江西鄱阳湖湖口水域船舶通行对长江江豚发声行为的影响

江西鄱阳湖是长江江豚(Neophocaena phocaenoides)的重要栖息地,湖中栖息着约400头江豚。多年的观察表明,船舶交通是鄱阳湖中江豚面临的重要威胁之一。为了评估船舶通行对长江江豚发声行为的影响,尤其是了解船舶通行期间及其前后江豚的发声和行为特征,作者于2007年6月27日—7月1日在江西鄱阳湖湖口水域采用固定被动声学系统,即安装在监测点(29°42′38″N,116°11′11″E)的一套水下声学数据记录系统,对周边通行船舶的水下噪声及江豚声纳信号脉冲事件进行了定点监测和记录,并对所记录的数据进行了定量和统计分析。在整个监测的109h中,声学记录仪共记录到船舶494艘,江豚声纳脉冲串信号13413个。船舶出现与江豚出现存在弱的负相关关系(r=0.029,N=6550,P<0.05);船舶出现与江豚相邻脉冲串的时间差为(49.1±62.8)s,并且小于60s的占72.9%,同时,船舶经过之前和之后,该时间差未有显著性差异(Z=0.370,P>0.05);当有船舶经过时,江豚的发声频次显著降低(Z=10.050,P<0.05),但脉冲串持续时间、脉冲间间隔变化不显著(Z=0.275,P>0.05;Z=0.119,P>0.05);船舶通行之前和之后,江豚的发声频次、脉冲串持续时间、脉冲间间隔的差异性均不显著(χ2=5.255,P>0.05;χ2=3.511,P>0.05;χ2=5.155,P>0.05);在船舶经过时,江豚对游动方向没有明显的选择性(χ2=0.861,P>0.05)。基于分析结果推测,在狭窄水域中江豚躲避船舶干扰通常采取"临时性"策略,而非长距离逃避。由于鄱阳湖湖口水域水道相对狭窄,尽管研究的结果表明江豚对船舶有一定的敏感反应,但是在相对狭窄的水域中,江豚躲避船舶的行为难以充分表现。另外,江豚对该水域中高密度航行船舶的噪声可能存在一定的"适应性",导致当遭遇船舶时,江豚的声行为反应不十分强烈。因此,建议有必要在不同尺度的水体中采用声学数据记录仪继续开展类似的观察,以进一步了解江豚对船舶的行为响应,尤其是观察江豚躲避船舶的行为及发声特征。

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 < 0.05),The time difference between ships and adjacent click trains was 49.1s(±62.8s) and 72.9% of which were within 60s,and no significant difference was observed among pre-,during,and post-boat encounters(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 < 0.05),whereas both the duration of click trains and inter-click intervals did not show significant differences(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.