Testing the Confluence Exchange Hypothesis in a Colorado River Tributary Fish Community

Fishes may use various habitats depending on life history strategies and habitat availability. Habitats within a river network include mainstem rivers and tributaries varing in discharge, configuration, and confluence position. These different habitats are used – or avoided – by fishes depending on seasonal patterns of the environment coupled with life history trait(s) of the fish. The confluence exchange hypothesis is a conceptual framework that incorporates fish species movements into a river network where habitats are differentially accessed depending on species traits. One river network with dendritic configuration and dynamic flow regimes in the United States is the Colorado River Basin (CRB). Throughout the CRB, native fishes are intensively managed because of high endemism, anthropological modifications, and nonnative species. We tested the confluence exchange hypothesis using passive integrated transponder technology between 2012 and 2014 to classify species based on movements of the San Juan River basin fish community. These data showed interspecific diversity of movement patterns exists within fish community depending on habitats that vary in size, flow reliability, and network position. Moreover, intraspecific movements differed depending on body size and network position. Classifying species movements to stream network habitats can guide management of a spectrum of fish movements.