by Sara Moraca
A heart with a “sweet rhythm” marks the life of the largest animal on the planet. For the first time in the world, a research team from Stanford University managed to record the heartbeat of a blue whale, the largest animal in the world. The details of this important study were published last November in the scientific journal Proceedings of the National Academy of Sciences. Off California, in Monterey Bay, the researchers managed to record the heartbeat of an adult male specimen about 22 meters long for nine consecutive hours. The heart of the blue whale is itself a record: with its 180 kg of weight and 1.5 meters in width, it is the largest heart organ in the whole animal kingdom and manages to pump up to 220 liters of blood at each beat. Other research groups had managed to use the tag on smaller and captive cetaceans, but performing this type of operation on a blue whale that lives in its natural habitat is a very different challenge. First of all, whales that live in nature are not trained to turn over and put themselves on their stomachs, which ends up favoring the researchers’ work. In addition, the blue whales have an accordion-like skin on the belly, which tends to expand when the animal feeds, which could cause the tag to detach suddenly. To overcome these eventualities, the researchers resorted to a particular electrocardiograph, enclosed in a cage with suction cups.
What they found was surprising: when the cetacean dives to hunt for food, its heart rate goes from about 25-37 to 4-8 beats per minute. Diving deeply to be able to eat krill requires enormous effort for whales: blue whales, for example, swim at a speed of 4 meters per second and, opening their jaws wide, they swallow a volume of prey and water equal to 140% of their body. These are data that surprised the researchers, who expected a higher heart rate in both the resting and immersion phase, for which the expected range was 30-50% higher. Researchers believe that the surprisingly low heart rate can be explained by an elastic aortic arch that, in the blue whale, contracts slowly to maintain further blood flow between the beats. In the meantime, the higher rates observed when the whale is near to the water surface may depend on subtleties in the movement and shape of the heart, which prevent the pressure waves of each beat from disrupting blood flow. Based on these data, the researchers put forward the hypothesis that the whale’s heart is now touching the limits of its heart rate. This could help explain why no animal has ever been bigger: the energy needs of a more voluminous body, in fact, would exceed what the heart can support.
In the future the experiment could be replicated on other cetaceans such as
humpback whales and common whales; the researchers want to work to improve
the properties of the tag, also adding an accelerometer, which could help them
better understand how the different activities of the animal affect the heart rate.
In the future the experiment could be replicated on other cetaceans such as humpback whales and common whales; the researchers want to work to improve the properties of the tag, also adding an accelerometer, which could help them better understand how the different activities of the animal affect the heart rate.