Bottom feeder’s arrival in Nevada lakes worries wildlife officials

By Stephanie Tavares

Saturday, June 5, 2010 | 2:01 a.m.

Move over quagga and zebra mussels, a new invasive mollusk is making waves in Nevada.

Sport fishermen and state wildlife officials are worried about New Zealand mudsnails after a colony of the tiny critters was found on a boat ramp at Lake Tahoe last week.

Although they haven’t gotten the attention that quagga and zebra mussels have, mudsnails are in Lake Mead and Lake Mohave. They’re in Echo Bay and Boulder Basin and at Willow Beach.

The reason there hasn’t been much noise about them is they aren’t capable of the kind of damage that quaggas are. Unlike the quaggas, mudsnails don’t attach themselves to infrastructure such as hydropower generators and water pipelines.

The snails also aren’t thriving in the warmer waters of the lake the way quaggas are. Mudsnails prefer deeper areas of lakes because the water is colder, about 52 degrees. So far, the snails have not adapted to warmer waters.

But in the areas where they do live, they tend to push out other bottom feeders. In Yosemite National Park, mudsnails make up 95 percent of the invertebrate population of some stream beds.

“They’re very small, but they out-compete the native invertebrate species for food,” says Doug Nielsen, Nevada Wildlife Department spokesman. “So you see a decline in body condition of, say, trout in a stream, because the invertebrate population declines, and (the trout) don’t have the food source they need to survive.”

Native fish won’t eat mudsnails.

The largest of these light brown mollusks are about 5 millimeters — about half the size of Abe Lincoln’s head on a penny. But these minuscule mollusks pack a punch in the reproductive department.

Females can produce up to 120 embryos each. And although only about 5 percent of a colony are males, the females don’t need the boys around to have big families. They are parthenogenetic, meaning they can reproduce without a mate.

And in Nevada, they can reproduce year-round, so a lake can go from a population of zero to an all-out infestation in less than five years. They’ve been in Lake Mead since at least 2008.

The mudsnail also has no local predators and is virtually impossible to get rid of without poisoning the water in which it lives.

Redear sunfish, also known as shellcrackers, would likely eat mudsnails and quagga mussels, but scientists want to have a better idea of how they will affect the ecosystem before they are introduced into Lake Mead.