PHYSICAL HABITAT ASSESSMENT OF A REMAINING HIGH-BIODIVERSITY REACH OF THE UPPER YANGTZE RIVER, CHINA

Abstract

A scientific assessment on the physical habitat of a river in the only remaining free-flowing stretch in the Upper Yangtze, which has one of the world's highest fish diversity and is critically important. A field survey was tentatively conducted in this non-wadeable and data-limited reach (392 km river length, its 98.3% included the national protected area) of the Upper Yangtze River using a 200 kHz echosounder and a 600 kHz Acoustic Doppler Current Profiler in 2011. The water depth, acoustic backscatter characteristics of river bottom (hardness and roughness), and flowing characteristics (depth-averaged velocity (DAV), Froude number (Fr), and Reynolds number (Re)), which are popular in describing the habitat preference of aquatic organisms, were determined to describe the river habitat properties. The K-means clustering method using parameters river thalweg depth, DAV, and Fr categorized the 392 river segments into three biological meaningful habitat types, pool, run and riffle, with occupied 5.4%, 30.1% and 64.5%, respectively. Thus, the pool was the most comparatively rare habitat type and should be carefully protected. This study provides a fast and efficient method for assessing the habitat characteristics of a non-wadeable and data-limited river, moreover, the results supply fundamental information for better national protected reach management.