Wisconsin DNR steps up monitoring for invasive fish in Lake Winnebago

The Wisconsin Department of Natural Resources is increasing monitoring in Lake Winnebago for invasive round gobies that can force out native bottom-dwelling fish.

In June, an angler caught a round goby in Lake Winnebago at the Bowen Street Fishing Pier in Oshkosh, the first known detection there. The invasive fish is about 3 to 6 inches long with bulging frog-like eyes and a fused fin on their bottom side that looks like a suction cup. They can outcompete bottom-dwelling fish and they’ve been known to gobble up eggs of walleye and bass.

Round gobies are native to the Black and Caspian Seas between Europe and Asia, and it’s believed they were first introduced to the United States through the ballast water of oceangoing ships in 1990. They have since spread to the Great Lakes and connecting waterways like the lower Fox River.

After the initial discovery, DNR staff conducted trapping and monitoring, but no additional fish were caught in Lake Winnebago. However, another angler reported catching the invasive fish in August, and around a dozen round gobies have been caught to date.

Angelo Cozzola, a DNR fisheries biologist, said the fish can rapidly expand once they invade.

“That being said, since we are only finding them in one area right now, we are considering efforts for potential control,” Cozzola said.

The DNR and local fishing groups organized volunteers to help catch fish Thursday on the Winnebago System in Oshkosh, Neenah, Menasha and High Cliff State Park near Sherwood.

The Fox-Wolf Watershed Alliance is among those partnering with the DNR, including Chris Acy, the group’s aquatic invasive species coordinator. Acy said the “round goby blitz” is an effort to get more lines in the water to determine how widespread the fish is and what type of management may be needed.

“In some lakes that have them, they’ve seen bass populations be impacted,” Acy said. “They can be a nuisance for shoreline anglers. In places where they get really numerous along shoreline areas, people that are going out to fish for their favorite panfish are having less success…and more often than not, are catching gobies.”

Once established, the fish could significantly impact sportfishing. Acy noted recreational fishing has a $234 million impact on the local economy, according to a 2006 survey by the University of Wisconsin-Extension.

The DNR may consider other efforts to control the spread of round gobies, including the use of the chemical fish-killing agent rotenone. Cozzola said use of chemical treatment will depend on how far the fish has spread within the system. If round gobies are more widespread, chemical intervention would be less effective than treatment in a small, confined area.

In the meantime, the DNR is asking the public to report any sightings of round gobies within the Winnebago System, said Patrick Siwula, the agency’s aquatic invasive species biologist for southeastern Wisconsin.

“We’re talking about Lake Winnebago proper right now. But this system is huge and encompasses 17 percent of the state’s surface water drainage area,” Siwula said. “We’re talking about all the way up the Wolf River, the upper Fox River, the Winnebago pool lakes. Those are all areas we’re interested in receiving reports because they’re connected waters.”

The DNR said the agency doesn’t need reports of round gobies captured below the Neenah or Menasha dams or in Little Lake Butte des Morts because it’s not part of the Winnebago System and the invasive fish is already well-established there. Cozzola said the DNR will continue monitoring for round gobies in the system.

“Once they’re established and they’re reproducing and spreading, there is nothing that we can practically do to take them out of the system,” Cozzola said.

If anglers catch a round goby, the DNR advises them to kill it and take it to a DNR service center. People can also report any invasive fish they observe using the agency’s online reporting tool.