Narwhal hearts beat more slowly when they flee from threats, adding even more stress on their bodies. This may make their interactions with humans in the future dangerous.
A narwhal pod swimming off the coast of Greenland [Photo by the US National Oceanic and Atmospheric Administration]
Narwhals, called the “unicorns of the sea” due to the single tusk-like tooth protruding from their heads, inhabit Arctic waters around Greenland, Russia, and Canada all year round. Humans haven’t really come into much contact with narwhals, since the elusive cetaceans prefer to live in parts of the Arctic where sea ice have gotten very thick. Their habitats are so remote that we’ve never even actually seen a narwhal eat. These areas are inaccessible to our boats and ships, but lately, sea ice has been receding. We’ll soon be able to venture into narwhal habitats—for better or for worse.
According to a new study on the heart rate of these sea creatures, a close encounter with human sea vessels may just scare the narwhals to death. "Shipping and exploration for oil and gas is moving into the narwhals' world," said Dr Terrie Williams, lead researcher of the study.
One of the researchers attaches the heart rate monitor as well as a tracking device and tags on a narwhal's back. [Photo by M.P. Heide-Jorgensen]
Here’s how an animal usually responds to threats or dangerous situation: it slows down its heart rate and metabolism, essentially playing dead, until the danger passes; or, its body goes into overdrive in a flight or fight response. This makes the narwhal’s response quite strange. When, for example, narwhals get caught in fishing nets, they thrash as much as they can to escape. However, their heart rates also plummet to three to four beats per minute. As a reference, ground squirrel hearts beat about as many times when they’re hibernating.
Researchers worked with local indigenous hunters in Greenland to find narwhals trapped in nets. The researchers then disentangled each animal before using suction cups to attach heart rate monitors and accelerometers. Each narwhal was then pushed back into the water.
"The very first heart rate measurement was—as you would imagine fairly high," said Dr Williams. "When the animals were just sitting there, it was about 60 beats per minute—about the same as our resting heart rate. "But the moment those animals took off, their heart rate immediately plunged down to three or four heart beats per minute—15 to 20 seconds between each beat."
The researchers thought that the narwhals were frozen in the water, waiting for the threat to pass. However, said Dr. Williams, the narwhals were swimming just as quickly as usual.
How do we keep the unicorns of the sea safe from harm? [Photo by M.P. Heide-Jorgensen]
This strange stress response, according to the researchers, may be able to explain some whale strandings. Moving quickly with a very low heart rate could result in oxygen deprivation in the brain. This may lead to disorientation, which could in turn lead to strandings on a beach. Prolonged oxygen deprivation may also cause brain damage.
Narwhals aren’t used to our boats and ships, but there is a very large probability that sea vessels will soon ply narwhal habitats. Once the narwhals encounter these vessels, their strange and potentially dangerous stress response may occur. Dr. Williams thinks that placing certain areas under protection may help us keep the narwhals safe from harm.
Get weekly science updates in your inbox!