Comparison of Fish Community Composition and Structure Among River Reaches of the Upper Mississippi River: Determining the Effects of Lock and Dam 19 in Structuring Fish Assemblages

Completed in 1913, Lock & Dam 19 separates navigation Pool 19 from Pool 20 and created the first artificial impoundment on the Upper Mississippi River (UMR). Lock & Dam 19 is unique among most dams on the UMR in that it is a hydroelectric dam with a significant hydraulic head (~10 m) that created the largest impoundment on the system. This dam likely acts as a significant barrier to upstream migration for fish. In 2013 and 2014, standardized pulse-DC electrofishing was conducted in Pool 19 and Pool 20 to assess local and system scale variation in fish community composition and structure among reaches above and below Lock and Dam 19.  Sampling was consistent with standardized protocols from the Long Term Resource Monitoring Program (LTRMP) allowing for comparisons among the reaches we sampled and those sampled by the LTRMP (i.e., Pools 4, 8, 13, 26, the LaGrange Reach of the Illinois River, and the open Mississippi River). Cluster analysis and non-metric multidimensional scaling of fish community composition and structure was used to assess differences among all reaches. Preliminary results suggest Lock and Dam 19 serves as a transition for fish community structure and composition in the UMR.