Narwhals have become somewhat famous because of that catchy Weebl’s Stuff song, and although these "unicorns of the sea" look like something right out of a fiction movie, they’re actually a type of whale and very real.
Image Credit: Mads Peter Heide-Jorgensen via UC Santa Cruz
Animal experts don’t know a whole lot about narwhals because they’re particularly talented at avoiding humans. Nevertheless, that doesn’t stop them from venturing out into the Arctic to try and study the creatures.
In a recent expedition, researchers tagged a bevy of wild narwhals with suction cup-affixed GPS tags to learn more about them. Unlike most trackers, which merely record an animal’s movements, those used in this study sported integrated accelerometers and heart rate monitors.
While the GPS data will indisputably help researchers better understand narwhal behavior, it was what the researchers saw in the heart rate monitors that caught their attention the most, and a new paper published in the journal Science explains why.
The study underscores a paradoxical situation in which stressed narwhals exhibit two reactions: the first is that their heart rates slow down from 60 beats per minute to just 3-4, and the second is that they continue swimming at their usual speed without any indication of slowing down. The findings are so unexpected that they’ve left researchers flustered.
"How do you run away while holding your breath? These are deep-diving marine mammals, but we were not seeing normal dives during the escape period. I have to wonder how narwhals protect their brains and maintain oxygenation in this situation," noted the study’s first author Terrie Williams, a professor of ecology and evolutionary biology at UC Santa Cruz.
Most animals respond to danger either by freezing up in fear or pumping adrenaline to stimulate the ’fight or flight’ response. In the former, heart rate slows down, and the animal’s behavior follows suit; in the latter, the heart rate speeds up and so does the animal’s behavior.
As it would seem from the new data, narwhals respond to stress with a hybrid reaction. Their heartbeat slows down substantially, but they maintain perceptive behavior as they dive deep below the surface to swim far away from potential danger. In doing so, these air-breathing creatures risk depriving their brains and vital organs of oxygen.
"That's what is so paradoxical about this escape response – it seems to cancel out the exercise response and maintains extreme bradycardia even when the whales are exercising hard," Williams continued.
Researchers have never studied any whale species with heart rate monitors before, nor have they associated it with acceleration data. That said, these findings might even answer the longstanding question concerning how so many whales become beached.
Theoretically speaking, deep-diving whales of all kinds might respond to stress just like the narwhals did in this study, becoming disoriented in the process. Before they know it, they may end up stranded on a beach with nowhere to go as the tide leaves them behind.
But that’s not the only thing researchers gathered from this study. They also note how this reaction could make narwhals particularly vulnerable to stressful habitat disturbances such as extraneous noises produced by boats and sonar.
"Unlike threats from predators like killer whales, noise from sonar or a seismic explosion is difficult to escape. Problems can start if the whales try to outrun it," Williams said.
"The implications of this study are cautionary, showing that the biology of these animals makes them especially vulnerable to disturbance. This technology has given us a window into the narwhal's world, and what we see is alarming. The question is, what are we as humans going to do about it?"
As it would seem, this study raises entirely new questions about narwhals, whales, and how human behavior impacts the marine environment. Perhaps future studies could pick up where this one left off to uncover the answers.