Validation and application of a fish-based index of biotic integrity for small central Minnesota lakes

We evaluated the performance of an index of biotic integrity (IBI) based on 16 fish population metrics of three types: species richness, community assemblage, and trophic composition. Two sets of central Minnesota lakes independent from the original set of lakes used to develop the IBI model were used to validate it. One set of lakes (n = 15) had physical features similar to those used to develop the IBI, while the other set (it = 22) averaged 9 in shallower with 28% more littoral area. We used general linear models to test whether the relationships between IBI or individual metric score and indicators of lake quality (trophic state, floristic quality, or surrounding land use) were the same or differed for the original IBI data set and each new data set. Responses were similar among all data sets, lake IBI scores and individual metrics reflecting differences in land use, trophic state, and aquatic habitat. Sensitivity of individual metrics to different measures of stress varied, supporting the need for a multimetric approach when assessing the biotic integrity of lakes. Index of biotic integrity scores were most highly correlated with trophic state (rho = -0.80). Our results support the validity of the original fish-based IBI as a standardized method for quantitatively measuring the condition of fish assemblages and implied overall biotic integrity of small central Minnesota lakes. As with any model, however, continued evaluation is recommended, especially when applying this IBI to lakes with different physical, chemical, or biological characteristics.