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6.15.04

MARSHALL HALL, Md. (AP) — Stunned by 200 volts of electricity, a large carp emerges out of a muddy cloud, its mouth agape as if gasping for air. It rolls lazily onto its back, exposing an ivory underbelly for a moment, then disappears again into the mire with a powerful sweep of its tail.
Other dazed fish pop to the surface in front of a Maryland Department of Natural Resources boat, which uses equipment that sends a current coursing through the water of the Potomac River inlet. Leaning off the front, a biologist scans the water while holding a long net.
He’s looking for the torpedo-shaped body and toothy jaws of the northern snakehead, an invasive fish that scientists fear has made the river its home. Five have been caught so far either by the boats or anglers.
“This is not a viable method for recovering all the snakeheads in the river,’’ said Don Cosden, a DNR regional coordinator, while piloting another boat nearby. “But this should give us an idea how many there are.’’
That is the big question that scientists in Maryland and Virginia are trying to answer — whether the five found are part of a reproducing population and if there are others skulking in the river’s shallows.
Several times a week, boats from both states using nets and the electric fishing equipment hunt a 10-mile stretch of the river, from the Wilson Bridge just below Washington down to Indian Head.
Despite the recent snakehead catches, biologists aren’t yet ready to concede that the potentially destructive predator has established itself the Washington region’s biggest river. But the evidence so far suggests there are more.
“It would be very odd if we were catching the only fish out there,’’ said Steve Early of the DNR fisheries division. “I would have to take the devil’s advocate position and say there’s more fish than what we are seeing.’’
A breeding population could be a danger to fish that inhabit the river, including an ample population of largemouth bass that draws anglers from around the region for tournaments.
With a reputation as a fierce hunter that has little discrimination for prey, scientists fear the northern snakehead could dominate an ecosystem, eating or pushing out other species of native fish. It can even wiggle across land for short distances.
A delicacy in its native China, snakeheads have been kept as food in some Asian markets or pets in collector’s aquariums. It is illegal to import or transport across state lines the northern snakehead and 27 other types of the fish.
The fish gained a virtual horror-film status two years ago when several adults and thousands of young were discovered in a Crofton pond. This April, a single northern snakehead was caught by a fisherman in a Wheaton pond. The DNA of the Wheaton and Potomac fish are being matched against those of the Crofton snakeheads to determine if they are related.
In those cases, biologists were able to control the populations because the bodies of water were so small. In Crofton, the pond was poisoned. In Wheaton, it was drained.
“Your first effort is to prevent introduction. Your second goal, once you’ve got an introduction, is if you can eradicate, you eradicate,’’ said Eric Schwaab, former head of DNR’s fisheries division who handled the Crofton case. “But too often it simply becomes a control problem.’’
Control is likely the best scientists can hope for in the Potomac. The river has hundreds of miles of coastline, forming the border between Maryland and Virginia and running along West Virginia’s Eastern Panhandle, with inlets and ample vegetation for the fish to dwell in. If there is a reproducing population, eradication would be impossible.
For now, the goal is to find out for sure if the snakeheads are reproducing in the Potomac. There are several signs searchers on both sides of the river are looking for.
West Virginia wildlife officials are also on the lookout for the voracious fish.
Division of Natural Resources fisheries chief Bret Preston has said that just because no snakeheads have been spotted in West Virginia’s section of the watershed, that doesn’t mean they won’t be soon. Anytime you have an invasive species in a watershed, there’s a chance it can spread upstream or downstream, he said.
The most conclusive evidence would be a snakehead nest. When it spawns, snakeheads build nests in vegetation where females lay their eggs. The eggs float near the surface, and are aggressively guarded by the male and female, according to Gary Martel, director of fisheries for the Virginia Department of Game and Inland Fisheries.
Another sign is the capture of sexually mature fish. All five caught in the Potomac were two years old, and while some of the males had reached that stage, none of the females were capable of spawning, Martel said.
Finally, the biologists are looking for any young snakeheads, those that might have recently hatched and may be lingering near their nesting site.
So far, the fact that no nests, no females capable of reproducing and only a few fish have been found is an encouraging sign.
“It’s a sign the population really hasn’t exploded or expanded,’’ Martel said.
But even with several boats out each day, Maryland and Virginia have only searched a fraction of the river, concentrating on the 10-mile stretch where the five snakeheads were caught. If there are sexually mature snakeheads in the water, they haven’t started to spawn yet this year.
So what can be done if the snakehead is indeed breeding in the Potomac? The realistic option is to try to keep them in check.
That includes scooping up any nests and eggs that are found and catching the parents that stand guard. Scientists can also aggressively try to round up snakeheads if they are found in concentrations using the electric fishing technique.
The first line of defense, however, is not scientists.
Anglers, many of them fishing for bass, are the best means of catching and destroying snakeheads, Early said. The DNR has posted signs along the river encouraging anglers to kill and report any snakeheads they find. Most of those caught so far were reeled in on fishing line.
The final step may be conceding that the snakehead may be part of the Potomac’s ecosystem and studying the effect. Scientists know that the fish can be destructive, but have few examples of how it will affect other species over a longer term.
One possible comparison is in southern Florida, where the bullseye snakehead, a northern snakehead relative, has flourished in Broward County’s canal system since it was introduced around 2000. Biologists are trying to determine how it will be absorbed into the ecosystem, how other fish will be affected, and what control measures work best.
“Once they get established, neither man nor nature can get rid of them,’’ said Kelly Gestring, a Florida fisheries scientist. “We have to deal with that fact and develop management strategies.’’
Meanwhile, Maryland and Virginia officials are hoping they won’t have to get to that point. They get some encouragement from the fact their searches have turned up only a few fish.
“If there was a whole lot out there, you’d think we would’ve seen more by now,’’ said DNR biologist Mary Groves as she drove the electric fishing boat out of the inlet.