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Snakeheads are invasive and on the move
SNAKEHEAD FISH, AT HOME IN THE POTOMAC RIVER, COULD SWIM SOUTH TO RAPPAHANNOCK WATERS
BY RUSTY DENNEN
THE FREE LANCE-STAR
In eight years, invasive northern snakehead fish have made themselves quite at home in the Potomac River.
After showing up in a small tidal tributary in Fairfax County in 2004, “They’re clear down to the mouth of the river,” said John Oden-kirk, a fisheries biologist with the Virginia Department of Game and Inland Fisheries.
And because the supposedly freshwater fish have made it that far, he said it may only be a matter of time before they move south in the bay and into the Rappahannock River.
“When we get big rain events, fresh water is less dense” than the relatively salty water of the lower river, “and the fish use this as a dispersal mechanism,” said Odenkirk, who works out of the agency’s Fredericksburg office and has been studying the fish for years.
“When floodwaters recede, they just head for a feeder creek, wander up and hang out until the next storm.”
One surprising development: Researchers suspected that the river’s salinity would halt their spread downstream.
“They seem less susceptible to salinity issues” than first thought, Odenkirk said, with juvenile snakeheads tolerating moderately brackish water of 15 to 17 parts per thousand. That’s just under half the concentration of sea water, which is typically about 35 parts per thousand.
“We wouldn’t be surprised to hear about them making the mouth of the Rappahannock. We’ve been expecting it,” he said.
Fishermen have caught them in tributaries north and south of the mouth of the Potomac.
Snakeheads—named for the snakelike pattern on their skin—first showed up in a pond in Crofton, Md., in 2002. Two years later, in May 2004, one was caught by an angler in Little Hunting Creek in Fairfax County.
Conservationists were alarmed at the time, worrying that the top-tier predator could change the ecology of the river. But that has not been the case; researchers say there appears to be little impact on other species so far.
AQUIA HOT SPOT
They were dubbed “franken- fish” due to their ability to survive for short periods out of water, large teeth and a voracious appetite.
By 2009, snakeheads had made it as far south on the Potomac as Machodoc Creek in King George County. That summer, a boy fishing in Aquia Creek caught one 3 feet long.
Odenkirk said Aquia Creek continues to be a hot spot for the fish. Most of the snakeheads caught there in sampling, he said, weighed 3 to 7 pounds.
Earlier this month, a fisherman pulled an 18.4-pound monster out of the Occoquan River, which might have been certified as a world record had the fish not been eaten for dinner. The record northern snakehead, caught in Japan, weighed 17.4 pounds.
Odenkirk said he’s not surprised a fish that big was caught, predicting that even bigger ones will follow. The Potomac, he said, “is one of the most productive river systems.”
“All the precursors are there. The Occoquan is one of the biggest tributaries in [the snakehead’s] estimated range, and it’s an awesome nursery area.”
Odenkirk said biologists are understanding more about the fish.
For example: Younger fish “are growing faster than we originally thought, and older fish are not growing fast at all.”
Another finding: The fish’s relative abundance during regular sampling in tidal creeks upriver has grown every year since 2004, except for last year.
“Last year, it was stable,” he said, which could indicate that the fish populations are reaching a plateau in those spots, or it could be an anomaly in the data.
“If this year we see that static trend, perhaps some equilibrium has been established.”
There are no solid numbers on the size of the Potomac population.
WAY UP THE BAY
Don Cosden, director of inland fisheries for the Maryland Department of Natural Resources, said surveys there show steady increases in populations in tidal creeks.
Cosden said snakeheads have been found in the Patuxent River, the Rhode River south of Annapolis, and in several small tributaries north of the mouth of the Potomac.
“Some genetics testing work is being done,” he said, “and we have reason to believe those came out of the Potomac.”
He said Maryland’s approach is to encourage anglers to help limit the population, while looking at some other ways to complement that effort with public education about the problem of invasive species. Maryland commercial fishermen who catch snakeheads as by-catch in catfish nets are now permitted to sell them.
“There is a small niche market,” Cosden said.
In the case of snakeheads, “The cat’s out of the bag; maybe we can keep the next one in the bag.”
Odenkirk said researchers still have plenty of work ahead.
“There’s still a lot we don’t know,” he said. For instance, the fish appear to be spawning multiple times during a season, and may be spawning at different times during the summer.
In Virginia waters, anglers must kill any snakeheads they catch, and report them to the game department.
There is an upside to the story: Snakeheads are great on the grill and fun to catch, and those pluses have created a small but growing snakehead cottage industry.
Some Potomac fishing guides offer outings specifically targeting the fish. The Potomac Snakehead Tournament, in its second year, yielded over 1,400 pounds earlier this month. A celebrity chef there served up snakehead sandwiches using the mild, white, flaky fish.
Though the goal remains limiting the population, “It is kind of a glass-half-full kind of situation,” Odenkirk conceded. “If you’ve got to live with it, you might as well enjoy it.”
Native to China, Korea and Russia, northern snakeheads can grow to nearly 20 pounds and over 40 inches. They prefer weeded areas and will eat practically anything they can catch, researchers say.
They are raised for food in Asia and Africa, but U.S. officials banned import and transport of the fish in 2002. Virginia banned their possession the following year.
Rusty Dennen: 540/374-5431