Blue whales have a reputation for being massive, and as far as we know, they’re the largest living animal in existence today. Perhaps unsurprisingly, this means that blue whales’ hearts are massive too, and they work incredibly hard to keep blood pumping through the marine mammal’s enormous body.
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Like most marine mammals, blue whales often go for deep dives below the ocean’s surface in search of food, and this makes conserving oxygen very important. In most cases, marine mammals’ heart rates slow down during these critical deep-diving moments, helping to limit the animal’s blood-oxygen expenditure and enable longer deep dives. But while monitoring one blue whale’s heart rate during deep dives, researchers were particularly fascinated to learn just how low a blue whale’s heart rate can go. Their findings are now published in the journal Proceedings of the National Academy of Sciences (PNAS).
The data, captured with the assistance of a small, but effective GPS-enabled suction cup-based electrode, revealed that a deep-diving blue whale’s heart rate can slow down to as little as two beats per minute. At the highest end of the scale, its heart thumped as rapidly as 37 beats per minute on a deep dive, but on average, it rested between four and eight-and-a-half beats per minute during the deepest part of a deep dive.
The electrode was designed to be non-invasive. The suction cup didn’t harm the blue whale, and as such, it didn’t impact the animal’s stress levels in any way. The findings were particularly astonishing because researchers initially thought that a blue whale’s heart rate would sit at around 11 beats per minute on a deep dive. Learning that the estimations were this far off paints a very different picture of our understanding of blue whales and their bodily limits.
The research also showed that a blue whale’s heart rate can shift somewhat rapidly – sometimes in the span of just one or two minutes. Moreover, these heart rate fluctuations occurred continuously as the blue whale performed various tasks, be it casually swimming along at these depths or actually feeding.
As it would seem, blue whales may push their bodies to the limit when in search of food. The findings also raise some interesting questions about how blue whales’ nervous systems work and whether other whale species exhibit the same or similar heart rate fluctuations while performing the same or similar tasks.
“Sperm whales, beaked whales — some of those species can dive for an hour or more,” elucidated Dr. Jeremy Goldbogen, the lead author of the blue whale deep-diving heart rate study. “We would like to understand what their hearts are doing.”
It should be interesting to see if future research shows similar behavior with other blue whales, and perhaps more importantly, with other whale species. Only time will tell…