Past trends and future scenarios in the distribution of European catfish <i>Silurus glanis</i> in Spain

The European catfish (Silurus glanis) is a giant Eurasian freshwater fish that has become a high-impact invasive species in Western Europe. In Spain, it was first introduced in 1974 in the Ebro River for sport fishing, and has since spread to multiple river basins, despite bans. We compiled all known occurrence records in Spain (1974-2024) from scientific surveys, government databases and citizen science, standardizing them on a 10 × 10 km grid. Using first-detection data per waterbody, we reconstructed the invasion timeline and calculated decadal expansion rates. We then applied nonlinear models to project future spread up to 2030. S. glanis now occupies seven major Iberian basins, expanding from one grid cell in the 1970s to 129 cells by 2024. The invasion was initially slow (1970s-1990s), followed by a rapid expansion from 2000 to 2009, when the area occupied increased six-fold. Since 2010 its expansion has moderated, although new introductions in the Duero, Guadalquivir and Andalusian Mediterranean basins have driven localized explosive growth. Logistic and Gompertz models suggest the invasion may be approaching saturation in long-invaded basins (e.g. Ebro), projecting only a slight increase in total area occupied by 2030. However, model confidence intervals remain broad, reflecting uncertainty due to potential illegal translocations and climate-driven habitat changes in the future. Our findings underscore the urgent need for proactive management: preventing human-mediated jump dispersal, enhancing monitoring for early detection and enforcing regulations. Continued data updates and risk modelling are vital to inform policy and targeted control against this high-risk invader.