Shifting Responses of Beaked Whales to Long-Standing Naval Sonar Exposure Opens New Perspectives for Research and Mitigation

Predicting and mitigating the impacts of chronic noise on marine mammals is limited by sparce data on repeated disturbance. Naval sonar disrupts species behavior with lethal and sublethal risks, yet mitigation relies on short-term studies. We analyzed a decade of passive acoustic observational data to assess behavioral changes of goose-beaked whales ( Ziphius cavirostris ) at locations near and far from long-standing sonar operations. Whales remained present in impacted areas but exhibited patterns consistent with avoidance observed in exposure experiments. Interpreting these as responses, a 50% disturbance probability occurred at 122–132 dB pp re 1 µPa, below regulatory thresholds. With median 1-1.2 day intervals between exercises and 132–134 dB pp re 1 µPa daily received levels, disturbances imposed near-daily energetic and foraging costs. Differences in responses between areas with similar exposure suggest that ecological factors such as habitat quality may promote habitat persistence despite moderate disturbance. Over a decade, whales became more likely to be detected during shorter exercises and after exposure while maintaining sensitivity to moderate-to-high exposure levels. This suggests either reduced displacement responses over time or suitable prey conditions not found elsewhere as a result of changes in habitat conditions. These results suggest mitigation should prioritize sonar-free periods and limit exercise duration.