Fish Community Dynamics At the River-Reservoir Interface: Implications for Fish Conservation and Management in Regulated Rivers

While much is known about the fish communities, habitats, and ecology within rivers and reservoirs, little information exists regarding how reservoirs and their upstream tributaries function as single ecosystems.  Especially lacking is information about fish communities within the transitional habitats between rivers and their downstream reservoirs, hereafter referred to as river-reservoir interfaces (RRI).  To improve our understanding of river-reservoir ecosystems, we used a multi-gear approach to describe the fish communities of four RRIs in the Colorado River Basin, Texas.  All RRIs had high species richness and evenness values.  On average, species collected represented 74% (45 of 64 species) of the species available within this section of the river.  Dominant species were similar across RRIs, and observed temporal shifts in RRI fish community structure resulted primarily from shifts in abundance rather than changes in species composition.  Fish species responsible for temporal shifts in community structure represented species that likely used littoral habitats within the RRIs and species that migrated through the RRI to upstream habitats, suggesting multiple functions of RRIs within river-reservoir ecosystems.  Our results indicate RRIs function like natural ecotones, and provide evidence that RRIs are important to the biological function and viability of regulated river-reservoir ecosystems.