Seismic survey noise reduces fin whale vocalisations offshore northwestern Spain.

The ever-increasing level of anthropogenic noise in the ocean is a global concern, yet its impacts on marine life remain poorly understood. Offshore seismic surveys generate intense and repetitive sound pulses during the firing of airguns, which potentially affect the behaviour of marine taxa including marine mammals, but fine-scale behavioural impacts are rarely quantified. We assessed the impact of a 2013 seismic survey offshore northwestern Spain on fin whale vocalisations. Using a convolutional neural network trained on 50 h of manually labelled acoustic data (accuracy 85.6%, AUC 0.93), 63 days of continuous ocean-bottom recordings were analysed across four alternating periods with and without airgun shooting. Across three instruments, vocalisation detections decreased by 70% on average during shooting, with reductions of 52% after correcting for worst-case scenario masking. A negative binomial mixed-effects model indicated statistically significant (p = < 0.0001) reductions in calling during shooting compared to quiet periods. Calling declined rapidly within 1–2 days after shooting began, suggesting reduced vocalisation or temporary displacement. While the broader ecological implications cannot be determined from this dataset, these findings indicate short-term behavioural responses to seismic activity and underscore the need for further research into potential consequences for communication, foraging, and habitat use.