Exploring ways to use sound to safely deter the advance of invasive carp
When faced with the formidable goal of reducing the movement of invasive carp into and through Minnesota waters while also maintaining the ecological safety of native fishes, MAISRC researchers considered numerous options; everything from dams, to bubble curtains, lights, electricity, odor, and sound was discussed.
Although some of these options are used elsewhere, none was well-suited for Minnesota’s treasured lakes and rivers. Many options, such as closing locks and electrical barriers, halt the natural movement of all fish, both native and nonnative, and carry risks to the public. Here in Minnesota, researchers wanted to develop a new system that would preserve our native species and their ecosystems while also deterring the upstream movement of invasive carp, especially the silver or “jumping carp.”
With that goal in mind, MAISRC researchers developed a plan centered around certain qualities that make invasive carp unique: their super-sensitive hearing abilities as well as their apparent aversion to humans and their tendency to jump. Carp hear a wide range of frequencies, from approximately 100 to 3,000 hertz, while most native fishes – such as lake sturgeon and walleye – only hear sounds in the 100-6,000 hertz range, and then with much less sensitivity. (For reference, humans can hear from about 20 to 20,000 hertz.)
Armed with this information, along with the additional data that they are collecting on the swimming performance of carps (suggesting that carps often cannot pass through the gates in the locks and dams of the Mississippi River) MAISRC founder Peter Sorensen is now developing acoustical deterrents for use in locks. He and his team are employing an experimental approach to examine how certain sounds, perhaps when combined with other cues, can deter the movement of carps. Sufficient deterrence would mean that the critical number of adults needed to reproduce will not pass through, while native fish still do. This approach would not risk human safety or navigation through the locks.
This project kicked off in the winter of 2014. Now, it is currently focused on examining invasive carps (silver, bighead, and common carp) and lake sturgeon (pictured). Silver carp – the poster child for invasive carps – grow large and jump out of the water when disturbed by boaters. Lake sturgeon are of particular interest because they are threatened and migrate long distances to reach their spawning grounds.
Experiments presently focus on testing reactions to the sound of an outboard boat motor, chosen because of its complex and varied amplitudes and frequencies that fish seem to have a difficult time growing accustomed to. The sound is played into tanks, and researchers can observe the movement and behavior of the fish to determine their response.
The sound is turned on for two and a half minutes at a time, during which time researchers look for any change in fish distribution. “The carp exhibit an immediate response to this sound,” said MAISRC researcher Clark Dennis. “They seem agitated and clearly avoid the area near the sound source. On the other hand, the lake sturgeon didn’t seem to notice at all. The noise simply isn’t loud enough to them to inspire a behavior change.”
Following this success, researchers plan to test a large-scale acoustic deterrent in the auxiliary lock at Lock and Dam #1 in St. Paul this summer. They will use wild, acoustically tagged lake sturgeon and bigmouth buffalo to test their response to the sounds, which they will then compare to the behavior of common carp in the area.
“Ultimately, sound is a prevention tool with genuine potential – it can be targeted to carps, is safe and relatively inexpensive, and can be improved by combining it with other cues such as velocity at the gates.” Dennis added. “We also hope to combine its use with optimized eDNA detection. Overall, this is an extremely promising option that will have little impact on nontarget species.”