First data on an Index of Biotic Integrity (IBI) based on fish assemblages for the assessment of the impact of deforestation in a tropical West African river system

African tropical rainforests, and especially their freshwater biodiversity, are seriously threatened by ongoing industrial deforestation. Sound ecological management is needed to ensure the sustainability of these resources. For this purpose, an index of biotic integrity (IBI), based on fish assemblage characteristics, is developed in this paper. It is used to quantify the impact of industrial deforestation on freshwater biodiversity. Data from 30 non-impacted sites were used to develop a series of compositional, structural and functional metrics that reflect sites with a high biotic integrity, i.e. what a stream-fish community should look like in the absence of human perturbation. These data were compared to data collected from sites subjected to substantial forest watershed loss, in order to identify those IBI metrics that best distinguish streams with high and low biotic integrity. The overall IBI scores reflected the quality of the watershed conditions. In addition, there was a close agreement between an index of environmental quality, based on water and habitat quality and the IBI scores, suggesting that the different biological responses of the fish assemblages (observed differences in the IBI scores) were indicative of differences in physico-chemical quality of the streams. The ability of the proposed IBI to index water resource degradation, due to deforestation, suggests that it can be used as a tool for biological monitoring. However, more consistent and comprehensive data are needed to further refine the IBI, especially the assignment of integrity classes and metric threshold values.