A worrisome 81 northern snakeheads – an unstoppable, invasive fish species – were caught this spring in the fish lifts at Conowingo Dam on the Susquehanna River, about 5 miles downriver of the Pennsylvania state line, according to the Maryland Department of Natural Resources.
Only one snakehead – a predatory species native to Asia that can grow to nearly 5 feet in length –was found in the lifts in 2017, and none were found in the lifts last year.
The Conowingo Pond, the reservoir upriver of the dam, extends upriver 8 miles into Pennsylvania.
While all the snakeheads – sometimes referred to as “frankenfish” – were destroyed before moving upriver of the dam, the DNR described the spike in numbers seen in the lifts as “dramatic” and expressed concern over “a possible northern expansion by the aggressively invasive species.”
Snakeheads were first documented in the U.S. in 1977, in California, and subsequently in southeastern states. They were found in Maryland in 2002.
Northern snakeheads were first observed in Maryland waters in 2002, and shortly after its discovery in Potomac River in 2004, the species gained a foothold in tidal waters. Since then it has spread to every major tributary of the Chesapeake Bay.
They were first confirmed in Pennsylvania in July 2004, when two were caught in Meadow Lake in Philadelphia. The lake, part of a maze of interconnected bays and tidal slough, led to the commission to believe the fish were likely present in the Schuylkill and Delaware rivers.
A snakehead was caught in May 2017 in Bernhardt's Dam in Berks County and 2 were caught in Octoraro Creek in Lancaster County in July 2018.
The Pennsylvania Fish and Boat Commission notes that snakeheads “will compete with other fish species for forage and habitat” and in Pennsylvania it’s unlawful for anyone to possess, sell, buy or trade live specimens; to introduce or import them into Pennsylvania waters; or to transport them in or through the state.
The commission recommends that anglers catching snakeheads not release them and dispose of them properly, and report the catch.
The 2 fish lifts were installed on the east and west sides of the Conowingo Dam decades ago to allow passage of migratory fish such as American shad and river herring. They operate during the spring migration as part of restoration efforts for those migratory fish species. Spring is also when snakeheads are known to travel longer distances in the watershed.
After the snakehead was observed in the east fish life in 2017, an agreement was established between the Conowingo Dam’s owner, Exelon, and the Susquehanna River Anadromous Fish Restoration Cooperative “to implement voluntary, adaptive best management practices that reduce the spread of northern snakeheads while still allowing migratory fish passage,” according to the DNR.
Smaller dams upriver of Conowingo Pond, which include Holtwood, Safe Harbor and York Haven, in Pennsylvania, may help to slow the northward spread of snakeheads.
However, snakeheads can breathe air from the atmosphere using an air bladder that works like a lung, and are known to travel short distances on land.
Attempts to control the spread of snakeheads have not been permanently successful.