Aquatic Habitat Connectivity and the Proliferation of Non-Native Aquatic Species

Dams, often considered detrimental to riverine ecosystems, often play critical roles in blocking the spread or production of non-native species.  The Laurentian Great Lakes, having more than 185 non-native aquatic species, illustrate well this protective role.  Arguably, the sea lamprey is the most destructive invasive species in the Great Lakes.  Currently, a network of barriers blocks adult sea lampreys from accessing hundreds of miles of spawning and larval-rearing habitat, thereby reducing sea lamprey production, protecting fish from predation, and saving millions of dollars otherwise required for lampricide application to control sea lamprey.  In addition, dams prevent non-native species such as the round goby, steelhead, and VHS IVB from accessing upstream sections of rivers and disrupting native fishes and critical ecosystem functions.  The potential for negative ecosystem impacts resulting from dam removal and resultant proliferation of non-native aquatic species will vary between rivers and streams.  Therefore, as increasing pressures are exerted on fishery management agencies to decommission and remove dams, a decision framework needs to be developed that incorporates consideration of the threats posed by non-native species, as well as the  opportunities to restore aquatic habitat connectivity during the earliest stages of project planning.