After Solving Snakehead Puzzle, Md. Moves In for the Kill

With the death sentence issued, the question now is: How best to execute a fish?

For the untold number of northern snakeheads -- the nonnative, air-breathing, slithering fish discovered last month in a Crofton pond -- it is safe to say that the end will not likely come by salt. Back-of-the-envelope calculations quickly revealed the impracticality of trucking the hundreds of tons that would be required to choke the fish to death. Chlorine was considered but rejected because it's too caustic to humans and the effects could linger.

Instead, experts on a task force convening in Annapolis today will offer a small, but more effective menu of options to Maryland officials who hope to rid the pond of the strange fish that can gobble up huge numbers of other fish and then wriggle on land to new waters.

They include antimycin A, a chemical that has been used elsewhere to control rampant carp populations, and explosives, which can blow the fish out of the water. And there's also the low-tech option of capturing the snakeheads with nets.

But a poison known as rotenone has been the hands-down favorite of fish experts facing similar dirty jobs. Derived from the ground-up leaves and roots of trees found in India and South America, it has been used since the 1940s as an agricultural pesticide and piscicide.

Paul Shafland, director of the nonnative fish research laboratory for the Florida Fish and Wildlife Conservation Commission, has faced dozens of species of invaders and has vanquished a half-dozen with rotenone.

"We have a standing policy of eliminating [alien] fish" in isolated locations, said Shafland, one of the task force experts. "Rotenone is the only fish toxin I use."

It works by blocking the transport of oxygen through the gills of the fish. Biologists dump it in the water and mix it around using the propeller of a motor boat, and within minutes, fish should start floating to the top.

"The water turns milky, the fish suffocate, and an air-breathing fish like the snakehead will come to the surface," said Walter Courtenay, a leading expert on invasive species who confirmed that the creatures were snakeheads. "If you've got enough people out there with dip nets, you can just capture these little guys on the spot."

Last week, state biologists caught 80 baby snakeheads in the weed-choked pond behind a shopping center. It was a disturbing sign that two snakeheads had spawned in the two years since they were dumped in the pond by a man who had originally intended to make soup of them. Since then, scientists have been experimenting with different kinds and concentrations of chemicals to determine the most effective way of exterminating them.

The use of rotenone has grown somewhat controversial in recent years after several cases in which the poison was used with unintended results. In one of those cases, California officials poisoned a public water supply while applying rotenone to Lake Davis, which had become overrun with nonnative pike.

About 30 years ago in Maryland, flies swarmed for miles over an inland beach on Assateague Island, where wildlife managers killed off thousands of fish in a failed attempt to test the effectiveness of rotenone against other techniques.

"It was a good idea, but the execution failed," said retired state biologist Nick Carter, who supervised the kill at Inlet Slough. Workers spent days cleaning dead fish off the beach, he recalled. "Everybody remembers it and laughs at me. It got pretty smelly."

Don Boesch, president of the University of Maryland Center for Environmental Science, who is chairing the snakehead task force, said he hopes to recommend a course of action for the state within a month.