A Review of the Status of the Indo-Pacific Humpback Dolphin (<I>Sousa chinensis</I>) in Chinese Waters

Abstract

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.

C-values of Seven Marine Mammal Species Determined by Flow Cytometry

“…During a 1997 survey, only 13 individuals were sighted over the baiji's entire range (Zhang et al, 2003). The Chinese white dolphin, a disjunct population in Chinese waters of the Indo-Pacific humpback dolphin (Sousa chinensis), has an estimated population size of 1,580 (Jefferson and Samuel, 2004). The Yangtze finless porpoise, a subspecies of finless porpoise living only in the Yangtze River of China, has a population size of fewer than 2,000 individuals (Yu, 2003).…”

Vessel collisions with small cetaceans worldwide and with large whales in the Southern Hemisphere, an initial assessment

“…The Hong Kong/Pearl River Estuary population is the best documented (Parsons and Porter, 1995 20 ;Jefferson, 2000a;Jefferson and Hung, 2004). Traumata consistent with boat collisions were present in 10.7% (3 of 28) necropsied humpback dolphin carcasses from the Hong Kong area, however not all injuries result in death (Jefferson, 2000a;Parsons and Jefferson, 2000).…”

Possible age-related hearing loss (presbycusis) and corresponding change in echolocation parameters in a stranded Indo-Pacific humpback dolphin

“…However, the stranding locations or home range of the older dolphin (Pearl River Estuary, Fig.1B) and the younger dolphin (Beihai Bay, Fig.1B) were geographically adjacent. Historically, the Indo-Pacific humpback dolphin was fairly continuously distributed in the coastal waters between Beihai Bay and the Pearl River Estuary (Fig.1B) (Jefferson and Hung, 2004). The most logical explanation for the different click spectrum shapes between the two dolphins is that the older dolphin tended to shift the spectral content of its echolocation clicks downwards to where the animal's hearing is more sensitive to partially compensate for its high-frequency hearing loss.…”