Date of Award
Spring 5-15-2023
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Biology
First Advisor
Dr. James Whitney
Second Advisor
Dr. Andrew George
Third Advisor
Dr. Alicia Mason Collins
Keywords
Endangered, Razorback, Pikeminnow, Backwater, Nursery, San Juan River, Southwest, Monsoon
Abstract
The Razorback Sucker (Xyrauchen texanus) and Colorado Pikeminnow (Ptychocheilus lucius) are federally-endangered species occurring in the San Juan River of NM, CO, and UT, USA. These species have shown little natural recruitment in this system, with a lack of high-quality nursery habitats being one potential explanation for this phenomenon. The young-of-year of both species prefer backwaters, including those that form in secondary channels or in association with islands. However, it is unknown how factors that could limit imperiled fish recruitment, such as hydrologic stability, physicochemical features, resource availability, and nonnative fish densities, differ between secondary channel and island backwaters. Furthermore, how these environmental features vary during the critical post-spawning window of the July-September monsoon season within and across years is also poorly understood. As such, we compared hydrologic stability, shading, water temperature, dissolved oxygen (DO) concentrations, turbidity, percent substrate composition, mean backwater width and depth, large woody debris (LWD) area, chlorophyll-a concentrations, invertebrate biomass, and native and nonnative fish densities between the two backwater types across 20 sites (i.e., 10 of each type) sampled on five occasions each in 2021 and 2022. We found that values of several variables were similar between backwater types (e.g., hydrologic stability, turbidity, silt coverage, mean width and depth, zooplankton biomass), but several other variables differed. For instance, secondary channel backwaters had greater shading, cooler water temperatures, higher DO concentrations, and more macroinvertebrates and fishes compared to island backwaters, although island backwaters had a greater coverage of coarse substrates. Many of these variables changed over time however in response to the monsoon season, which included increasing coverage of silt and decreasing widths, depths, LWD area, and abundances of macroinvertebrates and fishes. Our results suggested that secondary channel backwaters have more favorable physicochemical properties and are more productive compared to island backwaters, although both backwater types experienced degradation in quality throughout the monsoon season. Chronic and acute monsoonal-induced deteriorations in backwater habitat may explain the limited recruitment of imperiled native fishes in the San Juan River. Identifying strategies for improving backwater nursery quantity and quality (e.g., environmental flows management) will be paramount in helping to alleviate the recruitment bottleneck of imperiled Razorback Sucker and Colorado Pikeminnow in the San Juan River, thus aiding their recovery.
Recommended Citation
Hansen, Blake, "SECONDARY CHANNEL BACKWATERS MAY BE SUPERIOR NURSERIES FOR NATIVE FISHES IN THE SAN JUAN RIVER OF THE AMERICAN SOUTHWEST, BUT MONSOON-DRIVEN DETERIORATIONS MAY LESSEN THEIR QUALITY" (2023). Electronic Theses & Dissertations. 447.
https://digitalcommons.pittstate.edu/etd/447
