Pacific herring respond to simulated odontocete echolocation sounds.

There has been a long-running debate as to if and how clupeoid fish, such as herring (Clupea sp.), respond to anthropogenic sound. Anatomical and physiological investigations have shown that members of the clupeoid suborder have highly developed hearing extending into ultrasonic frequencies and behavioural studies suggest that they respond to many sounds. However, only recently have the selective forces that have driven the evolution of this keen sense and behavioural repertoire played a major part in the debate. One explanation is the adaptation to predation from echolocating cetaceans. In this study, we investigate the responses of adult Pacific herring (Clupea pallasii) to broadband biosonar-type sounds with high-frequency similarities to those produced by odontocete cetaceans. Exposures to these sounds in an indoor tank and sea cage caused feeding fish to cease, drop in the water column, and begin to school actively. Fish already schooling dropped in the water column and increased their swimming speed. Exposures to electronic silence and an acoustic deterrent device for marine mammals did not elicit such responses. We discuss the potential suitability of the observed manoeuvres for avoidance of foraging odontocetes and consider their relevance for human-related fishing activities.