Scientists searching for endangered wild Chinese sturgeon recently stood on the banks of the Yangtze River, waiting for fishermen to pull a large net from the water.
After three hours of work, they came up with only a few gudgeon fish and some dead shrimp.
"The number of fish in the Yangtze River has been falling sharply, by at least two-thirds," said Chen Zhiming, who has been a fisherman in Yichang, Hubei province, for more than 30 years. "It seems all species are seeing a steady reduction in numbers."
The small fish Chen caught, mainly bronze gudgeons, were going to be dissected to determine whether the fish had eaten spawn laid by the rare wild Chinese sturgeon.
Scientists from the World Wildlife Fund and the Chinese Academy of Fishery Sciences are seeking to trace the sturgeon's spawning ground. They didn't find any in late November, when sturgeon usually release their eggs.
The wild Chinese sturgeon has existed for more than 140 million years, but is on the verge of extinction. No spawning sites have been detected in the polluted Yangtze since 2013.
Although a new spawning site was found in the Shanghai Yangtze Estuarine Wetland Nature Reserve in July, "one spot for reproduction doesn't mean much for a species on the brink of extinction," said Wei Qiwei, an academy investigator.
"We want to locate their spawning sites because we really need to protect them," Wei said. "If the population does not expand, extinction is only a matter of time."
The wild sturgeon could be extinct in as few as 37 years, "the time when the youngest sturgeon born in 2012 die", Wei said.
The population of adult Chinese sturgeon is estimated at about 100, compared to 10,000 in the 1970s, according to a protection plan for Chinese sturgeon released by the State Forestry Administration.
In the 1980s, there were at least 16 spawning grounds in the upper reaches of the Yangtze, where Chinese sturgeon laid their eggs after undertaking an annual 1,400-kilometer journey from the East China Sea, Wei said.
"Human activities are really putting them at risk," said Zhang Bo, an academy researcher. "Pollution is one significant factor, as urban sewage is discharged into the Yangtze River, but most importantly, their routes are blocked by hydro projects."
In recent decades, numerous dams have been built along the river's 6,300 km to boost the country's electricity supply.
Even if the Chinese sturgeon move to downstream spawning grounds, "higher water temperatures caused by slower water speeds are not suitable for reproduction," Zhang said.
The ideal temperature for reproduction is around 17 to 20 C, Zhang said, but the temperature was 21 C on Nov 19.
Local officials have made some efforts to safeguard the sturgeon. Sturgeon fishing was banned as early as in 1983, and a downstream conservation area was built.
"But we really don't know to what extent these efforts are enough to save the species from extinction until enough spawning grounds are found and we can make sure they are well-preserved," Wei said.