These mysterious single-tusked denizens of the Arctic have a paradoxical response to danger.
How narwhals flee danger. I’m Bob Hirshon and this is Science Update.
When faced with danger, some animals’ heartr ates shoot up as they either fight or flee. Others freeze and their heart rates drop. But narwhals, small whales with a single tusk resembling that of the legendary unicorn, paradoxically do a little of both. This according to UC Santa Cruz ecophysiologist Terrie Williams. Her team reports in the journal Science that when escaping from hunters’ nets, the deep-diving whales rapidly fled, while simultaneously slowing their heart rate to a near standstill, as if freezing from fear.
There’s about 15 to 20 seconds between every beat of the heart. And that’s a long time. But the narwhal was swimming as hard as it could.
Williams says this unusual response may make the whales particularly vulnerable to recent human disturbances to their Arctic home. I’m Bob Hirshon, for AAAS, the science society.
Making Sense of the Research
Narwhals are medium-sized toothed whales that possess a large tusk from a protruding canine tooth. These mammals can get to be as long 20 feet (6 meters) and weigh 3,000 pounds (1,360 kg).
Despite their great size, narwhals are among the world's most introverted animals and live in some of the most remote areas on Earth. Found year-round in the Arctic waters around Greenland, Canada, and Russia, these whales have been relatively isolated from human interference as compared to other whales.
That could be changing, though, as climate change continues to cause sea ice to shrink, allowing humans to travel through waters they haven't been able to in the past. The research conducted by Terrie Williams, Mads Peter Heide-Jørgensen, a marine biologist from the Greenland Institute of Natural Resources in Nuuk, and a team of other scientists may shed some light on how narwhals may react to the growing human presence. Unfortunately, the researchers think there may be cause for concern. As indicated in the podcast, it seems that when narwhals face some kind of danger, they exhibit the seemingly contradictory response of lowering their heart rate even while fleeing from danger.
The researchers were able to measure the whales' heartbeats by using a technique that Williams developed. They successfully attached suction cups with a package of instruments, including an electrocardiograph to measure heart rate, an accelerometer to track stroke frequency, and a depth monitor to see how far down the narwhals dove. Over the days they were studied, the researchers discovered that the narwhals lowered their heart rates from about 60 beats per minute to about 10 beats per minute as they swam down, which helps to extend their oxygen supply. And, as would be expected, they would increase their heart rate when they swam quickly.
However, when the whales were first captured and then released, they almost immediately lowered their heart rates from 60 beats per minute to as few as three beats per minute. This reaction is more typical of a "freeze" response in animals. Yet, at the same time, the narwhals were "fleeing," or accelerating at a rate of 36.6 strokes per minute after escaping the nets—roughly double their usual stroke rate on these dives.
Usually when narwhals want to escape a predator they sink down beneath the cover of ice. In this situation, though, after the narwhals had been stuck in nets and held for an extended period of time, their heart rates stayed at three beats per minute even as they sped away. The scientists postulate that the narwhals do this because they are getting conflicting signals. They want to swim down because they want to escape the threat but they also want to swim quickly. It seems like their bodies don't really know what they should do in this situation.
More research needs to be done to determine how this affects narwhals' health, but the researchers are concerned that this response could have harmful effects on the animals.
Now try and answer these questions:
- Where do narwhals live?
- How large can they get?
- What is happening to the sea ice that would make it likely that narwhals will have more frequent encounters with humans?
- What happens to the narwhal's heart rate when it swims down? Why does that happen?
- What happened to the narwhal's heart rate after it was captured and then released?
- Why are scientists concerned about this?
You can learn more about how narwhals respond to danger by watching Narwhal Hearts Beat Slowly in Panic, from Science.
You can listen to the Changing Oceans Science Update to learn more about how climate change is affecting our oceans.
You and your students can learn more about the research conducted by Williams and Heide-Jørgensen by reading Melting Sea Ice Is Stressing Out Narwhals, from Science.
In the Oceans lesson, students can obtain a better perception of earth's oceans and to understand earth's water cycle.
The Odyssey of KP2 lesson explores how scientific research of one declining species can increase knowledge about the natural world at large.