Theses and Dissertations at Montana State University (MSU)
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Item Macroinvertebrate diversity, community structure, and dispersal are affected by tributary identity and confluence conditions in a regulated river(Montana State University - Bozeman, College of Letters & Science, 2023) Maguire, Zachary John; Chairperson, Graduate Committee: Lindsey Albertson; This is a manuscript style paper that includes co-authored chapters.Tributaries are essential components of freshwater ecosystems, playing a crucial role in maintaining connectivity and providing habitat for a diverse array of aquatic organisms. The role of tributaries in creating heterogeneity in physical conditions and food resources for fishes could be critical, yet little is known about how variable conditions in different tributaries in regulated river systems influence the mainstem. Using field observations in five tributaries on the Madison River, Montana, we found that tributaries in the same network and within relatively short distances of 60km varied greatly in their environmental conditions, macroinvertebrate densities, and macroinvertebrate community structure. Downstream of confluences macroinvertebrate richness increased overall, and per capita weight of drifting macroinvertebrates decreased overall. These findings suggest that confluences may act as hotspots for biodiversity in regulated rivers and introduce smaller bodied macroinvertebrates to the drift. The amount that a tributary influenced benthic richness and mean per capita weight in the drift downstream of its confluence was related to land use and abiotic factors within that tributary; both macroinvertebrate metrics significantly increased in magnitude downstream of confluences with higher percentage of US Forest Service land, cooler temperatures, decreased discharge, and increased elevation loss (i.e. steeper watershed slope). In contrast, tributaries that had a larger proportion of agricultural land, warmer temperatures, and higher discharge more strongly influenced benthic macroinvertebrate metrics. These tributaries supported higher benthic density and biomass downstream of confluences. Our results offer insight into the ways that tributaries can create heterogeneous habitats that in turn structure macroinvertebrate communities in mainstem rivers and suggest that conservation and restoration of these essential components of freshwater ecosystems is a well-spent endeavor in rivers with regulated mainstems. Future research will need to test the ubiquity of the patterns we observed in other river networks and under other global changes such as pollution, invasive species, and drought. Continued understanding of the importance of heterogeneity imparted by tributaries and their confluences on diversity, availability, and quality of food for threaten fishes is needed to guide restoration efforts aimed at improving river condition and resilience.Item Effectiveness of the nature-like fishway at Huntley Diversion Dam, Yellowstone River, Montana(Montana State University - Bozeman, College of Letters & Science, 2022) Anderson, Ian Richard; Chairperson, Graduate Committee: Alexander V. ZaleWe evaluated passage of a diverse fish assemblage through the nature-like fishway built around Huntley Diversion Dam, the uppermost of six low-head diversion dams on the Yellowstone River in Montana. Although nature-like fishways purportedly facilitate the passage of many species, relatively few have been evaluated, particularly on large rivers with unregulated discharge regimes. We examined seasonal and diel use of the Huntley fishway, quantified efficiencies and temporal metrics, and determined which factors influenced attraction and passage. We implanted > 3,500 fish of 14 species with passive integrated transponder tags, released most fish 250 m downstream of the fishway, and used stationary antennas to monitor movements of fish through the fishway in 2019 and 2020. Seasonal use of the fishway was generally associated with pre-spawning movements and occurred from April to August annually, and diel use reflected the known biology of each species. Attraction efficiencies were apparently low (usually < 50%), probably because of low motivation or the inability of fish to locate the entrance. Suckers released on opposite riverbanks downstream of the fishway were similarly successful at locating the entrance. Entrance efficiencies were usually > 90%. Both transit and passage efficiencies were usually > 60%, but fewer individuals (particularly among certain species) successfully passed than were able to transit to near the fishway exit. High river discharges were associated with decreased passage success and increased exit delays, probably because of problematic hydraulic conditions near the exit. Conditions throughout the rest of the fishway were appropriate, as most fish transited to near the exit in < 1 h regardless of discharge. Fourteen species passed upstream, demonstrating the functionality of nature-like fishways on large, unregulated rivers. However, the placement of such fishways must be thoughtfully considered to ensure that they remain effective over a wide range of environmental conditions.