A new report has warned that the number of Yangtze finless porpoises has dropped to just 1,000 in the country's longest river - less than half of what there were in 2006 - making the species even rarer than the wild giant panda.

The 2012 Yangtze Freshwater Dolphin Survey Report, released in Wuhan, Hubei province, on Thursday, said that the endangered species is now declining by 13.7 percent a year, compared with 5 percent six years ago.

It blamed the decline in the mammal's numbers on food shortages and human disturbances, such as increased shipping traffic.

The findings were the result of a 44-day, 3,400-km expedition by researchers on the river, between Yichang, in Hubei province, and Shanghai that started in November.

It was led by researchers from the Ministry of Agriculture, the Institute of Hydrobiology at the Chinese Academy of Sciences, the World Wide Fund For Nature and the Wuhan Baiji Dolphin Conservation Fund.

The crew visually identified 380 individual Yangtze finless porpoises in the river's mainstream during the trip.

Based on that observation, scientists determined that the population of the species in the mainstream was about 500, down from 1,225 in 2006.

In October, research was also carried out in two adjoining lakes, the Poyang and Dongting, where the total population was assessed at about 540.

"The species is moving fast toward extinction," said Wang Ding, the general director of the research team, and a professor at the Institute of Hydrobiology.

According to data captured with acoustic equipment, the largest groups of finless porpoises were found in sections of the river east of Wuhan, with 67 percent of the total number recorded between Hukou, Hubei province, and Nanjing, Jiangsu province.

They were in a scattered distribution pattern, which could be the result of "shipping traffic that made migration harder, water conservancy facilities that altered hydrological conditions in the middle and lower reaches of the river, and habitat loss," added Wang.

The report said some small groups of finless porpoises living in comparative isolation were not a positive sign for future breeding of the mammal.

Scientists found fewer finless porpoises in the mainstream of the Yangtze while more discoveries were made in wharf and port areas.

"They may risk their lives for rich fish resources there. But the busy shipping traffic close to the port areas poses a huge threat to their survival," said Wang.

Researchers found denser distribution of finless porpoises in waters that are not open to navigation and attributed this to less human disturbance.

But evidence of illegal fishing practices were discovered in these areas, including traps.

Lei Gang, director of the freshwater program at WWF-China, warned urgent measures are essential to save the species from extinction.

With that in mind, the report called for year-round fishing ban for all river dolphin reserves, the establishment of a national reserve in Poyang Lake, and conservation reserves along the Yangtze.

Attempts to look for traces of the Baiji Dolphin, another rare cetacean and close relative of the finless porpoise, failed during the survey. As a result, the Baiji dolphin has been declared "functionally extinct" by the report.

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