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In just five hours, a contractor’s crew of 18 men poured over 100 cubic yards of specially insulated concrete to build an electric fish barrier at Mayhew Creek, shown in this late August photo. The contractors used two large fillable bladders to dam off the site and divert water through a culvert while the project was completed.

Two recently installed electric barriers east of Mankato will help protect several thousand acres of water, including a number of popular fishing lakes, from the threat of invasive carp. The barriers are set for commissioning later this month.

As first reported in the September 18, 2018 edition of the The Free Press, crews finished construction of both barriers this fall, completing a lengthy process of site identification, securing construction and maintenance easements on private land, and actual installation and construction.

The Outdoor Heritage Fund, one of four funds created by the Clean Water, Land and Legacy Amendment, appropriated funds in 2012 that paid for the two barriers, and ongoing maintenance costs will be paid by the state of Minnesota with help from county Aquatic Invasive Species funds in Waseca and Blue Earth counties.

The electric barriers were designed by Smith-Root Inc., a Washington-based fisheries research company that specializes in electrical applications for fisheries conservation. The barriers work by emitting a pulsed field of direct current that affects muscular control in fish. The barriers are made with a special mix of concrete that includes insulator fill and is reinforced with special fiberglass rerod to carefully control an electric field that works as a deterrent to upstream and downstream movement of fish.

Stopping all fish movement is a tradeoff that restricts movement of native fish but also prevents colonization of harmful invasive carp species.

Invasive carp represent a threat to aquatic resources in Minnesota. According to the United States Geological Survey Nonindigenous Aquatic Species website, invasive carp have been shown to affect zooplankton communities, which impacts native fish species that rely on plankton for food, including newly hatched larval fish, plankton-feeding adult fish — such as gizzard shad, bigmouth buffalo and paddlefish — as well as native, threatened mussel species.

Changing the zooplankton community can change trophic fish community relationship and structure. A worst-case scenario is the Illinois River where researchers at Southern Illinois University found that silver and bighead carp now comprise more than 60 percent of the total fish biomass in the river.

Black, silver, grass and bighead carp, a small set of carps in the same family, are the species commonly referred to as Asian carp, or, as legislated in Minnesota in 2014, referred to officially in the state as invasive carp.

Invasive carp individuals have been captured in the Mississippi, Minnesota and St. Croix rivers. Reproducing populations of bighead and silver carp exist in Iowa, Missouri and Illinois, and the fish have slowly been making their way upstream toward Minnesota. To date, only nomadic adults have been captured in Minnesota with no young fish as evidence of successful spawning.

In contrast, the longer-established but also invasive common carp has been in Minnesota for more than 100 years, wreaking ecological havoc in shallow lakes where it can outcompete native fishes and destroy habitat. If the stain of introducing common carp still lingers more than a century later, a bit of prevention is worth a great deal when it comes to the threat of invasive carp.

Craig Soupir, Minnesota Department of Natural Resources Area Fisheries Supervisor in Waterville, said his agency has been concerned about the threat of invasive carp for some time.

“The DNR has been seriously looking at this threat for many years, identifying where our lakes are protected, where we could use some help and continuing to learn more from state, federal, and academic partners,” he said.

Soupir’s nine-county DNR Fisheries Management Area has several watersheds. One of the major watersheds is the Cannon River watershed, which is protected from upstream movement of carp by the impassable Byllseby Dam.

The Albert Lea area lakes are protected by electric barriers installed by the Shell Rock River Watershed District.

Part of the Zumbro River watershed is protected by the Zumbro Lake dam.

Most of the Blue Earth River watershed is protected by the Rapidan Dam; however, the Le Sueur River’s mouth meets the Blue Earth River downstream of the Rapidan Dam, which means invasive carp have nothing stopping their upstream movement in the Le Sueur.

Invasive carp moving up the Mississippi River, into the Minnesota River and into the Le Sueur River could enter a couple of very important recreational lakes. Some initial proposals suggested barriers on the Minnesota River itself. However, it would have been a massive undertaking, unlikely to contain the river channel during flooding. And it would have had huge impacts to native fish species including some that are species of special concern.

Soupir and his DNR colleagues sought solutions that could prevent invasive carp from getting into the most important lakes in the state without blocking off the important ecosystem connections on the Minnesota River and the important need for connected habitats. In Soupir’s area, one lake stood out.

“(Madison Lake) may be our most important lake,” he said. “It’s close to a large metropolitan area, it’s well developed, it gets some of the highest use of our entire area for fishing and even for recreational use. Introducing invasive carp could have huge economic and environmental implications for the lake.”

Soupir’s team did its homework in preparing for such a large project, looking carefully at watershed boundaries and where there may be vulnerabilities.

“We did watershed assessments and looked at where we could put a barrier to protect these lakes,” Soupir said. “We also identified some breaches in the watersheds, that, while they are unlikely, had the potential as an end around for fish to get in.

“We identified two sites. One is at the outlet of Madison Lake, between Madison Lake and the LeSueur River, and the other is on Mayhew Creek, just south of the city of Janesville. The location of these two barriers prevents the migration of invasive carp in the Madison Lake and Lake Elysian watersheds.”

To date, invasive carp have not moved as quickly into Minnesota as feared but remain a potential threat.

Besides stopping invasive carp, there is a secondary benefit for the watershed and shallow lakes with electric barrier installation.

“With a number of shallow lakes, part of the protected watershed, a severe winter could knock out common carp,” Soupir said. “If that were to happen and common carp aren’t able to get back in, it would help improve water quality in those lakes. So not only do electric barriers have a benefit for invasive carp prevention, but also potentially to improve water quality in the entire watershed by eliminating movement of common carp back into the system.”

Soupir also pointed out that safety was a core part of the planning process. The barriers can receive high flows at times and are sized to pass water and debris. The electrodes in the barriers are spaced far enough apart that no human could contact two to complete a connection and electrocute themselves.

Scott Mackenthun is an outdoors enthusiast who has been writing about hunting and fishing since 2005. He resides in New Prague and may be contacted at scott.mackenthun@gmail.com.

Follow Shane Frederick on Twitter @puckato

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