The upper reaches of the Allegheny River are a high-quality resource that supports populations of a number of endangered species. Two endangered species of freshwater mussel, the northern riffleshell, Epioblasma torulosa rangiana, and clubshell, Pleurobema clava, are present in this river reach. Prior to a bridge-replacement project at the Allegheny River at Foxburg, Pa. (river mile 86.2), a mussel survey was conducted to determine if either of the protected endangered species are present and to assess the quality of the mussel bed at this site.
Shore and near-shore searches followed by SCUBA diving transects determined that a mussel bed is present at this location. The freshwater-mussel community consists of at least 14 species and includes both endangered species. Substrate type, stream velocity, and channel morphology combined with results from the transect searches documented that the mussel bed is largely limited to the east side of the river.
A two-stage sampling design was employed to estimate the overall mussel abundance within the bed. Twelve 4-m2 (square meter) cells were sampled with four 0.25-m2 quadrants per cell. The mean population density within the mussel bed is 8.4 mussel per square meter. The overall mussel population in the survey area is 225,567 individuals (95-percent confidence interval, 135,973 to 374,195). River-bed scour and acid mine drainage appear to limit mussel distribution in the center and left section of the channel. Overall, a healthy and diverse mussel bed exists at this site.
