La Crosse, Wis. — A four-and-half-mile-long narrow backwater slough blocked off from the Illinois River near Morris, Ill., has become the latest front line in the study of sound barriers to keep Asian carp out of the Upper Mississippi River and its watershed tributaries and lakes in Wisconsin and Minnesota.
In the study, starting in early August, telemetry-tagged adult carp handled by a federal research team based in Wisconsin are exposed to high-pressure shock waves emitted by sub-surface water guns to determine how the carp behave. The idea is to learn about their habitat and life cycles and how their management can be integrated with fisheries programs run by natural resources agencies.
The water gun “shock wave” technique is one of several barrier and chemical deterrents being studied by scientists at the Upper Midwest Environmental Sciences Center’s laboratories and ponds managed by the U.S. Geological Survey on a 65-acre site on French Island north of La Crosse. The lab has been conducting research on aquatic invasives for more than 55 years.
“We are not at the point where we’re ready to take them out in the field,” said Mark Gaikowski, a biologist who leads a branch of scientists focused on developing tools to control aquatic invasives. Besides locks and dams, the units could be placed at turbulent water areas where the carp spawn. Forcing the fish into sub-optimal spawning locations might lower their reproductive success and, in certain cases, make them vulnerable to commercial harvest.
Asian carp populations are highest in the Illinois River, but rogue specimens have been documented in the Upper Mississippi and St. Croix river systems since 1997.
Recently, two adult female Asian carp, a 20-pound silver and 40-pound bighead, loaded with eggs, were captured by contract netters at Cottage Grove, Minn. (Pool 2), raising the sense of urgency for carp controls.
“The collection of female bighead carp during periods when spawning could occur is of concern, and we’re working with state and federal partners to help monitor the Upper Mississippi and to better understand their life history in these waters,” Gaikowski said.
The plankton-feeding carp migrated over 30 years up the Mississippi River after escaping southern fish farms and next pose a risk to native fish. Moreover, the invasive carp threaten the $7 billion annual Great Lakes fishery, and in the case of silver carp, are a hazard to boaters, whose motor noise triggers dangerous leaping displays that can injure boaters.
In early August, a University of Minnesota team headed by researcher Peter Sorenson from the Minnesota Aquatic Invasive Species Center installed an underwater speaker system at Lock and Dam 8 on the Mississippi River at Genoa, Wis. Researchers at UMESC also are testing a speaker system to repel the sound-sensitive carp.
“These are the same speakers used for synchronized swimming,” Gaikowski said. “We play a series of different tones at certain frequency ranges, and in ponds we’ve been able to push the carp back and forth. We did silver carp last fall and this summer we’re doing the bigheads.”
Several sources provide silver and bighead carp specimens used in lab studies. Some were obtained from other research sites, some are spawned at the La Crosse center, some are caught in the wild, and some were raised at a fish farm in Missouri.
Chemical tests include injecting carbon dioxide to create a curtain that mixes with speaker barriers and altering a registered compound called antimycin. Packaging the control agent into microparticles targets silver and bighead carp, essentially suffocating carp by interfering with oxygen use at the cellular level, Gaikowski said.
“As a research agency we can figure how the technology works and situations it can be used,” he said. “But we have to work with (federal and state) agencies to determine where we can use that technology and how it could affect native fishes and the agencies’ fish management.”
Funding for the Asian carp work at five research centers, including La Crosse, amounts to about $3.5 million in USGS’s base budget.
Fish managers say heavy rains for several months have created a prolonged two-and-a-half-month “open river” environment from northeast Iowa north, enabling all fish to move more freely through locks and dams. Soon, river managers expect to proceed with a plan to close the Upper St. Anthony Lock on the river in Minneapolis, providing an absolute barrier on the river.
“I’m not sure we can block them,” said Ron Benjamin, of La Crosse, Wisconsin DNR fisheries supervisor for the Upper Mississippi River, in reviewing the possible solutions. “The public wants something rolled out tomorrow. I am not sure the (pending) sound barriers and chemicals are the silver bullets.”
While noting the river is resilient, Benjamin speculated that firmly established native fish populations could out-compete carp for food, and prey upon young Asian carp.
Those natural obstacles might prevent Asian carp from shouldering in on the river’s rich fishery. Furthermore, he said the public needs to be constantly reminded not to help Asian carp get established by moving them under any circumstance as small or larger fish.
Gaikowski, who has been researching Asian carp since 2009, said, in final analysis, “The ability to control an invasive organism depends on the level of resources society wants to commit to addressing the problem. Current technologies will never eliminate carp, but they have the potential to control the organisms at levels that will limit economic and ecological damage.”