Asian carp are here in the US to stay. This group of fishes are often called Bigheaded carps, and typically includes silver carp, bighead carp, grass carp, and black carp. Each species was brought to the US from Asia for different reasons—for example, grass carp were introduced for weed control as they eat vegetation. Each species was also likely introduced multiple times to natural habitats, and today these carps can be found across much of North America. You may recognize silver carp, which are well known for their jumping behavior in the presence of boats.
From multiple locations, Asian carp have been expanding their range in North America. The current concern is that they will make their way into the Great Lakes, where they will have many negative impacts on the ecosystems and fisheries of the Great Lakes. (But to be clear, the Great Lakes are home to many, many introduced species that have rendered the current Great Lakes into systems that already might not represent their former pristine selves.) Asian carp are well-established in the Illinois River, and migrating north through the Chicago Sanitary and Ship Canal—the connection between the Illinois and Mississippi Rivers and the Great Lakes—would mean their introduction into the Great Lakes.
Currently, an electric barrier exists in the Chicago Sanitary and Ship Canal, and an electric barrier is exactly what it sounds like—an electric field present in the canal’s water that acts as a strong deterrent against fish passage. Basically, fish have no incentive to swim through electrified water once they feel the shock. So far, the electric barrier seems to be working well, but no barrier is 100% effective. Electricity may fail, eggs or larvae may pass, or many other things may occur to permit fish passage. A redundant barrier is being sought.
Recently, there has been a lot of activity behind the idea of a using carbon dioxide as a redundant barrier to the electric barrier. Fish are generally repelled from CO2, which in high concentrations can sedate or even anesthetize fish. But weaker concentrations of CO2 in water are showing promise to repel fish, as if there were a foul smell in the air that would cause you to turn around and not want to approach.
The idea behind a CO2 barrier is not create a ‘bubble curtain’ but to actually infuse the water with high concentrations of dissolved CO2. Although river locations are still under consideration (you can’t infuse entire rivers), this infusion would likely take place in a small portion of the river through which everything must pass—like a shipping lock! Shipping locks could be pumped full of CO2, and then opened, as part of their regularly scheduled use. The plume of CO2-rich water would then dissipate downstream, pushing Asian carp back and ultimately discouraging them from any further migration.
Of course, CO2 impacts all fishes, and in fact other less mobile organisms, too, such as mussels and other aquatic invertebrates. So while it might be clear that CO2 use to deter Asian carp is a good thing, unintended impacts need to also be assessed. It could be that the CO2 doesn’t stick around in the water long enough to negatively impact other biota, or that other mechanisms exist to minimize CO2 on non-Asian carps species. CO2 impacts on fish is a very new field of study—namely because the need to create defenses against introduced species often come with little warning. However, much of the early work looking at CO2 use as a barrier suggests very good potential.
What do you think about pumping huge volumes of CO2 into rivers to contain invasive species? Leave us your thoughts in a comment.