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. This has resulted in significantly more noise from an array of human sources, including seismic surveys, mine blasts, port projects and cruise ships.
The new study from the University of Copenhagen and the Greenland Institute of Natural Resources found the threatened whale species are “highly affected” by noise from ships and seismic airgun pulses.
Narwhals are notoriously difficult to study because they only live in the High Arctic, the inner circle around the North Pole, which is often covered by ice. But the research team managed to tag a pod of narwhals – collectively known as a ‘blessing’ – in the Scoresby Sound fjord system of East Greenland.
For two weeks, researchers positioned a ship in the Scoresby Sound fjord system in East Greenland to expose a herd of narwhals to noise from the ship’s engine and a seismic airgun used for oil exploration, according to the study, and documented their response.
“The narwhals’ reactions indicate that they are frightened and stressed,” says Outi Tervo, researcher and marine biologist at the Pinngortitaleriffik.
“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. This behavior means that they have no chance of finding food for as long as the noise persists.”
The narwhals would respond to noise up to 40 kilometers away, and researchers observed the whales would “make an uncommon number of strokes” with their tails when trying to distance themselves from the ship. Researchers worry that the increased strokes could be dangerous for the whales since it depletes their energy reserves
“It is quite surprising that we can measure how something so far away can influence whale behaviour,” says Professor Susanne Ditlevsen of the University of Copenhagen’s Department of Mathematical Sciences.
Remarkably, “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.”
Everything in a narwhal’s life is sound
Narwhals rely heavily on sound for survival in part because they spend a huge portion of their lives in darkness. The Arctic is dark for six months out of the year and the whales hunt for food at depths of up to 1,800 meters where light can’t reach. Similar to bats, the species uses echolocation to orient themselves in dark waters as they travel or hunt.
Ship sonars have proven to be a serious problem for humpback whales, dolphins and orcas, a species that also uses echolocation, according to The Guardian, and researchers have been curious to learn more about how narwhals respond to sound as shipping activity is predicted to increase due to melting sea ice caused by climate change.
Sources:
https://royalsocietypublishing.org/doi/10.1098/rsbl.2021.0220