Effects of a seismic survey on movement of free-ranging Atlantic cod.

Geophysical exploration of the seabed is typically done through seismic surveys, using airgun arrays that produce intense, low-frequency-sound pulses that can be heard over hundreds of square kilometers, 24/7. Little is known about the effects of these sounds on free-ranging fish behavior. Effects reported range from subtle individual change in activity and swimming depth for captive fish to potential avoidance and changes in swimming velocity and diurnal activity patterns for free-swimming animals. However, the extent and duration of behavioral responses to seismic surveys remain largely unexplored for most fish species. In this study, we investigated the effect of a full-scale seismic survey on the movement behavior of free-swimming Atlantic cod (Gadus morhua). We found that cod did not leave the detection area more than expected during the experimental survey but that they left more quickly from 2 days to 2 weeks after the survey. Furthermore, during the exposure, cod decreased their activity, with time spent being "locally active" (moving small distances, showing high body acceleration) becoming shorter, and time spent being "inactive" (moving small distances, having low body acceleration) becoming longer. Additionally, diurnal activity cycles were disrupted with lower locally active peaks at dusk and dawn, periods when cod are known to actively feed. The combined effects of delayed deterrence and activity disruption indicate the potential for seismic surveys to affect energy budgets and to ultimately lead to population-level consequences..