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The unwelcome cacophony is caused by excessive boat traffic, says a study.

By Marisa Spyker

When we dive into the undersea world, we experience the ocean as a peaceful, majestic paradise, where fish move gracefully and plants dance in an environment devoid of sound. But when a dolphin moves through this same world, it’s a little more like rush hour in Times Square.

To the auditory systems of marine mammals like dolphins and whales, who rely on sound for communication, the ocean is getting a whole lot louder. And to make up for that extra noise, says a new study, they’re now changing the way they communicate.

"It's kind of like trying to answer a question in a noisy bar and after repeated attempts to be heard, you just give the shortest answer possible," said Dr. Helen Bailey, a marine biologist with the University of Maryland Center for Environmental Science.

Bailey and her colleagues recently studied the communication habits of bottlenose dolphins 20 miles off the coast of Ocean City, Maryland, where a steady increase in the amount of recreational boats and shipping vessels has caused the oceans to get increasingly louder. Using underwater microphones to record the dolphins’ signature whistles, the researchers found that when the background ship noise began to crescendo, dolphins reverted to flatter calls that communicate less information.

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The findings are concerning to biologists like Bailey, since sound is a cornerstone of dolphin communication. Dolphins are notoriously chatty animals, using sound for identification purposes, to alert others of nearby food sources, and—yes—simply to catch up with friends.

Meanwhile, the oceans have only been getting noisier over the past few decades. One study found that the loudness of shipping traffic off the coast of California had roughly doubled each decade since the 1960s.  

In 2016, the NOAA was tasked with developing a 10-year plan for lessening the effects of ocean noise on aquatic life (much of which is still unknown). And, according to Bailey, regulations are needed, as there are currently no rules for boat and shipping sounds comparable to ones that limit noise pollution on land. “If we can make everything [like ship engines] just a little bit quieter then we can reduce this problem,” Bailey told the Washington Post.