Michael K. Young

Flow regime, temperature, and biotic interactions drive differential declines of trout species under climate change

Broad-scale studies of climate change effects on freshwater species have focused mainly on temperature, ignoring critical drivers such as flow regime and biotic interactions. We use downscaled outputs from general circulation models coupled with a hydrologic model to forecast the effects of altered flows and increased temperatures on four interacting species of trout across the interior western United States (1.01 million km2), based on empirical statistical models built from fish surveys at 9,890 sites. Projections under the 2080s A1B emissions scenario forecast a mean 47% decline in total suitable habitat for all trout, a group of fishes of major socioeconomic and ecological significance. We project that native cutthroat trout Oncorhynchus clarkii, already excluded from much of its potential range by nonnative species, will lose a further 58% of habitat due to an increase in temperatures beyond the species’ physiological optima and continued negative biotic interactions. Habitat for nonnative brook trout Salvelinus fontinalis and brown trout Salmo trutta is predicted to decline by 77% and 48%, respectively, driven by increases in temperature and winter flood frequency caused by warmer, rainier winters. Habitat for rainbow trout, Oncorhynchus mykiss, is projected to decline the least (35%) because negative temperature effects are partly offset by flow regime shifts that benefit the species. These results illustrate how drivers other than temperature influence species response to climate change. Despite some uncertainty, large declines in trout habitat are likely, but our findings point to opportunities for strategic targeting of mitigation efforts to appropriate stressors and locations.

Effects of fire on fish populations: landscape perspectives on persistence of native fishes and nonnative fish invasions

Our limited understanding of the short and long-term effects of fire on fish contributes to considerable uncertainty in assessments of the risks and benefits of fire management alternatives. A primary concern among the many potential effects of fire is the effects of fire and fire management on persistence of native fish populations. Limited evidence suggests vulnerability of fish to fire is contingent upon the quality of affected habitats, the amount and distribution of habitat (habitat fragmentation), and habitat specificity of the species in question. Species with narrow habitat requirements in highly degraded and fragmented systems are likely to be most vulnerable to fire and fire-related disturbance. In addition to effects of fire on native fish, there are growing concerns about the effects of fire on nonnative fish invasions. The role of fire in facilitating invasions by nonnative fishes is unknown, but experience with other species suggests some forms of disturbance associated with fire may facilitate invasion. Management efforts to promote persistence of fishes in fire-prone landscapes can take the form of four basic alternatives: (1) pre-fire management; (2) post-fire management; (3) managing fire itself (e.g. fire fighting); and (4) monitoring and adaptive management. Among these alternatives, pre-fire management is likely to be most effective. Effective pre-fire management activities will address factors that may render fish populations more vulnerable to the effects of fire (e.g. habitat degradation, fragmentation, and nonnative species). Post-fire management is also potentially important, but suffers from being a reactive approach that may not address threats in time to avert them. Managing fire itself can be important in some contexts, but negative consequences for fish populations are possible (e.g. toxicity of fire fighting chemicals to fish). Monitoring and adaptive management can provide important new information for evaluating alternatives, but proper implementation is often hampered by inadequate study designs and inconsistent financial and institutional support. The challenge for providing better management guidelines will be to add solid empirical data and models to assess the relevance of emerging concepts and theories, and provide a sense of where and when fires pose significant risks and/or benefits to fishes.

Factors Influencing Success of Greenback Cutthroat Trout Translocations

Abstract Native subspecies of cutthroat trout Oncorhynchus clarki have declined drastically because of the introduction of nonnative salmonids, overharvesting, and habitat degradation. Conservation of most declining subspecies will include establishing new populations through translocation of genetically pure fish. Recovery of greenback cutthroat trout O. clarki stomias has been ongoing for 25 years, so the attempted translocations of this subspecies provide unique empirical information to guide recovery of other nonanadromous salmonids. We compared 14 translocations that successfully established populations of greenback cutthroat trout to 23 that failed to determine the factors that influenced translocation success. Of the translocations that failed, 48% were reinvaded by nonnative salmonids, 43% apparently had unsuitable habitat, and 9% experienced suppression by other factors. Reinvasion occurred most often because of failed artificial barriers or incomplete removal of nonnative salmonids in complex ha...

Status of native fishes in the western United States and issues for fire and fuels management

Conservation of native fishes and changing patterns in wildfire and fuels are defining challenges for managers of forested landscapes in the western United States. Many species and populations of native fishes have declined in recorded history and some now occur as isolated remnants of what once were larger more complex systems. Land management activities have been viewed as one cause of this problem. Fires also can have substantial effects on streams and riparian systems and may threaten the persistence of some populations of fish, particularly those that are small and isolated. Despite that, major new efforts to actively manage fires and fuels in forests throughout the region may be perceived as a threat rather than a benefit to conservation of native fishes and their habitats. The management of terrestrial and aquatic resources has often been contentious, divided among a variety of agencies with different goals and mandates. Management of forests, for example, has generally been viewed as an impact on aquatic systems. Implementation of the management-regulatory process has reinforced a uniform approach to mitigate the threats to aquatic species and habitats that may be influenced by management activities. The problems and opportunities, however, are not the same across the landscapes of interest. Attempts to streamline the regulatory process often search for generalized solutions that may oversimplify the complexity of natural systems. Significant questions regarding the influence of fire on aquatic ecosystems, changing fire regimes, and the effects of fire-related management remain unresolved and contribute to the uncertainty. We argue that management of forests and fishes can be viewed as part of the same problem, that of conservation and restoration of the natural processes that create diverse and productive ecosystems. We suggest that progress toward more integrated management of forests and native fishes will require at least three steps: (1) better integration and development of a common conceptual foundation and ecological goals; (2) attention to landscape and ecological context; and (3) recognition of uncertainty. Published by Elsevier Science B.V.

Assessing the Consequences of Nonnative Trout in Headwater Ecosystems in Western North America

Abstract Intentional introductions of nonnative trout into headwater lakes and streams can have numerous effects on the receiving ecosystems, potentially threatening native species and disrupting key ecological processes. In this perspective, we focus on seven key issues for assessing the biological and economic consequences of nonnative trout in headwater ecosystems: (1) effects of nonnative trout can span multiple biological domains, (2) effects of nonnative trout can extend beyond waters where they are introduced, (3) nonnative trout do not travel alone, (4) not all habitats are equal, (5) ecosystems vary in their resistance and resilience to nonnative trout, (6) prioritization can improve management of nonnative trout, and (7) economic costs of recreational fisheries in headwater ecosystems can be substantial. Assessments that address these issues could provide more effective guidance for determining where recreational fisheries for nonnative trout are justified in headwater ecosystems and where they ...

Slow climate velocities of mountain streams portend their role as refugia for cold-water biodiversity

Significance Many studies predict climate change will cause widespread extinctions of flora and fauna in mountain environments because of temperature increases, enhanced environmental variability, and invasions by nonnative species. Cold-water organisms are thought to be at particularly high risk, but most predictions are based on small datasets and imprecise surrogates for water temperature trends. Using large stream temperature and biological databases, we show that thermal habitat in mountain streams is highly resistant to temperature increases and that many populations of cold-water species exist where they are well-buffered from climate change. As a result, there is hope that many native species dependent on cold water can persist this century and mountain landscapes will play an important role in that preservation. The imminent demise of montane species is a recurrent theme in the climate change literature, particularly for aquatic species that are constrained to networks and elevational rather than latitudinal retreat as temperatures increase. Predictions of widespread species losses, however, have yet to be fulfilled despite decades of climate change, suggesting that trends are much weaker than anticipated and may be too subtle for detection given the widespread use of sparse water temperature datasets or imprecise surrogates like elevation and air temperature. Through application of large water-temperature databases evaluated for sensitivity to historical air-temperature variability and computationally interpolated to provide high-resolution thermal habitat information for a 222,000-km network, we estimate a less dire thermal plight for cold-water species within mountains of the northwestern United States. Stream warming rates and climate velocities were both relatively low for 1968–2011 (average warming rate = 0.101 °C/decade; median velocity = 1.07 km/decade) when air temperatures warmed at 0.21 °C/decade. Many cold-water vertebrate species occurred in a subset of the network characterized by low climate velocities, and three native species of conservation concern occurred in extremely cold, slow velocity environments (0.33–0.48 km/decade). Examination of aggressive warming scenarios indicated that although network climate velocities could increase, they remain low in headwaters because of strong local temperature gradients associated with topographic controls. Better information about changing hydrology and disturbance regimes is needed to complement these results, but rather than being climatic cul-de-sacs, many mountain streams appear poised to be redoubts for cold-water biodiversity this century.

Strategies for conserving native salmonid populations at risk from nonnative fish invasions: tradeoffs in using barriers to upstream movement

Native salmonid populations in the inland West are often restricted to small isolated habitats at risk from invasion by nonnative salmonids. However, further isolating these populations using barriers to prevent invasions can increase their extinction risk. This monograph reviews the state of knowledge about this tradeoff between invasion and isolation. We present a conceptual framework to guide analysis, focusing on four main questions concerning conservation value, vulnerability to invasion, persistence given isolation, and priorities when conserving multiple populations. Two examples illustrate use of the framework, and a final section discusses opportunities for making strategic decisions when faced with the invasion-isolation tradeoff.

Sampling large geographic areas for rare species using environmental DNA: a study of bull trout Salvelinus confluentus occupancy in western Montana

This study tested the efficacy of environmental DNA (eDNA) sampling to delineate the distribution of bull trout Salvelinus confluentus in headwater streams in western Montana, U.S.A. Surveys proved fast, reliable and sensitive: 124 samples were collected across five basins by a single crew in c. 8 days. Results were largely consistent with past electrofishing, but, in a basin where S. confluentus were known to be scarce, eDNA samples indicated that S. confluentus were more broadly distributed than previously thought.

Population Characteristics of Greenback Cutthroat Trout in Streams: Their Relation to Model Predictions andRecovery Criteria

Abstract Fishes listed under the U.S. Endangered Species Act receive intensive management, but evaluations of population characteristics are rare. We report population and habitat characteristics of federally threatened greenback cutthroat trout Oncorhynchus clarki stomias in 12 streams in north-central Colorado surveyed in 1998 and 1999. Our objectives were to assess population size, structure, and distribution, to evaluate a model developed by Harig and Fausch (2002) to assess translocation success, and to compare population characteristics to those reported in the recovery plan. Allopatric population sizes in 10 streams varied from 170 to 7,347 greenback cutthroat trout at least 75 mm long, whereas the 2 streams with brook trout throughout supported 0–142 greenback cutthroat trout. Populations displayed few upstream–downstream trends in fish abundance or mean length, and the coefficient of variation among sampled reaches within streams averaged 61%. As the density of fish at least 75 mm long increased,...

Introduction to the effects of wildland fire on aquatic ecosystems in the Western USA

The management of wildfire has long been controversial. The role of fire and fire-related management in terrestrial and aquatic ecosystems has become an important focus in recent years, but the general debate is not new. In his recent book, Stephen Pyne (2001) describes the political and scientific debate surrounding the creation of the U.S. Forest Service and the emergence of fire suppression as a central tenet of wildland management. Essentially, views in the first decade of the 20th century focused on fire as good or evil: a tool that might benefit other resources or interests (e.g. Indian burning) and mitigate larger more destructive fires, or a threat to the recruitment and productivity of newly designated forest reserves. The ‘‘great fires’’ in the Western USA in 1910 and the associated loss of human life and property largely forged the public and political will to suppress fire on a massive scale. In some forest types the fallacy of a management policy based on fire suppression at any cost has become obvious during recent decades. Fire suppression, coupled with selective silvicultural practices, livestock grazing, and other human disruptions, including climate change and an ever expanding urban– wildland interface, has led to the possibility of larger, more destructive fires, reminiscent of those in 1910. Large fires in the last two decades have again generated a public and political desire to respond. The National Fire Plan (U.S. Department of Agriculture, 2000) and linked initiatives outline a comprehensive strategy intended to protect communities, reduce fuel loads and the threat of large fires, and restore damaged ecosystems. The USA Congress has responded with significant funding and the President of the USA has proposed to constrain the environmental regulatory and review process that slowed the implementation of new management initiatives (see the President’s Healthy Forest Initiative available online: http://www.whitehouse.gov/infocus/healthyforests/ Healthy_Forests_v2.pdf). Despite these actions, the debate continues. As Pyne (2001) points out, there is no simple dichotomy of fire suppression versus the use of fire, or one of fuels treatments versus acceptance of the fires that may follow without them. These oversimplified perspectives are complicated by social and ecological tradeoffs that we are just beginning to understand based on our nearly century-old experiment in fire suppression. Among them are that fire and the effects of fire are important ecosystem processes, which fire management will also influence. Also, fires are not driven by fuels alone, but also by climate, and climate is changing. And large fires are natural; we cannot eliminate them—as recent events throughout the Western USA have illustrated—and it might be ill-advised even if we could. Thus, management to ensure that natural systems are resilient to or even benefit from large fires could be important. The management of fire is particularly relevant to the aquatic ecosystems of the Western USA. More than a century of human development has produced a legacy of habitat degradation, fragmentation, and loss, and an expansion of nonnative species across the lakes, rivers, and streams of the region. The result has been the accelerated extinction of species and stocks and increased listings of them under the Endangered Species Act and of impaired waters under the Clean Water Act. Because past land management is perceived as a primary cause of the disruption of aquatic ecosystems, new proposals for aggressive management of forest vegetation and fuels to mitigate the Forest Ecology and Management 178 (2003) 1–3