About Dams--What We Didn't Expect
A Sockeye salmon from Idaho's Sawtooth Mountains must pass
eight dams on its migration. Few, if any, complete this obstacle
course. How can this be? What about the fish ladders and fish
bypasses and all the other measures we have taken to help fish
get around these engineering monoliths? Some dams, such as
Hells Canyon and Grand Coulee, don't have bypasses. At other
dams, such facilities do exist. Some of them help; others create
even more problems for salmon. And regardless of all the
bypasses, salmon still have to deal with rivers that no longer flow
but are now backed up into reservoirs behind dams.
Engineers and biologists knew that salmon would need help getting around dams, but they didn't anticipate some of the other problems that would occur. For example, smolts now face a three-month journey instead of a one-week fast float to the ocean. Smoltification can begin to reverse if smolts are delayed in their migration for too long. This reversal often dooms the fish. Even if smoltification stays on schedule, smolts face increased predation from fish that thrive in the warm, slow waters of reservoirs.
Smolts that survive the slow-motion journey and predators can be killed by a dam's turbines or bashed about in a complex array of pipes and screens designed to save them from the turbines. Eventually they are spit out into raceways on the other side. One scientist who observed this process commented that "you come out wondering how we have any fish left."
Fisheries experts recognize the dangers at dams. So they have also tried collecting the smolts into barges and transporting them downstream past all the dams. Sounds like a good idea, but it isn't working too well. Put a bunch of fish into a crowded barge, and if one gets sick they all get sick.
How many of Idaho's smolts survive the bypasses, turbines, slackwater and barges? Very few. The few that do survive still have to face the hazards of ocean life and the return trip. For those salmon who survive to become spawning adults, they face their first human obstacle at Bonneville Dam in the lower Columbia River. There they need to find fish ladders--long, watery staircases that they must leap up, step by step, to reach the reservoir.
Many fish can climb fish ladders and continue on their journey, but they consume precious energy and endure extra stress. Salmon returning to Idaho must climb fish ladders at seven additional dams. If smolt survival were higher, wild salmon might not be in such trouble. That's why biologists, fisheries managers, and engineers focus on finding ways to help young salmon.
