The Impact of Tongling Yangtze Bridge on the Dolphins'' Habitats
铜陵长江大桥对豚类栖息地的影响

The Tongling River Section, with many zigzag river channel and well developed sandbars, is one of the few river sections of the Yangtze River where the Baiji (\%Lipotes vexillifer\%) can be found usually, and Yangtze finless porpoise (\%Neophocaena phocaenoides asaeorientalis\%) concentrated with relatively high density. However, along with the increase and expansion of human activities, especially the construction of anti flood, main dams and bridges, the habitat of the Yangtze dolphins has been fragmented and isolated. In order to preserve the critically endangered Baiji endemic to China, in situ conservation must be enforced besides ex situ conservation effort, based on the experience and lessons from the domestic and foreign conservation practices of endangered animals. According to 18 ecological surveys in the Tongling River Section from 1987 to 2001, the sighting per unit of effort (individual/day) in river section Chengdezhou Meigeng (henceafter the Bridge Section) was estimated based on the survey days and individual numbers observed. The water depth (m) and velocity (m/s) in the Bridge Sections when the water level was 8.5 m at Gaocheng, Wushong, were measured in 1989 and 2001. The influences of the alteration of river channel and sandbars on the Baiji and the Yangtze finless porpoises were analyzed according to the change of the maximum width, angles, refractive index, and ratio of width/length of the branch stream.Our studies showed that there was only a small change in the water surface, branch streams, beaches, and water flows after bridge construction. Thus, the Bridge River Section still has the necessary water conditions for the dolphins' inhabiting. However, the Tongling Yangtze Bridge slightly affected the river channel and sandbars in the upper stream and downstream of the Bridge waters. There are many newly silted beaches, and the difference between water convergence and diffluence became unclear. For this reason, the discovery rates of Baiji and finless porpoises in this river section decreased significantly. No Baiji was found around the water of Yangshanji and Heyue islet as surveying in field, where Baiji was feeding along Taiyangzhou to Meigeng. To sum up, the decrease of SPUE in the Bridge Section for the Baiji is consistent with the rapid population decline for Baiji, however, the derease in the Meigeng is not obvious. Rather, in some sections, e.g. Meigeng and Henggang, the SPUE of Yangtze finless porpoise increased to some degree, which is probably in relation to the change of riverbed and water flow caused by the bridge piers. In order to preserve the Baiji and the Yangtze finless porpoises and their habitat in the core area in the Tongling River Dolphins Reserve (i.e.Meigeng and Henggang), it is urgently need to prohibit any illegal activities of fishing operations and sand pickings, and the speed of ships and boats in this waters must be restricted strictly.