ABSTRACT
This chapter describes the situations where Index of Biotic Integrity (IBI) scores have been adjusted; and suggests additional modifications and criteria to further improve the responsiveness, sensitivity, and accuracy of the IBI. The application of the IBI in Ohio rivers and streams has been partly focused on assessing the effects of point source discharges on aquatic life, which during the late 1970s and early to mid-1980s were sometimes quite severe. Identification of stressors that are associated with impaired fish assemblages is an important benefit of biological monitoring. Habitat impacts result in shifts in the species and trophic composition except for total loss of habitat result in the significant reduction of species or severe reductions in abundance. Another situation where the IBI may require manual after-the-fact adjustment is at sites dominated by young-of-year (YOY) or juvenile fish. Schlosser and Angermeier and Karr have demonstrated the effect that YOY fish can have on the IBI and the subsequent interpretation of site quality.
