Several Forest Service samples were dominated by macroinvertebrate taxa not dominant in samples collected by other agencies for the same stream. This result may also be attributable to the sampling method, since the Forest Service does not limit its monitors to one location. Instead, it requires each monitor to obtain 125 or more individual organisms. As a result, Forest Service monitors may target certain microhabitats abundant with a particular taxa. An additional bias in this approach may result if monitors choose the larger, more visible organisms in their effort to reach the benchmark.
Net size is another issue.
The study showed that WDNR collected the greatest number of taxa from five of the six streams while the Forest Service collected the fewest. Another cause could be that WDNR generally sampled a larger area and may have encountered more microhabitats. Visual watershed survey results also varied significantly. No relationship could be found between physical watershed characteristics and the macroinvertebrate communities. Personal bias, differences in observations, and previous knowledge of the site are factors that may have influenced these results.