Too late? The Chinese river dolphin may already have succumbed to pollution in the Yangtze River. Credit: M. CARWARDINE/NATUREPL.COM

The world's most critically endangered cetacean, the Chinese ‘baiji’ river dolphin, may finally have a chance of being saved from extinction. But it could be too late; researchers who carried out a nine-day pilot search for the dolphins last month didn't find a single one.

If the giant panda is China's symbol of the destruction of forests, the baiji stands for polluted waters.

The freshwater baiji (Lipotes vexillifer) once thrived in their only habitat, the Yangtze River, which runs though central China. But fewer than 100 dolphins are thought to be left in the river, which has become a busy, polluted highway. “If the giant panda is China's symbol of the destruction of forests, the baiji stands for polluted waters,” says Wang Ding, from the Wuhan Institute of Hydrobiology.

An international team of scientists, led by Ding, is hoping to catch the animals and release them in a safer place, possibly the Shishou reserve, which is a 20-kilometre arm off the Yangtze.

But first the researchers —from China, the United States, Britain and Switzerland — need to find out exactly how many of the dolphins remain and where they are. They are preparing to conduct a search of 1,700 kilometres of the river in November, but carried out a pilot survey in March to refine their techniques.

The baiji are so few and far between that the best way to spot them is with acoustic devices. But that's a challenge. “The river is so noisy you can't use traditional acoustic equipment,” explains Jay Barlow, a marine mammalogist from the US National Marine Fisheries Service in La Jolla, California, who was on last month's cruise. He and his colleagues are working on a method to clean up recordings from hydrophones, to isolate the baiji's distinctive whistles.

The researchers were disappointed not to see a single baiji on their recent search, but their hopes are now focused on the full-scale survey in November. “If none are found then, the burden of proof will change,” says Barlow. “The species will be considered extinct unless proven otherwise.”