What can fisheries managers learn from spatiotemporal assessment of freshwater fish populations in three Tunisian reservoirs: Lahjar, Kasseb and Siliana?

Fisheries stock assessment is essential for sustainable freshwater fisheries management, and enhancing the management plans can improve the fisheries’ decision-making process. The present study assesses the status of fish assemblage aiming to provide recommendations for better fishery management in three Tunisian reservoirs: Lahjar, Kasseb and Siliana. Five surveys were conducted between March 2020 and June 2021 based on the European standard (CEN pr EN 14757), using the multi-mesh monofilament gillnets. This sampling method was applied to estimate species composition, abundance, yields, vertical distribution, and size structure. Eight species were caught in the reservoirs: Sander lucioperca, Chelon ramada, Mugil cephalus, Cyprinus carpio, Lucioberbus callensis, Rutilus rubilio, Scardinius erythrophtamlus, and Oreochromis niloticus. Fish abundance varied significantly among the sampling sites, seasons and depth. The highest catch per unit effort was observed in Lahjar Reservoir (820.08 ind.1000 m−2 / 162330.66 g.1000 m−2), followed by Siliana (161.59 ind.1000 m−2/ 28780.96 g.1000 m−2), while Kasseb Reservoir had the lowest values (4.17 ind.1000 m−2/1393.27 g.1000 m−2), suggesting it may be in an overexploitation state. RDA indicates unbalanced fish communities in Lahjar and Siliana Reservoirs. The findings showed that fish biomass distribution was influenced by depth, with the majority of catches occurring in the upper water layers. To conclude, Siliana, and especially Kasseb Reservoir, requires support to improve fish productivity and maintain biodiversity.