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demonstrates how native fish faunal regions provide a baseline from which we can assess contemporary changes in fish community structure. Definition of changes in fish assemblages can provide an important metric for inclusion in an IBI. To date, much of our research has sought to find meaningful patterns of variation in the organization of biological communities. Through study of the aquatic biota and the chemical, physical, and climatic features of their environment, we have identified factors responsible for the distribution and/or abundance of aquatic biota in New Mexico. Information about community structure, and how it is affected by underlying physical, chemical, and climatic processes, will enable us to determine expected biotic community structure for an aquatic ecoregion. Expected community structure then provides a baseline against which sites can be compared. The ability to compare sites within an aquatic ecoregion or a fish faunal region will facilitate development of IBI's that are sensitive and objective indicators of accumulative stress at the community level of ecological organization. Appended reports (appendices 1, 2 and 3) represent stages in a study to determine how knowledge of fish-environment relationships can be employed in the development of IBI's for New Mexico streams. To be effective, an IBI must be applied to a geographical set of waters that have similar ecological features (Stewart and Loar, 1994) defined either on the basis of environmental or faunal site attributes. However, it remains to be determined if the aquatic ecoregion classification will provide an adequate framework, or, if one of the fish faunal region classifications will prove more useful. The concept of ecoregions has been developed as a means of stratifying the landscape (Omernik, 1986, 1987; Hughes and Larson, 1988). Ecoregions group naturally similar ecosystems and therefore group sites that have potential to be similar in aquatic chemistry, physical features, and biota (Hughes and Larson, 1988). The use of ecoregions can enhance the effectiveness of an ecological monitoring program because ecoregional division of sites can control variance which in turn makes it easier to detect potential problems (Stewart and Loar, 1994). However, an ecoregion landscape stratification only groups streams by their potential to support qualitatively similar biotic communities. It ignores variation between sites caused by endemic fish species. With respect to development of IBI's, it seems necessary that the indices include information about the native fish species endemic to different drainages. With respect to the ultimate objective of our project to use fishes in IBI's, it is unclear if any single set of fish faunal regions will provide a sufficient basis for landscape stratification. The large number of fish species faunal regions (12) may yield an insufficient number of sites within one or more regions such that statistical power to detect habitat impairment may be lost. The genera faunal regions (6) would yield better statistical power, but they would not provide an accurate perspective with respect to endemic species. The guild faunal regions provide an attractive subdivision of the landscape into meaningful ecological zones, but the presence of only 12 guilds among the native fish fauna in the state could prove problematic.