I know what you did last winter: Bowhead whale anomalous winter acoustic occurrence patterns in the Beaufort Sea, 2018–2020

Global warming is affecting the Arctic at a faster pace than the rest of the world, causing an urgent need to monitor ecosystems to detect possible climate-related changes. To this end, five passive acoustic datasets were recorded in the southern Amundsen Gulf (eastern Beaufort Sea) from September 2018 to September 2020 and analyzed for Bering-Chukchi-Beaufort (BCB) bowhead whale calls using a combination of automated and manual detections. Results indicate a large variation in bowhead occurrence patterns between the two years. For 2018–2019, we obtained the first evidence of bowheads overwintering in what is typically their summer foraging ground. Examination of the following year’s recordings sheds light on whether this interruption in bowhead annual migration was an anomaly or part of an ongoing phenological shift due to climate change. Time series of remotely sensed sea ice concentration at the study area were considered over the last seven years in interpreting differences in migratory behavior of the whales. Statistical quantification of seasonal patterns and habitat preferences of bowheads, based on the 2018–2019 acoustic data, are presented to provide context to BCB bowhead ecology. Passive acoustic monitoring is an indispensable tool in discerning whale responses to a changing ocean in the Arctic.