Narwhals Have a Strange Stress Response

When the creatures are frightened, they both flee and freeze

Terrie Williams

When narwhals manage to escape hunters’ nets, they do exactly as one might expect: swim quickly away to avoid further dangers. But as Jason Bittel of National Geographic reports, scientists recently observed that the narwhal’s flight response is accompanied by an unusual, paradoxical physiological reaction. As the tusked cetaceans speed away, their heartbeat slows dramatically.

Known as “unicorns of the sea,” narwhals are elusive creatures that dwell in frigid Arctic waters, spending several months of the year beneath thick layers of sea ice. This makes it difficult for researchers to study the tusked beasts, but a team of scientists recently worked with Indigenous hunters of Ittoqqortoormiit, Greenland to track the whales. When narwhals got trapped in the hunters’ nets, researchers used suction cups to attach devices that measure heart rate, depth and motion to the narwhals’ backs. Then the animals were set free.

The data collected from the trackers stymied researchers. According to a study published recently in Science, the narwhals displayed a “paradoxical escape response,” exhibiting two fear reactions that were previously thought to be mutually exclusive.

When faced with danger, mammals will either engage in a “fight or flight” response, or become very still until the threat passes. The former reaction causes the animals’ heart rate to increase, while the latter causes it slow down. But as the narwhals sped away after being released from the nets, their heart rate slowed from 60 beats per minute to just three or four.

"They were exercising as fast as a narwhal exercises," Terrie Williams, an ecophysiologist at the University of California, Santa Cruz and lead author of the study, tells Nell Greenfieldboyce of NPR. "They were swimming constantly. They're trying to do a flight response superimposed on a down-regulation-type freeze response. And I hadn't seen that before."

The results were particularly strange because narwhals need to pump plenty of blood through their bodies so they can stay warm. “[W]hat I don’t understand is how these tissues are able to maintain function,” Williams tells Bittel of National Geographic.

Though researchers don’t yet know if other whales exhibit similar fear reactions, the narwhals’ unexpected physiological response might explain some whale strandings. As Victoria Gill reports for the BBC, moving quickly with a low heart rate could deprive the animals’ brains of oxygen, which could cause them to become disoriented. Prolonged periods of reduced oxygen supply could even lead to brain damage.

In her interview with NPR’s Greenfieldboyce, Williams stressed that the narwhals were displaying “an unusual reaction to an unusual kind of threat”—humans. Because they live in an icy and hard-to-access habitat, narwhals have long been relatively isolated from human disturbance. In recent years, however, Arctic sea ice has been melting, which has opened the region up to increased shipping and development.

As humans continue to encroach on their waters, the narwhals might need more protections to prevent the creatures from dying of fear.

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