To flee or not to flee: harbour seal behavioural responses to anthropogenic noise events using high resolution biologging tags
摘要
The English Channel stands out as one of the densest marine traffic areas in the world. Ships have become one of the main sources of anthropogenic noise in the ocean, impacting many marine species. Among these, harbour seals are particularly at risk due to their use of coastal habitats, with a high presence of marine traffic. The goal of this study was to assess potential behavioural responses of seals towards shipping noise. We used data from biologging tags (DTags) that record both noise and behavioural parameters. Vessel passes were identified using a high-level noise detector and classified as “vessel” by three evaluators. For each vessel pass, a 15 min window around the event was extracted, including a spectrogram, 3-axis accelerometer data, jerk (sharp acceleration) and swimming effort, depth, prey capture attempt positions, and a 2D movement track. Within the 15-min time window after, behavioural changes were classified into six categories by three evaluators. In this study, the category “Unknown” was excluded and the remaining categories were simplified into a binomial response variable (“change”; “no-change”). Overall, seals showed behavioural changes in 30% of the 418 events coinciding with noisy events. Their behavioural changes depended significantly on the characteristics of the noise and the seals’ initial behaviour. Seals were more likely to change behaviour when noise levels were high (pvalue ≤ 0.01). Additionally, seals showed a higher probability of behavioural change when sleeping and a lower probability when foraging (pvalue ≤ 0.01). During foraging, an increase in the number of prey capture attempts was associated with a lower probability of behavioural change (pvalue ≤ 0.01), suggesting that seals may tolerate noise in areas with high prey availability. The coincidence of behavioural change during a noise event suggests a response of seals to anthropogenic noise. In conclusion, harbour seals’ responses to disturbance may vary according to the costs and benefits associated with their initial behaviour.