MT sites test positive for mussels

SANDPOINT — Water samples collected in north-central Montana have tested positive for the larvae of dreaded invasive mussels, according to Montana Fish, Wildlife & Parks officials.

The positive samples were gathered from Lake Elwell, a reservoir formed by the Tiber Dam on the Marias River. Located east of Shelby, Mont., Lake Elwell is approximately 380 miles east of Sandpoint via U.S. Highway 2.

“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.”

Zebra and quagga mussels are prolific bivalve mollusks introduced in North America by freighters discharging ballast water into the Great Lakes, causing their prolific spread. The filter feeders strip water of nutrients and adhere to boats, docks and other infrastructure in prodigious colonies.

Their range has spread from the Midwest to the Southwest, although they have not turned up in the Inland Northwest yet due to Idaho’s boat inspection program. In 2016, 13 mussel-fouled boats had stopped in Idaho since March, according to the Idaho State Department of Agriculture.

Statewide, 89,390 inspections were conducted in 2016, which led to the interception of 19 mussel-fouled vessels, according to ISDA.

In the West, quagga and zebra mussels have populated Arizona, Nevada, Utah and California costing those states millions every year to manage.

Montana resource officials also announced earlier this month that samples collected from the Canyon Ferry Reservoir near Helena show “suspect” or “inconclusive” results, which is prompting further testing.

“I’m not sure when to expect more definitive answers. We’re looking for adult mussels now, but haven’t found any yet,” Greg Lemon, information bureau chief for Montana Fish, Wildlife & Parks said on Wednesday.

Idaho, meanwhile, has a rapid-response plan for early detection of dreissenid mussels, which is integrated into a broader response plan developed for the Columbia River Basin.

Under Idaho’s plan, a water body will be flagged as “positive “ for mussels if settled adult mussels are found and verified by two qualified experts or if mussel veligers are confirmed through microscopy or genetic identification.

Idaho’s plan seeks to halt the spread of mussels by minimizing pathways and utilizing available control measures such as chemical treatments or drawdowns. However, invasive mussels are notoriously difficult to control once they gain footing in a water body.

Montana officials admitted that the recent test results are disheartening, although they did indicate that the state’s detection system is working.

“The results from Tiber Reservoir show the larvae exist at very low densities, which improves our chances for containment.”

The discovery also serves as a reminder that all boaters have a hand in fighting aquatic invasive species by thoroughly cleaning, draining and drying their vessels before transporting them.