Efficiency of natural reproduction of sturgeons in the lower Volga under current conditions

Abstract

The reproduction of sturgeons in the Volga is an important source for replenishing their abundance and stock in the Caspian Sea. Prior to regulation of the Volga, the vast water area of its basin provided ample liv ing space for a large stock of sturgeons, which amounted to hundreds of thousands of spawners, allow ing them to disperse freely and effectively use spawning grounds of various types. This ensured a high survival rate of the offspring and consistent replenishment of the sturgeon stock in the Volga-Caspian Region.The results of long term studies (Veshchev and Guteneva, 2007;Veshchev, Guteneva, and Vlasenko, 2008) show that the amount of natural reproduction of sturgeons is determined mainly by the water level in the Volga and the abundance of spawners. In 1986-1990, for example, the river flow volume over the spring flood period was 114.7 km 3 , and the total num ber of beluga, Russian sturgeon, and stellate sturgeon spawners (without the nonmigratory sterlet) admitted to spawning grounds upstream of the commercial fish ing zone was 558500 ind.; under these conditions, the efficiency of their natural reproduction in terms of fishery yield reached 700040 t (Vlasenko and Vesh chev, 2008). A steady decline in the level of sturgeon reproduc tion since 1991 has made it necessary to reveal factors responsible for this situation and outline measures for improving the efficiency of their natural spawning. Our long term (1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)) data on censuses of stur geon larvae are used here to assess the effects of hydro logical conditions in years with different water levels and the numbers of breeders admitted to spawning grounds on the abundance of sturgeon offspring. The productivity of spring flooded and riverbed spawning grounds is also evaluated. MATERIAL AND METHODSRegular observations on the migration of sturgeon larvae were performed annually from May to August in 1991-2009, at eight stations in the lower reaches of the Volga near villages located at different distances from the Volgograd (Volzhskaya) Hydroelectric Power Plant (HPP): Barbashi (60 km), Staritsa (179 km), Solenoe Zaimishche (230 km), Enotaevka (279 km), and Shambai (408 km). In addition, quantitative cen suses of downstream migrating larvae of the stellate sturgeon and summer spawning Russian sturgeon were taken at stations near Kamennyi Yar (134 km) and Tsagan Aman (297 km) in July and August. The distances between the stations were taken into account to exclude recapture of the same larvae. The larvae were collected daily with IKS 80 cone nets (Rass and Kazanova, 1996) installed at four to six positions in the surface, middle, and bottom water horizons (3 m each). To this end, three nets were assembled on a col lapsible pole and simultaneously exposed for 10 min utes. At each station, the number of larvae caught per 24 hours was calculated, and the results were summed up over the entire period of downstream migration. The total abundance wa...

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“…Otherwise, insufficient numbers manifest themselves, as in social insects it leads to poor food availability and low survival of the offspring, in the Caspian sturgeon fish-to the loss of eggs at spawning grounds in the Volga River. The stellate sturgeon population practically died out and disappeared in the Caspian Sea before our eyes due to the failure of its artificial reproduction [5].…”

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Universal Method for Computational Modeling of Threshold Phenomenon in the Nonsteady Biological Processes

“…We received a change of stationary and two different chaotic modes of behavior. According to statistics [3], it turned out that the reproduction of three close species of sturgeon is expressed by completely different functional dependencies on the graphs. It is difficult to explain in ecology, but different species have a common population dynamics, like cod and anchovy populations.…”