By David A. Fahrenthold
Washington Post Staff Writer
Monday, October 2, 2006
The northern snakehead fish seems to be expanding its territory in the Potomac River, government researchers say, after a year in which the toothy Asian transplant has appeared in new places and at higher concentrations across the area.
In the third year that the fish has been studied in the Potomac, scientists are starting to build a portrait of the snakehead at home in the area. Some of the most frightening concerns have been dispelled: The fish turn out to be well-nigh helpless on land (early reports said the snakehead could wriggle short distances out of water), and the creatures haven't gobbled up or driven out the Potomac's famous bass.
But worries remain, because the snakeheads are reproducing rapidly and starting to push outward. The next few weeks will bring a crucial test of the snakeheads' growth, and science's understanding of them, as researchers wait to see if last October's startling mass snakehead migration is repeated.
"It looks like they're becoming pretty solidly entrenched, as far as establishing that beachhead here in the Potomac," said Steve Minkkinen of the U.S. Fish and Wildlife Service.
Over the past year, the snakeheads have spread out and become endemic in about 15 miles of the Potomac and some of its tributaries south of Washington from a home base of two creeks in Virginia, he said.
That has switched scientists' focus from eradication to coexistence. "As much as we can, we're just trying to collect information," Minkkinen said.
The story of snakeheads in the Potomac may have begun as early as 1998 or perhaps as late as 2002. The key event, scientists believe, was when a male and female were dumped into the water and found each other in Fairfax County's Dogue Creek. Since then, that stream, along with nearby Little Hunting Creek, has become the epicenter of the Potomac's snakehead population, scientists say.
Now, the two creeks are also the area's premier snakehead laboratory, as researchers seek to understand the life the fish have created in an alien home.
One obvious conclusion: Snakeheads are thriving. Virginia state scientists who use electric current to stun and capture fish in these creeks used to catch one snakehead every five hours. This year, they got 6.9 fish an hour, nearly 35 times more.
But the snakeheads don't appear to have had a serious impact on the river's largemouth or smallmouth bass, which are also top predators in the river. Scientists say they believe this might be because the snakeheads prefer shallower water or different prey.
"A bass is probably more likely to eat one of them" than a snakehead eat a bass, said longtime guide Ken Penrod, who said he hadn't seen any change in the bass fishing. "It's a lot about nothing, I think."
But scientists say they still have a lot to learn. They're unsure how the snakeheads nest, for instance. In their native habitat, they are said to clear out a "doughnut hole" in a thicket of underwater vegetation and lay their eggs there. But this year, a Virginia biologist spotted a cloud of 500-plus snakehead babies -- orange and black, with a minuscule version of the distinctive snakehead mouth -- swirling in Little Hunting Creek.
It was a nest, but there was no doughnut hole.
"The fish aren't behaving here the way they might be expected to behave in Asia," said John Odenkirk, a snakehead expert and a biologist with the Virginia Department of Game and Inland Fisheries.
Researchers are similarly confused about whether the river's snakeheads migrate. One Sunday last fall, Dogue Creek was suddenly full of hundreds of fish heading upstream, so thick that fishermen snatched out at least 80. This may have been a freak event caused by a large rainfall -- or it may have been the first running of an annual ritual. Researchers are keeping watch to see what happens this year.
What little scientists do know about the snakehead's habits was gathered this spring, when Odenkirk inserted small tracking devices into the body cavities of 20 fish. He found them to be mainly homebodies, lurking in the same weedy and shallow spots week after week.
But some strayed farther afield: Fish No. 1204 crossed the deep midsection of the Potomac to visit Maryland's Piscataway Creek. Fish 1301 disappeared completely, meaning that it was perhaps speared by a heron, caught by an angler or just moved so far away that Odenkirk can't get the signal.
"It tells me that some obviously are bucking the trend and being a little more adventurous and crossing the main-stem Potomac," Odenkirk said.
This year's catch of snakeheads has made it clear how widespread the fish have become. In Maryland, the fish have been found across an unprecedented swath of creeks in Prince George's and Charles counties.
On the Virginia side, snakeheads have moved north from their epicenter to a creek near Belle Haven Marina in the Alexandria section of Fairfax. To the south, Odenkirk said, their numbers have increased substantially in the Occoquan River basin, on the border between Prince William and Fairfax counties.
They've also appeared in another place puzzlingly far afield: Kenilworth Park and Aquatic Gardens in the District. In the late spring, more than 500 baby snakeheads and a handful of larger adults were found in ponds there, having eaten almost every other fish in the water.
D.C. officials think that this may be a separate population of snakeheads, descended from fish dumped directly in the aquatic gardens.
But because the ponds share connections with the Anacostia River, there's some chance the D.C. snakeheads might be adventurous specimens from the Potomac.
For all that's known about the snakeheads' expanding reach, much more is still in question. That was obvious Wednesday, when Odenkirk and two assistants set out on the Occoquan in a shallow boat with a spindly metal claw dangling from its front. They were electro-fishing.
After a few minutes in Massey Creek, a tributary of the Occoquan, a mottled green shape thrashed in the water. Nick Lapointe, a Virginia Tech graduate student, scooped a long net, bringing up a roughly seven-inch snakehead.
"Yeah, baby!" Odenkirk exulted.
"I saw those speckles, and I knew exactly what he was," Lapointe said.
"Beady little eyes," said Ryan Saylor, a technician.
In the spring, Odenkirk's team had not found any snakeheads in this inlet. But Wednesday, they found two, which he said were probably siblings born in the creek last year.
So if two were caught, how many more could there be here?
"Hundreds?" Odenkirk speculated. He looked back at an acres-wide expanse of snakehead-friendly shallow water and thick grasses.
"I mean, you look behind us, they've got all that habitat. They could be anywhere."