A panel of fisheries experts picked its poison yesterday - a plant-based substance called rotenone - to kill the voracious northern snakehead fish that have been multiplying rapidly in a Crofton pond and devouring native species like snacks.
The dozen fisheries experts unanimously agreed that poisoning the pond as quickly as possible is the only way to kill the exotic fish, a sharp-toothed native of China that breathes air, can walk on its fins and survive on land several days. A local man dumped two adult snakeheads in the pond two years ago, and scientists fear that hundreds of young offspring remain in the pond and could escape to the Little Patuxent River 75 yards away.
"Rotenone is definitely the way to go," said Carys Mitchelmore, an aquatic toxicologist with the Chesapeake Biological Laboratory on Solomons Island and a member of the panel assembled last month to study ways to eliminate the snakehead infestation.
The panel, which met for the first time yesterday, is advising the Maryland Department of Natural Resources on how to handle the alien fish. It will review panel chairman Don Boesch's draft report Tuesday and submit a final report to the DNR secretary by July 31. Officials expect the department to take action shortly after that.
The experts who met at the pond yesterday considered many options - doing nothing, killing the fish by draining the pond, or using chlorine or electroshock - before settling on rotenone.
Rotenone, made from plant roots, hasn't been used for fish eradication in Maryland for several decades, but several snakehead panelists were familiar with its potency. Once applied to a pond, it enters the fish's gills and disrupts the flow of oxygen. All fish that remain in the pond will die, most within a few days. Snakeheads that escape the poison will come to the surface to breathe air, where fast-working biologists can catch them.
Biologists say the substance degrades within a few days and poses no threat to humans. They say birds and other wildlife that eat the dead fish bobbing at the surface face minimal risk.
Rotenone is most effective in hot, dry climates. If DNR follows the panel's recommendation, officials said, the poison could be applied to the pond by next month.
The group must decide which herbicide to use in the weed-choked pond before DNR officials apply rotenone - the poison works best when vegetation is dead. Natural resources officials will need a permit from the Maryland Department of the Environment before applying chemicals to the pond, something MDE panel member Bob Summers said wouldn't be a problem.
Summers recommended further study to conclude whether the pond had overflowed and perhaps already reached the nearby river, a prospect DNR officials say is unlikely.
"We have got to get a handle on the hydrology of this pond, see if it's ever overflowed," he said.
Throughout the meeting, panelists deferred to its two Floridians - Walter R. Courtenay Jr. of the U.S. Geological Survey in Gainesville and Paul Shafland, of the Florida Fish and Wildlife Conservation Commission in Boca Raton - who have studied snakeheads and other exotic fish.
The two have disagreed about the snakehead's ability to infiltrate the river - Courtenay believes it's likely while Shafland doubts the fish can walk that far. But both endorsed using rotenone in the Crofton pond.
"When I walked into this room, I was afraid that it could drag on and on, but I'm very pleased that clearly there's an urgency here," said Courtenay, who called the meeting "extremely productive."
Courtenay, who has studied snakeheads for a year under a contract with the U.S. Fish and Wildlife Service, was not surprised to learn that DNR officials caught five more young snakeheads yesterday.
This month, after an angler caught an adult snakehead in the Crofton pond, officials caught about 100 young snakeheads - many of which will be used to determine what doses of rotenone will work best.
Surrounded by television cameras at the pond yesterday, the 68-year-old ichthyologist shook his head.
"Without question, they are a reproducing population here," Courtenay said. "It's not good news. Not good news at all."