6). While the distributions of Δheading both before and after the breakpoint are centered around zero, the angular standard deviation of the data after the breakpoint

was 27.4º less than that before. This reduced standard deviation indicates that the tagged whale maintained a more directed find more course after the cessation of the killer whale playback. This study utilized a playback experiment to test the behavioral reaction of a tagged Blainville’s beaked whale to MFA sonar and the calls of killer whales that feed on marine mammals. Due to the difficult nature of finding and tagging M. densirostris, this study represents the only playback experiment to date for these whales with an extended monitoring period after exposure. Determining what features of MFA sonar cause beaked whales to strand is an important but difficult task. A whale living in deep water must swim far from its typical habitat before it is at risk of stranding. Baleen whales avoiding predation by killer whales have been observed to strand (Ford et al. 2005, Ford and Reeves 2008), suggesting that directed avoidance in reaction to predators may increase a whale’s risk of stranding. Therefore, we use heading data here to study whether a beaked whale responded to playback

of MFA sonar or killer whale calls GSK3235025 cost with a straighter course of travel that would cause it to swim far from its foraging site, potentially raising the risk of stranding. The small sample size limits the conclusions that can be drawn from the experimental scenario. However, utilizing the heading data from the Dtag, we are able to employ a novel statistical technique to draw some basic conclusions about the data. During exposure to each of the playback stimuli the whale ceased clicking early in the deep foraging dive at a received level of 138 dB re 1 μPa SPL for the MFA playback and 98 dB re 1 μPa SPL for the killer whale playback. In each case, after cessation of clicking,

the whale initiated a slower than normal ascent to the surface (Tyack et al. 2011). While there is a temporary avoidance reaction to the MFA sonar playback, observed as a 上海皓元 straightening of course (Fig. 2), the whale appeared to resume normal foraging about two hours after surfacing (Tyack et al. 2011). A test of the heading data before and after cessation of the MFA playback revealed that there were no significant differences in the whale’s heading after this playback (Fig. S2). An extended avoidance reaction was observed only after the killer whale playback. However, because the stimuli were played in sequence, we cannot rule out the possibility that the behavioral response was cumulative, and that the MFA sonar playback only several hours earlier had a potentiating effect on the response to the killer whale playback.