Compositional and Functional Shifts in Fish Community Structure in Response to Low-head Dam Removals
Graduate Program
Biological Sciences
Degree Name
Master of Science (MS)
Semester of Degree Completion
Spring 2026
Thesis Director
Robert E. Colombo
Thesis Committee Member
Eden L. Effert-Fanta
Thesis Committee Member
Scott J. Meiners
Abstract
Low-head dams serve as intermittent barriers to aquatic connectivity and directly alter both upstream and downstream habitats and biotic communities. In 2018 and 2019, two low-head dams in the Vermilion River watershed of eastern Illinois were removed, reconnecting over 1,700 kilometers of upstream habitat within the basin. To determine the impacts of these dam removals, fish community surveys were conducted at 12 fixed sites across three reaches in two rivers from 2012-2022. This study assessed reach-specific temporal responses of the fish community and habitat characteristics. I linked trait expressions within the fish community to abiotic variables using the co-inertia RLQ (R-mode linked to Q-mode) analysis. Linkages between abiotic variables and functional traits provide insight into the functional ecology of an ecosystem and key abiotic drivers of community structure. Using a cluster analysis on the first two RLQ axes, I classified fishes into four functional groups based on a suite of reproductive, life-history, and ecological traits. Habitat quality and diversity improved across all reaches following dam removals, with the greatest changes occurring in sites that had been impounded by the dams. Two functional groups of fishes exhibited strong responses to the dam removals. Generalist species that prefer pools decreased in relative abundance, whereas intolerant, fluvial-specialist species increased after dam removals. Additionally, species richness increased throughout the study area, with 18 new fish species collected upstream of at least one dam. The trait-based approach used in this study gives these results greater applicability to other ecosystems to better understand the ecological impacts of improving habitat characteristics and connectivity resulting from barrier removals.
Recommended Citation
Bruegge, Joshua D., "Compositional and Functional Shifts in Fish Community Structure in Response to Low-head Dam Removals" (2026). Masters Theses. 5121.
https://thekeep.eiu.edu/theses/5121
