Differential Predation Risk in Juvenile Fish: Assessing the Role of Habitat and Turbidity in a Large River Ecosystem

Many management actions in aquatic ecosystems are directed at restoring or improving specific habitat types thought to be critical for fish growth and survival. In the Grand Canyon reach of the Colorado River, experimental flow operations as part of the Glen Canyon Dam Adaptive Management Program often consider the creation of sandbars and associated backwater habitats as critical for juvenile native fish conservation.  We evaluated whether different habitat types (backwaters and complex boulder habitat) have different relative predation risks for juvenile fish.  We also assessed whether this risk changed under different levels of turbidity through the use of a simple tethering experiment. Under low turbidity conditions, boulder habitat showed higher relative predation risk compared to backwater habitat.  During high turbidity conditions, relative predation risk in the boulder habitat was reduced and the backwater site showed higher relative predation risk.  These results suggest that management for a certain habitat type, such as backwaters or boulders, does not necessarily create a habitat type with lower predation risk without considering the role of turbidity.