Stock assessment of Caspian mullets in the Iranian waters of the Caspian Sea (2015-2017)

Abstract

This study was conducted to determine growth parameters, catch and fishing effort trends and stock assessment of mullets in the Iranian coastal waters of Caspian Sea in the years 2015-2016 and 2016-2017. According to the result, the numbers of beach seines were 123 and 120 and their fishing efforts were observed 43588 and 42230 beach seining, respectively. The total catches (including illegal fishing) were also obtained 1542 mt and 2505 mt during 2015-2016 and 2016-2017, respectively. The mean (± SD) of fork length were observed 33.4±5.24 and 33.3±5.72 cm and for total weight were 395.8±142.8 and 395.5±264.52 g in 2015-2016 and 2016-2017, respectively. The frequency of immature individuals were observed 14.2 and 15.7 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 75.4 and 70 percent, respectively. In fork length – weight relationship a and b were calculated 0.029 and 2.690 for 2015- 2016 and 0.0207 and 2.7914 for 2016-2017, respectively. The Growth parameters of golden gray mullet were K=0.16/yr, L∞ = 64.3 cm, t0 = -0.26/yr. The total and naturaly mortality, Z and M, were calculated 0.81 and 0.35, respectively. Based on catch-at-age data, in the years 2015-2016 and 2016-2017, the total biomass, from the biomass-based cohort analysis were estimated 8170 mt and 7960 mt for golden gray mullet, respectively. In the years 2015-2016 and 2016-2017, the instantanuse fishing mortality F, were 0.25 and 0.46 year-1 and explotation ratio were 0.46 and 0.57, respectively.