Scientists who adapted heart rate monitoring labels to Arctic narwhals have discovered a strange paradox in the way animals respond to threats.
When these fang whales are frightened, their hearts become slow, but at the same time they swim quickly to escape.
Scientists say the answer may be "very expensive" because they strive for a limited blood supply.
The findings are published in the journal Science.
They raise questions about how the enigmatic "unicorns of the sea" will face the growing human intrusion into their Arctic habitat.
Historically, narwhals have not been in contact with many human disturbances, since they live mainly hidden among the Arctic sea ice. But in recent decades, as the ice has decreased, this is changing.
"Oil and gas shipping and exploration are moving into the world of narwhals," said lead researcher Dr. Terrie Williams of the University of California, Santa Cruz.
Having developed technology to study the physiology of dolphins at his home institute, he explained that his collaborator in this study, Dr. Mads Peter Heide-Jorgensen, of the Greenland Institute of Natural Resources, contacted with her to see if their labels could be used in wild narvales.
"His research allowed him to work with hunters: instead of killing the animals, he launches them with satellite tags," explained Dr. Williams. "So this was an incredible opportunity to observe the biology of a deep-diving whale."
The labels he developed incorporate a cardiac monitor with depth and acceleration measurement, as well as a satellite tracking device.
"We & # 39; & # 39; Ride on the back of a narwhal for days with this technology surprises me & # 39; & # 39; said to BBC News.
Freeze but flee
Researchers worked with hunters to find narwhals already entangled in nets. They released each animal, placing a tag on its back with a sucker, before pushing it into the deep waters of the East Greenland fjords.
"The first measurement of heart rate was, as you might imagine, quite high," Dr. Williams recalled. "When the animals were sitting there, they were about 60 beats per minute, about the same as our resting heart rate.
" But by the time those animals were taking off, their heart rate was reduced to three or four heartbeat. per minute ̵
At first, Dr. Williams and his colleagues thought that the animals might be showing a proverbial "rabbit to light" response, freezing and waiting for the threat to pass.
"But when we looked, they swam as fast as they do," said Dr. Williams. "So you have these two opposite things happening at exactly the same time, the heart rate is very low, and that overlaps a response to exercise." It was crazy. "
This reduction in heart rate, the scientists suggest, could Help explain some whale strandings. If the animals move quickly to escape a threat, but their heart rate is very low, this could deprive their brain of oxygen and leave them disoriented.
Long periods of this low blood flow and reduced oxygen supply to the brain can even cause permanent damage.
"I think we've identified a real physiological challenge here and we're going to look into the details of that to see if we can find out what's going on," said Dr. Williams.
For the narwhals and other marine mammals of the Arctic, the discovery highlights some troubling implications of the navigation and exploration of minerals that move to arctic oceans increasingly free of ice.
"When you think about the escape response and the new types of threats from ships and other noises, you really have to move cautiously," Dr. Williams added. "We may have to protect certain areas, if we want the unicorns of the sea to stay alive."