New Distributional Records for Four Rare Species of Freshwater Mussels (Family: Unionidae) in Southwestern Louisiana

Abstract Recent studies of mussels have documented a gradient of extirpation that extends from Toledo Bend Dam to United States Highway 190 in the lower Sabine River. A similar pattern has been documented for the diversity and abundance of cyprinids. To evaluate whether impacts of the project have extended into nearby tributaries, we assessed the distribution and abundance of threatened species of mussels in Anacoco and Toro bayous, within Vernon and Sabine parishes, respectively. In total, 1,474 live mussels representing 15 species were collected during our survey. Of these, four are considered state-threatened: Fusconaia askewi (Texas pigtoe), Lampsilis satura (sandbank pocketbook), Obovaria jacksoniana (southern hickorynut), and Pleurobema riddellii (Louisiana pigtoe). In general, L. satura, O. jacksoniana, and P. riddellii appear to be rare in Anacoco Bayou and absent from Toro Bayou, whereas F. askewi is more abundant and widely distributed. Effects of backwater related to releases from impoundments,...