Dolphins and Noise Pollution: Using Lots More Energy to 'Holler' Over Ship Noise

In the widening world of animals responding to loud noises and noise pollution, it turns out that dolphins are using extra energy in responding to these sounds. Like some other creatures, they get louder in response--effectively shouting to be heard.

In order to sound off over the noise of ship traffic or other noise sources, dolphins whistle louder or make other vocalizations. They're using only a bit more energy than usual each time, but scientists at NOAA Fisheries' Northwest Fisheries Science Center (Seattle) and the University of California Santa Cruz think this may add up to a higher metabolic cost to the animals, according to a release.

"If they're repeatedly exposed to a lot of noise, the repeated effort to call louder or longer or more often -- that's where the impacts could become more significant," said Marla Holt, a research biologist at NOAA in Seattle and head author of a report recently published in the Journal of Experimental Biology.

The team also thinks that growing young animals or nursing mothers might be more affected. In addition, some of the mammals slap their tails on the water or jump out of the water (breach) in response to vessels and their noise-thus using more energy, said the release.

In this study, captive dolphins at UC Santa Cruz were taught to whistle quietly in low-noise situations and to make more noise in times of greater background sound. The dolphins' oxygen consumption (and thus energy use) was measured by plastic hoods over them.

When whistling more loudly, the dolphins used about 80 percent more oxygen than when at rest. Scientists also already know that dolphins whistle with more repetition when boats are nearing, which likely causes them to expend more energy, this study also concluded in the release.

"These data would have been impossible to collect from wild animals, so without these trained dolphins we could not have conducted this study," Noren said in the release.

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