Noise pollution affects dolphins
Source: By Alind Chauhan: The Indian Express
A new study has found that noise generated by human activity makes it harder for dolphins to communicate and coordinate with each other. As the levels of underwater noise increase, these mammals have to “shout” to each other, it added.
Published recently in the journal Current Biology, the latest study, ‘Anthropogenic noise impairs cooperation in bottlenose dolphins’, has been authored by researchers Pernille M Sørensen (University of Bristol, UK), Abby Haddock (Dolphin Research Center, Florida) and others.
Dolphins are social mammals that communicate through squeaks, whistles and clicks. They also use echolocation in order to locate food and other objects. Therefore, anthropogenic noise coming from large commercial ships, military sonars or offshore drilling can severely impact their well-being.
How was the study done?
To make their observations, researchers placed two dolphins, named Delta and Reese, at an experimental lagoon and trained them to press their underwater buttons located at either end of the enclosure within one second of each other. Both dolphins were also made to wear recording tags that documented their sound and motion.
Delta and Resse were released from a starting point during each trial, and in some trials, one was held back for five to 10 seconds while the other was released immediately. In case of delayed-release trials, the dolphins had to depend on just vocal communication to coordinate the button press.
Researchers conducted around 200 such trials and used underwater speakers to create different sound environments within the experimental lagoon.
What are the findings of the study?
It was found that as it got noisier underwater, both dolphins changed their behaviour to communicate and work together. Apart from raising the volume and increasing the length of their calls, they also changed their body language — they turned their bodies towards each other and swam across the lagoon to be closer to each other.
Researchers noted despite these attempts to compensate for the noisy background, the dolphins had less success with the task. According to the study, “cooperative task success decreased in the presence of noise, dropping from 85 per cent during ambient noise control trials to 62.5 per cent during the highest noise exposure.”
Previous studies have demonstrated that dolphins change their behaviour when they come across boats but, before the latest research, no one observed how anthropogenic noise can impact the coordination among these aquatic creatures.
What are the consequences of noisy oceans?
Marine animals are known to use sound to navigate, find food and protect themselves. As sound travels faster in water than air, it makes for an important mode of communication because it can convey a lot of information quickly and over long distances. Scientists believe that fish species rely on sounds during reproductive activities, including mate attraction, courtship and mate choice.
However, several studies and incidents have shown that sounds made by drilling, commercial ships and military operations lead to disruption of marine life.
In 2020, Australia witnessed one of its worst mass stranding of whales when around 200 of them died on Tasmania’s west coast. Researchers suggest that mass strandings are linked to noise pollution in oceans.
A 2018 study by researchers at the University of Maryland found “that when there was more ambient sound, mostly from passing boats and ships, the dolphins switched to higher frequencies and streamlined their whistles”, according to a report published by Mongabay.
Recently, The Guardian reported that the newly launched MV Ganga Vilas cruise, which will “make stops at about 50 tourist and heritage sites along the Ganga and Brahmaputra river systems”, could severely damage the habitat of the Ganges river dolphin, which already face a number of threats, including water pollution and poaching.
Speaking to the newspaper, environmentalists and conservationists pointed out that these dolphins are “almost blind” and an increase in cruise tourism might result in their extinction.
