Helen M. Neville

Potential Consequences of Climate Change to Persistence of Cutthroat Trout Populations

Abstract 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 subs...

Macroscale hydrologic modeling of ecologically relevant flow metrics

Stream hydrology strongly affects the structure of aquatic communities. Changes to air temperature and precipitation driven by increased greenhouse gas concentrations are shifting timing and volume of streamflows potentially affecting these communities. The variable infiltration capacity (VIC) macroscale hydrologic model has been employed at regional scales to describe and forecast hydrologic changes but has been calibrated and applied mainly to large rivers. An important question is how well VIC runoff simulations serve to answer questions about hydrologic changes in smaller streams, which are important habitat for many fish species. To answer this question, we aggregated gridded VIC outputs within the drainage basins of 55 streamflow gages in the Pacific Northwest United States and compared modeled hydrographs and summary metrics to observations. For most streams, several ecologically relevant aspects of the hydrologic regime were accurately modeled, including center of flow timing, mean annual and summer flows and frequency of winter floods. Frequencies of high and low flows in the summer were not well predicted, however. Predictions were worse for sites with strong groundwater influence, and some sites showed errors that may result from limitations in the forcing climate data. Higher resolution (1/16th degree) modeling provided small improvements over lower resolution (1/8th degree). Despite some limitations, the VIC model appears capable of representing several ecologically relevant hydrologic characteristics in streams, making it a useful tool for understanding the effects of hydrology in delimiting species distributions and predicting the potential effects of climate shifts on aquatic organisms.Related website: Western US Stream Flow Metric Dataset

Assessing connectivity in salmonid fishes with DNA microsatellite markers

Connectivity is a key consideration for the management and conservation of any species, but empirical characterizations of connectivity can be extremely challenging. Assessments of connectivity require biologically realistic classifications of landscape structure (Kotliar and Wiens 1990), and an understanding of how landscape structure affects migration, dispersal, and population dynamics (Dunning et al. 1992; Rosenberg et al. 1997; Hanski 1999; Taylor et al. Chapter 2). Empirical assessments of connectivity may be accomplished by studying spatial patterns of habitat occupancy through time (Sjögren-Gulve and Ray 1996; Hanski 1999; Moilanen and Hanski Chapter 3), spatially correlated changes in population demography (Bjornstad et al. 1999; Isaak et al. 2003; Carroll Chapter 15), and individual movements (Millspaugh and Marzluff 2001; Tracey Chapter 14). These approaches have provided important insights for many species, but they can be difficult to implement for species with slow population dynamics or turnover (extinction and recolonization), complex life histories, and long-distance migrations. For species with these characteristics, molecular genetic markers represent a valuable tool for understanding processes that influence connectivity (Avise 1994; Frankham et al. 2004; Frankham Chapter 4). In this chapter, we review applications of molecular genetic markers to assess connectivity in salmonid fishes, a group of relatively well-studied species with

Patterns of Hybridization of Nonnative Cutthroat Trout and Hatchery Rainbow Trout with Native Redband Trout in the Boise River, Idaho

Abstract Hybridization is one of the greatest threats to native fishes. Threats from hybridization are particularly important for native trout species as stocking of nonnative trout has been widespread within the ranges of native species, thus increasing the potential for hybridization. While many studies have documented hybridization between native cutthroat trout Oncorhynchus clarkii and nonnative rainbow trout O. mykiss, fewer have focused on this issue in native rainbow trout despite widespread threats from introductions of both nonnative cutthroat trout and hatchery rainbow trout. Here, we describe the current genetic (i.e., hybridization) status of native redband trout O. mykiss gairdneri populations in the upper Boise River, Idaho. Interspecific hybridization was widespread (detected at 14 of the 41 sampled locations), but high levels of hybridization between nonnative cutthroat trout and redband trout were detected in only a few streams. Intraspecific hybridization was considerably more widespread...

Monitoring Demographic and Genetic Responses of a Threatened Inland Trout to Habitat Reconnection

AbstractFreshwater fishes living in streams and rivers can be affected strongly by isolation, which causes a disproportionate degree of fragmentation in such dendritic systems. Isolation disrupts important ecological and migratory processes as well as the ability to access refuge habitats during disturbances. The restoration of habitat connectivity, then, should be a productive strategy for improving the resiliency of freshwater fish populations, but the local and broader ecological benefits of barrier removal are still poorly understood. We report on a long-term, spatially intensive effort to monitor the responses of inland trout to stream habitat reconnection at a watershed scale, using both demographic and genetic techniques. Individual-based genetic assignment uncovered clear evidence of movement into the primary tributary of interest, which had been blocked by an assumedly complete barrier, but the source population generating this movement varied over time. A linear mixed-effect model suggested trou...

Genomic Analysis Reveals Genetic Distinctiveness of the Paiute Cutthroat Trout Oncorhynchus clarkii seleniris

AbstractThe Paiute Cutthroat Trout (PCT) Oncorhynchus clarkii seleniris is classified as a subspecies within the greater Cutthroat Trout O. clarkii ssp. complex and is federally listed as threatened under the Endangered Species Act. However, genetic studies to date have revealed very little genetic differentiation between the PCT and its closest relative, the Lahontan Cutthroat Trout (LCT) O. clarkii henshawi. These results casted doubt on whether the PCT is a genetically distinct subspecies or merely a phenotypic variant of the LCT. Here, we present a genomic analysis of Cutthroat Trout subspecies and populations to resolve the genetic and phylogenetic relationship between PCT and LCT. Our results demonstrate substantial genetic structure and differentiation between PCT and LCT populations. In contrast to current thinking, our phylogenetic reconstructions show the PCT to be a distinct evolutionary lineage that diverged from LCT before the LCT differentiated into its current populations (i.e., rather than...