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A Complexity-Entropy Based Approach for the Detection of Fish Choruses

1
Underwater Acoustic Laboratory, Department of Engineering Sciences and Ocean Engineering, National Taiwan University, Taipei 106, Taiwan
2
Department of Life and Environmental Science, Polytechnic University of Marche, 60131 Ancona, Italy
*
Authors to whom correspondence should be addressed.
Entropy 2019, 21(10), 977; https://doi.org/10.3390/e21100977
Received: 3 September 2019 / Revised: 24 September 2019 / Accepted: 30 September 2019 / Published: 6 October 2019
(This article belongs to the Section Complexity)
Automated acoustic indices to infer biological sounds from marine recordings have produced mixed levels of success. The use of such indices in complex marine environments, dominated by several anthropogenic and geophonic sources, have yet to be understood fully. In this study, we introduce a noise resilient method based on complexity-entropy (hereafter named C-H) for the detection of biophonic sounds originating from fish choruses. The C-H method was tested on data collected in Changhua and Miaoli (Taiwan) during the spring in both 2016 and 2017. Miaoli was exposed to continual shipping activity, which led to an increase of ~10 dB in low frequency ambient noise levels (5–500 Hz). The acoustic dataset was successively analyzed via the acoustic complexity index, the acoustic diversity index and the bioacoustic index. The C-H method was found to be strongly correlated with fish chorusing (Pearson correlation: rH < −0.9; rC > 0.89), and robust to noise originating from shipping activity or natural sources, such as wind and tides (rH and rC were between 0.22 and −0.19). Other indices produced lower or null correlations with fish chorusing due to missed identification of the choruses or sensitivity to other sound sources. In contrast to most acoustic indices, the C-H method does not require a prior setting of frequency and amplitude thresholds, and is therefore, more user friendly to untrained technicians. We conclude that the use of the C-H method has potential implications in the efficient detection of fish choruses for management or conservation purposes and could help with overcoming the limitations of acoustic indices in noisy marine environments.
Keywords: Eastern Taiwan Strait; ecoacoustics; acoustic indices; marine environments; fish choruses; passive acoustic monitoring Eastern Taiwan Strait; ecoacoustics; acoustic indices; marine environments; fish choruses; passive acoustic monitoring
MDPI and ACS Style

Siddagangaiah, S.; Chen, C.-F.; Hu, W.-C.; Nadia, P. A Complexity-Entropy Based Approach for the Detection of Fish Choruses. Entropy 2019, 21, 977.

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