- Title
- Passive acoustic monitoring of coastal dolphins (Sousa plumbea and Tursiops aduncus) in Plettenberg Bay: temporal patterns and group dynamics
- Creator
- Hlati, Kuhle
- Subject
- Marine mammals -- Effect of noise on -- Research
- Subject
- Oceanography Aquatic ecology
- Date Issued
- 2018
- Date
- 2018
- Type
- Thesis
- Type
- Masters
- Type
- MSc
- Identifier
- http://hdl.handle.net/10948/30050
- Identifier
- vital:30813
- Description
- In this study, passive acoustic monitoring (PAM) was used to investigate the diel patterns of occurrence and activities of coastal dolphins (Sousa plumbea and Tursiops aduncus) in Plettenberg Bay, during April 2015 - July 2017. Automatic detectors were used to extract dolphin whistles and echolocation clicks from the acoustic recordings. The vocalizations were extracted without identifying the dolphin species due to insufficient visual observation data collected concurrent with the acoustic recordings to conclusively discriminate the two species. The correct detection performance and false alarm rate of the detectors for each acoustic recorder were evaluated and automatic detection protocols were developed. For a recorder that was initially deployed in the study (DSG recorder), the detectors achieved 64 - 80% true detection rates with false alarm rates of 10 - 22%. A more modern recorder (MicroMARS recorder) which replaced this one had a lower signal-to-noise ratio (SNR) and could sample at a higher frequency, the detectors achieved greater than 80% true detection rates and less than 5% false alarm rates. It was evident that SNR and sampling rate influenced the detection performance of the detectors. When acoustic recordings were compared to visual observations which were conducted concurrently with some of the recordings, it was apparent that acoustic recorders performed nearly twice as well as land-based observers in terms of overall detection of dolphin groups. Group size and behaviour affected acoustic detection rates of dolphins; large groups that were visually detected and which were foraging at the time, were more likely to be acoustically detected than small groups or single animals or groups associated travelling at the time. The detection rates of echolocation clicks and whistles showed a diel pattern of occurrence of coastal dolphins in Plettenberg Bay with a higher nighttime than daytime occurrence. The detection rates were higher from midday to midnight with a peak during dusk. The high activity of dolphins in the late afternoon and evening reported in this study was also supported by visual data (afternoons) in the area and acoustic studies in other regions. Comparison of acoustic detection rates and visual data from this study with past observations suggest that the occurrence patterns of T. aduncus in the bay appear to have changed; such a change may be influenced by changes in prey behaviour or distribution, or other factors. The significally higher detection rates of echolocation clicks than whistles and dominant foraging behaviour based on visual data suggest that Robberg may be an important feeding ground for the coastal dolphins that are frequenting Plettenberg Bay. The current study builds on a growing body of literature demonstrating that PAM and automatic detectors are powerful and effective tools for monitoring cetacean species. However, there are several factors that limit the detection of vocalization such as direction of the sound source, distance from hydrophone, sound propagation conditions, low SNR and acoustic masking. Regardless of these limitations, results from PAM showed diel patterns of occurrence of the coastal dolphins in the bay which could have not been achieved from visual monitoring, in particular the high nighttime occurrence patterns. PAM holds potential to be largely utilized in South Africa for dolphin and other cetacean studies. Further research and monitoring using PAM could potentially assist to better understand the drivers of the dolphin occurrence and activity patterns in the bay.
- Format
- iv, 125 leaves
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
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