Description and classification of echolocation clicks of Indian Ocean humpback (Sousa plumbea) and Indo-Pacific bottlenose (Tursiops aduncus) dolphins from Menai Bay, Zanzibar, East Africa

Last modified: 
March 19, 2020 - 10:18am
Type: Journal Article
Year of publication: 2020
Date published: 03/2020
Authors: Liangliang Yang, Matt Sharpe, Andrew Temple, Narriman Jiddawi, Xiaomei Xu, Per Berggren
Journal title: PLOS ONE
Volume: 15
Issue: 3
Pages: e0230319

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 Splumbea and Taduncus 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 Splumbea clicks had significantly higher peak, centroid, lower -3 and lower -10 dB frequencies compared to Taduncus, 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 Splumbea and Taduncus, respectively. Both species were classified at a higher rate than expected at random, however the identified classifiers would only be useful for Taduncus monitoring. The frequency and bandwidth parameters provided most power for species classification. Further study is necessary to identify useful classifiers for Splumbea. This study represents a first step in acoustic description and classification of Splumbea and Taduncus in the western Indian Ocean region, with potential application for future acoustic monitoring of species-specific temporal and spatial occurrence in these sympatric species.

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