Narwhals almost freeze their heartbeat in fear when encountering humans

The 'unicorns of the sea' are at risk of interacting with more humans as ice melts in the Arctic, exposing them to dangerous levels of stress (Credit: Paul Nicklen/Nat Geo)

When escaping from humans, narwhals don’t just freeze or flee. They do both.

Narwhals live in relative isolation in the Arctic. But due to climate change, the ice that has given these ‘unicorns of the sea’ refuge from humans is now starting to melt. This has led to a surge in human exploration of the region for oil and natural gas, among other things.

But narwhals may not be able to handle such close encounters with humans. When these whales are exposed to hazards they aren’t used to, their bodies react in a troubling way, biologists reported in Science today. After being freed from nets, their heart rates plummet to near-arrest while they also start swimming frantically to escape. This amount of stress can lead to their brains being deprived of oxygen, leading to all kinds of dangers.

“They’re sensitive animals,” says coauthor Terrie Williams, an ecophysiologist at the University of California, Santa Cruz. “When it’s an unanticipated threat, I think that they just pull out all the stops.”

When mammals swim into cold water, their heart rate typically slows as part of a dive reflex that allow them to hold their breath for as long as possible. But in the narwhals Williams studied, this drop was severe.

“That was astounding to us because there are other marine mammals that can have heart rates that low but not typically for that long a period of time, and especially not while they’re swimming as hard as they can,” says Terrie Williams, a biologist at the University of California, Santa Cruz. So far, this dangerous escape has been observed only after a prolonged interaction with humans.

Narwhals don’t usually respond to danger in this way either. When narwhals detect killer whales on the hunt, they sink deeper below the ice sheets. “They move fairly slowly, they’re not like a high-speed orca,” Williams says. “But they can out-dive a killer whale because of their oxygen stores.”

“When narwhals detect humans, they often dive quickly and disappear from sight,” says Kristin Laidre, an ecologist at the University of Washington in Seattle who studies marine mammals in the Arctic.


A female narwhal’s heart rate dropped dangerously low at times when she performed a series of dives after escaping a net (top graph). The red box shows periods of “cardiac freeze,” when her heart only beat a few times per minute. Around 2 days later, the same narwhal was back to performing regular deep dives (bottom graph), in which her heart rate dropped to 10 to 20 beats per minute, an adaption that allows the sea mammals to conserve energy during stretches underwater. (T.M. Williams et al/Science 2017)

This study “provides a new physiological angle on the vulnerability of narwhals to anthropogenic disturbance, which is likely to increase in the Arctic with sea ice loss,” Laidre says.

Human-influenced climate change is not just affecting us, but every biome in the world. Our ability to engineer ecosystems to this level is transforming the planet to the point that other species are forced to adapt at accelerated rates, or die.


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A. Jama

Jama is a researcher in biochemistry and molecular biology, with a focus on metabolism and cancer. You can find him on twitter discussing a broad range of topics, from US politics to Game of Thrones. He also has the best memes.

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