Historical Changes in Large River Fish Assemblages of the Americas
A Comparison of the Pre- and Postimpoundment Fish Assemblage of the Upper Mississippi River (Pools 4-13) with an Emphasis on Centrarchids
Jeffrey A. Janvrin
Abstract.—An investigation of historical fisheries information for pools 4–13 of the upper Mississippi River (UMR) was conducted to 1) determine the pre-1938 relative abundance and distribution of bluegill Lepomis macrochirus and largemouth bass Micropterus salmoides, 2) determine the composition and relative abundance of the preimpoundment fish assemblage, and 3) determine if a shift in frequency of occurrence and relative abundance has occurred due to impoundment.
Many of the preimpoundment information sources did not include a detailed description of the fish assemblage, but did yield qualitative statements regarding the preimpoundment abundance of bluegill, largemouth bass, and other species. This qualitative assessment indicated bluegill and largemouth bass were widely distributed and abundant prior to impoundment in pools 4–13 of the UMR.
Preimpoundment (1900–1938) quantitative seining data were obtained from the Wisconsin Department of Natural Resources (WDNR) fisheries database and annual reports of federal fish rescue operations. Postimpoundment (1993–1999) quantitative seining data were obtained from the Environmental Management Program’s Long Term Resources Monitoring Program (LTRMP) database, maintained by the U.S. Geological Survey (USGS). Pre- and postimpoundment data were compared for similarity in the rank of 13 groupings of fish based on summaries of catch reported by the federal fish rescue. There was a significant correlation between the preimpoundment datasets but no correlation between the preimpoundment datasets and the USGS postimpoundment dataset. This indicates that the relative abundance has changed for the groups included in this analysis.
A comparison of fish species (n = 75) common to the WDNR and LTRMP database showed significant correlation for ranks of percent frequency of occurrence and relative abundance. In general, what was common and abundant prior to lock and dam construction is common and abundant today. However, the ranks of percent frequency of occurrence and relative abundance have changed for some species.