Chapter 21: Warmwater Rivers
Craig P. Paukert and David L. Galat
Warmwater rivers are diverse ecosystems with substantial spatial variability, both longitudinal and lateral. Management of warmwater rivers is challenging and requires creative and diverse solutions to management problems. In addition to the biological and physical complexity of warmwater rivers, the human component is also complex. Warmwater rivers often traverse many political boundaries (e.g., states, provinces, and countries) and have multiple stakeholder interests that affect management actions. Warmwater rivers provide transportation corridors and serve as centers of human settlement. While a fisheries manager may be concerned with how river modification may affect fish abundance, growth, or movements, other stakeholders may be interested in commercial development in riparian areas, hydroelectric power generation, flood control, or commerce. Therefore, management of warmwater rivers involves input from multiple users. In fact, fisheries are a small portion of the management focus and economic benefits of warmwater rivers.
Warmwater rivers have been altered throughout North America and the world; only about 23% of the discharge of the world’s large rivers remaining unaltered (Dynesius and Nilsson 1994). In North America, unaltered rivers are typically in northern regions, such as the Yukon River (Benke and Cushing 2005). Most warmwater rivers occur in areas to the south, where human populations have altered riparian zones, vegetative cover across watersheds, hydrologic regimes, and floodplains.
Fisheries management in warmwater rivers has lagged behind management of lakes, ponds, and reservoirs for several reasons. Warmwater rivers are one of the more demanding aquatic habitats to sample because of their size, diversity of habitats, and variation in flow. Because most warmwater rivers have been altered, there is little preregulation information on reference conditions (Emery et al. 2003), which is critical for determining the “natural” state of rivers to aid management. Similarly, warmwater rivers are typically unique within a region, so unaltered spatial references for management or restoration are also lacking.