Beluga
Huso huso (Linnaeus, 1758)
Order Acipenseriformes
Family Acipenseridae
Conservation status: in Bulgaria: Critically endangered CR [A1ad], BDA-II, IV; International: IUCN [EN A2d], BeC-II, III, CITES-II.
General distribution. The Black Sea, the Sea of Azov, the Caspian Sea and the Adriatic Sea, as well as the adjacent rivers. In the Adriatic region, the finding of single specimens near Venice, in the lower and middle reaches of the Po River, and rarely, along the Albanian coast have been reported. In the Black Sea region, the beluga enters the large rivers, such as: the Danube, Dnieper, Southern Bug and Dniester, for spawning. In the Danube River, the species enters its tributaries Morava, Drava, Sava, Tisa, etc.
Distribution and abundance in Bulgaria. In the past, it was a comparatively rare species along the entire Bulgarian Black Sea coast and the Bulgarian section of the Danube River [1, 2, 3]. Recently, its population has declined sharply and only single specimens have been caught [4].
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 10-13 years, and females at 13-15 years [5]. Spawning lasts from February through May at water temperature of 4–11°C [6]. Eggs are laid in deep water with strong current and sandy and gravel bottom [1]. The fecundity ranges between 267 000 and 924 000 eggs [5]. The juveniles feed on insect larvae and the adults – on mollusks, crustaceans and fish [4, 7].
Similar species. In the Bulgarian section of the river Danube and the Black Sea, another 5 species of sturgeons have been found: the Russian sturgeon (Acipenser gueldenstaedtii), the ship sturgeon (A. nudiventris), the sterlet (A. ruthenus), the starry sturgeon (A. stellatus) and the common sturgeon (A. sturio). The beluga is distinguished by its large crescent-shaped mouth and gill membranes broadly connected with each other.
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 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 moratorium on sturgeon fishery in the Danube River and the Black Sea. Reintroduction of the species into the Danube River.
References. 1. Kovatcheff, 1923; 2. Drensky, 1951; 3. Stojanov et al., 1963; 4. Karapetkova, Zivkov, 1995; 5. Pirogovskii et al.,1989; 6. Banarescu, 1964; 7. Svetovidov, 1964.
Authors: Yanaki Sivkov, Tihomir Stefanov, Teodora Trichkova
