Future of Lake Tahoe clam-killing project uncertain | TahoeDailyTribune.com

Future of Lake Tahoe clam-killing project uncertain

Griffin Rogers
griffin@tahoedailytribune.com

A diver places a rubber barrier over invasive Asian clams at Emerald Bay. The barriers will be removed this month after being in place for about two years.

A project to suffocate Asian clams at Lake Tahoe's treasured Emerald Bay may be coming to an end this month, when divers help remove about 5 acres of rubber matting being used to cut off the species' oxygen supply.

Divers installed the thin rubber barriers about two years ago in an effort to reduce the invasive Asian clam population in the lake. The mats were placed at the mouth of Emerald Bay with the intent that they would be there for about a year, said Geoffrey Schladow, director of the U.C. Davis Tahoe Environmental Research Center.

However, after an initial 12-month assessment of the area showed a lower mortality rate than researchers were hoping for, the roughly $900,000 project was extended another year.

Now, researchers are expecting a 90 percent mortality rate when the mats are pulled in a couple weeks. Another assessment of the clam population will follow, but it is unclear whether the mats will be used again.

"It comes down to a community decision now of do we want to try to control these at a cost or throw up our hands and say, 'that's it,'" Schladow said.

The project is the largest effort to eradicate Asian clams in Lake Tahoe's history, and it followed a similar 2009 undertaking to suffocate about an acre of the species in Marla Bay.

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That Marla Bay project resulted in about a 99 percent mortality rate, but it didn't have the same geological challenges researchers face in Emerald Bay.

Shallow waters, swift currents and porous sediment have all been factors in the reduced mortality rate expected at Emerald Bay. They are some of the reasons why the current project took two years and the Marla Bay project took only about three or four months, Schladow said.

"Most places we know what to do," he said. "At Emerald Bay I think we could improve things, but it's challenging there."

Crews will begin removing the mats on Oct. 27, but the entire process could take a couple weeks, according to the Tahoe Regional Planning Agency.

The cost of removal is about $130,000, which is included in the approximately $900,000 price tag for the overall project.

Dennis Zabaglo, TRPA's aquatic resources program manager, said the agency would be interested in continuing to fund similar projects in Lake Tahoe, but it would like to see what the mortality results are of the Emerald Bay project first.

He also said a combination of methods would likely be needed if agencies hope to tackle the Asian clam population effectively. One idea the TRPA plans to "investigate" further involves a machine that scrapes the clams off the lake floor.

"(The program's) successful," Zabaglo said, "but there's a piece missing that we're still trying to look into."

The largest infestation is located in the southeastern portion of the lake, where about 1,000 clams per square meter are estimated to exist in certain areas. That number drops to about 100 per square meter in Emerald Bay.

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