Changes in Fish Assemblage Diversity in a Historic River Channel Following Removal of Two Dams on the Paw Paw River, Michigan

Fish barriers, such as dams, are known to be a contributing factor to blocking upstream access for migrating fish species.  While many factors contribute towards the decision to remove barriers, ones that no longer serve their original purposes are typically a higher priority.  In 2011 two dams located on the Paw Paw River near Watervliet, MI, were removed.  The removal of both dams re-opened the previously impounded historic river channel changing it from a lentic to a lotic environment.  Pre and post monitoring within the channel was conducted during the spring months of 2011 – 2013 to determine the success of restoring natural flow to the system on fish colonization.  A mark-recapture study was also conducted to determine successful upstream migration of potadromous fish species.  Results showed that fish assemblages changed following removal of the dams and diversity significantly increased one year following removal.  The second year following removal showed a decrease in diversity, likely due to the decreased presence of lentic species.  The presence of fin-clipped fish upstream of the former dams also indicated successful passage of potadromous species.  This study demonstrates the importance of sound habitat restoration practices following removal of dams in restoring fish community diversity.