Bayesian spatial modeling of cetacean sightings during a seismic acquisition survey

• Mysticeti sensitivity to anthropogenic noise is assessed during a seismic survey.
• No decrease in species occurrence during sound generation periods was found.
• Model shows that species occurrence was driven solely by environmental factors.
• Noise habituation or low occurrence in the seismic activity area is likely causes.
• Environmental context should be included in impact assessments of such activities.

A visual monitoring of marine mammals was carried out during a seismic acquisition survey performed in waters south of Portugal with the aim of assessing the likelihood of encountering Mysticeti species in this region as well as to determine the impact of the seismic activity upon encounter.Sightings and effort data were assembled with a range of environmental variables at different lags, and a Bayesian site-occupancy modeling approach was used to develop prediction maps and evaluate how species-specific habitat conditions evolved throughout the presence or not of seismic activity.No statistical evidence of a decrease in the sighting rates of Mysticeti by comparison to source activity was found. Indeed, it was found how Mysticeti distribution during the survey period was driven solely by environmental variables.Although further research is needed, possible explanations may include anthropogenic noise habituation and zone of seismic activity coincident with a naturally low density area.