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Stressed-Out Narwhals Don't Know Whether To Freeze Or Flee, Scientists Find

Dec 7, 2017
Originally published on December 8, 2017 9:21 am

Narwhals — the unicorns of the sea — show a weird fear response after being entangled in nets. Scientists say this unusual reaction to human-induced stress might restrict blood flow to the brain and leave the whales addled.

The narwhals swim hard and dive deep to escape after being released from a net, but at the same time their heart rates dramatically plummet, according to a newly published report in Science. It's almost like they are simultaneously trying to freeze and flee.

"This is an unusual reaction to an unusual kind of threat," says Terrie Williams, a researcher at the University of California, Santa Cruz. "I don't believe that this is the normal response when the animals are being pursued by a killer whale."

Male narwhals have a distinctive long, spiral tusk, and these elusive creatures live way up north in the Arctic. They aren't easy to study, as they live much of their lives surrounded by darkness and ice. But scientists sometimes monitor their movements by catching them with nets and tagging them in the summertime, when the whales are more accessible.

Williams and her colleagues recently traveled to waters off the east coast of Greenland to outfit narwhals with technology that lets researchers monitor the marine mammals' heart rates, swimming movements and other data.

"This is the first time that there's been a long-term record on an EKG for a wild cetacean," says Williams, who has used similar monitors on dolphins and seals. "I don't know that there's anything quite like it."

In the first dives after the narwhals were released from nets, she says, their heart rates dropped from 60 beats a minute to three or four beats a minute. This lasted for 10 minutes or so.

"And I'd never seen that in any animal that I've ever recorded a heart rate for," she says. "So that was the first clue that we were looking at something very different here."

What's more, the whales were swimming rapidly during this time. "They were exercising as fast as a narwhal exercises," Williams says. "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."

It makes her wonder how the whales can possibly get enough oxygen to their brains. And she also wonders if this might have any relevance to mysterious beachings of other deep-diving whales.

Kristin Laidre, a research scientist at the Polar Science Center at the University of Washington who has studied narwhals, says this is "a really interesting paper that provides a new physiological angle on the vulnerability of narwhals to anthropogenic disturbance in the Arctic."

The loss of sea ice in the Arctic, Laidre notes, means big changes in the ecosystem, plus a sudden interest in more industrial development, resource extraction and new shipping routes. "All of those things mean disturbance for narwhals," she says. "To my knowledge, this is really the first time we have quantified physiological disturbance effects on narwhals. So it's really important data."

Because narwhals have lived a life far north, surrounded by dense sea ice, they have been relatively insulated from human activity. "Any kind of disturbance," Laidre says, "is going to be a pretty new, potentially very disruptive thing for a species that's existed in an environment like that for so long."

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RACHEL MARTIN, HOST:

It's Friday. And we all need some wonder in our lives. So let's talk about narwhals, shall we? What's a narwhal, you ask? They are whales with a long, spiral tusk, which makes them the unicorns of the sea. These elusive creatures live in the far north in an icy world. But it turns out narwhals are not cool under stress. Here's NPR's Nell Greenfieldboyce.

NELL GREENFIELDBOYCE, BYLINE: When a colleague contacted Terrie Williams about doing a study of narwhals...

TERRIE WILLIAMS: I said yes 'cause they're cool (laughter), you know? And I didn't know at all what I was getting into at that point.

GREENFIELDBOYCE: Williams is at the University of California, Santa Cruz. She's investigated how dolphins and seals swim and dive by putting wearable monitors on the animals. She was intrigued by the idea of trying it with a deep-diving whale that can go down more than a mile.

(SOUNDBITE OF NARWHAL CLICKS)

GREENFIELDBOYCE: This is the sound of narwhals off the east coast of Greenland. That's where Williams joined scientists who were netting narwhals in shallow water to tag them. While the narwhals got tagged...

WILLIAMS: We were able to suction-cup electrodes on for the EKG, suction-cup our instrumentation on and have them swim with them anywhere from one day to four days at a time and collect thousands of dives.

GREENFIELDBOYCE: She was surprised to see that the dives that happened immediately after the narwhals were released from the net looked weird. The animal's heart rates plummeted, going from about 60 beats a minute...

(SOUNDBITE OF HEARTBEAT)

GREENFIELDBOYCE: ...To only three or four beats a minute. But at the same time, these narwhals were swimming away as fast as they could. Williams had never seen anything like it.

WILLIAMS: This is an unusual reaction to an unusual kind of threat.

GREENFIELDBOYCE: She says their heart rate suggested a freeze reaction to fear, even as they tried to flee. Her team's findings appear in the journal Science. Kristin Laidre is a narwhal researcher at the University of Washington. She says narwhals have long lived isolated from people in a distant, icy, often dark environment. So changes can have a big impact.

KRISTIN LAIDRE: So I think these data support that - you know, that this species is not used to any kind of disturbance. And it is definitely a physiological stressor for them.

GREENFIELDBOYCE: She says as the Arctic ice melts, there's more interest in oil and gas drilling and new shipping routes. So scientists need to understand how the narwhals might react. Nell Greenfieldboyce, NPR News.

(SOUNDBITE OF TAUK'S "HELLO NARWHAL") Transcript provided by NPR, Copyright NPR.