June 3, 2023 — The following was released by NOAA Fisheries:
In 2018, NOAA and partners removed Bloede Dam from the Patapsco River, opening up miles of free-flowing habitat to migratory species. A recent study has shown river herring are using the habitat upstream of the former dam. This news highlights the importance of dam removals in NOAA’s work to support migratory fish.
NOAA and partners have been monitoring the Bloede Dam site since before its removal to see how reopening the river would affect fish migration. Scientists at the Smithsonian Environmental Research Center and the University of Maryland Center for Environmental Science have been using environmental DNA, or eDNA, to monitor for the presence of river herring. Fish and wildlife constantly shed scales, tissue, and other bits of genetic material into the surrounding environment. Researchers can collect a water sample, analyze the eDNA found in it, and identify which species have recently visited a location.
A recent study published in PLOS ONE found eDNA evidence of alewife and blueback herring (collectively known as river herring) using the reopened habitat. In the 4 years prior to the dam removal, no river herring eDNA was detected upstream of the Bloede Dam site. After its removal, eDNA from both species was detected in the reopened habitat. The likelihood of detecting the eDNA of alewife upstream of the Bloede Dam site increased from 0 to 5 percent, and from 0 to 13 percent for blueback herring. In addition to eDNA evidence, biologists with the Maryland Department of Natural Resources recorded two adult river herring—one alewife and one blueback herring—upstream of the Bloede Dam site in 2021.