The SRA-TX will be studying native mussel populations on the Sabine River and its tributaries starting the summer of 2020. The Louisiana pigtoe and the Texas heelsplitter are two mussels of particular interest as they are the focus of the USFWS East Texas Mussel Species Status Assessment. The study is designed to supplement the available data on distribution and abundance of freshwater mussels in the basin. Genetic samples will be taken from a subset of mussels for species confirmation and to evaluate genetic diversity and structure, which will allow inferences about gene flow between populations of candidate species in the Sabine River basin. Genetic analyses will also allow for genotype by environment associations, allowing inferences about environmental parameters which can exert strong selection pressures on populations. In addition to distribution and abundance information, data on other population parameters such as population size, density, survival, longevity, and recruitment are needed to make an accurate assessment of conservation status. Mark recapture studies are an effective way to gather this information at specific locations through time. To evaluate these population parameters and provide for monitoring of populations through time, a minimum of two mark and recapture study sites will be established in areas occupied by the candidate species. These will be monitored using mark and recapture survey techniques to evaluate patterns in population parameters through time.