Qualitative assessment of Caspian kutum (Rutilus frisii kutum Kamensky 1901) stocks in Iranian waters of the Caspian Sea (1991-2011)

Abstract

The main objective of the present study was qualitative assessment of Caspian kutum (Rutilus frisii kutum Kamensky 1901) stocks by using indicators of overfishing, condition factor and relative weight in Iranian waters of the Caspian Sea during a long period (1991- 2011). Three fisheries indicators in catch were: 1) percentage of mature fish, with 100% as target; 2) percent of specimens with optimum length, with 100% as target; and 3) percentage of mega-spawners, with 0% as target, and if no upper size limit exists, 30-40% as representative of reasonable stock structure. Over this period, the condition factor and relative weight had a decreasing trend. The range of length with optimum yield was between 40 and 48 cm. The mega-spawner measured as fish a size larger than 48 cm. According to these three indicators, the percentage of mature (fork length>40cm), optimum size and mega-spawners were 62.0, 40.9 and 12.5% in 1991-92 which decreased less than 50, 38.2 and 8%, in the years 1992-2011, respectively. The length structure is a matter of concern. Therefore, for reservation and rebuilt of kutum in the Caspian Sea, the target was to let all (100%) fish spawn at least once, using bigger mesh size in cod end (e.g. 35mm, during whole fishing season). The aim was also to implement a fishing strategy that result no (0%) mega-spawners being caught, and the main catch focus on optimum length.