Acoustic propagation modeling indicates vocal compensation in noise improves communication range for North Atlantic right whales

Abstract

Sound from transoceanic shipping is a major component of ocean noise budgets. Baleen whale communication may be particularly vulnerable to shipping noise impacts due to overlap in the frequencies of signals and noise. Baleen whales rely upon acoustic signals to mediate a variety of social interactions when separated beyond visual range. We investigated the potential for noise to interfere with critical reunion events between mother-calf pairs of Endangered North Atlantic right whales Eubalaena glacialis, and whether vocal compensation can improve or maintain communication space between the sender and receiver. This information is necessary to inform future conservation efforts. We used acoustic propagation modeling to predict the transmission loss of the primary tonal communication signal used during mother-calf communication, the ëupcallí, to (1) estimate over what ranges a receiving whale can detect a signal in anthropogenic noise, and (2) determine the effects of vocal compensation on detection range. Our results indicate that both point-source noise from nearby container ships and increased background noise from distant shipping may significantly limit communication space. Additionally, we show how amplitude and frequency compensation can increase the likelihood of detecting communication signals in masking noise under present conditions. We discuss these impacts of ship noise on communication, as well as the evidence that documented noise compensation behaviors of right whales can improve communication range in the presence of low-frequency ship noise.