Why we need to stay vigilant to stop the introduction and spread of invasive species

Photo courtesy of the Chesapeake bay Program

The northern snakehead (Channa argus) is a mean-looking fish (not to mention it has teeth and can travel on land!), but for a long time we haven’t known what its presence means for the health of our native fish populations.

Not all non-native fish are invasive, afterall. For example, walleye, which are native to Canada and the northern US and were introduced to the Chesapeake Bay region in the 1800s, thrive in our waters but have no impact on native fish species.

For a species to be considered invasive, it has to negatively disrupt the ecosystem into which it is introduced.

So, is the northern snakehead a problem for the Potomac River? A recent study says they could be.

Snakeheads can breathe air and survive on land. Photo courtesy of VA State Parks

Snakeheads were introduced to the Potomac River in 2004. They are native to Asia and have no natural predators in our region, so scientists initially feared that they would cause catastrophic declines in the populations of their prey - which include everything from other fish to crustaceans, small birds, mammals, and reptiles.

Though snakeheads have significantly expanded their range throughout the Chesapeake Bay watershed in the years since their introduction, little evidence had been found to support initial concerns. In fact, despite their unpleasant appearance, they’ve become appreciated by anglers and eaters alike. (Don’t believe they’re yummy? Check out this taste test!)

Unfortunately, recent research conducted in the Blackwater and Little Blackwater Rivers in Maryland suggest that snakeheads are driving down the population size and biomass of native fish species.

How do they know? The researchers conducted the same survey in 2006-2007, before snakeheads reached those rivers. Comparison of the data from the two surveys indicates that 17 of the 21 native species saw declines (ranging from 30 to 97 percent).

By looking at the stomach contents of 125 caught snakeheads, scientists were also able to see what the invaders are preying on the most. Their diet included significant amounts of gizzard shad, bluegill, American eel (already a suffering species!), and dragonfly larvae.

A Gizzard Shad caught by a Great Blue Heron. This native fish species is now being eaten in large quantities by snakeheads. Photo Courtesy of Mark Watson/FLickr.

bluegills are also popular prey of snakeheads. Photo COurtesy of Mark Grapengater/Flickr.

Invaders affect local fish not just by eating them, but by eating their prey and driving them out of their ecological niches.

A goldfish recently found in the Potomac. Photo courtesy of Kate NiBlack Raby.

So what can be done? What the science shows is that we need to continue to be vigilant about fighting invasives. We can do this by:

supporting and funding further research.
continuing to limit the spread of snakeheads by fishing for them (find your local regulations about catching snakeheads here) and eating them.
not introducing new non-native species! Recently, goldfish have been found in the Chesapeake Bay and Potomac River. Be careful never to release pet fish into our waterways.

While eradicating snakeheads from our region is unlikely, studies like this show that by taking action to restrict their ability to grow and multiply, we can limit their damage to local biodiversity.