The New Zealand mudsnail (Potamopyrgus antipodarum) has made its way, uninvited, into Wisconsin streams and is sharing an environment with the native brook trout, a prized sport fish. In the unglaciated driftless region—a 24,000 square-mile area in southwestern Wisconsin, southeastern Minnesota, northeastern Iowa and northwest Illinois—600 cold water spring-fed streams provide an ideal habitat for brook trout and a fishing paradise for anglers. A 2016 study estimated that the annual economic impact of trout fishing in the driftless region is $1.6 billion.
The brook trout is the “canary in the coal mine as far as water quality goes,” says Matt Krueger, river restoration program director for River Alliance of Wisconsin. “If trout can exist in the stream, that’s a pretty good indicator that the land around it is being cared for pretty well. It’s a high value species.”
After environmentally punishing experiences with invasive species such as Zebra mussels and Eurasian water milfoil, scientists are not taking any chances with New Zealand mudsnails. Environmentalists are concerned about the potential impact of the mudsnail—a tiny creature that is born pregnant with an embryo inside of it, guaranteeing its perpetuation. In Wisconsin, only female mudsnails have been discovered so far. In addition, the snails have an operculum, an extra piece of shell that allows them to seal themselves off completely. They “can pull their head into their shell like a turtle and completely seal themselves off from the outside world,” Krueger says. “They can stay inside their shell for 28 days and then come out, and they can still stay alive because they stay moist” in their tightly sealed shells. This is another survival advantage for a species that Wisconsin environmentalists are watching closely.
The Wisconsin Department of Natural Resources (DNR) and other environmental groups such as Trout Unlimited, the River Alliance of Wisconsin and the Sugar River Watershed Association are working together to educate trout anglers about “clean angling” so that they do not become vectors for the spread of New Zealand mudsnails. “Trout fishermen are environmentally minded,” says Maureen Ferry, statewide aquatic invasive species monitoring coordinator for the DNR. She says trout anglers are well-educated, understand stream dynamics, fish and what fish need. “They’re just really cognizant of natural resources.”
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Scrub Those Boots!
Matt Krueger says trout anglers often move several times a day and could potentially carry the tiny mudsnails on their muddy boots or equipment from stream to stream. Anglers are being asked to use a stiff brush and a water sprayer to clean off any mud on their boots and gear before entering another stream. “The baseline is everybody should be carrying water and a scrub brush,” Krueger says. “Every time someone leaves a stream, they should scrub down before they move. That’s the baseline clean angling practice to adopt.”
A long-term study to evaluate if and how the mudsnails are impacting the fish in the stream (as well as the small insects in the stream) is underway. It is possible to take water samples and determine if DNA from mudsnails is in it, Ferry says. “They could be benign, but they might not be,” Ferry says. “Any time you have something eating and metabolizing, they are going to be excreting. It could alter the stream metabolism, and it could alter the nutrient dynamics of streams. We’re not quite sure what’s going to happen. That’s why we’re working to monitor the streams.”
With two recent discoveries of the invasive New Zealand mudsnail in Wisconsin’s Rowan and Mount Vernon creeks, four trout streams in the region are now infested with the snails. Mudsnails were first discovered in Black Earth Creek in 2013 and in Badger Mill Creek in 2016. The DNR reports no other infestations of the snail in inland Wisconsin streams.
Krueger says that mudsnails could pose a serious problem. “We’ve seen scenarios out west where there are parts of streams where the populations of these snails have just skyrocketed,” he says. “Anything that could potentially harm our unique streams and trout fishery is something that very much concerns me,” he continues. “Maybe down the road, we’ll find out, ‘well, maybe the mudsnails didn’t have the negative impact we thought they would,’ but at this point, that’s not a chance I’m willing to take. I’m not willing to tell other anglers that you shouldn’t be worried about this. I think they should be taking steps to make sure they are not part of the problem spreading these things around.”
Signs warning of invasive species have been posted at access points to many streams, and wader-wash stations have been installed at many locations. “Trout fishing is really important to Wisconsin,” Ferry says. “What we’re telling fishermen and the general public is to clear their gear using a stiff bristle brush and to clean their gear with water to rinse off any sediment because those snails are so small.”
While long-term research is underway, citizen monitors are assisting the DNR by taking samples and educating people about best practices to prevent further spread of the mudsnails. “There are a lot of volunteer activities with Trout Unlimited and UW-Extension out there monitoring and talking to other people,” Ferry says.
