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From the February 2014 Conservationist

A front view of an open-mouthed northern snakehead

Northern Snakeheads in New York

The fish behind the headlines

By James MacDonald

"Rash of Frankenfish terrorizing Central Park waters!" screamed the Huffington Post headline. The same article described the fish as "ruthless and evil." Terror? Evil? They can only mean one thing: the northern snakehead.

The northern snakehead's alarming reputation inspires both fear and fascination. But behind the myth, what is the truth about snakeheads? What are they like? What kind of threat do they pose to New York ecosystems? Eight years of monitoring in New York City and the Potomac River are beginning to hint at answers.

Ever since their discovery in a Crofton, Maryland pond in 2002, biologists have been concerned about the potential ecological impacts of northern snakeheads. Part of a group of fishes of the genera Channa and Parachanna, snakeheads are native to Asia and Africa. There are 29 species, but only the northern snakehead (Channa argus) is established in New York.

A person holds a juvenile snakehead over a jar
juvenile snakehead (Photo: Susan

Snakeheads arrived in the U.S. through the food and aquarium trade, and some were subsequently released into local waters. It is not unusual for introduced species (not just fish but also plants, crustaceans, insects, etc.) to become highly disruptive in their new habitats, where their natural predators, usual parasites, and competitors are absent and local species are not adapted to their presence. In their native range, northern snakeheads are top predators, leading to concerns that snakeheads will heavily prey on and out-compete local species, like largemouth bass, for available food.

Snakeheads are obligate air breathers, meaning that they need access to air. A snakehead kept under water for too long will drown. Adapted to shallow, low-oxygen waters in their native range, snakeheads do possess a limited ability to move on land, can survive out of water for an extended period, and can tolerate a wide range of environmental conditions. Thus, there were concerns that snakeheads would easily disperse to new areas. Because of this, Maryland Department of Natural Resources staff eradicated the fish's population in the Maryland pond where they were first discovered. However, despite their efforts, a population of northern snakeheads became established in the Potomac Basin, most likely prior to the Crofton eradication.

Two biologists spray rotenone into a pond from a boat
Biologists spray rotenone into a lake to
kill snakeheads (Photo: Susan Shafer)

Northern snakeheads have been in New York since at least 2005, when DEC fisheries staff caught three in a hoop net during a routine survey in Meadow Lake, Flushing Meadows Corona Park, Queens. Since then, DEC has caught additional specimens in Meadow Lake and the connected Willow Lake each year during electrofishing surveys. In April 2008, an electrofishing survey in Central Park's Harlem Meer turned up a single specimen. That same year, in May, a property owner in Orange County, NY killed two snakehead fish in Ridgebury Lake behind his house. As that water body connects to the Hudson River via several small creeks, DEC acted quickly and treated the lake and connecting creeks with rotenone (a pesticide used to kill fish) and collected hundreds of adult and juvenile snakeheads. A follow-up treatment was conducted the next year to remove any survivors, and there were no more sightings of snakeheads outside of Queens until 2012, when an angler reported catching one in the Harlem Meer-the first in that pond since 2008. However, electrofishing surveys by DEC failed to find any additional specimens in the Meer.

As biologists took action to monitor and control the invader, the image of a toothy, air-breathing fish with "snakehead" for a name proved too much for popular imagination to ignore. Soon, the legend grew and the fish's limited ability to move over land became the perceived ability to walk on land. Concerns about predation on local fish species evolved into fears of predation on pets and children. A Queens Tribune article about the 2005 discovery described the fish as "flesh-eating" and deadly. Even the staid New York Times described snakeheads as "nightmarish." There were several horror movies released that featured the snakehead as a villain, and the angler's report of a snakehead in the Harlem Meer in 2012 was reported internationally, in multiple languages.

So, all the hype aside, what is the current situation in New York? As far as anyone knows, there is no evidence of an established population anywhere else in New York besides Meadow and Willow Lakes in Queens. Fortunately, these are isolated ponds, only connected to each other and by a long tributary to Long Island Sound. While northern snakeheads have been shown to tolerate a certain amount of salinity (as high as 18 parts per thousand), they cannot survive in full saltwater, so the Sound provides a natural barrier to their spread. DEC fisheries staff continue to keep tabs on these lakes, annually monitoring for any changes in populations of snakehead or other fish species. New regulations regarding snakeheads are in place (see sidebar below) and signs warn anglers not to release any snakeheads they might catch.

So far, repeated surveys indicate that while snakeheads are breeding in Meadow and Willow Lakes, they have yet to dominate these waters. In fact, the percentage of snakeheads vs. other fish species caught has remained fairly constant since 2006, and indications are snakeheads don't seem to be increasing in population. In addition, survey results show that other fish species populations (e.g. pumpkinseeds) are not decreasing, and largemouth bass, a species biologists feared might be harmed by competition with snakeheads, were captured in electrofishing surveys for the first time in both lakes in 2010, after the snakehead introduction. These are hopeful signs.

A nearly 20 inch-long northern snakehead fish
Adult northern snakeheads can grow to
three feet long!

The real question mark is the future. While the population in NYC is contained, the population in other areas, such as the Potomac basin, is not, and is so firmly established that it never will be. However, reports from Maryland and Virginia indicate a tenuous coexistence of snakeheads and native species, despite a steady population increase in the Potomac River and the spread of snakeheads into adjoining tributaries and watersheds, like the lower Delaware River.

Snakeheads grow quickly in North America, faster than in their native countries. This has led biologists to fear that these fish will reach sexual maturity earlier and perhaps have greater reproductive success. Snakeheads are believed to spawn multiple times per year, meaning they possess the potential to outbreed native species. A few large specimens (more than 32 inches) have been found in Queens, and a certified 17 lb., 6 oz. world-record fish was recently caught in Maryland. When biologists dissected several larger snakeheads found in Queens, they discovered numerous sunfish and other local species in the stomachs, a clear indication that snakeheads prey on native species.

In the meantime, the question remains how best to handle the snakeheads that are here. Several states, including Virginia, have hosted snakehead angling tournaments. In New York, snakeheads are identified and regulated as a fish that is dangerous to native fish populations. As such, all snakeheads that are caught must be euthanized, as possession of live snakeheads is prohibited. The federal Lacey Act prohibits importation and interstate transportation of live snakeheads. Anglers who catch one are required by New York State law to report their catch to DEC.

So where does the situation stand? The bottom line is that while it is very difficult to eradicate a nuisance species after it is firmly established, it is possible to prevent a population from expanding. Given the continuing uncertainties surrounding snakehead impacts, biologists will work to prevent their spread into new river basins, like the Hudson, while continuing to monitor established populations. Eradicating an outbreak can be costly and comes with considerable collateral damage to other species, so it is not undertaken lightly.

For now, though, there is no need to panic, and apart from what you may have read, your children can still play outside.

James MacDonald works in DEC's fisheries office in New York City