Millions of young salmon pass through the turbines each year on their way to the Pacific from spawning grounds in the Northwest's rivers and streams. Hundreds of thousands die, battered by the whirling blades, torn apart by the turbulence, smacked against metal surfaces. In their struggle to reverse dwindling salmon runs in the Columbia River Basin, scientists measure turbine death rates by periodically sending live salmon fingerlings through the turbines. But live fish can't tell scientists what they experienced during the three-minute trip through the dam.
Mechanical fish can.
Each of these robofish comes equipped with a rechargeable battery, data-storage chips, instruments that measure acceleration and pressure, and wires poking from a rubber tail. Teams of biologists in boats downriver from the dam use radio locators to triangulate on the signal. After retrieving an ersatz fish, biologists reconstruct its account of the voyage by plugging the dangling wires into a desktop computer. Metal grates covering two-thirds of each turbine entrance keep most fish that stay in the river out of the spinning machinery. They go over the spillways or through fish-bypass systems.