Potential exposure of beluga and bowhead whales to underwater noise from ship traffic in the Beaufort and Chukchi Seas

Abstract

Sea ice loss associated with a changing climate is resulting in increased levels of ship traffic in the Arctic, which in turn is causing increased underwater noise levels and associated impacts on marine life. Estimating the possible, present levels of exposure of marine life to underwater noise is a crucial step in understanding and managing contemporary exposures and underwater noise levels, and will inform future planning actions and mitigation. In this study, we examined the overlap between modeled underwater noise from ship traffic from 2015 to 2017 and monthly utilization distributions of beluga (Delphinapterus leucas) and bowhead whales (Balaena mysticetus) calculated from satellite telemetry data collected between 1995 and 2018 in the Beaufort and Chukchi seas. We first modeled noise propagation from observed vessel traffic in the Pacific Arctic from Amundsen Gulf in the east to Bering Strait in the west. We modeled the propagation loss of underwater noise from different classes of vessels that were transiting the area, and then applied these values to actual ship tracks (derived from satellite automatic identification system data) to model monthly noise footprints between July and October in each year between 2015 and 2017. We overlaid the monthly noise footprints with monthly 50% utilization distributions for satellite-tagged eastern Beaufort Sea beluga whales (1993–1997, 2004–2006) and Bering-Chukchi-Beaufort bowhead whales (2006–2018). Vessel traffic and its associated underwater noise were highest in all months in the southern Chukchi Sea near Bering Strait, particularly along the Russian and Alaskan coastlines. In comparison, traffic was lower in the western Canadian Arctic and in offshore areas; within the western Canadian Arctic, traffic was higher in August and September than in July and October. In July, low ship traffic resulted in low levels of overlap between modeled underwater noise and the utilization distributions for both whale species because the whales tend to use habitats in the eastern Beaufort Sea and Amundsen Gulf. Conversely, in August through September, there was medium to high overlap between underwater noise and the distributions for both species as ship traffic increased in those months and the distribution of both species began shifting towards the Chukchi Sea. Both beluga and bowhead whales migrate through areas with the highest levels of traffic in the Pacific Arctic, and are potentially exposed to a high number of acoustic disturbance events in three national jurisdictions. Without proactive vessel management and effective mitigation measures, acoustic disturbance of whales is expected to increase, and eventually expand to more months of the year, as ship traffic continues to increase in step with increases in the length of the open water season.