Population dynamics of stellate sturgeon Acipenser stellatus Pallas, 1771 in the southern Caspian Sea

In the last three decades, several ecological factors were changed and affected the most important commercial fish stocks in the Caspian Sea. This paper aims to assess the effects of these pressures on the population structure, stock status and the vulnerability risk of stock extinction of the stellate sturgeon (Acipenser stellatus Pallas, 1771) in the Southern Caspian Sea, in the years 1990-2011. For this period, we estimated growth parameters, the age structure of catch, sexual maturity, age at first capture, natural and fishing mortality, biomass and risk of stock extinction of stellate sturgeon by IUCN Red List categories. Fork lengths of individuals ranged from 82 to 206 cm and ages from 4 to 29 years. The growth parameters were L∞=215.0 cm, K= 0.064 year−1, t0=−3.2 years. The majority of the catch (67.4-90.1%, averaged 80.0%) belonged to 9-13 years old. The biomass had a descending trend from 4983.5 mt in 1990-91 declined to 10.6 mt in 2011-12. The generation length was 16 years. Stock status indicators showed that 89% of catch were mature individuals, mature and optimum fish length comprised 74% and 10% of the fish captured comprise mega-spawners. This study revealed that the stock of the stellate sturgeon is being overfished for the whole years and critically endangered.