October 24, 2016 — BANGOR, Maine — Joseph Zydlewski, a research biologist with the Maine Cooperative Fish and Wildlife Research Unit of the United States Geological Survey, drifted in a boat on the Penobscot River, listening to a crackling radio receiver. The staccato clicks told him that one of the shad that his team had outfitted with a transmitter was swimming somewhere below.
Shad, alewives, blueback herring and other migratory fish once were plentiful on the Penobscot. “Seven thousand shad and one hundred barrels of alewives were taken at one haul of the seine,” in May 1827, according to one historian.
Three enormous dams erected in the Penobscot, starting in the 1830s, changed all that, preventing migratory fish from reaching their breeding grounds. The populations all but collapsed.
But two of the dams were razed in 2012 and 2013, and since then, fish have been rushing back into the Penobscot, Maine’s largest river.
“Now all of a sudden you are pulling the cork plug and giving shad access to a truckload of good habitat,” Dr. Zydlewski said. Nearly 8,000 shad have swum upstream this year — and it’s not just shad.
More than 500 Atlantic salmon have made the trip, along with nearly two million alewives, countless baby eels, thousands of mature sea lamprey and dozens of white perch and brook trout. Striped bass are feeding a dozen miles above Bangor in waters closed to them for more than a century.
Nationwide, dam removals are gaining traction. Four dams are slated for removal from the Klamath River alone in California and Oregon by 2020.
Just a few of these removals have occurred on such large rivers, which play an outsize role in coastal ecosystems. But the lessons are the same everywhere: Unplug the rivers, and the fish will return.