A cross-modal effect of noise: the disappearance of the alarm reaction of a freshwater fish.

Anthropogenic noise pollution is recognized as a major global stressor of animals. While many studies have assessed the unimodal impacts of noise pollution with a focus on intraspecific acoustic communication, little is known about noise pollution on the perception of visual and chemical information. The 'distracted prey hypothesis' posits that processing noise interferes with processing other information in the brain. Here, we found evidence for such a cross-modal effect of noise on the antipredator behaviour of a freshwater prey fish, the fathead minnow, Pimephales promelas. In laboratory trials, exposure to noise from a motorboat caused the total absence of the classical fright reaction of minnows to conspecific alarm cues, whereas an ambient noise control had no such impact. In natural habitats, the impairment of such antipredator behaviour due to noise pollution could have major fitness consequences. We discuss how our findings translate to animal ecology and the need for future studies that target specific management decisions regarding noise pollution.