Invasive New Zealand mud snails found at Shanty Creek in County Antrim


September 3, 2021

Fishers urged to step up prevention efforts during salmon season

Invasive New Zealand mud snails have been detected at the mouth of Shanty Creek, a tributary of the Grass River in County Antrim. The snails were found during routine surveillance in May by the Grass River Natural Area Stream Watch project and confirmed by DNA analysis by Oakland University in August.

New Zealand snails were first discovered in the United States in the Snake River of Idaho in 1987. Since then, snails have spread to all western states and regions of the Great Lakes by attaching to boats, waders and equipment.

The Grass River is now Michigan’s sixth river system known to be infested by snails. Their discovery in the Pere Marquette River in August 2015 marked the first detection in a Michigan waterway. In 2016, populations were confirmed in the Boardman and Au Sable rivers. In 2017, invasive snails were found in the Upper Manistee and Pine rivers.

Michigan’s salmon season, which peaks in September and October, draws thousands of anglers to Michigan’s major rivers.

“This is a time when people are likely to visit multiple rivers and streams in a matter of days,” said Lucas Nathan, aquatic invasive species coordinator for the Michigan Department of Natural Resources. “If they don’t clean the equipment thoroughly each time, it is possible to introduce New Zealand snails into new waters.”

What harm can a snail do?

This brown to black, one-eighth-inch-long mud snail native to New Zealand is considered invasive and is banned in Michigan due to the environmental damage it can cause to rivers, streams, and lakes. Because the snail reproduces by cloning (females develop complete embryos without fertilization), a single snail can create an entire population.

Small New Zealand snails on woody debris in a stream.

A snail can produce more than 200 young in a year. Since there are few natural predators or parasites of this species in North America, their numbers are increasing rapidly each year. In parts of the western states, researchers have documented snails reaching densities of 300,000 per square meter. With so many mud snails, food for other stream invertebrate populations can become scarce.

Fish that feed on native invertebrates like mayflies and caddisflies may have more difficulty feeding in rivers invaded by New Zealand snails. Fish eat New Zealand snails, but due to the thick shell of the snail, fitted with a tight-fitting “hatch” called the operculum, they are difficult for the fish to digest, offer the fish little value. nutritious and can be excreted alive. Substituting mud snails for native food sources can reduce the growth, condition, and ultimately the abundance of major sport fish, including trout.

What is done?

Since the initial detection, MNR and the Department of the Environment, Great Lakes and Energy have integrated monitoring of mud snails into their standard sampling procedures, increasing the potential for early detection in several rivers and streams every year.

Volunteers from across the state, like those with the Grass River Natural Area Stream Watch, conduct regular monitoring of streams and rivers across the Michigan Clean Water Body, or MiCorps, to determine the health of streams and search for invasive species. Other partners, including universities and cooperative invasive species management areas, are also engaging in annual monitoring.

New Zealand snails next to a penny

Emily Burke, conservation and education specialist at Grass River Natural Area, Inc., said she was able to identify New Zealand snails while sampling Shanty Creek through training on the identification of invasive species provided by the CAKE (Charlevoix, Antrim, Kalkaska and Emmett) CISMA in the spring.

“Michigan’s Invasive Species Grants Program has been instrumental in promoting the development of CISMAs statewide, creating a network of local invasive species resources,” Nathan said. “At the same time, the grant program supports research efforts such as the Oakland University Mud Snail Project in New Zealand, which has educated fishermen, trained citizen scientists and developed a partnership. important with Trout Unlimited, which helped launch the New Zealand Mudsnail Collaborative.

Following Burke’s report, a team from Oakland University conducted surveillance at 15 sites in the Grass and Elk Rivers, but found no additional infestations. Local and state partners will continue to monitor the area and use outreach opportunities like Aquatic Invasive Species Awareness Week to educate the public on preventing the spread of New Zealand snails and other pest species.

What can you do?

The most important prevention is to practice good recreational hygiene. After a visit to one of Michigan’s lakes, rivers, or streams, be sure to clean, dump, and dry your boat, trailer, and gear before heading to a new destination.

The small size of the New Zealand snail requires careful examination and cleaning of areas where plants, mud or debris can be found on poles, nets, waders, boots, buckets, kayaks, canoes and flotation devices. Anything that has been in the water or at the water’s edge should be inspected before it is packed or loaded.

The NZMS collaboration offers these simple steps to clean boots and waders:

  • Trample and inspect as soon as you leave the water to remove any attached debris.
  • Brush waders, soles and laces to loosen remaining debris and mud.
  • Spray boots and waders carefully with a disinfectant.
  • Rinse after 20 minutes.
  • To dry thigh boots carefully before next use.

The short video, New Zealand Snail Ecology and Michigan Fishing Gear Decontamination, available at, provides a demonstration of this cleaning technique as well as information on how to identify the invasive snail.

Additional information on the New Zealand snail, including how to report a suspected snail find, can be found at

Michigan’s Invasive Species Program is a collaborative effort of the Department of the Environment, Great Lakes and Energy, the Department of Natural Resources, and the Department of Agriculture and Rural Development.

/ Note to editors: The accompanying photos are available below for download. Suggested captions and credit information follow:

Menu: River systems invaded in Michigan, to date. Red dots indicate locations where New Zealand snails are confirmed to be present. Map courtesy of Jeremy Geist, Trout Unlimited.

Debris: New Zealand snails can be seen on this woody debris near the mouth of Shanty Creek. Photo courtesy of Emily Burke, Grass River Natural Area, Inc.

Snails: A close-up view of the snails is displayed. /


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