Research Project
Full description Seismic air guns, widely used in offshore resource exploration, are a major source of anthropogenic noise in marine environments. For cetaceans, these impulsive sounds can disrupt acoustic communication critical for breeding and social interactions. Male humpback whales (Megaptera novaeangliae) produce long, highly structured songs as part of their reproductive display, often within areas overlapping seismic activity. This study investigated whether air gun noise alters the organisation and rate of humpback whale song. Four temporal parameters (inter-call interval, phrase duration, theme duration, and song cycle duration) and one organisational variable (phrases per theme) were measured in the presence and absence of air gun pulses. Song cycle duration decreased by ~10 s for every 1 dB increase in received level (sound exposure level) above 135 dB re 1 µPa²·s. Principal component analysis revealed two phrase types, simple and complex, and showed that reductions in the repetition of complex phrases shortened theme and song cycle durations. Other parameters, such as inter-call interval and phrase duration, showed no consistent change, confirming that reduced complex phrase repetition was the main driver of song shortening. These findings suggest that seismic air guns do not mask song but are interpreted by singers as socially meaningful cues, prompting adjustments to a perceived social context. Such reductions in complex phrases may decrease detectability by distant receivers while increasing display rate for nearby individuals. Overall, this study highlights the need to consider sound type as well as amplitude when evaluating the impacts of anthropogenic noise and reinforces the view that humpback whale song is a flexible, context-dependent breeding display.