Carp Stocked In Clarks Hill As Corps Fights Hydrilla

Herbicide and grass-eating carp are being utilized to limit the impact of hydrilla in the lake.

Jeremy S. Buddemeier Corps Communications | August 16, 2019

(Editor’s Note: GON policy has always been to use the original local names for lakes, rather than names later enacted by Congress to honor fellow politicians. So this lake is always referred to in GON as Clarks Hill rather than J. Strom Thurmond. Likewise, we use Lake Eufaula rather than Lake Walter F. George. The following article was written by the U.S. Army Corps of Engineers, so Clarks Hill will be called J. Strom Thurmond Lake in this article.) 

Once upon a time there was a terrible invasive weed-queen named Hydrilla who grew so fast she pushed out every other aquatic plant at J. Strom Thurmond Lake (Clarks Hill). With the help of her toxic underling, blue-green algae, the pair wreaked havoc on local waterfowl and birds of prey.

After a thorough study and survey, residents decided to introduce legions of sterile, grass-eating carp (combined with targeted herbicide treatments, of course) to combat Queen Hydrilla’s stranglehold on the ecosystem.

Although this covers the first 25 years of the story, the next chapter is just beginning.

We spoke with Ken Boyd, chief ranger for forest, fish and wildlife at J. Strom Thurmond Lake Project last week for an update on the reservoir’s Aquatic Plant Management Plan (APMP), which seeks to limit hydrilla’s impact.

Boyd said between October 2017 and March 2019, officials stocked Thurmond Lake with approximately 50,000 sterile, grass-eating carp in accordance with the APMP.

In addition, they applied herbicide in the fall of 2017 to about 200 acres of the lake in areas where bald eagle mortality had historically been an issue. Those areas included Bussey Point, Parksville and Cherokee day-use areas.

Workers release the first batch of more than 17,000 sterile, grass-eating carp into Clarks Hill Lake on Oct. 25, 2017. The fish form a part of management strategies identified in the April 2016 Avian Vacuolar Myelinopathy (AVM) Plan for the J. Strom Thurmond Project. The sterile carp should reduce the abundance of hydrilla by 50 percent, according to research by the Corps of Engineers. Incremental stockings will occur over the next three years. A licensed contractor will release an estimated 17,725 grass carp during the initial operation. Hydrilla is an invasive, noxious aquatic weed found throughout much of the United States. Hydrilla affects shoreline uses in shallow areas especially during the late summer and autumn, however, the vast majority of the lake remains navigable. Hydrilla goes dormant during the winter and re-sprouts from the root system during late spring and summer. Research shows AVM transmitted through hydrilla kills a variety of waterfowl that eat hydrilla and raptors that feed on the waterfowl. The weed carries a blue-green toxin called cyanobacterium. Cyanobacteria attach to aquatic vegetation during late autumn and winter (November-February). Species known to be affected include bald eagle, American coot, great horned owl, killdeer, Canada goose, mallard, ring-necked duck, scaup, and bufflehead. (U.S. Army Corps of Engineers photo by Kenneth Boyd.)

The following year, natural resources staff conducted surveys and determined that additional herbicide treatments were not necessary.

This fall, Boyd and his team will conduct another survey and a random sampling of areas around the lake to gauge the plan’s effectiveness.

“It’s like a gut check to see where we’re at,” said Chris Spiller, natural resources manager at Thurmond. Spiller said it typically takes about four to six years to see any real impact produced by the grass-eating carp.

A comprehensive, lake-wide survey is planned for 2022 to further assess hydrilla control levels and out-year plans, according to Boyd.

In addition to the carp and herbicide fronts, Thurmond has been aggressively bolstering its native aquatic plant nursery, which it started this past winter.

The nursery focuses on plants such as water willow and maiden cane, which can thrive in drought and flood conditions. Establishing strong populations of these native plants is essential to ensuring the health of growing fish and aids against erosion. Thurmond officials plan to plant about 2,000 water willows by September.

Additionally, Boyd said his staff is felling trees, and adding cable and deep water attractor refurbishments to encourage the fish populations in the lake.

He said they continue to monitor bald eagle populations around Thurmond Lake but it’s too early to link current mortality rates to grass-eating carp additions. However, he said he’s not aware of any bald eagle deaths since December 2017. There were four successful nest attempts at Thurmond Lake during the 2018 nesting season.

We will continue to provide updates on the Aquatic Plant Management Plan as information becomes available. Until then, we’re striving to ensure hydrilla and blue-green algae do not live happily ever after.

In case you’re joining the story late, here is some additional background information on hydrilla and Thurmond Lake’s Aquatic Plant Management Plan.

Hydrilla is an invasive aquatic plant that has proliferated at Thurmond Lake since the 1990s. Hydrilla adversely impacts the ecosystem because it grows so quickly that it pushes out native aquatic plants. It has been said that hydrilla grows faster than any living thing.

Blue-green algae grows on hydrilla, and this algae produces a toxin. When coots and other waterfowl eat the hydrilla, the toxin causes them to become sick and develop avian vacuolar myelinopathy (AVM). These fowl then become easy prey for eagles and other birds of prey, which then also develop AVM.

AVM affects the bird’s brain, causing them to become disoriented, fatigued and eventually die. It is strongly associated with American bald eagle deaths, but also with owls, hawks, geese and ducks.

By 2013, Thurmond officials had documented 76 bald eagle deaths that were related to AVM. Corps officials along with Georgia and South Carolina DNRs and the University of Georgia’s Warnell School of Forestry conducted a comprehensive lake-wide survey in 2010 and 2015, combined with a public survey to gauge awareness and determine stakeholder sentiment for proceeding with a course of action against hydrilla.

The stakeholder’s survey report was released in 2013. More than 70 percent of respondents indicated they would support or were indifferent to stocking the lake with grass-eating carp. Almost 66 percent supported the removal of aquatic vegetation, even at the cost of reducing fish and waterfowl habitats.

Officials stocked grass-eating carp in October-November 2017 (17,725), April 2018 (23,040) and March 2019 (8,750).

Previous articles on this subject can be found here.

Written by Jeremy S. Buddemeier, U.S. Army Corps of Engineers, Corporate Communications Office

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