Predation risk for crayfish differs between drought and nondrought conditions

Predation risk for aquatic prey is affected by habitat characteristics and the predator community. Relative predation risk for aquatic prey from terrestrial and aquatic predators may differ in drought and nondrought conditions because access to aquatic prey may be affected by water depth.We compared predation risk for crayfish in a human-dominated landscape during severe drought conditions to that during a nondrought year with a standardized assay in which tethered crayfish were exposed to predators. We placed trail cameras at tethering locations to detect whether mortality was from terrestrial or aquatic predators. We evaluated effects of crayfish size, in-stream characteristics, and landscape context on crayfish mortality. Risk factors for crayfish changed between the drought and nondrought conditions. During the drought of 2012, predation risk was associated negatively with cover of submerged vegetation, whereas crayfish size was the main risk factor in 2013 when streams returned to normal or above-normal streamflow. Risk was driven primarily by aquatic predators, although predation by terrestrial predators increased during the drought. Predation risk was related positively to stream size and negatively to urbanization but only during nondrought conditions. Increased variability in hydrology expected under climate change may alter predation risk for crayfish and other aquatic prey in streams.