Validation of a fish-based index of biotic integrity for streams and rivers of central Mexico

An existing version of a fish assemblage-based index of biotic integrity (IBI) for the streams and rivers of west central Mexico was tested with independent data to validate its usefulness as a measure of ecosystem quality and to determine the geographic area where it is effective. Fish assemblages from 63 upland sites in 10 basins in central Mexico ( Armeria, Ameca, Coahuayana, Marabasco, Purificacion, Grande de Morelia, Grande de Santiago, Lerma, Balsas and Panuco) were assessed using the metrics and scoring criteria from the existing IBI and then compared with independent evaluations of habitat and water quality. IBI scores were congruent with habitat and water quality values in the Armeria, Purificacion and Marabasco basins, where the IBI was first developed, as well as in the adjacent Ameca and Coahuayana basins. We conclude that the IBI can be used without modification to assess environmental quality in non-coastal streams and rivers within these five basins. Further data are needed from the Grande de Morelia, Grande de Santiago and middle Lerma basins, but our results suggest that the existing IBI may also be effective here. However, the existing IBI does not consistently reflect habitat and water quality conditions in the Balsas and Panuco basins and must be modified before it can be applied there. Necessary modifications in the Balsas basin appear to be small and related primarily to changes in the scoring criteria for metrics. However, in the Panuco basin more substantive changes in the nature of the metrics are required. Changes in the IBI for these basins are proposed. The IBI is now validated for use in river monitoring, conservation and restoration efforts in 5 basins in west central Mexico and suggestions for its application in other basins are available here.