Technical Support Document for Conducting and Reviewing ... - Water

they are typically not present. 14 In each stratum, the mussel surveyor might choose a different
sampling design and sampling method. The stratified sampling design keeps the cost of the
survey low but ensures that high priority areas receive special attention.
Figure 3 displays an example of a stratified sample that divides the area into two zones: deep
water (highlighted gray) and shallow water (not highlighted). Sample locations are chosen
randomly with twice as many sample locations in the shallow water compared to the deep water.
Each sample location is indicated with an “x.” This example illustrates where a less expensive
method sampling method (e.g., wading) is used in the shallow water (and is, therefore, able to
cover more sampling area) and a more expensive sampling method (e.g., diving) is used in the
deeper water.
Figure 3: Example of stratified sampling design with random site selection (adapted from
Strayer and Smith 2003)
Complete Coverage
Complete coverage entails sampling with sufficient effort to collect all or most mussels in a
study area and is typically limited to salvage efforts or intensive research projects. Surveyors
should consider the habitat damage that may ensue from the use of this method. Complete
coverage assumes the same sampling method will be used throughout the entire study area. A
challenge with this sampling design is that, depending on the type of sampling method, the cost
of the mussel survey can be prohibitively expensive on all but the smallest streams. In large
waterbodies, complete coverage may prove too costly to undertake and even impractical, but in
smaller waterbodies, this approach may be a viable option due to the lower cost of surveying
smaller areas.
14 This approach assumes that the survey designer has a thorough working knowledge of the preferred types of
habitat where mussels are likely to be present. Designs based on habitat preferences should be used with caution
because even experienced malacologists can be surprised where mussels are found. One reviewer noted finding
fatmuckets in small pool under a bridge despite the rest of the stream being dry.
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