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Officials Test Suspicious Larvae Found In Flathead Lake


Monday, November 15, 2010

Montana Fish, Wildlife & Parks may have found signs of exotic mussels in a routine plankton sample taken in July from the northern end of Flathead Lake near Woods Bay.

 Eileen Ryce, FWP's aquatic invasive species coordinator, said microscopic larvae suspected to be from exotic mussels may be contained in four of 17 plankton samples collected from the 200-square-mile lake between May and August. Samples were sent to three out-of-state laboratories for testing last week.

Test results from independent labs in the Midwest suggest that tiny organisms within the sample have characteristics consistent with zebra and quagga mussels. Results from a lab in Oregon, however, suggest the sample shows no sign of mussel contamination.

"These larvae are notoriously difficult to identify at this stage of development," Ryce explained.  "With this sample the question mark is the size of the larvae, which are significantly smaller than what we'd expect. But we'll err on the side of caution."

Ryce said FWP will send a team of divers to several locations on the north end of Flathead Lake to search for adult mussels, which could be as tiny as sesame seeds.

The sample that contained the suspicious, microscopic larvae was among 11 collected from Flathead Lake by volunteers from the Whitefish Lake Institute in July and delivered to FWP in late September. The remaining suspected samples will be submitted for additional DNA testing.  

FWP, a member of the Columbia Basin Interagency Invasive Species Response Plan team, contacted downstream partners in Idaho, Washington, and Oregon on Nov. 12 to alert them of the suspicious finding. Those states agreed that the evidence was not sufficient to trigger the group's rapid response program, which would immediately include evaluating control, containment, and eradication options. Ryce noted that the states will remain in close communication as follow-up testing continues.

FWP has routinely sampled Montana waters for a number of aquatic invasive species since 2004. So far this year, with the help of volunteers, FWP obtained about 600 samples from 77 different waters.

FWP's top three aquatic invasive test sites are Fort Peck Lake in northeastern Montana, Flathead Lake near Kalispell and Canyon Ferry Reservoir near Helena—all areas popular with nonresident boaters. Neither zebra nor quagga mussels have ever been found in Montana.

First discovered in the U.S. in Great Lakes in the 1980s, zebra mussels have since spread throughout most major rivers in the midwestern and mid-Atlantic states. They were likely transported in boat livewells, where the microscopic larvae can survive for weeks. Western states sounded the alarm in 2007 when quagga mussels appeared in Nevada’s Lake Mead—the first infestation documented west of the Rockies.

The exotic mussels do not have a predator to keep numbers in check, so they can reproduce and spread rapidly, especially on hard surfaces like marina docks and piers and on boat hulls. The mussels can also block water intake pipes, clog irrigation systems, disrupt water purification and hydropower plant operations, and may impact fishery populations.

Lakes in Colorado and Utah have similarly produced what appeared to be larvae-stage zebra mussels in recent years but as yet no adult mussels have been found there, Ryce said.

“Montana’s best defense against invasive species is for boaters and anglers to inspect, clean, and dry their boats, trailers, and fishing gear after each use," Ryce said. 

For more information, visit FWP’s website at . Click “ Inspect. Clean. Dry .”