A marine conservationist says the plight of the Chinese white dolphin may worsen because the number of the threatened marine mammals seen in Hong Kong waters has fallen by more than a half in seven years.
All three key dolphin concentrations - west, northwest and northeast Lantau - saw declines of varying extents. The northeast, near the Brother Islands and east of the airport, recorded a 75 per cent drop.
The decline will add to the debate about the environmental effects of a plan for a third airport runway under which 650 hectares of marine habitat in North Lantau would be reclaimed.
The Hong Kong Dolphin Conservation Society says the average number of dolphins regularly seen in local waters has fallen from 158 in 2003 to 75 last year. But it was unclear whether the fall was because of increased dredging and declining food supplies or whether the dolphins have been driven away by rising vessel traffic.
"The vessel traffic is one of the biggest threats to the dolphin," society chairman Dr Samuel Hung Ka-yiu said. "But the third runway will further aggravate the cumulative impacts which will become even more unbearable."
More than 300 fast ferries to the mainland and Macau from the inner harbour or the airport pass through or near the dolphin habitats every day, a 50 per cent increase since 1999, generating noise that bothers the dolphins.
Hung said the Airport Authority might have deliberately played down the significance of the dolphin habitat north of the airport in its consultation paper on the expansion although more than 90 per cent of the dolphins active in North Lantau regularly used the area.
Hung also accused the authority of twisting the argument for reclamation when it said contaminated mud pits, created when Chek Lap Kok was built in the mid-1990s, had led to fewer dolphins in the area so the impact of the work would be minimal.
"It is like the notorious development approach of 'destroy first and build later'," he said. "Who knows if the seabed would recover if the pits were closed and properly covered, and whether dolphins would come back?"
Hung urged the authority to reveal the real environmental impacts of the runway project and not leave these issues hanging until the impact assessment process begins.
The authority said the dolphin data in its paper was accurate and that it welcomed views from stakeholders including green groups. It said conservation and development were not necessarily confrontational.