Effects of Lowhead Dams on Freshwater Mussels in the Vermilion River Basin, Illinois, with Comments on a Natural Dam Removal

We sampled freshwater mussels at 12 sites centered around three lowhead dams in the Vermilion River basin (Wabash River drainage) to address their effects on the freshwater mussel fauna and to obtain baseline data prior to their removal. Compared with reference sites, impounded areas and plunge zones had lower mussel abundance and extant species richness. We also examined literature accounts and museum collections to determine species distributions in the basin and compared those data to locations of the three dams and location of the former Homer Park Dam, which was removed over 50 years ago. Two species, Yellow Sandshell ( Lampsilis teres ) and the state-threatened Black Sandshell ( Ligumia recta ), are now found only downstream of the Danville Dam. Pimpleback ( Amphinaias pustulosa ) and Mapleleaf ( Quadrula quadrula ), which was found only downstream of the Homer Park Dam prior to 1950, has expanded its range upstream since the dam was removed. Data collected during this study contributes insights into the effects of lowhead dams on freshwater mussel abundance and species richness in Midwestern streams, and will be used as a baseline to compare to future post-dam removal collections.