Officials have snared about 200 snakehead fish from a Potomac River tributary in Northern Virginia, suggesting that the burgeoning population of the invasive species appears to be irreversible and raising fears that it could diminish bass and other commercially valuable catches in the Chesapeake Bay watershed.
Three years after Maryland biologists poisoned a Crofton pond in an effort to stamp out the species before it spread, experts say the sharp-toothed fish might be prevalent in the 14-mile stretch of the Potomac that extends south from the Woodrow Wilson Bridge to Dogue Creek near Fort Belvoir, Va.
"The water is black from these schools of fish," said John Odenkirk, a biologist with the Virginia Department of Game and Inland Fisheries, after visiting the creek yesterday and Tuesday. He said that removing these fish would have practically zero effect on the population.
Before last weekend's torrential rains, officials had seen a total of 70 snakeheads all season, he said. Officials visited the creek after fishermen reportedly captured about 80 snakeheads there last weekend.
When asked whether the department hoped to eradicate the fish, Odenkirk said, "There is no way. It could never be accomplished if we wanted to. We're not even really trying to reduce the numbers."
Because snakeheads are not native to the region, anglers, environmentalists and state officials worry that the fish might have no natural predators and could reproduce incessantly and gobble up food that other native species eat, disrupting the delicate ecosystem in rivers.
"We've got highly desirable species like largemouth bass," said Steve Early, assistant director of fisheries for the Maryland Department of Natural Resources. "Snakeheads are going to compete for food with them."
Researches do know that the snakehead is a freshwater fish, and therefore they don't believe it poses a direct threat to the Chesapeake Bay.
A native of China, the northern snakehead, nicknamed "Frankenfish" for its ability to slither on its fins and survive on land for up to three days, gained national notoriety in 2002 after an angler hooked one in a Crofton pond. A local resident had dumped two snakeheads, a male and a female, into the pond off Route 3 after they had become too large for an aquarium.
Concerned that the snakehead could make its way to the Little Patuxent River 75 yards away, state officials devised a plan to kill the fish by putting poison in the lake. They declared victory in November 2002 after killing six adult snakeheads and more than 1,000 juveniles, but then the fish started showing up in other places: Pine Lake in Wheaton in spring 2004, and particularly in the Potomac.
Odenkirk said he learned about the recent population surge Monday after a Virginia fisherman e-mailed his department a photograph of his weekend catch -- a cooler full of snakeheads. The catch was first reported by The Washington Post.
Odenkirk rushed out the next day to see for himself. He said he alone netted 112 snakeheads in a 200-meter swath of Dogue Creek. The fish stayed in shallow waters and munched mostly on killifish.
There has not been any DNA testing done on these fish, but state officials believe that they are related to the fish found last year in the Potomac. Those were different, genetically, from the fish found in Crofton and other parts of Maryland, indicating that the fish aren't spreading rapidly across the region.
Still, biologists said they don't know why the fish appeared last weekend in such great abundance. Early theorized that the dry summer followed by a sudden heavy rainfall created good conditions for them, but he conceded: "We're at square one with understanding the fish."
It is a mystery how the fish survive the winter, he said. Also, it is unclear why or how fast the populations spread, he said.
But environmentalists worry that any disruption to the rivers that feed the bay will affect it.
"You run the risk of them multiplying and causing problems with the native populations, which are very important for the health of the bay and the health of the rivers," said Erin Fitzsimmons, the Chesapeake coordinator for the Waterkeeper Alliance.
It is also too soon to know how the snakeheads will affect the ecosystem and bass population. But the recent surge is affecting the region's fishing reputation.
"I get asked, `Has bass fishing been affected?'" said Steve Chaconas, a bass fishing guide on the Potomac. "I say `No.' Then the next question is, `Where can we go to catch a snakehead?'"
Chaconas has taken one client out to catch snakeheads.
"Some people were downplaying the fish," he added. "I'm not. I'm worried that these fish will become aquatic hitchhikers."
At the Bass Pro Shops Outdoor World at Arundel Mills mall, which had been offering up to $50 for snakeheads, managers were stressing yesterday that they had agreed to pay only for those caught with a hook and line.