Chinese officials added an extra 50,000 carp to the waters of Poyang Lake this week to help feed the endangered Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) that live there, according to a report from the Xinhua news agency.

Around 300 to 500 porpoises live in Poyang Lake in northern Jiangxi Province, representing between one third and one half of the subspecies's global population. The porpoises have experienced a dramatic population crash in recent years, falling from 2,700 individuals in 1991 to around 1,000 in 2011.

Things haven't gotten any better this year: Six dead porpoises have been found in Poyang Lake, and another 12 dead, including a pregnant female, have been found in Dongting Lake in northeastern Hunan Province. A survey earlier this year found only 65 porpoises in Dongting, so the deaths are a terrible blow for that tiny population. Xinhua reports that at least five more dead porpoises turned up in the Yangtze River, which connects the two lakes, putting the death toll above 20, but a report from the World Wide Fund for Nature puts the total fatalities much higher at 32 porpoises.

Experts blamed the spate of deaths on pollution as well as low water levels due to drought and climate change. Other theories include disease or damage from electrified fishing nets. Many of the dead porpoises showed signs of starvation, which may have influenced China's decision to stock Poyang with extra fish. At least one of the dead mammals from Dongting had been severely injured by a boat propeller.

Finless porpoises—so named because have low ridges on their backs instead of full dorsal fins—can also be found in the coastal waters off Japan, Indonesia and Korea, but the Yangtze variety are the only ones that live in freshwater. The adults of all finless porpoise varieties grow to about 1.5 meters in length, compared with up to 1.9 meters for their more famous cousins, harbor porpoises (Phocoena phocoena).

Poyang used to be China's largest freshwater lake. The construction of Three Gorges Dam and subsequent droughts have reduced it in size by nearly 95 percent and weakened the region's ecology.

Previously in Extinction Countdown: "China's Yangtze Finless Porpoise Faces 80 Percent Decrease in 30 Years"

Photo: A related Japanese finless porpoise by Kiuko via Flickr. Used under Creative Commons license