DataSheet_1_Click-click, who’s there? Acoustically derived estimates of sperm whale size distribution off western Ireland.pdf

Understanding the structure of populations is a critical element to the establishment of management and conservation measures. Sperm whales Physeter macrocephalus are characterised by a demographic spatial segregation, associated with a conspicuous sexual dimorphism reflected in their vocalisations. These characteristics make acoustic techniques very relevant to the study of sperm whale population structure, especially in remote, challenging environments. The reliability of using inter-pulse intervals of sperm whale clicks to infer body size has long been verified and extensively used. We provide the first size structure estimates of the sperm whale population in an area where assumptions on population structure mainly relied on sparse observations at sea, whaling records and stranding data. Over 10,000 hours of acoustic data collected using both static acoustic recorders and towed hydrophone arrays in Irish offshore waters were processed using a machine learning-based tool aimed at automatically extracting inter-pulse intervals from sperm whale recordings. Our analyses suggested that, unlike previously thought, large males would not account for the majority of the animals recorded in the area. We showed that adult females/juvenile males (length 9-12 m) were predominant, accounting for 49% (n = 788) of the number of individuals recorded (n = 1,595), while the proportions of immature individuals (length<9 m) and adult males (length >12 m) were well balanced, accounting for 25% (n = 394) and 26% (n = 413) of the recorded whales, respectively. Our data also suggested some size segregation may be occurring within the area, with smaller individuals to the south. The implications of such findings are crucial to the management of the population and provide an important baseline to monitor changes in population structure, particularly relevant under changing habitat conditions.

解析种群结构是制定种群管理与保护措施的核心环节。抹香鲸（*Physeter macrocephalus*）具有典型的种群空间分化特征，其发声行为亦体现出鲜明的性别二态性。这些特性使得声学技术成为研究抹香鲸种群结构的重要手段，尤其适用于偏远且环境复杂的海域。长期以来，利用抹香鲸咔嗒声的脉冲间隔推断个体体型的方法，其可靠性已得到验证并被广泛应用。此前该区域的抹香鲸种群结构推测主要依赖零散的海上观测、捕鲸记录及搁浅数据，本研究首次基于声学数据给出了该区域抹香鲸种群的体型结构估算结果。本研究对爱尔兰近海水域中通过固定式声学记录仪与拖曳式水听器阵列采集的逾10000小时声学数据进行处理，所用工具为一款基于机器学习开发的自动提取抹香鲸发声脉冲间隔的程序。分析结果显示，与此前学界的认知不同，大型雄性个体并非该区域记录到的抹香鲸主体。研究表明，成年雌性与亚成年雄性（体长9~12米）为该区域的优势类群，在总计1595个记录个体中占比49%（n=788）；未成熟个体（体长<9米）与成年雄性（体长>12米）的占比则较为均衡，分别为25%（n=394）与26%（n=413）。本研究数据同时显示，该区域可能存在一定程度的体型空间分化，小型个体多分布于南部海域。上述研究结果对抹香鲸种群管理具有重要指导意义，同时可为种群结构变化的长期监测提供关键基线，在栖息地环境不断变化的当下尤为重要。