Truly, the heart of a blue whale can be detected up to 2 miles away. In the last few years, scientists have figured out how to listen to the heartbeats of wild whales. The largest animal ever to have lived.
These marine giants can be longer than two school buses, and their hearts — roughly the size of a loveseat and weighing over 1,000 pounds — beat as few as twice per minute. In this article, we’ll discover more facts about these blue whales…
Why are blue whales so big?
The short answer: food. Several million years ago, blue whales evolved to binge-eat tiny crustaceans called krill, which are superabundant in some coastal regions during part of the year. All of that food can fuel a big body, and being big allowed these animals to take larger gulps of krill and swim efficiently from one krill buffet to the next.
But what’s interesting is that there are enough krill and other aquatic critters in the ocean for the whales to be even bigger. Food, alone, does not seem to limit the potential body size of whales, said Max Czapanskiy, a doctoral researcher at Stanford who studies marine mammals.
“There has to be something about their bodies that’s keeping them from getting even bigger,” he said. The answer, scientists suspect, may lie in the heart.
Whales hold their breath as they’re feeding on krill, which tend to aggregate hundreds of feet underwater. That causes carbon dioxide to build up in their blood. When these marine mammals return to the surface to breathe, their hearts beat fast to rid their bodies of CO2 and replace it with fresh oxygen, so they can dive back down and continue foraging.
The Whale’s Heart
Larger hearts beat more slowly and take longer to replenish oxygen in the body. That means whales have to spend more time on the surface, catching their breath, which eats into precious time they have to feed on a seasonal resource like krill. Too big a heart and these behemoths might not have enough time to eat.
If heart size limits whales in some way, these organs should, theoretically, be maxing out their speed when the animals come up for air. That’s one thing that scientists wanted to figure out when they set out to measure a blue whale’s heartbeat in 2018.
Each time a whale’s heart beats, it sends out a wave of blood that causes its body to shake ever so slightly (not unlike how a hose kicks back when you turn on the faucet). When a whale is otherwise still, accelerometers can pick up those subtle movements.
Like an EKG sensor, accelerometers only work if they’re strapped to a whale. But these devices offer a big benefit: Scientists have been putting them on whales for roughly 20 years to measure other things, Czapanskiy said, which means there’s already plenty of potential heart rate data out there that just needs to be analyzed.
How to Dissect a Whale
When a whale beaches itself in the Long Island area, dead or alive, one man’s cell phone rings first. That man is Robert DiGiovanni. He’s the founder of the relatively new Atlantic Marine Conservation Society and its stranding response team, whose Facebook page becomes pocked with crying emojis when a dead or dying whale collapses onto the sand.
I first met Rob at a beer and cheese tasting at The Whaling Museum, where he gestured to the whale models as he talked. While we chatted, he mentioned he was going to be performing a necropsy on a young Humpback whale spotted swimming the day before in Reynolds Channel in Far Rockaway.
Now it was floating dead on a sandbar near Atlantic Beach Bridge – the 4th dead humpback on Long Island in less than a month. A necropsy would help explain why.
What you can learn from a whale’s beating heart
Heart rate data from the blue whale shows that these animals essentially have two different heart rates. One of them is slow, like the clip you heard above; that’s when the whale is diving and trying to conserve oxygen. The other is fast when the whale is back at the surface and its heart is racing to replenish oxygen.
As researchers suspected, it’s there, on the surface, where big-bodied-ness could become a problem.
The EKG data shows that a single beat of the blue whale’s heart takes about 1.8 seconds, which means its heart can only beat roughly 33 times per minute. But as the whale was catching its breath, its heart was maxing out slightly above that number.
This suggests something critical: The blue whale’s heart is working at “peak performance,” Czapanskiy said, and it literally can’t beat any faster.
But what does that have to do with the limits of body size? If the whale were any bigger, it would need a bigger heart and more food. But, again, a bigger heart would beat slower and require the animal to spend more time at the surface, giving the whale less time to forage for krill.
So basically, any bigger, and these animals likely wouldn’t be able to consume enough food to sustain their hulking figures.
That’s why Czapanskiy has a hard time imagining even a hypothetical animal evolving to be larger than a blue whale. These animals live in an environment with an enormous amount of food, yet their bodies limit how quickly they can consume it.
Unless a new and massive source of nutrient-rich food appears — or an animal evolves a highly novel and efficient physiology — the blue whale may not only be the largest animal to have lived but the largest animal to live, period.
Conclusion
A blue whale’s heartbeat slows dramatically during dives to over 1,000 feet. In one study, a diving blue whale’s heart slowed to 4-8 beats a minute, with an extreme low of only two beats, a drastic measure to save oxygen. When the whale came to the surface to breathe, its heart raced to 25-37 beats a minute.
Scientists think that a whale’s heart works close to physical limits and cannot beat faster, which is why whales have reached their largest size possible.
