Files
Abstract
Fishes of streams and rivers are a highly diverse group of animals that play important roles in freshwater ecosystems and sustain many human populations. However, stream fishes are globally imperiled by dams, water extraction, pollution, exploitation, and the spread of invasive species—stressors that will be exacerbated by climate change. Stream fish conservation is hampered by a poor understanding of the status of many species and an inability to predict how species will respond to changes in environmental variation like streamflow. In this dissertation, I used long-term datasets and hierarchical models to provide insight into stream fish population trends and response to streamflow variability to inform their conservation and management. First, I assessed population trends of an endangered stream fish, the Amber Darter Percina antesella, and demonstrated that both of its known populations are declining precipitously and in synchronous fashion, which compounds its overall extinction rate. I then compiled over twenty long-term fish time-series datasets from across the contiguous U.S. to perform two largescale analyses. First, I assessed characteristics of stream fish population trends in over 200 subwatersheds. I found that stream fishes at the subwatershed scale are declining by a median annual rate of 0.3% but that patterns in trends are spatially variable: systems in the arid Southwest and Great Plains have declined, losing opportunistic and periodic fish taxa, while Eastern sites demonstrated more positive trends, driven by increases in cosmopolitan species. Using the same large dataset, I next explored whether fishes of two ubiquitous guilds—riffle dwellers and nest builders—responded to low- and high-flow events based on hypothesized mechanistic flow-ecology relationships. I found few consistent responses to flow among guild members and little overall support for the hypotheses that stable low flows benefit nest fishes, moderate flows benefit riffle fishes, and extreme high flows harm both guilds. Overall my results highlight important variability in both how stream fish populations are changing through time and how they respond to extreme flows, information that can be employed to better conserve and manage these important animals.