However, if naval sonar exercises are either very loud, very extended or both, it is possible that they could elicit this same prolonged find more avoidance response in beaked whales that could lead to stranding. In addition to the extreme response of mass strandings, it is possible that lower levels of MFA sonar exposure could produce
lesser behavioral reactions that could still have adverse effects on the whales. The greater variation in the Δheading before the killer whale breakpoint likely represents standard foraging search patterns. These whales forage on deep dwelling prey items that may be located in discrete patches (Johnson et al. 2008), therefore they likely employ a foraging search pattern that maximizes their likelihood of encountering these patches. While we filtered out the smaller scale movements, the whales are still likely to move between feeding sites over the longer term. The light gray tracks in Figure 2 indicate the restricted area search typical for undisturbed beaked whales in the Tongue of the Ocean. The reduced variation in the Δheading of the tagged whale after the killer whale breakpoint indicates that it maintained a relatively straight course. Analysis of the acoustic
record of the tag shows that the number of buzzes produced, which indicate prey capture events, was reduced during the sonar and killer whale playbacks and then increased in subsequent foraging dives (Tyack et al. 2011). These factors AZD1208 manufacturer together may indicate that the whale was immediately reducing foraging effort in favor of directed flight from the area of playbacks. Areas with frequent sonar exercises may cause the resident population of beaked whales to abandon their preferred foraging habitat during sonar playbacks, possibly reducing their foraging intake or foraging
selectivity (Tyack et al. 2011). The whale reacted to a much lower received level for the killer whale playback than for the MFA sonar playback, however these stimuli were played in sequence so we cannot rule out the possibility that the effect of the playbacks was cumulative. Additionally, the AUTEC range is frequently used for naval sonar exercises including those utilizing MFA sonar signals. The repeated exposure selleck kinase inhibitor to this signal may have habituated the tagged animal to these sounds, leading to the reduced reaction to the MFA playback. By contrast, killer whales are very rare in AUTEC waters. The calls of killer whales are likely a much less frequent sound heard at AUTEC than MFA sonar, so we cannot determine if the beaked whale recognized the sound as a potentially lethal predator, or whether it simply interpreted it as a novel sound, thus causing the stronger response to the killer whale playback. Two other factors make it possible that the killer whale playback stimulus could have been interpreted as a novel sound rather than recognized as killer whales.