On a warm October day in 2003, Mary Poplett from Peoria was jet skiing on the Illinois. While moving slowly on the river, the sound of her jet ski made a 30-pound Asian carp leap from the water, smacking her hard in the head. “Imagine being hit in the face by a bowling ball,” she said, “it was like that.” The fishy head-butt knocked her unconscious, breaking her nose and fracturing a vertebra. [Reeves, 2019]
As dramatic as that moment was, it’s not nearly unique. Boaters are often injured by flying Asian carp in the waterways of the Mississippi. These fish, which can grow to 30 pounds and leap more than 10 feet vertically and 30 feet horizontally, take to the air when disturbed by a passing boat. The real question is why—how did leaping carp from Asia come to be a dangerous fish in the middle of America?
Strangely, Asian carp were intentionally introduced into North America by aquaculture managers in the early-1970s to control algae, weeds, and parasites in their watery farms, and coincidentally as a kind of sewage treatment. (There’s little limit to what the Asian carp will eat, which makes it a handy all-round fish farm animal.)
When they were first introduced to North America, it was believed that the requirements for successful reproduction were fairly restrictive, and that it was unlikely the carp would be able to expand outside of their original range. They’re native to tropical regions of the world, and their possible range in the US was believe to be limited by cold water and winter weather. But, as Jon Stanley predicted in 1976 (in what may be the first risk assessment for a potentially invasive fish), the grass carp would reproduce easily in the Mississippi River Basin within the next two years. [Stanley, 1976] He was correct, but only in retrospect: the first grass carp larvae were later found in samples that had been collected in 1975, he was off by a mere negative year or two. [Conner, et al., 1980]
There are four types of imported Asian carp now living in US waters that were brought into the country for use in ponds: the bighead, silver, grass, and black carp, each with distinct living styles and preferred foods. Over the years, through flooding, accidental releases and the occasional intentional release, all four kinds of carp have found their way into the greater Mississippi River system. This network of rivers, brooks, streams, lakes, and ponds are collectively a giant freshwater highway that has given these four carp species access to many of the country’s rivers and streams.
From that start in farm ponds in the southern US, they’re slowly making their way up the Mississippi River and its tributaries, and have been found as far north as Minnesota, with individual silver and bighead carp in the Mississippi National River and Recreation Area that runs through Saint Paul and Minneapolis.
Beyond the obvious flying fish problem, Asian carp cause serious damage to the native fish populations in the lakes and rivers that they occupy—they just plain out-compete other fish by being omnivorous and voracious eaters, particularly the small fry and larvae of other fish. (These omnivorous and voracious qualities of newly introduced species is a theme that you’ll keep seeing in the stories of other invasive species.)
Once you get used to the idea that Asian carp are everywhere in the greater Mississippi basin, you start to worry about other places they might invade—are there other North American waters they might eat through? What consequences might we anticipate? Short answer: The biggest concern now is that they’ll make it out of the Mississippi river basin area and into the Great Lakes, and from there, start to munch their way through the $7B fishing industry and $16B recreation boating business that currently flourish in the Lakes.
This wasn’t an issue before 1900 as the catchment basins of the Great Lakes and the Mississippi were completely disconnected. A drop of water that fell in near Chicago would either end up in New Orleans via the Mississippi, or in the North Atlantic via the Great Lakes. That was true since the Lakes were first formed at the end of the Last Glacial Period (the Wisconsin glaciation that ended 10,000 to 12,000 years ago), and when the Laurentide Ice Sheet receded.
But then at the turn of the 20th century, the two water systems were connected by completion of the Chicago Sanitary and Ship Canal (CS&SC), which famously reversed the flow of the Chicago River, allowing the city of Chicago to flush its sewage and waste southward into the Mississippi watershed rather than Lake Michigan. Since it’s been in place for over 100 years, shipping and recreational boating now relies on the connection being there. So the obvious avenue for the carp to make it into Great Lakes is via the Des Plaines river that flows south through Joliet, Illinois and has a connection to Lake Michigan through Chicago on the CS&SC.
While this is a (now) single an unbroken waterway from the Mississippi into the Great Lakes, Asian carp (especially silver carp) may be capable of jumping over some barriers, including low dams. High water during spring flooding often creates an "open river" condition as Mississippi River dams open their gates, which may allow invasive carps to move past what is otherwise a barrier. Flooding can spread these fish as well, because flooding can connect water bodies that aren't normally connected.
Invasive carp are also spread by humans. The release of live bait containing young carp has introduced these fish to other water bodies. To make things worse, boat traffic—especially barge and recreational watercraft moving through Mississippi River locks—also permit invasive carp to move through as well.
20/20 hindsight shows us that connecting the Mississippi Basin with the Great Lakes system so directly was not a great idea. Doing so allows invasive species to move between the river system and the Great Lakes, and vice-versa.
While the carp move northward, to date, that same CS&SC waterway from the Great Lakes into the Mississippi basin has let the round goby and the justly infamous zebra mussel slip from the Lakes south into the 2300 miles of river basin. But those have moved south with the river flow, and now the Asian carp is moving north upstream. The challenge is to keep them—and their eating habits—out of the Great Lakes and avoid devastation of the Great Lakes.
As a finger-in-the-dike measure, the Army Corps of Engineers has installed an electrical fish barrier on the canal, while the Illinois Department of Natural Resources poisoned the canal twice to kill all the fish. At the same time, just downstream from the Army barrier, fishermen hired by the government have pulled tons of bigheads and silver carp from the upper reaches of the Illinois. One fish, two fish; a thousand fish, a million fish.
The Army Corps maintains that the invasion of the Asian carp has been halted short of the Great Lakes. However, that argument is a bit fishy. In June 2010, a 19-pound bighead carp was caught in Calumet Lake, upstream of the barriers and just six miles from Lake Michigan. Meanwhile, DNA traces of silver carp has been detected in the water north of the barriers, very near the Lake. While people have demanded that the canal be closed down, the magnitude of the project is enormous and it would be removing a 100+ year old piece of infrastructure that many businesses now rely on—making the whole thing very unlikely. What’s more, a lawsuit was filed by neighboring states to demand the CS&SC be closed, yet has failed to proceed, with an appeals court agreeing with the state of Illinois to keep the canal open for now. [Vicini, 2010]
Although eDNA (environmental DNA, that is, DNA found floating freely in the water) has been found in Lake Michigan waters, so far no Asian carp has been landed by a fisher in the Great Lakes. But it seems clear that the eDNA is telling us what we don’t want to know—the invasion has begun, and it’s just a matter of time before the carp start leaping from the waters off the shore of Chicago.
Does this matter in the long run? That’s what we’ll talk about in the next installment of Invasion of the Species. Stay tuned.
. . . . . . . . . . . . . . . . . . . . . . . REFERENCES . . . . . . . . . . . . . . . . . . .
[Conner, et al., 1980] Conner, J.V., Gallagher, R.P., Chatry, M.F., 1980. Larval Evidence for the Natural Reproduction of the Grass Carp (Ctenophayngdon idella) in the Lower Mississippi River, in: Fuiman, L.A. (Ed.), Fourth Annual Larval Fish Conference, Mississippi, pp. 1–19.
[Jerde, et al., 2013] Christopher L. Jerde, W. Lindsay Chadderton, Andrew R. Mahon, Mark A. Renshaw, Joel Corush, Michelle L. Budny, Sagar Mysorekar, and David M. Lodge. Detection of Asian carp DNA as part of a Great Lakes basin-wide surveillance program. Canadian Journal of Fisheries and Aquatic Sciences • 4 April 2013 • https://doi.org/10.1139/cjfas-2012-0478
[Reeves, 2019] Reeves, A. (2019). Overrun: Dispatches from the Asian carp crisis. ECW Press. (Originally covered in the PJStar newspaper Oct 21, 2003 - https://web.archive.org/web/20031204114654/http://www.pjstar.com/news/luciano/b13elb9l030.html )
[Stanley, 1976] J.G. Stanley Reproduction of the Grass Carp (Ctenopharyngodon idella) outside its native range. Fisheries, 1 (1976), pp. 7-10
[Vicini, 2010] Vicini, James (19 January 2010), Michigan request denied in Great Lakes carp case. Reuters, archived from the original on 23 January 2010. https://www.reuters.com/article/idUSN1920892420100119?type=marketsNews