WUHAN, Nov. 16 (Xinhua) -- Scientists have sighted highly endangered finless porpoises for more than 70 times in six days in the Yangtze, China's longest river.

A scientific expedition sent by the Ministry of Agriculture is currently surveying the number of finless porpoises along sections of the river. On Sunday alone, they located porpoises for 40 times in the Jianli section of the Yangtze, a number much higher than previous surveys of that section undertaken in 2006 and 2012.

"The increase in the population could be related to the improving river environment in recent years, or the changes in the habitat of the finless porpoise," said Hao Yujiang, with the Institute of Hydrobiology under the Chinese Academy of Sciences.

Hao, leader of the expedition, said that their observation does not necessarily confirm the exact size of the porpoise population, and that number will be given out after "comprehensive" calculations.

The team will continue their journey to the lower reaches of the river. Their final survey results will be announced in March 2018.

Finless porpoises are a freshwater animal. Around 1,000 finless porpoises are believed to live in the Yangtze River and two lakes linked to the busy waterway. The government has been trying to increase their population with breeding programs.