Stocking Lake Norman with Sterile Grass Carp to Combat the Invasion of Non-Native Hydrilla

On April 16th, approximately 4,000 sterile grass carp were released from Ramsey Creek Park to control the growth of hydrilla on Lake Norman. The total number of the grass carp will be about 12,330. A recent comprehensive survey performed by NC State found active hydrilla growth in 640 acres on Lake Norman. The addition of 12,330 grass carp along with the previous 10,200 that were stocked May 2018 will help largely eliminate active hydrilla growth in the next 2-3 years.

Charlotte Water owns and operates two drinking water intakes as the water supply for our community; one at Lake Norman and another at Mountain Island Lake. Aquatic weeds can pose a nuisance to water suppliers at their drinking water intakes by clogging pumps or as a biological contaminant that must be treated. There are a variety of ways to manage aquatic weeds. Complete eradication is often impossible but suppression is achievable.

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Mr. Fish truck that transported grass carp to Ramsey Creek Park

The Lake Norman Marine Commission releases these fish because hydrilla is an aggressive invasive non-native aquatic weed that the grass carp like to eat. Left unchecked, hydrilla can devastate the balance of the lake’s ecosystem. It forms nearly impenetrable mats of stems and leaves at the surface of the water, crowding out other vegetation with its rapid growth. Hydrilla was originally introduced in the U.S. as an aquarium plant decades ago and can now be found in many water reservoirs nationally due to accidental releases.

The problem with many invasive species is that they have no natural predators in the regions where they are accidentally introduced. This leads to explosive population growth which puts a heavy strain on the resources available. Native species are then having to compete for those limited resources and are often out competed, leading to fewer and fewer of those native species.

The carp are transported to Ramsey Creek Park by a large truck with multiple water tanks containing the grass carp. Next a large hose is attached to one of the 10 holes on the bottom of the water tanks located on the side of the truck. After hooking up the hose securely to the water tank, the opposite end is lain out into the lake far enough so that when the carp come out they will be in water deep enough for them to swim in. It is important that the hose is set straight so the carp do not get stuck halfway through their journey from tank to lake. The carp are then released from the tank and rapidly slide down the hose all the way into the lake where they begin to cluster up as a seemingly endless number of carp exit the hose. It takes them a few minutes to orientate themselves and recover after their long car ride and short slide to freedom. They slowly but surely disperse into their new home, Lake Norman. This process is repeated for all the tanks situated on the back of the truck. While more carp take the slide from captivity to open waters, some of the grass carp that have already recovered can be seen a little further out jumping out of the water and splashing about enjoying their new-found freedom.

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Hose that carp use to get from truck to lake at Ramsey Creek Park

Wouldn’t adding the grass carp do the exact same thing to the ecosystem as the hydrilla? The carp are sterile which means that they cannot breed. The grass carp help combat the hyrdilla which in turn helps native species return to the area. The stocking of sterile grass carp on Lake Norman is a cooperative effort with the NC Department of Environmental Quality (NC Aquatic Weed Program), NC Wildlife Resource Commission, Duke Energy, Charlotte Water and the Lake Norman Marine Commission.

 

 

 

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