Chronic ocean noise and cetacean population models

Abstract

Recent years have seen the rapid development of tools and approaches to model the population consequences of disturbance in several marine mammal populations from high-Amplitude, acute sound sources. Ocean noise from shipping and other maritime activities is now recognised as a chronic, habitat-level stressor. Advances are needed in several key areas in order to understand the population consequences of chronic ocean noise to cetaceans and their populations. One promising approach is to predict population-level consequences of noise-mediated disruption of feeding, which can include both behavioural responses and foraging opportunities lost due to acoustic masking. Masking may be defined as both the process and the amount by which the threshold of hearing of one sound is raised by the presence of another. Parameterising any model of population consequences of the masking caused by chronic ocean noise requires information on sensitivity and vulnerability of large whales to ocean noise, in which sensitivity is the degree to which marine organisms respond to a stressor (e.g. behavioural responses to noise or proportional reduction in foraging efficiency due to masking), and vulnerability is the probability that whales are exposed to noise to which they are sensitive. Our review draws from case studies inspired by the Population Consequences of Disturbance framework, as well as those that use Population Viability Analysis approaches. Much of the work completed to date focuses on odontocetes, particularly coastal odontocetes. Efforts are underway to provide muchneeded information on hearing sensitivity in baleen whales, the role of acoustic cues in foraging, and deriving links between long-Term variability in prey availability and whale demography. As new information becomes available, we expect rapid advancement on modelling population consequences of acoustic masking in baleen whales, because those efforts can leverage substantial investments in statistical methodological approaches to model population consequences of disturbance. Although the models presented explore population consequences of noise via a tractable approach that considers noise-mediated impacts on foraging, other pathways of effects (e.g. stress hormones affecting reproduction or disease) are possible. By considering only one pathway of effects, the modelling approaches discussed may underestimate the magnitude of effects of noise on cetacean populations. Case studies of local, national, international, and inter-governmental efforts were highlighted to monitor and reduce the contribution of global shipping to ocean ambient noise, and outline approaches that can be used to assess the risk to cetacean population recovery of existing levels of ocean noise, and consequently, predict the benefits likely to arise from reducing chronic ocean noise.