Apparent extinction of native mussels in Lower Mill Creek and Mid-Jordan River, UT

Native mussels likely occurred in Mill Creek and the Jordan River, Utah, in the past. However, humaninduced impacts have virtually eliminated the possibility of their continued existence in these waters. We conducted an intensive native mussel survey upstream and downstream of a water reclamation facility discharge into Mill Creek and the Jordan River to determine its effects on mussel populations. The survey was conducted from September to October 2017 and resulted in approximately 7.6 m³ of >4 mm-sized substrate particles being thoroughly examined at near 100% efficiency. We then used statistical models to estimate population densities as a function of probability of detection and search efficiencies based on this and other surveys. Regrettably, no live or recently dead native mussels were found. Given that our survey methods provided near perfect search efficiency, native mussel densities were estimated to be <<0.03 per m², which is much lower than what we consider to be a viable population density. Combined with multiple lines of evidence from other surveys, this low density strongly points toward the conclusion that native mussels are extinct in the survey area. Reasons for the demise of native mussels in Mill Creek and the Jordan River are numerous, and these factors need to be aggressively addressed if native mussels are to survive in the drainage.