Every finless porpoise kept at the Institute of Hydrobiology, Chinese Academy of Sciences, is cared for by a designated staff member. These porpoises are highly intelligent and can recognize their human feeders and trainers. Their health is also monitored through regular physical examinations. Here a staff member trains a porpoise.

The Yangtze River dolphin and finless porpoise on the brink of extinction.

The Baiji dolphin (Lipotes vexillifer) was once a common sight in the Yangtze River. This was verified by Dr Zhou Kaiya from Nanjing University, who has studied the species for many years. Eyewitness accounts from fishermen in seven provinces have provided strong support for the accuracy of historical records - that the Baiji indeed once flourished in the river.

However, since the 1990s, no more Baiji have been sighted in the sections upstream of Shashi in Hubei Province and downstream of Jiangyin in Jiangsu Province.

Between 1997 and 1999, two expeditions to search for the Baiji were organized by the Ministry of Agriculture and the Institute of Hydrobiology of the Chinese Academy of Sciences. The first expedition found 13 dolphins; the second only four.

Another observation conducted in 2003 by the institute found zero dolphins. The world was further stunned in 2006 when the six-nation Yangtze Freshwater Dolphin Expedition announced its findings. Not a single dolphin was found after six weeks of surveying the Yangtze River, and the Baiji dolphin was declared functionally extinct.

End of the road

The Baiji was wiped out by human interference in their habitat, says Dr Wang Ding, deputy director of the Institute of Hydrobiology.

"The rapid degradation of the Yangtze River, the construction of dams and canal locks on lakes along the river and the widespread use of destructive fishing methods have directly affected the Baiji, as these greatly reduce the dolphin's food sources," Wang says.

The Baiji have also been exposed to many hazards in the river. Since 1998, dead Baiji dolphins have been discovered with broken skulls, multiple fractures and wounds caused by fishhooks. An explosion to clear a waterway in Lake Honghu, Hubei Province, killed a family of four dolphins - including two pregnant females.

Human population pressure and economic growth along both sides of the river have led to a rapid decline in the Baiji population. In 2004, a panel of 14 international experts declared the Baiji the world's most endangered cetacean. Furthermore, as the Baiji is the only known member in its family (Lipotidae), its demise spells the end of not just one species, but an entire natural family.

With eyes smaller than green peas, the dolphin has poor eyesight. It relies on its highly developed sonar to navigate and find food in the silt-laden waters of the Yangtze.

The Baiji's sophisticated sonar is of great interest to science, with potential applications in diverse fields such as bionics, medicine and defense.

The passing of Qiqi, a Baiji that died after 20 years of care at the institute, is still mourned by its caregiver Dr Wang Kexiong.

"Although other river dolphins and porpoises also possess their own sonar systems, none are as advanced as that of the Baiji," says Wang, who still finds it hard to accept the fact that Qiqi is gone.

The doctor had recorded Qiqi's unique calls and whistles before it died and he still listens to them every day as he works on his laptop computer.

In practice, a species is considered extinct when no members are found in their natural habitat for 50 consecutive years. Although Wang Kexiong, Wang Ding and other experts believe there could be a handful of Baiji dolphins left, they fear for the fate of these last survivors.