After three months of endless searching, scientists scouring the Yangtze River for the spawning ground of the critically endangered Chinese sturgeon have come up dry.

Fearing extinction of the prehistoric fish after failing to find any signs of breeding for two years, the mood is anxious but determined for those on the hunt.

"It is our hope that the fish changed its spawning site to an unknown place, rather than stopping natural propagation," Wei Qiwei, one of the main investigators for the Chinese Academy of Fishery Sciences, said. "We will keep on searching."

Chinese sturgeon, or acipenser sinensis, have existed for more than 140 million years. Sometimes called aquatic pandas for their critical endangerment, it is under top national protection.

Scientists found signs of hope earlier this year after discovering a large school of juvenile sturgeon during the spring and summer. The last time they had solid proof the fish spawned was 2012.

"It is similar to white-flag dolphins. They disappeared for a year and were spotted the next year before they finally became extinct," said Wang Chengyou, associate researcher with the research institute of aquatic animals in the Yangtze River under the Chinese Academy of Fishery Sciences.

The white-flag dolphin, an aquatic mammal which shares a home with the sturgeon in the Yangtze River, China's longest waterway, was recently announced "functionally extinct."

"If the Chinese sturgeon disappears, it is not only a tragedy for the species, but a woe for the whole river," said Wei Qiwei. "Condition of fish species is an important barometer for the ecology of a river."

The Chinese paddlefish, white-flag dolphin, finless porpoise and Chinese sturgeon are among the most endangered animals native to the Yangtze.

Experts put the population of Chinese sturgeon at around 200 and finless porpoises at 1,040. The other two species have not been seen in the wild for more than a decade.

CAUSE OF THE DECREASE

Overfishing is believed a major cause for flagging fish populations. In the 1970s, more than 10,000 Chinese sturgeon reproduced in the river each year. In 2000, the number dropped to 363.

The fish travels for more than 1,600 kilometers to reproduce. Despite protection measures, human activity along the way often threatens the fish.

In 2007, Wang Chengyou tagged a Chinese sturgeon and began tracking its movement. In 2009, they saw the fish moving upstream to lay eggs but the signal soon disappeared. "Local authorities confirmed that the fish was caught by a local fisherman and died," he said.

Pollution is also blamed for the decrease of life in the river. A report in 2012 showed that enterprises in the middle and lower reaches of the river discharged 12.4 billion tons of sewage that year.

Compounding problems, the Three Gorges project led to a change in water temperature of the river, so the Chinese sturgeon couldn't lay eggs because the water was not cold enough, Wei Qiwei said.

PROTECTION MEASURES

The government is protecting endangered species in the Yangtze River using habitat restoration, relocation and artificial breeding.

But Cao Wenxuan, a scholar with the Chinese Academy of Sciences, points out that protection involves the conservation and restoration of the whole environment they live in.

He suggested the government ban fishing on the Yangtze River to give the environment time to recover. Another effective way to prevent the species from dying out is to place them in new reserves.

This was the strategy used by Tian'ezhou National Nature Reserve in Shishou City of Hubei, which has witnessed an increase of the finless porpoise population from 22 to around 60 with four to five newborns each year since 2010.

Artificial breeding programs for Chinese sturgeon were also implemented in the 1980s. Researchers succeeded in artificially inseminating and spawning a culture of sturgeon in 2009. In 2013, they realized asexual reproduction for the fish.

Since then, people have released Chinese sturgeon into the river every year, though concerns remain whether the artificially-bred fish can help pass on the species' natural genes.

Chinese companies and NGOs also lend a hand to scientists fighting for the survival of the species.

China Three Gorges Corporation plans to invest around 550 million yuan (about 85 million U.S. dollars) to establish a protection center and gene bank for critically endangered species in the Yangtze River.

More than 200 volunteer journalists, teachers, businessmen and fishermen established an association to protect endangered species in Yueyang City of Hunan.

"More NGOs have joined us to pass the relay baton in protecting finless porpoises, including patrolling their habitats, rescuing the injured and helping authorities supervise polluting factories," said volunteer Zhang Tuodong, "we are really racing against time." (Xinhua)