By David A. Fahrenthold
Washington Post Staff Writer
Sunday, May 29, 2005
This is the summer of the snakehead, Part II. A year after 20 of the toothy Asian fish were found in the Potomac, the creatures are growing in size, number and legend.
They are far from the river's only invaders. Over time, the Potomac has been so altered by man that it has become the underwater equivalent of the "Star Wars" alien bar. There are carpets of Asian clams and thickets of grass originally from Southeast Asia. Largemouth bass and channel catfish, transplants from other parts of the United States, share the Potomac with carp native to Asia.
Feral goldfish have been spotted -- bigger and browner than usual after being liberated from their fishbowls -- along with the occasional piranha. And scientists estimate that 35 percent of the Potomac's fish species were not there 200 years ago.
So why worry now about a few dozen snakeheads? Because all the previous nonnative species found a niche without throwing the river's ecosystem out of whack. Some scientists said they believe the same might not be true of snakeheads, which are known for their voracious appetites and rapid reproduction.
"It might change the balance, and that's not something you want to happen," said Thomas Orrell, a Smithsonian Institution researcher.
Jim Cummins, a scientist for the Interstate Commission on the Potomac River Basin, compared it to Russian roulette. "We've been lucky in the roulette game of introduced species," he said. "We might be pulling a loaded chamber" with the snakehead.
The northern snakehead, a native of China and Korea that was brought to the United States as food and as aquarium fish, first appeared in the area in 2002. That was when six adults and about 1,000 babies were found in a pond in Crofton. Authorities poisoned the pond to kill those snakeheads.
Last year, however, the fish appeared again -- in the Potomac and some of its tributaries. No one is certain who put the snakeheads in the river, though genetic tests have eliminated any connection to the Crofton fish.
Fifteen more have been caught this year, including one by fisherman Tom Woo that measured more than two feet long. Woo, of Fort Belvoir, said he cast an artificial worm lure at the Mount Vernon Yacht Club's marina, then felt something hit the bait "like a freight train." A torpedo-shaped fish jumped a foot and a half out of the water, he said.
"I was like, 'Whoa, that's a snakehead,' " he said, recognizing the fish because he had caught three.
The other snakeheads caught this year included some as small as 11 inches long. Scientists have said the size differences probably mean that several generations are living in the river. They also said it's a sign that the fish are breeding.
For the Potomac, this is a very old story.
Nonnative species, many of them brought in for the benefit of anglers, are so prevalent that a Potomac snakehead might swim through thickets of such Asian plants as hydrilla and Eurasian watermilfoil. They might go past thousands of Corbicula clams, also from Asia, which first appeared in the river about 1980.
The Potomac's bass and carp were put there in the 19th century. Other aliens are clearly former aquarium fish, such as the goldfish and the piranha. (A piranha, by the way, does not fare well against a mid-Atlantic winter.)
In other cases, mysteries persist. How to explain that the blue catfish can grow several feet long in the Potomac? The clear presumption is that they didn't get to this area on their own.
Among some scientists, the concern over the snakehead is on behalf of the river's native species. American shad, for instance, could be hurt if snakeheads gobble up baby fish migrating downstream.
Yet in an irony of modern environmentalism, much of the concern is about what the snakehead will do to a previous invader: largemouth bass.
Like the snakeheads, the bass are ambush predators, lurking under plants or below docks and snapping up prey as it passes.
If the snakehead displaced them, it would ruin a fishing industry that brings hundreds of anglers and millions of dollars to the region annually.
"It's really on the minds of the bass fisherman now," said Steve Chaconas, a bass-fishing guide based in Alexandria.
For now, however, the bass population doesn't seem to have changed. So scientists are left with few solid conclusions about the snakehead's potential.
On Thursday, two Virginia state biologists motored into a creek off the Potomac, steering what amounted to a gigantic fish taser. They turned on the juice. Their "electrofishing" boat sent 1,061 volts into the water through an array of wires, and twitching fish began floating to the surface.
Their catch provided a quick lesson in the Potomac's recent history, in which human experiments and mistakes have turned the river into a kind of open-water aquarium. Up popped largemouth bass, common carp, a couple of goldfish.
But the biologists were looking for something else.
"I think I saw one, John," said Steve Owens at one point, calling to his partner from the bow of their flat-bottomed boat.
The boat surged, and Owens stabbed his dip net into the water. He came up holding a mottled-green monster, with a mouth big enough to fit around a soft-drink can.
"There's a snakehead!" said his partner, John Odenkirk of the Virginia Department of Game and Inland Fisheries.
Later in the day, Owens and Odenkirk stood on a dock and measured the two snakeheads they caught. The crew of a Fairfax County fireboat walked over and marveled at the fish, each nearly two feet long.
"It's another mouth to feed," Owens said to them.