The sight of a 100-pound fish flying ten feet out of the water and onto boats (and sometimes people) has made the invasive Silver Carp the frequent star of youtube videos.
Their unusual jumping habits, and tendency to monopolize entire lake ecosystems, has become cause for concern for everyday boaters and environmental scientists.
University of Minnesota Duluth graduate students Brooke Vetter and Kelsie Murchy have been studying the invasive Silver Carp with their advisor Dr. Allen Mensinger. While the field research is done outside of Minnesota, most of the lab work is done on campus or at the U.S. Geological Survey facility in La Crosse, Wisconsin, called the Upper Midwest Environmental Sciences Center.
Their research goal is to determine what causes the carp to jump out of the water, and find a way to use that knowledge to our advantage.
The fish seem to respond to the noise made by motors underwater. Recording the sounds of the motors, Vetter found their frequencies and developed large underwater speakers. The speakers emit a single tone of up to 160 decibels, mimicking the motors. Compared to our pain threshold of 120 decibels, it’s a pretty intense frequency.
Over the summer the trio ran field experiments in a tributary of the Illinois river, finding that the sound alone was enough to stimulate the Carp to jump.
In videos taken of their experiments, hundreds of carp jump in response to the speakers, flying over and into fallen trees, landing in the boat-- some even hitting the camera.
If it sounds unhealthy for the fish, that's because it is.
“They bleed everywhere,” Vetter said.”They hit the logs and usually that makes them bleed; it can kill them to do this, so the fact that they do this in response to just motors is a little bit unusual.”
Although there isnt hard evidence as to exactly why the fish have such a physical response to the noise, understanding that they do and how we can control it is what will really benefit us.
In her first controlled experiments Vetter set up speakers on either side of a tank, and played the tone alternating between sides.
“We found that it was really, really effective in moving them,” Vetter said.
They were able to get the fish to move away from the sound and to the other side of the tank 37 times in only 10 minutes.
“In the world of fish behavior, it’s really interesting results because usually fish just stop responding after a while.” Vetter said.
Their next challenge was to see if the same techniques could be used to herd the fish or stop their travel completely. This was when her partner Murchy became a part of the project.
“Basically the only thing that restricts their movement right now into the Great Lakes is this electrical barrier that’s in the Chicago Sanitary and Ship Canal,” Murchy said.
Although effective, the electrical barrier makes the water dangerous to people.
“Once we saw that we could move them with sound we wanted to see if we could create a nonphysical barrier,” Vetter said.
Murchy wanted to create another line of defense. Working at the UMESC facility, she created a cinder block barrier that split a small pond in two sections. A one meter opening in the center was surrounded by four speakers.
“They would cross the barrier every three to five minutes and when we played the speakers we were able to actively restrict them to that one side of the pond,” Murchy said.
Although there were initial doubts on how effective the experiment would be, after three days they were able to keep the fish to one side of the pond 90 percent of the time, using the speakers alone. The same tests were also run on ten other native species, who either did not respond to the sound or acclimated to it relatively quickly.
One of the problems is that these Carp outcompete native species for resources. They breed and grow at rapid rates, and take over entire ecosystems.
The main concern right now is the invasion of the Illinois river as it connects to Lake Michigan. If the carp invade Lake Michigan the entire Great Lakes system could soon follow.
Vetter and Murchy hope that their research can eventually be used in rivers and canals like the one in Chicago, as back-up measures when electrical barriers are down.
Photo via Flikr. Taken by Jason Jenkins.