Flying beneath the clouds at the edge of the world: using a hexacopter to supplement abundance surveys of Steller sea lions (Eumetopias jubatus) in Alaska

Aerial imagery is the most effective method National Marine Fisheries Service (NMFS) uses to assess abundance of Steller sea lions (Eumetopias jubatus). These images are traditionally captured from occupied aircraft, but the long distances between airfields along the 1900 km Aleutian Island chain, inclement weather during the survey season, and dangerous winds at sites adjacent to cliffs severely limit flying opportunities. Because of the pressing need for current trend information for a population in persistent decline we turned to a small unoccupied aircraft system (UAS), an APH-22 hexacopter. Our primary objective was to supplement traditional aerial surveys during the annual abundance survey. The second objective was to test whether the resolution of images captured with the hexacopter was adequate for sighting permanently marked individuals. From June to July 2014, NMFS biologists based on a research vessel assessed sites from Attu Island to the Delarof Islands (n = 23), surveying sites from land (n ...