Narwhals Caught in Nets Are So Stressed Their Hearts Almost Stop

Male narwhal on release, after having an EKG monitor suction-cupped to his body. T.M. Williams

Narwhals, bizarre-looking animals with enormous tusks protruding from their faces, have a surprising adaptation when trying to escape from predators, according to new research. Their heart rate dips so low that it almost stops.

Any athlete knows that when you exercise, your heart rate increases. So when researchers added heart rate monitors to narwhals, they suspected that the animals' heart rate would increase as they swam away. However, when they looked at the data, they found the opposite. The research was published in the journal Science.

Williams and a team of biologists had asked arctic hunters to allow the scientists to tag and release narwhals that showed up in their catch. Instead of harvesting the animals, the biologists added EKG monitors, fastened with suction cups. Then they released the animals and later retrieved the data.

"I almost threw the first few hours of recordings away, because I thought that it wouldn't be relevant to our study," biologist Terrie Williams told Newsweek. "Then I realized, my gosh, that is the study."

The researchers found that as the narwhals swam and dove down into the sea, their heart rate, which is normally 60 beats per minute, plunged down to three to four beats per minute.

"That's remarkable!" Williams said. "Our heart would beat 20 times in the time that these narwhals' hearts would beat once. I wasn't even sure how they would get oxygenated blood to their brains." The average human heart rate is 60-100 beats per minute.

Having an extremely low heart rate is not unheard of in the animal kingdom. In winter, nearly-frozen frogs will even stop their heart, only to be revived in the spring thaw. However, those frogs are resting and immobile. The narwhals are active, stressed and exercising vigorously to get away from their perceived threats, yet they went into what Williams calls a "cardiac freeze."

Researchers measuring the body length of an adult narwhal. M.P. Heide-Jorgensen

This research indicates that stress can severely impact narwhal physiology. While narwhal heart rates eventually returned to their original averages, Williams notes that there is a lot of human activity that they can't just swim away from, like ocean noise pollution. Furthermore, this is the first time that EKG monitors have been used on wild cetaceans in order to analyze heart rates, so it's unknown whether whales and dolphins might react in the same way.

When animals are constantly stressed, their physiology, health and reproduction can change. Williams hopes that scientists can use their new data to assess human impact on wild animals, including narwhals so that we can try to protect them from ourselves. "My overall concern is that we're going to be the generation that kills off the last living unicorn," she said.

Measuring tusk MPHJ
Researchers measuring the tusk length of an adult male narwhal. M.P. Heide-Jorgensen