وضعيت صيد و ساختار جمعيت ماهي سفيد RUTILUS FRISII KUTUM در سواحل ايراني درياي خزر

Catch Status and Population Structure of Kutum (Rutilus frisii kutum) in Iranian Coastal Water of the Caspian Sea

The population structure and fishery of kutum (Rutilus frisii kutum) in the Iranian coastal water of the Caspian Sea were investigated using a combination of size frequency and size- at- age data derived from regular monthly samples of commercial catches. Total catch of kutum (including poaching) was estimated 6612.5 tonnes that comprised 43.3 % of the total catch of all commercial bony fish species in 2004-2005 fishing season. Results showed that the mean fork length was 38.2 ± 5.9 cm. The kutum ranged in age from I to 8 years with a mean age of 4.2 years. The age group of 3, 4 and 5 years constituted 85.5 % of the age composition. Parameter values of the Von Bertalanffy growth equation fit to size at age data (males and females combined) were: K = 0.15 year ", L 00 = 60.7 cm (fork length) and 4>=-1.75 year. The annual instantaneous rate of total mortality (Z) derived from length converted catch curve was 0.88 year -I. The annual instantaneous natural mortlity (M) derived from Paulyʹs imperical formula Was estimated 0.31 year -I and annual fishing mortality was 0.52 year -I. Overall results showed that the growth rate of Caspian kutum had decreased in comparison to previous years. which seems to be due to non selective artificial breeding in more than 20 years of practice.