Monday, May 26, 2008 - 4:30 PM
97

Effects of sample collector and taxonomist on macroinvertebrate sample accuracy and bias

Eric Dinger1, Mark R. Vinson1, and Charles P. Hawkins2. (1) The BugLab and Department of Watershed Sciences, Utah State University, 5210 Old Main Hill, Logan, UT 84322-5210, (2) Western Center for Monitoring and Assessment of Freshwater Ecosystems, Department of Watershed Sciences, and the Ecology Center, Utah State University, 5210 Old Main Hill, Logan, UT 84322-5210

Sample collector and taxonomist are two sources of variation that may affect the list of taxa and taxon numbers reported for a sample.  We evaluated collector bias by comparing samples collected by experienced (n = 3) and inexperienced (n = 4) collectors from the same reach on the same day.  On average, 4 more taxa were collected by experienced than inexperienced collectors, but there were no differences in two bioassessment measures: RIVPACS O/E values and the Hilsenhoff Biotic Index.  These results suggest that sampling experience may be important if the objective is to compile more complete taxonomic lists, but less so for bioassessments.  Taxonomist bias among 5 experienced (> 6M specimens identified) taxonomists was evaluated by comparing the identifications produced by each taxonomist. Their individual results were then compared with the “truth”, which was defined as the identifications that the 5 taxonomists later agreed by consensus were correct. Cluster analysis and NMDS ordination showed that samples correctly grouped according to sample replicate and not taxonomist, suggesting little bias associated with taxonomists.  Precision among bioassessment measures was high as demonstrated by narrow 95% confidence intervals for O/E values (1.059 – 1.131) and the Hilsenhoff Biotic Index (1.75 – 1.91).


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