Consisting of researchers from the Ministry of Agriculture, the Chinese Academy of Sciences (CAS) and the World Wide Fund for Nature (WWF), the survey team set off in Wuhan, a central Chinese city along the Yangtze River.

The 40-day survey is the most comprehensive since 2006, when a survey found the population of finless porpoises down to 1,800 and pronounced the white-flag dolphin, a larger mammal native to the river, close to extinction.

There are probably only 1,000 finless porpoises in the Yangtze and two lakes linked to the waterway after continuous drops in the number, said Wang Ding, researcher from the Institute of Hydrobiology under the CAS.

"Finless porpoises may die out within 10 to 15 years, if strong measures are not taken," Wang warned.

The survey team will trace the porpoises using sonar system along the middle and lower reaches of the river, collecting data on the species' population, which will assist in the making of future protection policies.

The initial results of the survey will be published in December.

"As the flagship species in the Yangtze, finless porpoises are the barometer of the river's ecological conditions," said Wang Kexiong, deputy commander of the survey team.

"NOT OPTIMISTIC"

Scientists said the survey may not produce optimistic results, as human activities including illegal fishing, sand dredging and pollution have pushed the species to the brink of extinction.

In 2006, a similar survey found no white-flag dolphins along the Yangtze River, suggesting them as being "functionally extinct," which means the population is too small for the species' reproduction.

Both mammals were regarded as the symbol of the river, with groups of them seen swimming around ships, a demonstration of better river ecology back then.

A 2010 WWF report said illegal fishing, inadequate water conservancy facilities and pollution in the Yangtze, China's busiest waterway, is to blame for the declining number of porpoises.

Since the beginning of the year, more than 20 porpoises have been found dead in the Yangtze River and the lakes of Dongting and Poyang.

Wang Ding said before the ongoing expedition, they have conducted several smaller surveys in the Yangtze River region, which suggested threats facing the porpoises have remained since 2006.

"We've just surveyed the section between Yichang and Wuhan, and caught rare sights of porpoises. We are not optimistic about the results of the mainstream survey either," Wang said.

Lei Gang, director of WWF China's Freshwater Program, said immediate action is needed if people wish to save the finless propoises from the same ill fate as the white-flag dolphins.

"This means better laws and enforcement -- we need to see harmful fishing practices stopped, sand dredging better controlled, and new reserves developed," Lei said.

Wang expected the survey could help put the porpoises onto China's top list of wildlife protection, which will bring more government investment to related conservation programs.

"We've discussed this for years as it involves complicated procedures, but as far as I know, the change may come soon," Wang said. (Xinhua)