Under threat in North African reservoirs: The decline of the Algerian barb, Luciobarbus callensis (Actinopterygii, Cypriniformes, Cyprinidae), in Tunisia as a case study

Despite numerous studies on stocked freshwater fishes in Tunisian reservoirs, the population status of native species remains poorly documented. This study aims to address a critical knowledge gap by assessing the decline in the population of the endemic Algerian barbel, Luciobarbus callensis (Valenciennes, 1842), in Tunisian reservoirs. Standardized fishing operations involving multi-mesh gillnets conducted across 21 reservoirs between 2013 and 2023 revealed that L. callensis was present in only 11 of these reservoirs. This indicates a significant reduction in the species’ range compared to historical records. The species exhibited alarmingly low catch rates (CPUE < 50 fish per 1000 m –2 of nets), except in Bir Mcherga reservoir. The application of data-limited stock assessment methods (CMSY++ and LBB) demonstrates widespread overexploitation across all the reservoirs studied. Length-frequency analysis revealed critical mismanagement: while most of the specimens caught were below the biological maturity threshold, they remain legally exploitable under Tunisia’s outdated minimum size limit. The decline of L. callensis stocks is primarily driven by unsustainable fishing pressure, facilitated by outdated regulations and habitat degradation. These findings highlight the urgent need for a comprehensive conservation management plan to prevent the continued decline of this important native species.