The already rare Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) faces an 80 percent drop in its population over the next 30 years, according to research by the Institute of Hydrobiology of the Chinese Academy of Sciences.

Currently, around 1,000 of the freshwater porpoises live in China's Yangtze River and its surrounding lakes, down from 2,700 in 1991 and 2,000 in the year 2000. That number continues to drop 6.4 percent a year, according to Wang Ding, principal investigator for the Institute, who told the Xinhua News Agency, "The next 10 years will be a critical period for the conservation of this species."

According to the International Union for Conservation of Nature and Natural Resources, "porpoise habitat in the Yangtze has been degraded by water development, including the Gezhouba and Three Gorges dams and about 1,300 smaller dams in tributaries." The river is also heavily polluted by sewage and industrial runoff, according to the World Wildlife Fund's (WWF) 2007 report, World's Top 10 Rivers at Risk. A 2008 study, also by Wang Ding, found that many finless dolphins were dying from exposure to mercury, insecticides, polychlorinated biphenyls and other pollutants.

In addition to the loss of quality freshwater habitat, the survey team also found that the presence of a large number of vessels on the Yangtze River, a major shipping route, could be causing the porpoises to breed less frequently, a troubling situation for a species that already has a low reproductive rate. According to the WWF, finless porpoises have an 11-month gestation period and give birth to just a single calf at a time.

Fishing, both legal and illegal, has also threatened the porpoises. Starting in the 1990s less scrupulous fishermen started employing a technique called electro-fishing, which discharged a lethal electric current into the water, killing everything in it for 20 meters around their boats, according to the Zoological Society of London.

Until recently, little was known about finless porpoises. Genetic tests conducted in 2010 revealed the Yangtze population to be genetically different from other finless porpoises that live in coastal waters of the South China and Yellow seas.

The Yangtze was also home to the baiji (Lipotes vexillifer), a freshwater dolphin that was declared functionally extinct in 2007.

Photo: Finless black porpoise, a related subspecies, by Kenichi Nobusue via Flickr. Used under Creative Commons license