ARTICLE: Repelling Invasive Species With Noisy Bubbles

[Ryan Goble]

From Wired

Cut the Carp: Repelling Invasive Species With Noisy Bubbles
By Damon Tabor 07.20.09

The Great Lakes are under attack. A swarm of Asian carp are advancing up the Illinois River, breeding wantonly and gorging on plankton. How can we halt the piscatory horde before it reaches Lake Michigan? Well, possibly with noisy bubbles.

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.

1 // Inside a shed on the riverbank, a signal generator emits eight chirps at varying intervals and varying frequencies up to 2,000 Hz. Two 400-watt amplifiers pump up the beeps to carp-deafening levels.

2 // A compressor pushes a continuous stream of air through a rubber pipe riddled with small holes. The pipe, housed in an open steel chassis, runs across the bottom of the riverbed.

3 // The pipe releases a sheet of bubbles illuminated by strobe lights flashing 200 to 400 times per minute. Alongside the pipe, 16 hundred-watt sound projectors shoot the chirping sounds into the fizz, where the noise is concentrated.

4 // Native fish like trout and salmon can't hear frequencies above 400 Hz and swim through the bubbles unfazed. Carp, which perceive sound as high as 2,000 Hz, hit the piercing noise and turn back.

Illustration: Webuyyourkids

From: http://www.wired.com/science/discoveries/magazine/17-08/st_acoustic...