The Irrawaddy dolphins (Orcaella brevirostris) are an endangered species. Thus, up‐to‐date information on the distribution pattern of dolphins is critical for its proper management and conservation. Using a towed passive acoustic monitoring device, the distribution pattern of the Irrawaddy dolphins in the middle reaches of the Ayeyarwady River, Myanmar, was investigated during a vessel‐based survey between Mingun and Katha. This region was successively divided into segments 1–4 from upstream to downstream. Sixteen echolocation encounters, with a series of click trains separated by <8 min and 26 dolphin acoustic trajectories were recorded. The mean dolphin detection rate (animals/kilometer) across the four segments progressively increased from upstream to downstream. High relative abundance was observed in segment 4 (46%) and segment 1 (23%) which was consistent with findings from historical boat‐based visual surveys. The averaged interclick intervals of each click train in segment 2 and 4 was significantly shorter than that in segment 3, indicating that the dolphins in these segments frequently use shorter‐ranged biosonar. More frequent and consistent surveys with a systematic sampling track design that incorporates other factors and covering the whole distribution range along the Ayeyarwady River and at varied water levels are needed in the future.

中文翻译：

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缅甸伊洛瓦底江中游伊洛瓦底海豚（Orcaella brevirostris）分布模式的被动声监测

伊洛瓦底海豚（Orcaella brevirostris）是濒临灭绝的物种。因此，有关海豚分布模式的最新信息对其妥善管理和保护至关重要。使用拖曳式无源声波监测装置，在Mingun和Katha之间进行的基于船的调查中，调查了缅甸伊洛瓦底江中游地区伊洛瓦底江海豚的分布方式。从上游到下游，该区域被依次划分为1-4段。发生了16次回声定位，并记录了一系列间隔时间小于8分钟的喀哒声，并记录了26条海豚声线。从上游到下游，四个部分的平均海豚检测率（动物/公里）逐渐增加。在第4部分（46％）和第1部分（23％）中观察到较高的相对丰度，这与基于历史的船用视觉调查的结果一致。第2段和第4段中每个点击序列的平均点击间隔比第3段中的要短得多，这表明这些段中的海豚经常使用较短距离的生物声纳。未来需要更频繁，更一致的调查，并结合其他因素，并覆盖整个伊洛瓦底江和不同水位的整个分布范围。