Stock enhancement and density-dependence of Caspian kutum (Rutilus kutum Kamensky, 1901) in Iranian waters of the Caspian Sea

The Caspian kutum (Rutilus kutum Kamensky, 1901) is an important economic species in the southern, uniquely Iranian waters of the Caspian Sea. The present study aimed to assess the desirable levels of the Caspian kutum for stock enhancement with two scenarios using fingerlings released (FR) and recruitments (R) density-dependence and macrobenthic production (P). Based on the results, in the years 1989-2018, the FR increased from 72 million in 1989 to 400 million in 2009 and then declined to 176 million in 2018. In contrast, the R with a lag of 2 years declined from 44.53 million in 1991 to 25.77 million in 1998, increased to 65.07 million in 2005, and then collapsed to 25.01 million in 2018. Based on FR-R relationships of Ricker and segment regression models, the lowest level of FR, which resulted in the highest R (39 million), was about 200 and 150 million fingerlings, respectively. Based on the P/Biomass ratio of macrobenthic species, the annual production was 241.6 thousand mt. It concluded that the desired number of the Caspian kutum fingerling concerning stock enhancement could be lower than 150 million to prevent overcompensation in the Iranian waters of the Caspian Sea.