Developments within the Pearl River Estuary (PRE) have caused underwater ambient sound levels to rise – to the point where communication between marine mammals could be masked and lead to stress. These developments include the Hong Kong-Zhuhai-Macau bridge construction, the HKIA Third Runway Project and Guishan offshore wind farm demonstration project.
Marine survey data between 2011 and 2016 showed that Indo-Pacific humpback dolphins had moved to southwest Lantau waters and the Soko Islands, away from the construction activity near their previous core-habitat north of Lantau Island.
The high-degree of marine traffic (particularly high speed ferries and fishing vessels) in the waters SW of Lantau Islands and south Lantau was creating two main risks to the dolphins’ health: auditory masking (potentially leading to reduced feeding efficiency, group cohesion and navigation) and dolphin-vessel collisions (leading to serious injury and death).
In 2016, World Wildlife Fund – Hong Kong (WWF-HK) started a comprehensive investigation into the diurnal occurrences of cetaceans along the busy ferry fairway in southwestern Lantau waters, including the Soko Islands. The aim of this investigation was to support conservation action to protect the Indo-Pacific humpback dolphin (Sousa chinensis) which is iconic for Hong Kong, as well as Indo-Pacific finless porpoises (Neophocaena phocaenoides).
WWF – HK required scientific services to inform their conservation directions for the dolphins in the region. They also required monitoring of Indo-Pacific finless porpoises, which also reside around Hong Kong waters.
With extensive experience in marine mammal detection in Chinese waters, we were able to work around the numerous issues in undertaking acoustic investigations in extremely busy seas and successfully monitor and report on marine mammal movements.
The technical reports from this monitoring program are being used by WWF-HK to justify and encourage the establishment of new marine protected areas around Lantau and Soko Islands to protect the last core area for Indo-Pacific humpback dolphins – a cause we are very proud to be directly involved in.
New signal processing software plugins for the PRE and Hong Kong was written to process the recordings and amplify dolphin clicks while reducing background noise. This proved essential for the successful detection of echolocation click signals in very noisy environments.
That software was incorporated into specific classifiers for Indo-Pacific humpback dolphins and validated against our datasets from the Beidu Gulf, Yangtze River (for finless porpoises) and mainland waters of the PRE.
Passive Acoustic Monitoring and Underwater Noise Measurement
Several aspects of this project have required advanced propagation noise modelling, from informing hydrophone placement to decision making by WWF-HK. With high resolution bathymetry for the study area and multiple sources for environmental data, we have built advanced range-dependent noise models for both shipping and ferries, as well as other sources, such as percussive pile-driving within the study area. These models are allowing us to investigate how noise exposure inside the dolphin’s core-use areas can be reduced.
We now regularly advise WWF-HK on underwater noise issues in their waters and continue to provide scientific services such as predictive noise modelling, and data analysis to assist in their public outreach.
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