To obtain critical information on distribution and abundance of Indo-Pacific humpback dolphins (Sousa chinensis) residing in the Pearl River Estuary (PRE), systematic line-transect surveys and photo-identification studies were conducted in the eastern and western sections of the estuary in 2005–2006 and 2007–2008, respectively. Dolphins in the eastern section occurred throughout Lingding Bay, whereas their distribution in the western section extended from the mouth of Modaomen to the channel between Shangchuan and Xiachuan islands. Variations in dolphin distribution during the wet and dry seasons were evident and probably associated with movements of their prey species. Photo-identification of individuals confirmed exchange of at least some individuals between the western and eastern sections of PRE, and thus dolphins from both areas almost certainly comprise a single population. Using line-transect analysis, the total population size of the PRE humpback dolphins was estimated to be 2555 during the wet season and 2517 during the dry season. However, these should be considered preliminary as the coefficients of variation in some survey areas were high. Further studies should focus on refining these estimates and working towards understanding the western boundary of the PRE population.

The status of Indo-Pacific humpback dolphins (Sousa chinensis) in Chinese waters (including Taiwan) is reviewed. Within China, humpback dolphins range from the Vietnam border north to the mouth of the Yangtze River, and there are estimated to be about eight populations in China. Little is known of stock structure, except for a preliminary conclusion that animals in Xiamen and Hong Kong represent separate populations. Abundance has been estimated only for Hong Kong and the Pearl River Estuary (about 1,500 animals) and Xiamen (80 dolphins). In the early 1960s, 36 animals were killed in Xiamen Harbor, but other direct takes appear to be rare. Incidental catches are known in Hong Kong and the Pearl River Estuary, but their impacts are not known. Only preliminary work on life history has been conducted. There appears to be a calving peak from spring to summer, and calves are about 100 cm long at birth. Scant data indicate that sexual maturity in females may occur at about 9-10 years of age, with males maturing later. Dolphins in Hong Kong and the Pearl River Estuary have individual ranges averaging 99.5 km 2 Hong Kong and the Pearl River Estuary have indi-2 Hong Kong and the Pearl River Estuary have indi-, only a small portion of the population's range. Humpback dolphins in China feed on several species of demersal and estuarine fishes, with little evidence of predation on cephalopods or crustaceans. Contaminants have been evaluated in some areas, and mercury and DDT concentrations in particular appear to be high and potentially health-threatening. An assessment of trends and stranding mortality in the Hong Kong and the Pearl River Estuary population suggests that this stock is probably not decreasing at present. The Xiamen stock is thought to be decreasing, but its status has not been reliably assessed. Essentially, nothing is known of the status of other populations in China, and this shortcoming should be addressed as a matter of priority.

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We studied life history characteristics of the Hong Kong/Pearl River Estuary population of Indo‐Pacific humpback dolphins (Sousa chinensis), based on data from 120 specimens stranded between 1995 and 2009, 40 individuals biopsied at sea, and a long‐term (14+ yr) photo‐identification study. Ages were determined for 112 specimens by thin‐sectioning teeth and counting growth layer groups. Estimated length at birth was 101 cm. Longevity was at least 38 yr, and there was little difference in growth patterns of males and females. Growth was described by a Bayesian two‐phase Gompertz model; asymptotic length was reached at 249 cm. The tooth pulp cavity filled at an average of 18.5 yr of age. Physical maturity was reached at between 14 and 17 yr of age, apparently a few years after attainment of sexual maturity. Maximum lengths and weights of about 268 cm and 240 kg were attained. Females appear to lose all their spots by 30 yr, although males may retain some spotting throughout life. Calving occurred throughout the year, with a broad peak from March to June. Of 60 females monitored at sea for >14 yr of the study, none were documented to have more than three calves, suggestive of low reproductive output or low calf survival.