Whale songs in the ocean around Antarctica have transformed; climate change could be why

Songs have lowered in frequency, in part because of changes to ocean water.

December 04, 2018, 6:54 PM

Whales in the ocean around Antarctica are changing their tune, according to a new study.

Publishing their findings in the Journal of Geophysical Research, scientists collected and analyzed more than 1 million songs from five populations of large whales in the southern Indian Ocean over the course of 7 years. They said that among other contributing factors, climate change and ocean acidification may have led to changes in the way that whales sing.

Male blue whales and male fin whales produce the loudest calls in the southern Indian Ocean, and their songs can be heard underwater up to 1,000 kilometers away, which enables them to maintain contact with each other.

“We measured precisely the frequency of the first tonal sound -- called unit A -- in each detected call. We observed that over the years, this frequency has decreased by about 0.14 hertz per year,” Jean-Yves Royer, one of the authors of the study, told ABC news.

PHOTO: A fin whale surfaces at 58°S in the southern Indian Ocean in a photo captured in January 2010 from the R/V Marion Dufresne, the research vessel that collected hydrophone data for the new study.
A fin whale surfaces at 58°S in the southern Indian Ocean in a photo captured in January 2010 from the R/V Marion Dufresne, the research vessel that collected hydrophone data for the new study.
J-Y Royer

Royer explained that one of the reasons the whales have lowered their frequencies could be because an excess of carbon in the water as the oceans become more acidic.

“This chemical change induces a change in the acoustic properties of the ocean, acidification favoring the propagation of low frequencies,” said Royer. “All large whales emit low-frequency sounds, hardly discernible by a human ear. If the ocean carries better the sound waves, then no need to shout as loud as before to communicate with other whales.”

PHOTO: Whale song pitch, ambient underwater noise and icebergs: the blue line traces seasonal changes in the pitch, or audio frequency, of blue whale calls.
Whale song pitch, ambient underwater noise and icebergs: the blue line traces seasonal changes in the pitch, or audio frequency, of blue whale calls. The red trend traces rising and falling ambient noise and the blue histograms show the number of free icebergs per week.
JGR-Oceans/AGU

Royer said that other contributing factors to changes in whale calls in the region could be the increased frequency of of icebergs breaking, and growing whale populations.

“Since the whaling ban, the populations may have recovered so that there is no need for crying out as loud as before to communicate,” Royer said.

PHOTO: Fin and blue whale call frequencies have declined in the southern Indian Ocean during the period of monitoring, from 2002 to 2015.
Fin and blue whale call frequencies have declined in the southern Indian Ocean during the period of monitoring, from 2002 to 2015. Data points are weekly averaged peak frequencies measured for selected units in the calls. Red points are data from the new study. Black diamonds are data digitized from previously published work.
JGR-Oceans/AGU
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