Tahoe Environmental Research Center
Species Introduction Timeline

Lake Tahoe Species Introduction Timeline


Corbicula fluminea found underwater at Marla Bay, Lake Tahoe 2009
Corbicula fluminea found underwater at Marla Bay,

Lake Tahoe 2009

 

Researchers installing bottom barriers to control Asian clam populations in Lake Tahoe

Researchers installing bottom barriers to control
Asian clam populations in Lake Tahoe

 

Aquatic Invasive Species

During the last 130 years numerous nonnative fish, invertebrate, and plant species have been introduced intentionally and unintentionally to Lake Tahoe altering aspects of its ecology. The first series of intentional fish introductions occurred at the end of the 19th century through the 1940’s. Of those, the rainbow trout, brown trout, lake trout, and brook trout and kokanee salmon still persist today. Other species, such as the crayfish and Mysis shrimp were introduced purposely by resource managers to improve the fishery.

More recent introductions of the popular sport fish largemouth bass and bluegill were illegal and not intentional. Some plant species (Eurasian water milfoil and Curly leaf pondweed) initially established in the Tahoe Keys lagoon and continue to spread to other locations around the lake. The Asian clam was initially identified in 2002 and today large, high density (~1500 clams per square meter) beds exist in the southeast portion of the lake.

Whether intentional, accidental or illegal, these species introductions can have profound impacts on Lake Tahoe's native ecosystems and water quality. Working in collaboration with other universities, state and federal resource agencies, TERC continues its history of understanding population dynamics and ecology of introduced species. During the past decade TERC has also been involved with the Basin’s resource management agencies developing control strategies for these species.

Asian Clam (Corbicula fluminea) at Lake Tahoe

Basic Biology and Ecology

Asian clam (Corbicula fluminea) is an invasive bivalve species that has spread rapidly in lakes, canals, streams, rivers and reservoirs throughout North America. Asian clam was first detected in the Western United States in 1938 and is known to aggressively out compete native invertebrate communities, limit phytoplankton biomass, biofoul water intakes, alter benthic habitats, add biologically available nitrogen and phosphorus to systems, and impact aesthetic and recreational values of public beaches, lake front properties and swimming areas.

Their high rates of filtration, metabolism, reproduction, tolerance to wide ranges of habitats, and juvenile dispersal allows Asian clam to aggressively expand ranges and to rapidly re‐invade areas; limiting management, reducing restoration efforts and impacting native benthic communities. Asian clam are capableof both filter feeding (feeding from the water) and pedal feeding (feeding directly from the sediment). One reason for why Asian clam is successful in so many different environments is that it can effectively filter phytoplankton and bacteria out of the water column and feed from the sediments when food from the water column becomes scarce. In Lake Tahoe they grow to be as large as 28 millimeters, but in other warmer systems can be as large as 55 mm. They are found in Lake Tahoe at water depths of 5 to 250 feet (2 to 80 meters), and within the sediments buried in up to 7 inches below the surface.

Asian Clam in Lake Tahoe

On April 25, 2008, TERC senior researchers Scott Hackley and Brant Allen observed large populations of clams in some nearshore areas in the southeast corner of Lake Tahoe. It has been confirmed that these are the invasive species Corbicula fluminea or the Asian clam.

Researchers from the UC Davis Tahoe Environmental Research Center and the University of Nevada Reno, in collaboration with the Tahoe Regional Planning Agency (TRPA), the Tahoe Resource Conservation District (TRCD) and other state and federal agencies have been conducting field surveys, literature reviews, laboratory experiments, and demographic studies on Asian clam populations in Lake Tahoe in response to the initial clam bed discovery in 2008. This information has been passed on to managers of the Tahoe Basin’s resource agencies and the Lake Tahoe Aquatic Invasive Species working group.

For details, see the 2009 State of the Lake Report chapter on Asian clams:

Gavia

Gavia Autonomous Underwater Vehicle

In collaboration with the University of British Columbia and the University of Nevada Reno, TERC researchers deployed an autonomous underwater vehicle (AUV) in Lake Tahoe. This project was funded by the Lahontan Regional Water Quality Control Board and the Nevada Division of State Lands License Plate Funds.

The AUV, known as Gavia, resembles a torpedo but is equipped with a broad suite of scientific instruments. These include high resolution cameras, side scan sonar, fluorometers for detecting algal chlorophyll and colored dissolved organic material (CDOM), water temperature and conductivity, and water current velocity. The Gavia is programmed ahead of time to tell it what course to follow, what depth to dive to and how far off the bottom to cruise.

The Gavia performed a complete circumnavigation of the lake at a depth of about 18 feet. This is the depth at which the heaviest concentrations of Asian clams have been found to date. There were also lateral transects conducted to depths of 300 feet at various locations where the clams were observed. Along the way the Gavia took high resolution images of the lake bottom four times every second, as well as measured other water quality parameters such as temperature, conductivity, turbidity, chlorophyll, and CDOM. These data help rapidly guide researchers to find new areas of the lake that are impacted by invasive clams. Researchers from TERC and UNR will groundtruth the Gavia observations using SCUBA survey and benthic sediment grab collections during the fall 2009 and winter 2010.  The many thousands of high resolution images taken by Gavia require extensive, post-processing before the data can be evaluated.  The science team is currently working on that analysis.

Research on Various Control Methods for Asian Clams at Lake Tahoe

In collaboration with various agencies of the Tahoe Basin, TERC and UNR are carrying out small-scaled pilot projects investigating two non-chemical methods to control Asian clam populations. To date, the techniques include the use of diver-assisted suction removal and bottom barriers. Diver-assisted suction removal consists of a vacuum system which removes the sediments containing the Asian clams from the bottom of the lake. Bottom barriers are sheets of various materials that are laid on top of clam beds with the intent of reducing oxygen under the barrier to levels that result in clam mortality. TERC and UNR researchers are observing and monitoring the impacts to Asian clam, native species and water quality as a result of these control strategies. These experimental efforts began in January 2009 and will continue through February 2010.

Additional Information:

Videos of Asian Clam in Lake Tahoe, June 2008 - September 2009:

Photos of Asian Clams in Lake Tahoe, April 2008 - September 2009:

Other Invasive Species Activities at Lake Tahoe

Watercraft Inspection Program

As of May 2009, all boats entering Lake Tahoe must be inspected for aquatic invasive species. For more information please see the Tahoe Resource Conservation District or Tahoe Regional Planning Agency watercraft inspection websites. Additional information is available at the Lake Tahoe aquatic invasive species information page.

Eurasian watermilfoil

In 2006, a partnership developed between the Tahoe Resource Conservation District Invasive Weed Program, Tahoe Regional Planning Agency, the California State Lands Commission, and the Divers Conservancy to begin locating and removing Eurasian watermilfoil, an aquatic invasive plant species, from Lake Tahoe. Trainings were held for volunteer scuba divers on how to hand remove this pest that harms water quality and native fish and plant communities. For more information, visit the Tahoe Resource Conservation District Aquatic Invasive Species website.

Warmwater Fishes (Bass and Bluegill) in Lake Tahoe

Researchers from the University of Nevada Reno (UNR) have been studying the distribution and movement of warmwater fish species around the nearshore of Lake Tahoe. Read about the ongoing studies and management efforts here. For additional details, visit the UNR Aquatic Ecosystems Analysis Laboratory website.

Quagga Mussel Research

Sudeep Chandra from UNR and TERC researchers collected Quagga mussels from Lake Mead and grew them in Lake Tahoe water in a laboratory for 51 days and found there is a possibility for Quagga mussel survival in Lake Tahoe with further research needed. Quagga mussels are not currently in Lake Tahoe and watercraft inspections are intended to reduce the risk of their introduction. For additional details, visit the UNR Aquatic Ecosystems Analysis Laboratory website.