Climate change reshapes freshwater fish distributions in a semi-arid basin of the middle East

Abstract Climate change alters habitat conditions, reshapes species distributions, and intensifies extinction risks across terrestrial, marine, and freshwater ecosystems. Freshwater systems in arid and semi-arid regions are particularly vulnerable to climate change due to their sensitivity to hydrological variability and the limited dispersal abilities of aquatic species. However, assessing these impacts is often challenged by data scarcity, particularly regarding species occurrences. We investigated how climate change will affect habitat suitability for endemic, native, and alien fishes in the Karun River basin, a critically important river system in the Middle East. We applied ensemble Species Distribution Models (SDMs) that combine Random Forest and MaxEnt algorithms with high-resolution environmental predictors. We then projected current and future habitat suitability under three general circulation models (IPSL-CM6A-LR, GFDL-ESM4, MPI-ESM1-2-HR) and two climate scenarios (SSP1-2.6 and SSP5-8.5). Ensemble models performed well across all fish groups, with mean AUC values of 0.96, 0.94, and 0.93 and mean TSS values of 0.88, 0.85, and 0.84 for endemic, native, and alien species, respectively. Sensitivity averaged 97%, 99%, and 93%, specificity 94%, 96%, and 88%, and overall accuracy 95%, 96%, and 88% across the three groups. Compound Topographic Index, temperature, and precipitation were the most important predictors of current habitat suitability. Climate change is projected to result in net habitat changes ranging from + 21% to + 13% for endemic species, + 57% to + 46% for native species, and + 5% to + 99% for alien species. These results suggest that alien fish may benefit from climate change, highlighting the need for local conservation and management strategies to protect vulnerable endemic species and control the potentially expanding ranges of alien species.