China's rapid industrialisation has likely made extinct a species of fresh water dolphin that had been on Earth for over 20 million years, Chinese and British biologists said Wednesday.

A baiji dolphin (File photo)

Scientists from China, Japan, Britain and the United States failed to find the white dolphin, known as the baiji, during a six-week search of its natural habitat in the Yangtze river last year.

"This result means the baiji is likely extinct," Wang Ding, co-author of the survey and one of the world's leading experts on the species, said.

The dolphin was a victim of devastating pollution, illegal fishing and heavy cargo traffic on the Yangtze, Wang said.

The findings mean the baiji is likely the first mammal to become extinct in more than 50 years. It is the cousin of the bottlenose dolphin, which is also on the critically endangered list.

Wang, from the Chinese Academy of Sciences, emphasised that not all hope was lost for the dolphin, which had made its home along the lower reaches of China's now heavily polluted Yangtze River for more than 20 million years.

"We are not saying the baiji is already gone," he said.

But he lamented that further searches this year had failed to find any sign of the dolphin.

Wang said that a letter written by the survey team had been published in the latest issue of the Royal Society Biology Letters journal in Britain to confirm the dolphin was believed to be extinct.

The baiji, identifiable by its long, teeth-filled snout and low dorsal fin, was last officially sighted more than two years ago.

The last confirmed count by a research team was conducted in 1997, when just 13 were recorded.

Up to 5,000 baiji were believed to have lived in the Yangtze less than a century ago, according to the baiji.org website, which was established by a range of international conservation groups.

"The decline in the baiji population has been caused by extreme human pressure on its freshwater habitat," the website said, blaming illegal fishing and massive discharges of industrial and agricultural waste into the river.

Other rare species that live in the Yangtze, such as the Chinese sturgeon and the finless porpoise, are also in danger of extinction.

The British-based zoologist who also worked on the six-week search meanwhile said the loss of the Yangste dolphin was a huge blow.

"The loss of such a unique and charismatic species is a shocking tragedy," said co-author Sam Turvey of the Zoological Society of London.

"The Yangtze River dolphin was a remarkable mammal that separated from all other species over 20 million years ago."

International environmental group WWF has warned that river dolphins are key indicators of a river's health and of the availability of clean water for people living on its banks.

"River dolphins are the watchdogs of the water," said Jamie Pittock, head of WWF's Global Freshwater Programme in a recent alert over their fate.

"The high levels of toxic pollutants accumulating in their bodies are a stark warning of poor water quality. This is a problem for both dolphins and the people dependent on these rivers," he added.

Turvey added: "This extinction represents the disappearance of a complete branch of the evolutionary tree of life and emphasises that we have yet to take full responsibility in our role as guardians of the planet."

(China Daily via Agencies August 9, 2007)