Common Sturgeon
European Sturgeon
Acipenser sturio Linnaeus, 1758
Order Acipenseriformes
Family Acipenseridae
Conservation status: in Bulgaria: Extinct EX, BDA-II, III; International: IUCN [CR A2d]; BeC-II; CITES-I; HD-II, IV.
General distribution. The European coast of the Atlantic Ocean to the Baltic and North Seas in the north and a large part of the Mediterranean region: the Tyrrhenian Sea, the Adriatic Sea, the Ionian Sea, the Aegean Sea, the Sea of Marmara and the Black Sea, as well as the large rivers flowing into them.
Distribution and abundance in Bulgaria. In the past, only single specimens were recorded in the Black Sea [1], mainly in the coastal area near Varna and Burgas [2]. In the Danube, the common sturgeon entered the area of the delta [3, 4], but it is doubtful whether it reached the Bulgarian section of the river [5]. In the past, in the Aegean Sea, the species entered the rivers Struma [2] and Maritsa, where it reached the city of Plovdiv [6]. In the past 50 years, it has not been recorded in Bulgaria [7].
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 male individuals reach sexual maturity at the age of 7-9 years, and the females at the age of 8-14 years [4]. Spawning is from April to May. Eggs are deposited in swift current over sandy or gravel bottom [1]. Fecundity ranges between 200 000 and 5 700 000 eggs. The young individuals feed on larvae of aquatic insects, worms, crustaceans and mollusks, and the adults - on mollusks, worms and small fish [8].
Similar species. In the Bulgarian section of the Danube River and the Black Sea, another five species of sturgeons have been recorded: the beluga (Huso huso), the Russian sturgeon (Acipenser gueldenstaedtii), the ship sturgeon (A. nudiventris), the sterlet (A. ruthenus) and the starry sturgeon (A. stellatus). The common sturgeon is distinguished by the lower number of lateral scutes (between 24 and 36) and the presence of dense cross-lines of smaller rhombic plates between the dorsal and lateral rows of plates.
Negative factors. Loss (degradation) of habitats, as a result of hydrotechnical activities leading to river regulation by dams and weirs; water pollution; poaching and overfishing in the past.
Conservation measures taken. The species was included in the Red Data Book of Bulgaria (1985) and in Annexes II and III 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).
References. 1. Stojanov et al., 1963; 2. Drensky, 1951; 3. Berg, 1948; 4. Banarescu, 1964; 5. Marinov, 1978; 6. Kovatcheff, 1923; 7. Vassilev, Pehlivanov, 2005; 8. Holcik et al., 1989.
Authors: Tihomir Stefanov, Yanaki Sivkov, Teodora Trichkova
