Whatcom is already home to several aquatic invasive species including: Asian
clams, Eurasian watermilfoil, fragrant waterlily, and curly-leaf pondweed. As was witnessed with the Asian clam
infestation in Lake Whatcom, it can take several years for a species
to become established and for its presence to become known. However, once a species becomes established,
it becomes increasingly difficult and costly to manage the population. By having an early detection and monitoring
program we can ensure that new infestations are reported, confirmed, and
responded to as soon as possible.
Asian Clam Response Strategy
The Asian clam (Corbicula fluminea) is an invasive bivalve that was first collected in the United States along the Columbia River in Washington State in 1938 and is currently found in 38 states and the District of Columbia. Since its introduction to the lake, this species has infested between 6-8 acres at three sites in Lake Whatcom. The Asian clam discovery in Lake Whatcom was confirmed by the Washington Department of Fish and Wildlife on September 19, 2011. Response efforts began soon after their initial discovery with over 30 shoreline surveys being conducted throughout the lake to determine the extent of the infestation.
Three established colonies were confirmed in 2011 at Bloedel Donovan, Lakewood/WWU Facility, and at the Wildwood Resort. Additional infestations were also discovered in Lake Padden and Whatcom Creek. In early 2012, staff continued to conduct shoreline surveys for Asian clams in Lake Whatcom at Dellesta Point, at additional sites in Basin 1, and in Sudden Valley. While no additional Asian clam colonies were discovered at any of the survey sites, these surveys gave staff a great opportunity to engage Lake Whatcom residents in invasive species prevention efforts.
In February of 2012, Lake Whatcom Management Program staff met with a dive team from the Washington Department of Fish and Wildlife (WDFW) to discuss options for conducting dive surveys to map the extent of the Asian clam infestation in the lake. WDFW divers conducted two preliminary surveys in Basin 1 of Lake Whatcom to aid in the development of a dive survey protocol for the lake.
In September of 2012, the Whatcom County Noxious Weed Board, with assistance from the Washington State Department of Ecology and the City of Bellingham, completed an aquatic invasive species inventory of Lake Whatcom. The goals of the inventory were to establish a baseline of aquatic invasive species present in the lake and their distributions to assist in the development of aquatic invasive species response strategies. The survey was conducted by boat over several days in August and September. As of October, 2012 no new Asian clam colonies have been discovered in Lake Whatcom as a result of shoreline surveys and the Lake Whatcom AIS inventory.
Staff continues to monitor the sites where Asian clams have been confirmed in Lake Whatcom. Studies from Lake Tahoe have observed the co-location of dense algal blooms of green filamentous algae and elevated calcium concentrations with Asian clam beds. While no dense filamentous algal blooms have been observed where Asian clam beds are present in Lake Whatcom, additional monitoring efforts in 2013 will focus on deciphering whether clam beds are associated with dense algal blooms and elevated calcium concentrations in the lake.
Staff continues to study Asian clam management efforts being undertaken at Lake George, New York and at Lake Tahoe, California/Nevada to determine the cost effectiveness of implementing a similar response strategy at Lake Whatcom. Since the initial infestations were discovered in 2010, Lake George has now spent over $1.5 million on Asian clam response efforts to manage four Asian clam colonies using benthic barriers and suction harvesting. Lake Tahoe is also engaging in its largest Asian clam control effort to date by installing benthic mats over a 5-acre area at Emerald Bay. This project will take over a year to complete and will cost approximately $810,000.
Management options are going to vary depending on the species in question, the location of the infestation, the uses of the waterbody, and permitting requirements. When eradication is not an option, efforts need to focus on: isolating the population, preventing its spread, and mitigating any impacts that may occur as a result of the infestation.
Asian clams (Corbicula fluminea)
Once introduced into a waterbody, it is very unlikely that an Asian clam population will be eradicated. While the Asian clam is preyed upon by various predators including raccoons, birds, fish, and crayfish, there are not enough of these predators to have a significant impact on an Asian clam population. Large-scale control options are limited to the following:
- Mechanical removal by labor intensive suction harvesting
- Drying, high salinity, and exposure to low concentrations of chlorine or bromine
- Covering clam colonies with acres of polyethylene benthic barriers to starve them of oxygen
A report outlining the control options being used at Lake George, New York, and Lake Tahoe, California/Nevada, can be viewed here (PDF).