Abundance of Type A killer whales (Orcinus orca) in the coastal waters off the western Antarctic Peninsula

Abstract

A diverse community of phenotypically, genetically, and culturally distinct killer whales (Orcinus orca; Types B1, B2, and A) are important top predators in the coastal waters off the western Antarctic Peninsula (WAP), but there are currently no data on their abundance or trends. Most research to date has focused on the distinctive and pagophilic Type B killer whales and much less is known about the Type A killer whale, an open-water form that is more typical in appearance. Here, we integrate satellite telemetry (n = 10 tags, median duration = 57 days) and photo-identifications (13 years, 15,828 photographs) collected during austral summers from 2004/2005 to 2016/2017 to describe the movement patterns of Type A killer whales and estimate their abundance and trends in the coastal waters of the WAP. Tagged whales typically ranged widely on the continental shelf in the austral summer, but also moved over long distances into the Southern Ocean and beyond off both sides of South America (up to 3048 km from tagging site). Photographic re-sightings within this core summer range were common across years (up to 13 years), and a Bayesian Mark–recapture analysis estimated high average annual survival (posterior median = 0.98, 95% probability interval 0.74–1), and an average annual abundance that increased from a low of 91 (95% probability interval 58–147) in 2009/2010 to a high of 149 (95% PI 101–226) in 2016/2017. This increase may be a response to changing ice conditions that increased access to new feeding areas, and/or an increasing local abundance of marine mammal prey species in the WAP.