The pulse can be very useful when assessing a person's health, but what can it teach us about the biggest animal on Earth? A team of Stanford University scientists have captured the first ever recording of a blue whale’s heart rate, and in doing so, have gathered some interesting insights into the massive mammal's behavior and evolution.
The sheer size and surface area of the blue whale might give the impression that slapping a research tag on its body would be a pretty straightforward affair. But the nature of wild blue whales actually poses a few challenges for research of this type. They don’t flip belly up like some other marine creatures, and the ripples of their accordion-like skin expand and contract as they feed, meaning that the tag could very easily come loose anyway.
“We had to put these tags out without really knowing whether or not they were going to work,” says David Cade, co-author of the paper. “The only way to do it was to try it. So we did our best.”
Cade actually stuck the tag on his first try, fitting a wild blue whale with a sensor-packed device that used embedded electrodes to measure its heart rate. The tag wound up nestled near the whale’s left flipper and proved effective at capturing data on its heart activity, which upon retrieval the researchers found to contain a wealth of fascinating information.
“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,” says Jeremy Goldbogen, assistant professor of biology at Stanford’s School of Humanities Sciences.
The most surprising revelation was that the blue whale’s heart rate could drop as low as just two beats a minute. This occurred as the whale dove for food, with the creature averaging between four and eight beats a minute across the plunge as a whole. The heart rate increased more than twofold as it lunged after and ate prey at the bottom, and then started to slow once again as it rose toward the surface.
Once at the surface and taking in some oxygen, the whale’s heart rate rocketed to as high as 37 beats per minute. This almost outpaced what the researchers expected, but it was the minimum heart rate that really caught the researchers by surprise, being around 30 to 50 percent lower than they’d expected.
With this new data in hand, the scientists are of the opinion that the whale’s heart is operating at its limits. This provides a possible explanation as to why the blue whale has never evolved to be bigger than it is, as the heart’s capabilities would be unable to keep pace with the energy requirements of a larger body. And it perhaps explains why no animal in history has surpassed it in size.
“Animals that are operating at physiological extremes can help us understand biological limits to size,” said Goldbogen. “They may also be particularly susceptible to changes in their environment that could affect their food supply. Therefore, these studies may have important implications for the conservation and management of endangered species like blue whales.”
The team is already busy upgrading its tag, looking to add an accelerometer to observe how different activities impact the heart rate of the blue whale.
“A lot of what we do involves new technology and a lot of it relies on new ideas, new methods and new approaches,” says Cade. “We’re always looking to push the boundaries of how we can learn about these animals.”
You can hear from the scientists involved in the video below, while the research was published in the journal Proceedings of the National Academy of Sciences.
Source: Stanford University
