Whales and dolphins change the way they communicate in a noisy ocean

Noise from ships changes the way that whales and dolphins communicate with each other, according to two studies published this week.

Marine biologists know that a cacophonous ocean, filled with the din of shipping, and seismic surveys, is undoubtedly impacting the animals that live there. Loud noises could be damaging the hearing of marine mammals that are dependent on the sound of their three-dimensional world, and sonar blasts have been linked to the mass stranding of whales around the world.

Now, two independent teams of scientists have shown that whales and dolphins alter the sounds that they make in response to the whirr of ships.

University of Maryland marine biologist Helen Bailey and her team recorded the whistles of bottlenose dolphins (Tursiops truncatus) off the coast of the U.S. state of Maryland and published their work Oct. 24 in the journal Biology Letters. The researchers analyzed the characteristics of those calls and took note when they changed. They found that when they were there, they were more ambient sound, mostly from passing boats and ships, the dolphins switched to higher frequencies and streamlined their whistles.

"It's kind of like trying to answer a question, you just give the shortest answer possible," Bailey said in a statement. "Dolphins simplified their calls to the masking effects of vessel noise."

A second team of scientists, led by biologist Koki Tsujii of the Ogasawara Whale Watching Association and Hokkaido University in Japan,Megaptera novaeangliae), In this case. Publishing their results in the newspaper PLOS ONE, also on Oct. 24, they recorded the changes in the songs by the passengers and cargo motored by.

The team's recordings of 26 singing whales revealed that when the ship passed and the singing whales were less than about 1,200 meters (3,940 feet) from the ship, they tended to cut their songs short. What's more, they often would not start up again for half an hour. They also were less than 500 meters (1.640 feet) from the ship's path.

The researchers note that, because they only do so in an effort to attract females, they can not be certain of the noise impacts young and female humpbacks. But it's clear that the sounds are changing behaviors, the authors said.

"Humpback whales seemed to stop singing rather than modifying sound characteristics of their song under the noise, generated by a passenger-cargo liner," the authors of the PLOS ONE paper said in a statement. "Ceasing vocalization and moving away could be cost-effective adaptations to the fast-moving noise source."

The team suggests that this research would help determine whether these sounds have increased stress levels of the affected humpbacks.

The authors of the dolphin

"These whistles are really important," Bailey said in the statement. "Nobody wants to live in a noisy neighborhood. If you have these chronic noise levels, what does this mean to the population? "

She and her colleagues suggest that, in the presence of these levels of ambient sound, dolphins might have trouble getting their full message.

"[The] noise-induced simplification of dolphin whistles can reduce the information in these acoustic signals and decrease effective communication, parent-offspring proximity or group cohesion, "the authors write.

Banner image to sounding whale humpback by John C. Cannon / Mongabay.

citations

Fouda, L., Wingfield, J.E., Fandel, A.D., Garrod, A., Hodge, K.B., Rice, A.N., & Bailey, H. (2018). Dolphins simplify their vocal calls in response to increased ambient noise. Biology Letters, 14(10).

Tsujii, K., Akamatsu, T., Okamoto, R., Mori, K., Mitani, Y., & Umeda, N. (2018). Change in singing behavior of humpback whales caused by noise. PLOS ONE, 13(10), e0204112.

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