Reach scale and sample design influences on Middle Mississippi River fishes

Native large river fishes have declined worldwide due largely to human alterations. The Long Term Resource Monitoring Program (LTRMP) was established to assess ecological integrity and to guide rehabilitation of the Upper Mississippi River System. I used multivariate analysis techniques to investigate an assemblage of 27 Middle Mississippi River fishes from the Open River Trend Analysis Area collected annually by the LTRMP between 1993 and 2003. I quantified the importance of fish assemblage influences attributed to sample location coordinates, environmental variables, and the LTRMP sample design. I decomposed the fish assemblage into its 27 member species to analyze environmental associations and to develop presence-absence models.; Analyses demonstrated that sample design influences accounted for large portions of assemblage variation. Gears were most important, which indicates plans for multi-gear assessments need to give considerable thought to how fishes are observed and how sample design effects are addressed during data analyses. Furthermore, fishes common to fast and slow water velocity habitats associated with sandbars illustrating how important these physical features are to a wide range of species. Eighteen fish species presence-absence models were developed by including predictor variables associated with the LTRMP sample design and reach-scale characteristics of the river. Each model included at least one reach-scale variable, which indicates the reach scale is an important assessment scale relevant to large river fishes.