Rivers of Snails

The on-going restoration of Boardman River to its natural, pre-industrial condition has been good news to trout fishermen, kayakers, canoeists and river-lovers of all kinds. The cold water is flowing free and the high-quality fish habitat is returning.  But there’s a tiny new invader threatening the health of the Boardman – and many other rivers – once again.

In this video, biologist Brian Keas, Ph.D. of the Au Sable Institute of Environmental Studies explains that the New Zealand mudsnail (NZMS) first showed up in samples taken from the bottoms sediment of the Boardman River in 2013. However, it wasn’t recognized  and confirmed as an the aggressive invasive species from another continent until 2016 when its population was exploding.

Measuring 1/8 of an inch or less, this prolific little snail reproduces asexually by cloning itself, creating hundreds of replicas a year, each of them cloning themselves. Through this process, known as parthenogenesis, a single Mudsnail can produce millions of replicants in just one year – resulting in explosive population growth over time.

Keas says the mudsnail showed up in the U.S. for the first time in Idaho’s Snake River in the early 1980’s; then, it was spread to many other rivers in the western states. In some cases, researchers have discovered over 300,000 mudsnails in a single meter of river bottom. Since the snails feed on the algae, bacteria and other microscopic organisms at the very base of the food chain (collectively known a periphyton), this invasive species can disrupt river ecology.

The impact of mudsnails on Boardman River ecology is still uncertain. However, their population growth has been explosive, reaching over 30,000 snails per square meter in some locations as sampled in 2017.

The Au Sable Institute is one of the contractors working for the Conservation Resource Alliance to track the ecological changes in the Boardman as the river is being restored through dam removal and habitat improvement efforts. As Nate Winkler explains, the ecological monitoring has shown that the restoration efforts are improving habitat for fish and the natural functions of the river. However, this new invasive species is a real threat to the ecology of the Boardman and all the rivers of Northern Michigan.

Winkler says he is concerned that large populations of the invading mudsnail could dramatically reduce the food available for aquatic insects including the larvae of stoneflies, mayflies, caddisflies and other macroinvertebrates.  And that’s the food trout and many other fish species need to survive.

A fisheries biologist with the Michigan DNR, Seth Herbst explains that the mudsnail is like the zebra and quagga mussels that invaded the Great Lakes about two decades ago, disrupting the ecology of the lakes (click here to learn more). There appears to be no turning back once a river is infected. Unfortunately, mudsnail populations have been confirmed in the Boardman, Au Sable, Upper Manistee and Pere Marquette Rivers – all popular with fishermen. Very probably, the snail was transferred to these rivers by accident when it hitched a ride from an infected stream on someone’s boat or gear. Clearly, it only takes one snail to create a serious problem.

Herbst says it’s up to all water users to prevent spreading this invasive species to other streams. This tiny snail easily attaches to boots, waders, fishing tackle, boats, kayaks and boards. Worse, it can live for two days out of the water and much longer in wet environments. So, we all need to clean our boots, boats and gear after each use or dry everything thoroughly between uses. The DNR has information available on how to clean gear with a stiff bristled brush or easily accessible chemical cleaners.

This river contagion can be stopped, Herbst says. But it will take a real commitment and consistent efforts by all water users to keep our rivers clean.