A tiny algae bloom linked to hundreds of bald eagle deaths across the Southeast is making an unwanted resurgence this winter at Thurmond Lake, where at least five dead or dying eagles have been recovered.
Related Stories
"One of them was a big, mature bird found between Tradewinds Marina and Lake Springs," Corps of Engineers wildlife biologist Ken Boyd said. "We picked up another one below Russell Dam."
The culprit is a disorder known as avian vacuolar myelinopathy, or AVM, that is spread from algae that grows on hydrilla -- an exotic weed from the aquarium trade first detected in the lake in 1995.
Hydrilla is a choice food for small waterbirds called coots, which in turn are eaten by bald eagles lured by the lake's erratic shoreline and nesting trees.
Coots and Canada geese are also vulnerable to AVM, which causes brain lesions that disorient and kill the infected birds.
Last winter, when hydrilla growth was minimal and much of the weed was deep underwater, only two dead eagles were recovered.
This season, however, the mats of hydrilla have grown dramatically because water levels recovered in 2010 after a long drought.
An increase in hydrilla typically means more AVM cases, and more dead eagles, said Susan Wilde, an assistant professor at University of Georgia's Warnell School of Forestry who is part of a research team studying AVM.
"Last year was a low year for hydrilla, and this year is a banner year," she said. "From our monitoring, we are seeing a lot more sick coots, so it looked like it would be a bad year. Unfortunately, that's what it's turning out to be."
The five eagles recovered this season bring the total known mortality at the lake to 59, but it is likely that there were more dead birds that were not found or recovered.
Richard Marshall spotted one such bird on New Year's Day as he and some friends were scouting for areas to duck hunt.
"We were up near Bussey Point and saw a big group of coots that went back into a cove," he said. "We pulled in there and he was sitting on the edge of the water. Usually, eagles are the first birds to fly off and this one just sat there."
As the men watched, the eagle turned, then stumbled.
"It tried to take off and fly, but it just went about 15 yards and hit the ground," Marshall said. "It was stumbling like it was drunk."
Such a description, Boyd said, appears to be a textbook case of AVM. Marshall reported the location of the sick eagle, but wildlife authorities who went out there to search for it on Sunday were unable to locate it.
I.B. Parnell, a senior wildlife biologist with Georgia's Wildlife Resources Division, said dead eagles recovered at the lake are taken to the Southeastern Cooperative Wildlife Disease Study facility in Athens, Ga., where tests typically confirm the presence of AVM.
"We know for sure there is an outbreak this year," he said. "If you go out there you can see lots of coots are acting strange."
So far there is no known solution for AVM, but Dr. Wilde and her colleagues are trying to learn as much as possible about the condition. Of the 17 lakes from North Carolina to Texas where AVM and bird mortality have been identified, the algae densities at Thurmond are among the greatest.
In addition to eagles, coots and geese, AVM has been confirmed in owls and ducks, but there is no evidence that it can be spread to mammals. In one experiment, infected coots were fed to pigs to see if they developed the fatal brain lesions; they didn't.
Hydrilla, an exotic weed used in the aquarium trade, was first found in Thurmond Lake in 1995, when it covered 55 acres. It has since affected 7,300 acres. The weed harbors a previously unknown algae species that is believed to produce a neurotoxin that can be fatal to eagles and waterfowl.
The condition, known as avian vacuolar myelinopathy, or AVM, has killed at least 59 bald eagles at Thurmond and many more elsewhere.
AVM creates lesions (or open spaces) in the brains of infected birds, causing erratic behavior -- and eventually death.
Small birds called coots, which eat hydrilla, are a frequently affected species. Coots are eaten by eagles, which in turn become affected.
Since AVM was first observed in 1995, it has spread to 17 lakes, from North Carolina to Texas. All are infested with invasive aquatic plants, primarily hydrilla. Scientists are considering the introduction of sterile grass carp that would eat hydrilla and could reduce eagle mortality.
Sources: University of Georgia; Army Corps of Engineers
More on AVM: www.nwhc.usgs.gov/disease_information/avian_vacuolar_myelinopathy/index.jsp
Teams of observers will fan out across Thurmond Lake today for an annual census that is part of the National Midwinter Bald Eagle Survey that has been conducted nationwide since 1984.
Not only does hydrilla affect birds but it also cuts the oxygen supply to fish resulting in their death. Fishermen use to fish in our cove but now cannot due to the increased growth of hydrilla. I have seen some docks that were not accessable by water due to the canopy of hydrilla. I've seen numerous boats and jet skies disabled because hydrilla became trapped in the engines/motors. Hydrilla is a huge problem for both wildlife and people. It certainly would be nice if the Corps of Engineers would address this issue and allow land owners to take action to eliminate this aquatic kudzu.
catfish20, there is ongoing discussion about introducing sterile grass carp at clarks hill to control the hydrilla - it would be expensive and the corps of engineers is hesitant to move ahead with it unless both georgia and south carolina jointly agree on such a program. so far, there is no such agreement, and of course, no such program. we will be covering that issue in the future, though.
The Corps of Engineers and the University of Fla. have done extensive studies regarding the eradication of hydrilla. These studies included the use of carp and chemicals. The longer the Corps waits the more expensive the treatment. Landowners affected by hydrilla are becoming less patient with the Corps lack of response to their concerns.
The Augusta Chronicle ©2012. All Rights Reserved.
