Duke, Hannah, Department of Biology, Lycoming College, 1 College Place, Williamsport, PA, 17701, dukhann@lycoming.edu; Rieck, Leslie, , Department of Biology, Lycoming College, 1 College Place, Williamsport, PA, 17701, rieck@lycoming.edu; Andrew, David, Department of Biology Lycoming College 1 College Place Williamsport PA, 17701, andrew@lycoming.edu.
There are growing concerns regarding the safe passage of aquatic organisms over large hydroelectric dams on major rivers like the Susquehanna River. It is unknown if efforts to mediate this issue such as increased stocking and fish passage facilities are significantly effective at restoring populations of a freshwater species of note, Anguilla rostrata. A. rostrata (common name American eel) faces population decline due to impediment of anadromous migration from the North Atlantic. They are major hosts of important native freshwater mussels such as Elliptio complanata (Eastern elliptio mussel) and are key food web members, serving as both predator and prey during different life stages. Eels are cryptic organisms, which poses a challenge for traditional electrofishing sampling methods; environmental DNA (eDNA) is a popular method for detection of cryptic species. Use of eDNA is also less invasive and poses less risk to organisms. The Susquehanna River Basin Commission (SRBC) has made great conservation efforts via stocking throughout the Susquehanna watershed in the past few decades. Preliminary trials of eDNA sampling in the Pine Creek watershed in September 2024 indicated that our procedures for aquatic eDNA sampling were feasible for detecting presence of eels around SRBC stocking locations. Our efforts have now shifted to sampling the entire Susquehanna basin in order to better understand how these eels are moving throughout the Susquehanna. We began sampling in the West Branch Susquehanna sub-basin in September 2025, targeting the main river as well as corresponding tributaries. Samples were taken and filtered onsite both upstream and downstream of major barriers throughout the watershed using the Smith-Root eDNA Sampler Backpack. Samples would be taken by filtering ~1L (±0.10) of water through 0.45 micron filters. Filters were stored in ethanol until they were processed via DNA extraction and qPCR. DNA was extracted using the Qiagen DNeasy Blood & Tissue Kit, and qPCR procedures were completed using a recently developed PCR marker for American eels referred to as AME1. The Bio-Rad CFX Opus 96 Real-Time PCR System was used for 15 μL qPCR reactions, and the CFX Maestro computer program was used to analyze PCR results. Water quality measurements were taken at each site to better our understanding on potential predictors of eel movement. Current findings indicate presence of eels downstream of major hydroelectric dams on tributaries feeding into the West Branch of the main river, but no presence around low head dams on the main river. More sampling will be completed in eastern and southern Pennsylvania, around the mouth in northern Maryland, as well as the headwaters in upstate New York. Understanding where eels are present as well as how they are moving will guide future stocking and conservation efforts, especially in relation to fish passage systems.
American eel, eDNA, Barriers, Susquehanna