Dolphins shout at each other over increasing levels of underwater noise pollution, new research suggests.

Sounds generated by humans may force the animals to make louder and less effective whistles, according to experts from the University of Bristol.

Dolphins rely on echolocation to hunt and reproduce, meaning activities like drilling and shipping could affect the health of wild dolphin populations.

“Within the last couple of decades, we’ve seen a dramatic increase in human-made noise, and noise pollution in the oceans is no exception,” said first author Pernille Sorensen.

She added: “Those same reasons that make sound so advantageous for animals to use also make them susceptible to disturbance from noise in the environment.”

Researchers put two dolphins, named Delta and Reese, in an experimental lagoon where they had to work together to press a button at each end within a second of each other.

During certain trials, one dolphin was released five to 10 seconds after the other, meaning they had to rely on vocal communication to coordinate the button press.

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Researchers discovered that when they raised the level of noise playing through an underwater speaker, both Delta and Reese changed the volume and length of their calls.

Their button-press success rate dropped from 85% to 62.5% between the lowest and highest levels of noise, the study found.

Dolphins’ communication impaired by noise despite being highly motivated

Ms Sorensen said: “This shows us that despite them using these compensatory mechanisms, their communication was impaired by noise.

“Our work shows that despite their attempts to compensate, despite being highly motivated and the fact that they know this cooperative task so well, the noise still impaired their ability to successfully coordinate.”

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As the volume of the speaker increased, the dolphins were also more likely to face each other or to swim to the other side of the lagoon to be closer.

Read more: Russia ‘deploys trained military dolphins at naval base’

Although the study was conducted with dolphins living in human care, researchers suggest human-made noise could have a detrimental impact on wild dolphins.

Co-author Stephanie King, associate professor at the University of Bristol, said: “If groups of animals in the wild are, for example, less efficient at foraging co-operatively, then this will negatively impact individual health, which ultimately impacts population health.”

The study was published in the Current Biology journal.

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