Environmental Studies Theses and Dissertations

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Understanding Freshwater Mussel Distribution, Abundance, and Demography in the South Umpqua River Basin, Oregon: Impacts of Land Use and Stream Hydraulics
(University of Oregon, 2021-04-27) Johnson, Laura; Hallett, Lauren
Freshwater mussels are both keystone and indicator species within aquatic ecosystems and are declining across their historic ranges within the Pacific Northwest (PNW). This thesis provides baseline information necessary for conservation and management of native mussel populations in the South Umpqua River basin. We documented all three PNW genera within the basin, but only one species (Margaritifera falcata) was widespread. Species richness and mussel abundances were lowest at downstream sites. We found widespread evidence of recent M. falcata reproduction, but the lower South Umpqua River populations are likely non-viable. The percentage of forest cover within the drainage basin area was the best predictor of mussel abundance, and indicates that the cumulative impact of anthropogenic land use may be degrading mussel habitats. Our data also suggested a relationship between invasive Asian clams (Corbicula fluminea) and suppressed mussel abundances. Additional research is needed to understand the competition dynamics between these species.