February 9, 2023

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Dolphins can scream underwater, but it’s never enough

Mammals swim in the ocean through a world of sounds. But in recent decades, humans have been increasing the size, Blowing water with noise From shipping operations, oil and gas exploration and military operations. New research suggests that such human noise may make it difficult for dolphins to communicate and work together.

When dolphins teamed up on a mission in a noisy environment, the animals weren’t all that different from city dwellers on Earth who were trying to be heard over the noise of jackhammers and ambulance sirens. they cried, Calls louder and longerthe researchers reported Thursday in Current Biology. “Even then, there is a huge increase in the number of times they fail to coordinate,” said Shane Jirou, a cetacean biologist at Carleton University in Ottawa who was not part of the work. The effect of the noise boost was “remarkably clear”.

The scientists worked with a dolphin duo, a male named Delta and Reese, in an experimental lagoon at the Dolphin Research Center in the Florida Keys. The pair was trained to swim to different places in their enclosure and press a button within 1 second of each other.

“They were always the most motivated animals,” said Pernelle Sorensen, a biologist and Ph.D. candidate at the University of Bristol in England. Dolphins talked to each other using whistles and often whistled before pressing a button, she said.

Ms. Sorensen’s team broadcast the sounds using underwater loudspeakers. The tags, which are stuck behind the animals’ blowholes, capture what the dolphins hear and call to each other as well as their movements.

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Through 200 experiments with five different acoustic environments, the team observed how dolphins altered their behavior to compensate for loud noises. The whales turned their bodies towards each other and paid more attention to each other’s location. Sometimes, they nearly double the length of their calls and amplify their whistles, meaning screams, to be heard over the crackling sounds of white noise or a pressure washer recording.

The higher the noise, the less successful the dolphins are at the task. In the highest case, they succeeded 62.5 percent of the time, hitting their buttons at the same time at about 20 percent lower ambient sound levels.

“It was surprising to see how low the success rate was,” said Ms. Sørensen.

Researchers have noted in the past that wild dolphins change their behavior when boats are around them. For example, scientists in Australian waters Notice fewer dolphinsThe number of dolphin-watching tour boats has increased. But no one has yet investigated how human voices can damage the animals’ ability to cooperate.

“Usually it’s really difficult to do these kinds of studies in the wild,” said Mauricio Cantor, a behavioral ecologist at Oregon State University in Newport, who was not part of the study. But the experimental setup Ms. Sorensen’s team used provided “clear evidence of a noise effect,” he said, because the researchers could control for most things that could interfere with their results.

Dolphins hunt together, using sound to communicate, and find their way through echolocation. They also use sound to stay with their families and whistle to signal their presence to their peers, Dr. Gero said. In noisy environments, “animals can’t talk to each other.” In the long term, conditions like these can affect their food intake and their ability to reproduce, said Dr. Kantor.

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Dr. Gero said there may indeed be parts of the ocean that are no longer usable for these animals. Dolphins may migrate from places where they cannot communicate successfully. He said this phenomenon may already be happening at major ports in places like Los Angeles or Boston.

Dr. Gero said ships are a major contributor to ocean sound noise, and in some locations, ships are being slowed down to protect wildlife from noise pollution. For example, along parts of the Pacific coast from Washington state to Chile, boats are instructed to slow down or change course to reduce noise that can disturb marine mammals.

“We’re already affecting animals in this way,” said Dr. Gero. “The unfortunate truth is, in some ways, this story is 35 to 50 years late.”