ABSTRACT
The Index of Biotic Integrity (IBI) incorporates fish-assemblage attributes (called metrics) that reflect predominant anthropogenic effects on streams. Each IBI metric describes a particular taxonomic, trophic, reproductive, or tolerance feature of the assemblage. An IBI score represents comparisons between metric values at a sample site and those expected under conditions least affected by anthropogenic disturbance. To set appropriate metric criteria for a geologically and hydrologically complex area (e.g., the state of Virginia), one should compare how fish metrics vary with stream size relative to how they differ across regions, drainages, and relevant environmental gradients within each. This chapter expands on the results of Smogor, who examined how potential IBI metrics varied at least-disturbed sites among physiographies, ecoregions, and drainage groups to determine the most appropriate regional framework for a statewide IBI in Virginia. A major advantage of adjusting metric criteria for stream size is that adjusted criteria increase the metric’s ability to reflect anthropogenic rather than stream-size effects.
