Warmer water, changes in stream flow, and the increasing frequency and intensity of other disturbances are among the factors associated with climate change that are likely to impact native trout populations in the western USA. We examined how three of these factors—increased summer temperatures, uncharacteristic winter flooding, and increased wildfires—are likely to affect broad‐scale population persistence among three subspecies of cutthroat trout Oncorhynchus clarkii. Our results suggest that as much as 73% of the habitat currently occupied by Bonneville cutthroat trout O. c. utah, 65% of that occupied by westslope cutthroat trout O. c. lewisi, and 29% of that occupied by Colorado River cutthroat trout O. c. pleuriticus will be at high risk from one or more of the these three factors. Within the next 50 years, wildfire, floods, and other disturbances may have a greater impact on population persistence than increasing water temperature alone. Our results also suggest that the risk will vary substantially within subspecies. For each subspecies, our analyses identified large portions of their ranges where all populations either currently fail to meet basic persistence criteria, are at high risk from climate change, or both, indicating a high likelihood of losing the genetic and life history diversity in those areas. Stress from climate change is likely to compound existing problems associated with habitat degradation and introgression from introduced salmonids. Recognition of the increased risk from climate change may warrant altering the management paradigm of isolation and require increased control efforts for invasive nonnative species. Regardless of the management avenue chosen, more populations are likely to become isolated and vulnerable in the near future. Our results argue for immediate restoration actions within certain subbasins to increase the resistance and resilience of at‐risk populations and habitats to additional disturbances caused by rapid climate change.

Peripheral populations-generally defined as those at the geographic edge of the range-often have increased conservation value due to their potential to maximize within-species biodiversity, retain important evolutionary legacies, and provide the fodder for future adaptation. However, there has been little exploration of their conservation value in aquatic systems. Inland cutthroat trout (Oncorhynchus clarkii) subspecies provide a unique opportunity to evaluate the distribution of peripheral populations and patterns of persistence across a wide range of environmental conditions. Our assessment analyzed range-wide losses of peripheral and core populations since the 1800s, and evaluated the likelihood of persistence for remaining populations of five cutthroat trout subspecies: Bonneville, Colorado River, Yellowstone, Rio Grande, and westslope. For all five, we found that core and peripheral populations have declined substantially, but the amounts of habitat occupied by peripheral populations generally have declined at a greater magnitude. The more isolated peripheral populations typically exhibited the greatest declines. Remaining peripheral populations often failed to meet minimum persistence criteria. Our characterization of peripheral populations and their losses emphasizes the need for closer evaluation of conservation priorities and management actions for cutthroat trout and other fishes if the values of peripheral populations are to be maintained.

Management strategies that increase biological diversity and promote varied approaches to population protection are more likely to succeed during a future in which global warming drives rapid environmental change and increases uncertainty of future conditions. We describe how the concept of a diverse management portfolio can be applied to native trout conservation by increasing representation (protecting and restoring diversity), resilience (having sufficiently large populations and intact habitats to facilitate recovery from rapid environmental change), and redundancy (saving a sufficient number of populations so that some can be lost without jeopardizing the species). Saving diversity for native trout requires the conservation of genetically pure populations, the protection and restoration of life history diversity, and the protection of populations across the historical range. Protecting larger stronghold populations is important because such populations will have a better chance of surviving future disturbances, including those associated with climate change. The long‐term persistence of populations is likely to require management for larger population sizes and larger habitat patches than currently exist for many native trout populations. Redundancy among these elements is important given that many populations are small and occupy reduced habitat in fragmented stream systems and therefore are increasingly vulnerable to extirpation. Application of the concept is further described in case studies of Yellowstone cutthroat trout Oncorhynchus clarkii bouvieri and Rio Grande cutthroat trout O. clarkii virginalis, two subspecies that illustrate many of the challenges that are common to management of western native trout. Received May 16, 2011; accepted January 12, 2012

Climate change is contributing to the severity and rate of stream degradation by changing the timing of peak flows, altering flow regimes, creating more frequent and intense disturbances, and increasing stream temperatures. Herein we describe three case studies of trout stream adaptation that address existing and climate‐driven causes of degradation through habitat restoration. The case studies vary in geography and complexity, but all include restoration efforts intended to address multiple causes of stream degradation and improve the resilience of these streams to floods, droughts, and wildfires. Four elements of successful climate adaptation projects emerge: (1) habitat assessments that help drive project location and design, (2) projects that directly address climate change impacts and increase habitat resilience, (3) projects that combine to achieve watershed‐scale impacts, and (4) projects that include sufficient monitoring to determine their effectiveness. We describe solutions to common challenges in conducting climate change adaptation, including how to balance scientific assessments with opportunities when choosing projects, how smaller projects can be aggregated to achieve watershed‐scale benefits, and how citizen science efforts can augment monitoring programs.

Cover. Westslope cutthroat trout (top) and Bonneville cutthroat trout (bottom). Photo courtesy of Kirk Dahle and Mike Ebinger.

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