Scientists Surprised by What First-Ever Recording of a Blue Whale's Heart Reveals

Among other things, the data reveals answers about the size of blue whales, the largest organisms to have ever lived on Earth.

Studying the details of blue whales isn't the easiest thing to do. They are big, and they don't live in tanks. And in big, I mean reaching lengths of 108 feet (almost 33 meters). They are the largest animal to have ever lived on the planet, even surpassing the largest of dinosaurs.

Because of this, recording the heart rate of one of these colossal cetaceans has been an elusive task. It's not like you can just grab their wrist and take a pulse.

Around a decade ago, two researchers, Paul Ponganis from the Scripps Institution of Oceanography and Stanford University's Jeremy Goldbogen, measured the heart rates of diving emperor penguins in Antarctica, and ever since have been wondering if they could do the same with whales, explains Stanford University.

And then they went and figured out how to do it. They created a sensor-packed tag that could be applied by four little suction cups to an area near a whale's fin.

“I honestly thought it was a long shot because we had to get so many things right: finding a blue whale, getting the tag in just the right location on the whale, good contact with the whale’s skin and, of course, making sure the tag is working and recording data,” said Goldbogen.

© Researchers from the Goldbogen Lab place a suction-cup tag on a blue whale in Monterey Bay. (Goldbogen Lab/Duke Marine Robotics and Remote Sensing Lab; NMFS Permit 16111)

“We had to put these tags out without really knowing whether or not they were going to work,” says David Cade, a recent graduate of the Goldbogen Lab. “The only way to do it was to try it. So we did our best.”

Cade managed to secure the tag on his first try and, over time, it slipped into position near the flipper where it could pick up the heart's signals. This marks the first time that a blue whale's heart rate had been recorded, and it revealed some surprises. Stanford explains:

When the whale dove, its heart rate slowed, reaching an average minimum of about four to eight beats per minute – with a low of two beats per minute. At the bottom of a foraging dive, where the whale lunged and consumed prey, the heart rate increased about 2.5 times the minimum, then slowly decreased again. Once the whale got its fill and began to surface, the heart rate increased. The highest heart rate - 25 to 37 beats per minutes – occurred at the surface, where the whale was breathing and restoring its oxygen levels.

The researchers were surprised by how both the low and high ends outpaced their predictions – the lowest heart rate was about 30 to 50 percent lower than they expected it to be. And really, two beats a minute is pretty wild.

"The researchers think that the surprisingly low heart rate may be explained by a stretchy aortic arch – part of the heart that moves blood out to the body – which, in the blue whale, slowly contracts to maintain some additional blood flow in between beats. Meanwhile, the impressively high rates may depend on subtleties in the heart's movement and shape that prevent the pressure waves of each beat from disrupting blood flow," Stanford explains.

They found that a blue whale's heart works near its limit, which could explain why blue whales haven't gotten bigger – the energy needs of a larger body would be more than what the heart could sustain. And it may also explain why no other animal has ever been larger than a blue whale.

"Animals that are operating at physiological extremes can help us understand biological limits to size," said Goldbogen.

It's fascinating, and a good reminder that research like this can help inform conservation efforts.

"Heart rate can give you so much more information than just about the metabolic rate; its reaction to stressful events, its reaction to feeding," says Cade in the video below. "In order to have any kind of conservation implication or any kind of big management or even any kind of understanding of, like, 'how do the largest organisms to ever to have lived actually function?' We can answer some of those basic questions now."

"A lot of what we do involves new technology and a lot of it relies on new ideas, new methods and new approaches," adds Cade. "We're always looking to push the boundaries of how we can learn about these animals."

The research was published in Proceedings of the National Academy of Sciences