Applying an Index of Biotic Integrity Based on Great-River Fish Communities: Considerations in Sampling and Interpretation

This chapter examines several properties of the Large and Great River Index of Biotic Integrity (IBI) to provide guidelines for some of the more pressing questions regarding its application and interpretation. It addresses the following questions: What sampling decisions are relevant to minimizing contributions to inherent natural variation in the final IBI score? How is the IBI affected by sampling effort, and what is a minimum sampling-reach length required for an adequate assessment? and What are the effects of excluding select abundant species from IBI computations, and how important are these effects in interpreting the IBI? The last two questions concern problems that affect data collection and interpretation and are not specific to ecological assessment studies and IBI. Simon showed that detection of subtle differences at Large River sites required collection of a "representative" sample of the entire fish community. Assessment differences in Large and Great Rivers are often due to seasonal considerations.