Army Corps adjusts Genoa dam to slow spread of invasive carp
La Crosse Tribune, 8/31/2017
The U.S. Army Corps of Engineers has modified operations of its lock and dam in Genoa in an effort to slow the upstream movement of invasive carp in the Mississippi River.
The changes, designed to stop Asian carp with minimal impact on native fish and barge traffic, are in response to recommendations from University of Minnesota biologist Peter Sorensen, who has been researching fish movement with a grant from the Minnesota Environmental Trust Fund.
Sorensen first studied how fast and far carp can swim and then used computer modeling to evaluate the flow of water through the gates.
“What we found was two things: for most of the time they were incapable of going through gates in most conditions — it was just too fast,” Sorensen said. “It really roars through most of the time.”
But under certain conditions, the flows were imbalanced, giving adult carp a chance to swim through where there was less current.
Sorensen recommended some minor adjustments that he said will even the flow and could cut carp passage, which he believes is relatively low, by more than half.
“To their credit they were very receptive to that idea,” Sorensen said. “It’s to their advantage, because by balancing velocities it also has the potential to reduce erosion. It’s a win-win.”
Corps project manager Nan Bischoff said the changes won’t cost anything and still allowing the Corps to fulfill its mission of maintaining a 9-foot shipping channel.
“We just revise our operational charts,” she said. “The lock master and lock staff knows what adjustments (to make).”
In 2014, Sorensen installed underwater speakers to keep carp out of the lock at Genoa. The speakers broadcast low-frequency sound waves that deter carp but don’t affect native species.
The Genoa dam is the first of the 29 on the Upper Mississippi River to undergo modifications, and Corps spokeswoman Shannon Bauer said it is the first time the Mississippi Valley Division has ever changed procedures in response to invasive species.
The flow models were also modified to accommodate the concerns of Mark Clements, whose family has operated Clements Fishing Barge immediately below the dam since 1936.
Sorensen is now studying flows at Lock and Dam 5 in Winona, the uppermost dam below the confluence of the Minnesota River. His researchers are also monitoring the impact of the changes on other fish species at Genoa.
According to the Minnesota Department of Natural Resources, bigheaded and silver carp are now abundant and reproducing in Iowa, about 100 miles south of Genoa and continuing to move north. In 2008, a silver carp was discovered in pool 8 of the Mississippi River. Bighead, silver and grass carp have since been found as far north as Hastings as well as on the St. Croix River.
The DNR warns invasive carp can devastate local ecosystems by overcrowding native species and eating all their food. Silver carp, which can weigh up to 60 pounds, are also startled by the sound of propellers and create a hazard for boaters when they leap out of the water.
“They’re probably just about everywhere, a few scattered ones,” Sorensen said. “It hasn’t been enough to spark reproduction. If we can reduce those with no cost … it’s low-hanging fruit.”