Outside Peter Sorensen’s office stands a life-size cutout of a large man holding a large fish by the gills.
The fish, a bighead carp, is close to five feet long and upwards of 80 pounds. A voracious eater, this carp can wipe out the base of an aquatic food chain.
Not the kinds of fish you’d want in your waters. Unfortunately, both are beginning to invade Minnesota, says Sorensen, a professor emeritus in the Department of Fisheries, Wildlife and Conservation Biology. They now infest the Mississippi River watershed in states from Mississippi to Iowa.
“With our great waters, we in Minnesota and adjacent Wisconsin are like a shining ornament sitting above a huge area of infestation,” Sorensen muses. “But Minnesota could soon become their next home base.
“Experience shows it’s critical to stop them now. If we can, we’ll be the first state to do so.”
Minnesota’s best chance: a single, strategically placed wall of vibrating bubbles known as a bioacoustic fish fence, or BAFF, which can be placed in navigation locks. Sorensen and his team have identified this “bubbling sound deterrent” as the best carp defense—and it will soon become reality.
High stakes for Minnesota waters
Silver carp, bighead carp, and two other carp species were introduced in Arkansas in the 1970s to clean pond water. But they escaped and have now damaged numerous fisheries and ecosystems severely, if not irrevocably.
“Silver and bighead carp are efficient ‘filter feeders’—they vacuum out the ecosystem,” Sorensen says. “Native fish larvae, including walleye and other gamefish, are starved and/or eaten by these carp.”
The carp could wreck Minnesota’s fisheries, while silver carp alone could end boating and waterskiing—a blow to areas that depend on water sports. They would also wipe out the economic benefits these activities generate.
It would be game over.
Turning carp’s biology against them
From St. Louis to Minneapolis, a series of locks and dams in the Mississippi River reduce the movement of all fish, including carp.
“We identified Lock and Dam 5, north of Winona, Minnesota, as having exceptional potential to stop carp from moving northward,” Sorensen says.
Sorensen’s team worked with a British company to perfect a BAFF system designed for lock openings. His team crafted a three-part deterrence strategy over a decade of research involving lab experiments, mathematical modeling of flowing water, fish tracking in the Mississippi River, and ongoing field tests of a BAFF in Kentucky.
This work gave them a unique understanding of fish movement through locks and dams and how to stop carp.
The key part of the strategy is to use a BAFF to stop carp from moving upstream along with boats passing through the lock and dam’s navigation lock. The system features a tubular, bottom-lying “air diffuser” laid across the lock entrance. Air forced through it creates a curtain of bubbles from tiny holes along its length, and sound projected into it turns the curtain into an acoustic wall.
Sorensen and his team discovered that this system causes bubbles to vibrate with a unique intensity and directionality that invasive carp detect and avoid.
“It’s because they have an exceptional sense of hearing—as evidenced by how silver carp respond to outboard motors,” Sorensen explains.
The system will also include flashing lights to further discourage fish from entering the lock.
Oregonstate News Blog 