A mature, egg-bearing northern snakehead has been discovered by scientists in a river just south of Annapolis, raising the possibility that low salinity in the Chesapeake Bay this year may have allowed the invasive fish to escape from the Potomac River.
The 23-inch snakehead was found in the Rhode River last Thursday by biologists from the Smithsonian Environmental Research Center taking annual fish samples by net.
"The water was very murky with a lot of sediment. When a fish is that large, you assume it's a carp," said Stacey Havard, a Smithsonian biologist. "An intern saw the pattern and almost instantly identified it."
The center tested the fish and reported the catch to the Department of Natural Resources and the U.S. Fish and Wildlife Service.
The toothy alien, a native of Asia, is an aggressive, rapidly breeding predator that can overwhelm habitat and push out local fish. It was first discovered in a Crofton pond in 2002 and eradicated, only to be found in Potomac River tributaries in Maryland and Virginia two years later.
Scientists have long believed that the salinity of the bay would keep snakeheads bottled up in the Potomac River. But last year, watermen found them in St. Jerome Creek, past Point Lookout on the bay side.
Finding this fish, said Havard, "was very disconcerting, especially when we found it was an egg-bearing female. I think there's concern across the board."
Earlier this year, near-record levels of runoff that coursed down the Susquehanna River and into the Chesapeake Bay created the lowest salinity levels seen in the upper bay since 1985, when water- monitoring stations were established. Freshwater floats on denser saltwater, rolling out a liquid carpet to provide an avenue of escape.
Dr. Gregory Ruiz, senior scientist at the Smithsonian center, said it is possible the fish that they found is the only one to make it that far north, but he noted that there are plenty of rivers between Point Lookout and the Rhode River and it is possible that low salinity levels might allow snakeheads to cross the bay to the Eastern Shore.
"Adult fish can withstand brackish water to some extent. At what point it becomes a barrier depends on a number of conditions," he said.
The Fish and Wildlife Service has submitted a plan to the Interior Department to prevent snakehead colonies from infesting other bodies of water, beef up invasive species laws, encourage local rapid response teams and educate watermen and recreational anglers.
The Northern Snakehead Control and Management Plan was requested by Congress, whose members were alarmed by the "potential impact on native fish populations." Northern snakeheads are established in Pennsylvania and New York, and small numbers have been caught in California, Florida, Massachusetts and North Carolina.
Meanwhile, Maryland and Virginia biologists continue to track them with radio telemetry and electrofishing to get a handle on population density.
"We don't know a lot about the snakehead, and you can never really know what a species will do," said Joseph Love, DNR's tidal bass manager.
Last year, Love, along with the Fish and Wildlife Service's Maryland office, conducted a survey of where snakeheads and largemouth bass overlap in habitat and diet. The research concluded that the two fish like to eat each other's offspring and thrive in shallow water beneath protective lilies and grass, but neither has yet gotten the upper hand.
It is illegal in Maryland to release snakeheads after they've been caught. Regulations require anglers to kill the fish and DNR is giving prizes through a drawing to anglers who catch, kill and enter photos of the snakeheads on the agency's Angler's Log website.
While no one believes it is possible to eradicate the snakehead — subject of books and science fiction movies — from local waters, they say every little bit helps.
Veteran Potomac bass guide Steve Chaconas, a member of the management plan work group, said reeling in an adult snakehead five years ago was "rare," but now they range in the "6- to 14-pound range."
"Killing even one means it won't reproduce and you prevent it from being transplanted," he said. "Taking that fish out of the equation could be like killing 6,000."