Diadromous fish conservation plans need to consider global warming issues: An approach using biogeographical models

Most of the European diadromous fish species are endangered and listed in the habitats fauna and flora directive, the bern convention and the IUCN Red List. Current conservation plans do not address global warming issues and consider the 1900 distribution range as the reference without taking into account the potential re-distribution of these species under global warming. However, for other taxa, predictive models have been used successfully to relate conservation assessment with the impact of global warming. We investigated the distribution of the various diadromous species regularly encountered in Europe, North Africa and the Middle East at the beginning of the 20th century. For each species, we related the observed distribution to a set of environmental variables describing the prevailing climate in the basins, the physical nature of the basins and reflecting historical events known to have affected freshwater fish distribution. We successfully built twenty-one accurate species-specific models out of twenty-eight during both the calibration and the validation phases. Longitude, a factor we interpret as related to biogeographical history, was selected in all models and temperature was included in fifteen models, in six it was the most explanatory variable. These models allowed us to separate the roles of ecology and history in explaining distribution patterns at species level. Historical events such as glaciations constrained the continental distribution of all diadromous species and six of these were also highly temperature-dependent. Based on these results, we claim that these models can be used to predict the potential distribution under changing climatic conditions and provide two relevant examples (i.e. for Alosa alosa and Pe tromyzon marinus). Predictive models could be useful as a preliminary tool to prepare long-term conservation plans on European, national and regional scales.