Stock assessment of kutum (Rutilus frisii kutum) in the Iranian waters of Caspian Sea

This study was conducted to determine catch and fishing effort trends, length and age composition, growth and mortality parameters and estimate biomass and acceptable biological catch of Kutum in the Iranian coastal waters of Caspian Sea from 2013 to 2015. The catch of Kutum was 6112.8 and 5599.2 tons and CPUE were 181.1 and 183.5 kg/haul in 2013-2014 and 2014-2015, respectively. The mean (± SD) of fork length were observed 39.4±6.1 and 40.7±5.6 cm and for total weight were 805.1±378.0 and 891.5±384.6 gram in 2013-2014 and 2014-2015, respectively. The most predominated of length class was obtained 40-42 cm and frequency of immature individuals were observed 37.8 and 44.4 percent during two sampling period, respectively. The range of age was from 2 to 11 year and fish with 4 to 6 years comprised up to 84 percent. In length – weight relationship a, b and r2 were calculated 0.011, 3.02 and 0.96 respectively. K value, L_∞ and t0 were calculated 0.19 (/year), 61.3 cm and -0.99 respectively. Mortality parameters such as Z, M and F were calculated 0.82, 0.36 and 0.46 respectively and Exploitation rate were calculated 0.56. The biomass of kutum estimated 41000 tons and the acceptable biological catch calculated 8250 to 9750 tons. The biomass of Kutum decreased in recently years in spite of produce and release of huge fingerlings. This recruitment (produce and release fingerlings) must be continued for stability of stocks and fishing stress must be decrease by anyway