Aquatic

Lake Tahoe Aquatic Invasive Species sub-program

The Tahoe RCD is a part of the Lake Tahoe Aquatic Invasive Species Working Group (LTAISWG).  This group was formed to better share resources and information, standardize methods for treatment and data collection, perform coordinated education and outreach activities, obtain grants, and organize effective control efforts.

Aquatic Invasive Species harm Lake Tahoe by:

1.  Severely decreasing recreational uses, such as swimming, boating, water-skiing, and fishing

2.  Degrading boats by clogging propellers and cooling intakes

3.  Facilitating invasions of other non-native species

4.  Altering nutrient cycles and increasing algal growth in the lake by adding phosphorous to the water column thus contributing to clarity decline

Native vs. Invasive Mollusk Identification Key

Asian Clam Pilot Removal Project

The Asian clam pilot removal project started in February 2009 with the objective of finding the most efficient method of controlling the existing clam populations. This project is a collabortive multi-agency effort utilizing various funding sources. A final report will be available early 2010.

Preliminary Project Findings:

1) Dissolved oxygen, under the bottom barriers, reached zero after an average of 36 hours

2) All of the clams in the samples migrated vertically within the sediment column under the barriers.

3) 100% clam mortality was reached after an average of 28 days

4) Impact to the native benthic community was significant

5) Bacteria counts are relatively high underneath the barriers, but decrease as you move away from them.

6) There is an abundance of Cladophora (filamentous algae) in Marla Bay, as

compared to the Zygnema sp. and Spirogyra sp. Compared to that observed last year. The bloom last year continued into October, there is still some time yet to determine the seasonal flux of this bloom.

Additional Findings:

1) Underwater Autonomous Vehicle (Gavia) surveys were conducted and produced preliminary results. This survey was a lakewide effort to determine the extent of Asian clam populations. The Gavia primarily surveyed the near shore (transects at 5m depth), but did detect a deep water population off Nevada Beach. This population was determined to be at a depth of 80m. Several ‘new’ populations of Asian clams were detected and include, Emerald Bay, Camp Rich and Glenbrook. Ground-truthing of the data needs to be conducted before a complete analysis can be completed.

Next steps:

1)      Pursue a ‘scale-up’ of the pilot project to management level, large scale operation

2)      Determine relationship between deep water populations and near shore populations

3)      Determine re-colonization of native invertebrates vs Asian clams

4)      Explore Asian clam removal opportunities in Emerald Bay

Aquatic Weed Removal Project