Divers lay barriers for invasive species in Lake Tahoe’s Emerald Bay
November 6, 2012
Divers started laying barriers in Emerald Bay last week as part of the largest Asian clam eradication project in Lake Tahoe's history.
The $810,000 Lake Tahoe Aquatic Invasive Species program aims to eliminate a 5.5-acre population of Asian clams from the mouth of Emerald Bay and control the invasive species whose numbers have grown exponentially since 2002 when the first clamshell was discovered on a beach.
For the next four to six weeks, crews will line the area with thin rubber barriers and organic material from Aspen trees to cut off the clams' supply of oxygen.
The isolated population in Emerald Bay represents about 5 percent of the total number of Asian clams in Tahoe, most of which are found in the southeastern quadrant of the lake.
UC Davis Tahoe Environmental Research Center Director Geoffrey Schladow said the goal of the project is to control an exploding population and that complete eradication just isn't feasible.
"Eradication isn't possible anywhere. You're laying down mats — there are going to be gaps between them. But control is possible, so the shells aren't affecting people, and the clarity isn't getting worse," Schladow said.
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"From a scientific point of view, I consider it a success already. From the point of view of the lake, it'll be a success when there's a sustainable control program in place," he said.
The UC Davis Tahoe Environmental Research Center pioneered the science behind the suffocation method, Schladow said. The Emerald Bay project, which uses a combination of biomass from Aspen tree fibers and the rubber barriers to prevent water from flowing horizontally through the silt and carrying oxygen to the clams, is a new concept.
Laying the mats, which weigh about 300 pounds each and are about 100 feet long, is taxing work, and divers on the project will ultimately spend days underwater to complete the project, UC Davis researcher Brant Allen said.
Allen surfaced in his wetsuit and his scuba gear Tuesday near the mouth of Emerald Bay with a bag of Asian clams gripped in his hand. The animals aren't hard to find, he said, but they do burrow beneath the silty lake bottom and aren't easily visible from above. Allen had helped place some of the mats in the bay, and he said despite the difficulty of the project, he's optimistic about the chances for success.
"It's an exhausting day of work, but things seem to be going OK. I'm very optimistic about the success of the project," Allen said.
One reason eradication is so difficult is the clams' ability to disperse rapidly. University of Nevada, Reno, researcher Timothy Caldwell has studied the animals' reproductive capabilities and said that each clam can contain 100 to 1,000 eggs. When the animal releases those eggs into the water as microscopic veligers, or larva, the baby clams can spread throughout the lake on currents, he said.
"Are we going to eradicate every clam in the lake? Probably not. What we can do is prevent them from spreading to other lakes," Caldwell said.
Axie Navas is a reporter for the Tahoe Daily Tribune, a sister publication of The Union.