| INTRODUC TI ONThe level of natural reproduction of sturgeons in the Volga-Caspian basin in the late 20th and early 21st centuries has varied widely, showing a general combined effect of both climatic factors (fluctuations of water level and salinity in the Caspian Sea depending on fresh water discharge) and anthropogenic impacts (the decrease in water discharge from the Volga River, deviations of its annual dynamics from the natural pattern, and reduction of spawning grounds and migration routes resulting from damming in 1958; excessive fishing; the impact of water pollution on gonad development, gametogenesis, and development of early life stages, etc.). The most dramatic situation became obvious after the dissolution of the Soviet Union in 1991 and formation of four new independent, Caspian bordering countries, with no effective fish protection system in place. The previously effective fish protection system deteriorated, resulting in a sharp increase of illegal sturgeon fishing in subsequent years. There is a wealth of publications available on the influence of various factors affecting sturgeon populations and their reproduction within the Volga-Caspian basin. However, the quality of data over time has not always been consistent as some studies were sporadic and monitoring did not always use a cohesive and standardized Abstract The review describes the changes in natural reproduction of three important sturgeon species in the Volga-Caspian basin: (a) the beluga (Huso huso Linneaus, 1758), (b) the Russian sturgeon (Acipenser gueldenstaedtii Brandt &Ratzeburg, 1833), and (c) the stellate sturgeon (Acipenser stellatus Pallas, 1771). Since the past 60 years, these species responded to severe influences of natural and anthropogenic factors. On the basis of original and published data, an analysis has been made of (a) the numbers of larvae migrating from spawning sites (according to plankton net survey), (b) fecundity and histological anomalies in gonad development, (c) the numbers of adult sturgeons in the Caspian Sea and of spawners migrating to the Volga River (according to trawl and beach seine survey), and (d) foraging resources for the sturgeons. The results show that their natural reproduction in the Volga-Caspian basin has declined drastically during the past decades under the impact of (a) fluctuations of the Caspian Sea level and flow discharge from the Volga River, (b) blockage of sturgeon migration routes and loss of spawning sites because of dam construction, (c) water pollution in the lower reaches of the Volga River and in the Caspian Sea, and (d) intensive and selective illegal and unreported fishing. The relative significance of these factors has been changing during the study period.

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