Early recovery of river herring spawning habitat use in response to a large-scale dam removal

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Historical loss of river and stream habitats due to impassable dams has contributed to the severe decline of many fish species. Anadromous fishes that migrate from the sea to freshwater streams to spawn have been especially impacted as dams restrict these fish from accessing essential spawning habitats. In 2018, Bloede Dam was removed from the Patapsco River near Baltimore, Maryland, restoring approximately 100 km (60 mi) of potential river and tributary habitat for migratory fish. This study assessed the response of anadromous river herring, alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), to this dam removal by monitoring environmental DNA (eDNA), ichthyoplankton, and passive integrated transponder (PIT) tags from 2015 to 2021 at locations upstream and downstream of the dam site during the river herring spawning migrations. Findings show early recovery of habitat use by river herring beyond the dam site within 3 years of the removal, including species-specific differences in relative abundance and upstream migration. No adult river herring, eDNA, or eggs were detected upstream of Bloede Dam prior to its removal. Post-removal, blueback herring exhibited the strongest response with DNA detected at two sites upstream of Daniels Dam, a remaining manmade waterfall. Although eDNA presence in restored habitat increased, there was no evidence of increased egg abundance upstream or downstream of the former dam site and no tagged fish were detected upstream of the dam site post-removal. While further monitoring is needed to determine a population-level response to the removal of the Bloede Dam, applying multiple monitoring methods provided a comprehensive picture of habitat use recovery by spawning river herring. These results will be key in informing future dam removal priorities for anadromous fish conservation in the Chesapeake Bay.





Huang, Claire (2022). Early recovery of river herring spawning habitat use in response to a large-scale dam removal. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/24881.

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