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New Zealand mud snail

New Zealand mud snails

For the first time in western Montana, an established population of New Zealand mud snails has been found at a private fish hatchery south of Hamilton.

Montana Fish, Wildlife and Parks discovered the invasive snails in August and quarantined the Bitterroot Hatchery immediately.

“We are now working with the facility on a decontamination strategy,” said FWP Aquatic Invasive Species Bureau Chief Thomas Woolf. “We’ll dewater, dry it up and let it freeze. It’s one of the best ways to deal with mud snails.”

The state has also identified at least 100 ponds stocked with fish from the hatchery and that therefore could be infected with the snails capable of affecting aquatic ecosystems through rapid reproduction. Most of the ponds are located in western Montana.

The snails, which are smaller than a grain of rice, were first detected in the Madison River above Hebgen Reservoir in 1995. Since then, the species has been found in the Missouri, Yellowstone and Bighorn rivers.

New Zealand mud snails were first discovered in the United States in the middle portion of Idaho’s Snake River in 1987.

“They have been here in the state for a while now,” Woolf said. “We are getting more familiar with them and what they look like. Since they have been found in eastern Montana as well as Idaho, Washington and Oregon, it’s been interesting that we hadn’t found them before now in western Montana.”

Unlike zebra and quagga mussels that rapidly colonize on hard surfaces and can cause serious economic problems by clogging water intakes or boat motors, New Zealand mud snail’s high reproductive rates and ability to live in marginal conditions create conditions where other native macroinvertebrates can’t compete.

The snails can survive being consumed by fish through a unique trap-door like appendage that keeps them intact through the digestive system.

“The impacts are usually localized as the snails go through a boom and bust cycle,” Woolf said.

The snails found at the Hamilton hatchery most likely arrived from a South Dakota hatchery that ships fish to the Ravalli County facility annually. Mud snails were discovered at the South Dakota hatchery this summer.

Woolf said inspections of the Hamilton hatchery for fish health and aquatic invasive species are completed every year.

“Last year, we didn’t see them,” he said. “We now think they’ve been there for several years because the density was fairly high when they were discovered this summer.”

Since the snails are so small, they are easy to miss.

Their populations can bump along at fairly low levels for a time, but once they hit a critical mass, their numbers can jump dramatically, Woolf said.

The water from the hatchery drains into a ditch that flows away from the Bitterroot River and Skalkaho Creek. So far, FWP biologists have been unable to find any sign of snails in those two water bodies.

Woolf urges fishermen and others who recreate in the river or nearby creeks to keep a close eye out for the tiny snails.

“They can survive being stuck on a boot or in a pet’s fur that running around in the mud,” he said. “They can stick in things like boot laces or mud attached to a boat or other gear. That’s why it’s so important to clean, drain and dry your gear every time you go out.”

One of the best ways to ensure that mud snails aren’t hitching a ride on your wading boots is to throw them in a freezer after every use, Woolf said.

The state has sent a letter to all the pond owners who received fish from the Hamilton hatchery.

“We are working our way through the ponds, with a focus on the ones with close proximity to open or flowing water. It’s important to note that we will not go onto private property without permission. We’ll contact landowners before we go check their ponds.”

FWP has a New Zealand mud snail fact sheet available at CleanDrainDryMT.com. For more information, contact Montana Fish, Wildlife & Parks, AIS Bureau, P.O. Box 200701, Helena, MT 59601 or call 406-444-2440.

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