An assessment of thermal-image acquisition with an unmanned aerial vehicle (UAV) for direct counts of coastal marine mammals ashore

We investigated the efficacy of infrared thermal imaging devices for detecting coastal marine mammals in forested coastal environments. Our objective was to determine whether pinnipeds could be detected through the forest canopy using thermal imagery. We used a UAV-mounted and a ground-mounted infrared camera to survey New Zealand fur seals (Arctocephalus forsteri) located in Ohau Stream and Point Kean coastal shrub forest on the east coast of New Zealand. These methods were compared to paired photographs and walk-through counts. Ground-mounted thermal images detected more seals than paired photographs during the cooler times of the day (morning and evening). In contrast, aerial thermal videos were successful in detecting fur seals in open areas, but were less successful in areas of high canopy cover (>80%). We discuss the advantages and limitations of thermal imaging for population sampling and provide some recommendations for future research.