Stage-structured prediction of establishment, spread and integration of non-native freshwater fishes: within-country translocations pose greater risk

Building on trait-based invasion theory, we developed a stage-structured profiling framework to evaluate both foreign introductions and extralimital species (within-country translocations beyond historical ranges) of non-native freshwater fishes in Greece, predicting establishment, spread and integration. We compiled a dataset of 63 species (36 foreign, 27 extralimital), and characterized each species with ecological, biogeographic, and anthropogenic attributes. Predictors were evaluated with cross-validated logistic/multiple regression and CART models including a taxonomy-based covariate to reduce bias from shared ancestry. Extralimital translocations were frequent and all 27 species established, emphasizing their disproportionate role in reshaping regional faunas. Establishment increased with physiological tolerance and proximity to the nearest native source, but declined with maximum body size, and propagule pressure showed only weak additional support. Spread across drainage basins was driven mainly by introduction effort and physiological tolerance. Integration increased with introduction effort, while CART identified distance from nearest native source as the primary discriminator of widespread and abundant outcomes, with trophic level further structuring outcomes among extralimital taxa. These results indicate that management frameworks focused solely on foreign non-native fish species may underrepresent risk. from within-country translocations. Incorporating both pathways into screening and surveillance can strengthen prevention and early detection, addressing a European policy gap where translocations remain more weakly regulated than foreign introductions. Our study provides a practical, trait- and pathway-informed screening tool that integrates organismal traits with invasion-history and biogeographic proxies to guide prevention, pathway management and targeted monitoring in Mediterranean river networks.