Disturbances due to unmanned aerial vehicles (UAVs) on harbor seal (Phoca vitulina) colonies: Recommendations on best practices

The increase in the use of unmanned aerial vehicles (UAVs) in marine mammal research has raised concerns, as its potential impacts remain largely unknown. To assess the effects of disturbances on harbor seals by a DJI Phantom 4 Pro, behavioral responses were recorded before, during, and after UAV approaches at two colonies. GLMMs were applied to assess proportions of seals displaying vigilance, resting, locomotion, and flushing behaviors. The proportion of time that selected individuals spent vigilant, and resting was also analyzed. Responses were evaluated as a function of UAV altitude, time of day, study site, group size, and environmental covariates. UAV presence triggered a significant increase in the proportion of seals vigilant and a decrease in resting. Greater reactions were observed at lower flying altitudes between 20 m and 10 m, although due to our study design, seals could have been reacting to lower flying altitudes and/or longer exposure times. Sound levels at different flying altitudes were investigated to aid interpretation of our results and to provide reference levels for future studies. Based on the disturbance thresholds identified, we devised recommendations on best practices to be implemented in future research on harbor seals using UAV techniques.