SYDNEY – A drop in the pitch intensity of whale songs in the last few decades could be related to climate change and an increase in its population, according to a study published on Monday.
“We think it is something non-voluntary from the whale,” Emmanuelle Leroy, who conducted the research, said in a statement published by the University of New South Wales.
The study, published in the American Geophysical Union’s Journal of Geophysical Research: Oceans, analyzed one million songs from Blue whale (Balaenoptera musculus), Fin whale (Balaenoptera physalus) and Pygmy blue whales (B. m. brevicauda) recorded with six stationary microphones in the Indian Ocean from 2010 to 2015.
The study found the songs of an Antarctic blue whale, which have a frequency of 15 to 30 hertz, fall 0.14 hertz per year, a trend similar to that of the other two species analyzed, whose calls fall 0.12 to 0.54 hertz every year.
These cetaceans are among the loudest animals in the oceans and their songs can travel more than 1,000 kilometers underwater.
“The speed and distance that sound travels are affected by the temperature, pressure and chemistry of the ocean,” the statement added.
According to Leroy, the whales might be singing a little flat as they do not need be so loud because sound travels even more in the ocean water as they have become increasingly acidic due to climate change.
The researchers also indicated that the fall in the pitch could also be an effect of the growing population of the whales since the end of commercial whaling in the 1970s.
“They can decrease their call intensity to keep in touch, because there are more whales. These calls are long-distance communication,” the researcher said.
The study also found a “correlation between the seasonal variations in the whale’s pitch with breaking sea ice in the southern Indian Ocean,” whose noise could compel the whales to increase the pitch of their calls.
“The noise is related to the increasing number of free icebergs in summer. When the ice sometimes cracks, like when you put ice in your drink, it makes noise,” Leroy said.