Animals exposed to anthropogenic disturbance make trade-offs between perceived risk and the cost of leaving disturbed areas. Impact assessments tend to focus on overt behavioural responses leading to displacement, but trade-offs may also impact individual energy budgets through reduced foraging performance. Previous studies found no evidence for broad-scale displacement of harbour porpoises exposed to impulse noise from a 10 day two-dimensional seismic survey. Here, we used an array of passive acoustic loggers coupled with calibrated noise measurements to test whether the seismic survey influenced the activity patterns of porpoises remaining in the area. We showed that the probability of recording a buzz declined by 15% in the ensonified area and was positively related to distance from the source vessel. We also estimated received levels at the hydrophones and characterized the noise response curve. Our results demonstrate how environmental impact assessments can be developed to assess more subtle effects of noise disturbance on activity patterns and foraging efficiency.
Presence/absence of buzzes and associated covariates: data_BACI.csv contains the data used for the analysis of buzz occurrence as a function of seismic period (before or during) and experimental block (control or impact). POD.no is the device number, to be used as a random effect; pres.buzzes indicates whether any buzz was detected in that hour. data_distance.csv contains the data used for the analysis of buzz occurrence as a function of distance from the source vessel. bootstrap_coef_sel.csv contains the bootstrapped coefficients of the relationship between SEL and the probability of buzz occurrence.
This work is licensed under a CC0 1.0 Universal (CC0 1.0) Public Domain Dedication license.
- activity budget
- Anthropogenic disturbance
- environmental impact assessment
- foraging efficiency
- Phocoena phocoena