Patterns in Fish-Assemblage Structure Over a Decade of Monitoring in the Upper Delaware River Watershed

The Upper Delaware River watershed has historically maintained high water quality and healthy fish assemblages. Emerging threats such as climate change could negatively affect this watershed as increased streamflow, precipitation, and temperature have been observed. We monitored fish assemblages at 6 tributaries in the Upper Delaware River watershed over the last decade (2013–2023). We found an overall stable state of assemblage structure with low amounts of variation, demonstrating the resilience of this community. We calculated index of biotic integrity (IBI) scores and found that biotic integrity appeared stable throughout the course of our study. Lastly, we identified trends in increasing densities for Rhinichthys cataractae (Longnose Dace) and Anguilla rostrata (American Eel) as well as an oscillating pattern in American Eel mean lengths over time.