SAVANNAH, Ga. – Integrated biological and chemical treatments to diminish the prevalence of hydrilla, an invasive waterweed and menace to the bald eagle population at J. Strom Thurmond Lake, awaits congressional approval, according to a U.S. Army Corps of Engineers report.
Incremental stocking of certified sterile triploid grass carp plus limited herbicide application in areas with potential for a lot of bald eagle activity will be used to reduce hydrilla by a goal of 50 percent.
Monecious hydrilla, the reservoir’s dominant aquatic plant, can develop a blue-green algae that carries carrying a toxin. Hydrilla also happens to be an irresistible food source for coots. The toxin is linked to a lethal neurological disease called avian vacuolar myelinopathy (AVM). Coots contract AVM crippling their movements making them easy prey for bald eagles which then also contract AVM, said Jeff Brooks, a Corps of Engineers wildlife biologist.
AVM occurs seasonally, November through February, when the blue-green algae produces toxins. During this time, water chemistry changes as the lake cools and begins to mix. While hydrilla goes dormant in the winter, the environmental factors that trigger toxin production have not been completely identified.
“Hydrilla can be somewhat cyclic in its growth,” said Kenneth Boyd, a Corps of Engineers conservation biologist.
The Corps partnered with federal and state partners to evaluate biological, mechanical and chemical treatments that were cost-effective and ecologically-sound. They also sought public input in a 2013 survey distributed to approximately 3,000 stakeholders. The survey was designed to gauge sentiment on hydrilla issues and potential treatments. Following the results of the survey, Corps officials sent a letter to the U.S. Fish and Wildlife Service and the Georgia and South Carolina DNRs requesting their concurrence with an integrated plan using sterile grass carp and herbicide to control hydrilla.
Survey results found that 74.3 percent of respondents were indifferent or in support of stocking sterile grass carp – the most controversial treatment method. Even more respondents, 84.5 percent, say they prefer less hydrilla or only native plants.
Grass carp, who consume hydrilla plants at high rates, will be stocked in locations determined to have historical eagle-to-coot interactions and known high hydrilla abundance, said Boyd.
“It will take 2 to 3 years before the effects of stocking will be noticeable to lake visitors,” he said.
Spot treatments of herbicide (at a minimum of 200 acres) will occur in areas where hydrilla is at or near the surface with priority given to areas known to have high concentrations of American coots and past eagle deaths. Only herbicides labeled as “aquatic use” by the Environmental Protection Agency will be used, said Boyd.
“If water levels are high, it makes it harder for coots to reach hydrilla-infested waters,” said Boyd.
The opposite is true during drought, which covered the Savannah River Basin throughout most of 2016. Lower lake levels provide easier access to areas with high concentrations of hydrilla.
There’s a greater potential for waterfowl to get sick,” he said.
Officials first discovered hydrilla at the reservoir in 1995. In 1998, AVM claimed its first bald eagle. Since that time, 81 bald eagle deaths (33 confirmed from AVM) have occurred in the Thurmond area with seven deaths recorded this past winter, said Boyd.
In early January 2017, a team of Corps of Engineers officials and volunteers identified about 27 bald eagles across 70,000 acres of water via boat and truck routes.
“We know where birds tend to congregate during the year and we know when primary months for AVM issues typically fall,” said Boyd. “We’ve picked up birds as early as November and the season runs through February. We target areas where most hydrilla occurs.”
District officials are developing a budget to compete in the government funding process for the treatment plan. If funds are approved, carp should be stocked in the autumn of 2017, said Boyd.
The Corps performs aquatic vegetation management at JST to support the goals of the Bald and Golden Eagle Protection Act to minimize or eliminate eagle deaths linked to hydrilla and its associated toxic, blue-green algae, also known as cyanobacteria. The goal of BGEPA is to maintain a stable or increasing population of bald eagles.
The AVM Reduction Management Plan, final Environmental Assessment and Finding of No Significant Impact can be found here.