Environmental and fishery-related threats to the population of Rutilus kutum (Kamensky, 1901) in the Caspian ecosystem: a comprehensive analysis

Context Rutilus kutum stocks in the Caspian Sea have experienced long-term declines owing to intensified fishing and environmental stressors. Despite its ecological and economic importance, no integrative assessment of population dynamics has been conducted over an extended period. Aims To evaluate the status and productivity of R. kutum stocks over three decades, by using biological indicators and environmental drivers, and to inform adaptive fisheries management strategies. Methods Biological data were analysed to estimate growth parameters, mortality rates and exploitation levels. Novel application of generalised additive models was applied to assess recruitment relationships with seawater temperature, sea level, marine heatwaves and hatchery releases. Key results Exploitation rates frequently exceeded 0.5, indicating unsustainable fishing pressure. The length at 50% capture declined below the maturity threshold, increasing juvenile vulnerability. By 2021, abundance had dropped to less than one-third of 2006 levels. Generalised additive models explained 72.8% of recruitment variation, showing strong non-linear associations with environmental variables and hatchery output. Stock condition was rated ‘good’ in only 1 year. Conclusions Climate variability significantly affects stock productivity, and overfishing continues to undermine population resilience. Implications These findings support the need for ecosystem-based, adaptive management approaches that integrate environmental variability and regulate exploitation to conserve R. kutum stocks.