WWF Bulgaria has implemented a project to release more than 50,000 baby sturgeons in the Danube to help bring the species back from the brink of extinction, AFP reported on Tuesday.

Only four of these species are left in the Danube out of the six varieties of sturgeons that once lived in the river flowing into the Black Sea, the newswire quoted  WWF Bulgaria country manager Vesselina Kavrakova as saying.

Three of these species are listed as critically endangered according to international classifications, while the fourth one - the Sterlet - “are listed as vulnerable but their condition is estimated as very bad,” Kavrakova said.

The lower part of the Danube in Bulgaria and neighbouring Romania is home to the EU's last still viable populations of sturgeons. WWF Bulgaria experts hope the released baby sturgeons will survive long enough to reach maturity and throw their own caviar into the river within another three or four years.

The  release of the little Sterlet sturgeons bred in artificial ponds by WWF Bulgaria is part of a BGN 1.35M project to improve the conservation of sturgeons in the Danube co-financed through EU funds under Operational Programme Environment 2007-2013.

Despite outlasting the dinosaurs, sturgeons are vulnerable to overfishing, poaching, contamination of water and interference in their natural habitat globally. According to the International Union for Conservation of Nature, they are "more critically endangered than any other group of species," WWF Bulgaria said on its website.