

Aerial view of Merrimack river system. Photo by: Doc Searls.

Dams create a largely impenetrable barrier for fish even when the dams were installed with specially-built passages, according to a new study in Conservation Letters. The scientists found that migrating fish largely failed to use the passages in the U.S., resulting in far fewer moving through the state-of-the-art hydroelectric dams than had been promised. The researchers say that their findings are a “cautionary tale” for developing nations.

“It may be time to admit failure of fish passage and hatchery-based restoration programs and acknowledge that ecologically and economically significant diadromous species restoration is not possible without dam removals,” the scientists write, dealing a large blow to the idea that hydroelectric projects can be fish-friendly. Diadromous fish refer to species that migrate between salt and fresh water, such as salmon, sturgeon, shad, river herring and eel. Many diadromous have seen historic declines worldwide, in part due to rapidly multiplying hydropower projects, many of which are now being constructed across the developing world.

The researchers looked at three river systems—the Merrimack, Connecticut and Susquehanna—in the northeastern U.S. After over a century of dam-building, these systems contain hundreds of dams, including several on the main stems, but the fish passageways built into the dams aren’t working.

The scientists found that some fish—such as sturgeon—don’t use the fish passageways at all. Others, such as American shad, have dwindled down to 2 percent of the conservation target on the Merrimack river system and zero percent on the other two rivers.

“These dams are contributing to reduced resilience of not only shad, but all diadromous species,” said co-author Adrian Jordaan of the University of Massachusetts Amherst. “The result is that other factors including climate change will have a greater impact on these populations that are at fractions of their historical levels.”

The result has been a decimation of U.S. fisheries, food production, and wildlife across the river systems.

“Once these rivers supported tens of millions of pounds of biomass of these species and provided valuable protein to a growing nation,” noted another co-author, Karin Limburg, with the SUNY College of Environmental Science and Forestry.

The researchers write that the plummeting of fish in America’s rivers provide “a cautionary tale for developing nations intent on hydropower development, suggesting that lasting ecosystem-wide impacts cannot be compensated for through fish passage and hatchery technology.” Mega dams are going up worldwide—from Brazil to China to Borneo—with governments and corporations often promising that fish will be little impacted.

Solutions to the problem in the U.S. may be dam removal—many of the dams generate little electricity—or more creative methods.

“The approach being employed on the Penobscot River, where dams are being removed or provided the opportunity to increase power generation within a plan to provide increased access to habitat, offers a good model for restoration,” the researchers conclude.

CITATION: J. Jed Brown,

Karin E. Limburg,

John R. Waldman,

Kurt Stephenson,

Edward P. Glenn,

Francis Juanes,

Adrian Jordaan. Fish and hydropower on the U.S. Atlantic coast: failed fisheries policies from half-way technologies. Conservation Letters. 2013.

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