Historical Changes and Persistence of Fish Assemblages in Iowa's Interior Non-Wadeable Rivers

Non-wadeable rivers are unique and complex ecosystems that are capable of supporting high fish biodiversity.  Unlike wadeable streams, much is uncertain about the ecology of fishes and their response to environmental stressors in non-wadeable rivers.  Agricultural and urban land use and construction of dams and other barriers to movement have fragmented Iowa’s interiors rivers and made these systems highly prone to pollution and habitat degradation.  The purpose of this study was to describe historical changes in fish distributions and characterize the relationship of potential anthropogenic stresses on fish species composition in five of Iowa’s non-wadeable rivers.  Temporal fish assemblage data (i.e., 1884 -2011) were collected from the Iowa, Cedar, Des Moines, Wapsipinicon, and Maquoketa rivers using the Iowa GAP database and recent survey data.  Historical and recent presence-absence data were compared to identify 101 spatiotemporal trends in species distributions.  Of these trends, 37 native fishes exhibited declines, including many intolerant cyprinid species.  Multivariate ordinations and permutation tests suggested that significant changes in species composition (r² = 0.48; P > 0.001) were associated with anthropogenic stresses.  The resulting influences of environmental stressors on fish distributions may help to establish new conservation efforts for riverine fishes in Iowa.