INDEX OF BIOTIC INTEGRITY BASED ON FISH ASSEMBLAGES FOR THE CONSERVATION OF STREAMS AND RIVERS IN WEST-CENTRAL MEXICO

The rivers and streams of west-central Mexico are becoming increasingl y degraded and warrant expanded conservation efforts. We have develope d an index of biotic integrity based on fish assemblage characteristic s to aid in the preservation of the biological integrity and biodivers ity of these waters Our version is an adaptation of previous versions of the index of biotic integrity, which have proven effective in envir onmental assessment and monitoring in the United States and elsewhere. It consists of 10 fish assemblage attributes, termed metrics, that ar e related to environmental quality, ecosystem integrity, and biodivers ity in west-central Mexican streams and rivers: number of native speci es, percentage of benthic species, number of water column species, num ber of sensitive species, percentage of tolerant species, percentage o f exotic species, percentage of omnivores, percentage of native livebe aring species, relative abundance, and percentage of diseased or defor med. Data on fish communities from 27 sites on streams and small river s in the vicinity of the Sierra de Manantlan, southwestern Jalisco, an d in the upper Rio Duero basin northern Michoacan, were used to develo p expectations and scoring criteria for each metric. The index value f or a site was the sum of the scores for the 10 metrics. Index values a nd associated ratings of biotic integrity for the 27 sites corresponde d closely with independent ratings based on habitat and water quality. However, additional tests of the index with independent data and refi nement of metrics and scoring criteria are clearly warranted. The inde x shows promise for identifying key watersheds for the protection of i ntact native biotic communities and individual endangered and threaten ed species and for the long-term monitoring and evaluation of biodiver sity and ecosystem integrity in the streams and rivers of west-central Mexico. Our version could serve as a model for the development of sim ilar indices for other regions and other types of aquatic ecosystems i n Mesoamerica.