During this spring's fish migration season, 81 northern snakeheads attempted to swim up the Susquehanna River through the Conowingo Dam, a “dramatic increase” in the invasive species, state natural resources officials said.
In the past two seasons, officials said, only one snakehead was observed passing through a fish lift designed to carry shad and herring over the dam so they can reach their spawning grounds upstream.
Biologists fear the toothed Asian invaders could outcompete native fish species and disrupt Chesapeake Bay ecology. First discovered in a Crofton pond in 2002, the invader has spread to all the major tidal river systems across the bay.
Officials said the multiple discoveries of snakeheads at the Conowingo raise concerns of a possible northern expansion, and provide more evidence the species is firmly established in the Chesapeake.
“The population is expanding, and the numbers are increasing in many areas,” said Joe Love, a freshwater fisheries program manager at the Maryland Department of Natural Resources.
The 81 fish discovered in the Conowingo this spring did not make it upstream — when they were observed in the dam’s western fish lift, they were removed and euthanized. When fish swim into a large trough at the base of the dam, the lift carries them up and over the dam.
But it’s possible others made it upstream through the dam’s eastern fish lift, which cannot be easily accessed to remove any snakeheads passing through, Love said. Two years ago, a single snakehead was observed in the eastern fish lift but could not be captured.
“They’re kind of knocking on the door of the Susquehanna River,” Love said.
Chicago-based energy company Exelon Corp. owns and operates the dam and its two fish lifts, about 10 miles north of the mouth of the Susquehanna and the Chesapeake Bay.