Din of the Deep: Noise in the Ocean and Its Impacts on Cetaceans

Abstract

Cetaceans rely on sound and hearing for all of their vital functions, such as food finding, avoiding hazards, mating, group coordination, navigation, and orientation. Human-made noise is a substantial stressor, though the full extent of the impact remains unknown. Low-frequency anthropogenic noise has risen two orders of magnitude since the industrial age. The main noise sources are commercial shipping, seismic airgun exploration for oil and gas, and naval and mapping sonars, and the potential area of impact can extend over hundreds of thousands or even millions of square kilometres. Documented noise impacts include fatal strandings, hearing damage, longer-term avoidance of the noisy area, higher energetic costs, stress responses, changes in vocalisations which can disrupt reproductive and foraging behaviour, direct interference in foraging and migration, masking or obscuring important sounds, and effects on prey. Both acute effects, such as shorter-range fatal strandings and hearing impairment, and chronic impacts sometimes occurring over the horizon, such as stress, habitat degradation, and the loss of communication space through masking, deserve attention and concern. Studying comparable populations in real-world noisy vs. quiet areas may provide us with the best knowledge, but reducing noise levels through spatial and temporal mitigation and technological solutions should be the immediate priority. These include shipping noise reduction technologies, quieter technological alternatives to seismic airguns, avoiding areas and seasons rich in marine life when siting noisy activities such as naval sonar exercises, and establishing acoustic refuges. Governmental regulatory agencies can encourage and expedite quieter technological developments. Limiting human-made underwater noise is critical to marine mammal welfare.