An intensive survey carried out to locate remaining individuals of the critically endangered Yangtze River Dolphin, or baiji, a freshwater dolphin endemic to that river and the only surviving representative of its family, has not been able to find any of the dolphins. According to IUCN criteria, however, this species cannot be formally classed as extinct because Red List rules stipulate that 50 years must have passed since the last verified sighting of the organism. However, very few surveys of such detail have been carried out for the Yangtze River Dolphin, so the IUCN Red List's entry on this dolphin is probably too optimistic in its estimates, and the baiji is probably either gone for good, or with too few numbers in the wild to survive for very much longer.
Numbers of baiji have always been low; estimates in the 1980s ranged from 100 - 400, with sightings of the animals usually in groups, but a more recent survey in 1997-9 sighted just over 20 individuals. This present survey covered the 1669 km length of the Yangtze between Yichang and Shanghai twice, using visual and acoustic methods. The authors point out that the baiji is primarily a victim of 'incidental mortality', unlike other recently extinct or endangered animals, such as the dodo and tiger, which are victims of hunting and trapping. What killed off the dolphin population was a combination of pollution and habitat degradation, as well as accidental killing from booming river shipping traffic and fishing activity.
The fact is that 'even large charismatic and nominally protected animals are still in grave danger of being lost', and just because an animal is on the Red List, is widely known, and is discussed at international meetings or in the media, doesn't mean that anything concrete is being done about its death and decline. In this respect it reminds me of the case of the Indian tiger and how its wild populations may have been systematically underestimated for years, while illegal poaching and trade in tiger parts has still persisted even in supposedly protected wildlife reserves. Furthermore, while the death of a big mammal is a tragic and dramatic wake-up call, it's clear that the extinctions that we're not aware of are still proceeding unabated and will continue to do so even if governments enforce conservation laws more strictly.
Reference: Turvey, S.T. et al. 2007. "First human-caused extinction of a cetacean species?" Biology Letters, 3(5): 537-540; published online: doi:10.1098/rsbl.2007.0292.