The mystery of where the critically endangered Chinese sturgeons go to spawn may soon be solved, as a group of ichthyologists plans to attach electronic tags to them.

Last Friday, six members of the Chinese Academy of Fishery Sciences went to a section of the Yangtze River downstream of Hubei Province’s Gezhouba Dam — the only known spawning ground of the species — to try to catch some of the rare fish.

An ultrasonic transmitter will be attached to any sturgeon caught and it will be tracked at 30 monitoring sites along the river.

Born in the Yangtze, the sturgeons migrate to the sea like salmon, before returning to their birthplaces to spawn. Previously, they returned to the Jinsha River, a major tributary of the Yangtze, but with the construction of the Gezhouba Dam in 1981, the migration route was cut off. However, they found a new spawning site, somewhere downstream of the dam.

For more than 20 years, researchers found spawning sturgeons in autumn and winter downstream of the dam, but not one has been seen since 2013. Researchers found signs of hope last April when they discovered a large school of juvenile sturgeons in the Yangtze estuary.

"This means they may have changed their spawning site to somewhere we know nothing about. We must find them and protect them as a matter of urgency," said Wei Qiwei, one of the lead researchers.

Sturgeons have been bred in captivity since 2009 and released into the river every year, but the number returning to spawn dwindled from 10,000 a year in the 1970s to just over 2,000 in the 1980s. Recent estimates put their numbers below 200.

The decline is believed to be the result of many factors: boat traffic, over-fishing, pollution, and the effects of the Gezhouba Dam.

Research has been complicated by restrictions on catching wild sturgeons introduced in 2008 in an attempt to stave off extinction. But this year the Ministry of Agriculture gave the academy clearance to collect and tag the fish.

The duration of the project will depend on how quickly the team can catch a significant number of sturgeons. "The tags should help us figure out their migration routes and new spawning grounds. It is a race against time to save this living fossil from oblivion," said academy researcher Wang Chengyou.

The Chinese sturgeon has existed for more than 140 million years and is a protected species.

"The state of this species is an important barometer of the whole river ecosystem," Wei said.