Scientists have found yet another way we’re disrupting wildlife: when cargo ships start producing a lot of noise, humpback whales reduce or even stop their singing.

Image credits: Christopher Michel.

Not only do whales (and other marine mammals) use sounds to communicate, but they’re much more dependent on sounds than land creatures because their other senses are so limited in water. For human ships, meanwhile, sounds are more of a side-effect.

When a ship cuts through the water, its engine working at full power, it’s a huge cacophony of sounds — and in our modern world, there are a lot of ships.

A team of Japanese researchers wanted to see how these ship sounds affect whales. The Ogasawara Whale Watching Association and Hokkaido University in Japan used two underwater recorders to capture whalesong and locations of animals between February and May 2017, in an area around the Ogasawara Islands, where a single ship passed by (more ships would have made the analysis more complicated).

Over the course of the study, only 26 singers were studied in total, but the results were conclusive. The team found that fewer male humpbacks sang in the area within 500 meters of the shipping lane than elsewhere.

“Remarkably, behavioral changes were observed with a ship’s passing except for when a whale was near a shipping line (<500 m),” the study reads. “This result indicates that whales which were under a ship noise exposure continued to sing as usual.”

Furthermore, up to 1,200 meters around the ship, most whales stopped their song, only resuming it 30 minutes after the ship had passed.

“Humpback whales seemed to stop singing temporarily rather than modifying sound characteristics of their song under the noise, generated by a passenger-cargo liner,” the study reads. “Ceasing vocalization, and moving away could be cost-effective adaptations to the fast-moving noise source.”

Researchers note that in the presence of a ship, most whales would rather pause their song rather than change its characteristics (ie frequency). However, in an area with more ships, the response might be quite different. Responses may differ where ship traffic is heavy, because avoiding an approaching ship may be difficult when many sound sources exist. Around crowded ship lines, pausing for 30 minutes every time a ship passes may simply mean you never get to sing your song. For future research, the team wants to see how sound exposure levels in different scenario affect the whales.

The study can only assess the reaction of male humpbacks — because only the males sing. However, there’s no reason to believe that the mothers and calves are spared from the disruption, though the strength of the impact is yet to be assessed.

The study has been published in PLoS.

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