Corps uses grass-eating carp to tame hydrilla at Thurmond

SAVANNAH, Ga. – The U.S. Army Corps of Engineers will begin stocking sterile triploid grass carp to reduce the abundance of hydrilla in the J. Strom Thurmond Lake Oct. 25 and will run through Nov. 15.

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.

The Corps will add additional fish in April 2018 and April 2019. The releases should lead to 15 grass carp per acre of hydrilla. In the autumn of 2019, a lake-wide survey will provide an estimate of hydrilla coverage to allow the Corps to adjust stocking rates.

Hydrilla is an invasive, noxious aquatic weed found throughout much of the United States.

Hydrilla affects shoreline uss 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 water fowl 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.

Hydrilla spreads easily, according to Kenneth Boyd, a wildlife biologist assigned to Thurmond Lake.

“Boaters should ensure boat trailers, boats, and live wells are free of aquatic plants before leaving the launching area,” Boyd said.

“While hydrilla may have some benefits to fish and waterfowl populations as it becomes established in some lakes, it is costly to manage and has negative impacts on lake users as plant growth clogs waterways especially along the shoreline and around docks.”

Anglers who use Thurmond Lake should become familiar with grass carp and how to identify the species. Removal of grass carp from the lake is prohibited by federal regulations and South Carolina state law.

In accordance with the Savannah District Aquatic Plant Management Plan, adjoining property owners may treat hydrilla around their docks provided they obtain a no-cost permit from the Thurmond Project Office. A state-licensed pesticide applicator licensed for aquatic herbicides must apply the herbicide.

Additional information on AVM and aquatic plant management at Thurmond Lake can be obtained at here or by contacting the Thurmond Project Office at 800-533-3478 or (864) 333-1159.

~ Billy Birdwell, Corporate Communications Office

About US Army Corps of Engineers Savannah District

The U.S. Army Corps of Engineers Savannah District oversees a multi-million dollar military construction program at 11 Army and Air Force installations in Georgia and North Carolina. We also manage water resources across the Coastal Georgia region, including maintenance dredging of the Savannah and Brunswick harbors; operation of three hydroelectric dams and reservoirs along the upper Savannah River; and administration of an extensive stream and wetland permitting and mitigation program within the state of Georgia. Follow us on Twitter @SavannahCorps and on Facebook.com/SavannahCorps
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  • Ferris

    Thanks Billy for keeping uss informed! TGC introduction finally begins, but the initial 17,725 release falls 35% below the EA implied 27,458 TGC (7.5 TGC/acre x 3,661 acres). I hope the lower initial release based on hydrilla abundance in a lower pool proves sufficient to “tame” hydrilla when the pool rises and dormant tubers begin growing. How many additional TGC will USACE add in Apr 2018 and in Apr 2019?

  • Ferris

    The project lead should have a ready answer for the revised implementation of this publically funded effort. The math is straightforward, except there is an error in the EA math for Year 3 that should show stocking 3.975 TGC/Acre rather than 3.75 TGC/Acre.

    Calculating the quantity of TGC to stock requires determining the biomass adjusted acres and maybe adjusting the Year 1 mortality rate for 6 months rather than one year. Perhaps the TGC quantity depends on pool elevations at the time while funding competition could affect the ability to stock desired quantities; however, a tentative revised plan should exist for public information. What is the revised plan?

    The EA plan stocked the following TGC quantities based on 3,661 biomass adjusted acres, after accounting for mortality and adjusting for the Year 3 error.
    Year 1: 27,458 (17,725 actual or 7.5 * 2,363 biomass adjusted acres)
    Year 2: 35,694 (? planned to achieve 15 TGC/Acre)
    Year 3: 14,452 (? planned to achieve 15 TGC/Acre)

    The EA plan implies 54,915 TGC total after Year 2 stocking and again after Year 3 stocking. The goal of a 50% reduction in biomass adjusted acres targets 1,830 acres, or just a 23% reduction from 2,363 acres.

    • Ferris:

      Your question exceeded my technical knowledge, so I called upon the experts at the Thurmond Project for help. Let me give you their answer exactly as they sent it to me.

      — Billy Birdwell, Corporate Communications Office

      In May 2017 representatives from the Corps of Engineers, Savannah District and J. Strom Thurmond Project (JST), U.S. Fish and Wildlife Service (USFWS), Georgia Department of Natural Resources (GADNR), and South Carolina Department of Natural Resources (SCDNR) met to discuss aquatic plant survey data compiled by Georgia DNR fisheries staff from 2014 thru 2016 and its potential impact on pending actions related to the Avian Vacuolar Myelinopathy plan (AVMP) for JST.

      As a result of this meeting and discussions with the state and USFWS the following modifications were made regarding the AVM plan. The Corps will stock carp starting from the fall in 2017 through 2019 to obtain an effective rate of 15 fish per vegetated acre by 2019. A variety of hydrilla known as monoecious hydrilla grows in the Thurmond reservoir. Rapid water level declines during key germination and growth periods can reduce monoecious hydrilla growth. As a result of record lake level declines during the early summer of 2016 we estimated that hydrilla acreages were reduced from the last full survey. To avoid concerns of overstocking, the number of fish stocked were based on 2,363 vegetated acres from the Corps 2015 survey results, instead of the 3,661 aces identified in the AVMP, which utilized the average of the 2010 and 2015 hydrilla surveys.

      An additional survey will be conducted in the fall of 2019. The purpose of the survey will be to assess carp effectiveness on the existing hydrilla coverage. If it is determined that hydrilla acreages have significantly increased supplemental stockings in 2020 may be implemented and will not exceed the quantities specified in the AVMP (76,880).

      • Ferris

        Thank you Billy, I know the research took valuable time that I appreciate; however, the experts did not directly answer my question. The next survey will occur after the Apr 2018 and Apr 2019 stockings, so reading between paragraphs 2 and 3 suggests both of those stockings will probably use 2,363 biomass adjusted acres. If I also assume the full year mortality rate, it appears USACE plans to stock ~23,037 TGC in Apr 2018 and another ~9,393 in Apr 2019.

        Balancing rapid TGC and hydrilla growth rates for moderate rather than drastic control presents a challenge in any lake, how much more so in one with relatively wide level fluctuations. I think a precise outcome for Thurmond requires as much instinct and luck as science, and appreciate the shared information for this effort to reduce AVM related deaths in Bald Eagles.