River Dolphin Declared Extinct

Calling it a "shocking tragedy," a team of marine scientists have declared the Yangtze river dolphin "likely extinct" after their failure to find a single animal in a recent research expedition. The scientists blamed massive over fishing along the Yangtze as the primary cause of the species' disappearance, the BBC reports.

But the World Wildlife Fund disputed the declaration. Organization officials said the dolphin can't be declared extinct because the search was conducted in a short period over a limited section of the river. Species aren't considered extinct until an animal hasn't been spotted in the wild for 50 years. The last confirmed sighting of a Yangtze river dolphin was in 2004. (More China stories.)