A Washington state company attracted national attention a few years back for introducing a flexible pneumatic tube, aka the “salmon cannon,” to help launch the migrating fish past dams and other barriers.
The peculiar gadget, owned and invented by Whooshh Innovations, so captured the public’s imagination that it earned a segment on comedian John Oliver’s HBO show, “Last Week Tonight,” in which Oliver lobbed fake fish at celebrities. “In your darkest moments of despair, when you see a world torn apart by war,” Oliver said with a smirk, people should remember the salmon cannon as evidence that “we can do great things.”
Now, in Minnesota, researchers are studying whether the salmon cannon could be put to a new — if morbid— task: sucking up thousands of invasive common carp from the state’s lakes and marshes.
Przemek Bajer, a research assistant professor at the University of Minnesota’s center for aquatic invasive species and owner of consulting company Carp Solutions, has been working to develop the novel approach to carp management for more than a year in the Rice Creek Watershed, aided by funds from Minnesota’s Environment and Natural Resources Trust Fund.
For the U team, the salmon cannon brings more than flash; it has serious potential advantages over typical carp removal methods around Minnesota, which Bajer said can be time and labor intensive.
For example, Bajer’s Carp Solutions has often used cracked corn to lure carp into a trap called a box net, where they can be hauled away in relatively large numbers. The company did just that in lakes that flow into Lake Minnetonka this fall.
Carp also tend to stick in large schools under ice during winter, so they can be tracked with radio transmitters and then caught in large bundles, often by fishermen, Bajer said. But nets used for the fishing can be difficult to use as they get hung up on rocks and trees in some waters, he said.
Bajer’s new system would instead use a guiding system — similar to a gentle electric fence — to direct fish toward the Whooshh entrance. From there, they would be flushed out of the water forever. Bajer said in a perfect world, the whole operation could be portable and be largely autonomous. Local governments could trade or rent them, too, he said.
Bajer said the idea sprung out of his past research on carp migration patterns. He has studied carp at the U since 2006, first tracking the fish with radio transmitters. Through that, he discovered carp have a “migratory life history” somewhat similar to salmon, he said. Adult common carp in Minnesota often spend most of their time in deep lakes, but in the spring they travel to shallow marshes to spawn, Bajer said.
“In some cases, more than half of the population, sometimes more than 90 percent migrate,” he said. That’s where Bajer would deploy his fledgling system: “So if you had some sort of a device that can catch those fish, you could remove 50, 80 to 90 percent of the population in maybe two weeks and just be done with it.”
There are still some major kinks to be worked out in the altered Whooshh system. Bajer said the salmon cannon has worked just fine, as has the guidance system. But getting the fish to actually enter the Whooshh, which sits above the surface of the water, has been more of a challenge.
“We have to elevate the fish,” Bajer said.
Researchers have tried various types of fish ladders, but the carp have been hesitant to swim up them, he said. Bajer said he hopes to try other tactics when he returns to field work in the spring. One option could be a version of the Archimedes’ screw, in which fish enter a tube with rotating blades that guide them upwards and block them from swimming elsewhere.
Bajer also said they could use the electric fish fence to guide migrating carp to a box net, where the Whooshh could be used in harmony with that current removal system.
That is all preliminary thinking for now, however, he said. “Long story short, we don’t have anything that works yet,” Bajer said.
The University of Minnesota team also needs to find a way to differentiate fish entering the Whooshh. Bajer said the Whooshh system was initially developed with imaging technology to sort fruit during harvest. That could hypothetically be copied to identify fish and redirect native species back into the water.
Bajer said he hopes the Whooshh system could eventually be used as an effective tool in the state’s fight against invasive carp, but not necessarily to replace existing techniques. Carp are one of Minnesota’s most common and damaging invasive species. First brought to the country in the 1970s as part of fish aquaculture, they escaped into the Mississippi River’s drainage system during large floods. They’re big fish with big appetites, and they destroy habitat for waterfowl, amphibians and other fish through their destructive food-foraging techniques, according to the Minnesota Aquatic Invasive Species Research Center.
In the north Metro area’s Rice Creek Watershed, where Bajer is conducting research, common carp are numerous. Matt Kocian, a lake and stream specialist with the district, said they’re trying to reduce carp to a threshold of roughly 80 or 90 pounds per acre. “When carp are more dense than that, they’re probably contributing to algae blooms and water problems,” he said.
Kocian said carp in the watershed, which includes Long Lake and the Lino chain of lakes, are currently between 500 to 600 pounds per acre.
Bajer said it’s a bit strange to be inventing strategies to kill an animal in droves, but he said the “positive thing is that carp really do have a very strong effect on lakes, especially shallow lakes,” and a reversal in lake health comes fast. (Most carp harvested by Carp Solutions is sent to the Wildlife Science Center in Stacy and fed to wolves and other wildlife, according to Bajer.)
“You remove the carp, say in March or April when they migrate — by June or July the lake is totally different than it used to be,” he said. “So that’s kind of rewarding, you know, you’re doing something that actually makes a difference.”