Acipenser gueldenstaedtii Brandt & Ratzeburg, 1833
Conservation status: in Bulgaria: Critically endangered CR [A1ad], BDA-II, IV; International: IUCN [EN A2d], CITES-II, HD-V.
General distribution. The Black Sea, the Sea of Azov and the Caspian Sea as well as the rivers that empty into them. The Black Sea rivers where the species migrate for spawning are: Danube, Dniester, Southern Bug and Dnieper. In the Danube River, it reaches Bratislava, entering also its main tributaries: Drava, Sava, Tisa and Morava Rivers. The Sea of Azov rivers where it spawns are Don and Kuban. The main river for spawning of the Russian sturgeon in the Caspian Sea is the Volga River.
Distribution and abundance in Bulgaria. In the past, the species was found frequently in the Danube River and along the Bulgarian Black Sea coast [1, 2, 3, 4]. In recent years, its abundance has declined considerably . In the period 2002-2005 alone, its annual catch in the Danube and the Black Sea has decreased 4-fold .
Habitats. In different periods of the year, it is found in different habitats. During the reproduction period, it inhabits permanent large rivers, and during the rest of the period – open sea, coastal areas and estuaries.
Biology. The males reach sexual maturity at the age of 11–13 years and females at 12–16 years . Spawning occurs in April–May at water temperature of 12–15°C . The fecundity varies from 50 000 to 1 165 000 eggs . Eggs are laid in deeper water over sandy and gravel substrate . The juvenile Russian sturgeons feed on insects and their larvae, worms and crustaceans, while the adults feed on mollusks, crustaceans and fish [7, 9].
Similar species: In the Bulgarian section of the Danube River and the Black Sea, another 5 species of sturgeons have occurred: the beluga (Huso huso), the ship sturgeon (Acipenser nudiventris), the sterlet (A. ruthenus), the starry sturgeon (A. stellatus) and the common sturgeon (A. sturio). The Russian sturgeon differs in having shorter, blunt snout and comparatively lower number of lateral scutes (21–50).
Negative factors. Loss (degradation) of spawning grounds, as a result of river regulation by dams and weirs; water pollution; poaching and overfishing.
Conservation measures taken. The species was included in the Red Book of the Black Sea (1999) and in Annexes II and IV of the Biological Diversity Act (2002). An Action Plan for the Conservation of Sturgeons in Bulgaria has been adopted (Ministry of Environment and Water, 2004). A temporary ban on catch of sturgeons in the Black Sea was initiated (Ministry of Agriculture and Forestry, 2006).
Conservation measures needed. Imposition of a total ban on sturgeon fishery in the Danube River and the Black Sea. Reintroduction of the species into the Danube River.
References. 1. Kovatcheff, 1923; 2. Berg, 1948; 3. Drensky, 1951; 4.; Karapetkova, Zivkov, 1995; 5. Vassilev, Pehlivanov, 2003; 6. Ministry of Agriculture and Forestry, 2002-2005; 7. Svetovidov, 1964; 8. Vlasenko et al., 1989; 9. Stojanov et al., 1963.
Authors: Yanaki Sivkov, Tihomir Stefanov, Teodora Trichkova