Stories of hope recently reached the world media and described, not for the first time, the plight of Hong Kong’s dolphins. Sadly, this was not a story of successful conservation, but the story of a young male dolphin called “Hope” who was fatally injured after being struck by a boat in Hong Kong’s shipping lanes. The graphic images of the wound caused shock and distress along with amazement that a dolphin could survive such horrific injuries, even in the short term.
There have been concerns over the fate of Hong Kong’s dolphin population, known also as the “Chinese white dolphin,” for decades. The fact that they have sustained in ever more-industrial waters, is a testament to the resilience, determination and sheer perseverance of a population which has been shaped by one of the world’s most dynamic habitats: the Pearl River Estuary. Although the modern story of Hong Kong’s dolphin started only 20 years ago, the population has been known from these waters for as long as man has been there to record it. Chinese chronicles circulating in the 16th and 17th Centuries describe dolphins paying homage to the Goddess of the Sky, Tin Hau, as they swam in the bays adjacent to her temples. Fisherman were known to revere the dolphins and considered them the messengers of the Goddess, sent to guide them to shore when stormy seas might otherwise have overwhelmed them. This then, is a story of a population whose forefathers saw the arrival of the first traders from Persia more than 1200 years ago; who witnessed wars and revolutions as Guangzhou became China’s greatest trading port, and who were the emblem of unity and peace when the dolphin was chosen as the symbol of Hong Kong’s return to China. Not many species can boast such a rich history in an environment that itself has been forged by nature, modified by man and has been the centre of the development of the Eastern empires.
Late in the last century, the history of Hong Kong’s dolphins was little known, until a large scale development was proposed in the waters they inhabited to the west of Hong Kong. The species itself was then poorly defined with differing opinions as to where taxonomic divisions lay between the widely dispersed populations of the Indo-Malay archipelago, the South China Sea and the Indian Ocean. Today, we know that the South China Sea populations, which include the Pearl River Estuary, are genetically distinct from elsewhere in the Asia Pacific. It seems certain that the Pearl River Estuary population of Chinese white dolphin is the largest left in the entirety of the South China Sea, and from more than two decades of study, we know the details of its daily behaviours and life history cycles.
The Chinese white dolphin is rarely white. Born dark grey, it can take more than a decade to lose this pigmentation. Through a series of steps, the dolphins become a mottled grey, then a spotted black on pink with a gradual disappearance of all colour except black eyes, a band of grey around the head and dark trailing edges on the tail fluke. Only in old age is all colour gone and the dolphins become truly white. It is through the identification of different dorsal fin shapes and the unique patterns of gradually changing dark spots and patches, that it has been possible to follow some individuals for more than a decade. This has been important in obtaining a solid understanding of the dolphin’s life history as individuals live 30 years or more, and mature slowly in that time. Mother-calf bonds sustain over many years and young females will stay with their mothers and care for their younger siblings. On occasion, when calves do not survive, mothers will often carry the remains of their offspring, perhaps unable to accept their loss, for many days. On a few occasions, other females have even been witnessed assisting a mother as she gives birth by both supporting her and by pushing the newborn dolphin to the surface. The ties that bind the females together are close and complex and seem to be the cornerstone of the dolphin community in Hong Kong. The males appear to have more relaxed affiliations within the population, the younger sub adults frequently mixing between groups and often exhibiting rough and tumble play that leaves them scarred with the teeth marks of their contemporaries. The adult males although now rare, are solitary and are only seen with females during mating bouts.
The decrease in the number of male adults appears to be due to pollution, the biggest threat the dolphins face in the Pearl River Estuary. Indeed, one of the greatest threats to marine mammals worldwide is the pollution of our oceans. In Hong Kong, dolphins which are found stranded on the shore or floating in local waters undergo full post mortems whenever possible. Over the twenty years that these dolphins have been studied, analyses suggest that males have consistently higher levels of toxins than females and there is a notable peak in male mortality at nine to ten years old. Females inadvertently pass their toxic burden onto their offspring when they utilise the fat in which these toxins are stored. Although more data is still required from this population, it is believed that the female’s first calf suffers the most, as the accumulated toxins from the mother are all passed on to the calf. At an average of three years between births, subsequent calves receive a much smaller toxin load from their mothers and the mothers too have a smaller toxin load. The males have no such mechanism and perhaps succumb to the overall burden of their toxicity at an earlier age. Toxins, of which many have been identified in the Pearl River Estuary dolphins, not only directly harm the dolphins, but may also disrupt the immune system thus making them more susceptible to the other threats that they face.
Competition with fisheries and entanglement in fishing gear is also a threat to the dolphin population. The rocky, reefy shores of Hong Kong provide ideal habitat for the estuarine fish species upon which the dolphins are known to prey. A tremendously productive area, the dolphins once occurred in small, evenly interspersed groups which used a variety of feeding behaviours throughout Hong Kong waters. In 1996, management authorities recognised the importance of this habitat and designated Hong Kong’s first marine park specifically for the protection of the dolphins. For nearly a decade, sightings of dolphins, particularly mothers and calves, increased in the park area, until, in less than a year, the number of dolphin sightings almost halved. The decline in dolphin numbers from the park and adjacent areas was concomitant with a dramatic reduction in the abundance and biomass of fishes. The exact mechanism that drove the drop in fish stocks is not known, however, an immediate knock on effect was the change in the dolphins’ distribution to areas outside the marine park and a change in their feeding behaviour. Some dolphins, mainly sub-adults, had previously been seen feeding in association with fishing trawlers, but now, this behaviour appeared to take on a greater importance for the whole dolphin community. Mothers and calves, juveniles and adults of both sexes relentlessly followed trawlers from dusk until dawn. At first it seemed that they were feeding on those fish that escaped the trawl nets, but later helicopter footage taken from above the trawlers revealed that the dolphins were swimming into the mouth of the net itself, risking entanglement and drowning, to feed on those fish which were already trapped. At the time, a scientific article that documented the incidence of trawler-feeding dolphins from around the world, opined that such desperate measures were indicative of the general poor state of global fisheries, which could no longer support dolphin populations as well as human demands. Recognising the unsustainability of the local fishing practices, again the management authorities in Hong Kong took bold steps and became the first authority within the region to have an outright and permanent ban on trawling within all waters that came under its jurisdiction. This was enforced at midnight on January 1st 2013 and within just two years, studies show that fish stocks are increasing both in mass and diversity, although there is still some way to go before historic levels once again prevail. Until such a time, the dolphins remain at risk from diminished prey stocks and from entanglement in the fishing gear used by the remaining non-trawler fisheries of Hong Kong.
Dolphins use sound for every aspect of their lives. The emission and reflection of high frequency, narrow beam buzzes and clicks are essential for navigation and foraging. The whistles produced by dolphins seem to be important for maintaining cohesion between groups, particularly mothers and their calves. The physiology of the dolphins acoustic apparatus is highly adapted to an estuarine environment, which not only has low visibility but high background noise levels from natural processes such as tide and current and other noise emitting aquatic species. The cochlear nerve of this species has the largest fibres known from any mammal. These fibres rapidly transfer very detailed sound information to the brain. An acoustic study of the dolphins in the Pearl River Estuary showed that the whistles, chirps, squawks, quacks and buzzes which they produce were of a much higher complexity and duration than any other population of this species. These dolphins have perfected their vocal repertoire and are physiologically ideal to use sound as their primary sense. In recent years, the numbers of ships have increased dramatically and underwater construction activities are currently underway throughout the Hong Kong habitat. The increase in underwater noise levels from these activities are overshadowing or “masking” the dolphins’ ability to perceive and process sound. This effectively handicaps their ability to communicate, forage and navigate in Hong Kong’s busy shipping lanes, thus increasing the risk of boat strikes.
Another major threat these dolphins face is the loss of the habitat itself. Throughout the Pearl River Estuary, the development of the entire area for industry, transport and city settlements has resulted in the widespread loss of the dolphins’ shallow water habitat through reclamation and seashore modification. The western islands of Hong Kong waters, as well as parts of the south western reaches of the estuary, remain intact and are vital to the productivity of fish stocks and thus the nutritional needs of the dolphins. This habitat must remain unmodified and unspoiled if the dolphins have any hope of surviving.
I am often asked if there is any hope for the dolphins and I firmly believe there is. This remarkable population has survived centuries of change and has successfully adapted. The population is currently in decline and the cumulative impacts of the intense pressure the dolphins face is responsible for this. Thought for human needs only has always driven the economy of the Pearl River Estuary, but people too can adapt. Management authorities have already shown they can effectively preserve habitat and can cease unsustainable practices for the benefit of the dolphins. What is needed now is the wider scale implementation of these initiatives that reaches throughout the dolphins’ entire estuarine habitat.
This tale of the Pearl River Estuary and the societies which occupy its banks is not new. The waterways of southern China have always bustled with cargo boats, passenger ferries and fishing fleets, which provided the goods, sustenance, and manpower required to sustain the region. Over the centuries, the communities of the Pearl River Estuary have survived, thrived and prospered because of the river and the resources it provides. Our challenge now is to ensure a future of health and prosperity for the river itself and the dolphin population whose home we have always shared.
Essay & photographs by Lindsay Porter PhD (see OG Issue 32)