Biological assessment of some wadable rivers in Turkey using fish data: a statistical approach

In this study, we present a preliminary multimetric fish-based index (Index of Biotic Integrity; IBI) developed using a reliable statistical approach for some wadable rivers in four river basins in Turkey. Fish and abiotic data were collected according to standard methods. A total of 33 fish species were caught in the whole sampling area. Fish species were assigned to different guilds. Candidate metrics were selected from the literature and metric values were calculated. Sampling sites were preclassified into habitat status classes representing various levels of anthropogenic pressures. The responsivity of the candidate metrics was tested with linear mixed regression models. Correlation tests were performed to avoid redundancy among responsive metrics. Finally, six metrics (Shannon–Wiener diversity index, relative percentage of intolerant, invasive alien, invertivorous, and rheophilic individuals and number of benthic species) were selected. Selected metrics were scored using the continuous scoring approach. The IBI values were calculated by summing up the final metric scores. Then the IBI values were transformed into ecological quality ratio (EQR) values. We did not observe a “high” integrity class in the whole sampling area. The index was proven to be responsive to anthropogenic pressures and environmental variables tested using several approaches, including correlation analysis, graphical examination of the final metrics patterns and comparing the EQR classes with the habitat status assignment. The index, with minor adjustments, has a potential to be used as an assessment tool for different data sets in wadable rivers in Turkey. Furthermore, the statistical design used here can be applied to other river basins in Turkey or any other country with similar data limitations.