Researchers working in Flathead Lake over the summer may have detected a deeply unwelcome presence: an invasive mussel species state and local agencies have been trying strenuously to keep out of Montana waters.
Microscopic larvae similar to that of zebra and quagga mussels were found in four of 17 water samples taken near Woods Bay by researchers between May and August, according to Eileen Ryce, aquatic invasive species coordinator for the Department of Fish, Wildlife and Parks. The researchers were collecting routine plankton samples at the time.
Ryce has since received differing assessments of the larvae identification. An independent lab in the Midwest suggested the sample has characteristics consistent with the zebra and quagga mussels, while an Oregon lab suggested the samples show no signs of mussel contamination. The small size of the larvae has made identification difficult.
“I’m in the process of sending samples off for DNA analysis,” Ryce said, adding that she does not expect to have results from that test back until early December. She also intends to send a dive team out “as soon as possible” to begin searching northern areas of Flathead Lake for adult versions of the mussels, which can be as small as sesame seeds.
Zebra and quagga mussels are a non-native species first discovered in the Great Lakes in the 1980s. Originally from the Black and Caspian Seas, they have since spread throughout much of the Mississippi River drainage and were discovered in 2007 in Nevada’s Lake Mead. Though small, the mussels have no natural predators, and reproduce so quickly they can rapidly encrust docks, piers, irrigation pipes, hydropower plant operations and other structures that can be expensive to replace or repair. They also harm fishery populations by filtering nutrients out of the water.
In 2009, Sen. Verdell Jackson, R-Kalispell, at the request of the Flathead Lakers, sponsored a bill that launched an awareness, prevention and emergency response campaign aimed at the invasive mussels – which have the ability to “hitchhike” by attaching to a boat that may not be sufficiently cleaned or inspected by its owner before transport from one waterway to another.
The top three aquatic invasive species test sites in Montana are in Fort Peck Lake in the northeastern corner of the state, Canyon Ferry Reservoir near Helena and Flathead Lake, because all three are popular with nonresident boaters. Should Flathead Lake prove to have a zebra or quagga mussel population, Ryce thinks it likely occurred as a result of them being transported on a boat insufficiently cleaned or inspected.
“In the Flathead there are a lot of people that use that lake who spend their winters down in the Lake Mead area, and they bring their boats up in the summer, so that’s definitely a way that it could have been introduced,” Ryce said.
As a member of the Columbia River Basin Interagency Invasive Species Response Plan team, FWP contacted Idaho, Washington and Oregon on Nov. 12 to alert them to the suspicious finding, though those states determined the evidence was not enough to trigger the group’s rapid response program. According to Ryce, in recent years lakes in Colorado and Utah have also produced what looked like larvae-stage zebra mussels, but no adult mussels have been found there.
While the mussels can’t move upriver on their own, it’s difficult to predict how fast the mussels could spread in the Flathead, or how difficult they may be to contain should a population be found in the lake, according to Ryce. The emphasis now is on figuring out whether the larvae are zebra or quagga mussels, and if so, to implement aggressive containment measures.
“Once we have more information we can start to make predictions as to what will happen,” Ryce said. “We’ll have divers out there as soon as we can.”