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Dolphins and Porpoises in Hong Kong

Hong Kong is truly blessed by her rich biodiversity, and we are beginning to reveal some of the magnificent creatures that have inhabited Hong Kong in recent years. For example, the charismatic Chinese white dolphins (also known as the Indo-Pacific humpback dolphins, Sousa chinensis) have captured the hearts of many Hong Kong people with their elegance, gorgeous colouration and great tolerance to the numerous threats we continue to impose on them. Here I want to share some of the pictures that I have taken during my weekly research trips in 2002 as an appreciation to these lovely creatures frolicking in our waters. As a dolphin conservationist, we not only collect the useful research data to help us understand the life of the dolphins, but also attempt to capture the beauty of the dolphins through photographs, and use these as a tool to convey the important message of marine conservation. Sometimes I feel that wildlife researchers in Hong Kong may not be able to stop development and pollution that continue to exert pressure on the local dolphins and porpoises, but through education such as dolphin watching trips and seminars, we can arouse the public interest in protecting their own marine environment.

Here I also want to share some interesting information about the Chinese white dolphins in Hong Kong. In our territorial waters of Hong Kong, there are two resident cetacean species - Chinese white dolphins and finless porpoises (Neophocaena phocaenoides), in addition to over a dozen species that were sighted or stranded here. Chinese white dolphins are one of the 86 species of cetaceans around the world. Globally they are known as "Indo-Pacific humpback dolphins" (scientific name is Sousa chinensis), and the common name "Chinese white dolphins" is only used by local Chinese. Belonging to the family Delphinidae, they are closely related to bottlenose dolphins and killer whales.

In the past, this species is poorly known throughout its range, except the resident populations in South Africa and Australia. To know about them, many research projects are initiated in many other places, such as Thailand, Indonesia, Malaysia, Singapore, Mozambique, Vietnam and China (including Hong Kong, the Pearl River Estuary, Xiamen, Taiwan and Beibu Gulf). In Hong Kong, these dolphins remain unstudied and no information was recorded until the 70's, when the Agriculture and Fisheries Department of the Hong Kong Government started to collect information on stranding of these dolphins in 1973. As the new airport project on Chek Lap Kok Island began in 1993, there were concerns that the dolphin habitat would be degraded and polluted, and the dolphins would be seriously threatened. To understand these impacts, the Hong Kong Government funded several projects to study their distribution and abundance, individual home ranges and movement patterns, behavior and life history.

Many people ask the same question when they first see the Chinese white dolphins in Hong Kong: why are they pink? A plausible explanation is that when they are moving, their blood vessels expand near skin surface to release body heat (i.e. thermoregulation). Since their skin color is white, the red blood vessels near skin surface make them look pink. This is similar to the blushing effect of our body; after heavy exercise, our face and skin turn red. When the Chinese white dolphins are first born, they are dark gray in color. When they proceed to the juvenile stage, their body color becomes grayish pink with heavy spotting. Finally, when they reach the adult stage, they become pinkish white in color, and the spotting slowly disappears. Experts also believe male may attain more spotting than female due to sexual dimorphism. By using systematic surveys in the last seven years, researchers now obtain a much more reliable abundance estimate of the dolphins. It is estimated that about 250 animals use Hong Kong waters every year, and the abundance estimate of resident dolphins in Hong Kong waters ranged from 45 dolphins in spring to 152 dolphins in summer. Surveys in the Pearl River Estuary suggested the whole population (including the ones in Hong Kong) has nearly 1,400 animals. Chinese white dolphins mainly occur in the western waters of Hong Kong (including North, East and South Lantau, Deep Bay and near Tai O), but do not occur in the eastern waters, where finless porpoises are commonly seen. They seem to have a strong preference for estuarine habitats. Among all the western waters, North Lantau appears to be their most favorite habitat as they are most frequently sighted there.

Chinese white dolphins are very playful and love to perform air acrobatics, which make them so much fun to watch! Here are several behaviours they commonly perform:

  1. Breaching is performed when the whole body of the dolphin leaps out of the water, and falls back into the water to create a gigantic splash. Some people say dolphins do this to scare off the preys underneath water surface, or to loosen the tiny creatures on their body (just like us scratching our own body), or simply to play!
  2. Spy hopping is when the dolphin lifts its body half way out of the water to the flipper, and peeks around at its surroundings in pure curiosity.
  3. Porpoising is when the dolphins want to move quickly toward an object (such as fishing boats), they will sometimes leap forward out of the water. They can drag themselves on the surface of the water much faster than trying to swim through it. They particularly love porpoising when they are tailing fishing boats.

The Chinese white dolphins love to feed behind fishing boats in larger groups, as trawlers can concentrate large amount of fish at the end of the trawl net. It will also stir up bottom-dwelling fishes. This feeding mechanism helps the dolphins get an easy meal. However, at the same time they are at risk of being entangled by the fishing net when trailing the boats.

Based on a five-year case study of stranded dolphins, researchers discovered that Chinese white dolphins are actually under serious threat due to human activities. These include fishery by-catch, vessel collision, water pollution, underwater noise and habitat loss due to land reclamation. We do not think that the Chinese white dolphins will become extinct soon. In fact, they are not even close to extinction for two main reasons: The species is widely distributed in the Indian and western Pacific Oceans, so even outside Hong Kong, there are still numerous populations of Chinese white dolphins (or humpback dolphins). Moreover, we have found that number of Chinese white dolphins in Hong Kong and Pearl River Estuary remains steady throughout years, so we may conclude that they are not in immediate danger of becoming locally extinct. Despite so, they are still facing numerous threats that we have discussed. If we do not monitor the population biology of the Chinese white dolphins in long term and formulate some conservation strategies to protect them, we cannot ensure the long-term survival of the dolphins. Therefore, we will continue to collect information about the dolphins to track the changes in trends in abundance, distribution and life history, and provide useful information to Hong Kong government to implement effective conservation measures.

Samuel Hung
Editor-in-chief, Hong Kong Discovery magazine
Research Director, Hong Kong Cetacean Research Project

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