Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Vibrations from passing motorboats lead silver carp to try and escape by leaping out of the water. © Chris Olds, USFWS

Vibrations from passing motorboats lead silver carp to try and escape by leaping out of the water.
© Chris Olds, USFWS

August 2009

Containing the threat

Natural resource managers work to keep invasive species like Asian carp from spreading in Wisconsin waters.

Julia Solomon

When you head out for a day on the water you keep an eye out for all sorts of hazards – bad weather, hidden shoals, motor trouble, even sunburn – but until recently, dangerous leaping fish were not likely on any boater's list of concerns. That may be changing.

In December 2008, the Wisconsin Department of Natural Resources confirmed Asian silver "jumping" carp had reached Pool 7 of the Mississippi River, near La Crosse – the first documented finding of this species in Wisconsin waters. Silver carp (Hypophthalmichthys molitrix) are notorious for leaping out of the water in response to the vibration of passing motorboats. Since these fish can grow up to 40 pounds and leap in the air six feet or more, they have been known to cause serious injury to boaters, and are also bad news for native fish and aquatic plants.

Several species of Asian carp (silver, bighead, grass and black) were imported to the southern U.S. to filter plankton and detritus from aquaculture ponds in Arkansas and Mississippi in the 1970s. They escaped to the Mississippi River during floods in the early 1990s and have been making their way upstream ever since. All species except black carp have now been reported in Wisconsin waters of the Mississippi.

Vulnerable borders

DNR fish biologists are realists when it comes to the Asian carp. "We weren't too surprised to hear about this recent finding in the Upper Mississippi. We have known for a long time that they were headed our way," says DNR Supervisor Ron Benjamin, who heads the Mississippi River Fisheries Team. He attributes their recent northward movement to the floods of spring 2008. "Locks and dams can be a barrier to upstream migration, but when flood waters overwhelm the dam, there's nothing to prevent fish from swimming upstream."

Benjamin is not about to give up hope, though. "We're worried about the impact of these invasive fish on the upper Mississippi," he says. "We donít know yet what those consequences will be. But diverse ecosystems with quality habitat fare better when coping with invasive species, so we'll focus on keeping the river healthy. Maybe the most important thing we can do is to prevent invasive species from spreading inland and to the Great Lakes."

This message of containment resonates with Jeff Bode, DNR chief of the Lakes and Wetlands Section. Bode also directs agency efforts to prevent and control aquatic invasive species. He points out that Asian carp are not the only species threatening Wisconsinís lakes and rivers.

"The Great Lakes contain over 180 non-native species, so unfortunately, Asian carp are just one of many potential invaders at our borders," he says. "People are familiar with invasive plants and animals like Eurasian watermilfoil and zebra mussels that are already found in Wisconsin lakes, but they may not know about some of the other species that we are working to keep out."

Bode mentions several lesser known invaders like the quagga mussel (a close cousin to the zebra mussel), the round goby (a small voracious fish that preys on native fish eggs and young), and didymo (an algae also known as "rock snot" that forms slimy, impenetrable mats in streambeds). All of these invasive species occur in Lake Michigan, Lake Superior or both waters.

Stopping the spread

Between the invasive species already established in Wisconsin lakes and the ones knocking at the door, halting the spread of unwelcome invaders can seem like a daunting task. It doesn't intimidate Bode, though. "Some people say that the spread of invasive species is inevitable, but what is indomitable is the will and energy of the people of Wisconsin who love our lakes and streams. Together we are making a difference."

Wisconsin's long track record of commitment to controlling aquatic invasive species is built on partnerships with dedicated, active volunteers. Citizens across the state have taken the initiative to inspect boats at local landings and educate boaters about the threat of invasive species. In 2008 alone, watercraft inspectors, many of them volunteers, talked with more than 100,000 boaters around Wisconsin. Citizens also actively monitor their lakes for invasive species and educate local communities about the threats posed by these invaders.

The invasive bighead carp is even larger than the silver carp. © U.S. Geological Survey
The invasive bighead carp is even larger than the silver carp.
© U.S. Geological Survey

"Volunteer commitment to this issue is truly inspiring," says Bode. "Folks routinely give up their holidays and weekends to stand at the boat launches talking to people."

The state of Wisconsin has also made big investments in aquatic invasive species. Since 2003, DNR grants have been available to local communities to fight aquatic invasive species. Funding for this program has increased steadily to its current level of $4.3 million per year.

DNR law enforcement professionals have also stepped up their efforts to stop the spread of aquatic invaders. Wisconsin has several laws designed to prevent the spread of invasive species and the fish disease VHS, and wardens take these regulations seriously. In 2008, the DNR secured funding for nine new Water Guard deputy wardens whose sole focus is preventing the spread of aquatic invasive species and VHS by providing education as well as enforcement. They've been enthusiastically received around the state.

Bode says that increased funding for grants and enhanced enforcement are signs of a broader statewide trend. "Wisconsin takes the threat of aquatic invasive species very seriously," he says. "In the past several years we have seen an increased commitment by the state and our partners to approaching this issue strategically."

Boaters & anglers

You can help prevent the spread of aquatic invasive species by taking these simpe precautions every time you boat or fish.

  • INSPECT boats, trailers and equipment and REMOVE plants, animals andmud;
  • DRAIN water from boat, motor, bilge, live wells, and bait containers;
  • DON'T MOVE live fish away from a waterbody;
  • DISPOSE of unwanted bait in the trash. Use leftover minnows only under certain conditions;
  • RINSE boat and equipment with hot or high pressure water or let the boat dry for at least five days.

A culture of containment

So what does it mean to strategically prevent the spread of aquatic invaders? Recent scientific research sheds some light on this question.

Dr. David Lodge and his research group at the University of Notre Dame have been looking for the most effective ways to keep aquatic invasive species from spreading, and their findings have profound management implications.

John Rothlisberger, a PhD student in Dr. Lodge's lab and one of the lead researchers in this work, explains that they set out to evaluate two common prevention approaches – containment and shielding. "In dealing with an invasive species, you can either contain it and focus your effort on keeping it from moving anywhere else, or you can shield the other places that it might spread to, focusing your efforts on keeping it out of those places. You can think of it as going on the offense (containment) versus playing defense (shielding)."

The defense or "shielding" approach is a common one – if you live on a lake that doesn't have invasive species, it is natural to want to keep them out, and the most obvious way to do that is to keep them from being introduced into that lake by incoming boaters. Rothlisberger agrees that if the goal is protecting a single lake, then, shielding is an effective tool. But if the goal is to reduce the overall rate of spread of invasive species across the landscape, the picture changes.

Mathematical models show that the offense or "containment" approach is actually more effective at reducing the overall rate of spread of aquatic invasive species in many situations. "Our models show that if less than half of the lakes on a landscape are invaded, then containing invaders where they are known to occur is the most effective strategy for reducing spread," Rothlisberger says. His findings with co-researcher Kevin Drury of Bethel College were published in the February 2008 issue of the ecological research journal Oikos.

Their conclusions were of great interest to DNR's Bode. "Only a small fraction of Wisconsin's lakes contain the most problematic invasive species," he says, "so at a statewide scale, containment is really our best strategy."

Bode hopes to create a statewide "culture of containment" to keep invasive species from spreading. Programs will focus on popular fishing and boating waters like the Great Lakes, Lake Winnebago and the Mississippi River that contain multiple invasive species. The Department of Natural Resources has put containment into practice this summer, sending its watercraft inspectors to high-use waters and giving priority to grant applications from these areas.

Bode doesn't plan to stop there, though. "What we really want to do is promote an understanding of why we are concentrating containment time and dollars in certain waters. This will mean a cultural shift for a lot of people who have been working hard to shield their lakes. We'd like to get to a point where people recognize that to really protect a lake, you might have to look beyond one particular body of water. You might also need to help contain invasive species at the lake or river down the road.Ē

Steps in the right direction

If you live in western Wisconsin, the river down the road is the Mississippi, of course, which brings us back to DNR fisheries supervisor Ron Benjamin, and those pesky jumping carp.

"In many ways, Asian carp are a perfect example for containment," says Benjamin. These jumping carp have not yet been found in any inland waters, so we're working to contain them to the Mississippi and its tributaries. Also, since they are a larger species, Asian carp are less likely to be transferred from one water to another accidentally – unlike many invaders that can spread undetected. "Small Asian carp can look a lot like common bait species," Benjamin points out, "but our current VHS rules already prohibit wild bait harvest in the Mississippi, so we're ahead of the game on that one."

The DNR has stepped up containment efforts on the Mississippi this summer. Watercraft inspectors and wardens are providing educational materials about the perils of Asian carp and other invasive species. The Water Guard will be spending more of its time on lakes and rivers that are known to contain multiple invasive species and are heavily used by transient boaters. More volunteers will also be recruited to talk with anglers and boaters in these riverside communities.

Boaters and anglers who want more information can pick up pocket-sized "watch cards," sort of a "wanted" poster about the size of a baseball card. They have pictures of the species on one side, information on the back on how to identify the invasive species and what to do if you believe you have caught an Asian carp or other invasive. Since Asian carp are filter feeders that don't readily bite a baited hook, most have been caught to date by commercial fishers who net their catch. Nevertheless, it is always wise for recreational boaters and anglers to be aware and vigilant. Note the water body and date where you caught it (GPS coordinates are helpful if you have them). Take photos, but do not bring the fish to DNR Service Centers or hatcheries. Contact the local fisheries biologist or call the DNR TIP line – 1-800-TIP-WDNR – 1-800-847-9367.

Though Ron Benjamin agrees that it is important to spread the word about the Asian carp, he points out how boaters can prevent spreading invasives by taking the same common sense precautions that are recommended statewide. "It's pretty simple, really," Benjamin says. "Clean your boat, drain water, never move live fish away from a landing. And always buy your bait from a registered Wisconsin bait dealer."

Jeff Bode agrees. "People are doing the right thing," he says. "We all love Wisconsin's lakes, and no one wants to see species like the Asian carp spread into our state. I am confident that together we can protect our waters for ourselves, our children and grandchildren."

Julia Solomon is an aquatic invasive species educator with a joint appointment at the Department of Natural Resources and the University of Wisconsin-Extension.

Keeping current in the electric curtain

Before 1900, there was no permanent open water connection between the Mississippi River and the Great Lakes. That changed in the late 1890s when a massive engineering project reversed the flow of the Chicago River to carry sewage away from Lake Michigan and create a canal for barge traffic between Lake Michigan and the Des Plaines River that eventually flows into the Illinois River and the Mississippi. The 28-mile drainage system nearest the lake, dubbed the Chicago Sanitary and Ship Canal, was blasted through miles of rock to connect the two waterways. It also opened the door to the potential exchange of many unwanted species.

Scientists and policymakers recognized the importance of preventing the passage of fish and other aquatic organisms, and in 1996 Congress authorized construction of an electric barrier designed to allow boat traffic but prevent the spread of non-native species between the Great Lakes and Mississippi River basins. Today, the most immediate threat for non-native species dispersal through this manmade connection is Asian carp moving from the Mississippi River into the Great Lakes.

This schematic shows where electrical currents will aim to form an effective barrier repelling invasive carp. © U.S. Army Corps of Engineers
This schematic shows where electrical currents will aim to form an effective barrier repelling invasive carp.
© U.S. Army Corps of Engineers

The U.S. Army Corps of Engineers has constructed two barriers in the Chicago Sanitary and Ship Canal. The first, constructed in 2002, was a demonstration project. That barrier has since been supplemented with a larger and more powerful version that went into service the first week of April 2009 near Romeoville, Illinois about 37 river miles southwest of Lake Michigan. The micro-pulsed DC electric barrier effectively prevents fish passage, but is not without drawbacks. Sparks between barges and the health risks for a person in the water when the electric current is activated caused the U.S. Coast Guard to issue warnings to mariners in the area of the barrier.

Asian carp have not yet reached this dispersal barrier, but monthly monitoring conducted since May 2004 indicates the carp are only 13 miles downstream and are separated from the barrier by two locks. This summer, research at the Army Corps of Engineers laboratory in Vicksburg, Mississippi will determine how strong the electrical field must be to repel juvenile Asian carp. Thereafter, appropriate adjustments will be made to the barrier. Technological additions to strengthen and supplement the barrier are also planned for the future.

Although scientists are optimistic about the success of the electric barriers in the Chicago Sanitary and Ship Canal, they caution that they are not a panacea. Electric barriers work by causing fish to turn around and swim back when they enter the electrified area, but the barrier has no effect on plankton or plants. Also, since the electric field is not selective, it is not an appropriate tool for natural systems where passage of some migrating fish species is desirable.

Technical information about the Chicago Sanitary and Ship Canal dispersal barrier provided by Dr. Phil Moy, Fisheries & Aquatic Invasive Species Specialist, UW Sea Grant.