Decadal‐scale regional variability in monitoring efforts significantly influences fish diversity trends in the Euphrates and Tigris catchments, Türkiye

Abstract This study investigates the temporal and spatial distribution of species richness in the Turkish portions of the Euphrates and Tigris catchments in Mesopotamia, aiming to identify areas lacking sufficient research and inform future conservation and management efforts. Data from 153 fish assemblages in the Euphrates catchment and 100 in the Tigris catchment, spanning from 1941 to 2022, were analysed using a combination of analytical occurrence, spatial and space‐for‐time mixed effect models. Results indicate an increase in reported species over time, attributed to heightened sampling efforts, and reveal significant differences in spatial species richness distribution influenced by uneven sampling and environmental suitability. Identification of areas with insufficient research, potential undetected species and biodiversity losses highlights the need for improved assessments to prevent unnoticed biodiversity loss and ecosystem degradation. Our results emphasize the importance of accurate biodiversity assessments for effective conservation and management interventions in these catchments.