“They stop emitting the click sounds that they need to feed, they stop diving deep and they swim close to shore, a behaviour that they usually only display when feeling threatened by killer whales,” said marine biologist Outi Tervo, one of the scientists whose findings have been reported in the journal Biology Letters.
“This behaviour means that they have no chance of finding food for as long as the noise persists.”
The researchers said the whales make an uncommon number of strokes with their tails when fleeing from a vessel. This may pose a danger to them because it depletes their energy reserves.
The scientists embarked on their research because of the impact of climate change, which has melted sea ice and brought more human activity to the previously pristine Arctic.
Narwhals spend much of their time in the dark — partly because the Arctic is dark for half of the year, and partly because they hunt at depths of up to 1,800m, where there is no light.
Sound is therefore key to the whales, and they orientate themselves by echolocation — which includes emitting click sounds as they hunt.
“Our data shows that narwhals react to noise 20-30km away from a noise source by completely stopping their clicking sounds. And in one case, we could measure this from a source 40km away,” said Prof Susanne Ditlevsen of the University of Copenhagen.
“Even when a ship’s noise is lower than the background noise in the ocean and we can no longer hear it with our advanced equipment, the whales can hear and distinguish it from other sounds in their midst.”
‘Unicorns of sea’ send seismic distress signal from Arctic to Wild Coast
Cape Town bureau chief
Image: Carsten Egevang
Narwhals, the “unicorns of the sea” that live in the Arctic, have transmitted a 12,000km distress signal to the sea creatures in the path of a seismic survey off the Wild Coast of SA.
Scientists who exposed the whales to a small seismic airgun say their reaction showed the animals became frightened and stressed, even if they were as far as 40km away.
The gun used in the Greenland experiments was similar to but much smaller than the battery of seismic guns aboard the world's largest survey ship, the Amazon Warrior, which is at work 20km off the Wild Coast, looking for evidence of oil and gas on behalf of Shell.
A research team from the University of Copenhagen and the Greenland Institute of Natural Resources tagged a herd of narwhals in the Scoresby Sound fiord system then exposed the animals to noise from the ship's engine and a seismic airgun.
WHAT ARE NARWHALS?
The narwhal is called 'the unicorn of the sea' because of the characteristic twisted tusk of the male. The tusk, which can grow up to 3m long, is a secondary sexual characteristic similar to a buck's horn or a peacock's tail. The global population of 70,000-80,000 is rated as 'not threatened'.
“They stop emitting the click sounds that they need to feed, they stop diving deep and they swim close to shore, a behaviour that they usually only display when feeling threatened by killer whales,” said marine biologist Outi Tervo, one of the scientists whose findings have been reported in the journal Biology Letters.
“This behaviour means that they have no chance of finding food for as long as the noise persists.”
The researchers said the whales make an uncommon number of strokes with their tails when fleeing from a vessel. This may pose a danger to them because it depletes their energy reserves.
The scientists embarked on their research because of the impact of climate change, which has melted sea ice and brought more human activity to the previously pristine Arctic.
Narwhals spend much of their time in the dark — partly because the Arctic is dark for half of the year, and partly because they hunt at depths of up to 1,800m, where there is no light.
Sound is therefore key to the whales, and they orientate themselves by echolocation — which includes emitting click sounds as they hunt.
“Our data shows that narwhals react to noise 20-30km away from a noise source by completely stopping their clicking sounds. And in one case, we could measure this from a source 40km away,” said Prof Susanne Ditlevsen of the University of Copenhagen.
“Even when a ship’s noise is lower than the background noise in the ocean and we can no longer hear it with our advanced equipment, the whales can hear and distinguish it from other sounds in their midst.”
R1bn at stake as Shell faces second court challenge to its Wild Coast exploration
After a week of sonic tests, the whales' behaviour return to normal. “But if they are exposed to noise for a long period of time ... the whales' success in hunting could be affected for a longer period, which could become quite serious for them,” said Tervo.
“In this case, we fear that it could have physiological consequences for them and impair their fitness.
“Changes are happening so quickly in the Arctic, that we are afraid that narwhals won’t be able to adapt unless more of an effort is made to protect them. Some areas are so important to narwhals that it could be argued that human disturbances should not be permitted there at all.
“Elsewhere, it may be possible to make rules about, for example, how fast you can sail, or that you can only sail with far quieter electric motors. Technology offers excellent opportunities to reduce noise.”
TimesLIVE
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