EFFECTS OF VESSEL TRAFFIC ON THE ACOUSTIC BEHAVIOR OF YANGTZE FINLESS PORPOISES (NEOPHOCAENA PHOCAENOIDES ASIAEORIENTALIS) IN THE CONFLUENCE OF POYANG LAKE AND THE YANGTZE RIVER: USING FIXED PASSIVE ACOUSTIC OBSERVATION METHODS

The Poyang Lake in Jiangxi Province is an important habitat of the Yangtze finless porpoises. There are about 400 individuals of porpoise inhabiting in the lake. The surveys conducted in recent years indicated that one of the threats faced by the animals might be from the heavy boat traffic in the lake. For estimating the possible negative effects of the boat traffic on the animals in the lake, an acoustic observation with the aid of an underwater acoustic data logger was conducted in the confluence of Poyang Lake and the Yangtze River from 27 June to 1 July 2007. In this observation, the passive acoustic data logger was fixed at the monitor station (latitude: 29°42′38″ N, longitude: 116°11′11″ E) and was deployed to monitor and record continually periphery underwater noise of the boat traffic and pulse events of sonar signals of porpoises that presented within 300 m around the station. During the 109h of investigation, 494 vessels and 13,413 click trains were recorded by the logger. These data were analyzed by using a customized program developed on Igor Pro 5.01 (WaveMetrics, USA), and the results were used for investigating the effects of boat traffic on the acoustic behavior of finless porpoises in the waters. A weak negative correlation between the presence of porpoises and ships was observed (r = -0.029, N = 6550, P Z = -0.370, P > 0.05). The phonation rate of click trains recorded by the acoustic data logger declined significantly during the vessel present (in-noise) situations (Z = -10.050, P Z = -0.275, P > 0.05; Z = -0.119, P > 0.05). No significant differences were observed in the phonation rate of click trains, the duration of click trains, as well as the inter-click intervals of the porpoises among pre-, during, and post-boat encounters (χ2= 5.255, P > 0.05; χ2= 3.511, P > 0.05; χ2= 5.155, P > 0.05). The porpoises did not have any preference for swimming direction during the encounters of ships (χ2= 0.861, P > 0.05). Although the porpoises have certain sensitivity in behavioral responses to presence of boats, the animals did not show distinct avoiding behaviors when encountering boats in the waters with little width. The results of this study seem to indicate that the porpoises in the narrow channel usually take “temporary” strategy to response the disturbance from the boat traffic. Additionally, boat traffic is the most frequently encountering of the porpoises in the waters, and it might result in the porpoises have certain “acoustic adaptation” to its presence, and therefore the animals do not show intensive acoustic responses to the noise from the boat traffic. It will be needed to conduct more observations on the behavior responses of the porpoises to boat presence in different waters with different size by using the acoustic observation system, and make further estimation about the avoiding behavior and acoustic responses of the porpoises to boat traffic.