Study: Clams in Lake George transported by boat anchor sediment

Amanda May Metzger
January 3, 2014
LAKE GEORGE ­­ Researchers have pried open some information on how Asian clams move around Lake George. At the December Lake George Park Commission meeting, the Darrin Fresh Water Institute’s Sandra Nierzwicki­Bauer and Jeremy
Farrell reported findings from their research on the aquatic invasive species first spotted by Farrell in August 2010 off Lake Avenue Beach in the village.
“I thought it was interesting, and good, to rule out certain methods of transport,” said Lake George Association Executive Director Walt Lender.
The study sought to examine possible human and natural means of clam mobility and also determine the settling velocity of juvenile clams. As far as human transport, the clams are likely to be moved by boat anchor sediment. Prop wash — water pushed by propeller­driven watercraft — is not likely to cause longrange travel, but could transport them a short distance, Farrell told the commission about the clams, which are much smaller and more circular in shape than native mollusks.
“The idea was that the wash from a propeller could blow Asian clams to a new area,” Farrell said, which testing determined did not cause long­range transportation. 
Specifically, the study found the presence and abundance of clams from sediments on anchors are related to the amount of clams at each location, so transport of sediments on boat anchors from contaminated areas, such as Park Lane and Pine Point, can provide a means for long­range dispersal.
“It gave us an understanding of how Asian clams move around the lake. I think the anchor outcome was very interesting. We have more questions that need to be answered,” said Lake George Park Commission Executive Director Dave Wick after the meeting. “I think it shows we’re learning, but we have a lot more to learn.”
The study also found that rooted plant material did not appear to be a primary vector for Asian clam transport. The research also found Asian clams as large as 10 millimeters can access the water column as a way to move around, while juvenile Asian clams can move locally from an established bed at least 40 feet.The water column is a section of water from the surface to the bottom sediments. The concept is used for environmental studies evaluating mixing of layers of the lake.
Last winter’s cold temperatures helped with the fight against Asian clams, which had been spreading rapidly the year before despite more than $1 million in eradication efforts. Specifically, the juvenile clams, 2 millimeters in diameter or so, seemed to be getting free from the benthic mats used to smother them.
Surveys last spring and summer found fewer clams in areas that had been infested. The clams generally infest shallow areas, and nearly 3 feet of ice accumulated on parts of the lake last winter, which was harsher than any since the Asian clams were first spotted. The Asian clam is native to temperate and tropical areas in southern Asia, the eastern Mediterranean and Australia. They are usually less than 1.5 inches.
“It’s strange. We’ll see them in an area. We’ll put mats down to eradicate them in an area, and not too far away, they pop up later. Jeremy’s research says they really don’t stay in the water column very long,” Lake George Association Executive Director Walt Lender said. “We never dealt with these creatures before 2010, so we’re learning as we go.”

The next step will be to “raise awareness about the human aspects of transporting, specifically the anchor transport. I think that’s a good opportunity to do some outreach and tell the public where they should and shouldn’t anchor and have a good scientific validation for that,” Lender said.
The Lake George Association is one of several organizations on a task force to eradicate Asian clams in Lake George. The Darrin Fresh Water Institute spearheaded a committee to coordinate efforts to respond to Asian clams, including representatives from the Lake George Park Commission, the Lake George Association, The Fund for Lake George, state Department of Environmental
Conservation, the Adirondack Park Agency, the Adirondack Park Invasive Plant Program and the Lake Champlain Basin Program.

“Now we’re focusing on getting some research we needed to do. Now that they’ve done research on the spread, the next step is to figure out reproductive cycles,” Lender said. Studies have found adult clams, which reproduce by self­fertilization, can have 400 offspring a day.

The recent research also examined how far juvenile clams can be found from the clam bed and concluded detailed circulation models, such as what’s being done through the Jefferson Project, may help define exact distances reached through water transport.
Asian clams are responsible for “biofouling,” which is the clogging of water intake pipes. The clams filter feed on plankton and compete with native mollusks for food and space. Nutrients from excrement of the clam can feed plant and algal growth, which is why, in large quantities, they’ve been associated with increased algal growth.

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