Angst surrounding invasive carp may have eased in parts of Minnesota, but behind-the-scenes work ramps up as the threat remains.
The first of the heavy-eating fish, originally known as Asian carp, was caught in Minnesota in 1991. At least one has been caught every year since 2006, with six so far this year. Scientists think they have just been individual fish, not part of a reproducing colony. No young fish have been caught.
The fear is that invasive carp will take over areas native fish need, eating their food and forcing them out.
"Minnesotans should be concerned about invasive carp," said Nick Frohnauer, the state Department of Natural Resources' invasive fish Mississippi River coordinator.
On the other hand, Frohnauer said, "they are not established," and native fish have not been harmed.
Researchers at a laboratory on the University of Minnesota St. Paul campus are trying to keep it that way.
Inside a building that decades ago housed a farm tractor repair program, researchers look for ways to stop the fish from moving into Minnesota. The No. 1 idea so far is using sound, perhaps with bubbles or light (maybe strobe lights), too.
"No barrier is 100 percent," Frohnauer said.
A U.S. Army Corps of Engineers lock and dam on the Mississippi River near La Crosse, Wis., already has a set of University of Minnesota speakers installed, playing boat motor sounds that seem to discourage invasive carp from moving past them. Speaker systems are planned by the DNR and university for upstream locks.
The emphasis is on the Mississippi River in an attempt to keep the carp from moving up that river, as well as the Minnesota River that winds through southern Minnesota and the St. Croix River that flows between Minnesota and Wisconsin from Iowa to north of the Twin Cities.
If fish are stopped in the Mississippi below Hastings, Minn., most Minnesota waters would be protected.
The university's Minnesota Aquatic Invasive Species Research Center released a report in May that shows invasive carp threats centered on the Minnesota and St. Croix rivers.
North-flowing streams, such as the Red River, are under less threat since the fish are coming from the southern Mississippi, near where they escaped in the 1970s after being brought to the United States from Asia to clean up sewage lagoons and fish farms.
There are concerns that streams dumping into Lake Superior some day could be threatened as some fear invasive carp will get into Lake Michigan, opening other Great Lakes to the species.
A few years ago, Minnesota lake country in the Mississippi River watershed was threatened, with resort owners and others fearing economic disaster if the invading carp reached them.
However, closing a lock at St. Anthony Falls in downtown Minneapolis and repairing an upstream dam at Coon Rapids has reduced that threat.
Clark Dennis is one of the university's researchers looking at ways to stop the fishes' progression.
Working in a lab established in 2012 and greatly improved a couple of years ago, Dennis tests young Asian carp that swim around an oval pool through various sounds. He can raise and lower volume and pitch, make a sound come or go quickly or slowly, and make any number of other alterations to see what might stop them the best.
Asian carp's body configuration makes them very sensitive to sound, much more than most native fish, Dennis said.
That makes a sound barrier promising because it could stop silver and bighead carp, the two presenting the most threat, while letting native fish move unfettered.
The laboratory has native fish that researchers use to see how they are affected.
Even with the improved lab, Dennis said, researchers will need to monitor how installations in the real world are working. One way will be to install radio transmitters on fish so their movements may be tracked.
What is the deadline for finding a way to stop the fish?
"As soon as possible," Associate Director Becca Nash of the invasive species center said. "It is a race against time."
Dennis is ready to move from the lab to locks and dams.
"The time is right now to put something out in the field," he said.
Sound systems may be used at locks, the large rectangular areas where boats and barges are raised and lowered. Dennis said the Corps of Engineers is working with researchers to find ways to regulate gates on the dams to keep fish from getting through.
One of the major issues researchers consider, Dennis said, is unplanned side effects from whatever is used to deter fish. If a method hurts native fish, for instance, it must be re-examined, he said.
The sound system in place in southern Minnesota originally was cracked up so loud that people on barges could not hear to use their two-way radios as they moved through the locks. The volume was lowered enough that it did not bother people above the water but the sound still filled the water.
An advantage of using sound over things like chemicals, Nash said, is "it is reversible," and if it has an unexpected impact on something, it can be turned off with no lasting effects.
Also with sound, Dennis said, is if one type does not work well, or fish become immune, it easily can be changed.
Besides looking at sound and other ways to stop fish, the university center also is looking at how to better detect if Asian carp are present and ways to catch them if they do establish colonies in Minnesota.
With dozens of researchers working on the problem, "we are pulling out all the stops," Dennis said.
A carp is not a carp
Asian carp: A fish native to Asia that was brought to the southern United States in the 1960s to clean up sewage lagoons, fish farms and other water systems. Due to flooding and other reasons, they escaped into the Mississippi River
Chinese carp: While some Asians say they are offended when the fish are called Asian carp, a Chinese delegation that recently visited Minnesota called them Chinese carp. The fish are not welcome in the United States, but ironically they are desired (but endangered) in China.
Invasive carp: A generic term used for a variety of Asian carp species.
Silver carp: The best known of the invasive carp because of videos showing them jumping 10 feet in the air around boats. Thirteen have been found in Minnesota waters. They can be up to 39 inches long and weigh 77 pounds.
Bighead carp: Grow up to 51 inches long and weigh up to 110 pounds. Twenty-six have been caught in Minnesota.
Bigheaded carp: A term sometimes used for both bighead and silver carp.
Grass carp: Fifty-eight have been caught in Minnesota, the most of any invasive carp. Many are thought to have escaped from an Iowa fish farm.
Black carp: A form of invasive carp that has not been found in Minnesota.
Common carp: Intentionally introduced from Europe and Asia in the 1880s. It is in 48 states and looks much like the native bigmouth buffalo. The Minnesota Department of Natural Resources says: "Common carp are one of the most damaging aquatic invasive species due to its wide distribution and severe impacts in shallow lakes and wetlands."