Daniel C. Dauwalter

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.

Influence of Rare Species on Electrofishing Distance When Estimating Species Richness of Stream and River Reaches

Abstract The electrofishing distance needed to estimate fish species richness at the stream or river reach scale is an important question in fisheries science. This distance is governed by the shape of the species accumulation curve, which, in turn, is influenced by a combination of factors, including the number of species, their overall abundances, habitat associations, the efficiency of the sampling method, and the occurrence of rare species. In this study we document the influence of rare species on the species accumulation curves from stream and river sites in data sets from five dispersed regions of the USA. Spatial discontinuity (i.e., a noncontinuous distribution within reaches) was observed in four of the five data sets, and the four data sets contained numerically rare species represented by one or two individuals (termed singletons and doubletons, respectively). Numerically rare species were typically proportionately rare (i.e., <1% of the total number of individuals captured), but proportionate...

Conserving Peripheral Trout Populations: the Values and Risks of Life on the Edge

Abstract 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 general...

The Role of Complexity in Habitat Use and Selection by Stream Fishes in a Snake River Basin Tributary

AbstractImpacts from grazing, agriculture, and other anthropogenic land uses can decrease stream habitat complexity that is important to stream biota and often is the goal of stream habitat restoration. We evaluated how microhabitat complexity structured a fish assemblage and influenced habitat selection by the Northern Leatherside Chub Lepidomeda copei, a recent candidate for listing under the U.S. Endangered Species Act, in Trapper Creek, a tributary to the Snake River in Idaho. Fishes were sampled using prepositioned areal electrofishing (about 1xa0m2), and microhabitat conditions were measured within a 1-m-diameter circle centered on the electrofishing anode. Constrained correspondence analysis showed complexity in water depths and velocity to structure the fish assemblage and partition habitat use by Northern Leatherside Chub, Rainbow Trout Oncorhynchus mykiss, and Redside Shiner Richardsonius balteatus. Habitat selection models showed that the chub used areas of heterogeneous depths and flows in addit...

Land Use Associations with Distributions of Declining Native Fishes in the Upper Colorado River Basin

Abstract The upper Colorado River basin contains one of the most imperiled fish faunas in North America. Anthropogenic land use and nonnative species impacts are considered among the top reasons for imperilment. We determined the association of anthropogenic land use intensity (road density, percentage of converted land, and oil and gas well density), relative abundance of nonnative white suckers Catostomus commersonii and their hybrids, and natural landscape features with the occurrences of three native fishes in the Colorado River basin, Wyoming, that have declined throughout their ranges: flannelmouth sucker C. latipinnis, bluehead sucker C. discobolus, and roundtail chub Gila robusta. We found that flannelmouth suckers occurred more frequently in large, low-gradient stream reaches, but their occurrence was not associated with land use intensity or the relative abundance of white suckers and hybrid suckers. In contrast, bluehead sucker occurrence decreased with increasing intensity of each land use typ...

Using Aerial Imagery to Characterize Redband Trout Habitat in a Remote Desert Landscape

AbstractRemote sensing products, including aerial imagery, can be used to quantify characteristics of watersheds and stream corridors that often predict the distribution and abundance of aquatic species. We conducted a supervised, object-oriented classification of imagery from the National Agricultural Imagery Program to develop a high-resolution (1-m) land cover data set with four cover classes, emphasizing accurate characterization of woody riparian vegetation along stream corridors in northern Nevada and southwestern Idaho. The overall classification accuracy was 76%, and producers accuracy (reflecting false positives) and users accuracy (reflecting false negatives) for the woody vegetation class were 84% and 70%, respectively. Using logistic and quantile regression models in a model-selection framework, we found woody vegetation to be positively associated with the occurrence and density of Redband Trout Oncorhynchus mykiss gairdneri. In addition, occurrence probabilities and densities were highest ...

Identification and Implementation of Native Fish Conservation Areas in the Upper Colorado River Basin

Abstract Freshwater fishes continue to decline at a rapid rate despite substantial conservation efforts. Native fish conservation areas (NFCAs) are a management approach emphasizing persistent native fish communities and healthy watersheds while simultaneously allowing for compatible human uses. We identified potential NFCAs in the Upper Colorado River Basin in Wyoming—focusing on Colorado River cutthroat trout (Oncorhynchus clarkii pleuriticus), flannelmouth sucker (Catostomus latipinnis), bluehead sucker (Catostomus discobolus), and roundtail chub (Gila robusta)—through a process that combined known and modeled species distributions, spatial prioritization analysis, and stakeholder discussions. The network of potential NFCAs is intended to serve as a funding framework for a National Fish and Wildlife Foundation (NFWF) Keystone Initiative focused on Colorado River Basin native fishes. We discuss current opportunities for and impediments to implementing the potential NFCAs we identified for the NFWF Initi...

Satellite and Airborne Remote Sensing Applications for Freshwater Fisheries

Remote sensing has been pivotal to our understanding of freshwater fisheries, and we review this rapidly changing field with a focus on satellite and airborne applications. Historical applications emphasized spatial variation in the environment (e.g., watershed land use and in situ primary productivity), but improved access to imagery archives facilitates better change detection over time. New sensor platforms and technology now yield imagery with higher spatial, temporal, and spectral resolutions than ever before, which has accelerated development of remote sensing products that more accurately characterize aquatic environments. Free access to imagery archives, cloud computing, and availability of derived products linked to national hydrography databases are all removing historical barriers to its use by fisheries professionals. These advances in remote sensing have allowed new questions to be answered at finer spatial resolutions across broader landscapes and longer time frames, providing a new big-pict...

Influence of Stream Condition on Habitat Diversity and Fish Assemblages in an Impaired Upper Snake River Basin Watershed

AbstractHabitat diversity reflects the range of available habitats used by species with different niche requirements and, therefore, influences species diversity. Land use influences stream condition, and streams in poor condition are often wide, shallow, sediment-laden channels with low instream habitat diversity. Our goal was to evaluate the effect of instream habitat diversity on fish species diversity, the effect of stream habitat condition on habitat diversity, and the effect of habitat diversity, stream condition, and other natural stream features on fish assemblage structure (proportional abundance) in an impaired upper Snake River basin watershed containing a locally diverse but regionally depauperate species pool. We sampled fishes and instream and riparian habitat at 41 sites, focusing on measures of instream habitat diversity and the following stream condition indicators: livestock trails on streambanks, streambank stability, channel width-to-depth ratio, percent fine substrates, and woody ripa...

Trout in hot water: A call for global action

Trout are one of the most culturally, economically, and ecologically important taxonomic groups of freshwater fishes worldwide ([ 1 ][1]). Native to all continents in the Northern Hemisphere, trout belong to seven genera, which are distributed across 52 countries. These cold-water specialists