Efficiency of gillnets with 170mm mesh size in reduction of immature Persian sturgeon, Acipenser persicus, catch

This study was carried out in Turkmen fishing station to examine suitable mesh size of gill nets for Persian sturgeon, Acipenser persicus, to decrease possibility of catching immature specimens and increase catch likelihood for larger fish. The Holt model was used to determine suitable length for catch and selection of mature Persian sturgeon females. Following preliminary studies some 920 experimental gill nets (mesh size 170mm) similar to those generally used by Iranian Fisheries except for mesh size (150mm) were set up in the Caspian Sea. During the experimental period, 128 and 110 sturgeons were caught in control and experimental nets, respectively. Out of those caught in control nets, 63 specimens were Persian sturgeon (49.2%), 57 were Stellate sturgeon, Acipenser stellatus (44.5%) while in the experimental nets, 95 specimens (86.4%) were Persian sturgeon and 7 specimens (6.4%) were Stellate sturgeon. Regarding maturity status of fishes, 42 Persian sturgeon caught in control nets were mature females while this figure was 83 (87.4%) in experimental nets. Mean fork length of the Persian sturgeon was 152.9±13.8cm and 162.4±13.6cm in control and experimental nets, respectively. The mean caviar yield of the Persian sturgeon in control nets was 6.4±1.7 kg and in experimental nets was 7.4±1.9kg. One way ANOVA and Tukey’s test showed significant differences between factors like age, mean caviar yield and fork length of the Persian sturgeon caught in control and experimental nets. The results showed increasing mesh size of gill nets to 170mm for the Persian sturgeon may help achieving objectives of stock managements including decrease in catch of immature fish and increase in catch of mature and larger sturgeons which can secure optimum and sustainable stock yield.