These fish escaped confinement in the 1970s: 50 years on, they are now massive invasive species threatening the Great Lakes
Over recent decades, four species of invasive carp have become “one of the most urgent, wide-ranging and complex environmental challenges of our time”.
Since the late 20th century, invasive carp have thrived in North America, posing a threat to native species in the Mississippi River system and beyond.
What are invasive carp?
The term ‘invasive carp’ (or ‘Asian carp’) is used in North America to refer to four types of carp - bighead, black, grass and silver - that are native to Southeast Asia.
Species that can grow to over four feet in length and weigh more than 100 pounds, the carp were originally imported to the United States around 50 years ago, to help with pest control in aquaculture facilities.
However, the species then escaped into the Mississippi - a 2,340-mile river that runs from Minnesota to the Gulf of Mexico - before proliferating and spreading.
According to the U.S. Department of Agriculture, they found their way into the wild thanks to a combination of the effects of “flooding and accidental releases”.
From the Mississippi River to the Great Lakes
Capitalizing on the Mississippi’s wide reach, the carp species have spread into a whole host of major tributaries of the river. “The Mississippi River system is like a giant freshwater highway that has given invasive carp species access to many of the country’s rivers and streams,” says the Great Lakes Fishery Commission (GLFC).
Notably, the Illinois River is the Mississippi’s chief tributary, serving as the major link between the river and the Great Lakes - a series of interconnected lakes that span several states and cross into Canada. The U.S.’s Fish and Wildlife Service (FWS) says grass carp is now found in all but one of the Great Lakes.
While grass is the only species of invasive carp with a confirmed current population in the Great Lakes, the FWS says, all four species represent a threat to the bodies of water, which comprise Lakes Superior, Michigan, Huron, Erie and Ontario.
The GLFC explains that, although black carp remain 300 miles from Lake Michigan - which the Illinois runs directly into - bighead and silver carps are now within less than 50 miles of the Great Lake.
What is being done to curb the spread of invasive carp species?
The chief danger posed by invasive carp species is their ability to “outcompete native desirable fishes”, the GLFC says, combined with their prolific feeding rate.
“Over five decades,” adds the FWS, “invasive carp have depleted the vitality of many rivers, lakes and reservoirs“. They “now represent one of the most urgent, wide-ranging and complex environmental challenges of our time”, the agency concludes.
To combat the proliferation of invasive carp in North America, mass-removal programs are underway in numerous states. In particular, schemes in Illinois, Kentucky and Tennessee are at the heart of an effort that leads to the extraction of millions of pounds of invasive carp each year.
In a social-media post in May, the FWS revealed that some 50 million pounds of invasive carp have been removed from the Illinois River alone over the past decade and a half.
A range of state-of-the-art barriers are also in operation to curb the carp species’ spread, harnessing a number of technologies. For example, in the Chicago Sanitary and Ship Canal, located in the Illinois River, an underwater electric field acts as a deterrent.
Meanwhile, in the Cumberland River in Kentucky, a ‘bioacoustic fish fence’ has been installed at Barkley Lock and Dam. Per the Invasive Carp Regional Coordinating Committee, this technology uses “an air-bubble curtain, lights, and sound” to deter the advance of the carp species.
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