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

An existing version of a fish assemblage-basedindex of biotic integrity (IBI) for the streamsand rivers of west central Mexico was testedwith independent data to validate itsusefulness as a measure of ecosystem qualityand to determine the geographic area where itis effective. Fish assemblages from 63 uplandsites in 10 basins in central Mexico(Armería, Ameca, Coahuayana, Marabasco,Purificación, Grande de Morelia, Grande deSantiago, Lerma, Balsas and Pánuco) wereassessed using the metrics and scoring criteriafrom the existing IBI and then compared withindependent evaluations of habitat and waterquality. IBI scores were congruent withhabitat and water quality values in theArmería, Purificación and Marabascobasins, where the IBI was first developed, aswell as in the adjacent Ameca and Coahuayanabasins. We conclude that the IBI can be usedwithout modification to assess environmentalquality in non-coastal streams and riverswithin these five basins. Further data areneeded from the Grande de Morelia, Grande deSantiago and middle Lerma basins, but ourresults suggest that the existing IBI may alsobe effective here. However, the existing IBIdoes not consistently reflect habitat and waterquality conditions in the Balsas and Pánucobasins and must be modified before it can beapplied there. Necessary modifications in theBalsas basin appear to be small and relatedprimarily to changes in the scoring criteriafor metrics. However, in the Pánuco basinmore substantive changes in the nature of themetrics are required. Changes in the IBI forthese basins are proposed. The IBI is nowvalidated for use in river monitoring,conservation and restoration efforts in 5basins in west central Mexico and suggestionsfor its application in other basins areavailable here.