Invasive Asian carp are populating the Great Lakes and forcing native species out of their traditional habitats. Scientists are taking steps to contain the invaders without affecting other species. They've developed an underwater "wall of sound" that takes advantage of the physical differences between Asian carp and native fish.
In a tributary near Havana, about 200 miles from Chicago, ecologist Greg Sass is testing a barrier that injects beeping sounds into an effervescent wall, which captures and magnifies the noise. The chirping bothers only the carp because it hears higher frequencies than native species do; a series of tiny bones connecting the carp's swim bladder to its auditory system amplifies sound. In hatchery trials, the acoustic "fence" stopped 95 percent of the invasive fish.