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Common carp are 'vandals'

Officials target greatest threat to Manitoba waterways

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Scientists, trade officials and rural Manitobans are plotting ways to capture, kill and otherwise restrict the movements of the greatest living threat to the province's waterways -- the common carp.

The ubiquitous invasive species is a voracious feeder and spawner that chews up the bottom of marshes, destroying vegetation and churning up sediment in a way that eliminates habitat, reduces biodiversity, increases nutrient levels in lakes and promotes algae blooms.

"They basically take a mouthful from the bottom of the marsh, filter out the bugs they want and spit out the mud," said Rick Andrews, who heads up Ducks Unlimited conservation programs in Manitoba.

"They increase phosphorus levels in water by resuspending the phosphorus trapped in the mud. Their feeding habits are disastrously bad," added Scott Forbes, a University of Winnipeg ecologist. "There's an ecological term for them -- they're ecological vandals."

Efforts to control the common carp have proven fruitless since the European species was introduced to Manitoba waterways deliberately in 1886 to serve as a familiar food source for immigrants. The carp remains popular in Europe, but has fallen out of fashion as a food fish in North America.

The Freshwater Fish Marketing Corp. used to pay a low price for carp and sell it to fish-processors. But the Crown corporation was forced to stop buying carp when the market bottomed out, mainly due to U.S. efforts to pay fishers in the Mississippi River basin to capture and simply destroy aggressive Asian carp.

Now, a broad coalition of Manitoba conservationists, academics, rural communities and business interests is waging war on the carp on a variety of fronts.

Yes Winnipeg, the city's business-development arm, is in the early stages of pitching a Chinese fish-processing company on the benefits of building a fish-meal plant at the CentrePort development. The proposed plant would see live-caught carp as well discarded fish guts converted into fish food.

Forbes has devised a laboratory process that converts carp and other unwanted fish into a liquid garden fertilizer. He's working with Fisher River Cree Nation on plans to scale-up the process and create a fertilizer plant at the Interlake community.

Meanwhile, Ducks Unlimited, the province, Ottawa and other funders have spent $3.5 million to install screens into seven channels that flow out of Delta Marsh in an effort to see whether the structures are successful at preventing the largest carp from entering the wetland that sits at the south end of Lake Manitoba.

Four new bridges were built and four others retrofitted this winter to allow 70-millimetre screens to be lowered into the channels about 25 days after freeze-up, when beneficial species such as walleye, perch and white sucker have already moved into the marsh. The plan is to deploy the screens to bar the largest, most destructive carp from entering Delta Marsh during the warmer months and then monitor the wetland over time to see whether there is a notable improvement in water quality and revegetation.

"We view this as one step toward the improvement of a world-class coastal marsh," Andrews said. "The big carp will not be able to get there and will go back out to the lake, for sure."

The riprap around the new bridges was designed with a flat surface that could allow fishers easy access to large carp.

Métis fishers from nearby St. Laurent could be tasked with catching the carp, should a processing plant be built in Winnipeg. CentrePort and Yes Winnipeg declined to discuss the venture.

Residents of Fisher River Cree Nation, meanwhile, could capture carp swimming upstream from Lake Winnipeg if Forbes is successful at scaling up his fish-into-fertilizer process to allow the construction of an industrial plant.

Forbes has already tested a laboratory-produced fertilizer on vegetable gardens at his own property at Twin Lakes Beach.

"It works better on some plants than others," he said. "It's really just a matter of calibrating how much to put on.

Forbes' fertilizer made from white sucker creates an almost odourless product good for use on indoor plants.

Carp are oilier and create a smellier fertilizer, likely only usable outdoors, he said.

"Ideally, I'd like to see carp gone completely, but that won't happen. They're too prolific," Forbes said. "What we can do is change the population dynamic."

Republished from the Winnipeg Free Press print edition April 20, 2013 A8

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