The latest annual dolphin monitoring report published by the Agriculture, Fisheries and Conservation Department (AFCD) indicates only 47 Chinese white dolphins remain in Lantau waters, with their highest occurrence recorded in west Lantau and southwest Lantau between April 2016 and March 2017, a drop of 27 per cent compared to data in 2016. Habitat destruction from coastal reclamation and busy marine traffic are the top two threats affecting their distribution, abundance and behaviour.
Chinese white dolphins were once abundant around north Lantau. Reclamation projects that are currently underway, or planned to take place over the next decade, have led them to move southwards, where they face an increasing number of threats from heavy marine traffic. In addition to the risk of collision, marine traffic interferes with the echolocation that dolphins rely on for hunting, communication and navigation.
WWF needs to expand its current hydrophone study to cover a wider range of the sea that the Chinese white dolphin now inhabits, particularly Tai O. This is one of the remaining Chinese white dolphin core habitats and is still unprotected. This scientific data gathered from this study will be used to lobby the government to establish marine protected areas, or to divert or restrict vessels traversing key dolphin habitats. We need your support!
The dangers posed to the Chinese white dolphin from heavy marine traffic in south Lantau waters was examined by WWF-Hong Kong in an underwater sound study conducted between October 2016 and September 2017. A total of seven underwater sound recorders collected the whistles and echolocation clicks of the Chinese white dolphin and finless porpoise, as well as the noise generated by vessels passing through the area.
A hydrophone is underwater microphone and connected to a water-proof, rechargeable, portable recorder. It can record for 2 minutes every 10 minutes, for up to 1.5-months. The hydrophones we use are specifically designed to record the high frequency clicks made by cetaceans, including dolphins, and the very low frequency calls of whales.
HOW TO DEPLOY A HYDROPHONE UNIT IN THE SEA?
- Scuba divers install a customized underwater stainless steel stand
- The hydrophone is then fixed to the stand
- The hydrophone is retrieved after 1.5 months
The data is downloaded, then the device is recharged and placed again on the stand, the whole unit is ready for the next recording in the water.
The data collected from the hydrophones show the amount of time the dolphins spend at each location and the number of Chinese white dolphins detected during the day (yellow) and night (grey). The size of each pie-chart represents the number of detections compared to other sites (i.e. larger circles represent more dolphin detections, while smaller circles represent fewer detections compared to the other sites).
Here is the sample data of the hydrophone taken at night time. The spectrogram is a sound frequency profile to show all noise signals recorded. Please click to listen.
- Fish calls
- Chinese white dolphin echolocation clicks
- Chinese white dolphin whistles
- High speed ferry
WWF identified an urgent need to expand the current hydrophone study to cover wider range of the sea where Chinese white dolphins now inhabit, particularly Tai O, one of the remaining Chinese white dolphin core habitats in Hong Kong yet unprotected. This will allow us to cover a comprehensive range to understand dolphin’s activity around the clock for the period of one year.
This scientific data will be used to formulate strategies to save the Chinese white dolphin, such as lobbying the government to establish marine protected areas, or to divert or restrict vessels traversing key dolphin habitats.
Audrey Tam, a 10th grade student at the Canadian International School of Hong Kong, was asked by her teacher to select a charity to help raise funds and chose WWF. Over the last few months, Audrey worked very hard, did a recital performance and photo exhibition, and collected $33,265 from her own network for our dolphin conservation work.
Audrey is very committed to helping wildlife and came with her mum to WWF’s hydrophone public seminar in December 2017. Her donation will be used for deploying a hydrophone at Tai O with her name written on it.
PS. The same campaign has also been launched on a WWF-Hong Kong minisite.