Mussel-infected boat intercepted in Yellowstone

JACKSON – For Sue Mills, it was simultaneously concerning and reassuring for her staff to find a quagga mussel attached to a boat that was about to hit the water in Yellowstone National Park.

As Yellowstone’s aquatic invasive species coordinator, it’s Mills’ chief professional responsibility to ensure that nonnative critters and plants don’t find their way into park waters.

And so Thursday, June 17, was a worst-case scenario kind of day: one of her seven seasonal inspectors discovered a lone quagga mussel aboard a rented pontoon that was intending to launch into Yellowstone Lake. That species of coin-sized mollusk, a native of Ukraine, has potential to devastate native mussels throughout the so-far uninvaded Yellowstone River watershed while upending the ecology of the high plateau’s esteemed 136-square-mile lake.

But Mills saw a silver lining to one of her technicians halting the infested boat and then preventing it from launching at the Grant Village marina.

“The protocols worked,” Mills told the Jackson Hole Daily, “and our training is working.”

“This was a first-year inspector, and this boat wasn’t a more-traditional, covered-in-mussels boat,” she added. “There was one definitely identifiable large adult found.”

Mills and Yellowstone’s public affairs office declined to name the AIS technician who inspected the boat, which came from Salt Lake City and was bound for a backcountry lakeside campsite. The reason for keeping the staffer anonymous, she explained, is security — Yellowstone’s inspectors have been harassed.

But whichever employee looked the pontoon over for a routine inspection discovered the first quagga mussel that’s ever been detected in Yellowstone. 

An equally concerning nonnative mollusk, the zebra mussel, was found in the park once before in 2017, Mills said, after hitching a ride to the Rockies on a Michigan boat that was also caught by AIS inspectors and decontaminated before it was allowed to launch.

The Yellowstone visitors who rented the Salt Lake City-area pontoon with a quagga mussel stowaway this year didn’t get that chance — the rig wasn’t allowed to enter the water.

“The biological risk was just too high to let that boat launch,” Mills said. “Luckily, they did have a second boat with them, so they were able to complete their trip.”

The infested vessel, Mills explained, was deemed worthy of a “high risk” inspection from the start. That’s because of where it originated from, not far from the southwestern United States waters where quagga mussels have taken over. The style of boat also was a factor because it is likely to stay in the water for an extended period of time. Plus, it was a rental that could have been anywhere.

Yellowstone handles less than a couple hundred of these “high risk” inspections a year — less than 5% of permitted boats. When they do come across one, technicians go to great lengths to sweep the vessel. They’ll get down on their hands and knees on hot asphalt and conduct full flushes of motors and live wells. Plugs get pulled, and they don’t even take a chance with dried debris.

“We actually vacuum gravel out from the bottoms of the boats,” Mills said, “and people think we’re nuts.”

Until a decade ago, Yellowstone’s AIS regulations were looser and there wasn’t a significant number of boats being inspected. That has changed mightily. Now inspections are mandatory. Some boats, like wakesurfing boats with closed ballast systems, are banned.

Staging an inspector all day at each of the park’s three motorized launches — Lewis Lake and Yellowstone Lake’s Bridge Bay and Grant Village — is a big investment. But so far it’s paying off, Mills said.

“Knock on wood, our surveys so far have not turned up any invasive plants within the park,” she said. “Since we’ve had the boat inspection program going, it appears to be very successful.”