Decreasing stream habitat for Greenback cutthroat trout under future climate projections in headwater streams of the southern Rocky Mountains, Colorado

Ma, Chenchen, author
Morrison, Ryan R., advisor
Nelson, Peter, committee member
Kanno, Yoichiro, committee member
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Headwaters are vital to the abundance and diversity of biota as they produce various temperatures, light, hydrologic regimes, water chemistry, substrate type, food resources, and species pools. Many studies have shown that headwater streams are especially vulnerable to changing climate, and coldwater fish are especially sensitive to the fluctuations in streamflow and water temperature during summertime low flows. Though previous studies have provided insights on how changes in climate and alterations in stream discharge may affect the habitat requirements for native cutthroat trout species, the suitable physical habitats have not been evaluated under future climate projections for the threatened Greenback Cutthroat Trout (GBCT) occupying the headwater regions in the Southern Rocky Mountains. Thus, this study used field data collected in the summers of 2019 and 2020 from selected headwater streams across the Front Range in the Southern Rocky Mountains to construct one-dimensional hydraulic models (HEC-RAS) to evaluate streamflow and physical habitat under four future climate projections. A principal component analysis (PCA) was then performed to demonstrate the importance of each morphological feature of these streams. Results illustrate high variations in both predicted streamflow reductions and physical habitat for all future climate projections. The projected mean summer streamflow shows much greater decline compared to the projected mean August flow. Moreover, sites located at higher elevations with larger substrate (D50 and D84) and steeper slopes may experience greater reductions in physical habitat under mean summer future climate projections. Future climate change studies on cold-water fisheries need to take multiple influential factors into account instead of heavily focusing on the thermal characteristics. Reintroduction and management efforts for GBCT should be tailored to the individual headwater stream with adequate on-site monitoring that can be applied in a more holistic manner as well.
2022 Summer.
Includes bibliographical references.
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