Baiji or the Yangtze Dolphin is classified by the IUCN Red List as a critically endangered species, and acknowledges the species as possibly extinct. In the 1950s, the population was estimated at 6,000, but declined rapidly over the subsequent five decades. Few hundreds were only left by 1970. Then the number dropped down to 400 by 1980s and then to 13 in 1997 when a full-fledged search was conducted. Now the most endangered cetacean in the world, according to the The Guinness Book of Records, the Baiji was last sighted in August 2007.