Invasive species in for a shock in New Brighton


During recent common carp removal from Long Lake carried out by the Rice Creek Watershed District and researchers from the University of Minnesota, trapped carp were sent through the Whooshh system, which rapidly transported the fish out of the water and into tubs, by suctioning them through a tube. (Bridget Kranz photos)

Employees of Carp Solutions, LLC, a company founded by researcher Przemek Bajer, assisted university students in preparing tubs of anesthetic to humanely kill the carp.

Conservation experts are hoping to make common carp a little more rare in the Rice Creek Watershed District. 

While the species was introduced to the area more than 100 years ago, in the last decade researchers have solidified the link between common carp and poor water quality. The district now hopes to remove a large portion of the invasive species in an effort to improve water quality and protect native flora and fauna. 

“What the carp do in their feeding behavior is root around in the bottom of the lake and destroy native plants,” said Matthew Kocian, lake and stream specialist with the Rice Creek Watershed District. “A lot of native fish species, like bluegill, croppy and other species rely on native plants.”

The current removal project focuses on the Long Lake-Lino Lakes chain, a common migration route for carp. The watershed district covers some 185 square miles, stretching from the north suburbs northeast to the City of Forest Lake, and then down to Mahtomedi.

For the past few years, researchers from the University of Minnesota’s Aquatic Invasive Species Research Center have been working in conjunction with the watershed district to track the movement of common carp in this particular system, making it a prime location for testing out new management strategies.

After wintering in the deeper, more oxygenated Long Lake in New Brighton, a significant portion of the carp population returns north for the summer. This year, just beyond the railroad bridge at the north end of Long Lake, a low voltage electric barrier greets them as they try to funnel into the creek. 

Most refuse to swim through the current, instead following the barrier across the width of the stream and into a holding pen. They are then sucked out of the water into tubs, euthanized and taken to the landfill. 

Overpopulation of carp, which were initially introduced to encourage fishing but have since reproduced exponentially, is a problem in almost every Minnesota freshwater system. 

“Long term, I would love to find another useful purpose for them. But right now, we don’t have one,” says Kocian. “We’ve donated them to the Wildlife Science Center in Forest Lake a couple of times. They’ll feed them to captive wolves and bears. But they don’t want any right now, their freezer is full.”

 

Wet tech

If the common carp population is kept underneath a certain density, called the ecological damage threshold, negative impacts on the ecosystem can be minimized. With this in mind, the district is hoping to remove around 50% of both the adult and juvenile carp populations annually for the next 10 years.

Researchers are also hoping to pilot new technologies for carp management that can make the process more efficient and economical. The electronic barrier being used in Rice Creek is a first in Minnesota, and only the second time one has been used in the U.S. If it proves successful, it could set a new standard for invasive species management, both in the state and across the country.

While the removal will still need to happen annually as carp migrate north through the system, researchers have found that the technologies in place can greatly increase the efficiency of the process. 

“It’s showing some promise,” said Przemek Bajer, assistant research professor with the University of Minnesota. “We’ve caught and removed about 2,000 fish so far this spring.”

Given that the entire system’s population is estimated to be between 12,000 and 20,000 common carp, that’s a significant percentage with a week or two to go in this year’s removal. For residents who are interested in learning more about the project, Bajer will be giving a talk at the Fraternal Order of Eagles in New Brighton on May 28. For more information about the talk call 651-636-9525.

Residents visiting Long Lake Regional Park are asked to refrain from fishing around the barrier and a portage has been set up for boaters. Although the voltage is not high enough to harm humans, interference with the barrier can cause holes that allow carp to more easily get through.

 

–Bridget Kranz can be reached at bkranz@lillienews.com or 651-748-7823.

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