VERONA — The sighting of an invasive snail in a second stream in Dane County is alarming officials, though it’s not clear the tiny mollusk will create the ecological havoc feared when it arrived in this country 30 years ago.
New Zealand mudsnails were found last month in multiple locations of Badger Mill Creek, just a few hundred yards upstream from where it connects with the Sugar River south of Verona, according to Susan Graham, lakes management coordinator for the state Department of Natural Resources.
“We are very concerned with how far they have spread in the system,” Graham said. “We are trying to figure out the extent of the range in the (Upper Sugar River) watershed.”
The mudsnail was found three years ago in Black Earth Creek near South Valley Road in western Dane County. That marked the first time it had been found in an inland waterway in the Midwest, and there was immediate concern that it could wreck the popular trout fishing destination.
Although the snail grows to just one-eighth of an inch, it is asexual and can clone itself into a colony of nearly a million snails in one year. When densities of the creatures reach more than 500,000 per square meter, they can starve out native prey that fish eat and that will lead to smaller fish and other ecological problems, experts believe.
But there is no evidence of that happening in any streams or lakes in the United States, including Black Earth Creek, according to Edward Levri, a mudsnail expert from central Pennsylvania.
Graham confirmed that there are no data showing that the mudsnails have increased in density in Black Earth Creek. “We don’t know how it will play out there yet,” she said.
She also said that experts believe the mudsnails in the Black Earth Creek were there long before they were discovered. “We’re finding out that not every location is a suitable habitat (for an explosion in snail density numbers),” Graham said.
Levri believes the snails found in Badger Mill Creek most likely came from Black Earth Creek and were spread by people who used both streams for recreational purposes. Snails can survive out of water for nearly a month on the soles of shoes, clothing, on fishing equipment and boats.
“If you take proper precautions you can limit their ability to spread,” Levri said. “The problem is not everybody will be as diligent as they need to be.”
The state DNR has put up signs notifying the public of the mudsnails at the locations where they were found in Badger Mill Creek, Graham said. The signs include techniques for removing the snails that include using tap water and a brush. The DNR also plans to install boot brush stations where the mudsnails have been found, she said.
The mudsnails were first detected in this country in the Snake River in Idaho in 1987. Theorists believe they arrived in the country via a shipment of fish bound for a hatchery in Idaho.
Since that time, the snails have been found in streams in nearly every state in the West, in all of the Great Lakes and tributaries in Illinois, Michigan, Minnesota and New York, and in streams in Pennsylvania and Wisconsin, according to the U.S. Geological Survey map that was updated last month.
How big an effect?
None of the ecological nightmares predicted by experts has occurred in any of the states, Levri said. “I’m sure they are having some kind of effect but the big question is if they are having a kind of effect people care about,” he said.
What experts are finding at many locations is that the snails tend to burst out into high densities when they first arrive in a stream or lake but their numbers eventually drop, Levri said. He cited a stream near Yellowstone National Park that once had snail density levels of 700,000 per square meter, and that is now down to 5,000 to 10,000.
“We don’t know why,” he said.
Levri didn’t rule out that the snail has a predator, which goes against some other experts’ theories. He said an aquatic flatworm may be the reason mudsnail numbers are down in the stream near Yellowstone and said a fish called a round goby has kept the mudsnails in check in the Great Lakes.
Levri also believes the mudsnails are located in many more places than what’s listed by the U.S. Geological Survey. While it’s possible that the mudsnails found in Black Earth Creek and the Badger Mill Creek could eventually reach the Mississippi River via the Wisconsin River and the Rock River, respectively, Levri thinks they are already living in the Mississippi River.
“A couple of years ago the snails were found on rocks in a pet store in Des Moines. The people who brought the rocks in said they got them from the Mississippi River,” Levri said. “So my feeling is people aren’t reporting sightings as much anymore. It’s not as an unusual thing. People are thinking it’s not a big deal.”
Badger Mill Creek snails
The DNR was notified about the mudsnails in Badger Mill Creek on Nov. 1 by employees of the Madison Metropolitan Sewerage District, who found them in samples of invertebrates, Graham said.
It’s too early to tell if Badger Mill Creek will become a more suitable habitat for the mudsnails than Black Earth Creek. But experts are watching it closely for a number of reasons.
For instance, the Madison Metropolitan Sewerage District discharges 3 million gallons of high-quality treated water into the Badger Mill Creek every day, according to Wade Moder, executive director of the Upper Sugar Creek Watershed Association.
The creek also has problematic levels of phosphorus it picks up on its course through the cities of Madison, Fitchburg and Verona before it empties into the Sugar River. That waterway is already on the DNR’s impaired list because it is loaded with phosphorus, Moder said.
“The treated water means it probably has high nutrient levels, which the mudsnails like,” Levri said. “If the PH level is high with a high nutrient content, the snail will probably do all right there.”