Under increasing anthropogenic pressure, species with a previously contiguous distribution across their ranges have been reduced to small fragmented populations. The critically endangered Yangtze finless porpoise ( Neophocaena asiaeorientalis asiaeorientalis), once commonly observed in the Yangtze River-Poyang Lake junction, is now rarely seen in the river-lake corridor. In this study, static passive acoustic monitoring techniques were used to detect the biosonar activities of the Yangtze finless porpoise in this unique corridor. Generalized linear models were used to examine the correlation between these activities and anthropogenic impacts from the COVID-19 pandemic lockdown and boat navigation, as well as environmental variables, including hydrological conditions and light levels. Over approximately three consecutive years of monitoring (2020-2022), porpoise biosonar was detected during 93% of logged days, indicating the key role of the corridor for finless porpoise conservation. In addition, porpoise clicks were recorded in 3.80% of minutes, while feeding correlated buzzes were detected in 1.23% of minutes, suggesting the potential existence of localized, small-scale migration. Furthermore, both anthropogenic and environmental variables were significantly correlated with the diel, lunar, monthly, seasonal, and annual variations in porpoise biosonar activities. During the pandemic lockdown period, porpoise sonar detection showed a significant increase. Furthermore, a significant negative correlation was identified between the detection of porpoise click trains and buzzes and boat traffic intensity. In addition to water level and flux, daylight and moonlight exhibited significant correlations with porpoise biosonar activities, with markedly higher detections at night and quarter moon periods. Ensuring the spatiotemporal reduction of anthropogenic activities, implementing vessel speed restrictions (e.g., during porpoise migration and feeding), and maintaining local natural hydrological regimes are critical factors for sustaining porpoise population viability.
长江江豚（ Neophocaena asiaeorientalis asiaeorientalis）仅分布于长江中下游干流以及鄱阳湖和洞庭湖，是我国特有的珍稀濒危水生哺乳动物。在历史上他们曾频繁出现在长江和鄱阳湖交汇的湖口水域，但是随着湖口水域2座跨湖大桥的建成和运营，近些年在该水域的考察却不见其踪迹。该研究采用被动声学监测方法，对湖口水域长江江豚的声呐活动规律进行了监测。进一步采用广义线性模型研究了疫情封控和船舶航运等人为活动以及水位和水流量等水文条件和光线水平等环境变量对其声呐活动的影响。在近三年的定点声学监测(2020-2022)中，江豚声呐信号在每天的监测概率是93%每分钟的监测概率是3.80%，与捕食相关的声呐信号在每分钟的监测概率是1.23%，这表明湖口水域仍然是江豚的重要活动水域，同时小规模的江豚江湖间迁徙可能仍然存在。此外，疫情封控和船舶航运等人类活动、水位和水流量以及光线水平等环境因子对长江江豚声呐活动规律的昼夜、季节性和年度间的节律有显著的影响。在疫情封控期间，江豚声纳信号的监测率显著高于非封控期。此外江豚的声呐信号监测率与船舶航运情况呈显著负相关。除了水位和水流量外，光线条件和月相变化也与江豚的声纳活动规律有显著的相关关系，并且在夜间、上弦月和下弦月期间江豚的声纳监测率显著高于白天以及其它的月相期。降低人类活动尤其是船舶航运对江豚的干扰，例如开展船舶的限航与限速管理以及通过生态调度维持和恢复水体原有的水文情势对该水域的江豚保护至关重要。.
Keywords: Boat traffic; Hydrological regime; Light level; Pandemic lockdown; Poyang Lake; Yangtze River; Yangtze finless porpoises.