The search for the rare Yangtze River dolphin by an international team of marine biologists is reaching the conclusion that it may no longer exist.
The white flag dolphin, long a feature of Asia's mightiest river, is probably now extinct - and died out only recently, the experts said.
"We had reports of a sighting earlier this year, but it couldn't be verified. On this expedition we have seen none so far," said Wang Ding, deputy director of the Wuhan Institute of Hydrobiology and a white flag dolphin expert. "The chances of there being any white flag dolphins left now look very slender indeed. Our only hope is that we can find a couple and keep them in a nature reserve."
The white flag dolphin, also known as the baiji, has been an endangered species for more than 10 years. Its dwindling population prompted an exhaustive search called the Yangtze Freshwater Dolphin Expedition 2006.
The effort involves two research vessels and covers the entire historic range of the white flag dolphin.
The boats departed Wuhan, capital of Hubei Province, early in November. They sailed upstream to Yichang in Hubei, then downstream to Shanghai and are now returning to Wuhan, a round trip of more than 3,400 kilometers. The expedition is expected to arrive in Wuhan around the middle of this month.
"There are four main factors that have contributed to the baiji's demise," said August Pluger, president and chief executive officer of baiji.org, a group dedicated to saving the creatures. "There's the ongoing usage of rolling hooks among fishermen, the loss of habitat due to dredging and the huge increase in shipping traffic and pollution."
Pluger hasn't entirely given up hope of seeing a baiji. But he concedes that even if there are any still out there, "they no longer exist in viable numbers."
The expedition boats travel one hour apart and along separate banks. Each vessel has a team of seven observers operating in rotation, four watching through daylight hours with high-performance optics. The ships anchor from dusk to dawn.
Hydrophone technology is also being used to detect the baiji's distinctive acoustic signals. So far, two-thirds of the way through the trip, none has been heard.
"Baiji are practically blind," said Tomonari Akamatsu, an underwater bio-acoustics expert from the Japanese National Fisheries Agency. "They hunt with sound, and they can communicate with each other over a large distance; however, due to the noise that the shipping on the river creates both of these functions must have been almost impossible for the baiji."
Bob Pitman, the international scientific director of the American National Oceanic and Atmospheric Administration, has spent 30 years studying marine mammals.
"This is the first cetacean to become extinct," he said, referring to a class that includes whales and porpoises, "and the first large mammal for over 100 years.
"This isn't just a loss for China but for all mankind."