Endangering factors

Over-exploitation

Catch of sturgeon species was always dependent on caviar demand. Use of caviar was not so globally spread until second part of XVIII century, when France started to import caviar from Russia. At the beginning of XIX century, the larger amounts of caviar have been imported to Europe from North America, then from Russia. Fisheries in Atlantic of white sturgeon have been closed in America up to year 1915.

Fishery is traditional and important commercial activity in Danube river basin. Sturgeon have predictable migration patterns, which is adding to their vulnerability. During the first decade of XX century average catch of Russian sturgeon was 350-400 t/year in Romania, 12-150 t/year in Bulgaria and 120 t /year in Serbia.

Danubian fishermen

Between years 1960 and 1996 data about fisheries in Serbia on sturgeon species were relatively well updated (Serbian Institute for Statistic). Maximum of the beluga catch was 20,7 t/year (1966, 1975), for Russian sturgeon 17,6 t/year (1975), for stellate sturgeon 8,6 t/year (1965). After ''Djerdap I'' dam was built, catch on stellate sturgeon decreased, as well as for the Russian sturgeon after ''Djerdap II'' dam was built. For that reason, in the Decree on Natural Rarities (''Official Journal of the Rep. of Serbia'' No 50/93) was established the I level of the protection of Russian sturgeon and stellate sturgeon species. By the Decree on establisment of closed season for the particular fish species in the fishing area or in the specific parts of that area and prohibition of catch of fish under the prescribed length ("Off. Journal RS'' no. 100/2003), stellate sturgeon is under permanent prohibition of harvest.

Construction of dams and regulation of river flow

During the period between 1890 and 1896, even before the dams were built, the flow regulation itself was denying sturgeon species access to upper parts of Danube.

Disturbance of continuum of river flow and significant endangerment of fish population by construction of hydropower plants, present a global phenomenon today. The dams have been built on majority of rivers populated by sturgeon species, with 50 percent of all dams built in the region of Eurasia during the period from 1960 to 1980. Dams block access to most of sturgeon fish spawning areas and therefore it is believed that it is the one of the main causes for the decline of their population abundance. Construction of hydro energetic system on the territory of Djerdap gorge led to formation of two reservoirs with total area of approximately 25,000 ha. "Djerdap I'' was finished in 1970 and "Djerdap II'' in 1984, on 943 and 863 km of river, respectively. Complex of technical and ecological factors caused changes in fish distribution as well as in commercial fishing. The construction of "Djerdap II" has shortened migratory ways of Black Sea migratory species and significantly reduced their catch.

There was only 17,8 km of flow accessible as spawning ground to sturgeon species left in Serbia after the construction of "Djerdap II''. The exact locations of spawning grounds on our territory still haven't been determined. In Bulgarian part of Danube 13 spawning locations have been determined, located between 840 and 750 km of river, while between 600 and 150 km of river 5 spawning locations have been registered.

‘'Djerdap II'' hydropower plant

Feasibility study for excavation of remains of German war shipwrecks (around 120) from World War II is being done this year. Remains of the ships are located downstream from "Djerdap II'' exactly in part of Danube where beluga is harvested. Construction works in this part of Danube could have significant influence on the migrating beluga.

Water pollution

Release of industrial, agricultural and communal waste water into environment caused contamination of aquatic ecosystems. Fish are often exposed to highly contaminated water, which can lead to different changes, from biochemical alterations of single cells to changes in the whole population. As mostly bentic feeding species, sturgeon are highly exposed to pollutants found in sediment, and as final predators in aquatic trophic chain are also exposed to high levels of bioaccumulation of persistent pollutants. Recent research show the connections between increased concentrations of heavy metals and anthracene in sediment and sub-lethal hystopathological changes on gills, skin and liver in Danube population of sterlet. Research on sterlet in Danube showed rise of activity of super-oxide dismutase and glutathione peroxidase, as the reaction to presence of certain contaminants in the ecosystem, originated from oil refinery.

Main reason for constant fall of sturgeon fish population in Volga starting in 70's is the negative effect of poor water quality on survival of juveniles. Negative effects of pollutants in Volga, Ural and Caspian Sea have been more than once confirmed to influence eggs, larvae and adult specimens and are recognized today as basic threat for their survival. Contamination of Northern Caspian Sea and surrounding lands is most probably responsible for such dramatic situation, with oil and gas industry as considerable sources of contaminations, along with biocides originating from agriculture and many other xenobionts.

Necrosis on sterlet liver

Black Sea is considered today as being one of the most endangered seas especially by nutrient release into rivers, with 70% of pollutants coming in by Danube. Rising concentrations of nitrates and phosphates have led to frequent hypoxy and unoxy as well as to drop of zoobentos and macroalgae abundance in Black Sea coast, which can seriously affect juveniles as well as adult specimens of sturgeon species.

Influence of political, social and economic changes on lower Danube territory on sturgeon catch

For countries in Lower Danube region, the last decade of 20 th century has been very turbulent politically, as well as economically. Ongoing transition has affected all segments of the society. Among other things strict fishing control ceased to exist, which resulted on increase of pressure on many economically important species of fish in Danube.

Main cause leading to unsustainable legal and illegal catch of sturgeon species lies in a fact that caviar, especially beluga caviar, is considered as one of the most precious fish products.

Aquaculture Center in Mala Vrbica

From 1947 to 2000 the main user of fishing territory "Danube IV'', where migratory sturgeon species are caught, was fishing household "Djerdap‘' from Kladovo. A modern and well equipped "Center for production of fingerlings'' was built in Mala Vrbica as a compensation for decrease of migratory ways by construction of ‘'Djerdap I'' dam, and started working in 1990. Main goals were to secure artificial propagation of sturgeon species by use of modern methods, and to enable the return of fry to Danube River. The Center was performing successful artificial spawning of beluga, Russian sturgeon and stellate sturgeon, as well as restocking of Danube with their larvae. In 2004, due to political and economical changes in Serbia and change of water users, the Center lost its managing rights over ‘'Danube IV'' and all activities connected to catch and artificial spawning of sturgeon species stopped. A private hatchery of sturgeon species ‘'Feniks'' was established in 2003, in Kusjak near "Djerdap II'' dam.

Taken from: Lenhardt, M., Hegediš, A. and Jaric, I. (2005). Action plan for sturgeon species management in fishery waters of Republic Serbia. Institute for Biological Research “Siniša Stankovic”, p. 21. Developed for Ministry of Science and Environmental Protection of Republic Serbia.

Internet presentation was funded by Minstry of Environmental Protection of Republic Serbia. Webdesign & maintenance: Ivan Jarić ijaric@ibiss.bg.ac.yu