Invasive species are not always easy to deal with and when it comes to aquatic species, they are one of the toughest to handle. Asian carps are a menace in the US and researchers have been working to find ways to deal with them.
Researchers at University of Illinois have found that these invasive species can be dealt with effectively by bubbling high concentrations of carbon dioxide (CO₂) into water for the adult Asian carps feel “woozy” when they come in contact with CO2 and they choose to swim away.
Cory Suski at the University revealed that through their study on juveniles of four species—largemouth bass, bluegill, silver carp, and bighead carp they were able to demonstrate that juvenile fishes of all four species actively avoid areas of water with elevated CO₂ once concentrations reached approximately 200 milligrams per liter.
Suski explained that the larvae they used were so tiny that their behavior couldn’t be tested so gene expression data were used. “Even at only eight days old, there are physiological problems happening to those animals when they are put into a high CO₂ environment,” he said. “The biomarkers of stress turned on. So we now have evidence all the way from large adult fish to eight-day-old fish that CO₂ causes disturbance.”
Believing that two barriers are better than one, Suski suggests that carbon dioxide be used to keep invasive species from entering Lake Michigan by working in tandem with electric barriers. The electric barriers emit a low-voltage charge. As large fish swim toward the electric barrier, they sense the charge and swim away. Unfortunately, no non-physical barrier is 100 percent effective against all fish in all situations so additional barriers would help with control.
Suski says the CO₂ method doesn’t pose safety risks, is relatively cheap to use, and is portable with little installation or equipment required. The gas can be easily pumped into a small backwater area where there are known populations of carp—basically with a hose and tank of CO₂.
So far, the CO₂ method has been tested in small laboratory tanks, ponds, and most recently at the Upper Midwest Environmental Science Center in Lacrosse, Wisc., on a much larger scale—1.6 million gallons of water covering half an acre. The preliminary findings from this test mirror the results from those on a smaller scale.
Tests have been conducted on a variety of scales and a range of species, including another Great Lakes invader, the sea lamprey. “Lamprey is an ancient species that predates animals with jaws,” Suski said. “So from an evolutionary perspective, we have data ranging from ancient species, to carp that originated in Asia, and largemouth bass and bluegill that originated in North America—a great diversity of fish that span a long timeframe.”
According to Suski, Asian carp grow rapidly and eat the zooplankton (small animals) and phytoplankton (small plants) that other fish and other aquatic organisms depend upon and pull the rug out from under the food chain. They’ve already invaded the Mississippi River all the way to Minnesota and are about 21 miles downstream from the electric barriers in the Chicago Area Waterway System.
“If they get into the Great Lakes, they have potential to spread throughout eastern North America,” Suski said.