A new study highlights the grim ecological consequences of hydroelectric power, noting the limited capacity of hydroelectric dams to offer an effective pathway for migratory fish runs. The results underline the risks of the global expansion of hydropower. Writes John Waldman:
Six colleagues and I undertook a study of the success — or, rather, failure — of Atlantic salmon, American shad, river herring, and other species in migrating from the sea to their spawning grounds past a gauntlet of dams on three rivers in the northeastern U.S. — the Susquehanna, Connecticut, and Merrimack. What we found was grimmer than we expected. For one species, American shad, less than 3 percent of the fish made it past all the dams in these rivers to their historical spawning reaches.
Results for other anadromous species (those that spawn in fresh water and migrate to the ocean and back again) were nearly as bad. And the sobering aspect of these contemporary studies is that they are based on the insubstantial number of fish today as compared to earlier massive migrations of these species, which numbered in the many millions. While investigating fish passage on the Merrimack River in New Hampshire, our project’s lead researcher, Jed Brown of the U.S. Fish & Wildlife Service, was struck by the long-term lack of recovery of the targeted fish populations — at some fish restoration meetings there were more people in the room than salmon in the river.
What has happened on the U.S. East Coast, as reported in our study published in the journal Conservation Letters in January, is of more than regional or national interest. There are important lessons, as well. Even as some large dams in the U.S. begin to be removed for environmental reasons, a hydropower boom is occuring worldwide. Thirty large dams have been announced for the Amazon River alone. Eleven major dams are planned for the lower Mekong River. The dam industry in Canada wants to dramatically expand its recent hydropower initiative.
And dam projects are proposed, planned, or in the works for Africa’s upper Nile, the Patuca in Honduras, the Teesta in India, the upper Yangtze in China, the Tigris in Turkey, the Selenge in Mongolia, and many others. Though most of these rivers lack anadromous fishes, many are home to richly diverse freshwater fish communities that make important seasonal migrations within these river systems.
For the international community, the record of fish passage on rivers in the northeastern U.S. is a cautionary tale. Hydropower has often been billed as a clean source of renewable energy, and generating electricity without polluting the air or producing greenhouse gases is commendable. But “clean” is in the eye of the beholder, and any claims to being sustainable ignore its multifarious aquatic effects, including blocking fish passage, fragmenting habitat, and undermining a river’s fundamental ecological services. . . .
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John Waldman, “Blocked Migration: Fish Ladders on U.S. Dams Are Not Effective,” Yale Environment 360, April 4, 2013.