Challenges for Diadromous Fishes in a Dynamic Global Environment

<em>Abstract</em>.-Diadromy is a life history attribute in a small number of fish species, and also some decapod crustaceans and gastropod mollusks, involving regular migrations at defined life history stages between freshwaters and the sea. Despite the relatively few species known to be diadromous, these are often of high fisheries importance owing in part to their migratory movements being spatially and temporally concentrated, making them vulnerable to exploitation. These migrations have important implications for a diverse array of aspects of biology: evolutionary, genetic, biogeographical, ecological, community, and conservation. There are also implications for the acclimatization of species into novel habitats, and deriving from these implications, diadromous fishes introduced into natural ecosystems may have seriously adverse impacts on the receiving ecosystems. As well, diadromy provides some species with the capacity to facilitate restoration of populations caused by adverse impacts on aquatic ecosystems across a broad range of spatial and temporal scales, from the effects of volcanism and glaciation to those of polluting discharges with anthropogenic sources. Allied with these questions is that relating to the importance of habitat connectivity and the vulnerability of diadromous species to events that interfere with up- and downstream migrations in fluvial ecosystems.