Defining the Riverscape: Tributaries as a Key for Great River Fish Conservation

Contemporary conservation strategies must balance conservation needs in the face of a growing human population in need of drinking water, hydroelectric power generation, and navigation.  Conservation strategies for great river (basin area >250,000 km²) endemic fishes, for example, are limited by impoundments that block movements and alter hydrographs but must be maintained for humans to access riverine ecosystem services.  Tributaries are an important part of the riverscape of a mainstem river and have been shown in numerous instances to enhance ecosystem function of altered mainstem rivers.  Tributaries are a prime driver in mainstem river biodiversity, population dynamics, and community organization and have been forwarded for use as a restoration strategy due to the numerous ecological functions they provide.  The ecological benefits tributaries provide to mainstem rivers coupled with their comparatively smaller scale and lesser degree of alteration, may make conserving or restoring tributaries an ecologically and economically viable substitute to restoring mainstem river channels.  Moreover, restoration and conservation of tributaries presents an economically feasible restoration strategy for great rivers in particular, in light of the need to conserve biodiversity while still allowing for access to their ecosystem services.  We summarize the ecological benefits that tributaries provide to great rivers in order to assess the conditions under which tributaries could be preferred restoration targets.  Specifically, we will discuss 1) size-dependent relationships between tributary-mediated ecological function and great river benefit and 2) life-history strategies of fishes that could see the most potential benefit from tributary restoration.