Dolphins ‘shout’ to announce noise pollution

One of the dolphins, Delta, used a sound tag to measure their clicks and whistles during the experiment.

One of the dolphins, Delta, used a sound tag to measure their clicks and whistles during the experiment.

A new study reveals that dolphins struggle to hear and cooperate with each other in a world of increasing noise pollution.

It is one of many marine mammals that rely on whistles and echolocation to work together to hunt and reproduce.

However, noise pollution from human activities such as transportation and construction has increased significantly in recent years.

This could have detrimental effects if they can no longer cooperate, the researchers said.

“If groups of wild animals are less efficient at foraging cooperatively, this will negatively impact individual health, which will ultimately affect population health,” said co-author Stephanie King, an associate professor at the University of Bristol.

Sound is one of the most important senses for marine animals. Unlike light, which is rapidly absorbed by water, it can travel tens, if not hundreds, of kilometers.

As a result, cetaceans – whales, dolphins, dolphins – have developed a complex range of sounds to “talk” to each other.

It was already known that they would increase the volume or frequency of their calls to compensate for the noise pollution from human activity.

Pernille Mayer Sørenson, PhD candidate at the University of Bristol, who led the research team that included the Dolphin Research Center and the University of St Andrews, said: “We knew from previous work that noise pollution affects animals, but from this study, what do we do first? See how it affects you.”

The study, published in the journal Current Biology, found that the dolphins’ efforts to compensate by “yelling” pollution were not enough and they struggled to work together.

The study was conducted in an experimental lagoon with two bottlenose dolphins, Delta and Reese, nicknamed “Reese’s Pieces” and their trainers. They had to perform a common task – in this case, each of them was pressing a button within a certain amount of time.

Each dolphin was fitted with a temporary sound and motion tag that sits behind the blowhole and measures their behavior and sounds.

The scientists found that when dolphins were exposed to increased levels of anthropogenic (human-created) noise, they nearly doubled their whistling duration as well as their loud voices to compensate for this interference.

Reese and Delta were also more likely to face off. Previous work has shown that this may be due to their sense of hearing being direction sensitive, meaning that looking at each other can help separate their partner’s signal and polluting noise – a process known as “spatial release.”

Despite their best efforts, Delta and Reese only succeeded 62.5% when exposed to very high noise pollution, compared to 85% in the control experiment with ambient background noise.

The highest noise level they were exposed to was 150 decibels (dB).

The sound a supertanker cargo ship makes as it moves through the ocean will reach up to 200 dB, according to the Natural History Museum.

reese in water

Reese’s whistles were on average 1.85 times longer in the loudest noise exposure trials.

Ms Sørenson explained why the inability of dolphins to communicate properly is a concern: “If you are exposed to noise and this prevents you from communicating with friends while foraging together, this can lead to missed opportunities and can have an impact on your individual health, if this is your survival. if it is a certain behavior that is necessary for

And he warned: “The longer you’re exposed to it, the greater the consequences at the population level.”

This work adds to existing research linking noise pollution to adverse effects for marine mammals.

Whales have been observed to suffer decompression sickness, behavioral changes, and stranding after exposure to noise pollution from ships, oil and gas exploration, and construction.

In this photo taken from social media, a killer whale lays ashore on a beach in Cadzand, the Netherlands, on October 15, 2022.

Whales can run aground if they are disoriented due to noise pollution from ships and other human activities.

The next step would be to repeat the experiment for dolphins in the wild, but this is a challenge due to the difficulties of constructing a controlled scenario with no noise pollution to compare.

However, Ms. Sørensen suspects that wild dolphins will outperform their peers at the research center when exposed to noise pollution.

He said: “These people [Delta and Reese] they are highly motivated and know this task well – they have done it hundreds of times for previous work. But if we go out into the wild, if an animal wants to initiate behavior with another person, it may not know that its mate wants to cooperate.”

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