London: Blue whales can be affected even by sounds that are outside their vocalisation range, according to a new study.
Mariana Melcon and colleagues from the Scripps Institution of Oceanography observed the response of blue whales in the Southern California Bight to mid-frequency sounds created by military sonar, which occur between 1000Hz to 8000Hz, much higher than blue whale calls, which are 100Hz and lower.
They collected thousands of hours of recordings over two summers, and found that, when mid-frequency active (MFA) sonar (which is used to find submarines) was active in the region, blue whales’ low-frequency vocalizations, known as “D-calls”, dropped by almost half: a sign, the authors posit, that despite being well outside the whales’ vocalization range, such relatively high-frequency sounds are within their hearing range.
One possible explanation for being able to hear sounds of such high frequency, Melcon and colleagues suggest, “is that it may be advantageous, for instance, to hear their predators, ie. killer whales, which vocalize in the same frequency range as MFA sonar,” Discovery News reported.
Conversely, when confronted with the noise of shipping, which does largely fall within their vocalization range, the whales increased their D-calls - which “may be the vocal response of the animals to overcome the noise”.
This new research just published in the online open-access journal PLoS One.