When an endangered species stops breeding, you know its days are probably numbered. In China the countdown has apparently begun for the critically endangered Chinese sturgeon (Acipenser sinensis). According to a report issued this week by the Chinese Academy of Fishery Sciences, only about 100 of the massive fish remain in the heavily polluted and dammed Yangtze River. Even worse, the academy found that the sturgeon did not reproduce naturally at all in 2013. Researchers found no evidence of either eggs or juveniles.

As a result of this lack of reproduction, researchers say the species is now at risk of extinction in the wild.

That's quite a change from just 50 or 60 years ago, when a healthy sturgeon fishing industry existed on the Yangtze and nearby rivers. But pollution and the construction of dams took a rapid toll. By the late 1970s, the sturgeon population had dropped to an estimated 10,000 adults. The 1980s saw another drop as the Gezhouba Dam cut off the upper Yangtze and blocked the sturgeons' migratory route. By 1984, the population of spawning adult sturgeon had fallen to under 2,200.

China did try to stop this decline by legally protecting the sturgeon and supplementing the wild population with millions of captive-raised juveniles and even recently hatched larvae. This practice continued for decades but the effort appears to have been for naught. Research published in 2009 indicated that the Yangtze's polluted waterways were contributing to sturgeon malformations, deformed larvae and a reduced egg quantity. In addition, because the Yangtze is heavily trafficked by boats and fishing vessels many of the fish have died from propeller strikes or in fishermen's nets.

The Chinese sturgeon species appears to have existed nearly unchanged for 140 million years. Although it will almost certainly persist in captivity, it seems likely that this will be its last century in the wild.

Previously in Extinction Countdown:

Photo: Shankar S. via Flickr. Used under Creative Commons license