Dear Librarian: Is it true that fish need elevators?
Dear Reader: Imagine that you are an American shad fish. You are born in a fresh water stream, and then migrate to the ocean where you live for a few years. When you are ready to spawn, you and many others of your kind will swim back upstream to the area where you were born, like all your ancestors did before you. There’s just one problem. There’s a dam in your way and you can’t get past it to get to your birthplace. You are determined to get there because you don’t know any other way to live. Some fish give up and turn back; others keep trying to find an opening and a few attempt to swim past the turbines, which leaves them stressed and susceptible to disease.
Fish that migrate from the sea to rivers to breed – like shad, salmon and river herring – are called “anadromous.” Dams have been a problem for these fish for hundreds of years. A few solutions, called fish passages, have been put in place to try to help them find their way past the barriers.
A “fish ladder” is really a series of steps that are low enough for the fish to leap up. It’s amazing to watch a creature with no arms or legs fling itself up a fish ladder with water pouring down it. Sometimes it takes a fish many tries to get up each step.
For tall obstructions like the Conowingo Dam, a fish elevator, or lift, is used during spawning season. The fish are first directed to a collection area at the base of the dam. After enough fish have gathered there, they are lifted up to an exit channel where they continue their upstream journey. The fish are counted as they move past the dam (through a viewing window), so dam operators and biologists can determine whether or not the fish passage is working.
American shad were an important food resource for Native Americans and early European settlers. Even George Washington had a shad fishery at his house. Commercial harvesting of shad, which had begun in 1800, peaked at more than 7 million pounds in 1890. By 1979, they could harvest only 18,000 pounds. Along with the commercial exploitation, forests were cleared, causing sediment, culverts were built to support roads, and many dams were constructed for flood control and hydropower. Something had to be done to help the fish get back upstream.
The $12 million Conowingo lift was the largest of its kind in the nation when it opened in 1991. Before the existence of the fish lift, shad were actually trucked around the four dams on the Susquehanna River. Shad populations rose during the first 10 years of lift operation – nearly 194,000 shad took the lift in 2001 – but since then the numbers have dwindled to an all-time low. Biologists are not sure why. Do the fish passages need to be improved? Could some dams be removed? Let’s hope a solution can be found soon.
