NANCHANG, April 5 (Xinhua) -- Another four finless porpoises from the eastern province of Jiangxi have been relocated to a reserve in central China, as the critically endangered species' natural habitat is under threat from pollution, over-fishing and river traffic.

The four endangered porpoises from Poyang Lake were transferred to Tian'ezhou reserve in Hubei Province on March 28. One day ago, the Hubei Hewangmiao reserve reported that the first group had settled in.

With clean water, little pollution and scant human activity, both reserves offer ideal habitat for finless porpoises.

"The relocation program aims to prevent inbreeding and improve genetic diversity," said Dai Nianhua, deputy head of the institute of biological resources under Jiangxi Academy of Sciences.

A total of 16 finless porpoises have been relocated from Poyang Lake since 2015.

The finless porpoises, known for their "grins," live exclusively in Yangtze River and the Poyang and Dongting lakes, which are both linked to the waterway.

Statistics showed that there are only around 1,000 porpoises living in the Yangtze River, including 450 in the Poyang lake.