Causal Analysis of the Smallmouth Bass Decline in the Susquehanna and Juniata Rivers

Elaine Langone Center, Terrace Room

In 2014, the DEP requested assistance from the United States Environmental Protection Agency (EPA) in identifying the causes of the smallmouth bass (SMB) declines on the Susquehanna River. EPA’s stressor identification process, as described on the Causal Analysis/Diagnosis Decision Information System website (CADDIS www.epa.gov/caddis) identifies the cause(s) of an environmental problem by determining which of a set of alternative candidate causes is best supported by the body of evidence. The CADDIS process was chosen because it provides transparency and reduces bias without restricting the types of evidence used. In cooperation with the PFBC, PADEP and EPA scheduled three workshops that included representatives from various State, Interstate, Federal, and academic organizations including, the Susquehanna River Basin Commission (SRBC), United States Geological Survey (USGS), United States Fish and Wildlife Service (USFWS), and Susquehanna River Heartland Coalition for Environmental Studies (SRHCES). Over 50 worksheets consisting of almost 400 pages describing data collections and analyses were reviewed by experts. A total of 14 potential candidate causes were initially identified for the decline in SMB recruitment during the first CADDIS workshop. The CADDIS process narrowed the scope of concerns that may be affecting SMB populations in the Susquehanna and Juniata Rivers. Based on all available evidence, eight candidate causes were not supported by the data analysis and were considered Unlikely for directly causing the decline of YOY SMB recruitment. The evidence for eight additional candidate causes was judged to be Uncertain.