For most species, only the realized climate niche can realistically be estimated through correlative distribution models. For some species, it has become possible to determine the fundamental niche based on physiological information and a mechanistic understanding. Predicting the future species distributions using both correlative and mechanistic distribution models under climate change scenarios remains as such a rare application. The Allis shad (Alosa alosa) benefited from the attention of the scientific community given its dramatically decreasing trend in all Western European fresh waters. Conservation and restoration measures for the species are undertaken in two key systems of its distribution range where the species was formally a highly abundant exploited natural resource. Both types of distribution models were developed for allis shad and used for predictions but conclusions were never confronted. In the present study, a joint analysis of their results were undertaken to refine conservation actions in the light of climate change impacts. We raised two main concerns regarding: (i) the potential local adaptation of northern populations and (2) the importance of managing a target watershed considering potential existing neighbouring sources of migrants.