Endangering factors

Overexploitation

Catch of sturgeon species was always dependant on the caviar demand. Use of caviar was not so globally spread until the second part of the 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, than from Russia. Fisheries of white sturgeon in Atlantic have been closed in America up to year 1915.

Fishery is traditional and important commercial activity in the Danube river basin. Sturgeons have predictable migration patterns, which is adding to their vulnerability. During the first decade of the 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 the year 1960 and 1996, data about sturgeon fisheries in Serbia were relatively well updated (Serbian Institute for Statistics). Maximum beluga catch was 20,7 t/year (1966, 1975), for the Russian sturgeon 17,6 t/year (1975), for the stellate sturgeon 8,6 t/year (1965). Stellate sturgeon catch decreased after ''Djerdap I'' dam was built, as well as Russian sturgeon catch after the construction of ''Djerdap II'' dam. For this reason, the I level of protection for Russian sturgeon and stellate sturgeon was established by the Decree on Natural Rarities (''Official Journal of the Rep. of Serbia'' No 50/93). Furthermore, by the Decree on measures for the protection of fish resources ("Off. Journal RS'' no. 36/09), permanent ban was established for the catch of beluga, Russian sturgeon, stellate sturgeon, ship sturgeon and Atlantic sturgeon.

Construction of dams and the 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 the upper parts of the Danube.

Disturbance of continuum of river flow and significant endangerment of fish populations by construction of hydropower plants, present a global phenomenon today. The dams have been built on the 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 this is the one of the main causes for the decline of their populations. 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 is only 17,8 km of flow accessible as spawning ground to migrating sturgeon species in Serbia after the construction of "Djerdap II''. The exact locations of spawning grounds on the territory of Serbia are still not determined. In Bulgarian part of the Danube, 13 spawning locations have been determined, located between 840 and 750 river km, while there are 5 spawning locations registered between 600 and 150 river km.

‘'Djerdap II'' hydropower plant

Feasibility study for the excavation of remains of German war shipwrecks (around 120 ships) from World War II was conducted in 2007. Remains of the ships are located downstream from "Djerdap II'', exactly in the section of the Danube where beluga catch is being conducted. Construction works in this part of the Danube could have significant influence on the migrating beluga.

Water pollution

Emission of the industrial, agricultural and communal wastewater into environment causes 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 predominantly benthivorous species, sturgeon are highly exposed to pollutants located in the sediment, and as the final predators in aquatic trophic chains, they are also exposed to a high level of persistent pollutants bioaccumulation. Recent studies have revealed the connection between increased concentrations of heavy metals and anthracene in sediment and sublethal hystopathological changes in gills, skin and liver in Danube sterlet population. Studies have also determined an increase of super-oxide dismutase and glutathione peroxidase activity as a reaction to the presence of certain contaminants in the ecosystem, originated from oil refinery.

The main reason for constant decline of sturgeon populations in the Volga since 70's is the negative effect of poor water quality on the survival of juveniles. Negative effects of pollutants in Volga, Ural and Caspian Sea have been confirmed to influence eggs, larvae and adult specimens, and are recognized today as the major threat for their survival. Contamination of the Northern Caspian Sea and surrounding lands is most probably responsible for such dramatic situation, with oil and gas industry as considerable sources of contamination, along with biocides originating from agriculture and many other pollutants.

Necrosis on sterlet liver

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

Influence of political, social and economic changes in the Lower Danube region on sturgeon catch

For countries in the Lower Danube region, the last decade of the 20th century has been very turbulent, from both political and economic perspective. Ongoing transition has affected all segments of the society. Strict fishing control ceased to exist, which has resulted in the increased pressure on many economically important fish species in Danube.

The main cause leading to the unsustainable legal and illegal catch of sturgeon species lies in the 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 the fishing territory "Danube IV'', where migratory sturgeon species are being 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 the decrease of the length of migratory pathways through construction of ‘'Djerdap I'' dam, and it became operational in 1990. Main goal of this Center was to provide artificial propagation of sturgeon species by the use of modern methods, and to enable the release of sturgeon fish fry in the Danube River. The Center was conducting 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 economic changes in Serbia and the change of water users, the Center lost its managing rights over the ‘'Danube IV'' fishing territory, and consequently all activities connected to the catch and artificial spawning of sturgeon species stopped. A private sturgeon aquaculture facility "Feniks'' was established in 2003, in Kusjak near the "Djerdap II'' dam.

Source: 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@imsi.rs