Last River Porpoises Dying in Polluted Yangtze
Kevin Holden Platt in Beijing, China
for National Geographic News
The planet's last river-dwelling finless porpoises are dying from exposure to insecticides and mercury in China, a new study says.
The mammals had already been declining as their natural habitat in and around the Yangtze River deteriorated.
In the new research, scientists also found high concentrations of polychlorinated biphenyls (PCBs) and other pollutants in the organs of porpoises found in central China's Dongting Hu Lake, which is connected to the Yangtze. (See China map.)
"In recent decades the [Yangtze finless porpoise] population
decreased sharply each year by approximately 7.3 percent because of
human activities on the river, including fishing, pollution,
transportation, and dam construction," said lead study author Wang Ding
of China's Institute of Hydrobiology.
A recent census turned up just 1,800 porpoises, and Wang warned that
"the Yangtze finless porpoise will become extinct within 24 to 94 years
if no protective measures are taken."
Wang and colleagues from the Chinese Academy of Sciences started
examining porpoise tissue and organ samples after the animal was
declared an endangered species by the World Conservation Union in 1996.
Some contaminants found in tissue samples, such as PCBs, likely
originated from industrial wastewater and agricultural pesticides and
herbicides, according to Beat Mueller, a geochemist at the Swiss
Federal Institute of Aquatic Science and Technology who has tested the
Wang said that some of the toxic substances were also found in water
samples taken in "heavily polluted areas near the sewerage outfalls of
a medicine factory and a paper mill around the lake."
Local agriculture and industry, including paper mills and oil
refineries, have increased dramatically in the region in the past few
decades, Wang said.
"It is estimated that approximately 800 million tons of wastewater are discharged into the lake each year."
During the same period, "declines of aquatic animal populations and
of species diversity in [the] lake have been observed," he added.
The study was published in a recent edition of the journal Environmental Toxicology and Chemistry.
In a companion study, Wang and colleagues discovered hazardous
amounts of mercury, a highly toxic and persistent pollutant, in
porpoise organ samples.
Porpoise calves were discovered to have the highest levels of
mercury poisoning, which could account for the dwindling porpoise
population, he said.
These discoveries provide additional evidence that contaminants need
to be reduced throughout the porpoises' habitat to avert its
extinction, said Swiss geochemist Mueller.
Li Lifeng, director of WWF China's freshwater program, agreed.
"Urgent measures need to be undertaken to save this porpoise.
"Pollution control is one of the most important, but this will take
time and huge efforts by the government and companies," he said.
WWF China has helped maintain a natural preserve for the Yangtze porpoise along an oxbow of the river at Tian-e-Zhou.
But the survival of the species will depend on reversing
contamination of the water and limiting harm caused by shipping and
"large infrastructure projects including dams, sluices, roads, bridges,
and harbors," Li said.
The Institute of Hydrobiology, meanwhile, has scored small successes
with its captive-breeding program, with a third calf expected to be
born at its dolphinarium this summer.