For the last two years, researchers on the Mississippi River have been studying the effectiveness of underwater acoustics as an invasive carp deterrent.
Halfway through the study, the results are promising.
Marybeth Brey, a research fish biologist with the Geological Survey and Christa Woodley, a research biologist with the Army Corps of Engineers, co-lead the project.
They designed and installed a 16-speaker soundbar at Lock 19 in the Mississippi River, a section of the river between Keokuk, Iowa, and Hamilton, Illinois.
There are four types of invasive carp in the Mississippi, brought in intentionally in the late 60s and early 70s.
“They filter feed, they eat a lot of phytoplankton, zooplankton, and so, some states brought them in to play clean-up,” said Brey.
But that led to unintended consequences. The carp compete with native species like the bigmouth buffalo and gizzard shad. Silver carp also are known to jump out of the water, causing injuries and property damage.
The carp can also reduce the water quality, leading to increased dredging and bank destabilization.
“When you’re thinking about something like the Mississippi River where we already have quite a bit of flood risk and flood elements, the fish can actually increase those impacts,” said Woodley.
There are many studies working to deter invasive carp in Midwest waterways, but the underwater acoustic deterrent system is one of few that specifically targets invasive carp, minimizing impacts on native species.
The soundbar plays sounds specifically at the frequencies the carp can hear, with the intention of irritating them so they don’t come up the river.
“In some cases, it should stop them from wanting to cross. Sometimes it will actually cause them to turn around,” said Woodley.
The soundbar can be controlled both on site and remotely. It is on for three days and eight hours, then off for three days and eight hours, while the researchers test its efficacy.
Brey and Woodley’s team puts transmitters in 700 to 800 fish a year. The fish are caught, given a minor surgery to insert the tag, then released.
This tagging is a group effort among several organizations, including the Fish and Wildlife Service, Missouri Department of Conservation, and both the Iowa and Illinois departments of natural resources.
The scientists can then compare how many fish cross the lock when the system is active and how many cross when it is inactive.
In data from 2022, they saw a 50% decrease in silver carp specifically.
“So, for every two fish that pass upstream when it’s off, one would pass when it’s on,” said Brey.
Most native species in the Mississippi do not hear at the same frequencies as the carp, and the noises don't seem to bother them.
Bigmouth buffalo are the fish the team has tagged the most, and they are crossing the lock at similar rates when the system is off and on. For every 1.2 fish that moved upstream when the system was off, one moved upstream when it was on.
They have also seen no significant impacts on the freshwater drum, the paddlefish, or the white bass.
The data from 2023 will be analyzed soon.
Though Brey and Woodley provide the results, they don’t decide if the system should be implemented on a broader scale — that decision is left to the states.
Besides studying the movement of fish, Brey and Woodley have also been tracking how well their equipment functions over longer periods of time. The soundbar has withstood a lightning strike, severe weather, and electrical issues caused by a mayfly event.
They switch the speakers every year due to normal wear and tear, but otherwise the soundbar is holding up well. The technology developed for this project can be used for other projects as well, like those trying to attract fish towards certain areas, or cover up construction noise.
“It’s had a lot of applicability and some really neat science going into it that we’re able to track and hopefully push out to the people that need it for whatever purpose,” said Woodley.
There are other deterrent strategies being studied. Carbon dioxide, electricity, and walls of bubbles can all be used to deter the passage of fish. But those methods all deter native fish as well.
Some groups are also working on combining removal methods with deterrent methods.
“We’re trying to say, how can we, if we’re deterring fish, how can we remove them at the same time,” said Brey.
The underwater acoustic deterrent system study is set to continue through the end of the year.
It may be extended with different research questions depending on needs of the partner agencies.
