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Dolphins Can Shout Underwater, but It’s Never Loud Enough

A dolphin with recording tag, which was used to record sound and motion in the study.  (Dolphin Research Center via The New York Times)
A dolphin with recording tag, which was used to record sound and motion in the study. (Dolphin Research Center via The New York Times)

Mammals in the ocean swim through a world of sound. But in recent decades, humans have been cranking up the volume, blasting waters with noise from shipping and oil and gas exploration. New research suggests that such anthropogenic noise may make it harder for dolphins to communicate and work together.

When dolphins cooperated on a task in a noisy environment, they called louder and longer, researchers reported Thursday in the journal Current Biology. “Even then, there’s a dramatic increase in how often they fail to coordinate,” said Shane Gero, a whale biologist at Carleton University in Ottawa who wasn’t part of the work.

Scientists worked with a dolphin duo at an experimental lagoon at the Dolphin Research Center in the Florida Keys. The pair were trained to swim to different spots in their enclosure and push a button within one second of each other.

Pernille Sørensen, a biologist and doctoral candidate at the University of Bristol in England, and her team piped in sounds using underwater speakers. Tags, stuck behind the animals’ blowholes, captured what the dolphins heard and called to each other as well as their movements.

Through 200 trials with five different sound environments, the team observed how the dolphins changed their behavior to compensate for noise. The cetaceans turned their bodies toward each other and paid greater attention to each other’s location. At times, they nearly doubled the length of their calls and amplified their whistles.

The noisier it got, the less success they had. At the loudest condition, they succeeded 62.5% of the time, simultaneously striking their buttons around 20% less than under ambient sound levels.

“It’s usually really hard to do these kinds of studies in the wild,” said Mauricio Cantor, a behavioral ecologist at Oregon State University in Newport who wasn’t part of the study. But the experimental setup used by Sørensen’s team provided “clear evidence for the effect of noise,” he said, because the researchers could control for most everything that could interfere with results.

Dolphins hunt together, using sound to communicate, and find their way through echolocation. In the long run, Cantor said, noisy conditions could affect food intake and ability to reproduce.

“We’re absolutely impacting animals in this way already,” Gero said. “The unfortunate reality is that, in some ways, this story is 35 to 50 years late.” — CAROLYN WILKE / NYT

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