Dolphins “scream” to be heard over noise pollution

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

They are one of many marine mammals that rely on whistling and echolocation to work together for hunting and breeding.

But noise pollution from human activities, such as shipping and construction, has grown dramatically in recent years .

If they are no longer able to cooperate, this could have disastrous consequences, the researchers say.

“If groups of animals in the wild are less efficient at foraging together, this will have a negative effect on individual health, which will ultimately affect population health,” said co-author Stephanie King, associate professor at the University of Bristol.

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

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

They have previously been known to increase the volume or frequency of their calls to try to compensate for noise pollution caused by human activity.

Pernille Mayer Sorenson, PhD at the University of Bristol, who led the research team, which included the Dolphin Research Center and the University of St Andrews, said: “From previous studies we knew that noise pollution affects animals, but from this study what we do for starters, time to look at how noise affects how animals work together.”

Research published in the journal Current Biology, showed that the dolphins’ efforts to compensate for pollution by “screaming” were not enough, and they had difficulty working together.

The study was conducted with two bottlenose dolphins, Delta and Reese, nicknamed “Reese’s Bits,” in an experimental lagoon with their trainers. They were required to complete a cooperative task, in which they each pressed a button within a certain time of each other.

Each dolphin was fitted with a temporary sound and movement tag that sits behind their snout and measures their behavior and sounds.

Scientists found that when dolphins were exposed to increased levels of anthropogenic (man-made) noise, they almost doubled the duration of their whistles, and also increased their volume to compensate for the interference.

Reese and Delta also saw each other more often. Previous work has shown that this may be because their hearing is sensitive to direction, which means that looking at each other can help separate their partner’s signal from contaminating noise – a process known as “spatial disengagement”.

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

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

According to the Museum of Natural History the sound produced by a cargo tanker when it moves through the ocean will reach 200 dB.

image captionReese’s whistle was on average 1.85 times longer in trials with the highest noise exposure

Ms Sorenson explained why it’s a concern if dolphins can’t communicate properly: “If you’re exposed to noise and it prevents you from communicating with your friends when you’re foraging together, it can lead to missed opportunities and it can affect your personality. health if it is a certain behavior that is essential to your survival.”

And she warned: “If you’re exposed to it for longer and longer periods of time, it can have more serious consequences at the population level.”

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

It was observed that whales suffer decompression sickness, change behavior and run aground after exposure to noise from ships, oil and gas exploration and construction.

A killer whale lies on the shore of a beach in Katzand, the Netherlands, on October 15, 2022, in this photo obtained from social media.
image captionWhales can become stranded if they are disoriented by 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 difficult due to the difficulty in creating a controlled scenario without noise pollution for comparison.

But Ms. Sorensen suspects that wild dolphins will do even worse under noise pollution than their research center counterparts.

She said, “These people [Дельта та Різ] are highly motivated and know the task well – they have done it hundreds of times in previous studies. But if we go out into the wild, if an animal wants to initiate a behavior with someone else, they may not know that their partner wants to cooperate.”

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