According to the International Union for Conservation of Nature sturgeon is the most endangered fish species on the planet. It emerged some 200 million years ago and the contemporaries of the dinosaurs are now endangered of extinction. We all know why - this is due to their extremely delicious caviar which caused an excessive catch over the past century. The Black Sea is the second biggest and most significant natural breeding pool of sturgeon fish after the Caspian Sea, although its population is at the critical minimum in both water basins. In Europe the lower flow of Danube between Bulgaria and Romania is the only suitable place for their breeding. Danube which flows into the Black Sea was until recently the river with the highest diversity of sturgeon worldwide, as six different types of sturgeon lived there. Today only four types of sturgeon swim in its waters. Moreover, their damaged populations can hardly survive without external help, experts from the WWF-Bulgaria contend. They intend to plant the Bulgarian section of Danube with nearly 50,000 small wild sturgeons.

The preparation has lasted for over one year. The participants in the Conservation of the Sturgeon Fish in the Lower Flow of Danube Project have been exploring the natural habitats of this fish and trying to find out where exactly the fish spawns and the small ones hatch. They also tried to find out how to catch enough wild sturgeon to take reproductive material. This is a very difficult task, explains Ivan Hristov who heads the WWF-Bulgaria’s Water Program.

“We have to make sure the fish used for breeding comes from natural population, instead of hybrid ones which are not well adapted to live in the Danube River. Moreover, the small fish has to be at the right place and in very good shape. Some colleagues contend that some breeding attempts in the past turned unsuccessful. The small fish was swimming in shallow waters where it fell pray to predators easily, or it was not in a good condition to escape from its enemy. In other words, the fish was previously bred in narrow spaces and it was not quick and active enough. One of the best approaches regards the possibility to let the newly-hatched fish cohabit in water environment with predators which can chase them and make them move quicker, so when we let them into the river, they can escape from their enemies.”

The team received in the beginning of May the first six Acipenser Stellatus sturgeon species which are later to be used for breeding. The small fish which hatch from their caviar will be transferred into the river at the end of the summer. Experts assume that the caviar donors are from the same shoal and their genetic memory will make the small ones return to the Danube when they start breeding. However, we have to wait a bit for that time to come.

“The maturity of the sturgeon fish comes quite late”, Mr Hristov specifies. “So, we can not tell for sure when the small fish will return again to the Danube. However, it will happen in at least ten years or so. The sturgeon spends most of its life in the Black Sea. When they enter the fertility period they go into the Danube once in every few years to spawn there. Breeding migration is quite difficult for this fish. It also wastes a lot of energy to form caviar. The fish needs between three and seven years to recover after spawning. Sturgeons can not reproduce each year. That is why the fish is more vulnerable. When a collapse appears, their population recovers extremely difficult.”

When and whether small sturgeons will return to the Danube depends on whether the projects aimed at improving the sailing conditions on the river will leave free space for the sturgeon to breed. In the 19^th century, the oldest inhabitants in Danube reached the upper stream all the way to Germany. Later, the water pollution and the construction of water power plants such as the Iron Gates in Serbia reduced their life space down to the Bulgarian section of the river. However, some technical plans in this section also hamper the migration of the sturgeon fish. Ivan Hristov says that a new shoot was built in the Romanian section of the river in a place where Danube splits in two arms also known as the old and the new arm.

“A project for the construction of a bed shoot is currently under way. It will close the old arm of the river and divert the water towards the new one, in order to ease sailing. The problem is that sturgeon has been migrating along the old arm for centuries. The research of the Danube Delta Institute in Tulcea, Romania, has proved in an experiment that the sturgeon fish would refuse to use the new channel and this would hamper their migration. Scientists have attached a satellite transmitter to a sturgeon which was swimming in the new river arm. When the migration period started the fish did not continue to swim along the new route and returned back to the main stream of the Danube and tried to swim along the old arm. Apparently, this fish is extremely conservative. It emerged before the dinosaurs and has not changed significantly ever since.”

In order to protect this fish from extinction Bulgaria and Romania imposed a moratorium on its fishing respectively in 2006 and 2008 in their Black Sea sections. Later the countries imposed a moratorium over their sections in the Danube River which is in force through 2016. However, the states will most probably extend this moratorium.

English version: Kostadin Atanasov