Population dynamics of Caspian Kutum, Rutilus frisii kutum (Cyprinidae) in southern Caspian Sea, Iran

The population dynamics of Caspian Kutum Rutilus kutum (Kamensky, 190 I), sampled from commercial beach seine catches from the southern Caspian Sea (Iran), was investigated. A random sample of 1,360 fish, representing a wide range of fish size (20 to 58 cm FL), was collected from early October 2006 to middle of April 2007. Length-frequency analyses and FiSAT software were used to study the population dynamics. The values of the von Bertalanffy growth function fit to size-at-age data were: L(infinity) = 59.85 cm fork length (FL), K = 0.27 yr(-1). C = 0.25, WP (winter point) = 0.40. Using the seasonalized length converted catch curve, the instantaneous total mortality coefficient Z was estimated as 1.28 yr(-1). The instantaneous natural mortality coefficient M was 0.46 yr(-1), while the instantaneous fishing mortality coefficient F was 0.82 yr(-1), giving the current exploitation rate E = 0.64. The mean length at first capture L(c) estimated from the analysis of probability of capture of each length class was 36.8 cm FL. The maximum exploitation rate E(max) predicted from the relative yield per recruit analysis was 0.76, while the current exploitation rate E is less than E(max). This indicates that Caspian Kutum is moderately exploited in the southern Caspian Sea.