What’s the Corps doing about hydrilla at Thurmond Lake?

By Tracy Robillard, Public Affairs Specialist

Chances are if you live near J. Strom Thurmond Lake, you’ve heard of hydrilla. It’s an invasive aquatic plant that has slowly expanded its reach along the lake’s shoreline since the mid-90s.

Over the years, the U.S. Army Corps of Engineers has used herbicides to minimize the impacts of hydrilla according to its Aquatic Plant Management Plan (APMP). The Corps has limited those herbicide treatments to public recreational facilities and areas where hydrilla presents navigational concerns, such as boat ramps, beaches, and marinas.

Natural Resources Managers with the Corps and the Georgia and South Carolina Departments of Natural Resources (DNR) estimate hydrilla currently occurs in various densities on approximately 11,000 acres of Thurmond Lake. That’s about 15 percent of Thurmond’s total water acreage (71,000 acres).

Army Corps of Engineers biologist Ken Boyd examines a strand of hydrilla, an invasive aquatic weed first discovered at Thurmond Lake in 1995. The plant harbors an algae linked to deaths of bald eagles at the reservoir. Photo by Rob Pavey (Augusta Chronicle), used with permission.

Army Corps of Engineers biologist Ken Boyd examines a strand of hydrilla, an invasive aquatic weed first discovered at Thurmond Lake in 1995. The plant harbors an algae linked to deaths of bald eagles at the reservoir. Photo by Rob Pavey (Augusta Chronicle), used with permission.

Hydrilla causes the Corps and our state partners grave concern because recent research links this invasive plant to the spread of avian vacuolar myelinopathy (AVM) – a disease strongly tied to deaths in American Bald Eagles.

According to Jeff Brooks, wildlife biologist for the Corps’ Savannah District, officials have documented 76 eagle mortalities to date at Thurmond Lake believed to be related to AVM. Although AVM is the suspected cause of mortality, confirmation is not always possible if the carcass has started to decompose, Brooks said. The disease has also been recorded in other bird species, such as owls, hawks, geese and ducks.

Researchers discovered the problem lies in small blue green algae that commonly grow on the leaves of hydrilla. During the winter months (November through January), this algae produces a toxin, which is consumed by coots and other waterfowl that migrate south for the winter. As the coots feed on the hydrilla leaves, they become sick from the blue green algae. These birds become easy prey for bald eagles. The eagles consume the coots, and in most cases contract AVM, which affects the brain and causes fatigue, disorientation, and eventually death.

Bald eagles perch at the U.S. Army Corps of Engineers J. Strom Thurmond Lake. USACE photo. December 2009.

Bald eagles perch at the U.S. Army Corps of Engineers J. Strom Thurmond Lake. USACE photo. December 2009.

Brooks and other staff with the Corps frequently coordinate with the Georgia and South Carolina DNRs and the U.S. Fish and Wildlife Service to address the AVM problem.

“By 2007 we had a good idea of what was causing the bald eagle mortalities,” Brooks said. “We started a cooperative effort with the Georgia and South Carolina agencies to get their input. Both states wanted us to get a better handle on how much hydrilla we have, which we did through a lake-wide comprehensive survey. They also requested we incorporate public involvement, so we partnered with the University of Georgia’s Warnell School of Forestry and sent surveys to the public.”

Completed this September, the survey reached 3,000 stakeholders in 12 Georgia and South Carolina counties surrounding Thurmond Lake. The survey assessed public knowledge of hydrilla and its link to AVM and public sentiment toward potential treatment options—particularly the use of sterile grass carp. The survey targeted five research groups: fishing license holders, state waterfowl stamp holders, registered boaters, campground visitors, and shoreline permit holders.

“When you look at the possible treatment options, the herbicides are short-term and very expensive,” Brooks said. “You have to apply them every year and they still aren’t very effective. If you’re trying to eliminate hydrilla all together, sterile grass carp is the most cost-effective.”

“But it’s not like you can do a one-time stocking of grass carp and then walk away,” Brooks explained. “As they grow larger, they eat less. Plus they have a shorter life span compared to some species. So you would have to do periodic stocking to maintain the appropriate amount.”

Coots arrive at the lake in huge numbers each fall to feed on hydrilla, which harbors an algae fatal to waterfowl and larger birds. Eagles eat the coots. Photo by Ken Boyd.

Coots arrive at the lake in huge numbers each fall to feed on hydrilla, which harbors an algae fatal to waterfowl and larger birds. Eagles eat the coots. Photo by Ken Boyd.

However, some feel the introduction of a new species to the lake poses its own set of problems.

“It’s a significant undertaking, so that’s why we want to look at it closely with our stakeholder groups and state and federal agencies,” Brooks added.

According to the UGA report, 44.5 percent of participants completed the public survey.

The results showed that users were largely supportive of stocking grass carp, as 74.3 percent of respondents indicated they are either indifferent to or would support stocking. Shoreline permit holders were significantly more supportive of general management actions to remove hydrilla than all other users. After being informed of AVM’s presence at Thurmond Lake, 65.8 percent of respondents support the removal of aquatic vegetation, even at the cost of reducing fish and waterfowl habitat.

Additionally, of those fishing at Thurmond Lake in the past year, 63.4 percent of respondents reported fishing around hydrilla. Similarly, 64.7 percent of users report seeing signs directing them to check their boat and trailer for aquatic plants, a critical step in preventing the unintentional spread of this invasive species.

View the complete report from the 2013 survey online at: http://1.usa.gov/1aT01L7

A map of J. Strom Thurmond Lake showing known locations of hydrilla along the lake's shoreline.

A map of J. Strom Thurmond Lake showing known locations of hydrilla along the lake’s shoreline.

While the survey provides valuable information about public opinion, introducing grass carp to Thurmond Lake is still a long way from reality. The Corps would need to complete an Environmental Assessment to evaluate potential environmental impacts and alternative analysis before it could revise its APMP to include the stocking of sterile grass carp. The Corps requested funding in the fiscal year 2014 budget for the Environmental Assessment, but that funding was not approved by Congress.

When funding does become available, the EA could take 18 – 24 months to complete. But paying for the actual stocking and monitoring of grass carp is another story.

“Who pays for it is one of the biggest issues,” Brooks said. “We are in discussions with both states to talk about potential funding. The goal of our aquatic plant management program is to minimize impacts to the authorized purposes of the reservoir; however, all programs must compete for limited funding.”

For more information about the Corps aquatic plant management plan, including hydrilla, visit the Thurmond Lake natural resources webpage at: http://1.usa.gov/18BNr3j

 

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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