The illustrious marine scientist and explorer, Sylvia Earle, once said of anthropogenic (man-made) noise: ‘Undersea noise pollution is like the death of a thousand cuts. Each sound in itself may not be a matter of critical concern, but taken all together, noise from shipping, seismic surveys, and military activity is creating a totally different environment than existed even 50 years ago. That high level of noise is bound to have a hard, sweeping impact on life in the sea’. The subtle, but key phrase in that quote is ‘bound to’. There is negligible doubt that some noise activities are detrimental to marine mammals (and, in some cases, will cause death), but quantifying this doubt is hard.