Bio Acoustic Fish Fence May Protect Great Lakes
A bio acoustic fish fence (BAFF) is being tested on a tributary about 200 miles from Chicago by ecologist Gregg Sass. The BAFF is basically an underwater sonic fence; a barrier created by outputting sounds into a wall of bubbles.
The intent is to stop invasive Asian carp species from swimming up the Illinois river and reaching the Great Lakes, which already have enough problems.
It uses an air bubble curtain to contain a sound signal which is generated pneumatically. Effectively, this creates a "wall of sound" (an evanescent sound field) field that can be used to guide fish around river structures by deflection into fish passes.
Physically, the BAFF comprises a pneumatic sound transducer coupled to a bubble-sheet generator, causing sound wave to propagate within the rising curtain of bubbles. The sound is contained within the bubble curtain as a result of refraction, since the velocity of sound in a bubble-water mixture differs from that in either water or air alone.
(An effervescent wall for 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.
The first place I read about this idea was in Roger Zelazny's 1976 novel My Name is Legion; he refers to sonic curtains that can be used to keep sharks out of selected areas in underwater parks. Amusingly, dolphins can be taught to use it, and in turn teach other dolphins.
From Wired via Neatorama. See also this article on the fish fence.
Scroll down for more stories in the same category. (Story submitted 8/16/2009)
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