Behavioral responses of satellite tracked Blainville's beaked whales (Mesoplodon densirostris) to mid‐frequency active sonar

Abstract

The vulnerability of beaked whales (Family: Ziphiidae) to intense sound exposure has led to interest in their behavioral responses to mid‐frequency active sonar (MFAS, 3–8 kHz). Here we present satellite‐transmitting tag movement and dive behavior records from Blainville's beaked whales (Mesoplodon densirostris) tagged in advance of naval sonar exercises at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. This represents one of the largest samples of beaked whales individually tracked during sonar operations (n = 7). The majority of individuals (five of seven) were displaced 28–68 km after the onset of sonar exposure and returned to the AUTEC range 2–4 days after exercises ended. Modeled sound pressure received levels were available during the tracking of four individuals and three of those individuals showed declines from initial maxima of 145–172 dB re 1 μPa to maxima of 70–150 dB re 1 μPa following displacements. Dive behavior data from tags showed a continuation of deep diving activity consistent with foraging during MFAS exposure periods, but also suggested reductions in time spent on deep dives during initial exposure periods. These data provide new insights into behavioral responses to MFAS and have important implications for modeling the population consequences of disturbance.

Context-dependent variability in the predicted daily energetic costs of disturbance for blue whales

“…Thus, this discrepancy remains unresolved. Generally, while recent efforts have engaged operational sources, many CEEs will continue to rely on weaker signals compared to real sonar sources, with potential implications for the characterisation of cetacean responses, but studies based on opportunistic exposures to real Navy activities could be useful ( Joyce et al, 2020 ). The continuous function for distance, on the other hand, predicted a relatively small footprint of each disturbance event because there were few experimental exposures beyond 5 km.…”

Critical threshold identified in the functional relationship between beaked whales and their prey

“…Previous efforts in these areas suggested that there were also biological differences in fish and invertebrates in the upper water column between these 2 zones (Hazen et al 2011). Two additional, similarly sized zones were sampled in areas adjacent to the north and south of the active range, as these areas are likely used by animals as a refuge during navy sonar exercises (McCarthy et al 2011, Tyack et al 2011, Joyce et al 2019. Data from these 4 zones were compared with a region approximately 170 km north of the range, on the southwest of Great Abaco Island.…”

“…There is considerable evidence of atypical mass stranding events of these species associated with military sonar exercises (Cox et al 2006, Filadelfo et al 2009). Recent evidence suggests that in addition to relatively rare mortality events, beaked whales that inhabit naval training ranges experience frequent behavioral disturbances including reduced dive rates and spatial displacement from preferred habitats (McCarthy et al 2011, Joyce et al 2019). These behavioral changes likely have energetic and reproductive consequences which may lead to changes in population demographics (King et al 2015, Hin et al 2019.…”

“…Inhabiting a submarine canyon in The Bahamas known as the Tongue of the Ocean (TOTO), this population is repeatedly exposed to high levels of military activities, including sonar. Although there have been no recorded atypical stranding events at AUTEC (such as those described by Fernández et al 2005, Cox et al 2006, frequent disruptions and displacements off of the range (Joyce et al 2019) may reduce the fitness of the population relative to a nearby population off Abaco Island that is less exposed to military sonar (Claridge 2013.…”

Oceanographic Drivers of Cuvier’s (Ziphius cavirostris) and Sowerby’s (Mesoplodon bidens) Beaked Whales Acoustic Occurrence along the Irish Shelf Edge

“…The lack of information on beaked whales is even more alarming given that they have been identified as sensitive to anthropogenic noise [25,31,32]. In particular, midfrequency military sonar exposure has been blamed in many atypical mass stranding events [33][34][35] and shown to induce behavioural changes [25,36,37]. Although much less studied, other intense sound sources such as shipping and seismic airguns are of concern [34,38,39].…”