Pearl River Estuary Humpback Dolphins

Last Updated: December 2019

The Species

The Indo-Pacific humpback dolphin (Sousa chinensis) is one of four currently recognized species in the genus Sousa. Its total range is in coastal waters from central China southward throughout Southeast Asia and westward to the Bay of Bengal, with highest densities in and around estuaries. The distribution is fragmented such that these dolphins are apparently absent from fairly long stretches of coastline. It is not always clear whether the fragmentation is ‘natural’ or caused by human activities.

Several populations of S. chinensis have been estimated to number in the hundreds or low thousands of individuals. All available estimates, combined, indicate that the world population may currently number no more than around 10,000 individuals. The species is red-listed as Near Threatened but this is expected to be changed to Vulnerable once an ongoing reassessment is completed. Although data on trends are rarely definitive, a declining trend in Hong Kong waters has been well-documented. Given the species’ very near-shore distribution and its overlap with large and growing human populations, there is reason to believe that dolphin numbers have declined and habitat has been lost in much of the Indo-Pacific humpback dolphin’s range.

A mother and calf humpback dolphin breach in the Pearl River estuary of Hong Kong, showing the characteristic pink colour of adults and the uniform grey colour of young animals. Photo Credit: Samuel Hung

The Region

The Pearl River Delta – the low-lying area surrounding the Pearl River Estuary (PRE) where the Pearl River flows into the South China Sea – is one of the world’s most densely urbanized areas. This means that the PRE dolphin population lives, and has been living for several decades, in a massively disrupted and disturbed habitat. The list of known and potential threat factors is long and diverse, ranging from agricultural, industrial, and urban pollution, to fishing, marine construction (including bridge-building and land creation for airport expansion and residential/office development) and transport (including fast ferries).

The humpback dolphins that inhabit the PRE are generally referred to as Chinese white dolphins. There are no physical barriers to their movement across the administrative boundary between the People’s Republic of China mainland in the west and Hong Kong in the east. Dolphin research has been intensive in Hong Kong since the mid-1990s. This has meant that a great deal more is known about the animals in that portion of the population’s range than in the central and western portions of the PRE. In fact, it is largely the difficulty of determining the western limit of the range that has stymied efforts to complete a Red List assessment of the PRE ‘sub-population’.

A humpback dolphin in the Pearl River estuary showing a deep scar in the tail stock. Photo Credit: Samuel Hung

The Project

Ever-growing concerns about the loss of suitable habitat, the mortality of dolphins from entanglements and vessel strikes, and the possible effects of chemical, sewage, and noise pollution on dolphin health led the Ocean Park Conservation Foundation in Hong Kong (OPCFHK) to seek funding from the Hong Kong International Airport Environmental Fund for a major research and conservation planning initiative. With assistance from the SSC Conservation Breeding Specialist Group and the Cetacean SG, OPCFHK used the funding to organize and conduct two workshops –one in March-April 2016 to develop a population viability analysis and the other in January 2017 to produce an initial conservation research and management framework to be implemented over the next several years. A small panel of scientists, chaired by the Cetacean SG chair, was established to oversee and advise on workshop outcomes and implementation of the recommended research and conservation actions. A major step in the first year of the project was to establish a mechanism for, and agreement among researchers, to share individual identification images and data in order to improve demographic analyses. This is being facilitated by Randy Wells and Carolyn Cush of the Chicago Zoological Society’s Sarasota Dolphin Research Program in Florida.

A humpback dolphin in the Pearl River estuary of China entangled in a fishing net. Photo Credit: Samuel Hung

Relevant references

Barros, N.B., Jefferson, T.A. and Parsons, E.C.M. 2004. Feeding habits of Indo-Pacific humpback dolphins (Sousa chinensis) stranded in Hong Kong. Aquatic Mammals 30(1):179-188.

Chen, B., Zheng, D., Yang, G., Xu, X., Zhou, K., 2009. Distribution and conservation of the Indo–Pacific humpback dolphin in China.Integrative Zoology 4, 240 – 247.

Chen, T., Hung, S. K., Qiu, Y., Jia, X., Jefferson, T. A., 2010. Distribution, abundance, and individual movements of Indo-Pacific humpback dolphins (Sousa chinensis) in the Pearl River Estuary, China.Mammalia 74, 117-125.

Chen, T., Qiu, Y., Jia, X., Hung, S. K., Liu, W., 2011. Distribution and group dynamics of Indo-Pacific humpback dolphins (Sousa chinensis) in the western Pearl River Estuary, China.Mammalian Biology – ZeitschriftfürSäugetierkunde76, 93-96.

Gui, D., Yu, R., He, X., Tu, Q., Chen, L., Wu, Y., 2014. Bioaccumulation and biomagnification of persistent organic pollutants in Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary, China.Chemosphere 114, 106-113.

Gui, D., Yu, R., He, X., Tu, Q., Chen, L., Wu, Y., 2014. Tissue distribution and fate of persistent organic pollutants in Indo-Pacific humpback dolphins from the Pearl River Estuary, China. Marine Pollution Bulletin, http://dx.doi.org/10.1016/j.marpolbul.2014.1007.1007.

Huang, S.-L., Karczmarski, L., 2014. Indo-Pacific humpback dolphins: A demographic perspective of a threatened species. In: Primates and Cetaceans: Field Research and Conservation of Complex Mammalian Societies. Eds. J. Yamagiwa& L. Karczmarski), pp. 249 – 272. Springer,Tokyo.

Huang, S.-L., Karczmarski, L., Chen, J., Zhou, R., Lin, W., Zhang, H., Li, H., Wu, Y., 2012.Demography and population trends of the largest population of Indo-Pacific humpback dolphins.Biological Conservation 147, 234-242.

Hung, C.L.H., Xu, Y., Lam, J. C. W., Jefferson, T. A., Hung, S. K., Yeung, L. W. Y., Lam, M. H. W., O’Toole, D. K., Lam, P. K. S., 2006. An assessment of the risks associated with polychlorinated biphenyls found in the stomach contents of stranded Indo-Pacific Humpback Dolphins (Sousa chinensis) and Finless Porpoises (Neophocaenaphocaenoides) from Hong Kong waters Chemosphere 63, 845-852.

Jefferson, T.A., 2000. Population biology of the Indo-Pacific hump-backed dolphin in Hong Kong waters.Wildlife Monographs 144, 1-65.

Jefferson, T. A., Hung, S. K. and Lam, P. K. S. 2006.Strandings, mortality and morbidity of Indo-Pacific humpback dolphins in Hong Kong, with emphasis on the role of environmental contaminants.Journal of Cetacean Research and Management 8, 181-193.

Jefferson, T.A., Hung, S. K., Robertson, K. M., Archer, F. I., 2012. Life history of the Indo-Pacific humpback dolphin in the Pearl River Estuary, southern China.Marine Mammal Science 28, 84-104.

Jefferson, T.A., Hung, S. K., Würsig, B., 2009. Protecting small cetaceans from coastal development: Impact assessment and mitigation experience in Hong Kong. Marine Policy 33, 305-311.

Leung, C.C.M., Jefferson, T. A., Hung, S. K., Zheng, G. J., Yeung, L. W. Y., Richardson, B. J., Lam, P. K. S., 2005. Petroleum hydrocarbons, polycyclic aromatic hydrocarbons, organochlorine pesticides and polychlorinated biphenyls in tissues of Indo-Pacific humpback dolphins from south China waters Marine Pollution Bulletin 50, 1713-1719.

Wu, Y., Shi, J., Zheng, G. J., Li, P., Liang, B., Chen, T., Wu, Y. & Liu, W. (2013).Evaluation of organochlorine contamination in Indo-Pacific humpback dolphins (Sousa chinensis) from the Pearl River Estuary, China.Science of the Total Environment, 444, 423-429.