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UPDATED: Invasive aquatic mussel larvae detected in Montana

UPDATED: Invasive aquatic mussel larvae detected in Montana


Larvae from aquatic invasive mussels have been detected in Montana for the first time.

Water samples from Tiber Reservoir east of Shelby tested positive for the larvae of aquatic invasive mussels, with similar tests from Canyon Ferry Reservoir near Helena showing “suspect” or inconclusive results, according to officials at Montana Fish, Wildlife and Parks.

FWP, along with other state and federal agencies and the Montana Invasive Species Advisory Council (MISAC), are now working to determine whether adult mussels are present in Tiber Reservoir and to get further test results on Canyon Ferry.

“This is the first positive test in Montana for the larvae of quagga or zebra mussels,” said Eileen Ryce, FWP fisheries division administrator. “Although we hoped we would never see these invasive species in Montana waters, we’ve been preparing for this possibility for some time, and we’re going to work together to address this threat.”

Quagga and zebra mussels are aquatic invasive species not known to be established in Montana. In other parts of the country, such as the Midwest, Southwest and the Great Lakes areas, mussels have impaired hydroelectric, municipal and agricultural water infrastructure. Mussels may also impact fisheries and other aquatic resources and damage recreation facilities.

FWP runs aquatic invasive inspection stations during the warmers months as well as the “Clean. Drain. Dry.” campaign to discourage unintentionally transporting invasives on watercraft.

Recent site inspections at Tiber and Canyon Ferry did not turn up any established populations of adult mussels, but officials will conduct more extensive inspections with the assistance of dam operators, marina concessionaires and other groups. State agencies are also making arrangements to bring in dogs that may detect mussels at Tiber and Canyon Ferry reservoirs.

FWP regularly tests the state’s rivers, lakes and reservoirs for aquatic invasive mussels. Water samples from Fresno, Holter and Hauser reservoirs have come back negative, as did samples from Lake Frances, the Marias River and the Milk River. Testing at Fort Peck Reservoir and the entire Missouri River system is ongoing.

“The recent test results are definitely bad news, but they do indicate our detection system is working,” Ryce said. “The results from Tiber Reservoir show the larvae exist at very low densities, which improves our chances for containment."

The coming winter also offers some hope of stifling a potential infestation.

At 50 degrees and below, the larvae are unable to reproduce, said Stephanie Hester, MISAC coordinator. “We’re in the process of determining what state the larvae are in … so timing-wise we’re in a pretty good spot."

“That’s not to say there isn’t concern because they’re just crazy in terms of what they’re able to do and hide and proliferate once adult mussels are established. We’re taking this very seriously," she added.

Officials are unsure of when the introduction may have occurred, although Hester suspects the larvae were transported via recreational boat.

A rapid response plan includes assessing the risks, coordinating state and federal agencies and other water users, contacting legislators and looking at possible control measures, she said. Recent work on the council and regionally to address invasive species has given officials a framework for responding, she added.

“We have a huge list of people we’re on the phone with right now letting them know we need their support and help,” Hester said. “I feel like we’re in really good shape with the goal to protect the resource and prevent any more issues.”

If adult mussels are detected, potential controls include aeration or dissolving potash in an attempt to eradicate them.

Bob Gilbert, executive director for Walleyes Unlimited of Montana, said he is hopeful the Canyon Ferry detection is a false alarm, but encouraged officials to get out ahead of potential infestations as soon as possible.

“Our organization is 100 percent behind keeping any invasive species out of Montana and especially these mussels,” he said. “They’re not only devastating to fisheries but to just about everyone who uses water in this state.”

This latest invasive species detection is much different than the high-profile detection of a fish-killing parasite which caused temporary closures of the Yellowstone River this summer, Ryce said.

“The Yellowstone River was much more of an emergency to prevent the spread to other waterbodies and reduce additional stressors on the fish,” she said. “For this situation it’s less of an emergency because we have the luxury of having the winter to come up with plans to minimize the spread and containment.”

As officials look at strategies, watercraft inspection and mandatory decontamination may be instituted to alleviate concerns of spreading larvae or adult mussels. Boating restrictions are not expected.

Reporter Tom Kuglin can be reached at 447-4076 or


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State Reporter/Outdoors Reporter

Tom Kuglin is the deputy editor for the Lee Newspapers State Bureau. His coverage focuses on outdoors, recreation and natural resources.

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