Exposure and behavioural responses of tagged bowhead whales (Balaena mysticetus) to vessels in the Pacific Arctic

Arctic marine mammals face many challenges linked to climate change, including increasing anthropogenic noise from vessel traffic. The bowhead whale (Balaena mysticetus Linnaeus, 1758), an Arctic endemic cetacean, relies on acoustic communication, with documented overlapping frequencies between communication and vessel noise. Bering-Chukchi-Beaufort (BCB) bowhead whales migrate through areas with the highest levels of vessel traffic in the Pacific Arctic. Here, we document the spatial and temporal overlap between 25 satellite-tagged BCB bowhead whales and vessels during July-December, 2012-2018. We report 1332 occasions when a vessel was within 125 km of a tagged whale, and where possible, quantified changes in swim speed to investigate individual behavioural responses to vessel approaches within a 50 km radius (n = 18 encounters). In the quantitative analysis, bowhead whales were not observed to alter swim speed within 8-50 km of vessels (we could not assess distances <8 km). Our results suggest that bowhead whales did not exhibit detectable long-range (i.e., up to 50 km) behavioural responses to vessels, consistent with observations of closely related North Atlantic right whales (Eubalaena glacialis (Muller, 1776)), for which vessel strikes are a leading cause of mortality. More work is required to assess how bowhead whales react to vessels at closer distances.