KENT COUNTY, Mich. — A tiny invasive snail that has spread through several of northern Michigan’s best-known trout rivers has now been found in the southern half of the Lower Peninsula for the first time, state invasive species officials said Monday.
New Zealand mudsnails were collected in Bear Creek, a small coldwater stream that feeds the Thornapple River in Kent County. The find sits roughly 75 miles south of the nearest known infestation, on the Pere Marquette River. Since the snail was first confirmed in Michigan in 2015, it has turned up in six northern rivers: the Pine, Grass, Boardman, Au Sable, Upper Manistee and Pere Marquette.
Volunteers from the Coldwater River Watershed Council spotted the snails during routine sampling of stream insects and other bottom-dwelling creatures used to gauge water quality. The state environment department identified them from photos, and specialists at Oakland University and a national trout conservation group confirmed the identification. Oakland University plans genetic tests to try to trace where the population came from.
The species is a problem because of how fast it multiplies. Every introduced mudsnail in North America is a female clone, so a single snail can start a colony, and each can produce more than 200 young a year. Federal scientists note the snails graze at night on algae and decaying plant and animal matter and tolerate muddy, disturbed water, while they usually measure only 4 to 6 millimeters long in the Great Lakes region. In some Western streams they have reached 300,000 per square meter, crowding out the mayflies and caddisflies trout depend on. Fish that eat the hard-shelled snails gain little nutrition and can pass them alive.
State biologists plan more sampling at Bear Creek and in other streams that feed the Thornapple across Kent, Barry and Ionia counties, and signs will go up at access points on affected waters. There is no proven way to wipe out an established population, so the state is asking anglers, paddlers and boaters to clean, drain and dry boats, trailers and gear, and to scrub and disinfect boots and waders, before moving to another lake or stream.
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