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Invasive clams spreading in lakes

Dive teams that spread underwater mats to smother invasive Asian clams in an Adirondack lake this spring are now sifting the sandy bottom of Owasco Lake in New York's Finger Lakes wine country to determine how widely the water-befouling mollusks have spread there.

An interim report released last week on a $475,000 effort to eradicate Asian clams in Lake George said mats spread on five acres of lake bottom have killed more than 97 percent of the clams. But it recommended additional work, such as suction harvesting, that could bring the cost to nearly $1 million.

A plan also is being developed to eradicate a new five-acre colony of Asian clams discovered last month in another bay of 32-mile-long Lake George, where the clear, cold water, sandy beaches and mountain scenery have long made it popular for vacations and second homes.

Albany-based InnerSpace Scientific Diving, which is involved in the Lake George clam project, is now working to determine the extent of an infestation in Owasco Lake, in Cayuga County. Divers plot their findings on a map, using GPS to pinpoint the location of clams. Populations also have been discovered in Cayuga and Seneca lakes.

Steve Resler, owner of InnerSpace, said Sunday that it looks like the clams are established on about 10 to 15 acres of Owasco Lake. The good news is that the water is only 6 feet deep or less where the clams are, making it possible to freeze the mollusks by lowering the lake level a few feet more than it's usually lowered next winter, he said.

"If they lower it six feet, that will kill most if not all of the clams," said Dan Marelli of Scientific Diving International, who's working with Resler on both lakes. Bruce Natale, an engineer with the Cayuga County Water Quality Management Agency, said he's looking into that option.

The Asian clam, Corbicula fluminea, is known as the "golden clam" in the aquarium trade and the "good luck clam" in its native southeast Asia, where it is used in traditional medicine as a liver tonic. The thumbnail-size clams multiply rapidly because of their ability to self-fertilize and release up to 2,000 juveniles a day during breeding seasons in May and August.

Infestations of the clams usually occur when someone dumps a bait bucket or aquarium into a body of water. The Owasco Watershed Network has asked lakeshore residents not to use Asian clams for bait or keep them in outdoor water gardens, and to notify the network if they find the clams.

The mollusk's excretions feed algal blooms and the sharp shells from dead clams wash up on beaches in large numbers. In Lake Tahoe, where a $1.4 million eradication effort was launched last summer, they have been blamed for algal blooms that have turned clear, blue bays a murky green.

In April, divers unrolled 825 50-foot-long plastic mats to cover the bottom of a five-acre bay of Lake George where the clams were discovered last fall. In June, about 100 of the mats were removed from beach areas in front of resorts. Sandra Nierzwicki-Bauer, director of the Rensselaer Polytechnic Institute Darrin Fresh Water Institute on Lake George, said last week that more than 97 percent of clams were dead in areas where mats had been removed.