It could already be too late for the Yangtze River dolphin, or baiji. There has not been a documented sighting of these cetaceans, which lived in China's Yangtze River and nearby lakes, since 2002. A search for the dolphin--and the signature sounds that they make--was conducted in late 2006 but turned up no evidence of the mammals. However, further surveys are still needed to determine whether the dolphins truly have disappeared forever. The baiji's population decline is due, in large part, to the development of Chinese waterways and the expansion of commercial fishing.

Read more on helping endangered species by breeding captive animals in DISCOVER's Recall of the Wild