A Risk Function for Behavioral Disruption of Blainville’s Beaked Whales (Mesoplodon densirostris) from Mid-Frequency Active Sonar

Abstract

There is increasing concern about the potential effects of noise pollution on marine life in the world’s oceans. For marine mammals, anthropogenic sounds may cause behavioral disruption, and this can be quantified using a risk function that relates sound exposure to a measured behavioral response. Beaked whales are a taxon of deep diving whales that may be particularly susceptible to naval sonar as the species has been associated with sonar-related mass stranding events. Here we derive the first empirical risk function for Blainville’s beaked whales (Mesoplodon densirostris) by combining in situ data from passive acoustic monitoring of animal vocalizations and navy sonar operations with precise ship tracks and sound field modeling. The hydrophone array at the Atlantic Undersea Test and Evaluation Center, Bahamas, was used to locate vocalizing groups of Blainville’s beaked whales and identify sonar transmissions before, during, and after Mid-Frequency Active (MFA) sonar operations. Sonar transmission times and source levels were combined with ship tracks using a sound propagation model to estimate the received level (RL) at each hydrophone. A generalized additive model was fitted to data to model the presence or absence of the start of foraging dives in 30-minute periods as a function of the corresponding sonar RL at the hydrophone closest to the center of each group. This model was then used to construct a risk function that can be used to estimate the probability of a behavioral change (cessation of foraging) the individual members of a Blainville’s beaked whale population might experience as a function of sonar RL. The function predicts a 0.5 probability of disturbance at a RL of 150dBrms re µPa (CI: 144 to 155) This is 15dB lower than the level used historically by the US Navy in their risk assessments but 10 dB higher than the current 140 dB step-function.

Marine mammals and sonar: Dose‐response studies, the risk‐disturbance hypothesis and the role of exposure context

“…Moretti et al. () provide an example of a risk function for defined responses generated from real‐world navy sonar sources, from an opportunistic exposure study of Blainville's beaked whales Mesoplodon densirostris , using passive acoustic monitoring data from bottom‐mounted hydrophones on a naval testing range (see also Melcón et al., ). There remains an important question of how functions derived from exposure to scaled or simulated sonar relate to exposure to actual naval sonar.…”

“…In recent years, much of the research within the marine environment related to behavioural response has focused on marine mammals, in particular cetaceans and their potential vulnerability to disturbance by naval sonar (e.g. Baird, Martin, Webster, & Southall, ; Henderson et al., ; Houser, Yeates, Crocker, Martin, & Finneran, ; McCarthy et al., ; Miller et al., ; Moretti et al., ; Sivle et al., ; Southall, Nowacek, Miller, & Tyack, ; Tyack et al., ). Other disturbance stimuli have received attention, including shipping (e.g.…”

Using passive acoustic monitoring to document the distribution of beaked whale species in the western North Atlantic Ocean

“…These events have raised concerns about the acute effects of anthropogenic noise on beaked whales (e.g., Parsons et al 2008), and prompted substantial research into behavioral responses to various noise stimuli (Tyack et al 2011;Pirotta et al 2012;DeRuiter et al 2013;Moretti et al 2014). As this work begins to shed light on species-specific responses to acoustic disturbance, there is a fundamental need to improve baseline information on the spatiotemporal occurrence of beaked whale species, particularly in regions where potentially harmful noise exposure is likely to occur (Weilgart 2007).…”

Using dose–response functions to improve calculations of the impact of anthropogenic noise

“…Miller et al (2014) provided a table of quantiles that we used for this purpose. As a useful alternative, Moretti et al (2014) provide a parametric equation that closely approximates the dose-response function they fitted for cessation of feeding dives in Blainville's beaked whales as a function of received sonar level. As a useful alternative, Moretti et al (2014) provide a parametric equation that closely approximates the dose-response function they fitted for cessation of feeding dives in Blainville's beaked whales as a function of received sonar level.…”

“…Risk assessments developed by the US Navy (2016; Moretti et al, 2014) and the methods described by Miller et al (2014) and Harris et al (2015) all estimate continuous functions of acoustic dosage and the probability of response. Risk assessments developed by the US Navy (2016; Moretti et al, 2014) and the methods described by Miller et al (2014) and Harris et al (2015) all estimate continuous functions of acoustic dosage and the probability of response.…”