Researchers in the Arctic have recorded audio data of narwhals hitting deep-sea hydrophones. Although they aren’t entirely sure what might be causing them to investigate the microphones so closely, the findings could raise questions around whether marine animals are disturbed by underwater acoustic monitoring in some way.
The ocean is a huge place and it’s impossible for researchers to find ways of monitoring everything, particularly without disturbing wild animals by getting close with noisy boats or taking samples. To make it easier to learn what's going on under the waves, many scientists use passive acoustic monitoring – devices that help them listen into the marine environment and use the sounds they record to learn about the species that live there.
“Using passive acoustic monitoring to detect acoustically active animals helps to census biodiversity, understand animal behaviour and habitat use, and reduce the negative impacts of human-made noise,” says Evgeny A. Podolskiy, associate professor of the Arctic Research Centre at Hokkaido University in Sapporo, Japan.
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Podolskiy and colleagues worked with local Inughuit hunters to place three underwater acoustic recorders between 190 metres and 400m deep in the waters of the Inglefield Bredning Fjord in north-west Greenland.
During the two-year study, they recorded noises of narwhals rubbing against the recorders, bashing into them, and producing clicks (which they use for echolocation). The narwhals also made a buzzing sound – which is related to foraging – which the researchers said got louder as the animals got closer to the hydrophones.
“Our results suggest that narwhals repeatedly dived to visit the moorings out of playful curiosity or, more likely, due to confusion with potential prey,” says Podolskiy.
Although 247 of these incidents were recorded, the experts believe there could have been hundreds more because the devices weren’t recording sound continuously. They estimated that the 'unicorns of the sea' (as narwhals are sometimes known) might have knocked the hydrophones an average of 10 or 11 times each day. Their findings are published in Communications Biology.
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Passive acoustic monitoring is often used because it is non-invasive and doesn’t bother the ocean animals researchers are eavesdropping on, but this new paper suggests that the narwhals are attracted to the moorings and that it could be changing their behaviour.
The foraging buzz heard close to the microphones made the scientists question whether the narwhals confused the scientific equipment with the cod they typically eat. But this buzzing was often followed by the sound of the creatures’ skin rubbing against the microphone.
“Inughuit hunters… joked that narwhals might scratch their backs, like cats,” says Podolskiy. “While this is possible, and other Arctic whales are known to rub their bodies over rocks, it is unlikely due to the high energetic costs of deep diving.”
For now, the mystery of why narwhals are so intrigued by the underwater recorders remains. But the scientists want to learn more so they can find ways of protecting these animals without disturbing them.
Top image: Inglefield Bredning Fjord, Greenland. Credit: Getty
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