Whales are singing more quietly, and it's likely our fault
Climate Change Reporter
Thursday, December 6, 2018, 2:37 PM - A whale's tongue can weigh as much as an elephant, so it is no surprise that they are among the largest and loudest animals in the ocean. But as their habitat warms and sea ice continues to melt, they are struggling to sing their usual songs and are becoming quieter.
Whale vocalizations, or songs, include clicks, whistles, and pulsed calls that help them identify their surroundings, navigate, and differentiate between friendly creatures and predators. Communication between pods, a group of whales, is critical for survival, so scientists are wondering why their songs are becoming flatter.
A new study published in the Journal of Geophysical Research studied five large populations of fin, Antarctic, and pygmy blue whales in the southern Indian Ocean and found that the frequencies of their vocalizations have consistently decreased each year since 2002 and steadily decreased since the 1960s.
The blue whales are highly social and vocal creatures, and have demonstrated seasonal frequency shifts, meaning that their vocalizations change with the seasons and are affected by ambient noise that is near their calls.
The amount of sea ice fluctuations with the seasons, and icebergs are one of the main sources of oceanic noise in the Southern Hemisphere. As sea ice has shown annual declines over the recent decades, researchers have noted that human-caused climate change has impacted the vocalizations of whales.
The researchers suggest that a lower amount of sea ice means that there is less ambient noise in the oceans, which reduces the amount of other noises in the ocean that the whales would have to sing over.
Fin and blue whale call‐frequency decline over the years in the southern Indian Ocean. Symbols (red, this study; black diamonds, data digitized from Gavrilov et al., 2012) are weekly averaged peak frequencies measured for selected units in the calls (black rectangles in the time‐frequency diagrams). The rates of frequency decrease in hertz per year are the slopes of the fitted dashed lines. Credit: Leroy et. al., 2018.
The study of vocal activities in marine animals has been critical for gaining knowledge of marine environments, protecting endangered species, and exploring the impacts of shipping and seismic activities.
While the researchers have correlated seasonal cycles of arctic ice to the decline in their vocalizations, it is noted that the reasons for the long-term decline remain unclear. Human activities that create marine noise, ocean acidification that is caused by warming global temperatures, and changing in whaling practices all contribute to changing whale behaviours.
The level of acidity in oceans impact the speed that sound travels at and how much sound is absorbed by the ocean. Based on this, it is suggested that whales will be able to communicate their songs over a longer distance, which could be why they are lowering their song frequencies.
Blue whale in Antarctica. Credit: Wikimedia Commons
The Antarctic ice shelf, which is located relatively close to the regions of the Indian Ocean that data was sampled from, produces powerful low-frequency cryogenic sounds from drifting icebergs that can travel through the entire Southern Ocean and reach tropical latitudes.
As warming atmospheric temperatures contribute to ice shelf cracking and melting sea ice, the projected future melting could play a greater role in impacting whale songs. The researchers state that while correlations do not confirm causation, the observations do hint that short-term and wide-range causes in the acoustics of marine environments may have a strong impact on the vocal behaviour of large whales.
It is noted that further research is needed to analyze the impacts of changing marine acoustics on whale populations, with focus on how increasing ocean acidification will impact the sound speed and absorption of ocean songs, particularly in the southern Atlantic and Pacific oceans.