The four species known as Asian carp have damaged economies and ecosystems from the mouth of the Mississippi to the gateway of the Great Lakes.
Below Barkley Dam in rural Western Kentucky, millions of pounds of the fish have been caught and processed. But above the locks, in the Cumberland River, the fish are not nearly as present.
So the dam is considered a pinch point for controlling the spread of Asian carp.
Looking over the edge, only a handful of fish can be detected. That changes when wildlife workers drop in long polls that look like electric mops.
A split second later, it’s a kind of “fish fry,” as hundreds — maybe thousands — of Asian carp leap into the air in response to the shock. The current stuns the fish, some fatally. They’re collected in a small boat.
This demonstration took place over the summer. It was not the show officials had planned. Floods delayed deployment of the sound barrier officials had hoped then to show off. But it demonstrated the size of the problem swimming just beneath the surface.
These were silverhead carp, just one of the species scientists are concerned about. They jump not only in response to electricity, but also to noise — a trait that British engineer David Lambert wants to use against them.
His product employs speakers built into a long concrete case sitting at the bottom of the river. It creates what he describes as a “bubble curtain.”
That might not seem intimidating, but each tiny bubble contains sounds up to 160 decibels — greater than the inside of a jet engine. The frequencies, though, will be tuned especially for carp, and Lambert says people won’t really notice.
“For anyone who comes across it, you’ll just see a line of bubbles across the surface of the water,” he says. “So it’ll have relatively little impact on anybody or any craft at all.”
The sound, disappointingly, will not be death metal or Kentucky bluegrass. A U.S. research fish biologist calls it a “disco barrier,” but that’s because it also uses lights shooting through the bubbles to scare away fish.
Lambert wouldn’t describe the actual sound, saying it’s proprietary.
But journalist Andrew Reeves, who’s written a book on Asian carp, got a chance to have a similar system demonstrated for him in Canada.
“It’s terrifying,” he recalled. “We’re not talking about a quiet, melodic sound. It sounds like an outboard motor that is constantly being revved, again and again and again. And for a species that is as sensitive to light and sound as Asian carp are … they want to get away from it as quickly as they can.”
The barrier is likely to keep some other fish away, too, but officials are most concerned, for now, with stopping carp. No one involved expects the system to be 100% effective, but Reeves says agencies who’ve been battling this for a while have been forced to redefine their idea of success.
“They really don’t talk much about eradication simply because they know, at this stage in the game, it’s impossible,” he says. “Asian carp will be a presence in American waterways forever.”
But if the “disco barrier” in Kentucky works well enough, officials plan to ask for more funding for other areas as early as next year.