1/20/2009 10:37:00 AM The mystery of carp Once thought to be a valuable addition to lakes, the lowly carp could be cause of some of the problems in Sauk Lake
Peter Sorensen, a University of Minnesota professor, scientist and researcher, explains to a crowd of 20 Sauk Lake enthusiasts about the complexities of the common carp. Sauk Lake has an abundance of carp and experts say the fish has a negative effect on water quality. HERALD PHOTOS BY BRYAN ZOLLMAN
By Bryan Zollman
In 1880 an article appeared in the New York Times relating to the transfer of 1,000 carp from the United States Fish Commission to the New York State Fish Commissioner. At the time the fish were considered a great asset and were to be distributed to carp farms to anyone in New York who had suitable waters.
Now, 128 years later, the carp population has ballooned to troublesome proportions. What's worse is that a half century ago it was decided that carp were not an asset, but a detriment to water quality and the ability for game fish to thrive. Attempts to rid waters of the bottom-feeder have gone for naught, but recent studies led by Peter Sorensen, a professor in the Department of Fisheries, Wildlife & Conservation Biology at the University of Minnesota, have shown there may be a way to outsmart the fish.
Maybe.
"This is a difficult enemy and it has to be thought through," Sorensen told a crowd of 20 concerned Sauk Lake enthusiasts Wednesday at Sauk Centre City Hall.
Sorensen was a special guest, along with DNR Area Fisheries Supervisor Eric Altena, for an informational seminar sponsored by the Sauk River Watershed District on the common carp.
Sauk Lake is dense with carp and some who live on the lake say they are seeing more and more of them. The problem is the fish do nothing for a lake. In fact, they cause harm.
"They destroy habitats and water quality," said Sorensen. "There are dozens of studies that support it."
Sorensen admits even he, a professor and scientist who has dedicated his career to studying fish biology, doesn't know much about carp simply because nobody has extensively studied the fish before and there is no scientific data recorded to support any specific theories.
"The reason you're puzzled," he told the crowd, "is frankly because it is poorly understood. We simply don't understand why there are so many carp out there."
Sorensen said carp populations are growing in Midwestern lakes and that he wouldn't be surprised if half the pounds of fish in Sauk Lake were carp. This is a concern because many believe the carp can drive down the populations of game fish such as northern, walleye and blue gill. In fact, Sorensen's studies have concluded that high carp populations almost always result in low blue gill populations.
The reason carp are considered a detriment is because they feed off the bottom of lakes, digging as much as a foot into the soil. This kicks up nutrients that are harmful to water quality and also disrupts natural habitats. Even the food carp eat off the bottom is digested and carp excrement further depletes water quality.
"Carp are like a constant pump of nutrients into the water," said Sorensen.
Sorensen said carp can even have a negative effect on waterfowl. Studies have shown that lakes with high densities of carp have poor waterfowl habitat, just another reason to rid lakes of the species.
But can it be done, and if so, how?
The DNR has spent a lot of time and money trying to remove carp from waters to no avail.
Sorensen said removing adult carp is one part of the solution, but not the entire solution. His research team is taking a three-pronged approach. First, he said, recruitment must be suppressed. In other words - keep eggs from hatching or young carp from surviving.
"You can remove adult carp until you are blue in the face," Sorensen said. "But if you can't get a handle on the recruitment process..."
A female carp can spawn up to two million eggs. So even removing 99 percent of the carp from a lake could backfire if one female is left.
"One female can repopulate an entire lake," Sorensen said.
The second part of the equation is to eliminate the risk of re-infestation. That could mean blocking the fish from coming in through streams. But this practice also runs the risk of keeping wanted fish from coming into the lake.
Finally, Sorensen says, adults must be removed from the lake.
Sorensen, along with a team of scientists and commercial fisherman re-cently pulled 3,000 carp out of Lake Susan in Chanhassen. They will now work on suppressing recruitment and keeping the lake from being re-infested. They will also monitor the water quality of the lake to see if it improves now that there are less carp.
Sorensen said carp have a hard time surviving and thriving in lake's with good water quality. Sauk Lake is on the state's list of impaired waters. By improving water quality will it rid the lake of it's carp population? Or will carp have to removed in order for the water quality to improve. That's the Catch-22 of the carp situation and what has many scratching their heads.
Some in attendance wanted the DNR to allow commercial fishermen to come in and harvest carp. Altena said he didn't have a problem with commercial fishermen doing so, but said it was unlikely to have much of an effect.
"We can certainly put a dent in the population," Altena said. "But ever control it?"
Altena's records showed that there have been 190,903 pounds of bullheads pulled from Sauk Lake since 1950. In that same time only 120 pounds of carp have been removed.
He said removing carp from Sauk Lake is not high on the DNR's list, partly because there are no management strategies that have proved effective.
Some also think the annual draw down of the lake is helping carp multiply because they like to spawn in shallow murky water. The draw down is done to help prevent flooding and protect shorelines.
Wednesday's meeting was for informational purposes and there are no plans in place to help alleviate the carp problem in Sauk Lake. Sorensen, meanwhile, will continue his studies in the metro area, which in the future could lead to a potential solution to the ever-growing problem that was created when the first carp was brought to the U.S. in 1880 with high hopes.
"It took us 120 years to get into this mess," said Sorensen. "It's going to take awhile to get us out."
