A standardized design for quagga mussel monitoring in Lake Mead, Nevada-Arizona

The discovery of quagga mussels (Dreissena rostriformis bugensis) in Lake Mead, Nevada-Arizona, on January 6, 2007 is the first known occurrence of dreissenid species in the western United States. This study developed elements of a cost-effective and standardized quagga mussel-monitoring program for Lake Mead using preliminary data to arrive at statistically based numbers of sampling sites. To represent the abundance of adult/juvenile quagga mussels in Lake Mead’s heterogeneous floor with 95% confidence, a stratified simple random sampling design revealed a requirement of 41 samples from hard substrates (i.e., rocky areas) and 97 samples from soft substrates (i.e., sandy and muddy areas). A simple random sampling design demonstrated that 42 samples from the lake’s water column are necessary to represent veliger abundance with 95% confidence. Other important elements of the sampling program, such as standardization of protocols and processes and suggested data analyses, are discussed. The monitoring program, which is based on reconnaissance data, is intended to be optimized with data from its first year’s samples. The sample number-selection approach and the other elements of this plan can be easily implemented by lake managers and can also be adapted to other locations where dreissenid mussel monitoring is needed.