Assignment 7

Researchers help curb invasive clam at Lake Tahoe

Monday, June 18, 2012

Boating season is now in full swing at Lake Tahoe. Extra safeguards are in place to make sure invasive species don't get in the lake, but some unwanted creatures are already there. The good news: experiments on getting rid of at least one harmful species appear to be paying off.

Researchers rolled out the "un-welcome" mat. A UC Davis video shows how researchers spread sheets of rubber on the bottom of Lake Tahoe. The rubber is intended to smother an invasive species called the Asian clam. It blocks the oxygen and the clams are underneath it.

Asian clams are tiny, but have potential to cause big problems. So a multi-agency task force is trying to control the clams before it's too late. They took an ABC7 News crew out on the lake to show us how it's going. In some areas, the clams are easily visible through a scope.

"Every white dot that we are looking at right now is a dead clam shell and there are a lot more live ones underneath them," said Ted Thayer with the Tahoe Regional Planning Agency.

The clams bury themselves in the sand. They were first discovered in Tahoe 10 years ago and they spread fast.

"These guys can grow faster and just more efficiently than the native clams," said Alyson Gamble, a UC Davis researcher.

The clams encourage algae which clouds Tahoe's famous clear water. Their shells are sharp and make beaches dangerous for bare feet. But scientists say the most serious threat may be that the clams change the water chemistry, so it's easier for other even more harmful species to survive.

"The combined effects of invasive species on Lake Tahoe could be as much as $22 million a year in lost property values, recreation, increased maintenance of boats and boat engines, water intakes," said Thayer.

One picture showed how thick the Asian clam infestation is in some spots now. So far, the clams are mostly in the southeastern part of the lake, but a small colony is beginning to grow at the mouth of Emerald Bay.

Emerald Bay is one of the most popular and beautiful parts of Lake Tahoe and it is the site of a pilot project that started a year ago. Divers put down 2,000 square feet of those rubber mats.

"It's a lot of work down there. These rubber mats are heavy and they have a lot of rebar on them to keep them in place because there are a lot of currents that flow back and forth under across the bottom of Tahoe," said diver Brent Allen.

We were there as researchers pulled the entire experiment out of the water piece by piece. The divers also took clam samples to send to a lab for analysis and after a few weeks the news is good.

"It was very effective," said Thayer.

The mats killed about 80 percent of the clams by cutting off their oxygen. That result combined with earlier research is leading the team to recommend a much larger project -- putting temporary rubber mats on five acres of Emerald Bay. It would cost about $800,000.

The invasive species team is reminding anyone who plans to bring a boat to Lake Tahoe that it must be inspected before it goes into the water. The best way to stop invasive species from getting into the lake is to make sure your boat is clean, drained, and dry when you arrive.

Written and produced by Jennifer Olney

(Copyright ©2014 KGO-TV. All Rights Reserved.)

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lake tahoe, assignment 7, dan ashley
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