May 07, 2013
Fish Ladders: A Great Idea That Doesn’t Always Work
By Bob Marshall
Many scientists consider a statement by Galileo to be a guiding principle in their professions: Who would dare assert that we know all there is to be known?
That came to mind as I came across this headline: Blocked Migration: Fish Ladders On U.S. Dams Are Not Effective
During the age of dam building, fish ladders were considered nothing less than penicillin in the world of fishery management. That’s because when the harm dams caused to migrating fish populations became evident, fish ladders were announced as the solution. Who can forget all those neat news features with film of fish charging up the ladders to the still waters above the dam?
But this group of researchers obviously didn’t consider the science settled. And when they looked into fish ladders on Northeast rivers, they discovered some surprising and sobering facts—one of which was that less than 3 percent of one key species was making it upriver to their spawning grounds.
As John Waldman, a professor of biology at Queens College in New York explains, the idea for the study began when colleague Jed Brown, of the U.S. Fish and Wildlife Service, was investigating passages on the Merrimack River in New Hampshire, and discovered “at some fish restoration meetings there were more people in the room than salmon in the river.”
So Waldman, Brown and four colleagues set out to see if this was a pattern on other regional rivers that depend on fish ladders to overcome the obstacles dams placed in the path of migrating fish. They looked at the success of Atlantic salmon, American shad, river herring, and other species in passing dams on the Susquehanna, Connecticut, and Merrimack.
“What we found was grimmer than we expected,” Waldman reported for Yale University’s Environment 360 website. “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.”
As Waldman points out, the record of success for fish ladders on other rivers is mixed; some work well, some poorly.
But the point is that sportsmen and others who care about the future of fish and wildlife should never stop observing and reading - and seeking explanations for what they discover.
Science is never settled, and neither should our quest to do our best for fish and wildlife.