Stock assessment of kutum in the Iranian waters of the Caspian Sea

Abstract

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 the Caspian Sea from 2015 to 2017. The catch of Kutum was 4282.9 and 3395.5 tons and CPUE were 98.3 and 80.4 kg/haul in 2015-2016 and 2016-2017, respectively. The mean (± SD) of fork length were observed 38.8±6.6 and 37.1±5.6 cm and for total weight were 790.8±435.2 and 637.2±392.2 gram in 2015-2016 and 2016- 2017, respectively. The most predominated of length class was obtained 34-36 cm in 2015-2016 and from 36-38 to 38-40 cm in 2016-2017 respectively and frequency of immature individuals were observed 48.1 and 55.5 percent during two sampling period, respectively. The range of age was from 2 to 11 year and fish with 3 to 5 years comprised up to 76.6 percent. In length – weight relationship a, b and r2 were calculated 0.01, 3.04 and 0.96 in 2015-2016 and 0.005, 3.19 and 0.92 in 2016-2017 respectively. K value, L∞ and t0 were calculated 0.2 (/year), 62.3 cm and -0.65 respectively. Mortality parameters such as Z, M and F were calculated 0.72, 0.37 and 0.35 respectively and Exploitation rate were calculated 0.49. The biomass of kutum estimated 25270 tons and 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.