveSpeckled Dace Rhinichthys osculus is small cyprinoid fish that is widespread in western North America. In California and elsewhere it is currently treated as a single species with multiple subspecies, many undescribed. However, these subspecies may represent evolutionary lineages that are cryptic species because they cannot be distinguished using standard morphometric techniques. In this study, we attempt to determine evolutionary lineages within California populations of Speckled Dace using the population genetic and genomic information.MethodsWe used restriction site‐associated DNA sequencing to extract thousands of single‐nucleotide polymorphisms across the genome to identify genetic differences among all the samples from 38 locations in the western USA, with a focus on California. We performed principal component analysis, admixture analysis, estimated pairwise values of the genetic differentiation index FST, and constructed molecular phylogenies to characterize population genetic and phylogenetic relationships among sampled Speckled Dace populations.ResultOur analyses detected three major lineages of Speckled Dace in California that align with geography: (1) Sacramento River, central California coast, Klamath River, and Warner Basin; (2) Death Valley and Lahontan Basin; and (3) Santa Ana River basin, in southern California. These lineages fit well with the geologic history of California, which has promoted long isolation of populations of Speckled Dace and other fishes.ConclusionThe presence of distinct evolutionary lineages indicates that Speckled Dace in California should be managed with distinct population segments to preserve within‐species diversity. This study highlights the importance of genetic analyses for conservation and management of freshwater fishes.

Understanding the conservation challenges and needs of culturally significant plant species through Indigenous Knowledge and species distribution models

Indigenous People in the Klamath River Basin have cared for and utilized ecosystems and component resources since time immemorial, proactively conserving species through continuous use and stewardship. Though many culturally significant plants are still tended and used by Indigenous people, many species are also experiencing prolonged stress from colonial forest management practices and environmental change. By integrating western and Indigenous ways of knowing, as part of a participatory and collaborative research and extension project, we present an approach to informing the conservation of four culturally significant plants (tanoak, evergreen huckleberry, beargrass, and iris) and understanding the influence of bioclimatic factors and stress on Indigenous people’s relationships with plants and the broader forest ecosystem. Mixed methods and ways of knowing generate a detailed assessment of each case study species that presence only species distribution models cannot supply alone. In this study we use MAXENT to model species distributions of our four study species and the flexible coding method in NVivo for qualitative interview and focus group data. Using species distribution models and 127 interviews and focus groups with cultural practitioners, we found significant shifts in huckleberry harvesting times, beargrass and iris cultural use quality, and tanoak acorn availability that must be addressed for the long-term vitality of these species and interconnected cultures and people. Tribes have generations of knowledge, experience, and connection to land that can help inform how to combat stressors and enhance productivity of forest foods and fibers and the health of forest ecosystems.

Using a mechanistic framework to model the density of an aquatic parasite Ceratonova shasta.

Ceratonova shasta is a myxozoan parasite endemic to the Pacific Northwest of North America that is linked to low survival rates of juvenile salmonids in some watersheds such as the Klamath River basin. The density of C. shasta actinospores in the water column is typically highest in the spring (March–June), and directly influences infection rates for outmigrating juvenile salmonids. Current management approaches require quantities of C. shasta density to assess disease risk and estimate survival of juvenile salmonids. Therefore, we developed a model to simulate the density of waterborne C. shasta actinospores using a mechanistic framework based on abiotic drivers and informed by empirical data. The model quantified factors that describe the key features of parasite abundance during the period of juvenile salmon outmigration, including the week of initial detection (onset), seasonal pattern of spore density, and peak density of C. shasta. Spore onset was simulated by a bio-physical degree-day model using the timing of adult salmon spawning and accumulation of thermal units for parasite development. Normalized spore density was simulated by a quadratic regression model based on a parabolic thermal response with river water temperature. Peak spore density was simulated based on retained explanatory variables in a generalized linear model that included the prevalence of infection in hatchery-origin Chinook juveniles the previous year and the occurrence of flushing flows (≥171 m3/s). The final model performed well, closely matched the initial detections (onset) of spores, and explained inter-annual variations for most water years. Our C. shasta model has direct applications as a management tool to assess the impact of proposed flow regimes on the parasite, and it can be used for projecting the effects of alternative water management scenarios on disease-induced mortality of juvenile salmonids such as with an altered water temperature regime or with dam removal.

Conceptualizing Indigenous Cultural Ecosystem Services (ICES) and Benefits under Changing Climate Conditions in the Klamath River Basin and Their Implications for Land Management and Governance

In the Klamath River Basin (KRB) of northern California and southern Oregon, climate-related changes, such as more intense droughts, varied and concentrated precipitation, earlier spring and later fall conditions, extreme temperatures, and decreased snowpack have contributed to increasingly unpredictable plant reproduction and harvest cycles. In this study, we explore contemporary relationships between plants and Indigenous People in the KRB, identifying benefits of cultural ecosystem services (CES) derived from Indigenous stewarding and gathering of culturally significant plants, and discuss how these services may change based on climate change observations and experiences. This study contributes to the conceptualization of Indigenous Cultural Ecosystem Services (ICES), providing a framework for the incorporation of Indigenous concepts, approaches, and perspectives into assessments of ecosystem services (ES) and, particularly, CES. It highlights the value of Indigenous perspectives and observations of climate change effects on plant reproduction and productivity, as well as their contribution to cultural ecosystem resilience and adaptation under changing climate conditions. We propose that incorporating Indigenous concepts and approaches to assessing CES and ES could lead to more holistic management decisions and better-informed climate adaptation initiatives with greater ES for all.

Development of a Tribally-led Gardening Curriculum for Indigenous Preschool Children: The FRESH Study

Development of a Tribally-led Gardening Curriculum for Indigenous Preschool Children: The FRESH Study

Successful Collection and Captive Rearing of Wild-Spawned Larval Klamath Suckers

AbstractShortnose Chasmistes brevirostris and Lost River Suckers Deltistes luxatus endemic to the Klamath River Basin on the California–Oregon border have experienced dramatic population declines in parallel with many other Catostomid species. Captive propagation has become a key element of many endangered fish recovery programs, although there is little evidence of their success in restoring or recovering fish populations. We initiated a novel rearing program for Klamath suckers in 2016 with the goal of developing a husbandry strategy that better balances the ecological, genetic, and demographic risks associated with captive propagation. We collected 4,306 wild-spawned Klamath sucker larvae from a major spawning tributary May–June 2016 and reared them at a geothermal facility established through a partnership with a local landowner and aquaculture expert. Mortality during collection was <1%. We reared larvae in glass aquaria for 17–78 d until they reached approximately 30 mm total length, upon which we moved them to round fiberglass tanks for 14–46 d or until reaching approximately 60 mm total length. Overall survival of larvae to ponding for final growout was 71%. Larval tank-rearing survival was 98% for 37 d until an isolated fish health incident affected three aquarium populations, reducing survival to transfer to 75%. Survival after transfer to round fiberglass tanks for 14–46 d was 94%. This study outlines the first successful collection and early life-history husbandry of wild-spawned endangered Klamath suckers that we are aware of.

Enhancing Food Sovereignty: A Five-year Collaborative Tribal-University Research and Extension Project in California and Oregon

A long history of tribal disenfranchisement through government policies has contributed to a lack of trust and participation by tribal communi­ties in nontribal organizations and initiatives. This article will discuss the process through which new partnerships were forged using a community-based participatory research (CBPR) approach among university researchers, local nontribal organiza­tions, and three Tribes in the Klamath River Basin of southern Oregon and northern California through a five-year federal food security grant. The partnership’s shared goal was to enhance tribal health and food security and food sovereignty in the Klamath River Basin by building a healthy, sus­tainable, and culturally relevant food system. We describe the context that gave rise to this collabo­rative partnership; share reflections on how project goals, objectives, and activities were co-created, adapted, and implemented; and highlight specific examples of research, education, and extension activities, informed by CBPR, that support the tribal goals of strengthening Indigenous food sovereignty. We also share lessons learned from navigating unforeseen challenges in ways that we hope can provide insight for scholars, cooperative extension advisors, nonprofit organizations, and government agencies seeking to build effective partnerships with tribes working toward food system change in Native American communities. See the press release for this article.

Reframing food security by and for Native American communities: a case study among tribes in the Klamath River basin of Oregon and California

Native Americans make up less than 2% of the population of the USA, but suffer from some of the highest rates of food insecurity, poverty, diet-related diseases, and other socioeconomic challenges. This study examined unique attributes of food security in Native American communities in the Klamath River Basin of southern Oregon and northern California to generate a more comprehensive and culturally relevant understanding of Native American food insecurity. Through an in-depth case study among the Karuk, Yurok, Hoopa and Klamath Tribes, in which access to native foods was a central focus, our study examined the experience of food insecurity among tribal members, as well as barriers to and opportunities for building a more healthy, affordable and culturally appropriate food system. We found extremely high rates of food insecurity in participant households, greater than that documented in previous studies of food insecurity in tribal and non-tribal communities in the USA. Additionally, we found that the majority of study participants lacked access to desired native foods, due to reduced availability from restrictive laws and habitat degradation under settler colonialism, and that limited access to native foods is a strong predictor of food insecurity. There is a strong demand for increased access to and consumption of native foods and Native communities are actively engaged in eco-cultural restoration activities to enhance their cultural foodways. To understand contributions and solutions to food insecurity in Native communities, we examined predictors of food security and native foods security and provide new insights into the relationship between these two categories. Results from our study suggest the need to expand the way in which food security is defined and measured in Native American communities, and in indigenous communities more broadly, incorporating more culturally relevant measures, while simultaneously calling for policy change to address the historical underpinnings of contemporary food insecurity among indigenous peoples. Our findings contribute to the growing literature on the value and importance of Native food systems in revitalizing culture and restoring community health and well-being among Native American communities, as well as sovereignty over their food systems.

Electrofishing, Snorkel Spearing, and Piscicide Eradicate Brook Trout From a Small, Isolated Bull Trout Population

Abstract In 1992, a sampling crew from a multiagency group discovered a population of Bull Trout Salvelinus confluentus estimated at approximately 50 individuals in Threemile Creek, Oregon threatened with competition and hybridization with nonnative Brook Trout Salvelinus fontinalis. The group implemented Brook Trout and Bull Trout × Brook Trout hybrid removal using multiple techniques to conserve this population of Bull Trout in the Klamath River basin. From 1996 to 2000, backpack electrofishing and night snorkel spearing were used upstream of a culvert barrier to eradicate Brook Trout and hybrid trout from a 3.59-km section of Threemile Creek over 101 total days of effort (274 person-days of effort). Night snorkel spearing removed a lower percentage (7%) of target fish relative to electrofishing (93%), although this technique eliminated the risk of electrofishing injury to Bull Trout. Concurrent with the reduction and subsequent removal of Brook Trout, Bull Trout observations increased over 15-fold from 19 in 1996 to 299 in 2012 and Bull Trout distribution more than doubled, from 1.48 to 3.43 km during that same time. Immediately downstream in a separate 2.3-km section, the group eradicated Brook Trout using backpack electrofishing and rotenone application upstream of two man-made barriers from 2004 to 2010 over 43 total days of effort (150 person-days of effort). By 2016, Bull Trout had expanded their distribution throughout the upper 3.59-km section of Threemile Creek. Effort expended to eradicate Brook Trout was similar to successful eradication in other streams with comparable habitat characteristics and similar treatment length (< 3.0 km). However, similar removal attempts have not been successful in streams with comparable habitat characteristics that had longer treatment length (> 7.0 km). Application of piscicide may be more cost effective than manual techniques to remove Brook Trout when there is no risk to native fish of conservation concern, where target species are allopatric, and when piscicide use is publicly accepted. Brook Trout eradication proved valuable in providing Bull Trout the opportunity for range expansion and increased abundance necessary for recovery in the Klamath River basin.

Wildfire Smoke Cools Summer River and Stream Water Temperatures

AbstractTo test the hypothesis that wildfire smoke can cool summer river and stream water temperatures by attenuating solar radiation and air temperature, we analyzed data on summer wildfire smoke, solar radiation, air temperatures, precipitation, river discharge, and water temperatures in the lower Klamath River Basin in Northern California. Previous studies have focused on the effect of combustion heat on water temperatures during fires and the effect of riparian vegetation losses on postfire water temperatures, but we know of no studies of the effects of wildfire smoke on river or stream water temperatures. Wildfire smoke is difficult to quantify, but we successfully used a newly available daily high‐resolution (1 km) data set of aerosol optical thickness (AOT) derived from satellite imagery to represent smoke density during 6 years with extensive wildfire activity (2006, 2008, and 2012–2015). Smoke reduced solar radiation by 121 W m−2 per 1.0 AOT relative to clear‐sky conditions. Linear mixed‐effects models showed that on average, smoke cooled daily maximum and mean air temperatures by 0.98 °C and 0.47 °C per 1.0 AOT, respectively, across 19 remote automated weather stations. Smoke had a cooling effect on water temperatures at all 12 river and stream locations analyzed. On average, smoke cooled daily maximum and mean water temperatures by 1.32 °C and 0.74 °C per 1.0 AOT, respectively. This smoke‐induced cooling has the potential to benefit cold‐water adapted species, particularly because wildfires are more likely to occur during the warmest and driest years and seasons.

Thinking inside and outside the box: local and national considerations of the Food Distribution Program on Indian Reservations (FDPIR)

The Food Distribution Program on Indian Reservations (FDPIR) provides a monthly box of U.S. Department of Agriculture foods to low-income, rural Native Americans and is a vital component of food security for recipient households. While the origin of government food annuities dates back hundreds of years to treaties between tribes, pueblos, and nations and the United States Government, FDPIR in its current form and function is 40 years old. The FDPIR food package has faced increasing scrutiny in recent years over the quality, nutritional value, and cultural appropriateness of foods included. Using data collected from three Tribes in the Klamath River Basin as well as national institutions that govern FDPIR, we investigate opportunities and challenges of FDPIR to achieve food security for its clientele, and the extent to which integration of traditional foods can enhance Native American food security, food sovereignty and wellbeing. We conclude with a set of policy recommendations on how to improve Native American food security and food sovereignty outcomes for FDPIR clients.

Considerations for the Propagation and Conservation of Endangered Lake Suckers of the Western United States

Abstract Decades of persistent natural and anthropogenic threats coupled with competing water needs have compromised numerous species of freshwater fishes, many of which are now artificially propagated in hatcheries. Low survival upon release is common, particularly in systems with substantial nonnative predator populations. Extensive sampling for Shortnose (Chasmistes brevirostris) and Lost River Suckers (Deltistes luxatus) in the Klamath River Basin on the California–Oregon border have failed to detect any new adult recruitment for at least two decades, prompting an investigation into artificial propagation as an extinction prevention measure. A comprehensive assessment of strategies and successes associated with propagation for conservation restocking has not been performed for any Catostomid. Here, we review available literature for all western lake sucker species to inform propagation and recovery efforts for Klamath suckers and summarize the relevance of these considerations to other endangered fishes.

Thermal Regimes, Nonnative Trout, and Their Influences on Native Bull Trout in the Upper Klamath River Basin, Oregon

AbstractThe occurrence of fish species may be strongly influenced by a stream's thermal regime (magnitude, frequency, variation, and timing). For instance, magnitude and frequency provide information about sublethal temperatures, variability in temperature can affect behavioral thermoregulation and bioenergetics, and timing of thermal events may cue life history events, such as spawning and migration. We explored the relationship between thermal regimes and the occurrences of native Bull Trout Salvelinus confluentus and nonnative Brook Trout Salvelinus fontinalis and Brown Trout Salmo trutta across 87 sites in the upper Klamath River basin, Oregon. Our objectives were to associate descriptors of the thermal regime with trout occurrence, predict the probability of Bull Trout occurrence, and estimate upper thermal tolerances of the trout species. We found that each species was associated with a different suite of thermal regime descriptors. Bull Trout were present at sites that were cooler, had fewer high‐temperature events, had less variability, and took longer to warm. Brook Trout were also observed at cooler sites with fewer high‐temperature events, but the sites were more variable and Brook Trout occurrence was not associated with a timing descriptor. In contrast, Brown Trout were present at sites that were warmer and reached higher temperatures faster, but they were not associated with frequency or variability descriptors. Among the descriptors considered, magnitude (specifically June degree‐days) was the most important in predicting the probability of Bull Trout occurrence, and model predictions were strengthened by including Brook Trout occurrence. Last, all three trout species exhibited contrasting patterns of tolerating longer exposures to lower temperatures. Tolerance limits for Bull Trout were lower than those for Brook Trout and Brown Trout, with contrasts especially evident for thermal maxima. Our results confirm the value of exploring a suite of thermal regime descriptors for understanding the distribution and occurrence of fishes. Moreover, these descriptors and their relationships to fish should be considered with future changes in land use, water use, or climate.Received March 4, 2016; accepted July 27, 2016 Published online October 11, 2016