Stream Flow Management as a Conservation Tool for Great Plains Fishes

Abstract

Flow alteration is one of the greatest threats to freshwater fish conservation. As climate change exacerbates existing demand for freshwater resources and depletes and fragments riverine habitats, conservation and management of freshwater fishes becomes more challenging. Flow alteration and habitat fragmentation in the Great Plains region imperils cyprinid fishes belonging to the pelagic-broadcast spawning (PBS) guild characterized by external fertilization and downstream drift of pelagic embryos. My research has three aims: first, to quantify flow-ecology relationships; second, to assess how drought influences these relationships; and third, to develop useful tools for conservation and management of environmental flows. I used random forest modeling to reveal the potential influence of several indicators of the natural flow regime on fish occurrence in a post-flow-alteration context. Once these flow-ecology relationships were delineated, I used a combination of field sampling, random forest and generalized additive modeling, and ecological hindcasting and forecasting to examine how flow interacts with fragmentation and environmental conditions such as drought or air temperature, to govern PBS fish occurrence.

My first chapter demonstrates that the occurrence of PBS fishes is associated with natural flow regime (NFR) components, and that flow requirements of PBS fishes are spatially variable, nonlinear, and nuanced. My second chapter found that PBS fish occurrence is negatively correlated with increasing drought intensity, but occurrence of non-PBS fishes is positively correlated with drier conditions. My third chapter found that future drought and temperature conditions as well as fragmentation are all strong predictors of PBS occurrence, such that increases in these values through time will lead to declines in likelihood of occurrence as well as range contractions. Conservation tools developed in this work include flow targets that are species-specific, guild-specific, or even river-basin-specific, prioritization of flow indices for individual stream segments, as well as updated contemporary range maps and future range projections for some of the most imperiled freshwater fishes in North America. Taken together, the results of this research will directly inform conservation efforts of a guild of imperiled fishes in the Great Plains as well as provide a framework for developing methods to aid fish conservation globally.