Abstract
AbstractThe 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.
Highlights
Between 2009 and 2015, tags were deployed on M. densirostris individuals within and near AUTEC in the Tongue of the Ocean (TOTO) region of the Bahamas, prior to multivessel naval exercises that exposed these beaked whales to intense MFAS during “Submarine Commanders Courses” (SCC; McCarthy et al, 2011; see 2.4 Sonar Data below)
In this study we present opportunistically collected observational data on M. densirostris individual behavioral responses to frequent, repeated, and intense MFAS exposure during SCC naval exercises
We documented transient changes in dive depths and the proportion of time allocated to deep diving that were consistent with a response to sonar, the strength of evidence relating to these changes in dive behavior was less pronounced
Summary
Between 2009 and 2015, tags were deployed on M. densirostris individuals within and near AUTEC in the Tongue of the Ocean (TOTO) region of the Bahamas, prior to multivessel naval exercises that exposed these beaked whales to intense MFAS during “Submarine Commanders Courses” (SCC; McCarthy et al, 2011; see 2.4 Sonar Data below). Using a fitted CTCRW model for each track we predicted maximum likelihood (ML) location of each individual (1) at regular 30-min intervals for the calculation of displacement distances and (2) corresponding to the time-stamp of each sonar ping in tracks where sound pressure RL data was available. As an index of the proportion of time occupied by deep dives consistent with foraging during each six-hour TAT summary period, we calculated proportion of time M. densirostris individuals spent below the 18C isotherm This isotherm corresponds to an estimated depth of 342.3 m (range: 191.2–462.9 m) in the Bahamas based on previous analyses (see Joyce et al, 2016). The maximum cell value in each 5 m depth raster layer was used as an indication of sound pressure near the sonar source (e.g., surface ship or dipping helicopter) associated with each modeled ping
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