Sturgeons are very sensitive to habitat changes. Altered habitats can immediately impact on their spawning, wintering and feeding success, and ultimately lead to their extinction.
Most sturgeon species today spawn on the clean gravel banks of the Lower Danube, where they lay their sticky eggs before migrating back to the Black Sea. Spawning takes place in deep waters, and at temperatures of at least 9–15ºC.
Sturgeon populations have been most seriously affected due to the loss of suitable habitat in the Danube River basin. Straightening and channelization of the river and the building of dikes along the banks to prevent flooding, has resulted in a dramatic loss of 80% of the natural floodplains and wetlands that are part of a river system. Navigation is a major threat to sturgeon habitats, mainly due to activities that have involved deepening, straightening and dredging of the river. Sand and gravel extraction, as well as bottom trawling, too, have had very harmful effects on sturgeon populations and will continue to be a threat for the fish in the river, especially but not only for sturgeon migrations in Romania near Calarași.
Our lack of knowledge of crucial sturgeon spawning sites in the Lower Danube means that unprotected key sturgeon habitats can be irreversibly destroyed.