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ScienceGlobal issues

Dolphins have to shout over noise pollution

Anna Tatlow-Coonan
January 19, 2023

In order to communicate, some dolphins have to shout over man-made noise pollution. How does this impact the way the animals interact and live?

Dolphins jumping from the ocean
Dolphins communicate with each other largely through whistlingImage: Gerard Lacz/Anka Agency International/picture alliance

It turns out human city dwellers aren't the only ones who have to shout over sound pollution to be heard.

In a study published earlier this month in Current Biology, researchers at the University of Bristol and the US-based Dolphin Research Center found that loud man-made interferences in and near the world's oceans — like ship engines, oil and gas drilling, construction along the coasts and nearby aircraft — are making it harder for dolphins to communicate with each other. 

"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," study author Pernille Sørensen said in a statement.

The researchers reported that, like humans, dolphins also resort to shouting when they can no longer be heard by their brethren.

Dolphin with open mouth
When noise levels were high, dolphins whistled louder than normal, researchers foundImage: K. Wothe/imageBROKER/picture alliance

Dolphins need communication to survive

Like humans, dolphins are social animals and require communication for survival. Instead of talking and using language, dolphins generally whistle and use something called echolocation, which allows them to navigate dark, murky waters. These communication rituals are key to dolphins' ability to hunt, reproduce, court and signify distress.

Researchers wanted to understand the degree to which this communication is harmed by noise pollution.

After discovering in past experiments that dolphins use communication to work together to complete cooperative tasks, the research team set out to understand how this cooperation could be impacted by varying noise conditions ranging from low to very high.

By monitoring the dolphins' whistles using suction cup sound recorders, the researchers found that the two dolphins involved in the experiment, Delta and Reece, changed the volume and duration of their calls to one another depending on how loud the background noise was.

As noise levels increased, the dolphins' communication success levels dropped from 85% with no noise to 62.5% with high noise.

The animals also changed their body language to face each other and swam closer together to better communicate.

"This shows us that despite them using these compensatory mechanisms, their communication was impaired by noise," said Sørensen.

Dolphins swimming together in the sea
Even after trying to adapt to excessively loud noise conditions, dolphins still had trouble communicating with each otherImage: Jody Watt/Design Pics/Pacific Stock/picture alliance


This discovery has potentially dire consequences for sea life.

"Since dolphins rely on their communication skills to successfully hunt and reproduce, noise levels can affect their behaviors, which in turn affect population health," co-author Stephanie King said in a statement.

As ocean predators, dolphins hunt fish, squid and cuttlefish for meals, and they are prey to many species of sharks. Dramatic changes in the ocean's dolphin population would cause an imbalance in the food chain and, subsequently, in marine life. These changes could affect us humans as billions of people rely on seafood as a main source of food and income.

Other animals are impacted by noise

Dolphins aren't the only animals affected by noise.

Male eastern bluebirds sing louder and at higher pitches in loud environments, while orca communication has been found to become impaired due to passing ships.

In 2002, a reported 14 whales were found upon the shores of the Canary Islands after becoming confused by sonar signals, which impacted their ability to navigate.

Noise pollution impacts millions of people on a daily basis. It can lead to hearing loss, high blood pressure and stress. Causes of sound contamination vary from industrial machines to fire crackers to aircraft. It is a terrible thing to live with, yet humans have imposed the same problems on animals all around us.

Reducing ocean noise pollution

Edited by: Clare Roth