| In this study, an adaptive fish index of biotic integrity (IBI) was developed to assess the influence of cascaded hydropower development on fish assemblages in Hongshui River, based on regional development characteristics and fish assemblages. The reference status and expected values were obtained from historical data on fish monitoring for the period 1982-1994. The monitoring data was taken from a fish community survey carried out in 2013 at 25 river sections, including three habitat types: 9 reservoir backwater sections, 6 reservoir sections and 10 tributary sections. The status value was obtained from the fish community survey of 2018. Based on the characteristics of fish assemblages in Hongshui River and the high-intensity hydropower development, ten metrics belonging to four attributes of fish assemblages (species richness and composition, tolerance, trophic structure and individual condition) were used to develop the biotic integrity index after preliminary evaluation. The ten metrics are expressed as ratios: (1) Total fish species collected to expected number of species, (2) Cyprinidae species to total fish species, (3) Bagridae species to total fish species, (4) Siluridae species to total fish species, (5) tolerant fish to total fish, (6) fish families collected to expected number of families, (7) omnivorous species to total species, (8) benthic insectivorous species to total species, (9) top carnivorous species to total species, (10) exotic fish species to total species. After weighting the metrics, IBI values were calculated and the range was 38-80 over the 25 sections in 2013, with a mean value of 62. The IBI score was classified as good at 24% of the sections, fair at 32% of the sections, and poor at 44% of the sections. From the perspective of habitat type, the IBI score for the tributaries was significantly higher than those in the reservoir and backwater areas, but the difference between the reservoir sections and backwater sections was not significant. The average IBI value for the 25 sections in 2018 was 64, slightly but not significantly higher than in 2013, and the biological integrity of all investigated sections was generally fair. |
