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US Fish & Wildlife Service FieldNotes
NEVADA FWO: Working Group Focused on Control Invasive Asian Clams in Lake Tahoe
Region 8, March 31, 2010

by Steve Chilton, Nevada FWO
Asian clam (Corbicula fluminea) populations in Lake Tahoe have expanded greatly since they were first detected in 2002.  At that time populations were sparse and not densely occupied.  Their growth and expansion in Lake Tahoe, coupled with filamentous green algal blooms in 2008 that have been linked to the increased populations triggered a significant effort by many agencies and research universities to control source and satellite populations.  While the clams can produce immediate problems, such as algae blooms, we are more concerned that they could chemically alter Tahoe's waters to allow successful invasion of other non-native species such as quagga or zebra mussels.

 Since 2008, the multi-agency Asian clam working group (ACWG) has been actively planning and implementing a pilot project to determine the most efficient treatment strategies to control Asian clam populations in Lake Tahoe.  In 2009 a strategy was implemented, incorporating the placement of small scale (10 ft x 10 ft plots) experimental applications of 45 mil rubber pond liner sheets.  

The Asian clam working group is comprised of members from the Tahoe Resource Conservation District (TRCD), US Fish and Wildlife Service (USFWS), Lahontan Regional Water Quality Control Board (LRWQCB), Tahoe Regional Planning Agency (TRPA), California Department of Parks and Recreation (CDPR), Nevada Division of State Lands (NDSL), Nevada Division of Wildlife (NDOW), UC Davis Tahoe Environmental Research Center (UCD-TERC) and University of Nevada-Reno (UNR). 

These rubber bottom barriers created a zero dissolved oxygen environment underneath the sheet, and after an approximate 30-day period at peak summer lake temperatures (16-19 °C) caused Asian clam and other benthic macroinvertebrate mortality. The small scale pilot project provided the ACWG with valuable information and the pilot is being scaled-up in July of 2010 to 10 ft x 100 ft sheets of this rubber material covering two half-acre plots.   This up-scaled pilot will provide needed information on the logistics and cost effectiveness of large-scale implementation, impacts to Asian clam and other benthic macroinvertebrates, and the recolonization rates of these species on a large scale. 

The bottom barriers will be installed during July 2010 and will remain for a 50 day period.  During this time, field delineation of the project area site, baseline condition sample collection, delivery of rubber materials from land to field site, placement of rubber material at field site (underwater), removal and decontamination of the barrier material and permit monitoring requirements (primarily water quality) will occur.  Post-treatment monitoring of the sites will continue throughout 2011.  Several domestic drinking water intakes are located adjacent to the implementation sites and those water purveyors have been continually involved in the planning and implementation of this project. 

A test run of the bottom barrier deployment apparatus (designed by UC Davis engineers) was conducted on March 19, 2010, at Sand Harbor in Lake Tahoe.  The test run showed that deployment and retrieval of one 10 ft x 100 ft section could be accomplished with little complication.   

The coalition of agencies involved in this project through the Lake Tahoe AIS Coordination Committee have been working together since 2007 to prevent new introductions of AIS, limit the spread of existing AIS populations, and abate harmful ecological, economic, social and public health impacts resulting from AIS. The group developed the Lake Tahoe Region Aquatic Invasive Species Management Plan in 2009.  The plan was signed by Governor Gibbons of Nevada and California Governor Schwarzenegger and approved by the national Aquatic Nuisance Task Force at their meeting in November 2009.  The work has been funded in part by appropriated FWS funds and Southern Nevada Land Management Act funds administered by the FWS.



Contact Info: Scott Flaherty, , Scott_Flaherty@fws.gov