Assessing the role of sampling uncertainty when predicting behavioral responses of tagged cetaceans exposed to naval sonar

Abstract

Concerns over cetacean mortality events coincident with maritime warfare exercises have motivated efforts to characterise the effects of anthropogenic noise on free-ranging whales and dolphins. By monitoring the movement, diving, and acoustic behaviours of individual whales before, during, and after sound exposure, behavioural response studies (BRSs) have supported significant progress in our understanding of the sensitivity of various cetacean species to high-powered naval sonar signals. However, differences in the designs and sampling capabilities of animal-borne tags typically used in BRS experiments prompt questions about the influence of data resolution in quantitative assessments of noise impacts. We conducted simulations to examine how uncertainty in the acoustic dose either measured on high-resolution multi-sensor biologging tags or modelled from position-transmitting satellite telemetry tags may affect predictions of behavioural responses in Cuvier’s beaked whales (Ziphius cavirostris) exposed to low- and mid-frequency active sonar. We considered an array of scenarios representative of real-world BRSs and used posterior estimates of dose-response functions obtained under an established Bayesian hierarchical modelling framework to explore the consequences of different tag choices for management decision-making. Our results indicate that (1) the zone of impact from a sonar source is under-estimated in most test conditions, (2) substantial reductions in the uncertainty surrounding dose-response relationships are possible at higher sample sizes, and (3) this largely holds true irrespective of tag choice under the scenarios considered, unless positional fixes from satellite tags are consistently poor. Strategic monitoring approaches that combine both archival biologging and satellite biotelemetry are essential for characterising complex patterns of behavioural change in cetaceans exposed to increasing levels of acoustic disturbance. We suggest ways in which BRS protocols can be optimised to curtail the effects of uncertainty.