Invasive mussels: The need-to-know

Since the Montana Fish, Wildlife and Parks’ Nov. 9 press release announcing the presence of invasive mussels in Tiber Reservoir, newspapers and newsfeeds have been flooded with information. Countless articles have detailed the arrival of Montana’s newest resident and the implications it could bring with it. As the new year arrives, and efforts to detect, contain and control these invasive mussels continue, a good understanding of the situation will be crucial to understanding its developments.

What are they?
According to Jeni Flatow, incident public information officer for the Montana Mussel Response team, positive water samples have indicated mussel larvae. She said the species cannot be determined from larvae alone, but the possibilities have been narrowed down to zebra or quagga mussels.

According to the DNRC, both species are freshwater mussels nonnative to the North American continent. The quagga originated in Ukraine, while the zebra came from the Caspian, Black and Asoz seas of Eastern Europe. They were discovered in the Great Lakes in the 1980s, and are thought to have been carried on transcontinental ships while in their larval stage.

The two mussels are similar: Microscopic as larvae, they grown to be about an inch wide and have dark and light bands or rings. The mussels live for three to five years and can release roughly one million fertilized eggs each year, with roughly 20,000 surviving to adulthood. The National Wildlife Federation says both species, once established, are impossible to eradicate without harming other wildlife.

But how does it affect me?
Montana is a big state, and it hosts over 3,000 water bodies. Regardless of the numbers, and the fact Tiber Reservoir is 150 miles away, the effects of an invasive mussel could hit Central Montana harder than residents might expect.

Economic effects
• According to the state’s Mussel Response website, national spending related to the ecological damage and control of invasive species is roughly $137 billion.

• The DNRC describes mussel settlements as “massive colonies” that can overtake whatever they build on. In Central Montana, that could apply to water containment and control structures such as Ackley Lake dam, East Fork Dam and Hanson Creek Dam, all of which would need extra monies for colony removal and prevention.

• Quagga and zebra mussels could decrease tourism revenues in Central Montana with lower fish numbers, infrastructure impacts and infested beaches.

Ecological effects
• New animals can have big effects on the food chain. Quagga and zebra mussels both eat plankton, a small organism readily available in Montana’s waters. Local Montana Fish, Wildlife and Parks Fisheries Biologist Clint Smith explained the potential impacts.

“Plankton is basically the base of the aquatic food web: It’s like the grass outside,” he said. “Aquatic invertebrates, like the caddisfly or mayfly, feed on plankton.”

Smith added even small fish, such as minnows, and young juvenile fish, including trout, can feed on the organisms.

“If we deplete the level of plankton in the environment, it leads to fewer of, or reduced growth, for species that consume them,” he said.

Recreational effects
• According to the Montana Mussel Response website, mussels outcompeting native fish species would decrease the number of fish available to recreationalists.

• The state’s Department of Natural Resources and Conservation reports both species of mussels attach to hard surfaces, including rocky lake bottoms and beaches. In turn, colonies of sharp-shelled mussels can create a hazard for beachgoers and swimmers.

• Mussel colonies often attach to recreational infrastructure, such as boat ramps, docks and watercraft. The DNRC said this can add scraping and repainting to regular maintenance schedules, as well as potentially damage vehicles and structures.

Current Status

Water sampling
• Confirmed/positive: Tiber Reservoir
• Suspect: Canyon Ferry Reservoir, a section of the Missouri River
• Inconclusive: Milk River

According to the Montana Mussel Response Team, and its Incident Public Information Officer Jeni Flatow, only one of the state’s water bodies has confirmed the presence of invasive mussels: Tiber Reservoir.

Flatow reported Canyon Ferry Reservoir and the Missouri River below Toston Dam are “suspect.” The response team’s website explains that label is used when one set of tests has found questionable larvae.

“There was something that they thought was there, but they weren’t sure what it was specifically,” Flatow said, adding the sites will undergo further containment and monitoring.

The Milk River is labeled as “inconclusive,” meaning scientists were not sure if mussel larvae were in the river’s samples or not.

“They saw something under the microscope that doesn’t necessarily meet all the items on the checklist that determines if it was or wasn’t one of these invasive species,” Flatow explained.

The river will continue to be monitored.

Response actions
The team’s latest weekly briefing on Dec. 22, hosted by Incident Commander Charlie Sperry, confirmed the state would not be using water drawdowns to control mussel populations this winter.

“The incident command recommended a drawdown not be done this winter due to logistical challenges,” he said. “The potential for drawdowns as a control measure is still up for future study and consideration.”

Sperry also reported on the results of statewide water samplings triggered by Tiber Reservoir’s positive results.

“We processed 610 samples from 182 water bodies,” he said. “We got all of the lab results back and can report good news: There are no new detections of invasive mussels based on the state’s samples.”

Despite the positive report, Sperry emphasized Montana’s response would be ongoing.

“We’re already in preparations and planning for spring sampling and monitoring, which is going to be critical in getting a better understanding of what we’re dealing with in Canyon Ferry, as well as portions of the Milk and Missouri Rivers,” he said.

As the state continues learning and containing its newest resident, local Montana Fish, Wildlife and Parks Fisheries Biologist Clint Smith encouraged people to keep an even keel.

“It’s very easy for us, and for the media, to get kind of doomsday about this,” he said.

Smith said Montanans’ best approach would instead be practical and thoughtful.

“Most of FWP’s effort is educating people to try and prevent their further spread, but I think it’s also important for people to realize the ecological effects these things can have,” he said. “I think people are going to learn these thing are going to have a very significant impacts to us and how we use the resources."

Protection via prevention
Jeni Flatow is confident a couple simple steps can stop the spread of invasive mussels in Montana. As the incident public information officer for the Montana Mussel Response Team, she is well versed in prevention.

“Montana Fish, Wildlife and Parks has had in place for a long time the clean-drain-dry campaign,” she said. “Anybody who’s boating should be aware of those principles.”

Flatow is referring to FWP’s mnemonic for its water contaminant removal process, something it encourages for any portable structures, from boats to docks. People are instructed to remove all material from an object before emptying any water and thoroughly drying it.

Despite the direct nature of FWP’s clean-drain-dry campaign, local FWP Fisheries Biologist Clint Smith sees some confusion with what should be cleaned.

“You should try to remove vegetation, sediment and any materials you got from a water body,” he said.

Clint recommended power washing, with hot water if possible, and had a suggestion for an easy place to do so.

“Car washes are great,” he said.

The FWP website explains all of the steps help eliminate aquatic invaders, as well as the water and wet areas they can survive in. This is especially true for quagga and zebra mussels, according to the DNRC. The department reported larvae live in water for two months before being visible to the human eye, and adults can survive up to a week out of water, with the right weather conditions.

Flatow emphasized how important the public’s effort would be in containing Montana’s newest, and perhaps most unwelcome, resident.

“It’s also going to take a lot of help from the public and a lot of education coming out of this incident to make sure we’re not transporting them,” she said.

• To report mussel sightings:

• To learn more about prevention:

• To find answers to frequently asked questions:

• For more on zebra and quagga mussels:

• To keep tabs on the latest developments:



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