There is a significant lack of data for the biological parameters of beluga or great sturgeon, the largest fish in the Caspian Sea. The age, growth and fisheries indices for the stock status of beluga was investigated in the south Caspian Basin of Iran between 1990 and 2011. Fork lengths ranged between 113-420 cm and weights from 8.0 to 725.0 kg. The growth parameters were L∞ = 440 cm, K = 0.027 year−1, t0 = − 5.8 years. The age at first capture (tc) was 13.1 years. The long-term age composition data showed age up to 63 years, and the ages 12-19 years comprised 76.7% of the total catch. The generation length was 33 years. The values of “KF” were close to 1 or >1, indicating that beluga sturgeon is in a favorable condition in the southern Caspian Sea. The length distribution showed that 24.2% of the catch is comprised of juveniles. Based on the age structure and age at first maturity, recruitment and growth overfishing occurred in beluga stocks. Therefore, increased length or age at first capture in future fishery policies should be implemented. The mega-spawners represented 4.4% of the fish captured and revealed an unhealthy population structure.

No abstract

Persian sturgeon, Acipenser persicus Borodin, has been the most significant proportion of Iranian commercial sturgeon catches in the Caspian Sea over in the last three decades. This endemic species has suffered continuous population declines from the impact of anthropogenic factors. The present study filled in information gaps on underlying population biology parameters, evaluated the population status, and determined the vulnerability risk of the stock extinction of Persian sturgeon in the south Caspian basin of Iran. Growth parameters were L∞ = 224.7 cm, K = 0.058 years−1, t0 = -3.4 years. Sexual maturity of 50% for males and females was FL = 127.2 cm and 137.5 cm, respectively. The long-term age composition data showed 35 age groups, and the ages of 14–18 years comprised 80% of the total catch. Natural mortality was 0.123 years−1, and fishing mortality ranged between 0.104 and 0.331 years −1. The total biomass trend decreased and collapsed from 6,071.3 tons in 1990–91 to 144.1 tons in 2014–15. Although >93% of the catch included maturing specimens, the Persian sturgeon stock is now critically endangered because of several anthropogenic factors.

Russian sturgeon (Acipenser gueldenstaedti Brandt & Ratzeburg, 1833) is one of the major commercial sturgeon species, but there is no adequate information and previous‐published about population dynamics and stock assessment of this species in the southern Caspian Sea. This paper examines the age structure, growth parameters, maturity, age at first capture, optimum length, natural and fishing mortality and amount of biomass in the southern Caspian Sea (Iranian waters), during a two decades time series period from 1990–1991 to 2008–2009. For a pooled data, the growth parameters were estimated as L∞ = 214.0 cm, K = 0.054, t0 = −4.5 year. Size at fifty percent sexual maturity was at FL = 118 cm for females and 113 cm for males. The age at first capture (tc) estimated to be 12.1 years. In the catch composition, bulk of the catch (75%) belonged to 13–17 years old. The instantaneous coefficient of natural mortality (M) was estimated as 0.120 year−1 and the instantaneous coefficient of fishing mortality (F) varied during the 19‐year period between 0.130 to 0.505 year−1. The biomass showed a descending trend from 1,941.2 mt in 1990–1991 collapsed to about 55 mt in 2004–2005, and then decreased to the lowest level and represented 18.5 mt in 2008–2009. The result revealed that, the stock of Russian sturgeon is being over‐fished. We concluded that to manage the sturgeons stocks, a coordinated regional and international effort are needed to provide immediate implementation of stock enhancement and management in the Caspian Sea.

No abstract