Acoustic evidence of year-round sperm whale foraging, population structure, and sex-specific migration near Svalbard.

Abstract

The Atlantification of the Arctic is driving a northward habitat shift of many cetaceans, including sperm whales (Physeter macrocephalus). As Arctic warming continues to decrease sea ice extent and contributes to the change in species distributions, it is crucial to study how the distribution patterns, habitat, and the demographic structure of sperm whale populations may continue to change. In this study, we assess the temporal presence of echolocating sperm whales on the continental slope southwest of the Svalbard archipelago and compare it with acoustic backscatter and temperature as a proxy for biomass. Size classes of echolocating whales were estimated using cepstral analysis. Echolocation rates were higher in summer and fall, suggesting a seasonality in the sperm whale presence; however, sperm whale clicks were present year-round and the acoustic backscatter and temperature were positively correlated with the recorded echolocation activity. The summer and fall size classes included a mix of large adult males, mid-sized sub-adult males and/or adult females, and social groups, which likely include immature animals and/or adult females and their offspring. We observed a shift to adult males in the winter, suggesting sex-specific partial migration at this site.