Hukou area is an important place which connects Poyang Lake and Yangtze River, and is one of the hot spots of Yangtze finless porpoise’s (Neophocaena phocaenoides asiaeorientalis) distribution. However, the survival of porpoises in this area may have been affected by the increasing of human activities, such as sand digging and bridge constructions. This study investigates the group size, distribution and movement pattern of the porpoises in Hukou area by using mobile and stationary acoustic observations. The main results and conclusions are summarized as follows:
4 mobile acoustic surveys were carried out around Hukou area in May and November 2007, February and December 2008, respectively. And 89, 62, 58 and 65 porpoises were recorded, respectively. The result indicates that porpoise distribution in this area probably presents a seasonal pattern. The low density of porpoises between Poyang highway and Poyang railway bridges may be caused by the barriers of these two bridges.
Between November 2007 and October 2008, we deployed a stationary data logger between the Highway Bridge and Railway Bridge to observe the presence and movement pattern of porpoises. Comparing to dry season, there were more animals in the study site during flood season and trend to stay longer time. We assumed that porpoise may seasonally migrate between Yangtze River and Poyang Lake.
Odontocetes' sonar signals can be used to assess anthropogenic disturbance, such as boat traffic. The results of this study show that the number of click trains recorded by the acoustic data logger declined when the ships were passing by. The duration of click trains and inter-click intervals didn't show significant differences when the ships kept closing. The porpoises didn't have any preference for swimming direction during the disturbance of ships.