Estimation of High-Frequency Auditory Masking in Beluga Whales by Commercial Vessels in Cook Inlet, Alaska

Abstract

Industrial development in Cook Inlet, Alaska, has raised concerns about the decline of the resident beluga whale ( Delphinapterus leucas) population over the past decades. Anthropogenic noise sources, such as commercial vessels, can cause auditory masking of cetacean vocalizations used in communication, navigation, and foraging. This study includes a source-level spectrum of a containership, positioned in Cook Inlet within the primary shipping channel, and audiograms obtained from a live, stranded beluga calf in Cook Inlet, in sound transmission loss modeling. The model uses a hybrid parabolic equation/raytracing solution to determine underwater sound pressure levels. Whereas the communication band of belugas can be fully masked by ambient noise and underwater radiated noise from a containership positioned at 5,000 m, the echolocation band (for navigation) is only partially masked at shorter ranges (≤2,500 m). Increased multipath reflections from the propagation of underwater noise in the upslope direction contributes significantly to the attenuation of high frequencies and minimizes masking in the echolocation band of the beluga whale. To assess the complex task of auditory masking, critical ratios were used to determine the difference between the energy of a pure tone and the noise in the masking band. A successful strategy to reduce underwater radiated noise must consider the interactions and contributions of mitigation measures that have already been shown to be effective. The technical and economic profitability of these measures will largely depend on the design, operating parameters, and mandatory requirements for a particular vessel.