First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar

Abstract

Most marine mammal­ strandings coincident with naval sonar exercises have involved Cuvier's beaked whales (Ziphius cavirostris). We recorded animal movement and acoustic data on two tagged Ziphius and obtained the first direct measurements of behavioural responses of this species to mid-frequency active (MFA) sonar signals. Each recording included a 30-min playback (one 1.6-s simulated MFA sonar signal repeated every 25 s); one whale was also incidentally exposed to MFA sonar from distant naval exercises. Whales responded strongly to playbacks at low received levels (RLs; 89–127 dB re 1 µPa): after ceasing normal fluking and echolocation, they swam rapidly, silently away, extending both dive duration and subsequent non-foraging interval. Distant sonar exercises (78–106 dB re 1 µPa) did not elicit such responses, suggesting that context may moderate reactions. The observed responses to playback occurred at RLs well below current regulatory thresholds; equivalent responses to operational sonars could elevate stranding risk and reduce foraging efficiency.

Extrapolating cetacean densities to quantitatively assess human impacts on populations in the high seas

“…The intense sounds they produce can disrupt diving behavior (DeRuiter et al. 2013), alter acoustic communication (Henderson et al. 2014), and cause displacements from productive habitats (Goldbogen et al.…”

The Challenges of Analyzing Behavioral Response Study Data: An Overview of the MOCHA (Multi-study OCean Acoustics Human Effects Analysis) Project

“…Each dive in the time-series was classified as either a deep foraging dive or a shallow dive, and the Mahalanobis distance was calculated relative to the average baseline dive of the corresponding type. The time-series of Mahalanobis distances for the two exposed Ziphius ( Figure 1) show large peaks in the distance metric around the time of the CEE exposures, corresponding to the strong avoidance response identified by expert scoring (DeRuiter et al 2013). In contrast, the incidental naval MFA exposure did not elicit a similar response.…”

“…Many diverse analyses have been applied to data from each BRS, and we do not attempt to review them all here (although see Tyack et al, 2011;Miller et al, 2012;Curé et al, 2012, DeRuiter et al, 2013. Typically the first stage has been to synthesize the observational data for each individual to determine whether it responded, gauge the magnitude of any response and relate the onset of response to exposure intensity ("dose").…”

“…The whale tagged in 2011 was additionally incidentally exposed to MFA from a distant naval exercise (approximately 118km away) with received levels of 78-106dB re 1μPa rms. Full details of the CEEs are given by Southall et al (2012) and an analysis of some observed responses is given by DeRuiter et al (2013). As is the case with all CEEs that involve tagged whales, the resulting dataset included a large number of measured and derived variables.…”

“…In contrast, the incidental naval MFA exposure did not elicit a similar response. The Mahalanobis distance was then used as a measure of response intensity and was modelled as a function of RL, source-whale range, and time since sonar exposure (DeRuiter et al 2013) (model fit shown in Figure 1); results indicated that both RL and source-whale range influenced the strength of response.…”