Midwest Fish & Wildlife Conference 2016

AUTHORS: Teresa J. Newton* and Steve J. Zigler, U.S. Geological Survey, Upper Midwest Environmental Sciences Center

ABSTRACT: Large floodplain rivers are fundamentally different from smaller systems in their lateral complexity and hydrology. However, conditions that constitute habitat for freshwater mussels in large rivers are poorly understood, greatly limiting our understanding of the conditions that promote high quality mussel assemblages. Over the past 10 years, we have modeled the abundance and distribution of mussels in the Upper Mississippi River (UMR) using physical and hydraulic variables. Analyses of data from small (0.4 km) to large (38 km) spatial scales indicated that computed hydraulic variables (e.g., shear stress, boundary Reynolds number) were more predictive than variables measured in the field (e.g., depth, velocity). Discharge-specific models suggested that episodic events such as droughts and floods were more important in structuring mussel distributions than conditions during average flows. Models also indicated distributions of adult mussels were considerably more predictable than juvenile mussels, suggesting that distribution of juveniles was less dependent on hydrophysical features than adults. Geospatial models have consistently predicted few mussels in poorly connected backwater areas and the navigation channel, whereas main channel border areas with high geomorphic complexity and small side channels were typically favorable to mussels. Our studies indicate that the spatial distribution of mussels in large rivers is determined by a complex interaction of biotic and abiotic factors acting at various spatial scales. Further, the interaction of geomorphology and discharge produces a template of hydrophysical conditions in the UMR that could be manipulated by managers to create quality mussel habitat to benefit restoration activities.