Effects of stream order and ecoregion on variability in coldwater fish index of biotic integrity scores within streams in Wisconsin

Most indices of biotic integrity (IBIs) are designed to represent the biological condition of individual sampling locations in a river or stream. Characterizing the biological condition of an entire stream is often of interest and requires data from multiple sites. The representativeness of these data depends on the variability in the scores between sampling locations. We compared the variability in IBI scores using two parameters whose values can be obtained easily - stream size and ecoregion. The variability in IBI scores tended to be greater in smaller Wisconsin streams (first and second order) than in larger ones (third and fourth order) but there was no difference in the variability between ecoregions. Thus, in order to confidently characterize the true mean IBI score for a smaller stream, essentially a census of the entire stream would be required. In order to confidently characterize the mean IBI score of a larger stream, approximately six scores are necessary, which is equivalent to one station per 2 km of stream given the mean length of third and fourth order streams in Wisconsin.