Noise from cruise ships, mine blasts, port projects, and seismic surveys triggers stress in narwhals, even when it comes from miles away.
For millennia, vast expanses of the Arctic Ocean have been untouched by humans, ocean where narwhals and other marine mammals lived undisturbed.
Now that climate change is causing sea ice to melt, there has been an uptick of human activity in the Arctic, resulting in significantly more noise, which, although not violently loud, is still disturbing for narwhals.
Narwhals are notoriously difficult to study because they only live in the hard-to-reach High Arctic, which is often covered by ice. But researchers managed to tag a herd of narwhals in the Scoresby Sound fjord system of East Greenland using a variety of measurement equipment. They then positioned a ship in the fjord, which exposed the animals to noise—both from the ship’s engine and from a seismic airgun used for oil exploration.
“Because narwhals are so well-adapted to the Arctic environment, they can’t just choose to go to the Caribbean instead.”
“The narwhals‘ reactions indicate that they are frightened and stressed. They stop emitting the click sounds that they need to feed, they stop diving deep, and they swim close to shore, a behavior that they usually only display when feeling threatened by killer whales,” says marine biologist Outi Tervo of the Greenland Institute of Natural Resources, one of the researchers behind the study.
“This behavior means that they have no chance of finding food for as long as the noise persists.”
Researchers can also see that 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 vastly depletes their energy reserves. Constant energy conservation is important for narwhals as they need a great deal of oxygen to dive several hundred meters below the surface for food and return to the surface for air.
Narwhals hunt in the dark
Narwhals spend much of their time in the dark—partly because the Arctic is dark for half of the year, and partly because these unicorns of the sea hunt at depths of up to 1,800 meters (about 5,900 feet), where there is no light. Thus, everything in a narwhal’s life is based on sound. And like bats, they orient themselves by echolocation—which includes emitting click sounds as they hunt.
“Our data shows that narwhals react to noise 20-30 kilometers [about 12-18 miles] away from a noise source by completely stopping their clicking sounds. And in one case, we could measure this from a source 40 kilometers [24 miles] away. It is quite surprising that we can measure how something so far away can influence whale behavior,” says Susanne Ditlevsen, professor in the mathematical sciences department at the University of Copenhagen.
Ditlevsen was responsible for the statistical analyses of the enormous and extremely complicated data sets that emerged from the experiments, where data was collected via underwater microphone, GPS, accelerometer (an apparatus that measures movement in three directions), and heart rate monitors.
“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. And so, to a degree, their behavior is clearly affected. This demonstrates how incredibly sensitive narwhals are,” she says.
Following a week of sonic tests, the researchers observed the whales’ behavior return to normal again.
“But if they are exposed to noise for a long period of time—for example, if a port is built nearby that leads to regular shipping traffic, the whales’ success in hunting could be affected for a longer period of time, which could become quite serious for them. In this case, we fear that it could have physiological consequences for them and impair their fitness,” Tervo says.
Changes in the Arctic
The researchers’ hope is that the authorities and other decision-makers will ensure for better management of the activities that create noise pollution in narwhal habitats.
“For the most part, narwhals live around Greenland, Canada, and Svalbard in Norway. As such, these countries have the main responsibility for looking after them. Because narwhals are so well-adapted to the Arctic environment, they can’t just choose to go to the Caribbean instead. It is being pressured both by warmer water temperatures and in some places, by fish catch. Now, noise enters the equation,” says Ditlevsen.
“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,” Tervo says. “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.”
The research is reported in studies in the journals Biology Letters and Frontiers in Marine Science.
Source: University of Copenhagen
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