The Yangtze River dolphin is no more – the first cetacean to disappear as a result of human activity.
After a fruitless search lasting six weeks, scientists failed to find a single Yangtze river dolphin, also known as the Baiji, in its natural habitat in China. They will now propose that the dolphin be formally reclassified this autumn as “possibly extinct” and say there is no longer any hope of resurrecting the species using a captive breeding programme.
During the expedition in November and December 2006, researchers in two boats scoured the river for the dolphin, using hydrophones to detect its underwater whistles. Listen to the dolphin’s whistle here.
They had planned to move any dolphins they found to a nearby lake to establish a breeding programme – a conservation strategy advocated since 1986.
Edge of existence
Yangtze River dolphins (Lipotes vexillifer) have long been recognised as one of the world’s rarest and most endangered mammals. The Zoological Society of London, UK, has made it the top priority of its new EDGE of existence programme (see Conservation bid targets world’s 100 weirdest creatures).
However, last year’s expedition “became crushingly depressing as it proceeded”, says Samuel Turvey of the ZSL. The World Conservation Union (IUCN) is now considering a proposal to change the Baiji’s status on its Red List of threatened species from simply “critically endangered” to “critically endangered (possibly extinct)”.
Randall Reeves of the IUCN told New Scientist he was in no doubt that the proposal would be accepted and the change would be made when the Red List was next updated on 12 September.
Originally only found in eastern China in the middle and lower Yangtze river and the neighbouring Qiantang river, the Baiji disappeared from the Qiantang in the 1950s. In the late 1970s, Chinese scientists estimated there were 400 individuals left in the Yangtze and its side channels. Two decades later they estimated that there could be as few as 13.
The dolphin’s decline was probably largely driven by fishing boats accidentally trapping Baiji in their gear. At least half of all known Baiji deaths in the 1970s and 1980s were the result of such by-catch.
The last confirmed sighting of a Baiji was in 2002, the same year that the sole surviving captive animal – a male called Qi Qi – died. Since then, fishermen have reported seeing Yangtze river dolphins on three occasions, but Turvey says it is impossible to confirm the sightings.
He adds that he and his colleagues cannot rule out the possibility that a few remaining dolphins could have been in the side channels of the Yangtze while they were patrolling the river. But he says all the side channels are too small to accommodate sustainable populations.
The researchers warn that a similar fate could await a subspecies of the finless porpoise Neophocaena phocaenoides, which only lives in the Yangtze and is already extremely rare.
They say the extinction of the Baiji “merely reflects the latest stage in the progressive ecological deterioration of the Yangtze region, home to approximately 10% of the world’s human population”. During their expedition they noted more than one large fishing boat for every 100 metres of river.
The world’s most endangered cetacean is now the Gulf of California porpoise Phocoena sinus, or “vaquita”, of which a few hundred remain. It is also threatened by accidental by-catch.
Journal reference: Biology Letters (DOI: 10.1098/rsbl.2007.0292)
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