A study has found that dolphins cannot communicate as effectively when exposed to human-generated noise, forcing them to change their sounds like people do when they shout.

An international team of researchers from the University of Bristol, the Dolphin Research Centre, Syracuse University, Woods Hole Oceanographic Institution, Aarhus University and the University of St. Andrews collaborated on the study. which was published in Current Biology on Thursday

“We wanted to investigate how noise affects animals working together,” Pernille Sørensen, first author of the paper and a PhD candidate at the University of Bristol, said in an interview with CNN. “So basically we look at the entire communication network, from a sender to a receiver, and if there is any impact on that transmission.”

Previous studies have documented the damaging impact that noise pollution can have on other aquatic mammals, such as whales. The constant noise from ship engines and military sonar makes it difficult for marine mammals to communicate with each other and has been linked to an increase in whale-ship collisions.

The researchers focused on dolphins because the aquatic animals are highly social and intelligent, using whistles to communicate with each other and clicks to echolocate and hunt. And communication by sound is particularly crucial for underwater animals because below the surface of the water, “sound travels very far and very fast,” Sørensen said.

In addition, dolphins have a “broad vocal repertoire” that they use “in basically all aspects of their lives, including coordinating cooperative behaviors.”

To understand how noise pollution affects the dolphins’ ability to cooperate, the scientists worked with two specific dolphins named Delta and Reese that live at the Dolphin Research Center in Florida. The dolphins had a mission: they needed to each press an underwater button at the same time. The dolphins were asked to perform the task in ambient noise conditions and under four “noise treatments” intended to simulate human-caused underwater noise pollution. A total of 200 tests were performed on the pair of dolphins, with each dolphin wearing an acoustic tag that recorded its sound production.

The findings were twofold, Sørensen said. First, they found that the dolphins used “compensatory mechanisms” to compensate for their impeded vocal communication. As the underwater noise increased, they made louder and longer sounds, and changed their body language to look at each other.

But the most important finding, according to Sørensen, was that despite using their attempts to compensate for noise pollution, the dolphins were even less successful in completing the task. Their success rate dropped from 85% to 62.5% from the lowest to the highest noise levels.

“We are showing, to our knowledge for the first time, that animals working together are affected and that compensatory mechanisms are insufficient to overcome noise impacts,” he explained.

This could have real-world impacts on dolphins in the wild, which rely on cooperation for feeding and breeding. “They need sound to connect,” she said.

Sørensen added that the researchers “would have loved to introduce or include more dolphins in our experiment” and that future experiments could expand the sample size to a larger group of dolphins.

Additionally, more research is needed on the specific types of whistles and sounds that dolphins use for cooperative tasks.

“This research definitely contributes as part of the puzzle to our understanding of how noise pollution affects animals,” Sørensen said.

He said he hopes the research will help support “solutions for how we can better manage noise in our oceans.”

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