Migrating marine mammals in Hong Kong
by Thomas Gomersall
It has been one year since a young male pantropical spotted dolphin — a non-resident species in Hong Kong — was sighted in waters off Ap Lei Chau. He has since appeared to have settled here long-term, dividing his time between Deepwater Bay, Repulse Bay and Aberdeen Marina, where local residents have affectionately christened him ‘Dave’.
But while Dave appears to be the first non-resident cetacean (NRC) to have stayed on in Hong Kong, he’s far from the first to turn up here. Since the 1950s, consistent anecdotal records have confirmed at least 17 species in Hong Kong waters — representing 20 per cent of all known marine mammals — with some possibly being regular visitors. Some scientists speculate that this could be an attractive feeding ground for these nomadic animals, particularly following the 2012 trawling ban.
“Hong Kong is a very productive area. […] Fish species biomass and diversity is probably quite high in our waters,” says Dr. Lindsay Porter of the Sea Mammal Research Unit (SMRU) of St. Andrews’ University. “So for animals that rely on patchily distributed prey, an area that might be a hotspot for these patches of prey like Hong Kong would be a good place to come.”
However, little is definitively known about NRCs in Hong Kong. Current records come mostly from washed-up carcasses and a few sightings of live animals near heavily populated areas, which reveal little about the full range of visiting NRC species, their distribution, or how regularly they visit. Obtaining more comprehensive information would require surveying large areas of ocean in Hong Kong, measures that would be too expensive and difficult to carry out through conventional methods like boat or aerial surveys. “We know absolutely nothing about the 17 transient species,” says Naomi Brannan, SMRU Research Scientist. “But in Hong Kong, we have an opportunity to study them.”
That opportunity is an upcoming project to study NRCs in Hong Kong’s eastern waters, where they are thought to most likely occur. Similar to WWF’s projects studying resident cetaceans, it involves installing underwater microphones (hydrophones) on the seabed, leaving them to record the calls of cetaceans, then analysing the frequencies of those calls to identify the species that made them.
But to stand a chance of recording unpredictably occurring NRCs, hydrophones will have to be installed across as large an area as possible. To do this, SMRU has turned to Hong Kong’s scuba diving community for help. Being frequent visitors to even the most remote areas of the eastern waters, scuba divers could potentially deploy hydrophones there during their usual activities. And with a strong commitment to protecting marine life, many are likely to do so voluntarily.
“Our vision is to inspire divers to explore and protect our ocean,” says Madalin Prout, Chair of the South China Diving Club. “So this project appealed to many people. […] There was no hesitation from the club about helping out.”
The project will involve finding a suitable location for deployment, then lowering a concrete block to anchor the hydrophone to the seabed. Once the base is in position, the hydrophones can easily be attached and retrieved on a monthly basis. The South China Diving Club — the only group so far attached to the project — has even offered to assist in analysing the hydrophone data using a software algorithm that can differentiate the clicks and whistles made by different cetacean species based on differing frequencies.
Due to limited funds, only two hydrophones are currently available for deployment (with the first to be deployed in Mirs Bay at the end of May). However, SMRU hopes to attract more funding to deploy multiple hydrophones across a wider area. If successful, this project could determine exactly how many NRC species visit Hong Kong, how often they visit and which areas they frequently use, which could potentially be helpful for designating marine protected areas (MPAs).
“We really need systematic data collection so we can say without speculation how important Hong Kong waters might be,” says Dr. Porter. “If [MPA planning] is missing key habitats for transient marine mammals, then this project will help us capture that, so we can better inform WWF on [protecting] important areas.”
As for Dave, he has remained in surprisingly good condition since his arrival and in the absence of other dolphins, has been actively seeking out humans for company. However, with the resulting increase in popularity has come an increase in the number of people wanting to interact with the dolphin, leading to some inappropriate behaviour from overexcited swimmers.
“I don’t think he likes it too much when he’s surrounded by people squealing and splashing around and getting overly excited. […] It causes him stress,” says swimmer Edie Hu. “It worries me that there are some people trying to grab his fin or ride him. Those actions are quite inappropriate.”
Other observers have noticed scars on Dave similar to those caused by collisions with watercraft, implying that the increased human activity may be threatening the dolphin’s physical and psychological wellbeing, which could worsen as more people start hitting the beaches during the summer.
That’s why it’s important to behave responsibly if you are lucky enough to encounter Dave. Allow him to approach you but don’t touch, chase or crowd around him. Instead of splashing and making noise, try to swim like a dolphin as this mimics the interactions he would normally have with other dolphins. Don’t get close to the dolphin in a motorised watercraft, and report inappropriate behaviour to the Hong Kong Marine Department at 2542 3711, or contact the government hotline:1823.
If you would like to assist in the SMRU project or help experts monitor Dave’s progress, please send any photos, videos or reports of sightings to “Hong Kong Sightings” at smruhongkong@gmail.com
