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Dolphins ‘shout’ to cut through noise pollution, study finds

The highly social mammals struggle to communicate in noisy water, the research revealed.

(CN) — Noise pollution and cetacean responses have been curious to researchers for years. But, as humans brought louder vessels into the sea, marine mammals who audibly communicate with one another have had to adapt. New research published Thursday in Current Biology examines the whistles between two dolphins as they try to communicate and work together.   

"We already know from previous studies that animals are able to compensate for noise by adjusting their behavior in response to the noise. However, what we haven't known up until now is how noise may impact animals working together," said lead study author Pernille Sørensen in an interview. 

There is no full graph of how much noise pollution has increased across all oceans. However, some estimates claim that the racket has doubled every ten years since 1950. Sørensen's research, made possible by the Dolphin Research Center in Florida, demonstrates how much sound impacts the ability of dolphins to accomplish collaborative tasks. 

Two dolphins, Delta and Reese, were previously trained to perform a button-pressing task. Two buttons were placed on each end of an experimental lagoon which the dolphins had to press within one second of each other. Researchers set suction-cup sound recorders on the dolphins to record their various whistles. Then, the dolphins were sent off to complete the button task with varying levels of noise pollution. 

"We saw that they increase the amplitude, so they are shouting or trying to increase the volume of the calls in order to be heard by their friend. They also tried to increase the duration of their calls to be heard," explained Sørensen. "Despite the fact that they did that, they were still less successful in performing this corporative task."

With ambient noise, Delta and Reese could complete the button press 85% of the time. When the loudest noise was played, their success rate dropped to a staggering 62.5%. Additionally, the dolphins would change their physical behavior — orienting themselves more toward their partner and spending more time in closer proximity, seemingly to hear better.

The dramatic drop in button presses in a 22.6-meter lagoon is cause for concern for wild dolphins. The highly social marine mammal relies heavily on vocalizations for collaborative behaviors from food foraging to dolphin alliances. 

"There is a high chance that there might be some missed opportunities for animals that are exposed to noise simply because they don't hear that first cue that would initiate a corporative act," explained Sørensen. 

If the communication impacts are significant enough in the wild, it could have severe ramifications on dolphin populations as foraging and other tasks fail. However, researching specific collaborative behaviors in the wild and their efficiency is challenging as the habits are unpredictable. The controlled environment of the Dolphin Research Center provided excellent conditions for studying noise pollution impacts and offered a repeatable experiment. 

"This is an international collaboration with international colleagues. You know, this couldn't be done without the Dolphin Research Center," said Sørensen. 

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