ST. PAUL, Minn. — Fitted with electrofishing equipment, the boat eased into the cattails along North St. Paul’s Casey Lake, two University of Minnesota technicians standing at the bow with dip nets ready to scoop up stunned common carp.
In short order, they did, plopping them into a pail so that small radio tags could be inserted into the largest ones, enabling researchers to track their movements.
That outing, on a recent sunny afternoon, was just one of a half-dozen ways university scientists are researching one of the state’s most vexing creatures. Brought to Minnesota in the 19th century, common carp have taken over thousands of shallow lakes and wetlands, rooting on the bottom for food and turning many of them into mud holes that no longer sustain ducks and other species.
Now, though, relief could be on the way.
Led by professor Peter Sorensen, university scientists are trying to figure out what makes these carp tick: where they go, when and why, and what attracts and repels them.
The goal: to come up with a coherent and sustainable set of approaches that will reduce their numbers and help Minnesotans recapture bodies of water they’ve damaged.
Over time, there would be bonuses — better fisheries, clearer water and new strategies that limit the impact of other invasive species such as Asian carp, large, voracious newcomers at the state’s border, if not already here.
“It’s doable— with good science, time, imagination and patience,” said Sorensen, a fish biology professor in the university’s College of Food, Agricultural and Natural Resource Sciences. “However, although doable, it’s not necessarily simple.”
As other federal and state researchers strive for ways to blunt the threat of Asian carp, the university is playing a role.
“I wouldn’t say there’s a lot of overlap, but there is a lot of connection between work we are doing and Dr. Sorensen is doing with common carp and Asian carp,” said Mark Gaikowski, supervisory biologist at the U.S. Geological Survey’s Upper Midwest Environmental Sciences Center in La Crosse, Wis.
Over the past eight years, University of Minnesota carp researchers have received funding and other help from the Legislative-Citizen Commission on Minnesota Resources, the Minnesota Department of Natural Resources, the U.S. Geological Survey, the Ramsey-Washington Watershed District, the Australian government and the Riley Purgatory Bluff Creek Watershed District.
They started out researching chemical signals or odors that carp emit in an attempt to control their populations. They have since used electronic signals to track and to help remove carp from lakes efficiently without resorting to poisons or building solid barriers. More recently, they have been fine-tuning acoustic, air-bubble barriers to come up with the most effective combination of bubbles and sound to discourage juvenile carp from passing through them.
Those barriers are seen by many as a promising way to stop Asian carp from moving up specific rivers and establishing reproducing populations.
Along the way, they have learned much about carp behavior, as well as ways to suppress their numbers: They have found, for example, that bluegills relish carp eggs and larvae and that carp young only survive in numbers in shallow, interconnected wetlands in years following severe winter-kills that eliminate bluegills and other predatory fish.
“We know you need a healthy native fish population to control carp,” said Sorensen, who stresses the importance of healthy aquatic ecosystems.
But continued funding is precarious.
Since 2003, the university has received four appropriations totaling $1.5 million from the state lottery-supported Minnesota Environment and Natural Resources Trust Fund. But the Legislative-Citizen Commission on Minnesota Resources, which recommends such research projects, is not providing more money in its next funding cycle. Dealing with its own budget problems, the DNR has not committed any, either.
Politicians, meanwhile, are fretting about what to do about Asian carp.
With silver and bighead carp caught in border waters in recent years, and environmental DNA evidence of silver carp in the Mississippi River up to the Ford Dam in the Twin Cities, they are giving the issue more attention.
One intriguing option is the acoustic, air-bubble barriers, which are being studied in an old, cluttered building on the university’s St. Paul campus.
Inside it, Dan Zielinski, a civil engineering doctoral candidate, oversees a pair of large covered vats, which he has outfitted with a system of PVC pipe, wires and tubing.
With tiny holes drilled in the pipe, allowing air to escape, the system creates a noisy wall of bubbles when activated.
“There’s nothing complicated about it,” Zielinski said. “Quantifying what is going on is the difficult part.”
The radio-tagged fish inside it are monitored electronically and, Zielinski said, show a clear reluctance to pass through the barrier.
“It reduces the number of passages by 75 percent,” he said.
Sorensen predicted those barriers, which also are being tested elsewhere, could be built and installed in a couple of months if the state or anyone else is interested.
DNR spokesman Chris Niskanen said his agency continues to research the viability of bubble barriers, especially on the federally protected St. Croix River, but will not make any decisions until next year.
“We understand that this is not a 100 percent impermeable barrier and that there is a lot of skepticism about it,” Niskanen said. “We view it more as a means to manage carp instead of keeping them out entirely.”
Information from: St. Paul Pioneer Press, http://www.twincities.com