Mussel Inventory and Population Demographics of the Federally Endangered Potamilus capax (Green 1832) in the Lower Wabash River, Illinois and Indiana

The Wabash River is a key component of the freshwater mussel biodiversity of the Ohio River Basin. The basin historically supported approximately 75 mussel species, but currently only 30 are thought to be extant in the mainstem. Though the basin was historically well surveyed, the limited number of recent studies have primarily been small, and the last basin-wide survey effort is already over a decade old. This situation is problematic given that several rare species were historically present and populations of the federally endangered Potamilus capax may remain. We surveyed 46 sites within the lower Wabash River (river mile 0.0 to 117.0) to characterize mussel assemblages and distributional patterns. In total, we located 996 live mussels of 23 species. The assemblage was dominated by Obliquaria reflexa, P. capax, Potamilus fragilis and Potamilus ohiensis, and shell-length frequencies indicated ongoing recruitment of several species, including P. capax (multiple size classes). We did not find any evidence of major changes in species distributions or occurrences compared to other recent surveys but we did note a shift from species with equilibrium life-history strategies to species with opportunistic strategies moving downriver. Though the lower Wabash River appears to remain a sanctuary for P. capax and other smooth-shelled species, many species that were present historically remain absent.