Spatial Effects of Reservoirs on Fish Assemblages in Great Plains Streams in Kansas, Usa

Reservoirs are important components of modern aquatic ecosystems that have negative impacts on native aquatic biota both upand downstream. We used a landscape-scale geographic information system (GIS) approach to quantify the spatial effects of 19 large reservoirs on upstream prairie fish assemblages at 219 sites in Kansas, USA. We hypothesized that fish assemblage structure would vary with increasing distance from a reservoir and that the abundance of reservoir fishes in upstream reaches would decline with distance from a reservoir. Ordination of sample sites showed variation in fish assemblage structure occurred primarily across river basins and with stream size. Variance partitioning of a canonical ordination revealed that the pure effect of reservoir distance explained a small but significant (6%; F1⁄4 4.90, P1⁄4 0.002) amount of variability in fish assemblage structure in upstream reaches. Moreover, reservoir species catch per unit of effort (CPUE) significantly declined with distance from a reservoir, but only in fourthand fifthorder streams (r1⁄4 0.32, P< 0.001 and r 1⁄4 0.49, P< 0.001, respectively). Finally, a multivariate regression model including measures of stream size, catchment area, river basin, and reservoir distance successfully predicted CPUE of reservoir species at sites upstream of Kansas reservoirs (R1⁄4 0.45, P< 0.001). Overall, we found significant upstream effects of reservoirs on Kansas stream fish assemblages, which over time has led to a general homogenization of fish assemblages because of species introductions and extirpations. However, characteristic reservoir species are present throughout these systems and the importance of spatial proximity to reservoirs is probably dependent on the availability of suitable habitat (e.g. deep pools) in these tributary streams. Copyright # 2005 John Wiley & Sons, Ltd. key words: reservoirs; introduced species; stream fish assemblages; spatial effects; Great Plains; Kansas; upstream