Status of freshwater native mussels (Unionidae) in the Oklahoma section of the Verdigris River after introduction of the zebra mussel (Dreissena polymorpha Pallas, 1771)

The Verdigris River in Kansas and Oklahoma, USA once held a diverse native unionid mussel fauna although a number of these populations have declined in richness and abundance. There is recent evidence that populations of some species of unionid mussels are increasing in parts of the Verdigris River in Kansas, but no current data exist for Oklahoma. In addition, zebra mussels (Dreissena polymorpha Pallas, 1771) have been introduced into a major impoundment on the Verdigris River, Oologah Lake, and may further threaten mussel populations downstream from this reservoir. This study updates the distribution and abundance of native mussels in the Oklahoma portion of the Verdigris River upstream and downstream of Oologah Lake, and documents the current distribution of zebra mussels in this region. Thirty-one sites were sampled and a significant increase in species richness and abundance of native mussels was observed as compared to a 1997 study. Two species of special interest, Cyprogenia aberti (Conrad, 1850) and Quadrula cylindrica (Say, 1817), were found. Zebra mussels were not found at sites upstream of Oologah Lake but were present at every downstream site. In September 2006, zebra mussel byssal threads were observed on shells of a number of native mussels downstream from Oologah Lake, but unionid richness and abundance were not significantly different between sites above and below the reservoir.