Of the fifteen species of cetaceans recorded in Hong Kong waters, either as live sightings or strandings, five are whales, including three members of the Balaenopteridae (the Minke whale, Balaenoptera acutorostrata, Bryde's whale Balaenoptera edeni, and the Fin whale, Balaenoptera physalus), one member of the Physeteridae (the Pygmy sperm whale, Kogia breviceps), and one member of the Delphinidae (False Killer whale, Pseudorca crassidens). However, none of these whales is resident in Hong Kong waters and most have only been recorded on one or two occasions.

The local (Guangdong) population of Sousa chinensis is reported to be centred around the Pearl River Estuary and Hong Kong waters are thought to represent the eastern portion of its range. There were an estimated 967 Chinese White Dolphin in the eastern Pearl River estuary during the winter of 1997, and a Pearl River estuary population of 1054 individuals. Dolphins residing in the large western portion of the Pearl River estuary were not surveyed and may have been excluded from this estimate (Jefferson 1998a). The population in Hong Kong waters varied seasonally from about 92 individuals in winter to about 163 individuals in autumn. It is speculated that heavy Pearl River flow during the summer might contribute to the higher numbers of dolphins dispersing into typically oceanic waters in Hong Kong (Jefferson 1998a).

Chinese white dolphins in Hong Kong waters are born year-round, with peaks in late spring (May/June) and late summer (August), after an estimated gestation period of 11 months (Jefferson 1998a). This species feeds mainly on fish (Jefferson 1998a, Parsons 1997) and has often been recorded feeding behind pair and shrimp trawlers. When feeding was not associated with trawlers, it usually was close to shore or near rock outcrops.

Annual strandings of Chinese white dolphins were less than 3 per year through 1985 and then increased rapidly to 15 strandings in 1996. It was reported that 59% of the 22 strandings that occurred between January 1996 and March 1998 were neonates, suggesting the mortality rates for newborns might be high, as is the case for most cetaceans (Jefferson 1998a). The cause of mortality may be related to bacterial disease, as exhibited by several strandings, or due to elevated levels of organic contaminants which have been found in stranded dolphins (Parsons 1997). This latter finding has prompted concern that Chinese White Dolphins are being adversely affected by pollution in the environment.

The finless porpoise, Neophocaena phocaenoides, is a small cetacean endemic to southern and eastern Asia. In general, marine areas around Lamma Island appear to be the most important habitats for this species (ERM 1998e). The main areas used by the porpoises around the island are the nearshore waters off the southwestern coast although this appears to vary on both a spatial and temporal basis. Ongoing studies are providing information on the population distribution, density, habitat ecology and behaviour of the species with a goal of establishing a long-term conservation and preservation programme for the species. Like Chinese White Dolphins, Finless Porpoise are protected under the Wild Animal Protection Ordinance (Cap 170), the Marine Parks Ordinance (Cap 476) and listed on Appendix 1 of CITES.