Geomorphic Assessment and Flow Modeling of Pearl Darter (Percina aurora) Habitat in the Pascagoula River Watershed

Freshwater ecosystems are complex ecosystems driven by hydrologic, geomorphic, and biological processes. Considering both abiotic and biotic factors is important to understanding resident species habitat. Geomorphology is a known, but often neglected factor in habitat assessment for freshwater fishes. A crucial feature commonly seen in alluvial stream systems are sandbars, which are dynamic and variable sediment structures that are known to have many associated species. One such species is the Pearl Darter, Percina aurora, a federally threatened species that only resides in the Pascagoula River watershed. Despite its status, habitat preference remains unclear. To fill this knowledge gap, I developed a novel approach to summarizing morphological characteristics of over 500 sandbars across 3 tributaries and mainstem of the Pascagoula River watershed. I then used HEC-RAS, a flow modeling program, to assess quantitative characteristics of Pearl Darter reproductive habitat, including sandbar morphology. We found that sandbar morphology differed between rivers of the same watershed, and Pearl Darter occurrence, and sampling effort, differed by sandbar morphological traits. For reproductive habitat, we found that mean velocity is likely an important factor in habitat preference. Additionally, we propose that the updated reproductive habitat description is shallow, fast flowing water near morphological units that have a shallow longitudinal slope, multiple ledges, and reside on a river straightaway. Overall, this study provides further context of habitat preference for the Pearl Darter as efforts to protect this species continue.