A boater affixes a permit to his boat in Yellowstone National Park. All boats must be inspected and permitted before launching. Inspectors check boats for aquatic invasive species including zebra and quagga mussels. (Jacob W. Frank/National Park Service)

Yellowstone National Park is prepared to ban all boats if invasive zebra and quagga mussels are discovered even near its boundaries.

Officials in the world’s first national park take the potential invasion seriously and are alarmed that invasive mussels have been found nearby. Last year mussels were discovered in Montana’s Tiber and Canyon Ferry reservoirs, a couple hundred miles from the park, the closest the invasives have been discovered, said Morgan Warthin, a park public affairs specialist.

The discovery caused Glacier National Park, closer to Tiber Reservoir than Yellowstone, to temporarily ban boats on its waters.

Each year inspectors check boats entering Yellowstone for invasive mussels, but this year the park is taking extra precautions, Warthin said. “The difference is that the threat is closer,” she said.

Yellowstone is requiring boats to be dry and drained at inspection. Rangers have placed barriers at Bridge Bay, Grant Village and Lewis Lake boat ramps to block un-permitted and un-inspected boats from launching after hours when rangers are not present. Wyoming has its own AIS program that requires boats to be stickered, but Yellowstone’s requirements and stickers are independent of any state rules.

Park staffers are working on a rapid response plan that would outline how to efficiently close waters to boats and how to contain any invasion. Park Service boats would be exempt from a ban.

The threat is serious because mussels can be hard to find and, once introduced, are virtually impossible to eradicate. “One boat with one mussel — there is no return so to speak,” Warthin said. The best staff could do is attempt to protect the other bodies of water in the park.

Already the park has been stung by the illegal introduction of exotic lake trout to Yellowstone Lake. The invasion has turned the lake ecology on its head, diminishing cutthroat trout, an important food for grizzly bears. It has cost millions of dollars to reduce the non-native species, that might never be eliminated.

To avoid introducing another invasive that could impact the ecosystem, Yellowstone is considering banning boats if mussels are even found outside park boundaries but nearby, Warthin said.

Zebra and quagga mussels can attach to other items and each other to create layers 18 inches thick, said Susan Mills, a park biologist. “They can pretty well turn an ecosystem upside down,” Mills said.

Quagga mussels attach to a boat’s propeller in this photo from outside Yellowstone. The invasive mussels are most commonly introduced into other ecosystems by motorized boats. Yellowstone National Park could ban non-Park Service boats if the mussels are found near or in park waters. (National Park Service)

Mussels filter plankton, which serve as the base of the aquatic food chain and feed young, native fish. They also create clear water, which allows sunlight to penetrate to deeper depths and foster an unnatural proliferation of plants.

The mussels are also prolific reproducers, Mills said. They don’t have a breeding season and can lay millions of eggs in a lifetime.

Mussels most commonly enter ecosystems by attaching to the exterior of a boat, or by hiding in standing water in tanks or ballasts on board, Mills said. That’s how it’s believed mussels arrived in the Great Lakes from Eastern Europe in the 1980s.

“As invasive species, the mussels are very successful,” Mills said. Once in the water, mussels are most commonly detected by fine nets dragged behind boats that can catch veligers or mussel larvae. Yellowstone drags Yellowstone and Lewis lakes, where motorized boats are allowed, once a year. Mills would like to see that increased to at least twice a year if not more.

Researchers are experimenting with chemicals and other ways to kill mussels, but there isn’t yet a way to eradicate them from natural bodies of water, Mills said. If mussels enter an artificial body of water, like a reservoir, the reservoir can be drained and dried to kill the mussels.

If mussels were found in Yellowstone, the park would “hit the pause button” and ban boats in the park, Mills said. The situation — where the mussels were found and in what stage — would dictate the long-term management plan. The park might do the same, depending on the circumstances, if mussels were found in nearby waters.

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Those type of scenarios will be laid out in the rapid response plan. “We need to know how we would react to those various situations,” Mills said.

While inspections haven’t discovered any zebra or quagga mussels on boats in the park, they have caught other invasive species.

“The mussels are the poster child,” Mills said. “They are the ones everyone thinks about. There’s nothing like an engine covered in mussels. But in terms of near misses, we had nine suspect (aquatic invasive species) that were discovered on boats last year.”

Six of the suspect species found last year were snails. One was an Asian clam. The others were invasive aquatic plants. Any of them could have caused serious problems had they made it into park waters.

“Even the lesser known [aquatic invasive species] would be a game-changer for us,” Mills said.

Kelsey Dayton is a freelancer and the editor of Outdoors Unlimited, the magazine of the Outdoor Writers Association of America. She has worked as a reporter for the Gillette News-Record, Jackson Hole News&Guide...

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