Fish preference for hydraulic habitat in typical middle reaches of Yangtze River, China

This study presents a method of combining hydroacoustics and hydraulic data to estimate fish preference in a large and rapidly flowing river system. A typical middle reach of the Yangtze River with three islands and two wandering sections was taken as the research object to interpret schools of fish with different sizes and densities for their preference of physical habitat features such as water depth and velocity by using Geographic Information Systems (GIS). Fish density and size were determined based on the hydroacoustic data, and hydraulic variables were simultaneously collected using an Acoustic Doppler Current Profiler (ADCP) system. Results show that fish sizes are correlated with water depth and velocity and that fish density correlated only with water depth. Small fish prefer high water depth average velocity (WDAV), lower vertical average velocity (VAV), deep water, as well as a wide depth and velocity range; large fish prefer low WDAV, high VAV, deep water, and a narrow depth and velocity range. High fish densities appear around islands and areas with deep water. The results show that large fish may be sufficiently strong enough to select their preference for water depth and velocity. Areas of deep water can provide broad velocity diversity and more space to accommodate fish. The island littoral zone could provide a variety of habitats with a diverse pattern of depth and velocity for fish. This study provides a contributive method for the field habitat suitability assessment for fish.