Results of a Mussel Survey from the Upper Rock River, Wisconsin and Illinois, and the Discovery of Live Cyclonaias tuberculata (Purple Wartyback)

Abstract - Freshwater mussels are one of the most diverse and critically endangered organismal groups in the world. In North America, many of the ∼300 species are imperiled to some degree, and numerous states, including Illinois, have instituted surveys and safeguards to protect their remaining mussel resources. In Illinois, the status of many mussel species is unknown, and additional efforts are needed to determine the health of rare and endangered mussels. The Rock River system was historically a stronghold for mussels in Illinois; however, studies over the last decade are lacking. To obtain current data on the health and status of mussels within a portion of the Rock River, we conducted survey efforts throughout the upper Rock River. We sampled mussels semi-quantitatively at 30 sites using bank-to-bank transects in July of 2021 to determine whether rare and endangered species were still extant. We also examined the abundances of species currently considered common and assessed shell-length data to determine the overall viability of the mussel fauna. We surveyed a total of 4360 m of the river and obtained 2506 live mussels of 19 species. The assemblage consisted primarily of Potamilus ohiensis (Pink Papershell) and Cyclonaias pustulosa (Pimpleback), and approximately half the assemblage consisted of recent recruits (juveniles). We collected live Cyclonaias nodulata (Wartyback), Cyclonaias tuberculata (Purple Wartyback), and Truncilla donaciformis (Fawnsfoot), all Illinois or Wisconsin state-listed species. The Purple Wartyback consisted of 2 cohorts and are the first live individuals recorded from the Rock River since the late 1980s. Furthermore, the presence of numerous juveniles indicates successful reproduction and recruitment for multiple species. Continued work on managing stream habitats is vital to protecting and reinforcing their remaining diversity, and the upper Rock River warrants further protections.