A Meta‐Analysis on Environmental Triggers of Spawning Migrations Reveals a New Classification of Thermal Guilds in European Freshwater Fishes

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Abstract
Fish migration through river networks is essential for completing life cycles and accessing critical habitats, but fragmentation increasingly disrupts spawning movements. In Europe, over one million barriers limit connectivity and create trade‐offs between ecological integrity and human uses, such as hydropower, flood control, fisheries and water storage. Furthermore, climate change can decrease habitat suitability, reinforcing migration needs to escape local extinctions. Limited knowledge of environmental triggers constrains species‐specific migration predictions. Here, we quantified the influence of seven environmental triggers—water temperature, flow, turbidity, cloud cover, rain, air pressure and radiation—on spawning migration of European freshwater fishes. A meta‐analysis of 112 studies (685,333 individuals, 953 effect sizes, 50 species) showed that water temperature was the dominant migration trigger. Radiation, turbidity and cloud cover showed weaker, context‐dependent effects, while effects of flow, rain and air pressure were non‐significant. Species‐specific average spawning migration temperatures correlated with upper limits of species‐specific thermal tolerances, indicating that migration timing reflects physiological constraints. Following this argument, we derive a new classification of thermal sensitivity for European freshwater fishes, distinguishing three thermal spawning guilds: cold (< 11°C), cool (11°C–15°C) and warm (> 15°C), with positive migration responses to temperature most frequently in warm‐water, less in cool‐water and rarely in cold‐water species. Our synthesis identifies gaps for species and triggers beyond temperature and flow, providing a quantitative basis for predicting spawning migration timing to guide conservation and connectivity restoration in European rivers.

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