Assessment of Fish Passage Use in Facilitating Movement o



Alexander, Samantha B

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Diadromous fish are particularly vulnerable to anthropogenic alterations in watersheds, such as road construction and the establishment of flow control areas like dams and weirs. In northern Virginia, two anadromous species of concern, Blueback Herring (Alosa aestivalis) and Alewife (Alosa pseudoharengus), collectively managed as river herring, rely on well-connected waterways to complete annual spawning runs from the Atlantic Ocean into inland streams. Water passage infrastructure, hereafter fish passages, are installed at road-stream intersections in order to maintain the structural integrity of roads as flow conditions fluctuate, while also supporting continued up- and downstream passage by fishes and other aquatic organisms. Successful fish passages are those that permit upstream movement by the anadromous species as they travel inland to spawn. However, little information is available surrounding which passage characteristics are most important in permitting river herring movement. This study aimed to confirm areas theorized to host river herring spawning runs in Potomac River tributaries throughout northern Virginia, while also identifying passage characteristics that promote successful upstream passage by river herring. Environmental DNA (eDNA) samples were collected at 18 road crossings, one dam, and three weirs between 2018 and 2019 to determine species presence above and below each passage. This study documented the presence of river herring in upstream reaches of 9 Potomac River tributaries previously lacking confirmation of recent use by the species. Additionally, this study found evidence to support that many currently used fish passage designs including bridges, culverts, and weirs perform equivalently in allowing the upstream movement of river herring, with the exception of large round culverts. Furthermore, environmental variables did not appear to influence river herring presence across locations evaluated, however, did influence the observed frequency of upstream passage suggesting that river herring may persist in a variety of conditions but require more specific conditions in order to move through fish passages. Understanding the variables that correspond with successful fish passage use by anadromous fish species is key to guide future management strategies and plans for the recovery of river herring populations.



River herring, Fish passages, Road-stream intersections, EDNA, Potomac River