Small snails are big problem

Millions of invaders are creeping along Utah's rivers and streams, threatening unpredictable damage.

The invaders are tiny aquatic New Zealand mud snails (the scientific name is Potamopyrgus antipodarum), which reproduce at an alarming rate. They out-compete native snails and other invertebrate species and might not be readily digested by our trout.

A somewhat analogous invasion of nonnative mollusks has been taking place in the East, where the zebra mussel has been jamming intake pipes and dam works, damaging watercraft and muscling out native species.

Apparently Utah fishers are inadvertently spreading New Zealand mud snails, as they are found "all along the favorite trout waters," said Mark Vinson, Utah State University assistant research professor.

Vinson, with the National Aquatic Monitoring Center, has been monitoring the snail invasion since it began in Utah probably three years ago. The center, nicknamed the Bug Lab, is a cooperative research facility funded by the Bureau of Land Management and USU. Much of the aquatic habitats threatened by the snail invasion are on BLM land.

"None of the native species have grown up or adapted to living with something like this," Vinson said. The snails are small and hard, so may not be good food for larger animals. But they out-compete and out-reproduce native snails and other invertebrates, with the possibility of killing off the Utah animals.

According to a March 20 update he wrote, if they stay moist and are not exposed to excessive heat, the snails are able to live several weeks out of the water, protecting themselves by closing a tiny flap at the end of the shell. At Polecat Creek near Yellowstone National Park, New Zealand mud snails can reach population densities greater than 100,000 per square meter.

He wrote that the snails can comprise more than 95 percent of the invertebrate biomass in some river sections.

As their name indicates, the snails are native to New Zealand. How they got to the United States nobody knows, but they showed up in the Columbia River around 1970.

Throughout the 1990s, researchers found no mud snails in Utah. They were collected in this state on Sept. 18, 2001, near Swallow Canyon on the Green River, downstream from Flaming Gorge Dam. Since then, he wrote, they were discovered at 20 out of 477 locations checked throughout Utah.

"They moved quickly from the Green River to the Great Basin Drainage, as we found them in the Little Bear and in the Provo River in October 2001," Vinson wrote. "In 2001 they were found in three basins, in 2002 they were found in eight basins, and in 2003 they were found in 12 basins."