Annual variations of biotic integrity in the upper Yangtze River using an adapted index of biotic integrity (IBI)

Adaptive modification and use of Karrʹs index of biotic integrity (IBI) for the upper Yangtze River, including 12 metrics in five categories, have typically occurred in line with the data collected by 6-year commercial fisheries investigation. These investigations were undertaken annually in four sections of the Upper Yangtze main channel between 1997 and 2002. These four monitoring sections (Yibin – YB, Hejiang – HJ, Mudong – MD, and Yichang – YC) were selected because they represent the part of the river that will be covering a 1000 km stretch that includes the future Three Gorges Reservoir (TGR), upstream of the Three Gorges Dam (TGD), an area influenced by the construction of TGD. In addition, historical data were used to show changes in the watershed by comparison with field investigations recently. The biotic integrity of the four sections were calculated and classified into different levels annually for recognizing its spatial and temporal variations. It was observed that IBI scores were becoming lower diminishingly since 1997 in all the four sections. Because all the data were collected before the impoundment of the Three Gorges Reservoir, it is obvious that human activities, especially over-fishing, must be crucial factor instead of damming in the upper Yangtze River in that period.