Increasing abundance of Type A killer whales (Orcinus orca) in the coastal waters around the Antarctic Peninsula

The physical marine environment around the Antarctic Peninsula (AP) is rapidly changing and we need to understand the impact on marine ecosystems. A diverse community of killer whales (Orcinus orca; Types B1, B2 and A) are important top predators around the AP, but there are currently no data on their abundance or trends. Most research to date has focused on the pagophilic Type B killer whales that are phenotypically, genetically and culturally distinct and rarely sighted away from Antarctica. In contrast, less is known about the Type A killer whales that are more typical in appearance to killer whales sighted in other parts of the world.  Sightings of Type A around the AP have been increasing in recent years, including observations of predation on a number of whale and pinniped species. Here we integrate satellite telemetry (n = 10 tags) and photo-identifications (13 years, 15,828 photographs) collected between austral summers 2005/06 to 2016/17 to describe the movement patterns of these whales and estimate their abundance trends in the coastal waters around the AP. Whales tagged off the western AP typically ranged widely on the continental shelf in the austral summers, but also moved over long distances into the Southern Ocean and beyond into the South Atlantic and South Pacific Oceans (up to 3048 km from tagging site). Photographic re-sightings of the same whales were common across years (up to 13 years), and a Bayesian mark-recapture analysis estimated that the average annual abundance has increased significantly in recent years from a low of 92 (95% probability interval = 52-147) to a high of 148 (95% PI = 101-226). This increase may be a response to changing ice conditions that increased access to new feeding areas, perhaps combined with increasing local abundance of key prey species such as southern elephant seals (Mirounga leonina).