Population viability analysis of the Danube sturgeon populations

Abstract: Populations of six sturgeon species in the Danube River (Beluga, Russian sturgeon, Stellate sturgeon, Sterlet, Ship sturgeon and Atlantic sturgeon) have experienced severe decline during the last several decades, mostly due to the unsustainable fishery, river fragmentation and water pollution. In the present study, the question of viability of Danube sturgeon populations and the poor knowledge of their ecology have been addressed through three different research activities: 1) statistical methods that infer extinction based on sighting records have been used to assess probability of extinction of the Ship and Atlantic sturgeon, whose presence n the Danube basin is uncertain; 2) assessment of microelement accumulation in sturgeon pectoral fin rays, especially of strontium and calcium, has been conducted as a method that can reveal migration patterns of anadromous sturgeons; 3) population viability analysis in a Vortex simulation model has been conducted in order to assess the state of the six Danube sturgeon species, their future risk of extinction and to determine the most suitable conservation and management measures. Methods for inferring extinction based on sighting records provided a significant probability that the Atlantic sturgeon is extinct, with extinction occurring somewhere between 1966 and 1970, and that the Ship sturgeon is probably still present in the Danube basin, but that extinction may occur within a few decades. A new model has been also developed within the present study, able to infer probability of extinction based on the trends in sighting intervals, since this issue was not adequately considered in the existing models. Although the analysis of the strontium to calcium ratio in sturgeon pectoral fin rays has revealed changes that might indicate probable migration of juvenile fish from the river to the sea, further studies are needed for improvement of this method. Population viability analysis has revealed a large sensitivity of the Danube sturgeon populations to changes in the natural mortality, fecundity, age at maturity and spawning frequency. It was also confirmed that the sturgeons are highly susceptible to even moderate levels of commercial fishery, and that their recovery is a multi-decadal affair. Stocking with adult individuals was shown to produce considerably greater effect on population persistence than stocking with juveniles, but the latter approach is probably still preferable since it avoids many inherent problems of aquaculture cultivation. This study represents the first population viability analysis of the Danube sturgeons.