The Hennepin & Hopper Lakes in Putnam County will be closed to all public sport fishing in 2012 as a renewed effort is undertaken to remove invasive common carp from the lakes, The Wetlands Initiative and the Illinois Department of Natural Resources (IDNR) announced today.
Despite efforts to remove this aggressive non-native species, common carp are again present and degrading the lake and marsh system. The 2011 fish survey conducted by IDNR fishery biologists identified a large number of common carp within the lakes, located 40 miles north of Peoria along the Illinois River.
The Wetlands Initiative (TWI), a nonprofit organization, created and manages the Sue and Wes Dixon Waterfowl Refuge at Hennepin & Hopper Lakes. Since 2001, the Initiative has been restoring the 2,700-acre site from row crops to diverse native ecosystems, including lakes, wetlands, and prairies. Throughout the project’s history, the IDNR has partnered with the Initiative to lend expertise in managing fisheries, stock native fishes, and assist in monitoring the lake and marsh.
In the fall of 2009, the Initiative pumped out the water in the lakes so that IDNR could apply the fish toxicant rotenone to remove the common carp. In the spring of 2010, the healthy marsh habitat returned, and the IDNR restocked the lakes with native and sport fish. Other native flora and fauna returned, including thousands of migrating canvasback ducks in the spring of 2011.
By last summer, however, TWI ecologists and other observers could see that the vegetation in the lakes was decreasing.
“Once the carp reach a tipping point, they begin to take over,” said Paul Botts, Initiative executive director. “We could see the vegetation vanishing before our eyes.”
The Initiative and the IDNR now believe that enough common carp survived the 2009-10 removal effort to have led to what appears to be a carp comeback in the Hennepin & Hopper Lakes.
“During the rotenone operation, some common carp were taking refuge in active remnants of the tile system draining the 1,250-acre lakes,” said Initiative senior ecologist Gary Sullivan. “This became apparent as we were pulling up tile outlet tubes and live carp were sliding out by the bucket-load as water sluiced out each end.”
“We didn’t anticipate that the carp could use the drain tiles, because tile lines are groundwater outlets and should contain extremely little oxygen,” said Wayne Herndon, IDNR fishery biologist. “That’s what the scientific literature has long predicted about circumstances such as this.”
For most of the 20th century, the lakes were drained―using a system of clay tiles, ditches, and a pump―to support a vast sea of corn and soybean fields. Although most of the drain tiles were disabled during the 2009 draw down, Sullivan said it was not possible to get heavy equipment to tile lines in the soft, saturated sediments in what was the deepest part of the lakes.
The Initiative says that its next removal effort will directly address what remains of the drain tile system.
“We aren’t going to repeat the same draw down steps,” Botts said. “Rather, we are going to do something more sophisticated: we are dividing the remnant drainage ditches into segments to create smaller wetland cells that can be drained independently. This will allow us to drain each cell completely and make it easier to locate and disable every last drain tile line.”
Another advantage of this strategy is that the first of the stair-stepped cells will be used as refuge to hold many of the desirable native fish surviving in the lake. The bulk of the de-watering operation, followed by IDNR’s application of rotenone, will begin this coming summer.
“There are never any guarantees when we attempt to restore habitat at this large scale,” Herndon said. “But a functioning marsh at this location on the Illinois River is of great value and well worth any effort.
“Every site is different and you have to learn and adapt to it,” Herndon added. “We know from our success at Spring Lake—where the native fish have controlled the carp since we conducted three drawdowns in the 1980s—that we can get ahead and stay ahead of this invasive species.”
“The Hennepin and Hopper Lakes are one of the few places in the state that certain rare native fish species now live because so little of their habitat remains,” Herndon said. “Our goals for this area are all interconnected and center around the desire to sustain a vibrant marsh. To do that, we must maintain a diverse native fish population. Diversity makes the system more resilient and helps us to manage rare fishes, as well as common species.”
For more information, visit www.wetlands-initiative.org