Investigation of growth parameters, mortality and sex ratio of stellate sturgeon (Acipenser stellatus Pallas, 1771) from the southern of Caspian Sea

The aim of this study was to record growth parameters, mortality and sex ratio of Stellate Sturgeon (Acipenser stellatus) from the south basin of the Caspian Sea. 894 specimens were caught by fixed gill net and beach seine during April 2010 to March 2014. Male to female sex ratio was obtained 1:1.05 that was not differed significantly (p>0.05). The minimum and maximum length of the fish specimens ranged from 35 cm to 170 cm (for male) and 105 cm to 214 cm (for female), respectively. Mean (±S.D) total length was calculated 129.67±15.22 cm and 148.02±12.67 cm for male and female, respectively. The maximum frequency of length was 120-130 cm and 140-150 cm for male and female, respectively. The b value of the length-weight relationship for male was 3.074 that showed isometric growth (p>0.05) and for female was 3.209 that showed positive allometric growth (p<0.05). Total mortality (Z), natural mortality (M) and fishing mortality (F) were calculated (0.535, 0.222 and 0.313 year-1) and (0.465, 0.22 and 0.245 year-1) for male and female, respectively. Also exploitation rates (E) were obtained 0.59 and 0.53 for male and female, respectively. Estimated Von Bertalanffy growth parameter values were (L∞ = 187.54 cm, K = 0.15 year-1 and t0 = -0.32 year) and (L∞ = 195.00 cm, K = 0.14 year-1 and t0 = -0.25 year) for male and female, respectively. Also infinity weights (W∞) were estimated 21435 g and 26258 g for male and female, respectively. Tmax values (maximum length) were calculated 20 years and 21.43 years for male and female, respectively. Growth performance index (ϕ) was calculated 3.72 and 3.73 for male and female, respectively. Estimated logistic growth parameter values were (β1 (L∞) = 188.00 cm and β2 (growth-at-hatch) = 5 cm) and (β1 (L∞) = 190.00 cm and β2 (growth-at-hatch) = 5 cm) for male and female respectively. Based on the results, Acipenser stellatus stocks have unfavorable conditions in the south basin of the Caspian Sea, and the management measures are necessary to preserve and restore the remaining stocks of this species in the ecosystem.