Chinese scientists said they will continue to search for the rare white-flag dolphin although it is possibly extinct as a 38-day search failed to find any in the Yangtze River.

Wang ding, head of a team of scientists that concluded their fruitless white-flag dolphin search on Wednesday, said the efforts to search for and protect the dolphin should continue as there might be some such dolphins still living.

"We will try every effort to save them as long as it is not announced to be extinct," said Wang, who is also vice director of the hydrobiology institute of the Chinese Academy of Sciences.

Wang said human beings had achieved successes in the protection of endangered species such as David's deer, which has grown into a population of 3,000 worldwide from the verge of extinction.

Wang said the monitoring of hot spots and small-scale searches will continue.

"The 3,400-km expedition only covered the main section of the Yangtze River and the scientists only searched for the dolphins eight hours a day, which means some dolphins might have been missed," said Wei Zhuo, an engineer from the hydrobiology institute of the Chinese Academy of Sciences.

Wang Ding and his colleagues insisted it was still too early to say such dolphin is extinct, while some foreign experts said "we have to accept the fact that the white-flay dolphins, also known as baiji, is extinct."

The white-flag dolphin, unique to China's Yangtze River, is listed as one of the 12 most endangered species in the world. Its population dropped to below 150 in the early 1990s from around 400a decade earlier.

Before the search, scientists estimated there would be no more than 50 dolphins in the river, a prediction that appears wildly optimistic with hindsight.

If the white-flag dolphin is extinct, it will be the first cetacean to vanish as a result of human activity as it is on the top of food chain in Yangtze River and has no natural enemy, according to Wang.

The mammals share the river with ships, towboats and fishing vessels, as the Yangtze has developed into China's busiest waterway. The research team's monitoring results show that there are 12 vessels per km on the river.

"If the Yangtze River can not support the white-flag dolphin at present, maybe it can not support human beings in the future," Wang Ding said. "We must learn a lesson from it."

The research team also found the population of an endangered subspecies of the finless porpoise has halved over the past 15 years due to water pollution, over-fishing and sand dredges.

They estimated the population of the state-protected Yangtze cowfish at between 1,200 and 1,400, only half the figure in 1991.

Scientists picked up sonar signals from 700 to 900 cowfish in a 1,750-kilometer Yangtze section from Yichang to Shanghai.

They estimated that another 500 are living in the adjoining Poyang and Dongting Lakes, China's largest freshwater lakes.

(Xinhua News Agency December 18, 2006)