Population biology and stock status of common carp (Cyprinus carpio Linnaeus, 1758) in the Caspian Sea

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Common carp Cyprinus carpio Linnaeus, 1758 includes one of the most significant proportions of the Iranian commercial catch in the Caspian Sea (CS). The catch of this endemic species has suffered a high fluctuation over the last decades due to anthropogenic effects and management strategies. Age, growth, natural mortality, and age at first capture were investigated. Also, the stock assessment, fishing mortality (F), exploitation rate (E), and stock management in different strategies were estimated. In the period 1997/98–2021/22, the fork length and weight ranged between 15 and 71 cm and 100–5452 g. This fish showed a hypo-allometric growth pattern in the CS. The calculated growth parameters L∞, K, and t0 were 73.1, 0.125 yr-1, and − 0.91 yr, respectively. The annual population peaked at 35.3 million in 2002/03, then continuously declined until 2012/13, which represented only 1.9% of the peak. Over the period (25 yrs), in 21 yrs the E was more than 0.5, indicating fishing pressure on the C. carpio population in the area. The Fcurrent (0.57 yr-1) was greater than the related reference points of F0.1 (0.28 yr-1) and F30% (0.25 yr-1), indicating overfishing. The current tc was lower than the optimal tc (3.3 yr), indicating a growth overfishing. The current spawning potential ratio SPR (10%) was lower than the optimal value of 30%, indicating recruitment overfishing. It was recommended the F should be reduced half of the Fcurrent to avoid recruitment overfishing. The FL should be limited to 30 cm as minimum legal size of catch to avoid growth overfishing.