The chairman of the Hong Kong Dolphin Conservation Society, Samuel Hung Ka-yiu, said there was a discrepancy between the mainland and Hong Kong governments in conservation efforts.

While the Hong Kong government had been funding dolphin research projects regularly over the past 10 years, Mr Hung said, funding from the mainland government had not been consistent.

He also noted that while data collected about Chinese white dolphins was sufficient in assessing the impact of local projects on their habitat, more data about the waters in the Pearl River estuary was needed to study the species as a whole.

'However, the Hong Kong government can't fund projects carried out beyond Hong Kong waters,' Mr Hung said. 'We need more effort and co-operation from the mainland government.'

Ben Wilson, principal investigator and lecturer of the Scottish Association for Marine Science, also emphasised the need for a regional study to help conservation efforts.

Despite the threat posed to the dolphin, Dr Wilson said its endurance was impressive.

'We heard about Chinese white dolphins 15 years ago, and they are still there,' he said, referring to the threatening environment. 'Hong Kong is the only place where I can find all the human threats at the same spot. If we don't take action to manage those human threats now, their impact on the population status of these dolphins may be showing in five or 10 years' time.'

Last month a report by Mr Hung, who carried out research for his doctorate at the University of Hong Kong, recommended the government expand marine parks and scrap the idea of constructing a third airport runway to protect the dolphin's habitat.

Clarus Chu Ping-shing, senior marine conservation officer of WWF Hong Kong, said data on the Chinese white dolphins in the Pearl River estuary should be revised as soon as possible.

According to the IUCN Cetacean Specialist Group, an international concern group on conservation of dolphins, whales and porpoises, the Chinese white dolphin is classified as 'data deficient' on its red list of threatened species.

A spokeswoman for the Agriculture, Fisheries and Conservation Department said the department had been monitoring the dolphins for more than a decade. The department said it was also co-operating with the mainland authorities on conservation efforts.

Shrinking numbers

There are about 200 Chinese white dolphins in HK waters

In the Pearl River estuary, according to the HK government, there are up to: 1,500