The state of Montana will convene a scientific advisory panel to study the use of DNA testing for aquatic invasive species, and how to interpret inconclusive testing results from the past season.
After mussel larvae were detected in Tiber Reservoir in 2016 and a suspected sample was found in Canyon Ferry, Montana significantly increased its efforts to detect and stop the spread of AIS. The state doubled inspection stations, nearly tripled water testing and instituted mandatory watercraft decontamination at Tiber and Canyon Ferry. The state also now requires mandatory inspection for out-of-state watercraft and watercraft crossing to the western side of the Continental Divide.
In 2017 Montana Fish, Wildlife & Parks AIS inspectors checked more than 85,700 watercraft and intercepted 17 boats transporting zebra or quagga mussels into the state.
FWP and partner agencies tested more than 1,500 plankton samples from 240 waterbodies and found no adults or larvae.
But using a different methodology and sampling for mussel DNA did return some positive tests in Tiber. The conflicting tests and questions about using environmental DNA, or eDNA, for mussel detection has led FWP and the Montana Invasive Species Council to convene an expert panel, said FWP AIS bureau chief Tom Woolf.
“Something was observed using the DNA methods for mussel detection, but it’s not an established science, there’s not much literature published on it … and we think this is a good opportunity to have that conversation, because we’re not really sure what it’s telling us,” he said.
Plankton tow sampling is considered the standard for early mussel detection. Using a net, large amounts of water and debris is collected and then concentrated for microscopic examination. That’s how the 2016 positive samples from Canyon Ferry and Tiber were identified and the waterbodies earned mussel-positive designation.
FWP, in cooperation with the U.S. Geological Survey, collected eDNA samples from Tiber this season to compare early detection sampling methods. The eDNA sampling involves taking a gallon of surface water and screening it through filter paper before testing. That’s how a couple of Tiber eDNA samples returned positive this year, Woolf said.
After the eDNA positives, FWP sent corresponding tow samples to a different lab for DNA testing. Those tests came back negative, which raises a number of questions about reliability and interpreting the data, Woolf said.
“One issue we have with DNA is there are no standard methods, no agreement between labs on a preferred way to … collect samples,” he said. “With this panel, we’re going to ask specific questions about whether we can make (eDNA) another tool in the tool box and what these results really mean.”
Tiber is already considered a mussel-positive waterbody, so the testing does not impact its classification. Due to the uncertainty about eDNA, Woolf said a positive DNA sample alone would not change the status of a previously mussel-free waterbody, but would lead to more testing.
FWP is also evaluating the overall AIS program ahead of the 2018 season. Changes will include enhanced training for inspection staff, improved efficiency at inspection stations and expanded AIS early detection monitoring.
Mandatory inspection and decontamination requirements will remain in effect in 2018.