The population of an endangered freshwater porpoise in China has plunged by two-thirds in the last six years, Chutian Metropolis Daily reported Nov 27.

The number of finless porpoises, a rare species of freshwater marine mammals living in China's Yangtze River, has dropped sharply since 2006, a scientific expedition has found.

Researchers said a recent visual inspection has spotted 39 porpoises, while acoustic tests found another 19.

Wang Kexiong, leader of the expedition from the Institute of Hydrobiology under the Chinese Academy of Sciences, told the newspaper that those numbers are in stark contrast with the 2006 results, when researchers spotted 116 porpoises by eye and another 50 via acoustic equipment.

Zheng Xinqiao, finless-porpoises program officer of the World Wide Fund for Nature, said that shipping and fishing are among the reasons that the rare animal is threatened.