Wednesday, March 14, 2012

City maps Asian Clams clamming up Lake Whatcom

Since invasive AsianClams were found in Lake Whatcom in September 2011, the city has been working to understand the extent of the infestation and is currently considering hiring a dive team to fully map the distribution of clams in the lake.

“We have met to ascertain the cost and timing of a dive team mapping,” said Clare Fogelsong, Environmental Resource Manager for the BellinghamPublic Works Department. “That will help us in turn determine our response.”

The Asian Clam, scientifically known as Corbicula fluminea, is an invasive specie that, according to Julian Olden, associate professor of Aquatic & Fishery Sciences at the University of Washington, poses a threat not only to native clams, but also to Whatcom County citizens who depend on the lake for drinking water.

Live Asian Clams and dead shells damage and clog water intake pipes, costing the U.S. about a billion dollars per year according to U.S.Geology Survey estimates.

The issue was originally brought to the attention of the city on Sept. 17 when a resident brought unidentified clams a city-sponsored presentation about boat inspections. Since then, the city has confirmed significant infestations in Lake Whatcom around Bloedel Donovan Park, Lakewood, Sudden Valley and Wildwood.

Fogelsong said he doesn't believe it is coincidental that all the sites where the clams have been found are sites where there is high boat traffic or where float planes land.

The infestation in the lake has “precluded [the city] doing anything simple” according to Fogelsong, but he hopes the mapping will lead to a management solution.

A History of invasion
Native to southern Asia, Australia, and the Mediterranean, Asian Clams were first found in the U.S. in 1938 when they were discovered in the Columbia River in Washington. They are commonly thought to have been introduced as a food source by Chinese immigrants. According to Olden, the clams may also have been brought in ballast water of Asian ships or with the importation of the Giant Pacific oyster, also from Asia.

The clams have now spread through the country, traveling in mud and sediments left in watercraft or in bait barrels used by fisherman, according to Fogelsong's suspicions. Clams can also travel passively along water currents and may be introduced intentionally for harvesting purposes as they are a tasty addition to many Asian soups.

Lake Whatcom was home to the first reported clam populations in Whatcom County, but in October 2011 clams were also discovered in Lake Padden and Whatcom Creek.

Laurel Baldwin of the WhatcomCounty Noxious Weed Board said there are a number of sites where clams have been found on the Lake Whatcom, mostly on the south shore, but the city is still doing surveys to establish were the largest concentrations are.

The latest survey conducted on Jan. 12 at Dellesta Point yielded no clams.

Clam populations were found at North Point Park in Sudden Valley and the Sudden Valley Marina in December 2011, though this location is not thought to be a point of introduction as only two clams were found. According to the city, clams were most likely spread from the Lakewood site, home of Western Washington University's watersports facility.

Some county officials think there is a link between boat use and population concentrations, including Baldwin who said she believes the older colonies are certainly associated with boat traffic. 

The impact on the lake
The tiny gold clams measuring under an inch in length may seem like an unlikely culprit, but can have devastating effects on water bodies.

Baldwin said the clams reproduce so rapidly that the dead shells can accumulate and replace the natural substrate. This means sharp, course sand that can be rough on the feet of swimmers and beach goers.

Clams are even more than a nuisance for citizens though, as they are carried into water filtration systems, clogging pipes that treat and distribute Bellingham's drinking water.

A native mussel
Photo by Mikey Jane Moran
Baldwin also suspects that the clams may intensify Lake Whatcom's phosphorous level concerns, as they release significant amounts of phosphorous into the mud, encouraging toxic algae growth that can also clog water pipes.

The Asian Clam is capable of living in polluted water bodies better than native clams. Lake Whatcom's native mussels and clams, Anodonta oregonensis and Anodonta kennerlyi, may find it harder to compete for food and space to live as the Asian Clams multiply.

Olden said Asian Clams are also superior filer feeders, meaning they can consume particles and pollutants from the water very quickly. 

“Although this may seem good for water quality, there are examples of native ducks feeding on these Asian clams,” Olden said. “It causes the ducks to be poisoned themselves and can cause reproductive problems for waterfowl.”

According to the city, an area south of survey site in Sudden Valley is heavily used by water fowl and evidence of the birds eating clams was found.

Baldwin also said Asian Clam concentrations can be used as an indication of other forms of pollution. She said the shells of dead Asian Clams provide other invasive species, like Zebra Muscles, with the dissolved calcium needed to form shells. Populations of Asian Clams could mean future populations of Zebra Muscles, which Baldwin said would be disastrous.
A reminder to boaters
Photo by Mikey Jane Moran

Plans for the future
Right now the city is focusing their efforts on mapping the populations to better understand the best approach for removing clams.

“Over time if a lake doesn't have a management strategy you are sort of rolling the dice,” Fogelsong said.

Clams can be removed from the lake manually, but this method is labor intensive and time consuming. Plastic sheets can also be laid over clam beds, cutting off their oxygen supply and eventually smothering them. Both of these methods were applied in infested regions of California Lake Tahoe in 2010 and they proved effective in reducing clam populations. The City of Bellingham is considering this strategy.

“There is talk about bottom barriers but if you put them down, you pretty much kill everything,” Baldwin said. “We have to be careful about what ever strategy we decide to use.”

Olden said chemicals can also be used to kill adult and juvenile clams, though there are definite drawbacks to consider.

“The feasibility of these management efforts, particularly for large lakes like Lake Whatcom, is questionable,” Olden said. “Bottom line: prevention is the best line of defense when dealing with Asian Clams.”

With boating season around the corner, Baldwin said the city will step up it's prevention efforts with outreach programs for boaters. She advocates the use of boat wash stations to decrease the amount of species transported from lake to lake and as a location for boater education and awareness about invasive species.

Fogelsong, on the other hand, said boat wash stations will be useless to the effort as clams are not carried on boats themselves, but in standing water and in bait buckets.

Baldwin said that boat wash stations are effective as long as you have the right people manning them and informed citizens using them.

“It's more than just a car wash,” Baldwin said. “It's more technical.”

What ever strategy the city decides on, they still encourage boaters to read their boaters hand book and to remove any plants or animals attached to watercraft or trailers, flush engine water and bait storage with hot water and let boats dry for at least five days before launching them at another location. They emphasize the individual holds a large responsibility for helping curb invasive clam populations. 

1 comment:

  1. Nice article about an important invasive species issue!