Invasive Snails Found In Lake WA Trib

UPDATE 9:54 A.M., JUNE 2, 2011: KING 5 did a story on the “invasive creeps,” wading Thornton Creek with USGS biologist Bob Black who found several on different rocks.

Somewhere downstream of my home a new species has arrived in Thornton Creek, one that we don’t want in the watershed, however.

New Zealand mudsnails are now in the tiny tributary which winds through Shoreline neighborhoods, disappears below busy interstates and arterials, and flows past Seattle dentist offices before draining into Lake Washington.

It’s unclear how they got there, but during routine testing recently, a 2009 sample analyzed by the U.S. Geological Survey’s Denver Lab came back positive. The presence of adult and juvenile specimens at the creek’s mouth was confirmed last week during sampling by the Washington Department of Fish & Wildlife, said the USGS in an announcement made early this afternoon.


The worry is that because mudsnails are difficult to control, have no natural predators and little nutritional value, they could outcompete native snails and insects that young fish in the stream depend on. Stream watchers report seeing Chinook, coho and sockeye salmon as well as rainbow and cutthroat trout here.

Just downstream, Western Washington’s largest lake.

“Unfortunately, it only takes one to begin a new population,” says a WDFW Web page on the subject. “Females ‘clone’ themselves, producing approximately 230 new female snails each year. Based on a single snail and each offspring in turn reproduces itself, by year two there may be over 52,000 snails, by year three over 12 million snails, and by year four over 2.7 billion snails carpeting the bottom of a river or lake.”

John Clemmons, a USGS spokesman in Tacoma, says that 500,000 were found in one particular single square-meter sample.

“A recent study by the U.S. Bureau of Land Management and the Utah State University linked these invasive snails to poor condition of trout due to lack of a regular food source and that the snails did not provide sufficient nutritional value when consumed,” adds WDFW’s Web page.

Thornton Creek is the fourth location in Washington the mudsnails have been found, the others being the lower Columbia River, canals on the Long Beach Peninsula and Capitol Lake near Olympia, according to WDFW.

Though native to New Zealand, they have since hitchhiked their way around the world and occur in Asia, Europe and since the late 1980s, parts of the Western U.S. They’ve probably spread in the ballast of ships, the bottoms of wading boots and the gullets of introduced fish.

In Oregon, they’ve been found along parts of the Deschutes, Rogue, Malheur, Owyhee and Umpqua Rivers and in Garrison, Floras, Devils and Coffenbury Lakes and Coos Bay. A bill to ban the sale of felt-soled waders in the Beaver State fell short this past legislative session.

Mudsnails were found in Capitol Lake in 2009 and initial attempts were made to freeze them out during cold weather by drawing water levels down. Now managers are testing their tolerance to salt and monitoring their presence.

“Control and eradication is on the table,” says Allen Pleus, WDFW’s invasive species coordinator, “but it’s just difficult to move forward with the (state) budget.”

Clemmons says that the U.S. Fish & Wildlife Service — which has offices at Sandpoint just south of the mouth of Thornton Creek — WDFW, King County, the Cities of Seattle and Shoreline, and other Thornton Creek watershed stakeholders, have been advised and along with the USGS are “putting heads together to come up with a control plan.”

“They’re all looking at this very seriously. It could be many places in the Lake Washington ecosystem. We don’t know,” says Clemmons.

Pleus says the Thornton Creek invasion could be a “stepping stone” to other locations, but points out that problems might be decades down the road from the initial discovery, as with spartina grass on the Washington coast.

“That’s the thing with invasive species: You never know when they’re going to take off,” he says.

It’s possible that the mudsnails arrived in the creek during restoration work or scientific research. Pleus says that managers are talking about holding a big seminar on how to avoid spreading the invertebrates.

Authorities say to thoroughly inspect, clean and dry your waders for at least 48 hours before going into new waters, or freeze or boil it, or soak in a 50 percent solution of Formula 409 Cleaner Degreaser Disinfectant Solution for five minutes.

“One simple thing to do is to stay out of the creek or off its banks so you don’t get hitchhikers in the first place,” Clemmons adds.

The local watershed council is advising people to stay out of the creek.

“They’ve been found to be very hard to eradicate,” Clemmons says.


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