Shipping noise in a dynamic sea: a case study of grey seals in the Celtic Sea

Shipping noise is a threat to marine wildlife. Grey seals are benthic foragers, and thus experience acoustic noise throughout the water column, which makes them a good model species for a case study of the potential impacts of shipping noise. We used ship track data from the Celtic Sea, seal track data and a coupled ocean-acoustic modelling system to assess the noise exposure of grey seals along their tracks. It was found that the animals experience step changes in sound levels up to ~20dB at a frequency of 125Hz, and ~10dB on average over 10-1000Hz when they dive through the thermocline, particularly during summer. Our results showed large seasonal differences in the noise level experienced by the seals. These results reveal the actual noise exposure by the animals and could help in marine spatial planning.

Differences in sound level between the advanced and basic models are up to 40dB  Sound energy propagates further by tens of kilometres in shallow seas in winter  The model is able to estimate the sound from moving ships received by moving seals  Sound exposure experienced by seals is highly seasonally variable  Seals experience step changes of up to ~20dB (at 125Hz) across the thermocline