They reveal that this climatic phenomenon stimulates the communication of these marine mammals
Despite its large size, the Whales They are difficult animals to study using conventional systems, since they are shy and solitary beings. However, these slippery creatures like to sing (these are the sounds they make to communicate), and scientists can study those melodies to learn more about their behavior.
Researchers at the University of New South Wales (UNSW Sydney, in Australia) have been using a network of underwater listening devices to monitor pygmy blue whales off the coast of Western Australia. Their study, published in Frontiers in Marine Science, analyzed nearly two decades of continuous underwater recordings to see if their calls match environmental changes in their surroundings.
The scientists found that while the number of whale call detections changed from year to year, its variability was related to the La Niña climatic phenomenon. The findings suggest that climate cycles may influence the migration of the pygmy blue whale. in the eastern Indian Ocean, which may have important implications for its conservation.
La Niña is the cooling phase of the natural El-Niño-Southern Oscillation (ENSO) cycle that causes variations in sea surface temperatures across the Pacific, although it is also known to have far-reaching effects on weather conditions. climatic and oceanic conditions throughout the world, including the Indian Ocean.
“We found that the number of ‘song’ detections was related to the strength and timing of La Niña events.suggesting that it may be an important factor influencing their movements,” says Gary Truong, lead author of the study and a Ph.D. candidate at UNSW Science.
“Specifically, we saw that the number of songs detected during La Niña years is up to 10 times higher than in El Niño or neutral years, indicating that these whales respond to changes in weather cycles“, he added.
Tracking the whale tunes
For the study, the researchers used acoustic data from a network of underwater sensors deployed in the Indian Ocean by the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO). The devices, known as hydrophones, were originally designed for unauthorized nuclear testing. But they also record the sounds of marine mammals, such as pygmy blue whales.
“Whale song is a very low frequency range that is picked up by these underwater listening devices,” Truong says. “Their sounds typically range from zero to 100 hertz, which is lower than we can detect with our ears.”
It is estimated that there are about 10 different populations of acoustic pygmy blue whales, the smallest subspecies of blue whale, in the southern hemisphere, each with distinct sounds that researchers use to identify them. Currently it is believed that only male whales sing. Researchers can analyze those songs to gather information about populations and their movement.s.
“Greater numbers of pygmy blue whale calls or songs could indicate that whales are migrating in greater numbers and having more reproductive success“Now that we are no longer under La Niña, the number of calls we detect may decrease, which could mean a period when the whales may not be as productive,” he says.
The emerging climate threat
The findings may have important implications for the management of pygmy blue whales in the region, which have historically been threatened by commercial whaling.
“Hunting came close to driving the species to the brink of extinction, and although they are now slowly recovering, their numbers have not rebounded strongly,” says Professor Tracey Rogers, lead author of the study and an ecologist at UNSW Science.
“From a conservation perspective, we know relatively little about them, so studies like these are important.” And it is that more information about the movements of the whales it can help administrations predict when the largest numbers of individuals will migrate and help other ocean users plan their activities.
“Commercial shipping and the search for oil and gas can be harmful to whales“Properly managing those activities, particularly during the busiest migration years, can help reduce the impact on these animals as they swim by,” Troung says.
food availability
While blue whales are no longer in decline, the researchers warn that climate change also looms as a growing threat to this species. As the ocean warms, the availability of food sources such as krill, which researchers suspect may be the determining factor in the migration of whales.
“We are not only seeing the impacts of climate change on the terrestrial landscape, but also in the oceans and the animals that live in them,” recalls Professor Rogers. “Science suggests that we will see more frequent La Niña events. This will likely affect food availability for these large whales and perhaps put more stress on population recovery.”
The researchers say more research is needed to understand the impact of changes in food availability during La Niña years.
“The climate is changing quite rapidly, and the question is whether animals like the pygmy blue whale can adapt to these conditions in the long term“Truong says.
Reference study: https://www.frontiersin.org/articles/10.3389/fmars.2022.850162/full
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