Dose-response relationships for the onset of avoidance of sonar by free-ranging killer whales

Abstract

Eight experimentally controlled exposures to 1À2 kHz or 6À7 kHz sonar signals were conducted with four killer whale groups. The source level and proximity of the source were increased during each exposure in order to reveal response thresholds. Detailed inspection of movements during each exposure session revealed sustained changes in speed and travel direction judged to be avoidance responses during six of eight sessions. Following methods developed for Phase-I clinical trials in human medicine, response thresholds ranging from 94 to 164 dB re 1 lPa received sound pressure level (SPL) were fitted to Bayesian dose-response functions. Thresholds did not consistently differ by sonar frequency or whether a group had previously been exposed, with a mean SPL response threshold of 142 6 15 dB (mean 6 s.d.). High levels of between-and within-individual variability were identified, indicating that thresholds depended upon other undefined contextual variables. The dose-response functions indicate that some killer whales started to avoid sonar at received SPL below thresholds assumed by the U.S. Navy. The predicted extent of habitat over which avoidance reactions occur depends upon whether whales responded to proximity or received SPL of the sonar or both, but was large enough to raise concerns about biological consequences to the whales.

The significance of respiration timing in the energetics estimates of free-ranging killer whales (Orcinus orca)

“…Individual tag records ranged from 1.67 h to almost 12.5 h in length (Table S1). Some whales were tagged simultaneously and data records of four whales included time periods in which they were experimentally exposed to sonar (Table S1) (Miller et al, 2011), which probably affected the speed of these individuals during some periods of their tagging record (Miller et al, 2014).…”

“…This observation could be explained by characteristics of the O 2 -uptake model in combination with behavioural state. While porpoising, the animal is driven by the motivation to move fast (in this case as a response to sonar; Miller et al, 2014) and therefore respire in the most efficient way to reduce the number of surfacings, which lead to increased surface drag (Hertel, 1966;Costa and Williams, 1999). Thus, this male killer whale changed its respiration behaviour in a manner that appears to functionally increase T O2 during a period of high-speed travel.…”

The Severity of Behavioral Changes Observed During Experimental Exposures of Killer (Orcinus orca), Long-Finned Pilot (Globicephala melas), and Sperm (Physeter macrocephalus) Whales to Naval Sonar

“…The behavior of the animals was studied using a combination of tags that record sound and movement, visual tracking of individual animals, and visual observations of each tagged whale's group. Summaries of these observational data streams, associated to experimental exposure to sonar and control stimuli, have been compiled into a comprehensive technical report describing each of the experiments (Miller et al, 2011). Visual tracking of a tagged whale and its associated group, aided by radiotracking of the VHF beacon of the tag and data recorded with the movement-recording Dtag, allow us to reconstruct a detailed 3-dimensional (3-d) movement track of each subject (e.g., Miller et al, 2009).…”

Experimental field studies to measure behavioral responses of cetaceans to sonar

“…Within the experimental contexts tested, received sound level has been associated with the probability of responses in an experimentally controlled dose-escalation context to generate preliminary, probabilistic dose-response functions (e.g. Miller et al 2014). In some conditions, individualspecific factors such as behavioral state may interact with exposure variables such as received level to influence the probability of re sponse (e.g.…”