Investigation Into Mass Mussel Die-off Events

Assessing Impacts of Emerging and Established Diseases to Aquatic Ecosystems

The decline of native freshwater mussels has the potential to devastate aquatic communities. Although factors such as habitat degradation, pollution, and invasive species have been linked to this decline, these potential causes cannot fully explain the large-scale mussel die-offs that have occurred in the past 20 years. These die-offs have taken place in relatively “healthy” streams across the U.S. and occasionally only one or a few species out of many are affected. Several of these mass mussel mortality events have involved federal and state-listed species. Mass mortality in the Clinch River, Tennessee and Virginia, has been ongoing since 2016 and threatens the U.S. Fish and Wildlife Service’s efforts to restore imperiled species in the Upper Tennessee River Basin. In these and other cases, no cause of the die-off has been identified, despite patterns of spread that suggest a disease process in which an infectious agent or agents may be involved. These die-offs are under investigation to find underlying causes for the mass mortalities.