Largest Asian clam control project in Tahoe’s history begins
October 16, 2012
When Andrew Cohen drove up to South Lake Tahoe last weekend with his family to watch the celebrated Kokanee salmon run in Taylor Creek, he was struck by the irony of the situation. Just days after he would return to Richmond, Calif., the Lake Tahoe Aquatic Invasive Species program would begin implementation of the largest Asian clam control project in the history of the lake.
Both the salmon and the clams were introduced to Tahoe, but while the fish are termed a non-native species, the clams are an invasive. It’s a question of semantics which ultimately comes down to whether or not an introduced species is harmful to the environment and what sort of values society places on the animal, Cohen said.
“People make choices. Society has made a choice that in this case, people seem to value the salmon. But in general, we try and keep the exotics out,” said Cohen, the director of the Center for Research on Aquatic Bioinvasions.
According to US Forest Service officials, the Kokanee don’t disrupt the lake’s natural cycles and they don’t prey on the food sources of native fish. The Asian clams are a different story.
Cohen has experience with the clams in the San Francisco Bay Area, and he knows some of the threats the filter-feeding animals pose to ecosystems.
“We’ve seen them change ecosystems dramatically. If the clams become abundant, it would change the food web and it would affect bottom conditions of the lake,” Cohen said.
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By creating greater calcium concentrations, the clams can increase the potential for other exotics like quagga mussels to live in Lake Tahoe. They promote the growth of algae that decreases water clarity by releasing highly concentrated nutrients, and they compete with native animals for habitat and food, according to a Tahoe Regional Planning Agency press release.
California State Parks staff discovered Asian clam shells on a beach in Emerald Bay in May 2009. Later that summer UC Davis conducted an underwater survey to document the infestation. Three years later, the Lake Tahoe Invasive Species program, a coalition comprised of 40 public and private organizations, will begin an attempt to smother about 5.5 acres – approximately 6 million to 12 million individual clams – of infested lake bottom near the mouth of Emerald Bay.
Divers will cover the population with thin rubber barriers to limit the clams’ oxygen starting in mid-October. It’s a strategy that’s proven successful, but only if total extent of the population is known, Cohen said.
“If you give them time, they’ll die. The barriers make it impossible to live in the chemical conditions. But the success depends on being able to delineate the exact populations. They must have confidence they’ve found the whole population,” he said.
The $810,000 Emerald Bay project isn’t about completely eradicating clams from Tahoe. Rather it’s about preserving one of the lake’s most beautiful and popular spots, Lahontan Regional Water Quality Control Board Assistant Executive Director Lauri Kemper said.
“We know we don’t have the whole population. But it’s important to address the issue at Emerald Bay because it’s a fairly small population. But there are others,” Kemper said.
TRPA Public Information Officer Kristi Boosman said the full extent of Asian clams in Tahoe is unknown, but that the animals are located primarily in the southeastern quadrant of the lake in addition to the mouth of Emerald Bay.
As the Lake Tahoe Invasive Species program prepares to start laying bottom barriers, a project that can take up to six weeks to complete, the Lake George Park Commission on the opposite end of the country gets ready to tackle four newly discovered Asian clam beds with the same suffocation method.
Commission Executive Director Dave Wick said the efforts to eradicate Asian clams in the New York lake are modeled after the science and the work done in Tahoe. They’ve had mixed success in treating the 35 acres of infested lake bottom, but the population still hasn’t become completely unmanageable, he said.
It’s an expensive project – about $2 million in a little over two years – and one that needs almost 100 percent eradication for success. When one of the spring attempts to suffocate the clams only killed about 60 percent to 80 percent of the population, Wick said the whole area needed to be remapped.
In bids to potential donors, Wick said his sales pitch doesn’t vary. There’s still time to save Lake George, and organizations need to act before it becomes too late, he said.
“We don’t want to end up like Tahoe where the population is simply impossible to manage. We can reference some of Tahoe’s history and use that as a call to action,” Wick said.