Spatial distribution patterns and causes of decline of threefreshwater species with different biological traits (white-clawedcrayfish, bullhead, freshwater pearl mussel) : a review

Abstract

White-clawed crayfish, bullhead, and freshwater pearl mussel are different model organisms in terms of biological traits.Analysing their distribution patterns, habitat demands, and causes of decline may thus help to derive broader frameworks forconservation projects. This paper includes a wide-ranging literature review for these three threatened freshwater animals, thenuses general patterns to make suggestions about broader protection measures for freshwater species. Each species has a patchydistribution, from local to broad spatial scales. However, we point out the difficulty to summarise such knowledge, because manyvariables were not consistently and/or accurately recorded by workers, and because the range of colonised habitats depends onthe environmental heterogeneity within study areas. Causes of decline are chiefly related to human activities which modify thebiological, chemical, and physical features of the aquatic environment, and can be classified into four types: physical habitatalterations, interspecific interactions, overfishing and poaching, and natural disturbance. By analysing causes of decline andpossible actions, we develop seven general trends that could be adopted for a wider array of species. However, protection planscannot be effective without actual collaborations between river managers, local inhabitants, and authorities. Finally, there-introduction procedure itself (if needed) depends on the biology of the species under survey, and remains specific. At the sametime, further fundamental research is needed to generalise relationships between population and habitat dynamics at differentspatial and temporal scales.