IMPACTS OF CASCADE DAMS ON FISH IN THE MAINSTREAM OF MISSISSIPPI RIVER AND THE MITIGATION MEASURES

How to mitigate the influence of dam construction on fish diversity and develop effective conservation and restoration measures are the main content of river ecological protection. This study overviewed dam constructions in the mainstream of Mississippi River and their influence on fish. Additionally, the conservation measures of fish resources and their effectiveness were analyzed and summarized. It was found that 41 lock and dams were constructed in the upper Mississippi River. The height of most dams were no more than 15 m and their capacities were less than 0.3 km³. These dams blocked the migration path of fish in the Mississippi River but no one had fish passage facilities. Many studies showed that navigation dams in the Mississippi River may function similarly to weirs, because most are low-head dams with bottom release gates that allow fish to pass under some conditions. However, increased dams decreased the passage efficiency, and they had less effect in maintaining the fish population, especially for sturgeon species. Influenced by the impoundment of dams, the spatial variation of fish composition in the upper Mississippi River suffered a community-level fragmentation. In 1984 and 2000, the Upper Mississippi River System-Environmental Management Program (UMRS-EMP) and the Restoration and Maintenance Strategies (UMRS-RMS) were implemented respectively, including the long term fish recourses monitoring program (LTRMP) and 9 habitat restoration measures. Benefiting from these measures, the Mississippi river still maintains high species diversity. This can provide us with successful experience in future fish resources protection and watershed management in dammed Chinese rivers.