School of Natural and Environmental Sciences, Newcastle University, Newcastle upon Tyne, England, United Kingdom.
Key Laboratory of Underwater Acoustic Communication and Marine Information Technology of the Ministry of Education, College of Ocean and Earth Sciences, Xiamen University, Xiamen, China.
PLoS One. 2020 Mar 13;15(3):e0230319. doi: 10.1371/journal.pone.0230319. eCollection 2020.
Passive acoustic monitoring (PAM) is a powerful method to study the occurrence, movement and behavior of echolocating odontocetes (toothed whales) in the wild. However, in areas occupied by more than one species, echolocation clicks need to be classified into species. The present study investigated whether the echolocation clicks produced by small, at-risk, resident sympatric populations of Indian Ocean humpback dolphin (Sousa plumbea) and Indo-Pacific bottlenose dolphin (Tursiops aduncus) in Menai Bay, Zanzibar, East Africa, could be classified to allow species specific monitoring. Underwater sounds of S. plumbea and T. aduncus groups were recorded using a SoundTrap 202HF in January and June-August 2015. Eight acoustic parameters, i.e. -10 dB duration, peak, centroid, lower -3 and lower -10 dB frequencies, and -3 dB, -10 dB and root-mean-squared bandwidth, were used to describe and compare the two species' echolocation clicks. Statistical analyses showed that S. plumbea clicks had significantly higher peak, centroid, lower -3 and lower -10 dB frequencies compared to T. aduncus, whereas duration and bandwidth parameters were similar for the two species. Random Forest (RF) classifiers were applied to determine parameters that could be used to classify the two species from echolocation clicks and achieved 28.6% and 90.2% correct species classification rates for S. plumbea and T. aduncus, respectively. Both species were classified at a higher rate than expected at random, however the identified classifiers would only be useful for T. aduncus monitoring. The frequency and bandwidth parameters provided most power for species classification. Further study is necessary to identify useful classifiers for S. plumbea. This study represents a first step in acoustic description and classification of S. plumbea and T. aduncus in the western Indian Ocean region, with potential application for future acoustic monitoring of species-specific temporal and spatial occurrence in these sympatric species.
被动声学监测（PAM）是一种强大的方法，可以研究野生回声定位齿鲸（齿鲸）的发生、运动和行为。然而，在一个以上物种占据的区域，需要对回声定位咔哒声进行物种分类。本研究调查了东非桑给巴尔梅奈湾（Menai Bay）的印度洋驼背豚（Sousa plumbea）和印太瓶鼻海豚（Tursiops aduncus）小、处于危险中的、共生的种群产生的回声定位咔哒声是否可以进行分类，以便进行特定物种的监测。2015 年 1 月和 6 月至 8 月，使用 SoundTrap 202HF 在 S. plumbea 和 T. aduncus 群体中记录水下声音。使用 -10 dB 持续时间、峰值、质心、较低的 -3 和较低的 -10 dB 频率以及 -3 dB、-10 dB 和均方根带宽等 8 个声学参数来描述和比较这两个物种的回声定位咔哒声。统计分析表明，S. plumbea 的咔哒声峰值、质心、较低的 -3 和较低的 -10 dB 频率明显高于 T. aduncus，而持续时间和带宽参数在两种物种之间相似。随机森林（RF）分类器用于确定可用于从回声定位咔哒声中对两种物种进行分类的参数，S. plumbea 和 T. aduncus 的正确物种分类率分别为 28.6%和 90.2%。这两个物种的分类率都高于随机预期，但确定的分类器仅对 T. aduncus 监测有用。频率和带宽参数为物种分类提供了最大的能力。需要进一步研究以确定 S. plumbea 的有用分类器。本研究代表了在西印度洋地区对 S. plumbea 和 T. aduncus 进行声学描述和分类的第一步，具有在这些共生物种中进行特定时空出现的未来声学监测的潜在应用。
