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Browsing by Author "Fausch, Kurt D., advisor"

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    Cold summer stream temperatures reduce recruitment of native cutthroat trout populations
    (Colorado State University. Libraries, 2007) Coleman, Mark Anthony, author; Fausch, Kurt D., advisor
    Translocation is a key strategy for conserving subspecies of native cutthroat trout Oncorhynchus clarkii, which have declined markedly throughout their native ranges in North America. Previous research showed that translocation success in high-elevation southern Rocky Mountain streams was more likely in warmer streams, and suggested that cold temperatures could limit juvenile trout recruitment and explain translocation failures. However, the effects of cold temperature on recruitment had not been previously investigated. I studied these effects using an integrated laboratory and field approach. In the lab, age-0 Colorado River cutthroat trout O. c. pleuriticus were subjected to one of three natural temperature regimes during two years, which averaged 7°C, 8.5°C and 10.0°C during the warmest summer month. From hatching to swimup, mean survival was high during both years, ranging from 97% (warm regime) to 85% (cold). After swimup, warm regime fry had much greater survival and grew more than 60% larger, on average, than cold regime fry by the onset of winter in the 2003 experiment. The pattern of lower survival in colder temperature regimes held through mid-winter, with 76% survival (warm regime), 62% (intermediate), and 29% (cold). Likewise, during the 2004 experiment, survival to early winter ranged from 44% (warm regime) to 10% (cold). Most mortality in all treatments occurred during a recruitment bottleneck encompassing a 4- to 6-week period following swimup. A response surface analysis of percent dry weight data indicated that the energy content of fry at swimup was lower in colder regimes, and declined during the recruitment bottleneck in all regimes. In the field, I monitored temperatures and conducted surveys to estimate densities of age-0 fry at peak emergence in six headwater streams that varied in thermal characteristics. Density and growth increased with Celsius degree days during the growing season. My results indicate a strong recruitment bottleneck after swimup, when temperature-related energy deficits probably cause significant mortality. Fisheries managers in the southern Rocky Mountains may increase translocation success of native cutthroat trout by selecting sites with ≥800-900 degree days during the growing season, and fry grow to ≥30-35 mm by the end of the growing season.
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    Effects of groundwater withdrawal and drought on native fishes and their habitats in the Arikaree River, Colorado
    (Colorado State University. Libraries, 2009) Falke, Jeffrey Arron, author; Fausch, Kurt D., advisor
    Great Plains streams are harsh environments for fishes, and are increasingly degraded by human-caused impacts, including overuse of groundwater. Plains stream fishes are in decline, due in part to interactions between natural drought and anthropogenic stream drying. To address these issues, in a collaborative study we developed a model of groundwater and surface water that predicted fish habitat quantity within the Arikaree River basin in eastern Colorado into the future, based upon three scenarios of land and water use (e.g., irrigation pumping). We found that under the status quo of pumping, >50% of remaining refuge habitats in the wettest segment of river will be dry in 35 years, and will be isolated in a 1-km fragment along the river. Loss of critical habitats due to stream dewatering, and subsequent negative effects on native fishes, are not unique to eastern Colorado but are in fact widespread across the western Great Plains. Secondly, to set this research in context, I conducted a review of metapopulation and metacommunity research in the stream fish literature. Stream fish populations and communities are spatially structured at multiple scales, and easily fragmented. To date, this spatial structure has not been incorporated into stream fish population and community models. However, recent research in this area should improve our understanding of processes that regulate stream fish assemblages. Next, I developed a spawning phenology for Arikaree River fishes and found that cumulative growing season degree days had the strongest effect on hatching initiation. Occupancy by larvae of most species was related to local scale spawning habitat characteristics (e.g., habitat size and type). Among years, colonization and extinction rates for individual species differed in segments that were fed by groundwater, versus those that were not, and were influenced by climate variability among years. Last, I investigated when and where the threatened brassy minnow, Hybognathus hankinsoni, spawns, and what environmental factors influence growth and survival of this species within and among years. Interannual variability in climate, and the hydrologic context of segments along the riverscape, had a strong influence on habitat availability and recruitment of brassy minnow in the Arikaree River.
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    Effects of riparian grazing on terrestrial invertebrate subsidies that feed trout in central Rocky Mountain streams
    (Colorado State University. Libraries, 2010) Saunders, William Carl, author; Fausch, Kurt D., advisor; Kondratieff, Boris, committee member; Clements, Williams H., committee member
    Habitat degradation is the leading cause of biodiversity loss worldwide, affecting plant and animal populations directly through habitat loss, but also indirectly by decoupling important linkages among habitats. Linkages between streams and the terrestrial environments they drain are likely to be especially important because streams have small habitat area but long boundaries with the adjacent riparian zone. Riparian livestock grazing reduces riparian vegetation, altering the stream-riparian interface, and so may reduce the flux of terrestrial invertebrates to streams. To evaluate the potential for riparian grazing to affect trout populations by reducing this flux, I conducted two large-scale field studies. In the first, a study of three commonly used grazing systems at sites on 16 streams in northern Colorado, I compared invertebrate resources and salmonid populations among stream reaches managed for season-long (i.e., continuous) or two types of rotational livestock grazing, as well as streams grazed by wildlife only. Rotational grazing generally supported greater inputs of terrestrial invertebrates to streams (2-5 times more), and trout at rotational grazing sites consumed 2 - 4 times the biomass of these prey as trout at sites grazed season-long. However, factors influencing the flux of invertebrates to streams were complex and resulted in variable responses by trout populations. In the second field study, a large-scale grazing experiment conducted in four streams in western Wyoming, I evaluated whether two levels of grazing intensity (i.e., the amount of vegetation removed) and manual removal of streamside woody vegetation influenced terrestrial prey resources for trout when compared to controls with wildlife grazing only. Two grazing treatments, designed to reduce vegetation to 10-15-cm stubble height (moderate intensity grazing) or 5-7.5-cm stubble height (high intensity grazing) within a few days, had no detectable effect on terrestrial invertebrates entering streams, whereas high intensity grazing combined with manual removal of two-thirds of streamside woody vegetation reduced inputs of terrestrial invertebrates to streams by 45%. In contrast, all treatments reduced the biomass of these prey in tout diets by 50 - 75%, relative to control sites. However, neither grazing nor removal of woody vegetation affected the biomass of fish that remained in treatment reaches. Finally, I conducted field research and computer simulations to validate removal estimates of trout abundance, based on night-time electrofishing, to address recent concerns over the accuracy of these types of estimators. I found that night-time electrofishing was highly effective for estimating abundance of trout in small streams like those where I studied the effects of cattle grazing in Colorado and Wyoming. Furthermore, I show that modern analytical methods provide powerful tools to account for heterogeneity in capture probability among individual fish.
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    Evaluating the success of Arkansas darter translocations in Colorado: an occupancy sampling approach
    (Colorado State University. Libraries, 2011) Groce, Matthew Christopher, author; Fausch, Kurt D., advisor; Bailey, Larissa L., committee member; Poff, N. LeRoy, committee member
    Like many fishes native to western Great Plains streams, the Arkansas darter Etheostoma cragini has declined, apparently in response to changes in flow regimes and habitat fragmentation. I investigated the effectiveness of translocation as a management strategy to conserve this threatened species in the Arkansas River basin of southeastern Colorado. I used a multiscale design to sample darters and several attributes of their habitat at the local 10-m site scale, the 3.25-km translocation segment scale, and the 10-km riverscape scale, in 19 streams where darters were previously translocated. I used multistate occupancy estimation, based on two consecutive dipnetting surveys, to determine habitat characteristics correlated with site occupancy and detectability of Arkansas darters. Darters were present in 11 of 19 streams, although 5 were completely dry when visited. Darters had reproduced in 10 of the 11 streams (one criterion in the state recovery plan), and 6 streams also met a second criterion for abundance (>500 individuals). However, populations in only two streams unequivocally met the third criterion of being self-sustaining, because the other four streams had been stocked annually with hatchery-reared darters. Detectability of darters at sites where water was present was high for both age groups, 91% for age-0 darters and 76% for age-1 darters, and was a function of Julian date (age-0) and habitat depth (age-1). Residual stream temperature (a site-scale variable) and the total length of available habitat (a riverscape-scale variable) were the strongest predictors of site occupancy for both age groups. The models were useful in identifying fragmentation by a road culvert as a potential impediment to success in another stream where conservation biologists have proposed translocating darters. These models can be used to guide habitat conservation and land management practices that seek to conserve, protect, and restore current and future critical habitat for Arkansas darters.