Geoff Smith, a biologist with the Pennsylvania Fish and Boat Commission (PFBC), unfurled a weighted seine and plunged it into the water Monday at John Heinz National Wildlife Refuge.
Smith and two other PFBC scientists dragged the net through the shallows of the Heinz impoundment, a sprawling wetland in Philly fed by Darby Creek. Their target: invasive Northern snakeheads.
The impoundment had been drained for fall migrating shorebirds, exposing the muddy bottom to help make swift work of the hunt. Snakeheads flopped openly in the muck, demonstrating their remarkable resilience — a keen ability to survive in shallow water or open air without suffocating.
“They are a prized food fish. They were brought here mainly for people to eat. And they’ve been liberated into waters around the area,” Smith said, with a sarcastic smile on the word liberated.
Snakeheads feast on native fish, and the PFBC has labeled them “voracious predators.” They are seen as such an environmental threat that it is illegal to transport them live in the state.
Smith and his team at PFBC, along with Pennsylvania State University student Matt Chotlos, are collaborating on a study of the snakehead invasion into impoundments — local lakes, ponds, and wetlands.
A major goal of the team is to determine levels of contamination in snakeheads by synthetic per- and polyfluoroalkyl chemical compounds, known as PFAS. The team is also examining tissue samples for other biomarkers, and to assess the species’ broader ecological impact.
“Since they are a popular food item,” Smith said, “we want to have an idea what those contaminant levels look like.”
How did snakeheads get to Philly?
Native to China, Russia, and Korea, Northern snakeheads (Channa argus) were first documented in Pennsylvania in 2004 at Meadow Lake in Philadelphia’s FDR Park. The lake is fed by interconnected waterways that ease the spread.
“We don’t know who first brought them,” Smith said, “but they were probably brought for live fish markets.”
Snakeheads grow big and have become a sport fish for anglers. Their white meat filets are tasty to some who share recipes. Anglers debate online whether they should be killed after they are caught — or cooked and savored.
Snakeheads are present not only in Philly, but also in the Rancocas, Woodbury, and Raccoon Creeks in South Jersey, according to recent research by David Keller, fisheries section leader for the Academy of Natural Sciences at Drexel University.
“The impact, the concern, is as high as it gets,” said Keller, who hopes to publish a study soon on snakeheads in the Delaware River Basin. “From my perspective, the concern for Northern snakeheads is how they are impacting the Delaware basin and the fish fauna and the ecology.”
Members of Keller’s team found 46 species of fish in waterways they studied. They found 21 species in the stomachs of captured Northern snakeheads. Particularly tempting to snakeheads are killifish, sunfish, and eels.
Of the waterways Keller studied, Darby Creek had the highest concentration of Northern snakeheads in the region.
“It’s a top predator, and has spread very quickly,” Keller said. “It was first documented in the Delaware basin in 2004, and within about 10 to 15 years, they were found basically in the entire length of the Delaware basin.”
Northern snakeheads have been found near the headwaters of the Delaware River in New York in areas inhabited by ironcolor shiners, which are endangered in Pennsylvania, New Jersey, and Delaware, Keller said.
Keller said snakeheads are particularly adaptable to shallow water and wetlands. Unlike other freshwater fish, they have a special chamber that allows them to gulp air for periods of time out of the water. They can also survive in stagnant shallow water, or polluted waterways with low oxygen levels.
The study at Heinz
Smith, the PFBC biologist, chose Heinz as his location for collecting Northern snakeheads because of its impoundment. He traveled 200 miles from Centre County with Chotlos and two other PFBC biologists, Ben Frick and Garret Kratina.
“When we take the fish, we’re also archiving samples for genetics, for diet, and for other health aspects,” Smith said.
Snakeheads’ impact
Erin Lacour, a wildlife biologist for the U.S. Fish and Wildlife Service at Heinz, said the refuge has already seen the impact of snakeheads.
“They out-prey other species,” Lacour said. “We have some sensitive frogs and other species here. They will absolutely prey on those. Our number of frogs has gone down.”
Chotlos, the Penn State student pursuing a master’s degree in ecology, said the five fish caught for sampling at Heinz will be taken back to a lab, sedated, and sampled for contaminants. They will then be euthanized and dissected.
In the field, he extracted tissue from the gills of newly caught snakeheads with a pair of forceps.
“We don’t really know that much about them in general,” Chotlos said while reaching into the pink gill of one. “We don’t have a lot of data.”
Snakeheads were first discovered in Maryland in 2002, according to the National Invasive Species Information Center.
The snakehead has a long torpedo-shaped body that can grow to 3 feet. Its scaled head resembles that of a snake. It has a large mouth and sharp teeth. It is colored tan to black with irregular blotches. It is often mistaken for native burbot and bowfin fish.
Snakeheads are so big and ubiquitous that many anglers now seek them out.
Catching snakeheads
Back in June, Jessica Day, of Bucks County, was fishing with her boyfriend, Aidan Fioravanti, along the tidal Schuylkill below Fairmount Dam. She was casting for carp when she spotted a group of snakeheads.
“I was just casting for like an hour,” she said.
Eventually, one snakehead bit. She took a picture and tossed it back.
“There is a concern,” Day said of the fish as invasive. “Obviously they’re not meant to be here, but … they have adapted. Now that snakeheads are here, I don’t think there’s really anything we can do.”
Day says she would not eat a snakehead caught in Philly because of potential pollutants. But nor would she kill it out of hand.
“I believe that you should not kill a fish unless you’re doing something with it, like eating it, giving it away, or using it for fertilizer,” Day said. “I wouldn’t mind killing the fish if I knew that would stop the spread … but there were at least 20 other snakehead there. There’s nothing that killing one fish was going to do.”