Narwhals are not cool under pressure. When stressed, they use up almost all of their energy in an instant by essentially stopping their hearts while thrashing as hard as they can to swim away. It’s one of the most panicked reactions to stress scientists have documented in the animal kingdom.
Evolution has equipped all creatures with the tools to deal with stressors or threats. Sometimes, the body does a quick shot of adrenaline to give itself a rush of super-strength, either for fighting off an enemy or running for the hills. Other times, the body takes the opposite approach and slows itself way down, in theory, so the animal will look dead and a predator will lose interest. In most creatures, these two reactions can’t happen simultaneously because of the way the nervous system is wired.
Researchers previously thought narwhals fell into the latter category. When threatened by a killer whale or another predator, narwhals dive deep, requiring them to lower their heart rates in an effort to save oxygen. However, when researchers tagged five narwhals off the east coast of Greenland with the porpoise equivalent of a Fitbit and trapped them briefly in a net to temporarily stress them out, they found that the animals somehow combine the two common stress reactions. The narwhals end up struggling with every ounce of their strength, while lowering the hearts to between three and four beats per minute. Normally, a narwhal’s resting heart rate at the surface is around 60 beats per minute, based on recordings the team took of nine other narwhals during the experiment. That’s just 5% of their normal average. The findings, from researchers at the University of California- Santa Cruz and the Greenland Institute of Natural Resources, was published (paywall) Dec. 7 in the journal Science.
The two responses together could potentially strangle the animal’s vital organs; the creature’s body is essentially force its muscles to exert maximum firing power with no fuel. It doesn’t seem like something any creature’s body would be designed to do.
The authors of the study write that narwhals have likely made it this long despite these apparently maladaptive stress responses because they’re able to escape natural predators by swimming deep beneath them. Once they’ve escaped, they can swim more slowly in the ocean depth, using only about half of the usual oxygen supply, the scientists calculated.
But the researchers are worried what may happen when shipping, seismic exploration, and fishing in the Arctic become more common as climate change melts sea ice and opens the region up to human activity. If narwhals exert themselves forcefully to try to swim away from pervasive, human-made underwater noise, or get caught up in nets, they may run out of oxygen too quickly to keep their bodies going even at their deep-water, slow-paced swimming. The threat to these creatures won’t be human activities themselves, but rather narwhals’ innate overreactions to it. If we plan to do more in narwhal territory, we’re going to have to figure out how to keep them calm, or else risk the demise of the closest thing nature has to a mystical sea mammal. Luckily, the International Union for Conservation of Nature states that narwhals have a healthy population size at the moment.
