Abstract
Concerns over cetacean mortality events coincident with maritime warfare exercises have motivated efforts to characterize the effects of anthropogenic noise on free-ranging whales and dolphins. By monitoring the movement, diving, and acoustic behaviors of individual whales before, during, and after sound exposure, behavioral 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 modeled from position-transmitting satellite telemetry tags may affect predictions of behavioral 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 modeling 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 characterizing complex patterns of behavioral change in cetaceans exposed to increasing levels of acoustic disturbance. We suggest ways in which BRS protocols can be optimized to curtail the effects of uncertainty.
Highlights
Sound plays a critical role in the lives of cetaceans, with many species of whales, dolphins, and porpoises shown to be sensitive to the adverse effects of both chronic and acute exposure to anthropogenic underwater noise (Duarte et al, 2021)
Many behavioral response studies (BRSs) focus on deep-diving oceanic species in offshore habitats, where the onerous costs of running dedicated CEEs (Harris et al, 2016) provide a strong impetus for integrating multiple sampling approaches, including visual focal follows and combinations of archival biologging and near real-time biotelemetry (Berga et al, 2019; von Benda-Beckmann et al, 2019)
Commonly used animal-borne tags like digital acoustic recording tags (DTAGs) and satellite tags (S-TAGs) capture ecological processes on fundamentally different spatio-temporal scales (Hazen et al, 2012), and generate data burdened with varying levels of uncertainty
Summary
Sound plays a critical role in the lives of cetaceans, with many species of whales, dolphins, and porpoises shown to be sensitive to the adverse effects of both chronic and acute exposure to anthropogenic underwater noise (Duarte et al, 2021). In the United States, the Marine Mammal Protection Act of 1972 (MMPA, 16 U.S.C. 1361 et seq.) regulates the take (defined as the “harassment, hunting, capture, or killing”) of marine mammals by U.S.based organizations worldwide, including areas beyond national jurisdiction (i.e., on the high seas). The U.S Navy is legally bound to assess the potential impacts of military readiness training activities on cetaceans to meet compliance requirements under the MMPA as well as other U.S Federal laws pertaining to protected marine taxa (e.g., the Endangered Species Act ESA 16 U.S.C.1531 et seq.) (Zirbel et al, 2011). LFAS and MFAS systems were developed in the 1950s for anti-submarine warfare (D’Amico and Pittenger, 2009; Bernaldo de Quirós et al, 2019), and have been implicated in a number of atypical lethal mass strandings largely involving deep-diving toothed whales from the Ziphiidae family (D’Amico et al, 2009; Filadelfo et al, 2009; Fernández et al, 2012; Parsons, 2017)
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