Just as a federal advisory panel on invasive species made its way through Maryland, a group of state biologists declared victory over the most notorious of all invasive fish - the northern snakehead that took over three Crofton ponds last summer.
State biologists electro-shocked the ponds yesterday and did not see any stunned fish float to the surface. That means the regimen of poisons applied in the summer - herbicides followed by the fish poison rotenone - managed to kill the fin-walking Asian interloper that fisheries managers worried would devastate native populations if left unchecked.
"As far as we can tell, the fish are done," said Steve Early of the Department of Natural Resources. "We did what we set out to do."
Early said recent cold temperatures killed off all of the pond vegetation, giving his crew its first clear view of the water.
Even before they knew the results of yesterday's testing, members of the Federal Invasive Species Advisory Committee hailed the snakehead eradication as a rare triumph. The group, which advises the chiefs of federal agencies on ways to control exotic and non-native species, spent yesterday morning touring the Patuxent Research Refuge to learn about invasive weeds.
In the afternoon, they boarded the M.V. Cape Wrath, a 700-foot vehicle transport that looked like a giant parking garage, to learn about new ways to control pathogens and other pests in ships' ballast water. Ballast water - used to help balance a ship as it loads and unloads cargo - is one of the most common means of unintentionally introducing invasive species into new habitats, since the water is drawn from one port and often discharged hundreds or thousands of miles away. Most times, the problem is nearly intractable by the time it's discovered, because the organisms have already infiltrated large bodies of water and have no natural predators there.
Not so Crofton's snakeheads. Despite biologists' fears the fish would find its way into the Little Patuxent River 75 feet away, the state managed to contain it in the pond.
"It's a great success story. I talk about it a lot in my classes," said David Lodge, an ecologist with the University of Notre Dame. "You don't often expect to be able to eradicate invasive species. Unlike a lot of forms of pollution, these things reproduce."
Despite the success with snakehead in Maryland, the fish are a problem elsewhere in the country, and there are plenty of other invasive species that have yet to be dealt with. The advisory committee will make recommendations to the National Invasive Species Council, an interagency group charged with examining laws regarding invasive species and policies for managing them. The group has yet to finish its report, but members said they are focusing on detecting unwanted species early and on informing the public of its role in unintentionally spreading problems.
They point to examples such as nutria, a rodent introduced 60 years ago for its fur that is still destroying marshlands, and the monk parakeet, which can devour whole crops of grain if it has no predators.
And then there are the snakeheads, which arrived in the pond when a local man decided they'd outgrown his aquarium. He plunked in two fish - a male and a female - they reproduced, and in two years hundreds of the sharp-toothed predators were discovered in the water.
"People don't get it. People don't understand," said Nelroy Jackson, a California-based consultant who spent much of his career developing herbicides for Monsanto Corp. "When you introduce something into a new ecosystem, it comes without its natural predators."
Early, the Maryland biologist, said the state had not tallied the cost of the summerlong snakehead eradication project, but others estimated the price at $50,000 - mostly for staff overtime and equipment. The state is waiting to hear whether the two pond owners want the state to restock their waters with traditional local fish next spring.
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