Thursday, June 17, 2004

The northern snakehead is a fierce predator with a voracious appetite and a scary reputation. Don Cosden is a patient biologist with a boat and a trick up his sleeve. One will prevail.

Mr. Cosden, a 51-year-old fisheries biologist and regional coordinator at the Maryland Department of Natural Resources, is among a small group of people who set out on the Potomac River and its tributaries once a week in search of snakeheads, the invasive fish that scientists fear could overtake the region’s waterways.

Mr. Cosden and others have been searching the Potomac since May, but they still are trying to figure out whether it is rife with elusive snakeheads that they can’t track down or whether they eliminated the fish.

“That’s still somewhat open for debate,” Mr. Cosden says.

Snakeheads caused a frenzy two years ago when several adults and thousands of young were discovered in a pond in Crofton, Md. Officials poisoned the pond to destroy the fish.

Mr. Cosden and scores of others were involved in that aquatic dragnet. Two years later, he and a few others still pursue the fish.

Because Mr. Cosden and other state biologists can search only small portions of the vast Potomac and its tributaries at a time, their work is tedious and time consuming.

So far, it hasn’t produced a significant number of the invasive fish.

Just six snakeheads have been found in Maryland and Virginia this year. Commercial and sport fishermen found nearly all of them.

Five snakeheads were discovered in the Potomac River basin south of the Woodrow Wilson Bridge, from Little Hunting Creek to Mason Neck. One was found in Wheaton, in a pond that later was drained in search of more.

Scientists are in pursuit of the creature because they fear the snakehead could devour other species, jeopardize the Potomac’s role as a spot for largemouth bass tournaments and throw the ecosystem out of whack.

“No one can predict what kind of impact they would have, but there is the potential for them to have a negative impact,” Mr. Cosden says.

The creepy-looking snakehead appears to be a formidable opponent. It can grow up to 33 inches and survive on land up to three days, which adds to its legend as a seemingly unstoppable menace.

So Mr. Cosden steps into a boat at the Fort Washington Marina in southern Prince George’s County with Tim Groves and Ross Williams, biologists for the state of Maryland. They leave the marina on Piscataway Creek unsure whether the overcast skies are going to clear or bring rain. In two hours, it is sunny and sweltering.

They have hats, sunscreen and a light breeze to protect them from the sun.

Mr. Cosden and his colleagues are searching near the five Potomac locations where snakeheads have been caught this year to look for the fish and nests that might spawn others.

Mr. Williams navigates the metal, flat-bottom boat out of Piscataway Creek, north on the Potomac and into Broad Creek.

But their hunt bears little resemblance to a standard fishing expedition.

Once Mr. Williams guides the vessel near a bank, Mr. Cosden and Mr. Groves break out their secret weapon — jolts of electricity.

Two poles with spokes attached to them dangle in the water about 7 feet in front of the boat. They are connected to a generator under Mr. Williams’ seat. When Mr. Groves steps on a peddle next to his foot, an electric charge bursts through the water.

They call it electro-fishing, and the charge is equivalent to a mild shock and stuns the fish. The jolts affect a small area, but still send scads of fish to the surface each time. They go belly up and become temporarily motionless, flop or swim in circles. That’s when Mr. Cosden and Mr. Groves scan the water in search of snakeheads.

Blue gill, carp, perch, catfish, eels and dozens other species, including long-snouted gar, float to the surface. Bass are present in unexpected abundance. Turtles swim away before the boat gets close to them. A bald eagle and scores of osprey and heron also fly away from the approaching boat.

But there is no sign of the dreaded snakehead.

The team of biologists repeats the exercise hundreds of times, then moves to Piscataway Creek to try their luck there.

They discover no snakeheads.

Snakeheads are so reviled that a resolution that takes effect in Maryland in September prohibits possession of a live snakehead. Virginia officials made owning a live snakehead illegal last year.

Mr. Cosden says the search might have been fruitless, but failing to reveal any snakeheads may prove another point.

“I guess when you go looking, you want to catch something. But it also may be a sign that there aren’t many,” he says.

There is an urgency in the mission to find and eliminate snakeheads before they become established in the river, but the weekly expeditions underscore the difficulty in tracking them and the near futility of electro-fishing in a massive body of water such as the Potomac.

“I wouldn’t consider this an effective method of eradication. But what we’re looking for is an area of concentration,” Mr. Cosden says.

All they have discovered so far is that tracking down the elusive fish is difficult.

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