| Summary: | Many man-made marine structures (MMS) will have to be decommissioned in the coming decades. While studies on the impacts of the construction of MMS on marine mammals exist, no research has been done on the effects of their decommissioning. The complete removal of an oil and gas platform in Scotland in 2021 provided an opportunity to investigate the response of harbour porpoises to decommissioning. Arrays of broadband noise recorders and echolocation detectors were used to describe noise characteristics produced by decommissioning activities and assess porpoise behaviour. During decommissioning, sound pressure levels in the frequency range 100 Hz to 10 kHz were 30-40 dB higher than baseline, with the presence of vessels being the main source of noise. The study detected small-scale (< 2 km) and short-term levels of porpoise displacement during decommissioning, with porpoise occurrence increasing immediately after this. These findings can inform the consenting process of future decommissioning projects. Funding provided by: Department for Business, Energy and Industrial Strategy Crossref Funder Registry ID: https://ror.org/019ya6433 Award Number: OESEA-20-125 Funding provided by: Department for Business, Energy and Industrial Strategy Crossref Funder Registry ID: https://ror.org/019ya6433 Award Number: OESEA-21-133 Broadband sound recorders (SoundTraps; Ocean Instruments NZ) and echolocation click detectors (CPODs; Chelonia Ltd) were deployed during the decommissioning of an oil and gas platform to describe noise characteristics produced by decommissioning activities and assess porpoise behaviour.
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