An Overview of Stream Flow Effects on Western Native/Nonnative Fish Interactions

Many western North American streams and rivers are known for their exceptionally variable hydrographs.  Periodic flood events clean and redistribute substrate, provide nutrients, and flush out nonnative species that have not evolved under such variable hydrological regimes.  Regulating the flow of Western rivers has often led to changes in species composition favoring nonnative species.  Many nonnative faunas are more adapted to slower, pooling waters.  Here I provide specific examples from the western United States on the effects of flow alterations on native/nonnative fish species interactions.  Modelling of potential effects and case histories of changes in aquatic communities following flow alternations have been important in litigation to conserve natural stream flow effects for native species.  A working knowledge of native/nonnative fish interactions, and their response to stream flow alteration is important for fisheries biologists and managers.