A report to be released within days is expected to partly blame the impact of construction work on the Hong Kong-Zhuhai-Macau bridge for a continuing steep decline in the number of pink dolphins in Hong Kong waters.
The average number of pink dolphins - also known as Chinese white dolphins - in Hong Kong waters has already fallen from 159 in 2003 to 78 in 2011. A further dramatic fall in 2012 is expected to be revealed in the new report.
Dr Samuel Hung Ka-yiu, who has worked with government officials to prepare the latest figures, declined to say what the numbers were, but indicated there had been a significant fall.
"The decline is most likely related to the increased amount of construction work in relation to the Hong Kong-Zhuhai-Macau Bridge in Hong Kong waters that began in 2012 and the work that began across the border in 2010/11," Dr Hung said.
"This additional threat should be viewed on top of the existing threats, including the increased amount of vessel traffic, such as the traffic originated from Sky Pier at Hong Kong International Airport."
Pink dolphins have been recorded in Hong Kong waters for 400 years and the animal was the city's symbol at the time of the 1997 handover.
Janet Walker, spokeswoman for Dolphinwatch, which runs dolphin-spotting boat trips, said: "I wouldn't want to put a figure on it but with all the dead ones we've found this year, the trend can only be downward and I suspect it will be dramatic.
"The long term prognosis is not good because several dead babies were found this spring, which of course means in 10 years or so when they should be maturing, you have a smaller breeding pool."
Walker appealed to people to keep up pressure for action to save the dolphins.
The government's Agriculture, Fisheries and Conservation Department says it has had a conservation programme for Chinese white dolphins since 2001 and plans to designate more marine parks for them.