ROMEOVILLE, Ill. — The now two-decades-old battle to keep invasive Asian carp out of the Great Lakes, being waged at numerous sites around the Midwest, has evolved into an uneasy standoff of sorts here on the Chicago waterway that is universally considered the front line in this biological conflict.
All indications are that bighead and silver carp, the most feared of the four Asian carp species due to the devastating impact they would be expected to have on the food web in the lakes, have not made their way past the electrical barriers here that are intended to stop their march up the Mississippi River watershed.
These two aggressive and prolific filter feeders that rob the young of native species of the nutrients those fish need to grow, are not yet pressing up against the barriers, which are maintained by the U.S. Army Corps of Engineers in the canal system that corrupts the continental divide and creates an artificial connection between the Great Lakes and Mississippi River watersheds.
“We’re holding our ground — that’s a good way to describe it,” said U.S. Fish and Wildlife Service Midwest Regional Director Charlie Wooley. “With all of the extensive sampling and testing being done there in the Chicago area, we’ve seen things become more or less a stalemate.”
These exotic carp, brought to the U.S. more than 40 years ago to help control algae in southern fish farms and wastewater treatment ponds, escaped into the Mississippi River system during periods of flooding and have been surging throughout this vast waterway. Bighead and silver carp, which can produce a million eggs a year and reach massive size, are now found in the Mississippi and its myriad tributaries from New Orleans to Minnesota, and in the Ohio River and Missouri River, but it is their charge up the Illinois River and its feeder waterways that has put them ominously close to Lake Michigan.
Two other invasive Asian carp species — grass carp and black carp — also pose threats to the ecosystems of the U.S. rivers and lakes where they might become established. Black carp feed primarily on mussels and snails, and where present are competing with native wildlife for these mollusks.
Grass carp, sterile and fertile specimens of which have been found in very small numbers in several of the Great Lakes, including Lake Erie, consume large amounts of vegetation, thus altering the aquatic environment and destroying habitat needed by native fish and waterfowl.
“They are all a big concern, because any invasive species has the potential to disrupt the environment in the lakes and displace native fish, but I believe it’s fair to say the bighead and the silvers present the biggest threat to the Great Lakes because they impact the bottom of the food chain,” said Travis Hartman, the Lake Erie Program Administrator for the Ohio Department of Natural Resources.
“The prospect of bighead and the silver carp reaching the Great Lakes is a very serious thing, since they have a track record of dominating large sections of the Mississippi.”
Biologists are much better equipped in their conflict with Asian carp today than they were when the threat was still in the assessment stage. Marc Gaden, the communications director and legislative liaison for the Great Lakes Fishery Commission, said dozens of agencies, public and private, state, federal and provincial, and in both the U.S. and Canada have joined the battle, and he is encouraged by what he calls an “unprecedented” level of cooperation.
“A war is what we view this as,” he said, “so we have to use any weapons we can. We want to keep these invading fish out of our territory, and push them back, if possible.”
Besides intensive study of the fish, their habits and tendencies, and probing for genetic weaknesses, the consortium of biologists have exhibited a heightened sense of urgency when dealing with Asian carp.
He said the overall approach with Asian carp involves intense monitoring, mostly conducted by the Illinois DNR, active management of the existing Illinois River population of Asian carp, a series of well-mapped-out contingency plans in the event the fish do breech the barrier or show up in increased numbers closer to the barrier, and the development of long-term solutions to the crisis.
Kevin Irons, the aquaculture and aquatic nuisance species program manager for the Illinois DNR said these extensive removal efforts have depleted the ranks of breeding fish in the sections of river closest to the barriers.
“We are continuing the good fight,” said Mr. Irons, who spent 10 days studying these fish in their native China, where the carp are intensively farmed and a staple of the diet. “The leading edge of these fish in the Illinois River has not advanced at all. Working together, we are keeping them away from the electric barrier system and out of Lake Michigan.”
Some studies have questioned the effectiveness of the electrical barrier on juvenile fish, and there is heightened concern about Asian carp eggs and larval fish slipping past, hidden in voids in barges. Many biologists favor a system that would treat the water around barges as they move through the locks, to kill any Asian carp larvae or eggs that could be present.
“That is the best way, in many people’s eyes, to move toward a permanent solution,” Mr. Gaden said.
Mr. Irons said seining efforts and underwater cameras are on the lookout for those smaller fish, and part of the contingency options call for the use of the poison rotenone to kill everything in sections of the waterway near the barriers, if needed.
Across Lake Michigan, on the banks for the Grand River charter boat captain Willis Kerridge worries about the Asian carp threat, and the devastating impact these invasive fish could have on his business, which includes a bait and tackle shop in Nunica, near where the river dumps into the big lake.
“It’s been a concern for a long time, because from what we’ve learned these things could do a lot of harm in a hurry,” he said recently. “We don’t hear a lot of new information, but it’s still a worry for all of us fishermen.”
Block News Alliance consists of the Pittsburgh Post-Gazette and The Blade of Toledo, Ohio. Matt Markey is a reporter for The Blade.