Soundscapes experienced by southern resident killer whales (Orcinus orca) in the Salish Sea and implications of vessel noise

Abstract

Endangered southern resident killer whales (SRKW, Orcinus orca) use waters of the Salish Sea around southern British Columbia and northern Washington State to forage, following the in- migration of prey. However, these waterways experience heavy vessel traffic, with important SRKW foraging areas near to international shipping lanes. Here we use recordings from six passive acoustic moorings to characterize the soundscape, and determine spatiotemporal patterns on daily to annual scales. Particular focus is given to the noise levels in frequencies used by SRKW to communicate and echolocate. A numerical model is used to map the sound field between the mooring locations and examine the anthropogenic inputs in SRKW critical habitat in the Salish Sea by commercial traffic. Extrapolation of the model output to higher frequencies allows an examination of the impact this may have on the range of effective acoustics use, with implications for SRKW navigation, foraging success and group cohesion. Finer scale analysis of vessel signatures as they transit the study area aids in identifying areas of increased risk of disturbance for whales. In addition, differences in modelled to observed data will help the characterisation of other sonic inputs to the soundscape, including smaller recreational vessels.