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. 2012;7(2):e32681.
doi: 10.1371/journal.pone.0032681. Epub 2012 Feb 29.

Blue whales respond to anthropogenic noise

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Blue whales respond to anthropogenic noise

Mariana L Melcón et al. PLoS One. 2012.

Abstract

Anthropogenic noise may significantly impact exposed marine mammals. This work studied the vocalization response of endangered blue whales to anthropogenic noise sources in the mid-frequency range using passive acoustic monitoring in the Southern California Bight. Blue whales were less likely to produce calls when mid-frequency active sonar was present. This reduction was more pronounced when the sonar source was closer to the animal, at higher sound levels. The animals were equally likely to stop calling at any time of day, showing no diel pattern in their sensitivity to sonar. Conversely, the likelihood of whales emitting calls increased when ship sounds were nearby. Whales did not show a differential response to ship noise as a function of the time of the day either. These results demonstrate that anthropogenic noise, even at frequencies well above the blue whales' sound production range, has a strong probability of eliciting changes in vocal behavior. The long-term implications of disruption in call production to blue whale foraging and other behaviors are currently not well understood.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Example of D calls in presence of MFA sonar.
Long-term spectral average of 5 hours. Each orange “D” represents presence of D calls in 5-minute bins in the lower frequency band (25–100 Hz). Note the continuous presence of D calls for over 2 hours until the onset of MFA sonar (not a particularly close event, with signals every 10–30 seconds), at which time at which the whales cease production of D calls. After sonar cessation, blue whales start producing D calls again.
Figure 2
Figure 2. Probability of D calls as a function of SPL.
Proportion of hours containing D calls ± s.e. as a function of the maximum sound pressure level (rms) of each hour for non-anthropogenic noise, MFA sonar, explosions and ship noise. P values are given for each condition and parentheses represent the number of hours contributing to each data point. Whereas, the probability of D calls given non-anthropogenic noise and explosions showed no significant dependency on the received level, the probability of MFA sonar decreased with increasing received levels. The probability of D calls given ship noise, on the contrary, increased as a function of the SPL in the mid-frequency range.
Figure 3
Figure 3. Diel pattern of D calls and sensitivity to MFA sonar.
Upper panel represents the probability of D calls as a function of the time of the day for both feeding seasons (2009–2010). Middle and lower panels show, respectively, the ratio of the probability of D calls given MFA sonar and the probability of D calls given ship noise divided by the probability of D calls given non-anthropogenic noise as a function of the time. Values below 1 indicate a lower incidence of D calls given MFA sonar or ship noise; whereas, values above 1 indicate the opposite.

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