Noise modelling and environmental risk assessment of a geophysical survey and its impact on herring and minke whales in Irish coastal waters

Abstract

This study aimed to conduct a summarised risk assessment of the impact of underwater noise generated during a geophysical survey planned in the Celtic Sea on marine mammals and fish. In order to provide representative data on the possible effects on baleen whales and fishes where the swim bladder is involved in hearing (primarily pressure detection), two species were chosen – the common minke whale (Balaenoptera acutorostrata) and the Atlantic herring (Clupea harengus). Both are important components of the local marine ecosystem. The investigation was conducted via numerical modelling, based on which noise impact ranges and impact areas were derived. The modelling was performed for one location and included two scenarios with different sound sources: 1) sparker, 2) mini airgun. The results showed that both in the case of the minke whale and the herring, the overall impacts from the planned surveys are predicted to be higher if the airgun is used. For the minke whale, the impact ranges were highest for the cumulative TTS, while for herring – behavioural reactions led to largest impact distances. Based on knowledge about the occurrence of the studied species in the survey region and the biological importance of the area to the analysed animals, it was concluded that geophysical surveys should be taken with caution. The use of the sparker instead of the airgun was recommended, along with the application of additional mitigation measures during the survey activities