On April 13, the world’s only known female Yangtze giant softshell turtle died in China’s Suzhou Shangfangshan Forest Zoo following an attempt to artificially inseminate her, leaving behind just three confirmed individuals of the species.

The female turtle had been moved more than 1,000 kilometers (600 miles) from Changsha Zoo to Suzhou Zoo in 2008 in the hope that she would mate and produce offspring with the 100-year old male turtle that also lived in captivity at Suzhou.

The old turtle couple, however, failed to produce any offspring naturally, and several attempts at artificial insemination did not yield viable eggs.

After the fifth attempt at artificial insemination, the female died during recovery from anesthesia. The male recovered from the procedure.

Until recently, there were just four known Yangtze giant softshell turtles in the world. On April 13, the only known female among them died in China’s Suzhou Shangfangshan Forest Zoo following an attempt to artificially inseminate her, according to local media. She was more than 90 years old.

Three known Yangtze giant softshell turtles (Rafetus swinhoei) are now left behind: a geriatric male living in Suzhou Zoo, a wild individual in Vietnam’s Dong Mo Lake, and another wild turtle discovered recently in Vietnam’s Xuan Khanh Lake.

To protect the incredibly rare turtle species, Chinese zoos along with experts from international conservation groups, the Wildlife Conservation Society (WCS) and the Turtle Survival Alliance (TSA), made a “desperate move” by relocating the female Yangtze giant softshell turtle more than 1,000 kilometers (600 miles) from Changsha Zoo to Suzhou Zoo in 2008. The experts hoped that she would mate and produce offspring with the 100-year old male turtle that also lived in captivity at Suzhou. Over the next few years, the two turtles did produce several clutches of eggs, but none were viable.

Since 2015, experts have been attempting to artificially inseminate the female softshell turtle. Again, while the female did lay eggs, none hatched.

On April 13, after the fifth attempt at artificial insemination, the female died during recovery from anesthesia. The male recovered from the procedure.

“The male and female turtles, which have failed to produce offspring naturally since they were brought together in 2008, were determined to be healthy for the procedure, and similar anesthesia procedures had previously been performed without incident,” WCS said in a statement. “Sadly, this time the female turtle did not recover normally as she had in the past and she died despite 24 hours of nonstop emergency care. A necropsy will be performed and ovarian tissue has been frozen for potential future work.”

One of the world’s 50 most threatened turtles, the Yangtze giant softshell turtle was once known from the Red River in China and Vietnam and from China’s lower Yangtze River floodplain. But the loss of wetland habitats from infrastructure development and river damming, poaching for meat and eggs, as well as capture for the pet trade, have pushed the species toward extinction.

While only three individuals are currently confirmed, there may be more in the wild that have simply gone undetected.

“The species is very secretive and the lakes and large rivers that they are found in [are] large and complex,” Timothy McCormack, program coordinator of the Hanoi-based Asian Turtle Program of Indo-Myanmar Conservation (ATP/IMC), a U.K.-based conservation charity, told Mongabay last year. “If you see how difficult it is to observe these animals, even when you know they are in a relatively small area then you’ll understand how hard they will be [to] find.”

Researchers are continuing their efforts to find more individuals from this highly elusive species.