Dolphins in Sea

The sounds of crashing waves and calling whales rumble beneath the surface of the ocean, but those aren’t the only sounds that circulate there. In fact, over the past few hundred years, humans have added a cacophony of new noises to the marine soundscape, harming many marine species that rely on sound to survive.

Dolphins constitute a major component of these sound-dependent species. And according to a recent paper published in Current Biologyalthough these animals try to communicate with each other through their increasingly stressful environment, their attempts to “shout” are not always the most successful.

Delphine Dean

Armed with an assortment of whistles and clicksdolphins use sounds to identify and communicate with each other to mate, capture prey, avoid predators and navigate their underwater environment. But while their ability to produce and perceive sound amounts to one of their strongest points as a species, the introduction of new noises into dolphin habitats thanks to human activities such as shipping and drilling reduces their ability to cooperate and survive.

Read more: How do dolphins choose their name?

“The same reasons that make sound so advantageous for animals to use also make them susceptible to interference from environmental noise,” says Pernille Sørensen, study author and a student of behavioral biology at the University of Bristol, in press release. “Over the last few decades we have seen a dramatic increase in human-caused noise, and noise pollution in the oceans is no exception.”

In this new study, Sørensen and a team of researchers investigated the effect of sound on the ability of two captive dolphins to perform a joint task.

Eventually they discovered that the two dolphins changed their calls and changed their body position to better communicate and cooperate with each other. But despite these tactics, the dolphins’ ability to communicate successfully still dropped from about 85 percent to 63 percent due to the presence of unnatural sounds.

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“This shows us that despite the use of these compensatory mechanisms, their communication was disrupted by the noise,” Sørensen said in a press release. “Despite their attempts to compensate, […] the noise still disrupts their ability to coordinate successfully.

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To test the limits of dolphin communication, the team temporarily confined two bottlenose dolphins in a small arena filled with speakers, where the animals had to use voice communication to simultaneously press two separate buttons on two separate sides of the arena.

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When the team increased the amount of artificial, “anthropogenic” from the loudspeakers found that the dolphins adjusted their communication calls by increasing their volume and range. The team also found that the dolphins turned to each other while communicating, or sometimes swam to the opposite side of the arena to improve the ability them to work together.

However, regardless of these adjustments, the dolphins’ ability to complete the task faltered as the volume of the artificial sound increased, dropping from an 85 percent success rate to a 63 percent success rate at peak volume.

“Our work shows that these adjustments are not necessarily sufficient to overcome the negative effects of noise on human communication,” concluded Stephanie King, another study author and professor of behavioral biology at the University of Bristol, in a press release. “This will negatively impact individual health, which will ultimately impact population health.”

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